JP3944302B2 - Adsorbent and production method thereof - Google Patents

Description

【００２４】
水蒸気吸着量
２０℃、水蒸気圧２ｍｍＨｇでの平衡吸着の際に、吸着剤がｇ当たり１０ｍｌ以上の水蒸気を吸着すると、吸着剤に割れが生じることが多くなる。尚、本発明方法の疎水化処理により、吸着剤の水蒸気吸着量は、１０ｍｌ／ｇ以下になるが、３ｍｌ−水蒸気／ｇ−吸着剤以下にするのは難しい。
【００２５】
吸着剤の使用態様
実際にＰＳＡシステムで吸着剤を使用する場合には、吸着塔の容積及び塔数、入り口ガス中のＶＯＣ濃度、ＶＯＣ捕捉率、操作温度等の運転条件に応じて、適宜、吸着剤の充填量、充填高さなどを決める。
本吸着剤は、ハイシリカゼオライト、アルミナ等の公知の吸着剤と組み合わせたり、混合したりして使用しても問題はない。ただし、他の吸着剤の市場価格は本吸着剤よりも高価であるから、公知吸着剤の混合量や組合わせ量が多いと、本発明の吸着剤の経済的な利点を失うことになる。
本発明の吸着剤の使用に先立ち、活性化処理を必要としない。湿度が極めて高い状態で永く保存されていた場合などには、常温〜３５０℃の範囲の温度下で減圧乾燥処理を、適宜、実施すれば良い。減圧乾燥時間は、ＰＳＡ装置によって一概に決まらないが、１〜２４時間が現実的な時間である。
【００２６】
吸着剤のＶＯＣ選択率
本発明で言う吸着剤のＶＯＣ選択率とは、吸着剤に吸着された水蒸気及び揮発性有機化合物の吸着量のうち、揮発性有機化合物の吸着量の割合を示す比率であって、次式で定義される値である。
ＶＯＣ選択率＝｛（Ａ）／（Ａ＋Ｂ）｝×１００
ここで、Ａは、温度２０℃での揮発性有機化合物の飽和蒸気圧の１／１０の圧力下、温度２０℃における吸着剤への揮発性有機化合物の平衡吸着量（ｍｌ／ｇ（stp)）である。
Ｂは、圧力２mmＨｇ、温度２０℃における吸着剤への水蒸気の平衡吸着量（ｍｌ／ｇ（stp)）である。
本発明で、吸着剤の揮発性有機化合物（ＶＯＣ）の平衡吸着量を規定するに当たり、ＶＯＣの飽和蒸気圧下でなく、ＶＯＣの飽和蒸気圧の１／１０の圧力下としているのは、飽和蒸気圧の１／１０の圧力になるまでに大部分のＶＯＣが吸着剤に吸着されてしまうからである。即ち、実際的には、飽和蒸気圧下での吸着量≒飽和蒸気圧の１／１０の圧力下での吸着量であるからである。
また、実際の圧力変動法によるＰＳＡの運転では、通常、吸着工程は、ＶＯＣの飽和蒸気圧まで加圧することなく、圧力がＶＯＣの飽和蒸気圧の１／１０の圧力に達するまで吸着工程を実施し、次いで脱着工程に移行する。
【００２７】
以上のことから、ＶＯＣ選択率は、ＰＳＡの運転時のＶＯＣ吸着効率を示す因子であると定義できる。
物理的には、吸着剤のＶＯＣ選択率の値が大きいほど、水蒸気存在下で、揮発性有機化合物の吸着が起こり易く、優れたＶＯＣ−ＰＳＡ向け吸着剤であると評価できる。従って、吸着剤のＶＯＣ選択率は、８０％以上、好適には８５％以上である。ＶＯＣ選択率が８０％以上の吸着剤は、ＶＯＣ選択率が低い吸着剤と比較して、吸着剤の使用量が少なくて済み、ＰＳＡ法の経済性の面及び運転効率の点で格段に有利である。
【００２８】
先に述べたＶＯＣ選択率の他に、吸着剤のＶＯＣ吸着量も重要なファクターとなる。
例えば、吸着剤のＶＯＣ選択率が高くても、ＶＯＣ吸着量が少ないと、所定量のＶＯＣを分離・回収するのに必要な吸着剤量が多くなり過ぎる等の問題が生ずる。したがって、ＶＯＣ選択率が高く、かつ所定レベル以上のＶＯＣ吸着量を示すことが必要となる。
ＶＯＣ吸着量は、温度２０℃での揮発性有機化合物の飽和蒸気圧の１／１０の圧力下、温度２０℃における吸着剤への揮発性有機化合物の平衡吸着量（ｍｌ／ｇ（stp)）により評価する。測定方法は、ＶＯＣ選択率の測定方法で示した方法と同様に行う。
温度２０℃での揮発性有機化合物の飽和蒸気圧の１／１０の圧力下、温度２０℃における吸着剤への揮発性有機化合物の平衡吸着量は、３０ｍｌ／ｇ（stp)以上が好ましく、３５ｍｌ／ｇ（stp)以上の吸着剤が更に好ましい。
ＶＯＣ吸着量の値がこれより小さいと、装置が同じ効果を得るために必要となる吸着剤の使用量が多くなるため、吸着塔が大型化したり、装置に付属する機器の規格も大きくなるため、装置全体のサイズが大きくなったり、電力消費量等も増加するなど運転経費が嵩む可能性が高い。逆に、上限は特に限定されないが、１５０ｍｌ／ｇ（stp)程度が現状の上限と考えられる。
【００２９】
【発明の実施の形態】
以下に、実施例を挙げて、本発明の実施の形態を具体的かつ詳細に説明する。以下の実施例及び比較例の試料吸着剤の多孔質物性、疎水化能及びＶＯＣ吸着能は、以下の測定法及び評価法により評価した。
比表面積、細孔容積及び平均細孔径等の多孔質物性の測定法
吸着剤原料の多孔質物性（以下、原料物性）および疎水化処理により得た吸着剤の多孔質物性（以下、吸着剤物性）は、高純度Ｎ₂ （高千穂化学、Research Grade）をプローブ分子（prove molecule） に用いて、自動表面積・細孔径測定装置（Belsorp28 、ベルジャパン社製）により測定した。多孔質物性の測定では、比表面積及び細孔径の測定に先立ち、先ず、前処理として試料吸着剤及び吸着剤原料の減圧加熱処理を行い、次いで所望の物性を測定した。
試料の減圧加熱処理では、約２００ｍｇの試料を硝子製試料管に入れて、１０^-1〜１０^-2mmHgの減圧状態を維持しながら、昇温速度６℃／分で室温から３５０℃まで昇温し、同温度で３時間保持した。その後、高純度ヘリウムガスによって常圧＋５ｍｍＨｇに保持しつつ降温速度５℃／分で室温まで冷却し、測定用の試料を得た。得た試料重量を正確に秤量し、多孔質物性の測定に供した。
多孔質物性の測定では、液化窒素自動供給装置（auto feeder ）を有する自動デュワー瓶を使用し、液化窒素温度（−１９６℃）に保持し、死容積（dead volume ）を高純度ヘリウムにて３回以上測定し、次いで減圧排気した後、プローブ分子（窒素）を導入してＢＥＴ法に従って比表面積を測定した。次いで脱着測定を実施し、これにより平均細孔径を求めた。
【００３０】
吸着剤の疎水化能の評価方法
吸着剤の疎水化能を評価するために、温度２０℃、圧力２ｍｍＨｇ下で水蒸気の平衡吸着量を測定した。
疎水化能の測定前に、前処理として以下の減圧加熱処理を試料吸着剤に施した。即ち、約１００ｍｇの試料を硝子製試料管に入れて、１０^-1〜１０^-2mmHgの圧力に減圧しながら昇温速度６℃／分で室温から３５０℃まで昇温し、同温度で１時間保持した。次いで、降温速度５℃／分で室温まで冷却して、試料吸着剤を得た。得た試料吸着剤の重量を正確に計り、測定の試料に供した。
水蒸気源として用いる水は、硝子製液溜にイオン交換水を５０ｍｌ入れ、これを減圧ラインでバブリング（bubbling）した後、ドライアイス−メタノール冷媒で、液溜底部を注意深く冷却して凍結させつつ、１０^-2mmHg程度で真空排気を行いながら溶存気体を放出させた。続いて、加温して解氷した。溶存気体の放出が無くなるまで、この処理を繰り返して、精製水を得た。
【００３１】
平衡吸着量の測定では、高精度蒸気吸着量測定装置（Belsorp18 、ベルジャパン社製）を用いた。空気恒温槽内で精製水の液溜を５０℃±１℃に保持しながら、液溜から発生する飽和水蒸気を５０℃±１℃に維持した硝子製リザーバー（reservoir 、容積１５０ｍｌ）に導入し、更に、試料吸着剤を収容した部分のみを２０℃±０．５℃に保った硝子製吸着管にリザーバーから自動流量調節バルブを介して徐々に水蒸気を導入し、２ｍｍＨｇの平衡圧になるまで導入し続けた。
２ｍｍＨｇの平衡圧に到達した時点、即ち１０分間の圧力変動が０．１ｍｍＨｇ以内になった時点で、キャパシタンスマノメータで測定した圧力と、系内容積から水導入量を求め、それを平衡吸着量とし、更に、前処理後の試料重量を基に吸着剤重量当たりの平衡吸着量を計算した。
また、疎水化能の一つとして吸着剤の水に対する割れ耐性を評価するために、試料吸着剤を２０℃の水に浸漬し、２週間経過後に割れ（crack ）の有無を調べた。
【００３２】
吸着剤のＶＯＣ吸着能の評価方法
試料吸着剤のＶＯＣ吸着能を評価するために、以下のようにしてＶＯＣの可逆吸着量を測定した。
測定前に、前処理として次の減圧加熱処理を試料吸着剤に施した。減圧加熱処理では、先ず、約１００ｍｇの試料を試料管に入れ、１０^-1〜１０^-2mmHgの圧力に減圧しながら昇温速度６℃／分で室温から３５０℃まで昇温し、同温度で１時間保持した。次いで、降温速度５℃／分で室温まで冷却して、試料吸着剤を得た。ＶＯＣ吸着能の測定では、得た試料吸着剤から所要の試料重量を正確に秤量し、測定に供した。
また、測定に供するイソペンタンを次のようにして精製した。先ず、イソペンタン（東京化成工業、試薬特級）を液溜に入れ、減圧ラインでバブリングした後、デュワー瓶に入れた液化窒素液面を注意深く液溜底部に接触させて冷却して固化させつつ、溶存気体を放出させながら１０^-2mmHg台で真空排気を行った。次いで加温し、溶融した。溶存気体の放出が無くなるまでこの操作を繰り返して、イソペンタンを精製した。
水蒸気源として用いる水は、疎水化能の評価時と同様に精製した。
【００３３】
測定に際し、精製した水、イソペンタンをそれぞれの液溜に入れ、恒温槽で５０℃±１℃の定温に保持した。
先ず、液溜から発生した飽和水蒸気を５０℃±１℃の温度に維持した硝子製リザーバー（reservoir 、容積１５０ｍｌ）に３０ｍｍＨｇの圧力まで導入し、更に、試料吸着剤を収容した部分のみを２０℃±０．５℃の温度に保った硝子製吸着管にリザーバーから自動流量調節バルブを介して徐々に水蒸気を導入し、１０ｍｍＨｇの平衡圧になるまで導入し続けた。次いで、キャパシタンスマノメータで測定した圧力と、系内容積から、１０ｍｍＨｇの平衡圧に到達した時点の水吸着量を求めた。
次いで、液溜から発生したイソペンタン蒸気を５０℃±１℃の温度に維持した硝子製リザーバー（容積１５０ｍｌ）に５４０ｍｍＨｇの圧力まで導入し、更に、試料吸着剤を収容した部分のみを２０℃±０．５℃の温度に保った硝子製吸着管にリザーバーから自動流量調節バルブを介して徐々にイソペンタン蒸気を導入し、５４０ｍｍＨｇの平衡圧になるまで導入し続けた。
平衡吸着量は、１０分間の圧力変動が０．１ｍｍＨｇ以内になった時点の吸着量とした。イソペンタンの吸着量は、キャパシタンスマノメーターで測定した圧力変化と系内体積から求め、更に、前処理後の試料重量を基に吸着剤重量あたりの吸着量を計算した。
水蒸気吸着量およびＶＯＣ吸着量の測定は、高精度蒸気量測定装置（Belsorp 18，ベルジャパン社製）を用いて行い、流量調節バルブ等の開閉及び調節は、パソコン（PC9821、日本電気製）でオンライン（on-line）制御した。
【００３４】
本発明に係る吸着剤は、ガソリンスタンドや油槽所等周りの大気中のＶＯＣ低濃度のＶＯＣ、即ちある程度空気と混合したＶＯＣを選択的にかつ効率的に吸着できる吸着剤である。このような低濃度ＶＯＣの吸着回収において、問題となるのは、空気中に含まれる水分の影響であって、水分を吸着することにより、ＶＯＣ吸着能が低下することである。換言すれば、低濃度ＶＯＣ用の優れた吸着剤とは、水分の影響を受けにくい吸着剤である。
水分とＶＯＣが共存する場合、吸着剤は、通常、水の方を優先的に吸着するために、吸着剤のＶＯＣ吸着能が低下する。本評価方法では、吸着剤に先ず水分を吸着させ、次いでＶＯＣを吸着させ、その吸着能を評価している。これは、水分が多いこと、即ちＶＯＣが低濃度である状態に近似した状態でＶＯＣ吸着能を評価していることになる。換言すれば、本評価方法のように、予め水分を吸着させておくことにより、吸着剤は、低濃度のＶＯＣ雰囲気、又はそれ以上の過酷な条件下にあることになるので、水分吸着の後でも多量のＶＯＣを吸着できるということは、低濃度のＶＯＣの吸着能が優れていることと高い確度で相関する。
【００３５】
吸着剤のＶＯＣ選択率の測定方法
圧力２mmＨｇ、温度２０℃で吸着剤への水蒸気の平衡吸着量（ｍｌ／ｇ（stp)）の測定は、吸着剤の疏水可能の評価方法で説明した水蒸気の平衡吸着量を測定する方法に従って行う。
温度２０℃での揮発性有機化合物の飽和蒸気圧の１／１０の圧力下、温度２０℃における吸着剤への揮発性有機化合物の平衡吸着量（ｍｌ／ｇ（stp)）の測定は、次に説明するようにして行う。
測定に使う有機化合物を前もって精製する。例えば、イソペンタンを例にすると、先ず、試薬特級のイソペンタンを液溜めに入れ、減圧ラインでバブリングした後、デュワー瓶に入れた液化窒素面を注意深く液溜め底部に接触させて、イソペンタンを冷却し、固化させつつ、１０^-2ｍｍＨｇのオーダの真空で真空排気しつつ溶存気体を放出させる。次いで、固化したイソペンタンを加温して溶融した。溶存気体の放出が無くなるまで、この操作を繰り返して、イソペンタンを脱気、精製した。なお、液化窒素温度で固化し難い揮発性有機化合物の場合には、予め液体窒素温度付近まで冷却したモレキュラーシーブス（分子篩）等に揮発性有機化合物を吸着させ、加温し、モレキュラーシーブスから最初に脱離して来るガスをガス溜めに集積する。
【００３６】
このように脱気、精製したイソペンタン蒸気を５０℃±１℃に維持した硝子製リザーバ（容積１５０ｍｌ）に約５４０ｍｍＨｇ程度まで導入し、更に、試料吸着剤を収容したリザーバ部分を２０℃±０．５℃に保った硝子製吸着管にリザーバからイソペンタン蒸気を導入し、温度２０℃でのイソペンタンの飽和蒸気圧の１／１０の圧力下、温度２０℃における１０分間の圧力変動が、１気圧における蒸気圧の１／１０の圧力で、１０分間の圧力変動が、０．０２ｍｍＨｇ以下になった時点の吸着量（平衡吸着量）を、２０℃でのイソペンタンの飽和蒸気圧の１／１０の圧力下で、２０℃でのイソペンタンの平衡吸着量（ｍｌ／ｇ（stp)）とした。
以上の説明では、揮発性有機化合物の例としてイソペンタンを挙げて説明したが、揮発性有機化合物はイソペンタンに限るものではない。
【００３７】
以下に、具体的な実験結果を示す。
実施例１
比表面積が６００ｍ²/g 、細孔容積が０．４０ｍｌ／ｇ及び平均細孔径が２．５ｎｍの原料物性を有するシリカゲル粉末を３．２ｍｍ（直径）×３ｍｍ（高さ）の円柱状のペレットに打錠成形した。次いで、ペレットをマッフル炉で昇温速度１℃／分で室温から５５０℃にまで加熱し、続いて５５０℃の温度で５時間保持した。その後、室温まで冷却して、実施例１の試料吸着剤を得た。
【００３８】
実施例１の試料吸着剤の物性を測定したところ、比表面積が５７０ｍ²/g 、細孔容積が０．３８ｍｌ／ｇ、及び平均細孔径が２．５ｎｍであった。従って、原料のシリカゲル粉末に対する試料吸着剤の比表面積の減少率は５％になった。また、上述した疎水化能の評価方法に従って測定した２０℃、２ｍｍＨｇでの水蒸気飽和吸着量は、９．８ｍｌ／ｇ（ｓｔｐ）であった。ｓｔｐとは、標準状態（Standard Temperature and Pressure ）のことであり、０℃、常圧に換算した吸着量を示している。また、水に浸漬し、２週間経過した後でも、試料吸着剤には割れが発生していなかった。上述したＶＯＣ吸着能の評価方法に従って２０℃で水１０mmHg平衡吸着後に測定したイソペンタン吸着量は、３．１ｍｌ／ｇ（ｓｔｐ）であった。
実施例１の原料の物性、疏水化処理条件、吸着剤の物性、疏水化能及びＶＯＣ吸着量は、それぞれ、表１の実施例１の欄に記載されている。以下、実施例２から５についても同様である。
【表１】

【００３９】
実施例２
比表面積が６６０ｍ²/g 、細孔容積が０．１０ｍｌ／ｇ及び平均細孔径が０．６ｎｍの原料物性を有するシリカゲル粉末を実施例１と同様な形状のペレットに打錠成形し、マッフル炉で昇温速度５℃／分で室温から６００℃にまで加熱し、続いて６００℃で４時間保持した。その後、室温まで冷却して、実施例２の試料吸着剤を得た。
実施例２の試料吸着剤の比表面積は５８１ｍ²/g 、細孔容積は０．０９ｍｌ／ｇ、及び平均細孔径は０．６ｎｍであった。従って、原料のシリカゲルに対する試料吸着剤の比表面積の減少率は１２％になった。また、実施例１と同様にして求めた水蒸気飽和吸着量及びイソペンタン吸着量は、それぞれ、７．５ｍｌ／ｇ（ｓｔｐ）及び４．５ｍｌ／ｇ（ｓｔｐ）であった。また、水に浸漬した後２週間経過時点で、試料吸着剤には割れは発生していなかった。
【００４０】
実施例３
比表面積が６９０ｍ²/g 、細孔容積が０．３０ｍｌ／ｇ及び平均細孔径が２．０ｎｍの原料物性を有する粒径２〜３ｍｍの球状シリカゲルをマッフル炉により昇温速度１０℃／分で室温から６５０℃にまで加熱し、続いて６５０℃の温度で３時間保持した。その後、室温まで冷却して、実施例３の試料吸着剤を得た。
実施例３の試料吸着剤の比表面積は４４８ｍ²/g 、細孔容積は０．２０ｍｌ／ｇ、及び平均細孔径は１．８ｎｍであった。従って、原料の球状シリカゲルに対する試料吸着剤の比表面積の減少率は３５％になった。また、実施例１と同様にして求めた水蒸気飽和吸着量及びイソペンタン吸着量は、それぞれ、５．３ｍｌ／ｇ（ｓｔｐ）及び４．１ｍｌ／ｇ（ｓｔｐ）であった。また、水に浸漬した後２週間経過時点で、試料吸着剤には割れは発生していなかった。
【００４１】
実施例４
比表面積が７００ｍ²/g 、細孔容積が０．３０ｍｌ／ｇ及び平均細孔径が１．５ｎｍの原料物性を有する粒径２〜３ｍｍの球状シリカゲルをマッフル炉により昇温速度２０℃／分で室温から７００℃にまで加熱し、続いて７００℃で３時間保持した。その後、室温まで冷却して、実施例４の試料吸着剤を得た。
実施例４の試料吸着剤の比表面積は４２０ｍ²/g 、細孔容積は０．１８ｍｌ／ｇ、及び平均細孔径は１．７ｎｍであった。従って、原料のシリカゲルに対する試料吸着剤の比表面積の減少率は４０％になった。また、実施例１と同様にして求めた水蒸気飽和吸着量及びイソペンタン吸着量は、それぞれ、３．２ｍｌ／ｇ（ｓｔｐ）及び３．７ｍｌ／ｇ（ｓｔｐ）であった。また、水に浸漬した後２週間経過時点で、試料吸着剤には割れは発生していなかった。
【００４２】
実施例５
比表面積が７８０ｍ²/g 、細孔容積が０．３０ｍｌ／ｇ及び平均細孔径が１．５ｎｍの原料物性を有する粒径２〜３ｍｍの球状シリカゲルをマッフル炉により昇温速度１５℃／分で室温から６２０℃にまで加熱し、続いて６２０℃の温度で２時間保持した。その後、室温まで冷却して、実施例５の試料吸着剤を得た。
実施例５の試料吸着剤の比表面積は６５５ｍ²/g 、細孔容積は０．２５ｍｌ／ｇ、及び平均細孔径は１．５ｎｍであった。従って、原料のシリカゲルに対する試料吸着剤の比表面積の減少率は１６％になった。また、実施例１と同様にして求めた水蒸気飽和吸着量及びイソペンタン吸着量は、それぞれ、１０．０ｍｌ／ｇ（ｓｔｐ）及び５．９ｍｌ／ｇ（ｓｔｐ）であった。また、水に浸漬した後２週間経過時点で、試料吸着剤には割れは発生していなかった。
【００４３】
比較例１
比表面積が４５０ｍ²/g 、細孔容積が０．６９ｍｌ／ｇ、平均細孔径が６．１ｎｍの原料物性を有するシリカ粉末を実施例１と同様な形状のペレットに打錠成形し、マッフル炉により昇温速度１０℃／分で室温から６５０℃にまで加熱し、続いて６５０℃の温度で３時間保持した。その後、室温まで冷却して、比較例１の試料吸着剤とした。
比較例１の試料吸着剤の比表面積は３８３ｍ²/g 、細孔容積は０．５９ｍｌ／ｇ、及び平均細孔径は６．２ｎｍであった。従って、原料のシリカゲルに対する試料吸着剤の比表面積の減少率は１５％になった。また、実施例１と同様にして求めた水蒸気飽和吸着量及びイソペンタン吸着量は、それぞれ、７．５ｍｌ／ｇ（ｓｔｐ）及び１．５ｍｌ／ｇ（ｓｔｐ）であった。また、水に浸漬して２週間経過時点で、試料吸着剤には割れは発生していなかった。
比較例１の原料の物性、疏水化処理条件、吸着剤の物性、疏水化能及びＶＯＣ吸着量は、それぞれ、表２の比較例１の欄に記載されている。以下、比較例２から６についても同様である。
【表２】

【００４４】
比較例２
比表面積が６５０ｍ²/g 、細孔容積が０．４０ｍｌ／ｇ及び平均細孔径が２．５ｎｍの原料物性を有する粒径２〜３ｍｍの球状シリカゲルをマッフル炉により昇温速度３０℃／分で室温から８００℃にまで加熱し、続いて８００℃の温度で６時間保持した。その後、室温まで冷却して、比較例２の試料吸着剤を得た。
比較例２の試料吸着剤の比表面積は２８０ｍ²/g 、細孔容積は０．７９ｍｌ／ｇ、及び平均細孔径は１１．３ｎｍであった。従って、原料のシリカゲルに対する試料吸着剤の比表面積の減少率は６５％になった。また、実施例１と同様にして求めた水蒸気飽和吸着量及びイソペンタン吸着量は、それぞれ、４．８ｍｌ／ｇ（ｓｔｐ）及び０．１ｍｌ／ｇ（ｓｔｐ）であった。また、水に浸漬した後、２週間経過した時点で、試料吸着剤に著しいひび割れが発生していた。
【００４５】
比較例３
比表面積が７８０ｍ²/g 、細孔容積が０．３０ｍｌ／ｇ、平均細孔径が１．５ｎｍの原料物性を有する粒径２〜３ｍｍの球状シリカゲルをマッフル炉により室温から昇温速度０．５℃／分で室温から５２０℃にまで加熱し、続いて５２０℃の温度で１時間保持した。その後、室温まで冷却して、比較例３の試料吸着剤を得た。
比較例３の試料吸着剤の比表面積は７６０ｍ²/g 、細孔容積は０．２９ｍｌ／ｇ、及び平均細孔径は３．０ｎｍであった。従って、原料のシリカゲルに対する試料吸着剤の比表面積の減少率は３％になった。また、実施例１と同様にして求めた水蒸気飽和吸着量及びイソペンタン吸着量は、それぞれ、２６．６ｍｌ／ｇ（ｓｔｐ）及び０．３ｍｌ／ｇ（ｓｔｐ）であった。また、水に浸漬した後、２週間経過した時点で、試料吸着剤は粉化していた。
【００４６】
比較例４
比表面積が６９０ｍ^２／ｇ、細孔容積が０．３０ｍｌ／ｇ、平均細孔径が２．０ｎｍの原料物性を有する球状シリカゲル（２〜３ｍｍ径）をマッフル炉で室温から昇温速度１０℃／ｍｉｎで加熱し８００℃にまで加熱後、同温度で３時間保持した。その後、室温まで冷却して比較例４の試料吸着剤とした。
比較例４の試料吸着剤の比表面積は２４８ｍ^２／ｇ、細孔容積は０．３２ｍｌ／ｇ、及び平均細孔径が５．２ｎｍであった。したがって、原料のシリカゲルに対する試料吸着剤の比表面積の減少率は６４％になった。また、疎水化能を示す、２０℃、２ｍｍＨｇでの水蒸気飽和吸着量は４．８ｍｌ／ｇ（ｓｔｐ）、水に浸漬後の２週間経過後の割れは見られなかった。２０℃で水１０ｍｍＨｇの平衡吸着後のイソペンタン吸着量は０．２ｍｌ／ｇ（ｓｔｐ）であった。
【００４７】
比較例５
比表面積が７８０ｍ² ／ｇ、細孔容積が０．３０ｍｌ／ｇ、平均細孔径が１．５ｎｍの原料物性を有する球状シリカゲルを、マッフル炉で室温から昇温速度５℃／ｍｉｎで加熱し、５２０℃にまで加熱後、同温度で３時間保持した。その後、室温まで冷却して比較例５の試料吸着剤とした。
比較例５の試料吸着剤の比表面積は７５５ｍ² ／ｇ、細孔容積は０．２９ｍｌ／ｇ、及び平均細孔径が１．５ｎｍであった。したがって、原料のシリカゲルに対する試料吸着剤の比表面積の減少率は３％になった。また、疎水化能を示す、２０℃、２ｍｍＨｇでの水蒸気飽和吸着量は２５．８ｍｌ／ｇ（ｓｔｐ）、水に浸漬後の２週間経過後には粉化した。２０℃で水１０ｍｍＨｇ平衡吸着後のイソペンタン吸着量が０．２ｍｌ／ｇ（ｓｔｐ）であった。
【００４８】
比較例６
比表面積が６５０ｍ² ／ｇ、細孔容積が０．４０ｍｌ／ｇ、平均細孔径が２．５ｎｍの原料物性を有する球状シリカゲルを、マッフル炉で室温から昇温速度３０℃／ｍｉｎで加熱し、７００℃にまで加熱後、同温度で３時間保持した。その後、室温まで冷却して比較例６の試料吸着剤とした。
比較例６の試料吸着剤の比表面積は３９０ｍ² ／ｇ、細孔容積は０．６０ｍｌ／ｇ、及び平均細孔径が６．２ｎｍであった。したがって、原料のシリカゲルに対する試料吸着剤の比表面積の減少率は４０％になった。また、疎水化能を示す、２０℃、２ｍｍＨｇでの水蒸気飽和吸着量は３．７ｍｌ／ｇ（ｓｔｐ）、水に浸漬後の２週間経過後にはひび割れが発生していた。２０℃で水１０ｍｍＨｇ平衡吸着後のイソペンタン吸着量が１．５ｍｌ／ｇ（ｓｔｐ）であった。
【００４９】
実施例と比較例との比較から判る通り、全ての実施例のＶＯＣ吸着量は、比較例のＶＯＣ吸着量の２倍以上であった。また、比較例の試料吸着剤は、粉化したり、又は割れが発生したりしていた。
また、試料吸着剤の比表面積が４００ｍ² ／ｇ以下では、比較例１及び２のように、ＶＯＣ吸着能が極めて悪く、逆に、比表面積が７００ｍ² ／ｇ以上では、比較例３のように、吸着剤に割れが発生し易い。また、原料シリカゲルの比表面積が６００ｍ² ／ｇ以下では、比較例１のように、試料吸着剤のＶＯＣ吸着能が極めて悪い。
【００５０】
比較例１は、本発明で特定した条件で疎水化処理したので、良好な疎水化能を示すものの、比表面積、細孔容積及び平均細孔径がそれぞれ本発明の特定範囲から外れているために、ＶＯＣ吸着能が悪い。
比較例２は、原料シリカゲルの原料物性は本発明の特定範囲にあるものの、疎水化処理条件、即ち昇温速度及び加熱処理温度がそれぞれ本発明で特定した範囲の上限を超えているために、シリカゲルにシンタリング或いは歪み等が発生し、結果として、水蒸気吸着量は比較的低いものの、ＶＯＣ吸着能が極めて悪く、また試料吸着剤に割れが発生した。
比較例３は、原料シリカゲルの原料物性は本発明の特定範囲にあるものの、疎水化処理条件、特に加熱処理温度が本発明で特定した範囲の下限未満であって、疎水化処理が不足するために、疎水化能が悪く、しかもＶＯＣ吸着能が極めて悪い。
【００５１】
比較例４は、原料物性は実施例３と同じであるものの、疎水化処理温度が８００℃であって、本発明で特定した温度範囲の上限より高い。従って、吸着素材の疎水化は成されるものの、比表面積減少率が著しく大きくなって、得られた試料吸着剤の比表面積が本発明で特定した範囲の下限に届いていないため、十分なＶＯＣ吸着量が得られず、吸着剤として不適格であった。
比較例５は、原料物性は実施例５と同じであるものの、疎水化処理温度が５２０℃であって、本発明で特定した温度範囲の下限より低い。その結果として、原料物性を保つために、比表面積減少率が小さくなっている。しかしながら、温度範囲が低いため疎水化が不十分となり、水蒸気吸着量が著しく大きく、水に浸漬した試料吸着剤の粉化が著しい。この結果、ＶＯＣ吸着量も極めて低くなった。比較例６は、原料物性は本発明で特定した範囲にあるものの、疎水化処理の際の昇温速度が３０℃／分であって、本発明で特定した昇温速度範囲の上限より大きい。このため、吸着剤に歪みが発生しやすい状況にある。加熱処理温度が特定値以内にあるので、水吸着量で見る限りでは、疎水化は成されているが、歪みが多いために、水に浸漬した際に割れが生じた。また、ＶＯＣ吸着量も不満足な値であり、吸着剤としては不適格であった。
【００５２】
表１の実施例１から５の結果と、比較例１から６の結果とを比較することにより、疎水化能は、５５０〜７００℃の範囲の温度に昇温速度１〜２０℃／分で到達させ、同温度範囲で２〜５時間保持することにより、効果的に発現する。
また、原料物性が本発明の規定範囲内にあるシリカゲルを用いることにより、水に対する割れ耐性及び撥水性等の良好な疎水化能と、高いＶＯＣ吸着能とを示す、吸着剤を得ることが出来る。
【００５３】
ＶＯＣ選択率による評価
ＶＯＣ吸着能を示す因子の一つとして、試料吸着剤のＶＯＣ選択率を測定した。実施例１から実施例５及び比較例１から比較例６の試料吸着剤について、表３及び表４に示すようにＶＯＣを特定して、前述した方法に従って、ＶＯＣ選択率を測定し、表３及び表４に示す結果を得た。実施例３の試料吸着剤については、３種類のＶＯＣについて、ＶＯＣ選択率を測定した。
表３と表４との比較から判る通り、実施例１から実施例５の試料吸着剤は、そのＶＯＣ選択率が、８５％以上であって、７４％以下の比較例１から比較例６のＶＯＣ選択率に比べて、格段に大きなＶＯＣ選択率を示している。実施例３の試料吸着剤による試験から、実施例３の試料吸着剤は、ＶＯＣの種類が異なっても、ほぼ同程度のＶＯＣ選択率を示すことが判る。
【表３】

【表４】

【００５４】
以上の実施例は、本発明を説明するための例示であり、本発明を限定するものではなく、原料シリカゲルの多孔質物性、疎水化処理条件、揮発性有機化合物ガス用吸着剤の多孔質物性等は、本発明の要旨を逸脱しない限り、以上の実施例の条件により制限されるものではない。
【００５５】
【発明の効果】
本発明は、特定の多孔質物性を備えたシリカ又はシリカゲルの多孔質成形体から吸着剤を構成することにより、良好な疎水化能と高いＶＯＣ吸着能を有し、炭素数が１から１２の揮発性有機化合物ガスを選択的に吸着する、揮発性有機化合物ガス用吸着剤を実現できる。
更に、特定の多孔質物性を備えたシリカ又はシリカゲル原料に特定の条件で疎水化処理を施すことにより、揮発性有機化合物ガスの吸着に最適な本発明に係る吸着剤を経済的に製造することができる。
また、本発明のコストの低い揮発性有機化合物ガス用吸着剤をＶＯＣ−ＰＳＡ装置に使用することにより、経済的な吸着剤コストでＶＯＣ蒸気を回収することができ、大気環境保全に有効で、経済的なＶＯＣ−ＰＳＡ装置を実現できる。また、本発明の揮発性有機化合物ガス用吸着剤の優れた疎水化能及び水に対する高い割れ耐性により、長期間にわたり安定してＶＯＣを回収することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a volatile organic compounds (hereinafter referred to as VOC) gas adsorbent and a method for producing the same, and more specifically, by a pressure swing adsorption separation method (hereinafter referred to as PSA method). The present invention relates to an adsorbent that is optimal as an adsorbent for recovering low-concentration VOC gas, and a method for producing the same. In particular, the VOC gas adsorbent of the present invention is suitable as an adsorbent for recovering low-concentration VOC gas in the atmosphere at a gas station, an oil tank station or the like by the PSA method.
[0002]
[Prior art]
Liquid organic compounds such as gasoline, organic solvents for painting, and chlorinated organic solvents for cleaning contain a large amount of various organic compound components having a high vapor pressure. An organic compound having a high vapor pressure tends to volatilize and is therefore generally called a volatile organic compound (VOC). Nowadays, liquid organic compounds are used in large quantities in various fields such as painting, printing, and washing in addition to the use of gasoline as a fuel for internal combustion engines. VOC gas (hereinafter simply referred to as VOC) is volatilized and diffused in the atmosphere on a daily basis.
VOC is a fairly low concentration when it is volatilized and diffused into the atmosphere._x, SO_xTherefore, it is necessary to suppress the emission of VOCs into the atmosphere.
[0003]
However, it is technically very difficult to efficiently recover low-concentration VOCs, such as those volatilized during use, so as not to dissipate them into the atmosphere. At present, VOC capture technology is still established. It has not been.
For example, as one of the VOC capture technologies, the PSA method using an adsorbent has been studied, but adsorption that can efficiently adsorb and capture low-concentration VOCs when released to the atmosphere from a gas station or an oil tank. Since no adsorbent is found, the development of adsorbents has become an issue for application of the PSA method.
[0004]
Activated carbon that is a typical adsorbent is 1000m²If the adsorbent has only a large specific surface area of at least / g and is only adsorbed, it is the most suitable adsorbent for VOC.
However, since activated carbon is flammable, it can be used as an adsorbent for the VOC adsorption device by the PSA method at a VOC emission place such as a gas station or an oil tank where flammable gas is handled. Is difficult.
[0005]
Therefore, inorganic oxide-based adsorbents such as zeolite have been attracting attention as non-flammable adsorbents, and pressure-temperature fluctuation adsorption separation method (Pressure and Temperature Swing Adsorption, hereinafter referred to as PTSA method), which is almost the same as the PSA method. There is an example that has been tried by a temperature swing adsorption separation method (Temperature Swing Adsorption, hereinafter referred to as TSA method).
These methods use a very common inorganic oxide adsorbent such as zeolite and incorporate a step of swinging the temperature in order to desorb moisture adsorbed with VOC from the adsorbent.
However, these adsorption separation methods have practically been used for capturing relatively low concentration VOCs, such as those released from gasoline stations or oil tanks, where the adsorption target is a relatively high concentration VOC. I can't find it so far.
The reasons why it is difficult to apply these methods to the recovery of low-concentration VOCs are, first, that VOCs are difficult to adsorb because of their low concentration, and secondly, saturated water vapor affects the adsorption of VOCs. is there.
[0006]
It seems that low-concentration VOC can be efficiently adsorbed and desorbed by using a high surface area inorganic oxide-based adsorbent, but the surface of the inorganic oxide-based adsorbent has a highly polar hydroxyl group (OH) or the like. Therefore, only water molecules having a high dipole moment are selectively adsorbed, and the amount of adsorption and desorption of VOC is extremely reduced.
For example, although zeolite has a large specific surface area, the ratio of silica to alumina (SiO₂/ Al₂O_Three) Is low, it develops acid properties, increases its affinity with water, and selectively adsorbs water.
The problem of affinity with water becomes particularly prominent when VOC is at a low concentration.
[0007]
Furthermore, silica (silicon oxide, SiO₂) Itself exhibits strong water repellency, but a large number of hydrophilic silanol (Si-OH) groups usually remain on the surface of silica having a high surface area.
In the VOC-PSA adsorption process of VOC-PSA, competitive adsorption of water vapor and VOC proceeds. Therefore, if a large number of hydrophilic groups are present, a large amount of water is adsorbed. The amount decreases. In addition, in order to absorb a large amount of water, there is a problem that water penetrates into the interior and cracks occur in the adsorbent.
[0008]
To prevent the silanol group from remaining, for example, methoxytrimethylsilane (CH_ThreeO-Si- (CH_Three)_ThreeThere is a method in which an organosilicon compound such as) is brought into contact with silica and coupled with a silanol group on the surface.
On the other hand, high-silica zeolite (HS-Zeolite) in which the zeolite is hydrophobized without deteriorating the excellent porous properties such as large specific surface area, etc., by dealumination by acid extraction, etc. so as not to cause crystal destruction of the zeolite ) Is attracting attention as a low concentration adsorbent for VOCs.
[0009]
[Problems to be solved by the invention]
By the way, the environmental protection apparatus is not limited to VOC collection, and generally a new cost burden is imposed on the company to be introduced, and therefore an economical process with low cost is strongly demanded. For example, in the PSA process, it is extremely important to develop an inexpensive adsorbent because the weight of the adsorbent occupies the entire process cost.
However, since organic silicon-based organic compounds such as methoxytrimethylsilane are volatile, the coupling reaction equipment becomes complicated, and silicon-based organic compounds are expensive, so the coupling method is used for industrial processes. Thus, the hydrophobization treatment has a problem that it cannot be economically attracted. Further, high-silica zeolite has a high dealumination cost, and there is a problem that it is not economically suitable for use in an industrial process.
As described above, there is no economical adsorbent that can efficiently capture low-concentration VOCs and is suitable for industrialization processes.
[0010]
Accordingly, an object of the present invention is to provide an adsorbent capable of efficiently recovering a low concentration of VOC and a method for producing the same.
[0011]
[Means for Solving the Problems]
  Therefore, the present inventors remove hydrophilic groups to reduce moisture adsorption ability, that is, improve hydrophobicity, in order to efficiently adsorb low-concentration VOCs and increase the cracking resistance to water. With VOC suckingI thought it was necessary to improve wearing ability. And the result of repeated experiments,ratioHas specific porous properties such as surface area, pore volume, average pore diameter, etc.Of silica or silica gelIt has been found that the adsorbent composed of the porous molded body has excellent hydrophobizing ability and adsorption ability for VOC, and the present invention has been completed. In addition, the inventors have found that such an adsorbent can be produced by heat treatment under specific conditions, and have completed the method of the present invention.
[0012]
  In order to achieve the above object, the adsorbent according to the present invention is silica.Alternatively, the silica gel is heated to a predetermined temperature in the range of 550 ° C. to 700 ° C. at a temperature increase rate in the range of 1 to 20 ° C./min, and held at the predetermined temperature for a predetermined time in the range of 2 to 5 hours. ,Specific surface area of 400-700m²/ G, average pore diameter of 0.4 to 3.0 nm, and water vapor adsorption amount of 3 to 10 ml-water vapor / g-adsorbentOf silica or silica gelIt is characterized by selectively adsorbing a volatile organic compound gas having 1 to 12 carbon atoms, which is a porous molded body.
  Here, “selectively adsorb volatile organic compound gas having 1 to 12 carbon atoms” refers to selectively volatile organic compound gas having 1 to 12 carbon atoms in gas and gas components excluding water vapor. It means to adsorb to.
[0013]
  The adsorbent production method according to the present invention is an adsorbent production method for selectively adsorbing a volatile organic compound gas having 1 to 12 carbon atoms, and has a specific surface area of 600 m.²/ G or more and pore volume of 0.05 to 0.5 cm³/ G and silica or silica gel molded pellets having an average pore size in the range of 0.4 to 3.0 nm to a predetermined temperature in the range of 550 ° C. to 700 ° C. at a heating rate of 1 to 20 ° C./min. Raise the temperature at the specified temperatureIn the range of 2-5 hoursIt is characterized by holding for a predetermined time. The adsorbent produced by the method of the present invention has a specific surface area reduction rate of 5 to 40% and a water vapor adsorption amount of 3 to 10 ml / g.
[0014]
  The present inventionVolatileAdsorbent for adsorbing organic organic compound gas (hereinafter referred to simply as “adsorbent”) can be used to adsorb VOCs generated from light and medium fractions such as gasoline, naphtha, kerosene, and light oil. Because of its high performance, it is particularly suitable as an adsorbent when adsorbing a relatively low concentration of VOC released from a gas station, an oil tank, or the like by the PSA method.
  In the present invention, VOC refers to a volatile organic compound gas having 1 to 12 carbon atoms, and VOC adsorption capacity refers to the ability to adsorb VOC. The volatile organic compound means a hydrocarbon, a halogenated hydrocarbon, or an oxygen-containing organic compound. An oxygen-containing organic compound is an organic compound containing —O— and / or ═O in the chemical formula, and examples thereof include alcohols, ethers, esters, carboxylic acids, ketones, and aldehydes.
  Further, the specific surface area, pore volume and average pore diameter showing the porous physical properties of the adsorbent of the present invention are values measured by the BET method.
[0015]
Adsorbent raw material
The adsorbent material of the present invention has a specific surface area of 600 m measured by the BET method using nitrogen molecules as a probe.²/ G or more, preferably 650 m²/ G or more, pore volume of 0.05 to 0.5 cm^Three/ G, preferably 0.1-0.3 cm^Three/ G and silica or silica gel having an average pore diameter in the range of 0.4 to 3.0 nm.
Here, the silica means one that does not contain moisture, and the silica gel means one that contains moisture. Moreover, as long as the objective of this invention is achieved, the adsorbent raw material and the adsorbent may contain inorganic components other than silica or silica gel.
In addition, the practical upper limit of the specific surface area of silica gel material available on a scale at the industrialization level is currently 800 m.²/ G, but the adsorption capacity increases as the specific surface area increases.
[0016]
Average pore diameter of raw material
  The large specific surface area of the adsorbent means that the VOC molecule adsorption area per unit weight or unit volume of the adsorbent is wide, and the adsorption capacity increases accordingly. Adsorbents with a large surface area may be used, but on the other hand, low concentration VOCs volatilized and diffused into the air as in the present invention are targetedWhenIn this case, in addition to a large specific surface area, it is important to provide the adsorbent with an optimum pore diameter that facilitates the adsorption of VOCs. This is because VOC molecules are thought to be condensed and adsorbed in relatively small pores. Therefore, it is important that the adsorbent has a large surface area, a high contact probability with the VOC molecule, and a porous structure having small average pore diameter in order for the condensation process to proceed efficiently. .
  From this viewpoint, the average pore diameter of the raw silica gel or silica is preferably in the range of 0.4 to 3.0 nm, and more preferably in the range of 0.6 to 1.5 nm. In the BET method, the lower limit in the measurement of the pore volume and the pore distribution is a gap or a pore into which nitrogen molecules can enter, so a monomolecular element such as a rare gas or a hydrogen molecule smaller than nitrogen is used. When comparing with a numerical value measured by a probe or an analysis method other than the BET adsorption theory, for example, the T-plot method, it is necessary to normalize it by converting it.
[0017]
Raw material pore volume
In order to have an optimum average pore diameter, the preferred pore volume of the raw silica or silica gel is 0.05 to 0.5 cm from the correlation between specific surface area, pore volume and average pore diameter.^Three/ G, more preferably 0.1 to 0.3 cm^Three/ G.
Above this, the pore diameter becomes too large and it becomes difficult to smoothly promote the adsorption of VOC molecules. Conversely, 0.05cm^ThreeIf it is less than / g, the pore diameter becomes too small, making it difficult for VOC molecules to enter the pores.
[0018]
Raw material pellet shape
As the material shape of the adsorbent raw material of the present invention, various shapes such as a spherical shape, a cylindrical shape, and a tablet shape can be preferably used. Silica powder or silica gel powder can be used, but in this case, it is preferable to use it after forming into various shapes. As the molding method, a general molding method such as compression molding or extrusion molding can be preferably used. In addition, in order to make shaping | molding easy, you may add a binder suitably.
The size of the molded body is determined by factors such as the size of the adsorbent packed bed and the allowable pressure difference, but the diameter and length are preferably 2 mm to 10 mm, and more preferably 3 mm to 8 mm. If it is less than this, the differential pressure becomes too large, and if it exceeds this, the gap between the molded bodies becomes too large.
[0019]
Heating rate
The adsorbent of the present invention can be obtained by subjecting the silica gel raw material exhibiting the above physical properties or a predetermined hydrophobic treatment to the silica raw material. In the hydrophobization treatment, the temperature is raised to a specified heat treatment temperature within a specified range at a temperature increase rate within a specified range, and held at the predetermined heat treatment temperature for a predetermined time. The predetermined temperature heating temperature does not have to be constant during a predetermined time, and may vary within a specified temperature range.
The heating rate may be 1 to 20 ° C./min, and more preferably 5 to 15 ° C./min. If the rate of temperature rise is higher than this, the temperature difference between the surface and the inside of the raw material particles becomes too large, so the possibility that the raw material particles will crack is high, and since distortion occurs, it becomes easy to crack during water adsorption. Furthermore, a heating rate faster than 20 ° C./min is not preferable because there is a risk of exceeding a predetermined temperature range (overshooting) when shifting from temperature rising to temperature holding. Conversely, even if the rate of temperature rise is slow, there is no theoretical problem, but 1 ° C./min is a practical lower limit for economic reasons that productivity is low.
[0020]
Heat treatment temperature and holding time
After raising the temperature to the specified heat treatment temperature, the raw material particles are fired while maintaining this temperature range for 2 to 5 hours. During this time, it is necessary to pay sufficient attention to temperature control. The range of the heat treatment (firing) temperature is preferably 550 ° C to 700 ° C, more preferably 600 ° C to 700 ° C, and most preferably 620 ° C to 700 ° C.
Although baking time is not conditional compared with temperature conditions, 2 hours-5 hours are preferable, More preferably, they are 3 hours-5 hours.
[0021]
When the hydrophobization proceeds by decomposing / eliminating or condensing a number of silanol groups (Si—OH) present on the surface of silica or silica gel according to the following formulas (1) and / or (2) In order to allow these reactions to proceed sufficiently, it is necessary to maintain a predetermined temperature within the above temperature range for a predetermined time.
(SiOH)_n→ SiO₂              Decomposition / desorption (1)
(SiOH)_n→ (Si-O-Si)_{n / 2}    Condensation (2)
If the upper limit of the specified temperature range is exceeded, the sintering of silica or silica gel proceeds significantly, the reduction of the specific surface area exceeds 40%, and the desired porous physical properties cannot be obtained. Conversely, if the temperature is less than the lower limit of the temperature range, the hydrophobization treatment becomes insufficient, so that the possibility that the adsorbent breaks during the pressure swing cycle of the PSA method increases.
Compared to the temperature range, the severity of the time range to be maintained is not high, but if it is less than 2 hours, the chemical reaction of the formulas (1) and (2) may not proceed sufficiently. Productivity is inferior.
[0022]
In order to prevent cracking due to thermal expansion, etc., the hydrophobization ability is improved by removing the surface OH groups as shown in formulas (1) and (2) at a temperature of 550 ° C to 700 ° C at a predetermined temperature rise rate. To do.
If the purpose is only to improve the hydrophobizing ability, heating and firing are sufficient, but in order to recover low concentrations of VOCs in the atmosphere, maintaining a high surface area and excellent hydrophobizing ability. Therefore, the physical properties of the adsorbent raw material (silica or silica gel) are important as described above.
[0023]
Specific surface area reduction rate
In the PSA method, adsorption is not performed until a steady state is reached, as is the case with an isotherm adsorption line (adsoption-isotherm), but the pressure is swung every adsorption process for a predetermined time, so that a low partial pressure VOC molecule is quickly adsorbed. The adsorption rate is one of the important factors. Therefore, in order to effectively adsorb VOC molecules, it is important to have a specific specific surface area, average pore diameter, and hydrophobizing ability. As a result, the adsorption speed is increased.
In order to achieve a high adsorption rate, it is preferable that the specific surface area reduction rate is small. When the specific surface area reduction rate is 40% or more, the pore diameter changes due to sintering, the VOC adsorption capacity decreases, and cracking and distortion occur due to volume change. Such inconveniences occur. By performing the heat treatment for hydrophobization under the conditions shown above, the reduction rate of the specific surface area shown in the formula (3) remains at 40% or less, and the average pore diameter is also close to that of the silica gel raw material. As a result, an adsorbent having both excellent hydrophobizing ability and VOC adsorption ability and a high adsorption speed is realized.

[0024]
Water vapor adsorption
In the case of equilibrium adsorption at 20 ° C. and a water vapor pressure of 2 mmHg, if the adsorbent adsorbs 10 ml or more of water vapor per g, the adsorbent is often cracked. In addition, by the hydrophobization treatment of the method of the present invention, the water vapor adsorption amount of the adsorbent becomes 10 ml / g or less, but it is difficult to make it 3 ml-water vapor / g-adsorbent or less.
[0025]
Use of adsorbent
  When the adsorbent is actually used in the PSA system, the adsorbent filling amount is appropriately determined according to the operating conditions such as the volume and number of columns, the VOC concentration in the inlet gas, the VOC capture rate, and the operating temperature. Determine the filling height.
  This adsorbent can be combined with or mixed with known adsorbents such as high silica zeolite and alumina.didThere is no problem even if it is used. However, since the market price of other adsorbents is more expensive than the present adsorbent, if the amount of admixture or combination of known adsorbents is large, the economic advantage of the adsorbent of the present invention is lost.
  Prior to the use of the adsorbent of the present invention, no activation treatment is required. In the case where it has been stored for a long time in a state of extremely high humidity, a reduced-pressure drying process may be appropriately performed at a temperature in the range of room temperature to 350 ° C. Although the vacuum drying time is not generally determined by the PSA apparatus, 1 to 24 hours is a realistic time.
[0026]
Adsorbent VOC selectivity
The adsorbent VOC selectivity referred to in the present invention is a ratio indicating the ratio of the adsorbed amount of the volatile organic compound out of the adsorbed amount of the water vapor and the volatile organic compound adsorbed on the adsorbent. It is a defined value.
VOC selectivity = {(A) / (A + B)} × 100
Here, A is the equilibrium adsorption amount of the volatile organic compound to the adsorbent at a temperature of 20 ° C. under a pressure of 1/10 of the saturated vapor pressure of the volatile organic compound at a temperature of 20 ° C. (ml / g (stp) ).
B is the equilibrium adsorption amount (ml / g (stp)) of water vapor on the adsorbent at a pressure of 2 mmHg and a temperature of 20 ° C.
In the present invention, when the equilibrium adsorption amount of the volatile organic compound (VOC) of the adsorbent is specified, the saturated vapor is not under the saturated vapor pressure of VOC but under 1/10 of the saturated vapor pressure of VOC. This is because most of the VOC is adsorbed by the adsorbent until the pressure becomes 1/10 of the pressure. That is, in practice, the amount of adsorption under saturated vapor pressure≈the amount of adsorption under 1/10 of the saturated vapor pressure.
In PSA operation using the actual pressure fluctuation method, the adsorption process is normally performed until the pressure reaches 1/10 of the VOC saturation vapor pressure without increasing the pressure to the VOC saturation vapor pressure. Then, the process proceeds to the desorption process.
[0027]
From the above, the VOC selectivity can be defined as a factor indicating the VOC adsorption efficiency during the operation of the PSA.
Physically, the larger the value of the VOC selectivity of the adsorbent, the easier the adsorption of volatile organic compounds in the presence of water vapor, and it can be evaluated that the adsorbent is excellent for VOC-PSA. Therefore, the VOC selectivity of the adsorbent is 80% or more, preferably 85% or more. Adsorbents with a VOC selectivity of 80% or higher require a smaller amount of adsorbent than low adsorbents with low VOC selectivity, and are extremely advantageous in terms of economics and operating efficiency of the PSA method. It is.
[0028]
In addition to the VOC selectivity described above, the VOC adsorption amount of the adsorbent is also an important factor.
For example, even if the VOC selectivity of the adsorbent is high, if the VOC adsorption amount is small, there arises a problem that the adsorbent amount necessary for separating and recovering a predetermined amount of VOC becomes excessive. Therefore, it is necessary that the VOC selection rate is high and the VOC adsorption amount is equal to or higher than a predetermined level.
VOC adsorption amount is the equilibrium adsorption amount of volatile organic compound to adsorbent at 20 ° C. under 1/10 of the saturated vapor pressure of volatile organic compound at 20 ° C. (ml / g (stp)) Evaluate by The measuring method is the same as the method shown in the measuring method of VOC selectivity.
The equilibrium adsorption amount of the volatile organic compound to the adsorbent at a temperature of 20 ° C. under a pressure of 1/10 of the saturated vapor pressure of the volatile organic compound at a temperature of 20 ° C. is preferably 30 ml / g (stp) or more, 35 ml An adsorbent of more than / g (stp) is more preferable.
If the value of the VOC adsorption amount is smaller than this, the amount of adsorbent used for the apparatus to obtain the same effect increases, so the adsorption tower becomes larger and the standard of the equipment attached to the apparatus also increases. There is a high possibility that the operating cost will increase due to the increase in the size of the entire apparatus and the increase in power consumption. On the contrary, the upper limit is not particularly limited, but about 150 ml / g (stp) is considered as the current upper limit.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the present invention will be described specifically and in detail below with reference to examples. The porous physical properties, hydrophobizing ability, and VOC adsorbing ability of the sample adsorbents of the following examples and comparative examples were evaluated by the following measurement methods and evaluation methods.
Measuring method of porous properties such as specific surface area, pore volume and average pore diameter
The porous physical properties (hereinafter referred to as raw material properties) of the adsorbent raw material and the porous physical properties (hereinafter referred to as adsorbent physical properties) of the adsorbent obtained by the hydrophobization treatment are high purity N₂(Takachiho Chemical, Research Grade) was used as a probe molecule and measured with an automatic surface area / pore diameter measuring device (Belsorp28, manufactured by Bell Japan). In the measurement of the porous physical properties, prior to the measurement of the specific surface area and the pore diameter, first, the sample adsorbent and the adsorbent raw material were subjected to heat treatment under reduced pressure, and then the desired physical properties were measured.
In the reduced-pressure heat treatment of the sample, about 200 mg of sample is put in a glass sample tube, and 10^-1-10^-2While maintaining the reduced pressure state of mmHg, the temperature was raised from room temperature to 350 ° C. at a temperature rising rate of 6 ° C./min, and kept at the same temperature for 3 hours. Thereafter, the sample was cooled to room temperature at a temperature drop rate of 5 ° C./min while being kept at normal pressure + 5 mmHg with high-purity helium gas to obtain a sample for measurement. The obtained sample weight was accurately weighed and subjected to measurement of porous physical properties.
For the measurement of porous properties, an automatic dewar with an automatic liquefied nitrogen feeder (auto feeder) is used, the liquefied nitrogen temperature (-196 ° C) is maintained, and the dead volume is set to 3 with high purity helium. After measuring more than once and then evacuating under reduced pressure, probe molecules (nitrogen) were introduced and the specific surface area was measured according to the BET method. Next, desorption measurement was performed, and thereby the average pore diameter was determined.
[0030]
Evaluation method of hydrophobicity of adsorbent
In order to evaluate the hydrophobizing ability of the adsorbent, the equilibrium adsorption amount of water vapor was measured at a temperature of 20 ° C. and a pressure of 2 mmHg.
Prior to measurement of the hydrophobizing ability, the sample adsorbent was subjected to the following reduced-pressure heat treatment as a pretreatment. That is, about 100 mg of sample is put in a glass sample tube, and 10^-1-10^-2While reducing the pressure to mmHg, the temperature was raised from room temperature to 350 ° C. at a temperature rising rate of 6 ° C./min, and kept at the same temperature for 1 hour. Subsequently, it cooled to room temperature with the temperature fall rate of 5 degree-C / min, and obtained the sample adsorption agent. The obtained sample adsorbent was accurately weighed and used as a measurement sample.
Water used as a water vapor source is 50 ml of ion-exchanged water in a glass reservoir, bubbled with a decompression line, carefully cooled with a dry ice-methanol refrigerant and frozen at the bottom of the reservoir. 10^-2Dissolved gas was released while evacuating at about mmHg. Subsequently, the solution was heated and thawed. This process was repeated until no dissolved gas was released to obtain purified water.
[0031]
In the measurement of the equilibrium adsorption amount, a high-accuracy vapor adsorption amount measuring device (Belsorp18, manufactured by Bell Japan) was used. Into the glass reservoir (reservoir, volume 150 ml) in which the saturated water vapor generated from the liquid reservoir is maintained at 50 ° C. ± 1 ° C. while maintaining the water reservoir of purified water at 50 ° C. ± 1 ° C. in an air thermostat, Furthermore, water vapor is gradually introduced from the reservoir through an automatic flow control valve into a glass adsorption tube maintained at 20 ° C. ± 0.5 ° C. only in the portion containing the sample adsorbent, and introduced until an equilibrium pressure of 2 mmHg is reached. I kept doing it.
When the equilibrium pressure of 2 mmHg is reached, that is, when the pressure fluctuation for 10 minutes is within 0.1 mmHg, the amount of water introduced is determined from the pressure measured by the capacitance manometer and the internal volume, and this is used as the equilibrium adsorption amount. Furthermore, the equilibrium adsorption amount per adsorbent weight was calculated based on the sample weight after the pretreatment.
Further, in order to evaluate the cracking resistance of the adsorbent to water as one of the hydrophobizing ability, the sample adsorbent was immersed in water at 20 ° C., and the presence or absence of cracks was examined after two weeks.
[0032]
Method for evaluating VOC adsorption capacity of adsorbent
In order to evaluate the VOC adsorption capacity of the sample adsorbent, the reversible adsorption amount of VOC was measured as follows.
Prior to measurement, the sample adsorbent was subjected to the following reduced-pressure heat treatment as a pretreatment. In the heat treatment under reduced pressure, first, about 100 mg of a sample is placed in a sample tube.^-1-10^-2While reducing the pressure to mmHg, the temperature was raised from room temperature to 350 ° C. at a temperature rising rate of 6 ° C./min, and kept at the same temperature for 1 hour. Subsequently, it cooled to room temperature with the temperature fall rate of 5 degree-C / min, and obtained the sample adsorption agent. In the measurement of the VOC adsorption capacity, a required sample weight was accurately weighed from the obtained sample adsorbent and used for measurement.
In addition, isopentane used for the measurement was purified as follows. First, isopentane (Tokyo Kasei Kogyo Co., Ltd., reagent grade) is placed in a liquid reservoir, bubbled with a vacuum line, and then the liquid nitrogen surface in a Dewar bottle is carefully brought into contact with the bottom of the liquid reservoir and cooled and solidified. 10 while releasing gas^-2Evacuation was performed on the mmHg stage. It was then warmed and melted. This operation was repeated until no dissolved gas was released to purify isopentane.
Water used as a water vapor source was purified in the same manner as in the evaluation of the hydrophobizing ability.
[0033]
In the measurement, purified water and isopentane were placed in each liquid reservoir and kept at a constant temperature of 50 ° C. ± 1 ° C. in a thermostatic bath.
First, saturated water vapor generated from the liquid reservoir is introduced to a glass reservoir (reservoir, volume 150 ml) maintained at a temperature of 50 ° C. ± 1 ° C. up to a pressure of 30 mmHg, and only the portion containing the sample adsorbent is 20 ° C. Water vapor was gradually introduced into the glass adsorption tube maintained at a temperature of ± 0.5 ° C. from the reservoir through an automatic flow control valve until the equilibrium pressure of 10 mmHg was reached. Next, the amount of water adsorbed when the equilibrium pressure of 10 mmHg was reached was determined from the pressure measured with a capacitance manometer and the internal volume of the system.
Next, isopentane vapor generated from the liquid reservoir was introduced to a glass reservoir (volume: 150 ml) maintained at a temperature of 50 ° C. ± 1 ° C. up to a pressure of 540 mmHg, and only the portion containing the sample adsorbent was 20 ° C. ± 0 Isopentane vapor was gradually introduced into the glass adsorption tube maintained at a temperature of 5 ° C. from the reservoir through the automatic flow control valve until the equilibrium pressure of 540 mmHg was reached.
The equilibrium adsorption amount was the adsorption amount when the pressure fluctuation for 10 minutes was within 0.1 mmHg. The adsorption amount of isopentane was obtained from the pressure change measured with a capacitance manometer and the volume in the system, and the adsorption amount per adsorbent weight was calculated based on the sample weight after pretreatment.
Water vapor adsorption and VOC adsorption are measured using a high-accuracy vapor meter (Belsorp 18, manufactured by Bell Japan Co., Ltd.). Opening and closing of the flow control valve, etc. are controlled by a personal computer (PC9821, manufactured by NEC). Online (on-line) control.
[0034]
  The adsorbent according to the present invention is an adsorbent capable of selectively and efficiently adsorbing VOC having a low VOC concentration in the atmosphere around a gas station or an oil tank station, that is, VOC mixed with air to some extent. In such adsorption and recovery of low concentration VOC, the problem is the influence of moisture contained in the air, and the adsorption of moisture reduces the VOC adsorption capacity. In other words, an excellent adsorbent for low concentration VOCs is an adsorbent that is less susceptible to moisture.
  When moisture and VOC coexist, the adsorbent usually adsorbs water preferentially, so the VOC adsorption capacity of the adsorbent decreases. In this evaluation method, moisture is first adsorbed on the adsorbent, then VOC is adsorbed, and the adsorption capacity is evaluated. This means that the VOC adsorption capacity is evaluated in a state where there is a lot of moisture, that is, a state in which the VOC is close to a low concentration state.In other wordsThen, by adsorbing moisture in advance as in this evaluation method, the adsorbent is in a low-concentration VOC atmosphere or more severe conditions, so even after moisture adsorption. The fact that a large amount of VOC can be adsorbed correlates with high accuracy with the ability to adsorb a low concentration of VOC.
[0035]
Method for measuring VOC selectivity of adsorbent
The measurement of the equilibrium adsorption amount of water vapor (ml / g (stp)) on the adsorbent at a pressure of 2 mmHg and a temperature of 20 ° C. is performed according to the method for measuring the equilibrium adsorption amount of water vapor explained in the evaluation method for allowing the adsorbent to be submerged. .
The measurement of the equilibrium adsorption amount (ml / g (stp)) of the volatile organic compound to the adsorbent at the temperature of 20 ° C. under the pressure of 1/10 of the saturated vapor pressure of the volatile organic compound at the temperature of 20 ° C. is as follows. This is done as described in
The organic compound used for the measurement is purified in advance. For example, when isopentane is taken as an example, first, reagent-grade isopentane is put into a reservoir, and after bubbling in a vacuum line, the liquefied nitrogen surface in a Dewar bottle is carefully brought into contact with the bottom of the reservoir to cool the isopentane. While solidifying, 10^-2Dissolved gas is released while evacuating with a vacuum of the order of mmHg. Next, the solidified isopentane was heated and melted. This operation was repeated until no dissolved gas was released, and isopentane was degassed and purified. In the case of a volatile organic compound that is difficult to solidify at the liquefied nitrogen temperature, the volatile organic compound is adsorbed on a molecular sieve (molecular sieve) that has been cooled to around the liquid nitrogen temperature in advance and heated. The desorbed gas is accumulated in the gas reservoir.
[0036]
The isopentane vapor thus degassed and purified is introduced to a glass reservoir (volume: 150 ml) maintained at 50 ° C. ± 1 ° C. to about 540 mmHg, and further, the reservoir portion containing the sample adsorbent is placed at 20 ° C. ± 0.00%. Isopentane vapor was introduced from a reservoir into a glass adsorption tube maintained at 5 ° C., and the pressure fluctuation for 10 minutes at 20 ° C. under 1/10 of the saturated vapor pressure of isopentane at 20 ° C. was 1 atm. The adsorption amount (equilibrium adsorption amount) when the pressure fluctuation for 10 minutes becomes 0.02 mmHg or less at a pressure of 1/10 of the vapor pressure is 1/10 of the saturated vapor pressure of isopentane at 20 ° C. Below, it was set as the equilibrium adsorption amount (ml / g (stp)) of isopentane at 20 ° C.
In the above description, isopentane has been described as an example of the volatile organic compound, but the volatile organic compound is not limited to isopentane.
[0037]
Specific experimental results are shown below.
Example 1
Specific surface area is 600m²/ g, silica gel powder having raw material properties with a pore volume of 0.40 ml / g and an average pore diameter of 2.5 nm was tableted into 3.2 mm (diameter) × 3 mm (height) cylindrical pellets. . The pellets were then heated from room temperature to 550 ° C. in a muffle furnace at a heating rate of 1 ° C./min and subsequently held at a temperature of 550 ° C. for 5 hours. Then, it cooled to room temperature and obtained the sample adsorption agent of Example 1.
[0038]
When the physical properties of the sample adsorbent of Example 1 were measured, the specific surface area was 570 m.²/ g, pore volume was 0.38 ml / g, and average pore diameter was 2.5 nm. Therefore, the decrease rate of the specific surface area of the sample adsorbent with respect to the raw silica gel powder was 5%. Moreover, the water vapor | steam saturated adsorption amount in 20 degreeC and 2 mmHg measured according to the evaluation method of the hydrophobization ability mentioned above was 9.8 ml / g (stp). “stp” is a standard state (Standard Temperature and Pressure), and indicates an adsorption amount converted to 0 ° C. and normal pressure. Moreover, even after being immersed in water for 2 weeks, the sample adsorbent was not cracked. The amount of adsorption of isopentane measured after the equilibrium adsorption of 10 mmHg of water at 20 ° C. according to the method for evaluating the VOC adsorption capacity described above was 3.1 ml / g (stp).
The physical properties of the raw materials of Example 1, the water-repelling treatment conditions, the physical properties of the adsorbent, the water-repelling ability and the VOC adsorption amount are described in the column of Example 1 in Table 1, respectively. The same applies to Examples 2 to 5 below.
[Table 1]

[0039]
Example 2
Specific surface area is 660m²A silica gel powder having raw material properties having a pore volume of 0.10 ml / g and an average pore diameter of 0.6 nm is tablet-molded into pellets having the same shape as in Example 1, and the heating rate is 5 in a muffle furnace. The mixture was heated from room temperature to 600 ° C. at a rate of 0 ° C./minute, and then kept at 600 ° C. for 4 hours. Then, it cooled to room temperature and obtained the sample adsorption agent of Example 2.
The specific surface area of the sample adsorbent of Example 2 is 581 m.²/ g, pore volume was 0.09 ml / g, and average pore diameter was 0.6 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 12%. Further, the saturated water vapor adsorption amount and the isopentane adsorption amount obtained in the same manner as in Example 1 were 7.5 ml / g (stp) and 4.5 ml / g (stp), respectively. In addition, no cracks occurred in the sample adsorbent at the time when 2 weeks had elapsed after being immersed in water.
[0040]
Example 3
Specific surface area is 690m²/ g, a spherical silica gel having a particle size of 2 to 3 mm having a physical property of a pore volume of 0.30 ml / g and an average pore size of 2.0 nm, from room temperature to 650 ° C. at a heating rate of 10 ° C./min. And subsequently held at a temperature of 650 ° C. for 3 hours. Then, it cooled to room temperature and obtained the sample adsorption agent of Example 3.
The specific surface area of the sample adsorbent of Example 3 is 448 m.²/ g, pore volume was 0.20 ml / g, and average pore diameter was 1.8 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent relative to the raw spherical silica gel was 35%. Further, the saturated water vapor adsorption amount and the isopentane adsorption amount obtained in the same manner as in Example 1 were 5.3 ml / g (stp) and 4.1 ml / g (stp), respectively. In addition, no cracks occurred in the sample adsorbent at the time when 2 weeks had elapsed after being immersed in water.
[0041]
Example 4
Specific surface area 700m²/ g, a spherical silica gel having a particle size of 2 to 3 mm having a physical property of a pore volume of 0.30 ml / g and an average pore size of 1.5 nm from a room temperature to 700 ° C. at a temperature rising rate of 20 ° C./min. And then held at 700 ° C. for 3 hours. Then, it cooled to room temperature and obtained the sample adsorption agent of Example 4.
The specific surface area of the sample adsorbent of Example 4 is 420 m.²/ g, pore volume was 0.18 ml / g, and average pore size was 1.7 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 40%. Further, the saturated water vapor adsorption amount and the isopentane adsorption amount obtained in the same manner as in Example 1 were 3.2 ml / g (stp) and 3.7 ml / g (stp), respectively. In addition, no cracks occurred in the sample adsorbent at the time when 2 weeks had elapsed after being immersed in water.
[0042]
Example 5
Specific surface area is 780m²/ g, pore volume of 0.30 ml / g, average pore diameter of 1.5 nm and the raw material physical properties of spherical silica gel having a particle diameter of 2 to 3 mm from room temperature to 620 ° C. at a heating rate of 15 ° C./min. And subsequently held at a temperature of 620 ° C. for 2 hours. Then, it cooled to room temperature and obtained the sample adsorption agent of Example 5.
The specific surface area of the sample adsorbent of Example 5 is 655 m.²/ g, pore volume was 0.25 ml / g, and average pore diameter was 1.5 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 16%. Further, the saturated water vapor adsorption amount and the isopentane adsorption amount obtained in the same manner as in Example 1 were 10.0 ml / g (stp) and 5.9 ml / g (stp), respectively. In addition, no cracks occurred in the sample adsorbent at the time when 2 weeks had elapsed after being immersed in water.
[0043]
Comparative Example 1
Specific surface area is 450m²A silica powder having raw material properties having a pore volume of 0.69 ml / g and an average pore diameter of 6.1 nm is tableted into pellets having the same shape as in Example 1, and the heating rate is 10 in a muffle furnace. The mixture was heated from room temperature to 650 ° C. at a rate of 0 ° C./minute, and then maintained at a temperature of 650 ° C. for 3 hours. Then, it cooled to room temperature and was set as the sample adsorption agent of the comparative example 1.
The specific surface area of the sample adsorbent of Comparative Example 1 is 383 m.²/ g, the pore volume was 0.59 ml / g, and the average pore diameter was 6.2 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 15%. Further, the saturated water vapor adsorption amount and the isopentane adsorption amount obtained in the same manner as in Example 1 were 7.5 ml / g (stp) and 1.5 ml / g (stp), respectively. In addition, no cracks occurred in the sample adsorbent after 2 weeks of immersion in water.
The physical properties of the raw material of Comparative Example 1, the water soaking treatment conditions, the physical properties of the adsorbent, the water soaking ability, and the VOC adsorption amount are described in the column of Comparative Example 1 in Table 2, respectively. The same applies to Comparative Examples 2 to 6 below.
[Table 2]

[0044]
Comparative Example 2
Specific surface area is 650m²/ g, a spherical silica gel having a particle size of 2 to 3 mm having raw material properties with a pore volume of 0.40 ml / g and an average pore size of 2.5 nm, from room temperature to 800 ° C. at a heating rate of 30 ° C./min. And subsequently held at a temperature of 800 ° C. for 6 hours. Then, it cooled to room temperature and obtained the sample adsorption agent of the comparative example 2.
The specific surface area of the sample adsorbent of Comparative Example 2 is 280 m.²/ g, pore volume was 0.79 ml / g, and average pore diameter was 11.3 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 65%. Further, the saturated water vapor adsorption amount and the isopentane adsorption amount obtained in the same manner as in Example 1 were 4.8 ml / g (stp) and 0.1 ml / g (stp), respectively. In addition, significant cracking occurred in the sample adsorbent at the time when two weeks passed after being immersed in water.
[0045]
Comparative Example 3
Specific surface area is 780m²/ g 2, spherical silica gel having a particle size of 2 to 3 mm having a physical property of pores of 0.30 ml / g and an average pore size of 1.5 nm is heated at room temperature from a room temperature at a heating rate of 0.5 ° C./min. To 520 ° C. and subsequently held at a temperature of 520 ° C. for 1 hour. Then, it cooled to room temperature and obtained the sample adsorption agent of the comparative example 3.
The specific surface area of the sample adsorbent of Comparative Example 3 is 760 m.²/ g, pore volume was 0.29 ml / g, and average pore diameter was 3.0 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 3%. Further, the saturated water vapor adsorption amount and the isopentane adsorption amount obtained in the same manner as in Example 1 were 26.6 ml / g (stp) and 0.3 ml / g (stp), respectively. Moreover, the sample adsorbent had been pulverized when two weeks passed after being immersed in water.
[0046]
Comparative Example 4
  Specific surface area is 690m²/ G, pore volume of 0.30 ml / g, and spherical silica gel (2 to 3 mm diameter) having raw material properties with an average pore diameter of 2.0 nm are heated in a muffle furnace from room temperature at a heating rate of 10 ° C./min. 800 ℃MaAnd heated at the same temperature for 3 hours. Then, it cooled to room temperature and set it as the sample adsorbent of the comparative example 4.
  The specific surface area of the sample adsorbent of Comparative Example 4 is 248 m.²/ G, the pore volume was 0.32 ml / g, and the average pore diameter was 5.2 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 64%. Moreover, the water vapor | saturation adsorption amount in 20 mm and 2 mmHg which shows hydrophobization ability was 4.8 ml / g (stp), and the crack after two weeks passed after immersion in water was not seen. The adsorption amount of isopentane after equilibrium adsorption of 10 mmHg of water at 20 ° C. was 0.2 ml / g (stp).
[0047]
Comparative Example 5
Specific surface area is 780m²/ G, Spherical silica gel with raw material properties having a pore volume of 0.30 ml / g and an average pore diameter of 1.5 nm are heated from room temperature to a temperature of 5 ° C./min in a muffle furnace up to 520 ° C. Thereafter, it was kept at the same temperature for 3 hours. Then, it cooled to room temperature and set it as the sample adsorbent of the comparative example 5.
The specific surface area of the sample adsorbent of Comparative Example 5 is 755 m.²/ G, the pore volume was 0.29 ml / g, and the average pore diameter was 1.5 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 3%. Moreover, the water-saturated adsorption amount at 20 ° C. and 2 mmHg showing hydrophobicity was 25.8 ml / g (stp), and pulverized after two weeks after being immersed in water. The amount of isopentane adsorbed after 20 mm Hg equilibrium adsorption at 20 ° C. was 0.2 ml / g (stp).
[0048]
Comparative Example 6
Specific surface area is 650m²/ G, Spherical silica gel having raw material properties with a pore volume of 0.40 ml / g and an average pore diameter of 2.5 nm are heated from room temperature to a temperature of 30 ° C./min in a muffle furnace to 700 ° C. Thereafter, it was kept at the same temperature for 3 hours. Then, it cooled to room temperature and set it as the sample adsorbent of the comparative example 6.
The specific surface area of the sample adsorbent of Comparative Example 6 is 390 m.²/ G, the pore volume was 0.60 ml / g, and the average pore diameter was 6.2 nm. Therefore, the reduction rate of the specific surface area of the sample adsorbent with respect to the raw material silica gel was 40%. Further, the water vapor saturated adsorption amount at 20 ° C. and 2 mmHg showing the hydrophobizing ability was 3.7 ml / g (stp), and cracks were generated after 2 weeks after being immersed in water. The amount of isopentane adsorbed after water 10 mmHg equilibrium adsorption at 20 ° C. was 1.5 ml / g (stp).
[0049]
As can be seen from the comparison between the example and the comparative example, the VOC adsorption amount of all the examples was more than twice the VOC adsorption amount of the comparative example. Moreover, the sample adsorbent of the comparative example was pulverized or cracked.
The specific surface area of the sample adsorbent is 400 m.²/ G or less, the VOC adsorption capacity is very poor as in Comparative Examples 1 and 2, and conversely, the specific surface area is 700 m.²At / g or more, as in Comparative Example 3, the adsorbent is easily cracked. The specific surface area of the raw silica gel is 600m.²/ G or less, as in Comparative Example 1, the VOC adsorption capacity of the sample adsorbent is extremely poor.
[0050]
Since Comparative Example 1 was hydrophobized under the conditions specified in the present invention, although it exhibits good hydrophobizing ability, the specific surface area, pore volume, and average pore diameter are out of the specific range of the present invention. , VOC adsorption ability is poor.
In Comparative Example 2, although the raw material physical properties of the raw silica gel are in the specific range of the present invention, the hydrophobization treatment conditions, that is, the heating rate and the heat treatment temperature exceed the upper limit of the range specified in the present invention, respectively. Sintering or distortion occurred in the silica gel. As a result, although the amount of water vapor adsorption was relatively low, the VOC adsorption capacity was extremely poor, and cracking occurred in the sample adsorbent.
In Comparative Example 3, although the raw material physical properties of the raw silica gel are in the specific range of the present invention, the hydrophobization treatment conditions, particularly the heat treatment temperature is less than the lower limit of the range specified in the present invention, and the hydrophobization treatment is insufficient. Furthermore, the hydrophobizing ability is poor and the VOC adsorption ability is extremely poor.
[0051]
In Comparative Example 4, although the physical properties of the raw material are the same as those in Example 3, the hydrophobizing temperature is 800 ° C., which is higher than the upper limit of the temperature range specified in the present invention. Accordingly, although the adsorption material is hydrophobized, the specific surface area reduction rate is remarkably increased, and the specific surface area of the obtained sample adsorbent does not reach the lower limit of the range specified in the present invention. The amount of adsorption was not obtained and it was not suitable as an adsorbent.
In Comparative Example 5, although the physical properties of the raw material are the same as those in Example 5, the hydrophobization temperature is 520 ° C., which is lower than the lower limit of the temperature range specified in the present invention. As a result, the specific surface area reduction rate is small in order to maintain the raw material properties. However, since the temperature range is low, the hydrophobization becomes insufficient, the water vapor adsorption amount is remarkably large, and the sample adsorbent immersed in water is markedly powdered. As a result, the VOC adsorption amount was also extremely low. In Comparative Example 6, although the raw material properties are in the range specified in the present invention, the heating rate during the hydrophobization treatment is 30 ° C./min, which is larger than the upper limit of the heating rate range specified in the present invention. For this reason, the adsorbent is likely to be distorted. Since the heat treatment temperature is within a specific value, as far as the amount of water adsorbed is concerned, hydrophobization has been achieved, but since there are many strains, cracks occurred when immersed in water. Further, the VOC adsorption amount was also an unsatisfactory value, and was not suitable as an adsorbent.
[0052]
By comparing the results of Examples 1 to 5 in Table 1 with the results of Comparative Examples 1 to 6, the hydrophobizing ability was increased to a temperature in the range of 550 to 700 ° C. at a temperature rising rate of 1 to 20 ° C./min. It is expressed effectively by being allowed to reach and maintaining in the same temperature range for 2 to 5 hours.
Moreover, by using silica gel whose raw material properties are within the specified range of the present invention, it is possible to obtain an adsorbent that exhibits good hydrophobizing ability such as crack resistance against water and water repellency and high VOC adsorption ability. .
[0053]
Evaluation by VOC selectivity
As one of the factors showing the VOC adsorption capacity, the VOC selectivity of the sample adsorbent was measured. For the sample adsorbents of Examples 1 to 5 and Comparative Examples 1 to 6, VOCs were specified as shown in Tables 3 and 4, and VOC selectivity was measured according to the method described above. Table 3 The results shown in Table 4 were obtained. For the sample adsorbent of Example 3, the VOC selectivity was measured for three types of VOCs.
As can be seen from the comparison between Table 3 and Table 4, the sample adsorbents of Example 1 to Example 5 have a VOC selectivity of 85% or more and 74% or less of Comparative Example 1 to Comparative Example 6. Compared with the VOC selectivity, the VOC selectivity is much larger. From the test using the sample adsorbent of Example 3, it can be seen that the sample adsorbent of Example 3 shows almost the same VOC selectivity even if the type of VOC is different.
[Table 3]

[Table 4]

[0054]
The above examples are illustrations for explaining the present invention, and are not intended to limit the present invention. The porous physical properties of the raw silica gel, the hydrophobizing conditions, the porous physical properties of the adsorbent for volatile organic compound gas These are not limited by the conditions of the above embodiments unless departing from the gist of the present invention.
[0055]
【The invention's effect】
  The present invention, SpecialWith constant porous propertiesOf silica or silica gelA volatile organic compound that selectively adsorbs a volatile organic compound gas having 1 to 12 carbon atoms with good hydrophobizing ability and high VOC adsorption ability by constituting an adsorbent from a porous molded body Adsorbent for gas can be realized.
  In addition, silica or silica gel material with specific porous properties can be hydrophobized under specific conditions.ReasonBy applying, the adsorbent according to the present invention, which is optimal for adsorption of volatile organic compound gas, can be produced economically.
  In addition, by using the low-cost volatile organic compound gas adsorbent of the present invention in a VOC-PSA apparatus, VOC vapor can be recovered at an economical adsorbent cost, which is effective for air environment conservation, An economical VOC-PSA apparatus can be realized. Moreover, VOC can be stably recovered over a long period of time due to the excellent hydrophobizing ability and high cracking resistance to water of the volatile organic compound gas adsorbent of the present invention.

Claims (4)

It is obtained by heating silica or silica gel to a predetermined temperature in the range of 550 ° C. to 700 ° C. at a temperature increase rate in the range of 1 to 20 ° C./min, and holding the predetermined temperature in the range of 2 to 5 hours at the predetermined temperature. The specific surface area is 400 to 700 m ² / g, the average pore diameter is 0.4 to 3.0 nm, and the water vapor adsorption amount is 3 to 10 ml-water vapor / g-adsorbent silica or silica gel porous molded body. An adsorbent characterized by selectively adsorbing a volatile organic compound gas having 1 to 12 carbon atoms. A method for producing an adsorbent that selectively adsorbs a volatile organic compound gas having 1 to 12 carbon atoms, having a specific surface area of 600 m ² / g or more and a pore volume of 0.05 to 0.5 cm ³ / g and silica or silica gel molded pellets having an average pore diameter in the range of 0.4 to 3.0 nm are raised to a predetermined temperature in the range of 550 ° C. to 700 ° C. at a temperature rising rate in the range of 1 to 20 ° C./min. A method for producing an adsorbent characterized by heating and holding at a predetermined temperature for a predetermined time in a range of 2 to 5 hours .   An adsorbent produced by the adsorbent production method according to claim 2, wherein the reduction rate of the specific surface area is 40% or less, and the water vapor adsorption amount is 3 to 10 ml-water vapor / g-adsorbent. An adsorbent characterized by being. The adsorbent according to claim 1 or 3, wherein the selectivity of VOC defined by the following formula is 80% or more.
VOC selectivity = {(A) / (A + B)} × 100
Here, A is the equilibrium adsorption amount of the volatile organic compound to the adsorbent at a temperature of 20 ° C. under a pressure of 1/10 of the saturated vapor pressure of the volatile organic compound at a temperature of 20 ° C. (ml / g (stp)). ).
B is the equilibrium adsorption amount (ml / g (stp)) of water vapor to the adsorbent at a pressure of 2 mmHg and a temperature of 20 ° C.