WO2005063619A2

WO2005063619A2 - Process for the removal of the inorganic acid and metal impurities present in essentially alcoholic solutions of hydrogen peroxide coming from direct synthesis

Info

Publication number: WO2005063619A2
Application number: PCT/EP2004/013656
Authority: WO
Inventors: Roberta Miglio; Giuseppe Paparatto; Giordano De Alberti
Original assignee: Polimeri Europa S.P.A.
Priority date: 2003-12-22
Filing date: 2004-11-29
Publication date: 2005-07-14
Also published as: JP2007515370A; KR101121850B1; JP5172150B2; CN1898153A; WO2005063619A3; KR20060111603A; ITMI20032553A1; CN1898153B

Abstract

Process for the contemporaneous removal of inorganic acids and heavy metals present in solutions of H2O2 coming from direct synthesis starting from hydrogen and oxygen, fed to a reactor containing a palladium and platinum catalyst, in an essentially alcoholic liquid reaction medium containing an inorganic acid and a halogen as promoters, which comprises treating the solution of H2O2 by putting it in contact with an anionic exchange resin.

Description

PROCESS FOR THE REMOVAL OF THE INORGANIC ACIDS AND METAL IMPURITIES PRESENT IN ESSENTIALLY ALCOHOLIC SOLUTIONS OF H₂0₂ COMING FROM DIRECT SYNTHESIS

The present invention relates to a process for producing a solution of hydrogen peroxide purified to a high purity. More specifically, the present invention relates to a process for the removal of the inorganic acids and metal impurities present in essentially alcoholic solutions of H₂0₂ coming from direct synthesis, by means of ion exchange . Hydrogen peroxide is an extremely effective oxidizing agent with the advantage of not having an environmental im- pact as the only by-product due to its use is water. The demand for H₂0₂ is predicted to increase in the next few years, mainly for its use in the synthesis of base chemical products or for new applications such as, for example, the desulfuration of gas oils. In the synthesis of a base product such as propylene oxide via H₂0₂, described in international patent applications WO 02/14297 and WO 02/14298, there is the advantage, for example, of eliminating the chlorine derivatives or the coproduction of other products such as styrene or tert- butyl alcohol, which, on the other hand, characterize the current synthesis of this product. In the ammoximation of cyclo-hexanone with H₂0₂, the coproduction of salts is avoided, as described i U.S. patent 4,794,198, whereas in the hydroxylation of benzene to phenol, as described in U.S. patent 6,133,487, the process is simplified, i.e. the coproduction of acetone in the synthesis of phenol from cumene, is avoided. The production on an industrial scale of aqueous solutions of H0₂ by means of a complex two-step process, is known. In this process, a solution of anthraquinone, such as butyl anthraquinone or ethyl anthraquinone, in an organic medium immiscible with water, is first hydrogenated and then oxidized with air to produce H₂0₂ which is subse- guently extracted in aqueous phase, concentrated by distillation and purified. This process, however, suffers from substantial disadvantages deriving from the necessity of operating with large volumes of reagents, the numerous steps required, the relatively high cost of the intermediates and production of inactive by-products . An alternative method to the synthesis of H₂0₂ via anthraquinone is the method defined direct synthesis from H₂ and 0₂. The reaction takes place in. the presence of a cata- lyst, consisting of palladium and platinum, optionally carried on a solid medium and a solvent mainly based on alcohol. Examples of direct synthesis processes of H₂0₂ are cited, for example, in international patent application WO 02/14217 and in US patents 6,630,118 and 6,649,140. The solution of H0₂ produced by direct synthesis can be used directly in the integrated processes mentioned above, when the solvent and levels of impurities, in particular the hydrogen peroxide acicL reaction promoters, are compatible with the downstream processes . This means se- lecting suitable operating conditions during the synthesis, as described in U.S. patent 6,284,213, or the solution produced by direct synthesis must be subjected to a purification treatment. If a concentrated aqueous solution is to be obtained starting from the solut±on obtained from direct synthesis, a separation of the solvent and concentration of H₂0₂ must be combined with the pmrification treatment, as described in WO 02/14217. The impurities present in tlie solutions produced by direct synthesis can be classified on the basis of their origin. Noble metals, in particular Pd and Pt, derive from the dissolution, by the action of acid promoters present in solution, of the active phase of the hydrogen peroxide synthesis catalysts . Acids are present in the H₂0₂ solution as they are added in the synthesis phase as reaction promot- ers . The main representative of this group is sulfuric acid or nitric, hydrobromic, hydrochloric and phosphoric acids. Heavy metals can derive from the chemical attack of the acid solution of H₂0₂ on the surfaces of metallic materials with which the apparatus is constructed. In this group of metals, Fe, Cr, Ni, Mn, Cu, Zn, Mo and W, can be mentioned. The Applicant has now found that it is possible to proceed in a simple and convenient way for a purification from inorganic acids, particularly H2SO4, and noble and heavy metals, particularly Fe, Cr, Ni , Mn, Cu, Zn, Pd, Pt, Mo and W, of the H₂0₂ solution produced in an essentially alcoholic solvent, with direct synthesis from hydrogen and oxygen, by putting the latter in contact with anionic resins. It has been observed that, thanks to this addition, there is not only the almost complete elimination of the acids present (for example residual H₂SO₄ < 10 ppm) without decomposing the hydrogen peroxide, but, surprisingly, the impurities of a metallic nature (noble and heavy metals) present in the solution are also removed from the solution. Solutions purified by ion exchange are more stabile than the original ones and do not necessarily require the addition of stabilizers for their handling and temporary preservation. This result can be considered surprising, also because exchange chemistry, in particular the coefficients of se- lectivity and stability of anionic resins in the presence of organic solvents and oxidizing agents, are unpredictable characteristics. In "Comprehensive Analytical^' Chemistry", G. Svehla et al . , ELSEVIER 1982, Vol. XIV, pages 52-122: Ion Exchangers in Analytical Chemistry, in fact, it is pointed out that exchange equilibriums depend not only on the chemical nature of the ion species, but also on the contemporary presence of several solvents and, above all, that the exchange capacity can be reduced in non-aqueous solvents present in the system. In particular, it is stated that the loss in exchange capacity increases with an increase in the concentration of the non-aqueous solvent and that the organic solvent can also react with the functional groups of the resin. The lack of predictability of the result in non-aqueous solvents is also based on the princi- pie, indicated in "DOWEX Ion Exchange Resins Fundamentals of Ion Exchange", R.M. Wheaton and L.J. Lefevre, that the ion exchange mechanism has to go through diffusion steps . Diffusion through the fluid film in contact with the surface of the resin represents the slow step of the whole ex- change, at the low concentration levels at which the metal ions are present in the solutions of H₂0₂. The nature of the solvent can cause significant modifications with respect to the reference systems in aqueous phase. An object of the present invention therefore relates to a process for the contemporaneous removal of inorganic acids and noble and heavy metals present in solutions of H₂0₂ coming from direct synthesis starting from hydrogen and oxygen, fed to a reactor containing a palladium and platinum catalyst, in an essentially alcoholic liquid reaction medium containing an inorganic acid and a halogen as promoters, which comprises treating the solution of H₂0₂ by putting it in contact with an anionic exchange resin. According to the present invention, the removal of inorganic acids can be effected in solutions obtained by the direct synthesis of H₂0₂ through any process using at least one inorganic acid, such as sulfuric acid or nitric acid, as reaction promoting- agent and in the presence of a solvent selected from C₁-C₄ alcohols, preferably methanol . Other inorganic acids can be selected from those cited above. Examples of processes of this type are described in international patent applications WO 02/14217, WO 02/92501, WO 02/92502, WO 03/14014 and in U.S. patents 6,630,118 and 6,649,140. Among the anion exchange resins that can be used in the process, object of the present invention, strong basic resins with a quaternary nitrogen atom capable of exchanging anions , are preferred. Among the various commercial resins containing quaternary nitrogen groups, those with a styrene-divinyl benzene or acrylic-divinyl benzene matrix with a functional group of the -N(CH₃)³⁺ type, are preferred, such as DIAION PA316 and SA10A resins of Mitsubishi and AMBERLITE IRA 400, IRA 900 and AMBERSEP 900-OH, of Rohm & Haas . Commercial resins are generally available in hydroxide forms . As resins in the hydroxide form are too ba- sic and cannot be used as such, as they would significantly decompose the hydrogen peroxide with consequent safety problems, they are converted into less basic forms, such as carbonate or bicarbonate forms, preferably bicarbonate, with reagents such as sodium, potassium or ammonium carbon- ate and/or bicarbonate. There are no particular restrictions on the concentration of the solutions to be used for converting the resins into the forms suitable for the present invention. The solutions normally have a concentration ranging from 1 to 10% by weight, preferably 3-7% by weight. The purification of the solution of H₂0₂ takes place by putting it in contact with the resin in the carbonate or bicarbonate form, for example by immerging the resin in the solution and then removing it after ensuring an effective contact by means of stirring or, alternatively, by putting the solution in contact by passing it through a fixed resin bed. The latter system, from an operating point of view, is preferred. According to the present invention, it is preferable to operate with a configuration which comprises two or more resin beds, arranged parallelly with respect to the flow of the H₂0 solution, so as to always have at least one bed operating in the purification step and at least one bed in regeneration or washing phase. Each resin bed is thus cyclically subjected to a purification phase (F) , a washing phase (C) , a subsequent regeneration phase (D) and a last washing phase (E) , after which the purification phase (F) is repeated. When the purification is carried out in a specific fixed bed reactor, the space velocity, Liquid Hourly Space Velocity (LHSV), at which the solution is put in contact with the resin bed, in the form of a carbonate or bicarbonate, ranges from 1 to 100 ϊi¹, preferably from 5 to 70 h^"1, whereas there are no restrictions as regards the pressure which should simply be sufficient to overcome the pressure drops of the resin bed. Suitable temperature are those lower than 60°C, preferably from 5 to 50°C. There are no restrictions with respect to the concentration of the H₂0 solutions which can also be treated, even if, 'within the scope of the present invention, solu- tions with a hydrogen peroxide content lower than 30% by weight, preferably from 2 to 30% by weight or from 5 to 15% by weight, are preferred. The quantity of solution it is possible to purify depends on the exchange capacity of the resin used and on the concentration of the impurities present in the solution. When the removal of the acidity and metals from the solution which has been put in contact with the resin is no longer sufficiently effective, the resin must be regenerated. The regeneration phase of the anionic exchange resin placed in a fixed bed is generally carried out with an LHSV of the regenerating aqueous solution ranging from 0.5 to 20 h^"1. The regenerating stream is used with a concentration ranging from 1 to 10% by weight, typically from 3 to 5% by weight. The regenerating stream is used in such a quantity as to be equal to or exceeding the stoichio etric quantity necessary for regenerating the resin. The reagents for the regeneration are selected from sodium, potassium or ammonium carbonate and/or bicarbonate. The regeneration phase of the resin must be separated from the purification phase of the solution of H₂0₂ by a washing phase, for example with demineralized water, in order to avoid contact between the hydrogen peroxide and streams with a pH higher than neutrality or the contamina- tion of the H2O2 solution with cations of Na⁺, K⁺, NH⁴⁺ used in the regeneration phase. At the end of the treatment with anionic exchange resins, the H₂0₂ solution has an overall content of inorganic acids, in particular sulfuric acid, lower than 10 ppm. Con- temporaneously with the removal of the inorganic acids, a practically total purification of the solution from noble and heavy metals is also obtained, as all of these metals, considered for example as a sum of Fe, Cr, Ni, W, Mo, V, Zn, Cu, Pd, Pt, Ag, Pb and Rh, can be removed up to overall residual values in the purified effluent lower than 20 ppb. The purification is consequently surprisingly effective for various groups of contaminants , producing H₂O₂ solutions with an improved stability with respect to the original solutions . A further purification step on a bed of cationic exchange or chelating resins can also be added to the purification process with anionic exchange resins, on the basis of the requirements of the operations which must be carried out downstream on the purified solution, for example for removing minimum quantities of alkaline or alkaline earth ions, such as Na⁺, K⁺ or Ca⁺⁺. The equipment containing the resin bed comprises distributors, mixers and filtration systems downstream of the resin bed and can be placed in the production site or the site for the final use of the non-aqueous HO2 solution. At the end of the purification, the hydrogen peroxide solution can be treated, for example by distillation, to produce an aqueous H0₂ solution with a concentration ranging from 15 to 60% by weight, or it can be used as such in integrated processes, such as processes for the production of epoxides or ammoximation processes of ketones . Some illustrative and non-limiting examples are provided herebelow for a better understanding of the present invention and for its embodiment. REFERENCE EXAMPLE A hydro-alcoholic solution of H₂0₂ at 7% by weight is prepared according to the process described in Example 5 of U.S. patent 6,649,140. The reaction solvent consists of MeOH/H₂0 in a ratio of 95/5 and contains H₂SO₄ and HBr as reaction promoters . The direct synthesis effluent of hydrogen peroxide from hydrogen and oxygen has the following macroscopic composition (Table 1) . Table 1

Analysis by means of ionic chromatography showed the pres- ence of the following acids (Table 2). Table 2

Analysis via ICP-MS showed the presence of the elements indicated in the following table (Table 3) Table 3

The stability of the solution of H₂0₂ was characterized by monitoring its concentration with time, by periodically removing aliquots of solution preserved at 25°C in a Pyrex container, in the dark and subjecting them to poten- tiometric titration using permanganate. Over a period of 3500 hours of observation, the decomposition rate of H0₂ expressed as follows : v[%/h] _ = (initial H₂0₂ [weight %] - final H₂0₂ [weight

%] /initial H₂0₂ [weight %] ) • 1007time [h] proved to be 0.0037 %/h. EXAMPLE 1 The commercial anionic resin AMBERSEP 900-OH of Rohm & Haas, in the form of spheres having an average diameter of 1.18 mm, is charged and packed into a Pyrex cylinder having an internal diameter of 0.84 cm for a volume equal to 25 ml. The resin is treated with 200 ml of deionized water (LHSV = 10^"1) , 200 ml of methanol (LHSV = 10^"1) , again 200 ml of deionized water (LHSV = 10^""1) , then treated with an aqueous solution of ammonium bicarbonate at 5% by weight (LHSV = 10^-1) , and finally treated again with deionized water until the water at the outlet has a neutral pH. The H₂0₂ solution, prepared according to the reference example, is put in contact with the resin, treated as specified above, at 25°C under downflow conditions and at an LHSV of 10^""1. After collecting 800g of solution at the outlet of the resin bed, a subsequent 200 g are removed. The following results were obtained on the liquid removed (Table 4) .

Table 4

The decomposition rate of the H₂0 in the liquid removed, monitored for 3900 hours under the conditions of the reference example, proved to be lower than 0.00001%/h, i.e. lower than 0.1%/year. EXAMPLE 2 Example 1 was repeated using sodium bicarbonate instead of ammonium bicarbonate. The following results (Table 5) were obtained on the liquid removed. Table 5

The use of sodium bicarbonate does not cause contamination of the solution purified with Na⁺ ions . EXAMPLE 3 The commercial anionic resin AMBERSEP 900-OH of Rohm & Haas , in the form of spheres having an average diameter of 1.18 mm, is charged and packed into a Pyrex cylinder having an internal diameter of 1.04 cm for a volume equal to 20 ml. The resin is treated with 200 ml of deionized water (A) , 200 ml of methanol (B) , again 200 ml of deionized water (C) , then treated with an aqueous solution of ammonium bicarbonate at 5% by weight (D) , and finally treated again with deionized water (E) and 2500 g of H₂O₂ solution, pre- pared according to the reference example (F) . The operations from A to F were carried out with an LHSV of 10 h^-1. Steps C to F were repeated 48 times under upflow conditions, stopping for the last time before step F. The resin is then put in contact with 2500 g of H0₂ solution at 25°C and at an LHSV of 58 h^"1, collecting the liquid at the outlet. The following results were obtained on the liquid removed (Table 6) . Table 6

The decomposition rate of the H₂0₂ in the liquid removed, monitored for 3000 hours under the conditions of the reference example, proved to be lower than 0.00003 %/h.

Claims

1. A process for the contemporaneous removal of inorganic acids and heavy metals present in solutions of H₂0₂ coming from direct synthesis starting from hydrogen and oxygen, fed to a reactor containing a palladium and platinum catalyst, in an essentially alcoholic liquid reaction medium containing a promoter consisting of at least one inorganic acid and optionally a halogen, which comprises treating the solution of H₂0₂ by putting it in contact with an anionic exchange resin.

2. The process according to claim 1, wherein the hydrogen peroxide solution is put in contact with the resin by passing it through a fixed resin bed.

3. The process according to claim 1 or 2 , wherein the re- action medium essentially consists of a C₁-C₄ alcohol .

4. The process according to claim 3 , wherein the alcohol is methanol .

5. The process according to any of the previous claims , wherein the inorganic acid is sulfuric acid or nitric acid.

6. The process according to any of the previous claims, wherein the anionic exchange resin is selected from basic resins with a quaternary nitrogen atom capable of exchanging anions.

7. The process according to claim 6, wherein the anionic exchange resin is converted into carbonate and bicarbonate forms by means of aqueous solutions of sodium, potassium or ammonium carbonate and/or bicarbonate at a concentration ranging from 1 to 10% by weight.

8. The process according to claim 2, wherein the contact of the H₂0₂ solution with the anionic exchange resin bed takes place at a space velocity ranging from 1 to 100 h^"1.

9. The process according to any of the previous claims, wherein the purification of the H₂0₂ solution is carried out at temperatures lower than 60°C, preferably from 5 to 50°C.

10. The process according to any of the previous claims, wherein the residual concentration of inorganic acids, at the end of the purification treatment, is lower than 10 ppm.

11. The process according to any of the previous claims, wherein, contemporaneously with the removal of the inorganic acid, a purification of the noble and heavy metals is obtained up to overall residual values in the purified effluent lower than 20 ppb.

12. The process according to any of the previous claims, wherein the regeneration or washing of the anionic resin is carried out with an LHSV of the regenerating aqueous solution ranging from 0.5 to 20 h^"*1.

13. The process according to claim 12, wherein the regen- erating stream consists of an aqueous solution of sodium, potassium or ammonium carbonate and/or bicarbonate with a concentration ranging from 1 to 10% by weight.

14. The process according to any of the previous claims, which comprises a further purification step on a bed of cationic exchange or chelating resins .

15. The process according to any of the previous claims, wherein the purified hydrogen peroxide solution is treated to produce an aqueous solution of H₂0₂ with a concentration ranging from 15 to 60% by weight.

16. The process according to any of the claims from 1 to 14, wherein the purified hydrogen peroxide solution is used as such in integrated processes for the production of epox- ides or in ammoximation processes .