EP2139809A1

EP2139809A1 - Adsorption process for removing inorganic components from a hydrochloric acid gas flow

Info

Publication number: EP2139809A1
Application number: EP08735019A
Authority: EP
Inventors: Wolf Aurel; Oliver Felix-Karl SCHLÜTER
Original assignee: Bayer MaterialScience AG
Current assignee: Covestro Deutschland AG
Priority date: 2007-04-17
Filing date: 2008-04-04
Publication date: 2010-01-06
Also published as: KR20090129476A; JP2010524814A; DE102007018016A1; CN101657380A; US20080257150A1; WO2008125235A1

Abstract

The invention relates to a method for removing inorganic components from a crude gas flow containing hot hydrochloric acid. Said method comprises the steps: A) introducing the hot crude gas that contains HCl and impurities to an adsorption bed, B) adsorbing the inorganic components from the HCl-containing crude gas onto an absorber, C) withdrawing the purified HCl gas from the adsorption bed.

Description

Adsorption process for removing inorganic components from a gas stream containing hydrogen chloride

The invention relates to a process for the treatment of hydrogen chloride-containing gas streams which are contaminated with inorganic compounds, by means of adsorption.

Specifically, the invention relates to the purification of hydrogen chloride-containing process gases of hydrogen chloride oxidation, in particular of the catalyzed hydrogen chloride oxidation.

There are various methods for removing organic contaminants from HCl-containing gas streams, eg. B. of benzene from HCl by washing with a mixture of H ₂ SO ₄ / HOAc / H ₂ O (DE 24 13 043 Al) or by adsorption on alumina (GB 1 090 521).

To purify HCl gas containing phosgene, phosgene is removed by washing with dichloroethane (DE-A 11 07 18), which is not particularly attractive due to the use of organic halogenated solvents.

For the removal of inorganic impurities from hydrogen chloride, only a few methods are described, which usually take place on the purification of hydrochloric acid, but not the gaseous hydrogen chloride.

For the purification of hydrochloric acid z. For example, as described in Hydrometallurgy (2005), 77 (1-2), 81-88, ion exchangers are used to remove traces of chromium, molybdenum and tungsten. A disadvantage is the low long-term stability of the ion exchanger in comparison to inorganic oxides (Al, Si) and their relatively poor regenerability.

The removal of arsenic from gaseous hydrogen chloride by an activated carbon bed is described in US-A-1,936,078. The temperatures used are generally very low (<100 ⁰ C), so it is not obvious whether an application at high temperatures is even possible. In addition, due to the Oxidationsempfmdlichkeit the activated carbon use for the purification of O ₂ -containing HCl gas streams at> 250 ⁰ C is not possible.

Additionally, in Deacon product gases, the presence of water of reaction leads to the formation of hydrochloric acid at a temperature below 100 ^° C. The illustrated cleaning methods of the prior art have the disadvantage that they are not suitable for a purification of HCl gas streams at a temperature in particular above 250 ⁰ C, as they occur for example in a Deacon process.

The object of the invention is to provide an improved purification process for a crude gas stream containing hydrogen chloride.

According to the invention this is effected by the inorganic impurities are removed at high temperatures (> 120 ° C normal pressure), in particular at more than 190 ⁰ C, by passing the raw gas through an adsorbent bed. Hydrochloric acid, which can be obtained from the thus purified hydrogen chloride, contains only traces of inorganic impurities and can be used, for example, in electrolysis processes or as a neutralizing agent or as a catalyst in chemical processes.

The present invention also has the particular aim of reducing the loss of valuable components such as ruthenium in the process gas purification of contaminated with inorganic compounds hydrogen chloride gas streams. This can be achieved by working up the adsorption bed.

The invention relates to a process for removing inorganic components from a hot crude gas stream containing hydrogen chloride, comprising the steps of:

A) Introduction of the hot HCl-containing contaminated raw gas in an adsorbent bed

B) Adsorption of metal components from HCl-containing crude gas to an adsorbent

C) Purification of purified HCl gas from adsorber bed

Inorganic impurities in the context of the invention are understood to mean titanium compounds, in particular titanium chloride, titanium oxides, titanium oxide chlorides,

Ruthenium compounds, in particular ruthenium oxides, ruthenium chlorides, ruthenium oxide chlorides, chromium compounds, in particular chromium oxides, chromium chlorides or chromium oxide chlorides, tin compounds, in particular tin oxides, tin chlorides, tin oxide chlorides, copper compounds, in particular copper oxides, copper chlorides or copper oxide chlorides, zirconium compounds, zirconium oxides, zirconium chlorides, zirconium oxide chlorides, furthermore silicon, aluminum oxides , Gold, silver, bismuth, cobalt, iron, manganese, molybdenum, nickel, magnesium and vanadium compounds, in particular in the form of oxide, chlorides or oxide chlorides. Tin compounds, ruthenium compounds or titanium compounds of the aforementioned type are preferably removed by the process. As an adsorbent for Adsoφtion B) here are usually zeolites, alumina, (especially as organometallic complex), SiO ₂ (especially in the form of silica gel), aluminum silicalites (in particular in the form of bentonite) and other metal oxides are used. Preferred is gamma-alumina.

The BET surface area of the adsorbent, in particular of the aluminum oxide, is preferably in the range of 10-1000 rnVg, more preferably in the range of> 25 m ² / g.

Common types of apparatus for producing an intensive gas adsorbent Kontaktes are simple fixed beds, fluidized beds, fluidized beds or as a whole movable fixed beds. Another possibility is to use the adsorber bed in a Deaconreaktor as a downstream bed to the catalyst bed.

The advantages of adsorptive removal of metal components from gas streams are that the highly purified HCl is suitable for use in HCl electrolysis, in particular by means of an oxygen-consuming cathode, as a catalyst and as a neutralizing agent for chemical synthesis without further aftertreatment. For example, in the case of HCl electrolysis by means of an oxygen-consuming cathode, especially tetravalent cations (eg tin or titanium compounds) increase the cell voltage and thus undesirably lower the life of the electrolysis cells.

The method is particularly preferably used when the hydrogen chloride-containing purified gas stream originates from a production process for the production of chlorine from hydrogen chloride and oxygen, in particular a catalyzed gas phase oxidation of hydrogen chloride with oxygen or a non-thermal reaction of hydrogen chloride and oxygen. The coupling with the catalyzed gas phase oxidation of hydrogen chloride with oxygen (Deacon method) is particularly preferred.

As described above, the catalytic process known as the Deacon process is particularly preferably used in combination with the process according to the invention. Here, hydrogen chloride is oxidized with oxygen in an exothermic equilibrium reaction to chlorine, whereby water vapor is obtained. The reaction temperature is usually 150 to 500 ⁰ C, the usual reaction pressure is 1 to 25 bar. Since it is an equilibrium reaction, it is expedient to work at the lowest possible temperatures at which the catalyst still has sufficient activity. Furthermore, it is expedient to oxygen in superstoichiometric Use quantities of hydrogen chloride. For example, a two- to four-fold excess of oxygen is customary. Since no loss of selectivity is to be feared, it may be economically advantageous to work at relatively high pressure and, accordingly, longer residence time than normal pressure.

Suitable preferred catalysts for the Deacon process include ruthenium oxide, ruthenium chloride or other ruthenium compounds on tin oxide, silica, alumina, titania or zirconia as a carrier. Suitable catalysts can be obtained, for example, by applying ruthenium chloride to the support and then drying or drying and calcining. Suitable catalysts may, in addition to or instead of a ruthenium compound, also contain compounds of other noble metals, for example gold, palladium, platinum, osmium, iridium, silver, copper or rhenium. Suitable catalysts may further contain chromium oxide.

The catalytic hydrogen chloride oxidation may be adiabatic or preferably isothermal or approximately isothermal, batchwise, but preferably continuously or as a fixed bed process, preferably as a fixed bed process, more preferably in tube bundle reactors to heterogeneous catalysts at a reactor temperature of 180 to 500 ⁰ C, preferably 200 to 400 ^0th C, more preferably 220 to 350 ⁰ C and a pressure of 1 to 25 bar (1000 to 25000 hPa), preferably 1.2 to 20 bar, more preferably 1.5 to 17 bar and in particular 2.0 to 15 bar are performed ,

Typical reactors in which the catalytic hydrogen chloride oxidation is carried out are fixed bed or fluidized bed reactors. The catalytic hydrogen chloride oxidation can preferably also be carried out in several stages.

In the case of the adiabatic, isothermal or approximately isothermal mode of operation, it is also possible to use a plurality of reactors with intermediate cooling, that is to say 2 to 10, preferably 2 to 6, particularly preferably 2 to 5, in particular 2 to 3, connected in series. The hydrogen chloride can be added either completely together with the oxygen before the first reactor or distributed over the various reactors. This series connection of individual reactors can also be combined in one apparatus.

A further preferred embodiment of a device suitable for the method consists in using a structured catalyst bed in which the catalyst activity increases in the flow direction. Such structuring of the catalyst bed can be done by different impregnation of the catalyst support with active material or by different dilution of the catalyst with an inert material. As an inert material, for example, rings, cylinders or balls of titanium dioxide, zirconium dioxide or mixtures thereof, Alumina, steatite, ceramic, glass, graphite, stainless steel or nickel alloys can be used. In the preferred use of shaped catalyst bodies, the inert material should preferably have similar external dimensions.

Suitable shaped catalyst bodies are shaped bodies with any desired shapes, preference being given to tablets, rings, cylinders, stars, carriage wheels or spheres, particular preference being given to rings, cylinders or star strands as molds.

Ruthenium compounds or copper compounds on support materials, which may also be doped, are particularly suitable as heterogeneous catalysts, preference being given to optionally doped ruthenium catalysts. Suitable support materials are, for example, silicon dioxide, graphite, rutile or anatase titanium dioxide, tin dioxide, zirconium dioxide, aluminum oxide or mixtures thereof, preferably titanium dioxide, zirconium dioxide, aluminum oxide, tin dioxide or mixtures thereof, particularly preferably γ- or δ-aluminum oxide, tin dioxide or their mixtures.

The copper or ruthenium-supported catalysts can be obtained, for example, by impregnation of the support material with aqueous solutions of CuCl ₂ or RuCl ₃ and optionally a promoter for doping, preferably in the form of their chlorides. The shaping of the catalyst can take place after or preferably before the impregnation of the support material.

For doping the catalysts are suitable as promoters alkali metals such as lithium, sodium, potassium, rubidium and cesium, preferably lithium, sodium and potassium, more preferably potassium, alkaline earth metals such as magnesium, calcium, strontium and barium, preferably magnesium and calcium, particularly preferably magnesium, Rare earth metals such as scandium, yttrium, lanthanum, cerium, praseodymium and neodymium, preferably scandium, yttrium, lanthanum and cerium, more preferably lanthanum and cerium, or mixtures thereof.

The moldings can then be dried at a temperature of 100 to 400 ⁰ C, preferably 100 to 300 ⁰ C, for example, under a nitrogen, argon or air atmosphere and optionally calcined. Preferably, the moldings are first dried at 100 to 150 ⁰ C and then calcined at 200 to 400 ⁰ C.

The conversion of hydrogen chloride in a single pass can preferably be limited to 15 to 95%, preferably 40 to 90%, particularly preferably 50 to 90%. After conversion, unreacted hydrogen chloride can be partly or completely recycled to the catalytic hydrogen chloride oxidation. The volume ratio of hydrogen chloride to oxygen at the reactor inlet is preferably 1: 1 to 20: 1, preferably 1: 1 to 8: 1, particularly preferably 1: 1 to 5: 1. The heat of reaction of the catalytic hydrogen chloride oxidation can be used advantageously for the production of high-pressure steam. This can be used to operate a Phosgeniemngsreaktors and or distillation columns, in particular of isocyanate distillation columns.

In a further step, the chlorine formed is separated off. The separation step usually comprises several stages, namely the separation and optionally recycling of unreacted hydrogen chloride from the product gas stream of the catalytic hydrogen chloride oxidation, the drying of the obtained, substantially chlorine and oxygen-containing stream and the separation of chlorine from the dried stream.

The separation of unreacted hydrogen chloride and water vapor formed can be carried out by condensation of aqueous hydrochloric acid from the product gas stream of hydrogen chloride oxidation by cooling. Hydrogen chloride can also be absorbed in dilute hydrochloric acid or water.

The loaded with inorganic impurities adsorbent material is replaced at appropriate intervals by fresh adsorbent. The valuable metal compounds present in the asorption agent (in particular ruthenium or other noble metal compounds) are removed from the adsorbent by suitable basically known digestion processes and fed to reuse.

Examples

Example 1 (comparison)

In a fixed bed reactor 50 g of catalyst of a tin dioxide-supported ruthenium chloride catalyst (content RuCl ₃ 4 wt .-%) diluted with 150 g of glass body and at 4 bar and 350 ⁰ C with 40.5 l / h of hydrogen chloride, 315 l / h of oxygen and Nitrogen flows through 252 l / h. The conversion of hydrogen chloride is> 95%. From the product stream, which consists in addition to unreacted educts and nitrogen in equal parts of chlorine and water, the water and the unreacted hydrogen chloride are separated in a condenser. The condensate is then analyzed by ICP-OES. This results in an average tin content of 72 mg Sn and a ruthenium content of 0.5 mg per kg condensate. The individual measured values are reproduced under D to F in Table 1.

Example 2 hi a fixed bed reactor 50 g of catalyst are diluted with 150 g of glass body and at 4 bar and 350 ⁰ C with 40.5 l / h of hydrogen chloride, 315 l / h of oxygen and 252 l / h of nitrogen flowed through. The conversion of hydrogen chloride is> 95%. The hot product gas stream (195 ⁰ C) is passed through an adsorber (γ- Al ₂ O ₃ , manufacturer Saint-Gobain, type SA3177, 3 mm pellets) to a condenser. From the product stream, which consists in addition to unreacted educts and nitrogen in equal parts of chlorine and water, the water and the unreacted hydrogen chloride are separated in a condenser. The condensate is then analyzed by ICP-OES. The result is a tin content of on average <1 mg Sn per kg of condensate. The ruthenium content is below the detection limit. The measured values are shown under A to C in Table 1.

Table 1: Tin and ruthenium content in the condensate in experiments with and without adsorber

Experiment A B C D E F

Sn [mg / kg Cond.] 1.17 0.94 0.50 63 75 78

Ru [mg / kg Kond.] <0, l <0, l <0, l 0.61 0.11 0.85

Claims

claims

A process for removing inorganic components from a crude hydrogen gas stream containing hot hydrogen, comprising the steps of:

A) introduction of the hot HCl-containing contaminated raw gas into an adsorbent bed,

B) adsorption of the inorganic components from the HCl-containing raw gas to an absorber,

C) Discharge of the purified HCl gas from the adsorber bed.

2. The method according to claim 1, characterized in that the adsorption B) at a temperature of at least 120 ⁰ C, preferably 190 to 400 ⁰ C, is performed.

3. The method according to any one of claims 1 or 2, characterized in that as adsorbent at least one of the series: zeolites, alumina, silica, aluminum silicalite, preferably γ-alumina, is used.

4. The method according to any one of claims 1 to 3, characterized in that the adsorbent has a BET specific surface area of 10 to 1000 m ² / g, preferably 25 to 1000 m ² / g.

5. The method according to at least one of claims 1 to 4, characterized in that the adsorbent is in the form of a fixed bed, in particular as a downstream bed to a fixed catalyst bed.

6. The method according to at least one of claims 1 to 5, characterized in that the inorganic impurity comprises one or more of the following metal compounds: titanium, ruthenium, chromium, tin, copper, zirconium, silicon, aluminum , Gold, silver, rhodium, iridium, platinum, palladium, bismuth, cobalt, iron, manganese, molybdenum, nickel, magnesium and vanadium compounds.

7. The method according to claim 6, characterized in that the metal compounds in the form of their chlorides, oxides or oxide chlorides are present.

8. The method according to at least one of claims 1 to 7, characterized in that the adsorption at a pressure of 1 to 25 bar, preferably 2 to 20 bar, more preferably 4 to 15 bar, takes place.

9. The method according to at least one of claims 1 to 8, characterized in that the raw gas still at least one of the gases from the series: chlorine, oxygen, water, inert gas, in particular carbon dioxide, nitrogen, helium, neon, argon, krypton comprises.

10. The method according to at least one of claims 1 to 9, characterized in that following the discharge C), the purified hydrogen chloride gas is dissolved in water or dilute hydrochloric acid and separated from the residual gas.

11. Use of the hydrochloric acid from the process according to claim 10 for hydrochloric acid electrolysis or as an acidic catalyst or as a neutralizing agent in chemical processes.

12. A process for the preparation of chlorine from hydrogen chloride and oxygen, in particular in the presence of catalyst (Deacon process), characterized in that the product obtained after the oxidation of unreacted hydrogen chloride comprising product gas stream of a purification according to a method of any one of claims 1 to 9 is subjected.