[1]'F T 21901,491 United States Patent Office Patented Aug. 25, 1959 2 ine rt anthraquinoiie de gradation products as residuo, recovering the anthrahydroquinone values from the aqueous extract, and dissolving the recovered values in the recovered solvent to obtain a reconstituted purified working solution. In one embodiaieiit of the -mvention, the degraded working solution is @ first hydrogenated so as to convert stibstantially all of the usable anthraquinone compounds present to an@Lhrahydroquinones. The latter are separated by extraction with an aqueous solution of sodium hydroxide in which they are soluble in the form of their soditim salts. Recovery of the anthrahydroquinone values from the aqueous extract solution is accomplished by o-,,cidizing the solution to convert the anthrahydroquinones to anthraquinones which precipitate. The latterare theii recombined with the organic solvent recovered by distflling the organic solution remaining after the sodium hydroxide extraction step. ln this embodiment, the residue remaining from the distillation step to recover the solvent will include both regenerable and nonregenerable inert materials. In another embodiment, the organic solution whir-h remains following the sodium hydroxide extraction step, and which will include both regenerable and non-regenerable inerts, is treated to reconvert the regenerable inerts to usable anthraquin(>ne compounds and the solution,@ in its reduced form, is again ectracted with sodium hydroxide solution to recover the regenerated anthrahydroquinone valties for reuse in the purified and reconstituted working sc)lution. Tn this embodiment, the residue of inert materials remaining from the distillation to recovor solvent wiR consist essentially of non-regenerable inerts and will be discaxded. An advantage of employing a second sodium@ hydroxide extraction step as indicated above is that it requires less vigorous hydrogenation conditions to obtain substantiall-y complete recovery of the antliraquinones since the hydrogenation can be effected in stages under relatively mild conditions. However, useful results can be obtained when such regeneration treatment precedes a single extraction with sodium hydroxide. Whether using one or mo - re extractions with sodium hydroxide, the workin.a solution extracted in the last of such extractions should have been hydrogenated to convert substantially aU anthraquijaones present to anthrahydroquinones, otherwise useful anthraquinones will be lost along with the inerts which remain as residue f-rom the solvent distillation step. On the other hand, the working solution which is extracted by the first of two extractions with sodium hydroxide, need not be completely hydrogenated and it will generally be most convenient to employ degraded solution as it comes from the hydrogenation stage of the hydrogen peroxide process where hydrogenation is usually effected only to about 40@ to 70% of completion. Recovery of anthrahydroquinone values from the aqueous extract of the extraction step can be effected in any desired manner. The hydroquinones can be separated for use in reconstituting the working solution by acidifying the extract to precipitate them. Preferably, the extract is treated with free or elemental oxygen which converts the anthrahydroquinones to anthaqw'nones which are precipitated for reuse. A convenient source of oxygen for this purpose is air. Most preferably, stich conversion is effected in the prescnee of the organic solvent employed in the working solution, e.g., solvent recovered from the solvent distillation step. In such operations, the anthraqumones fonned in the oxidation dissolve directly in the organic solvent to form the purified working solution which requires only wasmng with water to free it of traces of alkali before it is ready for reuse. 'fhe invention is illustrated by the forowing examples 2,901,491 PURIFICATION OF WORKING SOLUTIONS FOR PRODUCING HYDROGEN PEROXIDE 5 Carl W. Eller, Jr., and James M Snyder, Memphis, Tenn. assignors to E. 1. du Pont de'Nemours and C.ompany, Wilmington, Del., a corporation of Delaware No Drawing. ApoEcation May 24,1957 10 Serial No. 661,283 15 Claims. (Cl. 260-369) This invention relatos to tho purificatibn bf w6rking 15 solutions employed in produding hydrogen peroxide in cyclic operations involving the catalytic reduction of an anthraquiflone and subsequent oxidation of the reslilting anthrahydroquinone to reform the anthraquinone and sfh3ultdneously produce hy&o.-en peroxide. More par- 20 ticularly, it relates to a method of purifying such working solutions after they have become degraded through use in the peroxide-synthesis operations. Processes for producing hydrogen peroxide by operations of the above type are well known and many anthra25 quinone compounds (and their tetrahydro derivatives), particularly the lower alkyl anthraquinones in which the alkyl group is attached in the 2-position, have been proposed as working intennediates. The working solutions in such processes comprise a solution of the anthra30 qwnone intermediate in a water-imn-iiscible organic solvent. Many mixed and single-component solvents have been proposed. So far as the present invention is concemed the working solution can be a solution: of any anthraquinone compotind, or niixture of such compounds, 3 5 in any solvent or solvent niixttire, which are known to be suitable for peroxide synthesizing processes of the above type. It is well known that in such processes the peroxide synthesizing capacity of the working solution decreases 4 0 with continued use in the cyclic operations due to degradation of the anthraquinone working intermediate. Such degradation results in the formation of by-products which are inert, i.e., they do not synthesize hydrogen peroxide in the cyclic operation. The inert anthraquinone degra15 dation products are of two general types: (1) regenerable inerts, i.e., those which can be reconverted to anthraqwnone compounds usable in the synthesis of hydrogen peroxide; and (2) non-regenerable inerts, i.e., those which cannot readily be reconverted to usable compounds. Con50 version of the regenerable inerts to usable or active compounds obviously is desir@ble and ways of accomplishing this are known. On the other hand, the non-regencrable inerts serve no useflil purpose and, in fact, their removal is highly desirable if not essential since their - presence 55 at high concentrations adversely affects the specific gravity of the working solution and restricts the amount of useful working intermediate that can be successfully retained in the solution. It is an object of the inventibn to provide an effe,-tiv,- 60 method for removing inert anthraquinone degadation products from working solutions of the above type. A further object is to provide a method of separating nonregenerable inert materials from the other components of degraded working solutions. Still further objects w 65 be apparent from the following description. The objects of the invention are accomplished by removing the anthrahydroquinone values from - hydrogenated degraded working solution by extracting the working solution with an aqueous solution of a water-soluble metal 70 hydroxide, recovering the solvent component of the resulting@ working solution, e.g., by distiration, to leave
[2]3 in which all concentrations are weight percentages, unless Othenvise stated. Example I A -working solution -initially consisting -of. a @,solution of in a @mixture of a-met alene -and diisobutylearbinol was tised,in cyclic r eduction@oxidation -operations for the -production of @@hydrogeli peroxide until it had become degraded to a substantial extent. Tbe de,-raded solution, which:contained 16.01 % active anthraquinones (2-tbutylanthraquinone -and the corresponding tetrahydr oaiithraquinone) aiid 5@61 % inerl mateti6ls (regenerables and,non-regenerables), was hydrogenated @Lt 40' C. in - the presence of a catalyst com,prising metallic palladium on an,artivated alumina siipport Lintil 95% of the anthraquinones present were converted to anthrabydroquinones, i.e., hydro-enated to @95% of completion. The !hydrogenated solution (225 was extracted with 8 successive portions (200 ml. each) of an aqueous 10% sodium hydroxide solution leaving the solution of the inerts in the orgaiaic solven't The latter was distilled under reduced pressure.to recover 90% of the solvent in pure forin, the remainder of the solvent being discarded with the residue of inert mateiials. The aqueous extract containing the anthrahydroquinones in salt form was oxidized at room temperature with oxygen @in @the presence,of the recovered purified organic solvent, whereoy@the anthrahydroquinones were converted @to anthraquinones which were dissolved @as formed by @the organic solvent. The resulting organic @phase, after separation from the aqueous phase, was in effect a reconstituted, purified working solution in which 93% of the active anthraquinones originally present in the degraded working solution was recovered free, from inert degradation products. Example 2 To 129.ml. of a degraded worl@ing solution @similar to that of Example 1 containing 15.34% active.anthraquinones and 6.23% inerts, there-,vereadded 49.5-g.,granular zipc metal and 68.4,g. of a 19.6% aqueous sulf@ric acid solution. The mixture was agitated at room temperature for 18.5 hours, at which time hydrogenation of @the,anthraqtiinones was about 97% complete. The mixture was then treated as in Example I to recover solvent and active anthraquinones. The repovery of the latter was 97%. --Example 3 Three hundred milliliters,of a degraded working solution similar to that of Exari@ple 1 coitairiing 16.34% active anthraqiiinones and %5;42% inerts was mixed @with 55@5 g. powdered zinc metal. and 272 g. of a:10% aqueous solution of @ sodium hydroxide. The -mixture was stirred at room temperature for 4 hours, extracted-with aqtieous sodii-irn hydroxide and the resulting-extract and organic solution were worked up as in@Example 1. The recovery of active anthraquinones was 98.2%. Example 4 T,wo hundred milliliters of a-degraded -working solution similar to that-of ;Example 1 containing :15.62% active anthraquinones and 6.35 % inerts was; hydrogenated at 4o, c. in the presence of a-palladium catalyst and of 200 ml. cif a 10% Rqueous:solution of sodium@hydroxide until hydrogenation.was nearly.complete. -he organic was separated from the aqueous phase and extraqtcd with ftirther amounts of the sodium hydroxide soli.ition. ni c combined aqtieous extracts and. the organic phase 7!ere then worked ui) as described in Example 1. The recovery of active. anthraquinones was 96.4%. Example 5 A degiraded working solution (100 nil.) vi--.@ich contained 14.69 % anthraquinones and, 6.44 % inert materials @and had been, cqtalytically -hydrogptiated to 60 % of com2,901)491 4 pletion, was extracted with aqueous sodium hydroxide to give a raffinate solution containing 5.75% active anthraquinones. The raffinate was then hydrogenated substantially completely at 46' C. in the presence of a palladium-on-aluniina catalyst and again extracted with sodium hydroxide solution. :The combined extracts were blowia @.with air to recover 96.1% of the antlirqquinones originally present in the . degraded working sqlution. Degradect working solutions similar to those of the 10 P-,bE)ve,examrl es caii @be -irgedwith air for, 0.5 -to 5 hours at 125 to 200' C., to reconvert a subs - tantial part of the inert materials initially present to usable or active anthraqiiinones, as described in our application S.N. 661,282, filed of even date herewith. The re enerated anthraqui- . @-9 15 nones can then be recovered alon w h the anthraqui. g - @t@ nones originally present by a procedure similar to that of Example 1. In such a case, the itierts separated as the residue from :the sojvent distillation ste viould be P mainly.non-regenerable -inert.s. 20 If regeneration of r.egenerable inert.mlaterials as yvell as separation of non-regencrable inert materials is desired, the last extraction step with sodium h@dro'xide solution should be preceded by a treatment which - will convert at least a substantial part of the regenerable inerts 25 to usable anthraquinanes. @Such regeneration can I b . e effected by heatin- the degraded working s olution I in th . e presence of ..activated alumina or, active magnesia ..at a of at least 55' C., as described by Sprauer et,@l..in U.S. Patent 2,739,875. Another method is to 30 heat the de--raded solution to 125 to 200' C., while ptirgit with,free oxygen, e.g., in the presence of.a surface active catalyst, as described in our application S.N. 661,28?, 'iled of,even date herewith. The concentration of the metal hydroxide solution em35 .ployed in @the extraction step is not critical but sufficient of the extracting solution should be.employed to extr,act all anthrahydroquinones in the solution beina extracted. Generally, an excess of -the hydroxi.de solution will be used. Any - water-soltible metal hydroxide can be used 40 but the alk m .41i,metal hydroxides such as.sodiu and potassium hydroxides are preferred bezause of their excellent solubilities. SoOium hydroxide is espqcially preferredbecauseofitsrelative,chcai)ness. Metalhydroxide concentrations of from 5% to 30% are -preferred and 45 :those of 10 to 20% are most preferred. Concentrations below 59p, e.g., less than I% clan.be used. The. extractions with the metal hydroxide solution ordinarily will be @effer-ted at about ambient temperature. Higlier-and lower te mpQratures,,e.g., between the freezing 50 and boiling points of the liquids ,,,preferably 10 to 75' C., -.can.alsQ be used. Reduction prior tG extraction to conYert anthraquinones to - anthrahvdroquinones is 'preferably effpcted.by hydrogenating in the presence of a catalyst such,z!s Raney nickel,or a supported palladium or iylatiiium catalyst at ter@ii)er@attire and pressure conditions -kno@wn to be effective for the hydrogenation stage of cyclic anthr aquinone me . thods for producing hydrogen peroxide. The invention provides a practical. method for -purify60 ing,@l!pgraded workina solutions. It can be used to remove both rege;ierable and non-regenerable inert anthraquinone degradation products. When practic@ed in conjunction with -a treatment for converting regenerable inerts to usable anthraciuinones, it can a . Iso be used to re65 m(yve,stibstantially pply the non-reg@nerable inerts. 'HoNv-c@ver, in either type of, operation, extraction of the reduqed working -solution with the metal hydroxide solution will also remove acidic by-products, c.g., undesirable pheno I lie, cgmpounds,. of the hydrogen peroxide syn70 thesis operations, which by-products will normally be 1 retained by and discarded with the. hydrqxide solution after !he. latter, has been reused ' a number of times. Vpon rQccknstitut.ing,the.puriffed working solution by dissolvin , the. recovered anthraquinone values, in the reI g 75 cover.@,d solvent,,the resultin solution generally will be -9
[3]5 adjusted as required by the addition of more solvent or more anthraquinone to provide a solution of the composition desired for use in the hydrogen peroxide synthesis operations. The method of the invention can be usefully employed to purify periodically all of the working solution in the hydrogen peroxide synthesis system. Alternatively, only such a portion of the working solution will be periodically or continuously purified and returned to the synthesis system ag will maintain the working solution of the system at a desired or acceptable degree of purity. We
