EP2547643A1

EP2547643A1 - Method for manufacturing polymer-grade bio-based acrylic acid from glycerol

Info

Publication number: EP2547643A1
Application number: EP11713325A
Authority: EP
Inventors: Michel Fauconet; Nabil Tlili
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2010-03-18
Filing date: 2011-03-15
Publication date: 2013-01-23
Also published as: WO2011114051A1; FR2957594B1; US20130165690A1; FR2957594A1; JP2013522280A

Abstract

The present invention relates to the manufacture of a "polymer-grade" bio-based acrylic acid, said "polymer grade" being defined by a minimum ¹⁴C content and by the content-limiting thresholds for impurities detrimental to the polymerization methods, in particular total aldehydes, protoanemonin, maleic anhydride, and non-phenolic polymerization inhibitors. One aim of the invention is a method for manufacturing said acid from glycerol as a raw material, said method including a step of extracting the acrylic acid by means of a heavy hydrophobic solvent. The invention also relates to the use of said acid for manufacturing superabsorbent materials or for manufacturing polymers or copolymers by polymerizing derivatives of said acid in the form of ester or amide.

Description

PROCESS FOR PRODUCING POLYMER GRADE BIO-RESOURCE ACRYLIC ACID FROM GLYCEROL

The work leading to this invention has received funding from the Seventh Framework Program of the [European Union] [European Atomic Energy Community] ^([FP7 / 2007-2013] [PC / 2007 -2011]) under Grant Agreement No 228867.

The present invention relates to a process for the manufacture of a bioprocessed acrylic acid of polymer grade from glycerol as raw material. The bio-resourced term indicates that acrylic acid is primarily based on a naturally occurring carbon source.

Acrylic acid is a compound that is used as a polymerization monomer or comonomer for the manufacture of a very wide range of end products. The polymers or copolymers are produced by polymerization of the acid, or derivatives thereof, in ester (polyacrylates) or amide (polyacrylamide) form. These polymers are used as such or as copolymers in areas as varied as hygiene, detergents, paints, varnishes, adhesives, paper, textiles, leather, etc. A very important outlet for acrylic acid is the manufacture of superabsorbents in which a partially neutralized acrylic acid is polymerized (mixture of acrylic acid and sodium acrylate or other cations), or the acrylic acid is polymerized and the polyacrylic compound is partially neutralized got.

For decades industrialists have been developing processes for the synthesis of acrylic acid.

The first generation used as raw material acetylenic-type triple bond compounds which were reacted with a mixture of carbon monoxide and water in the presence of a nickel-based catalyst.

The second generation of processes, which today is the most widely exploited industrially implements a catalytic oxidation reaction of propylene and / or propane with the aid of oxygen or a mixture containing oxygen .

This reaction is generally carried out in the gaseous phase, and most often in two stages: the first step carries out the substantially quantitative oxidation of propylene to a mixture rich in acrolein, in which the acrylic acid is then the second stage selectively oxidation of acrolein to acrylic acid.

The reaction conditions of these two stages, carried out in two reactors in series or in a single reactor containing the two reaction stages in series, are different and require catalysts adapted to the reaction; however, it is not necessary to isolate the first step acrolein during this two-step process.

The raw materials used are derived from oil or natural gas, and therefore acrylic acid is made from a non-renewable fossil carbon feedstock. In addition, processes for the extraction, purification and synthesis of raw materials as well as the end-of-cycle destruction processes of finished products made from these fossil raw materials generate carbon dioxide, the latter being a direct by-product. oxidation reactions of propylene to acrolein and acrolein to acrylic acid. All this contributes to increasing the concentration of greenhouse gases in the atmosphere. As part of the commitments of most industrialized countries to reduce greenhouse gas emissions, it is particularly important to manufacture new products based on renewable raw materials that help to reduce these environmental effects.

In recent years, manufacturers have conducted research and development on so-called "bio-resourced" synthetic processes using natural renewable raw materials. Indeed, to limit the ecological impact of conventional production processes, alternative processes using non-fossil plant raw materials have recently been developed. These are for example processes using as raw material 2-hydroxypropionic acid (lactic acid), obtained by fermentation of glucose or molasses from the biomass. They are also processes starting from glycerol (also called glycerine), resulting from methanolysis of vegetable oils at the same time as the methyl esters which are, in particular, used as fuels or fuels in diesel and heating oil. Methanolysis of vegetable oils or animal fats can be carried out according to various well-known methods, in particular by using homogeneous catalysis such as sodium hydroxide or sodium methylate in solution in methanol, or by using heterogeneous catalysis. We can refer to this topic in the article by D. Ballerini et al. in the Chemical News of Nov-Dec 2002. Processes using hydroxypropionic acid as raw material have a major disadvantage from the economic point of view. They involve a fermentation reaction which is necessarily carried out under very dilute conditions in the water. To obtain acrylic acid, a very large amount of water must be removed by distillation at a very high energy cost. Moreover, the energy expended to separate water, energy produced from fossil materials, strongly degrades the initial advantage of producing acrylic acid from this bio-resourced raw material. There may be mentioned in this field the application WO2006 / 092271 which describes a process for producing polymers from acrylic acid prepared enzymatically, in particular from carbohydrate.

It has long been known that it is possible from natural organic materials such as polyols capable of being converted chemically to obtain acids or aldehydes having 3 carbon atoms per molecule which may constitute precursors of the acrylic acid. By way of example, mention may be made of the synthesis of acrolein obtained by dehydration of glycerol, which is described in particular in US Pat. No. 5,387,720. Glycerol (also called glycerine) comes from the methanolysis of vegetable oils at the same time as methyl esters, which are used in particular as fuels or fuels in diesel and heating oil. It is a natural product that has a "green" aura, is available in large quantities and can be stored and transported without difficulty. Many studies are devoted to the valorisation of glycerol according to its degree of purity, and the dehydration of glycerol to acrolein is one of the ways envisaged.

The reaction involved in obtaining acrolein from glycerol is:

CH ₂ OH-CHOH-CH ₂ OH CH ₂ = CH-CHO + 2H ₂ O

This step is followed by a conventional oxidation step of acrolein to obtain acrylic acid according to the reaction:

CH ₂ = CH-CHO + ½ 0 ₂ CH ₂ = CH-COOH

The patent applications EP1.710.227, WO2006 / 135336, WO2006 / 092272 and WO2007 / 0219521 describe processes for the synthesis of acrylic acid from glycerol comprising the step of dehydration in the gas phase in the presence of catalysts consisting of inorganic oxides (mixed or not) based on aluminum, titanium, zirconium, vanadium, etc., and the gas phase oxidation step of acrolein thus synthesized in the presence of catalysts based on iron oxides, molybdenum, copper etc., alone or in combination in the form of mixed oxides. However, they do not give precise details of the purification phase of the acrylic acid and do not describe at all which impurities contain or do not contain the acrylic acid obtained. For example, the application WO2006 / 092272 describes a process for producing acrylic acid and superabsorbent from glycerol. It states that 99 to 99.98% pure acrylic acid can be obtained without specifying how it is obtained and what are the residual impurities. In Example 2, it is simply stated that an acrylic acid which does not contain protoanemonin is obtained without considering the other impurities which may affect the subsequent polymerizations.

Acrylic acid is intended for the implementation by the industrialists of polymerization processes either of acrylic acid or of its ester derivatives, processes which are conducted in various forms in bulk, in solution, in suspension, in emulsion. These processes can be very sensitive to the presence in the feed of certain impurities, such as aldehydes or unsaturated compounds, which can sometimes prevent the expected use value from being obtained, for example by limiting the conversion of monomer to polymer, limiting the chain length of the polymer or interfering in the polymerization in the case of unsaturated compounds. Other impurities, such as saturated non-polymerizable compounds, can be particularly troublesome in the final application, by modifying the properties of the finished product, conferring toxic or corrosive properties on the finished product, or by increasing the organic pollutant discharges during steps of manufacturing the polymer and / or the finished product.

Operators are demanding in terms of quality specifications for acrylic acid (or its ester). It must meet strict thresholds for impurities. Indeed, users of acrylic acid or acrylic esters that produce polymers use recipes adapted for the production of their polymers from a "standard" quality of acrylic acid or esters manufactured today. only from propylene. A modification of the recipes used by these users, with a view to adapting them to a different quality of acrylic acid or esters produced by a route other than that of conventional ex-propylene processes, would have significant disadvantages for these user companies. Apart from additional research and development costs, the production of one type of polymer on the same unit from different grades of acrylic acid or esters depending on their origin, fossil or organic resourced products (such as glycerol) would result in significant adaptation costs and a more complicated production infrastructure.

The need is now felt for the placing on the market of an acrylic acid that meets all the constraints mentioned above as well upstream, that is to say an acrylic acid essentially based on a source of a natural non-fossil carbon, downstream that is to say an acrylic acid meeting quality standards allowing its exploitation in the manufacture of a wide range of technical polymers, without however requiring sophisticated purification and therefore expensive.

The use of carbonaceous raw materials of natural and renewable origin can be detected thanks to the carbon atoms used in the composition of the final product. Unlike materials made from fossil materials, materials made from renewable raw materials contain ^14C . All carbon samples taken from living organisms (animals or plants) are actually a mixture of 3 isotopes: ¹² C (representing 98.892%), ¹³ C (~ 1, 108%) and ¹⁴ C (traces: 1, 2.10 ^"10 %) The ¹⁴ C / ¹² C ratio of living tissues is identical to that of the atmosphere. In the environment, ¹⁴ C exists in two main forms: in mineral form, that is to say carbon dioxide (C0 ₂ ) and in organic form, that is to say carbon integrated in organic molecules .

In a living organism, the ¹⁴ C / ¹² C ratio is kept constant by the metabolism because the carbon is continuously exchanged with the environment. The proportion of ¹⁴ C being substantially constant in the atmosphere, it is the same in the body, as long as it is alive, since it absorbs this ¹⁴ C as it absorbs ¹² C. The average ratio of ¹⁴ C / ¹² C is 1, 2x10 ^"12 .

¹² C is stable, that is to say that the number of atoms of ¹² C in a given sample is constant over time. ¹⁴ C is radioactive and every gram of living carbon contains enough ¹⁴ C isotope to give 13.6 disintegrations per minute.

The half-life (or period) T _1/2, related to the decay constant of ¹⁴ C is 5730 years. Given this duration, it is considered that the ¹⁴ C content is practically constant from the extraction of vegetable raw materials to the production of the final product.

The bio-resourced acrylic acid of the invention has a mass content of ¹⁴ C such that the ratio ¹⁴ C / ¹² C is greater than 0.8.10 ^"12 , and preferably greater than 1.10 ^{" 12} . This bio-resourced acrylic acid can even reach a ratio equal to 1, 2.10 ^"12 in the case where all the carbon elements used for its manufacture will be of non-fossil natural origin. At present, there are at least two different techniques for measuring the ¹⁴ C content of a sample:

- by liquid scintillation spectrometry

- by mass spectrometry: the sample is reduced to graphite or C0 ₂ gas, analyzed in a mass spectrometer. This technique uses an accelerator and a mass spectrometer to separate ¹⁴ C ions and ¹² C and thus determine the ratio of the two isotopes.

All of these methods of measuring the ¹⁴ C content of the materials are precisely described in ASTM D 6866 (including D6866-06) and ASTMD 7026 (including 7026-04). The measurement method preferably used is the mass spectrometry described in the ASTM D6866-06 standard ("accelerator mass spectroscopy").

The object of the present invention is to overcome the previous disadvantages by proposing a process for producing a bio-resourced acrylic acid of polymer grade, this grade being defined by the limit thresholds for the content of impurities that are detrimental to a wide range of polymerization processes. .

The subject of the invention is a process for producing a polymer-grade acrylic acid with a weight content of acrylic acid> 99% and the following impurity contents:

total aldehydes <10 ppm

protoanemonin <5 ppm

maleic anhydride <30 ppm

non-phenolic polymerization inhibitors <10 ppm

and a mass content of ¹⁴ C such that the ratio ¹⁴ C / ¹² C> 0.8.10 ^"12 .

The acrylic acid obtained by the process of the invention will preferably have a content of

total aldehydes <3 ppm

protoanemonin <3 ppm

maleic anhydride <15 ppm

non-phenolic polymerization inhibitors <3 ppm

and a mass content of ¹⁴ C such that the ratio ¹⁴ C / ¹² C> 1.10 ^"12 .

The invention relates to a process for producing a polymer grade acrylic acid using glycerol as raw material which will be converted into two stages - dehydration and oxidation - as mentioned previously integrated into a global purification process.

This process has a great analogy with the synthesis process from propylene in that the intermediate product, acrolein, from the first step is the same and the second step is conducted under the same operating conditions. However, the first-stage reaction of the process of the invention, dehydration reaction, is different from the usual process propylene oxidation reaction. The dehydration reaction conducted in the gas phase is carried out using solid catalysts different from those used for the oxidation of propylene. The acrolein-rich effluent from the first dehydration stage, intended to supply the second acrolein oxidation step to acrylic acid, contains a larger quantity of water, and furthermore has significant differences in terms of byproducts resulting from the reaction mechanisms involved being concretized by different selectivities in each of the two pathways.

The acrolein-rich effluent from the first dehydration stage, intended to supply the second acrolein oxidation step to acrylic acid, contains a larger quantity of water, and furthermore has significant differences in terms of byproducts resulting from the reaction mechanisms involved being concretized by different selectivities in each of the two pathways.

To illustrate these differences, Table 1 below summarizes the data concerning the presence of acetic acid (main impurity) in the crude acrylic acid that is to say in the liquid phase leaving the second stage reactor.

Table 1

The impurity / AA ratios depend on the catalysts used, their "age" (degradation of the selectivities over time) and the operating conditions.

Table 1 illustrates the main difference, in terms of the constituents of the liquid effluent leaving the oxidation reactor, between the ex-propylene and ex-glycerol processes. Naturally, although this is not mentioned in the table, it is also found in the crude acrylic acid, that it comes from the ex-propylene process or from the ex-glycerol process a whole series of oxygenates, alcohols, aldehydes, ketones, certain other acids in small quantities etc, whose separation, necessary, is known to those skilled in the art.

The specifications for acrylic acid grades commonly used for the production of acrylic acid and acrylic ester polymers require that the levels of impurities in Table 1 in acrylic acid be reduced to the values shown in Table 2 below. -Dessous.

Table 2

Acetic acid is troublesome in particular because it is not transformed during the polymerization process, it is saturated and therefore not polymerizable; depending on the polymerization process involved and the targeted applications for the polymer, this impurity can remain in the finished product and risk giving the finished product undesirable corrosive properties, or be found in the liquid or gaseous discharges generated by the process of polymerization, and cause organic pollution also undesirable.

The problem is that of obtaining an acrylic acid of a degree of purity corresponding to the needs of users and meeting the specifications, total aldehydes <10 ppm, protoanemonin <5 ppm, maleic anhydride <30 ppm, polymerization inhibitors non-phenolic <10 ppm, as well as those given in Table 2 by implementing a process for synthesizing acrylic acid using glycerol as a feedstock which has the disadvantage compared to the conventional propylene oxidation process , to provide at the outlet of the oxidation reactor a gaseous mixture containing a lot of water and having high levels of acetic acid.

The water and acetic acid contents of the effluent leaving the oxidation reactor pose a very important economic problem because of the expensive energy required for the removal of water and the large number of distillation treatments required for the separation of acetic acid.

The Applicant has discovered that it is possible to overcome the above disadvantages by implementing a process for purifying the gaseous effluent from the oxidation reactor of a process for synthesizing acrylic acid from glycerol, comprising a first step of dehydration of glycerol followed by a second step of oxidation of acrolein, conjugating a step of absorption of acrylic acid with a heavy solvent at the outlet of the oxidation reactor and a phase of multi-step purification leading to polymer grade acrylic acid.

Although the state of the art describes various techniques that can be used in a process for purifying acrylic acid, it can not be established according to the prior art that the combination of these techniques would make it possible to obtain a biosourced acrylic acid which satisfies to the specifications of users, and overcoming the disadvantages inherent in the use of glycerol as raw material.

The implementation of a step of absorbing acrylic acid with a heavy solvent makes it possible to solve, upstream, most of the problems posed by the presence of water and light impurities soluble in the aqueous phase. The purification phase, by a sequence of distillations, makes it possible to eliminate at the same time the traces of heavy impurities, of intermediate impurities, that is to say those having a boiling point between that of the acrylic acid and that of the heavy solvent, essentially consisting of the "heavy" compounds from the dehydration and oxidation reactions and possibly some polymerization inhibiting stabilizers and remaining light impurities.

The invention relates to a process for the production of polymer-enriched acrylic acid with a content of> 99% acrylic acid and the following impurity contents: total aldehydes <10 ppm, protoanemonin <5 ppm, anhydride maleic <30 ppm, non-phenolic polymerization inhibitors <10 ppm, and a mass content of ¹⁴ C such as the ratio ¹⁴ C / ¹² C> 0.8.10 ^"12 , from glycerol, comprising the following steps:

i) dehydration of glycerol to acrolein,

ii) oxidation of acrolein formed in acrylic acid,

iii) extraction of the acrylic acid contained in the effluent of the oxidation step ii) by absorption in a countercurrent column using a hydrophobic heavy solvent, with cooling and removal at the top of the fraction light consisting of so-called incondensable gaseous compounds and light condensable compounds such as water, acetaldehyde, unprocessed acrolein, formic acid, acetic acid,

iv) separation by distillation by toasting of the liquid phase resulting from step (iii) of a light fraction containing water and residual light, in particular acetic acid and formic acid, and a heavy fraction containing the acrylic acid in solution in the hydrophobic heavy solvent, the light fraction being recycled in the preceding extraction step (iii),

v) distilling the heavy fraction from (iv) containing the acrylic acid in solution with a tailing off of the hydrophobic heavy solvent and at the top of the acrylic acid fraction containing the intermediate impurities and optionally traces of solvent, the fraction heavy end of this step (v), consisting essentially of the solvent, being recycled in step (iii) optionally after purification treatment, vi) distillation of the acrylic acid solution from the head fraction resulting from the previous step (v) to extract in tail the heavier compounds called intermediates and traces of solvent possibly entrained and at the head technical acrylic acid.

vii) purification by distillation of technical acrylic acid to obtain a grade of "polymer" grade acrylic acid, after addition to acrylic acid of an amine compound reacting with aldehydes still present.

In an alternative embodiment of the process, the gaseous reaction medium resulting from step i) of dehydration of glycerol which has a significant water content due to the glycerol charge (aqueous solution) and to the reaction itself is subjected to additional step (i ') of partial condensation of the water. This additional step is for example that described in the patent application WO 08/087315 in the name of the applicant; it will eliminate a portion of the water, so as to bring this gas to a composition substantially identical to that of the ex-propylene process, to feed the second step of oxidation of acrolein to acrylic acid. The water / acrolein molar ratio in the effluent resulting from the first propylene oxidation stage is generally between 1, 5/1 and 3/1 while it is of the order of 9/1 at the end. of the glycerol dehydration step. By substantially identical composition is meant in particular concentrations of acrolein, water and oxygen near. This partial condensation step (i ') must be carried out with cooling to a temperature which makes it possible, after removal of the condensed phase, to obtain a gas stream containing water and acrolein in a water / acrolein molar ratio. from 1, 5/1 to 7/1 This partial condensation of water which requires a lowering of the temperature of the effluent leaving step i) at a temperature between 280 and 320 ° C to reach a temperature of 70 to 140 ° C, before an increase to achieve the conditions of the acrolein oxidation step ii) about 240 ° C, however, avoids degradation of the ^2nd stage catalyst oxidation of acrolein to acrylic acid. It also avoids the costly disposal of large amounts of water at later stages, which may lead to loss of acrylic acid. In addition, it makes it possible to eliminate some of the "heavy" impurities formed during dehydration.

Glycerol is a chemical, 1,2,3-propane triol, which can be obtained either by chemical synthesis from propylene, or as a co-product formed during the methanolysis of vegetable oils or animal fats. The methanolysis of vegetable oils, which constitutes a preliminary stage of the process in the case of integration of the entire oil / fat chain with acrylic acid, leads, on the one hand, to methyl esters and, on the other hand, to glycerol. Methyl esters are used in particular as fuels or fuels in diesel and heating oil. With the development of fuels of renewable origins, and in particular vegetable oil methyl esters (VOMEs), the production of glycerol according to this route of production increases sharply, the glycerol representing of the order of 10% of the weight of the transformed oil.

Glycerol, denomination of glycerol when it is in aqueous solution, obtained from vegetable oils or animal fats may contain salts (NaCl, Na ₂ SO ₄ , KCl, K ₂ SO ₄ ...). In this case, there will generally be a preliminary step of removing the salts for example by distillation, by using ion exchange resins or by using a fluidized bed as described in the French application FR 2 913 974. Among the methods used or studied for the purification and evaporation of glycerol include those described by GB D'Souza, J. Am. Oil Chemists' Soc. November 1979 (Vol 56) 812A, by Steinberner U et al., In Fat. Sci. Technol. (1987), 89 Jahrgang Nr.8, pp. 297-303, and Anderson DD et al. in Soaps and Detergents: A Miami Beach Fia., Oct. 12-14, 1994, chapter 6 pp172-206. Ed: Spitz L, AOCS Press, Champaign.

Generally aqueous solutions of glycerol are used, the concentration of which can vary widely, for example from 20 to 99% by weight of glycerol, preferably using solutions comprising from 30 to 80% by weight of glycerol.

The principle of the process for obtaining acrylic acid from glycerol is based on the 2 consecutive reactions of dehydration and oxidation: CH ₂ OH-CHOH-CH ₂ OH CH ₂ = CH-CHO + 2H ₂ O

CH ₂ = CH-CHO + ½ 0 ₂ → CH ₂ = CH-COOH

The process can be carried out in two separate steps with two different catalysts.

The dehydration reaction, which is a balanced reaction favored by a high temperature level, is generally carried out in the gas phase in the reactor in the presence of a catalyst at a temperature ranging from 150 ° C. to 500 ° C., preferably between 250 ° C and 350 ° C, and a pressure between 1 and 5 bar. It can also be conducted in the liquid phase. It can also be carried out in the presence of oxygen or an oxygen-containing gas as described in applications WO 06/087083 and WO 06/1 14506.

The oxidation reaction is carried out in the presence of molecular oxygen or a mixture containing molecular oxygen, at a temperature ranging from 200 ° C to 350 ° C, preferably from 250 ° C to 320 ° C, and at a pressure ranging from 1 to 5 bar in the presence of an oxidation catalyst.

The dehydration reaction of glycerol is generally carried out on acidic solid catalysts. Suitable catalysts are homogeneous or multiphase materials which are insoluble in the reaction medium and which have a Hammett acidity, denoted H _{0 of} less than +2. As disclosed in US Pat. No. 5,387,720 which refers to the article by K. Tanabe et al in "Studies in Surface Science and Catalysis", Vol 51, 1989, Chapters 1 and 2, Hammett's acidity is determined by amino titration. using indicators or adsorbing a base in the gas phase.

These catalysts may be chosen from natural or synthetic siliceous materials or acidic zeolites; inorganic carriers, such as oxides, coated with inorganic acids, mono, di, tri or polyacids; oxides or mixed oxides or heteropolyacids or salts of heteropolyacids.

These catalysts can generally be constituted by a heteropoly acid salt in which protons of said heteropoly acid are exchanged with at least one cation selected from the elements belonging to Groups I to XVI of the Periodic Table of Elements, these heteropoly acid salts containing at least an element selected from the group consisting of W, Mo and V.

Among the mixed oxides, mention may be made especially of those based on iron and phosphorus and those based on cesium, phosphorus and tungsten.

The catalysts are chosen in particular from zeolites, Nafion® composites (based on fluorinated polymers of sulphonic acid), chlorinated aluminas, acids and salts of phosphotungstic and / or silicotungstic acids, and various solids of the metal oxide type such as tantalum oxide Ta ₂ O ₅ , niobium oxide Nb ₂ O ₅ , alumina Al ₂ O ₃ , titanium oxide TiO ₂ , zirconia Zr0 ₂ , tin oxide SnO ₂ , silica SiO ₂ or silico-aluminate SiO ₂ -Al ₂ O ₃ , impregnated with acid functions such as borate B0 ₃ , sulfate SO ₄ , tungstate WO ₃ , phosphate PO ₄ , silicate SiO ₂ , or molybdate MoO ₃ or a mixture of these compounds.

The foregoing catalysts may further comprise a promoter such as Au, Ag, Cu, Pt, Rh, Pd, Ru, Sm, Ce, Y, Se, La, Zn, Mg, Fe, Co, Ni, or montmorillonite gold.

The preferred catalysts are zirconium phosphates, tungsten zirconias, zirconium silicates, titanium or tin oxides impregnated with tungstate or phosphotungstate, phosphated aluminas or silicas, heteropolyacids or salts of heteropolyacids, iron phosphates and phosphates. iron phosphates comprising a promoter.

As the oxidation catalyst, all types of catalysts well known to those skilled in the art are used for this reaction. Solids containing at least one element selected from the list Mo, V, W, Re, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Te, Sb, Bi, Pt, Pd, Ru, are generally used. Rh, present in the metallic form or in the form of oxide, sulphate or phosphate. In particular, the formulations containing Mo and / or V and / or W and / or Cu and / or Sb and / or Fe are used as main constituents.

When the process is conducted in two stages with two different reactors, it may be advantageous to proceed between the two reactors to an intermediate condensation of water as described in the application WO 08/087315.

The conversion of glycerol to acrylic acid which is based on the 2 consecutive dehydration and oxidation reactions mentioned above can also be carried out in one and the same reactor. In this reaction scheme, called oxidation hydration, the exothermic nature of the oxidation reaction is compensated for by the endothermic nature of the dehydration reaction, which contributes to a better thermal equilibrium of the process. In this type of process, it is possible to use two different catalytic beds, upstream dehydration and downstream oxidation, each with its specific catalyst, ie a single bed with a "mixed" catalyst consisting of a mixture of dehydration and dehydration catalysts. oxidation. This version of the single-reactor process involves recycling (after separation) the unconverted acrolein to carry out the oxidation phase. The gaseous mixture resulting from the 2nd stage (oxidation reaction) consists, apart from acrylic acid:

- light compounds that are incondensable under the conditions of temperature and pressure usually used: nitrogen, unconverted oxygen, carbon monoxide and carbon dioxide formed in small quantities by ultimate oxidation,

condensable light compounds: in particular water, generated by the dehydration reaction or as a diluent, unconverted acrolein, light aldehydes, such as formaldehyde and acetaldehyde, formic acid and acetic acid; ,

- heavy compounds: furfuraldehyde, benzaldehyde, maleic acid and anhydride, benzoic acid, phenol, protoanemonin ...

The second stage of manufacture consists in recovering the acrylic acid contained in the gaseous effluent resulting from the oxidation reaction in order to transform it into the polymer grade acrylic acid of the invention.

The first step of this purification step (step iii of the process according to the invention) consists of an extraction of the acrylic acid by countercurrent absorption which is accompanied by a cooling of the assembly. For this, the gaseous effluent from the reactor is introduced at the bottom of an absorption column where it encounters against the current a solvent or a mixture of hydrophobic heavy solvents introduced at the top of the column. The flow of solvent introduced at the top of the column is from 3 to 6 times by mass that of the acrylic acid contained in the gaseous effluent of the absorption column. The light compounds under the conditions of temperature and pressure usually used (respectively more than 50 ° C. and less than 2.10 ⁵ Pa) are eliminated at the top of this absorption column.

A heavy solvent solution having an acrylic acid content generally of between 15 and 25% by weight and containing, in addition, intermediate compounds having a boiling point between that of the heavy solvent and that of the solvent is collected at the bottom of the column. acrylic acid. These intermediate compounds are constituted by the heavy products of the reaction: furfuraldehyde, benzaldehyde, maleic acid and anhydride, benzoic acid, phenol, protoanemonin and optionally by certain stabilizing products introduced into the medium to inhibit the polymerization reactions.

The light fraction, emerging at the top, consists of incondensable light compounds under the conditions of temperature and pressure usually used: nitrogen, unconverted oxygen, carbon monoxide and carbon dioxide formed in small quantities by ultimate oxidation, and light compounds. condensables: especially water, generated by the dehydration reaction or as a diluent, unconverted acrolein, light aldehydes, such as formaldehyde and acetaldehyde, formic acid, acetic acid. This hydrophobic heavy solvent extraction operation is well known and has even been described for the treatment of acrylic acid synthesized by oxidation of propylene. The following patents may be mentioned in this regard: French Patent No. 1,588,432, French Patent No. 2,146,386, German Patent No. 4,308,087, European Patent No. 0 706 986 and French Patent No. 2,756,280 which describe such solvents. These solvents have a boiling point greater than 170 ° C., for example between 200 and 380 ° C. and preferably between 270 and 320 ° C. French Patent No. 1,588,432 describes the use of aliphatic or aromatic acid esters with a high boiling point. They are most often constituted by binary mixtures capable of forming eutectics, such as, for example, diphenyl (DP) and diphenyl ether (DPO) which form a eutectic in a proportion of 26.5-76.5 (BF No. 2 146,386 and EP0706,986) or even ternary, DP-DPO-dimethylphthalate (DMP) (DE No. 4,308,087). French Patent No. 2,756,280 recommends the use of aromatic solvents having a boiling point greater than 260 ° C. and having one or two aromatic rings substituted with at least one alkyl radical having from 1 to 4 atoms. carbon, or cycloalkyl, especially ditolyl ether alone or in the form of a mixture of its isomers or ditolyl ether mixture (DTE) and dimethylphthalate.

The process of the invention can be conducted with these various solvents. However, the preferred solvents are those described in this French patent No. 2,756,280 which, in addition to improving the separation of the impurities contained in the reaction mixture, allow efficient recovery of the polymerization inhibitors. The operational conditions of this absorption step are as follows.

The gaseous reaction mixture is introduced at the bottom of the column at a temperature of between 130 ° C. and 250 ° C. The hydrophobic heavy solvent is introduced at the top of the column at a temperature of between 10 ° C. and 60 ° C. The respective amounts of water and gaseous reaction mixture are such that the weight ratio of heavy solvent to acrylic acid is between 3/1 and 6/1. The operation is conducted at a pressure close to atmospheric pressure of between 0.8 and 2.10 ⁵ Pa. In the second purification step, step (iv) of the process of the invention, the liquid solution of acrylic acid in the hydrophobic heavy solvent is then sent to a topping zone, to eliminate the traces of water and condensable light compounds that remained at the foot of the previous absorption zone. This heading zone is fed at the top by the foot flow of the absorption zone. The top-extracted stream enriched with light compounds is returned to the absorption zone of step iii), in order to eliminate these light compounds in the top flow of this absorption zone and to collect the acid at the bottom. acrylic in solution in the hydrophobic heavy solvent.

The third step of this purification step (step v) is a distillation of the heavy fraction resulting from step (iv), containing acrylic acid, to separate the heavy solvent at the bottom and at the top a fraction of acrylic acid. containing the intermediate impurities and possibly traces of solvent, the heavy fraction, essentially consisting of hydrophobic heavy solvent, from this step (v) being recycled to step (iii) optionally after purification treatment.

The fourth step of this purification step (step vi) is a separation step by distillation on the one hand of the intermediate compounds and on the other hand purified acrylic acid (technical acrylic acid). The foot flow of the preceding column of step (v) is introduced at the bottom of a distillation column operating at a head pressure of the order of 2.10 ³ to 2.10 ⁴ Pa. purified acrylic acid, technical grade, and tail intermediate compounds.

The technical acrylic acid product is then addressed in a step vii) to a final purification zone to achieve the quality of acrylic acid polymer grade. The fifth step of this purification step (step vii) is to finally purify the technical grade acrylic acid to polymer grade acrylic acid. To achieve this quality of acrylic acid to synthesize high molecular weight polymers, it is particularly important to eliminate some residual aldehydes, such as furfuraldehyde, benzaldehyde and acrolein, to extremely low levels, can be achieved economically by simple distillation, because of their volatility too close to that of acrylic acid. To do this, it is possible to eliminate the aldehydes by a chemical treatment with a reagent which forms with these aldehydes heavy reaction products more easily separable from acrylic acid by distillation. Among the reagents that can be used, it is possible to use amines, as described in US Pat. No. 3,725,208, and more particularly compounds of the family of hydrazines, such as glycine as described in patent JP 7,500,014, or the hydrate d hydrazine as described in US Pat. Nos. 3,725,208 or JP 7,430,312, or alternatively aminoguanidine as described in patent EP 270,999. These compounds can be used as such or in the form of their salts. The chemical treatments that are described all have the disadvantage of generating water during the reaction of the aldehyde with the amino reagent. The presence of water in acrylic acid can also be harmful for the manufacture of certain polymers. For this reason, it may be advantageous to carry out this chemical treatment operation by coupling it with a distillation step for the preliminary removal of water and the light compounds at the head, before a distillation step of the acrylic acid intended to separate heavy compounds, as described in patent JP 7,495,920.

In a preferred embodiment of the process of the invention, the flow of technical acrylic acid is fed to a distillation column operating at a head pressure of about 2.10 ³ to 2.10 ⁴ Pa, in a mixture with the amine elimination reagent of aldehydes, chosen from hydrazine derivatives, preferably hydrazine hydrate, introduced in a molar ratio of 2 to 10 relative to the aldehydes contained in technical acrylic acid. The overhead stream, consisting essentially of acrylic acid, water, and acetic acid, the latter in low concentration, can be recycled upstream of the process, preferably in step iii extraction, in order to recover acrylic acid. Column foot flow is in turn sent at the bottom of a second column operating under a head pressure of the order of 2.10 ³ to 2.10 ⁴ Pa, in which the elimination of heavy compounds in the bottom and the distillation of the acrylic acid at the head, to obtain a grade "polymer grade" of acrylic acid.

The different stages of separation by absorption or distillation make it necessary to add polymerization inhibitors to the treated streams in order to avoid the formation of heavy polymeric compounds detrimental to the proper functioning of the assembly. The polymerization inhibitors generally used for the acrylic acid purification steps are phenolic products, such as hydroquinone or methyl ether of hydroquinone, phenothiazine derivatives, compounds of the family of thiocarbamates, such as copper n-butyl dithiocarbamate, derivatives thereof amines, such as hydroxylamines, hydroxydiphenylamine, or the family of phenylene diamines, nitroxide derivatives of 4-hydroxy 2,2,6,6-tetramethyl-1-oxy-piperidine (TEMPO), such as 4-hydroxy -TEMPO or 4-oxo-TEMPO, or metal salts, such as manganese acetate. These inhibitors may be used alone or in combination, and are further preferably introduced in combination with an oxygen-containing gas.

These polymerization inhibitors are generally heavy compounds, whose volatility is lower than that of acrylic acid, but may in some cases be lighter than the solvent. They are eliminated at the bottom of the columns when the inhibitors are heavier than the solvent, or are divided between the head flow and the foot flow for inhibitors that are lighter or close to the solvent. In most columns, their concentration in the vapor phase inside the distillation columns is low and insufficient to prevent the initiation of polymers. To prevent the appearance and accumulation of polymers, these additives are usually introduced into the liquid feeds to equipment, but also to the head and at different points of the columns and equipment, so as to ensure a constant and homogeneous reflux of rich solution in polymerization inhibitors on all parts of the equipment. In general, they are sent in solution in a liquid, for example in acrylic acid or in the solvent if the purification step concerns flows containing the solvent.

The acrylic acid of polymer grade obtained at the top of the last distillation column (step vii) is supplemented with methyl ether of hydroquinone (EMHQ) at a concentration of 200 +/- 20 ppm; by adding this inhibitor to the overhead stream, the final product is stabilized.

The invention also relates to the use of polymer-grade bio-resourced acrylic acid for the manufacture of superabsorbents comprising the polymerization of said partially neutralized acid, or the polymerization of said acid followed by a partial neutralization of the polyacrylic acid obtained .

The invention also relates to the superabsorbents obtained by polymerization of bio-resourced acrylic acid of polymer grade.

The invention also relates to the use of bio-resourced acrylic acid of polymer grade for the manufacture of polymers or copolymers by polymerization of the derivatives of said acid in ester or amide form. It also relates to the polymers or copolymers obtained by polymerization of the derivatives in ester or amide form of bio-resourced acrylic acid of polymer grade. The method of the invention will be better understood on reading examples which are given below by way of illustration only.

EXAMPLES

The acrylic acid of the invention and its manufacturing process are illustrated in the following examples:

Example 1: preliminary step of purification of crude glycerol.

Example 2 Transformation of Glycerol to Acrolein followed by Partial Condensation of Water

Example 3: Oxidation of Acrolein to Acrylic Acid

Example 4: Recovery of the crude acrylic acid as a solution in the heavy solvent.

Example 5: solvent / crude acrylic acid separation to obtain technical acrylic acid.

Example 6: Purification of technical acrylic acid to obtain acrylic acid polymer grade.

In the following examples, the concentrations of the very low levels of impurities in the streams of technical acrylic acid and of acrylic acid of polymer grade are measured by the following methods (numbers in parentheses: precision, threshold of quantification):

by Lichrospher 100-RP-18 high performance liquid chromatography, with UV spectrometric detection and quantification by external calibration: protoanemonin (3%, 0.1 ppm), furfural (1.4%;

0.1 ppm), benzaldehyde (0.2%, 0.25ppm), maleic anhydride assayed as maleic acid (1.5%, 0.1 ppm), phenothiazine (2%, 0.2ppm)

by the same method, with prior derivatization in the presence of dinitrophenyl hydrazine: formaldehyde (3%, 0.1 ppm).

by UV-visible spectrometry, after reaction of acrolein with 4-hexyl resorcinol in an ethanol / trichloroacetic acid medium, catalyzed by mercuric chloride, and development of a blue color exhibiting a maximum absorbance at 603 nm: acrolein (5% 0.1 ppm)

by FFAP column gas chromatography, with flame ionization detection and quantification by internal calibration: acetic acid

(3%, 10ppm) Example 1

The first phase consists in purifying the crude glycerol obtained from the methanolysis of vegetable oils, by eliminating the salts. The crude glycerol solution comprises, by weight, 88.5% glycerol, 5.1% water and 5.1% sodium chloride. A flow of 8642 g is continuously fed to a stirred reactor of 2 liters heated by an external electric reactor heater. The glycerol vapors and water are condensed in a refrigerant and recovered in a receiver. This purification operation is carried out under a pressure of 670 Pa. 7695 g of a solution of glycerol free of sodium chloride are obtained.

Example 2 In a second phase, the glycerol dehydration reaction is carried out with acrolein. The dehydration reaction is carried out in the gas phase in a fixed bed reactor in the presence of a solid catalyst consisting of a Zr0 ₂ - WO ₃ tungsten zirconia at a temperature of 320 ° C. at atmospheric pressure. A mixture of glycerol (50% by weight) and water (50% by mass) is sent into a vaporizer, in the presence of air, in a molar ratio of 0 ₂ / glycerol of 0.6 / 1. The gaseous medium leaving the vaporizer to 290 ° C. is introduced into the reactor, consisting of a 30 mm diameter tube charged with 400 ml of catalyst, immersed in a salt bath (KNO ₃ eutectic mixture, NaN0 ₃ , NaN0 ₂ ) maintained at a temperature of 320 ° C. .

To carry out the optional step of condensing a portion of the water, the reactor gas outlet is sent at the bottom of a condenser. This condenser consists of a column containing a propak packing, equipped with a water-cooled overhead condenser. The cooling temperature in this exchanger is adapted so as to obtain at the outlet of the gas a vapor temperature of 64 ° C. under atmospheric pressure. Under these conditions, the acrolein loss at the bottom of the condensation column is less than 2%.

Example 3

In a third phase, the gaseous mixture containing 1.75 mol / h acrolein is introduced, after addition of air (molar ratio 0 ₂ / acrolein 0.9 / 1) and nitrogen in amount necessary to obtain an acrolein concentration of 5.4 mol%, feeding the acrolein oxidation reactor with acrylic acid. This oxidation reactor consists of a tube 30 mm in diameter loaded with 480 ml of mixed oxide catalyst Mo / V, immersed in a bath of salt identical to that described in Example 2, maintained at a temperature of 250 ° C. Before introduction on the catalytic bed, the gaseous mixture is preheated in a tube also immersed in the salt bath.

The composition of the reaction gas stream at the reaction outlet (% volume) is as follows: nitrogen (66%), oxygen (2%), water (15%), C0 ₂ (7%), CO (1%), acid acrylic (5.7%), acetic acid (0.5%).

Example 4

At the outlet of the oxidation reactor, the gaseous mixture is introduced at the bottom of an absorption column operating under an absolute pressure of 130 kPa to carry out step (iii). This column comprises 8 theoretical plateaus in total. In the lower part, over 1/4 of its total height, the column is equipped with a condensing section, at the top of which is recycled a portion of the condensed mixture recovered at the bottom of the column, after cooling to 67 ° C in a heat exchanger external. At the top of the column, a stream consisting of DTE (ditolyl ether) and DMP (dimethylphthalate) is fed at a temperature of 50 ° C. at a ratio of DTE / DMP mass of 0.85 / 0.15, with a solvent / acid mass ratio. acrylic acid contained in the 5/1 reaction gas, in which 1% of EMHQ and 0.01% of copper dibutyldithiocarbamate were previously dissolved as polymerization inhibitors. The temperature of the vapors at the top of the column is 65 ° C., that of the acrylic acid solution obtained at the bottom of the column is 83 ° C. The product obtained in the foot is cooled to a temperature of 64 ° C, then is sent using a pump at the head of a second column with an efficiency of 9 theoretical plates. The distillation is carried out in this column at a pressure of 107 hPa. The temperature at the bottom of the column is 97 ° C. and the temperature at the top of the column is 72 ° C. All condensed vapors at the top are returned to the external cooling loop of the absorption column.

Example 5 The flux extracted at the bottom of the second column of Example 4 is a solution of crude acrylic acid in the hydrophobic heavy solvent which titrates approximately 17% of acrylic acid. The flow of crude acrylic acid solution obtained in the preceding step is cooled to 45 ° C. and then fed to the top of a distillation column of efficiency 3 theoretical plates, said column operating under a pressure of 67 hPa . At the column head, a part of the extracted and condensed flow is returned to the upper plate, the other part is recovered. The temperature in the boiler is 152 ° C, and the head temperature reaches 82 ° C. .

The flow of AA withdrawn at the top of the column containing 98.2% of acrylic acid, with, as majority impurities, 0.17% of acetic acid, 0.33% of maleic anhydride, 0.06% of Ditolyl ether, is addressed in the lower part of a second column of 1 1 theoretical plates, operating under a pressure of 140 hPa and receives at the top a mixture of stabilizer (5% EMHQ in AA). The reflux ratio applied at the top (flow of liquid refluxed / liquid flow withdrawn) is 1, 5/1. The bottom temperature is 95 ° C, the head temperature 85 ° C.

The technical acrylic acid obtained at the top of this last column is 99.6% AA. The impurities in this stream are acetic acid (0.17%), furfural (0.005%), protoanemonin (0.009%), benzaldehyde (0.012%), maleic anhydride (0.05%), water (0.1%).

Example 6

The technical grade acrylic acid obtained from Example 5 is supplemented with hydrazine hydrate in a molar ratio of 7/1 relative to the aldehydes present (furfural, benzaldehyde, acrolein, etc.) and the stream is distilled in a column of 10 theoretical plates operating at a pressure of 90hPa, at the top of which 10% of the feed stream is extracted, with a reflux / withdrawal ratio of 1/1. The flux obtained at the bottom of this column is then fed to a final column of 10 theoretical plates, under a pressure of 90 hPa, with a head temperature of 69 ° C.

Analyzes of the polymer grade acrylic acid obtained at the top of this column show that the product contains 1 ppm protoanemonin, 0.8 ppm furfural, 0.5 ppm benzaldehyde, 0.2 ppm acrolein, <1 ppm formaldehyde, 0.08% acetic acid, 12 ppm maleic anhydride. The acrylic acid obtained, analyzed by the ASTM-D6866-08 method, has a mass content of ¹⁴ C corresponding to a proportion of biobased product / fossil product greater than 99%.

Claims

1. Process for producing a bio-resourced acrylic acid of polymer grade having a content of> 99% acrylic acid, and impurity contents of: protoanemonin <5 ppm, total aldehydes <10 ppm, maleic anhydride <30 ppm, inhibitors non-phenolic polymerization <10 ppm, and a mass content of ¹⁴ C such that the ratio ¹⁴ C / ¹² C> 0.8.10 ^"12 , from glycerol characterized in that it comprises the following steps:

i) dehydration of glycerol to acrolein,

ii) oxidation of acrolein formed in acrylic acid,

iii) extraction of the acrylic acid contained in the effluent of the oxidation step ii) by absorption in a counter-current column using a hydrophobic heavy solvent,

iv) separation by toasting by distillation of the liquid phase from step (iii) of a light fraction containing water and residual light, in particular acetic acid and formic acid, and a heavy fraction containing the acrylic acid in solution in the hydrophobic heavy solvent,

v) distillation of the heavy fraction from (iv) containing the acrylic acid in solution with a tailing off of the hydrophobic heavy solvent, and at the top of the acrylic acid fraction containing the intermediate impurities and optionally traces of solvent, the heavy fraction resulting from this step (v), consisting essentially of the solvent, being recycled in step (iii) optionally after the purification treatment, vi) distillation of the acrylic acid solution of the top fraction resulting from the step previous (v) to extract in tail the heavier compounds called intermediates and traces of solvent possibly entrained, and at the head technical acrylic acid.

vii) purification by distillation of technical acrylic acid to obtain a grade of acrylic acid of polymer grade, after addition to acrylic acid of an amino compound reacting with the aldehydes still present.

2. Method according to claim 1 characterized in that step iii) implements at least one absorption solvent immiscible with water and having a boiling point greater than 170 ° C, and preferably between 270 and 320 ° C.

3. Process according to claim 2, characterized in that the absorption solvent consists of ditolyl ether alone or in the form of a mixture of its isomers or the ditolyl ether (DTE) and dimethylphthalate mixture.

4. Method according to one of claims 1 to 3 characterized in that the gaseous reaction mixture from step ii) is introduced at the bottom of the column at a temperature between 130 ° C and 250 ° C, the hydrophobic heavy solvent being introduced at the top of the column at a temperature of between 10 ° C. and 60 ° C., and the respective quantities of solvent and gaseous reaction mixture are such that the weight ratio of heavy solvent to acrylic acid is between 3/1 and 6 / 1, the operation being conducted at a pressure close to atmospheric pressure of between 0.8 and 2.10 ⁵ Pa.

5. Process according to any one of the preceding claims, characterized in that steps i) and ii) are carried out in a single reaction zone.

6. Method according to any one of claims 1 to 4 characterized in that steps i) and ii) are carried out in two successive reaction zones.

7. A method according to claim 6 characterized in that one carries out a partial condensation of water between steps i) and ii) at a temperature between 70 ° C and 140 ° C.

8. Process according to any one of the preceding claims, characterized in that at the bottom of the absorption column of step iii) is collected a solution of heavy solvent having an acrylic acid content generally of between 15 and 25% by weight. and additionally containing so-called intermediate compounds, having a boiling point between that of the heavy solvent and that of the acrylic acid, constituted by the heavy products of the reaction, which solution is then addressed to an etching zone by distillation, step iv), to eliminate in the head the traces of water and condensable light compounds that have remained at the foot of the absorption zone of step iii) and collect in the foot acrylic acid in solution in the solvent heavy hydrophobic.

9. Process according to any one of the preceding claims, characterized in that during stage v) the heavy fraction resulting from stage (iv), containing acrylic acid, to separate at the bottom of the heavy solvent and at the top a fraction of acrylic acid containing the intermediate impurities and optionally traces of solvent, the heavy fraction, essentially consisting of hydrophobic heavy solvent, resulting from this step (v) being recycled to step (iii) optionally after the purification treatment, and then in step vi) is separated by distillation on the one hand intermediate compounds and secondly technical acrylic acid.

10. Process according to any one of the preceding claims, characterized in that step vi) is carried out in a column operating at a pressure of between 2.10 ³ and 2.10 ⁴ Pa.

1 1. Process according to any one of the preceding claims, characterized in that the acrylic acid resulting from stage vi) is subjected to a new distillation carried out in the presence of compounds capable of reacting with the aldehydes still present chosen from amines, and more particularly compounds of the family of hydrazines, such as glycine, or hydrazine hydrate, aminoguanidine, compounds which can be used as such or in the form of their salts.

12. Acrylic acid obtained directly according to the process of any one of claims 1 to 1 1