DE2042523C3 - Process for the regeneration of noble metal catalysts for hydrogen peroxide synthesis according to the anthraquinone process - Google Patents

Description

The invention relates to a process for the in-situ regeneration of noble metal catalysts in the anthraquinone process, where the active metal is a metal from the platinum group of the periodic table in a mixture is preferably used with other metals of the platinum group of the periodic table on supports.

It is known that hydrogen peroxide can be produced in a cycle process in which anthraquinone compounds are alternately hydrogenated and oxidized. Reduction and oxidation take place in one organic solvent or solvent mixture instead, which contains both the anthracnquinone and the Keeps anthrahydroquinone compounds in solution. That in the oxidation of the hydroquinone to the quinone formed hydrogen peroxide is isolated from the organic phase by known methods and the So-called working solution containing anthraquinone compounds is recycled to the hydrogenation.

In this cycle, there are undesirable side reactions in which compounds of the most varied Kind be formed. Resin and decomposition products have proven to be particularly troublesome proven unexplained constitution. For example, these connections do the gradual Decrease in the activity of the hydrogenation contact, resulting in excessively high catalyst costs compared to the total production cosia of hydrogen peroxide can lead. Usually, a reduced in its activity or spent catalyst is from the The system was removed and subjected to a work-up for reactivation, but at least the hydrogenation tower switched off during regeneration. Especially when working with fixed bed hydration contacts makes this way of working noticeable as time-consuming and costly.

So far, however, there is still no really useful method for reactivating the catalyst in situ known.

According to German patent specification 10 55 513, a resuscitation process for the hydrogenation catalyst is used of the anthraquinone process indicated, according to which the catalyst in the hydrogenation stage of a periodic Reduction of the hydrogen peroxide pressure with the simultaneous introduction of inert gas is exposed. However, the hydrogenation itself must take place during this time

ί either very throttled or even completely interrupted will.

The catalyst activity was also known by setting a certain water content in the working solution to increase (see US Pat. No. 2,867,507).

in But this could not prevent im

Activity obtained in this way over time

gradually decreased due to poisons that came with the working solution were introduced.

According to the method of the German patent specification

r> 913 888 is a working solution, which after the Extraction with water 0.01 to 0.03 mol of hydrogen peroxide still remained, in the hy-Jrierstufe recycled again The used or inactive hydrogenation catalyst must, however, after

.'ti removed from the working solution by this procedure and transferred to reactivated in a separate step with the aid of an oxidizing agent.

So it was not previously known that the regeneration of the hydrogenation catalyst at full driving performance in the

. ' > Carry out the hydrogenation stage yourself.

In contrast, it has now been found that in the production of hydrogen peroxide by the anthraquinone process the reactivation of hydrogenation catalysts on support materials from the platinum metal

Hi group of the periodic table, preferably palladium - if necessary in a mixture with other metals of the platinum group -, essentially when returning the Working solution, which has at least 250 mg hydrogen peroxide per liter, can be simplified if the

■ .. noble metal catalytic converters with full driving performance of the Hydrogenation can be regenerated without separate separation during the hydrogenation.

It was not foreseeable that the regeneration of the noble metal catalysts by the remaining water

Hi hydrogen peroxide proceeds faster than the hydrogenation Water. Therefore, special stages have been used for regeneration up to now.

There was also the fact that the professional world had hitherto taken the position that unchanged hydrogen

> i oxide, i.e. the active oxygen, although none noticeable harmful, but at least a damaging effect should exert on the catalyst. In addition, the Working solution with constant circulation changed by the constant presence of hydrogen peroxide.

> <> be changed. It turned out, surprisingly, that in In the presence of hydrogen peroxide, the catalyst will retain its activity and the working solution will not was attacked. Even after constant circulation, the work solution was in tact. Even the

· ■> Selectivity of the catalyst remained unchanged.

It is even possible to use a catalyst, the activity of which has been customary up to now by recycling Working solutions has decreased by adding

ho hydrogen peroxide in the specified amounts to regenerate back to the old values. In this way, the Avoid expensive regeneration equipment, which also requires extensive maintenance.

ι · '· The special levels required in addition to the actual Regeneration also involves various washing processes in order to make the catalytic converter fully operational again do. Certain losses also occurred here

Catalyst metal, d. H. of precious metal, on; unless, the oxidizing agents and detergents were worked up accordingly

There is a lot in the method according to the invention from 300 to 1000 mg hydrogen peroxide per liter of working solution is preferred

This amount of hydrogen peroxide can either by a correspondingly smaller extraction with Water or desorption with organic vapors remain in the working solution, or it can be in the Working solution after extraction or desorption can be adjusted again, either by feeding a side stream from the oxidation or by adding 100% hydrogen peroxide or highly concentrated aqueous solutions. These highly concentrated aqueous solutions can be simplest and most economical by extraction of the according to German patents 18 02 003 and 19 51 211 produced solutions with correspondingly small amounts of water (see German Offenlegungsschrift 20 42 522).

It is only essential that the working solution before entry has the minimum amount of reactive hydrogen peroxide in the hydrogenation tower

Silica-containing materials as well as aluminum oxides or activated carbon are used as supports for the catalyst in question.

The catalysts can be used both as suspension and as fixed bed catalysts.

The regeneration according to the invention is suitable - as mentioned - both for a system with water extraction as for a system with desorption of the hydrogen peroxide by organic vapors. in the in the latter case it is particularly effective, since experience has shown that the hydrogenation catalyst tires more quickly there than with water extraction.

The technical advance of the present invention lies in avoiding the separate regeneration stages and their difficulties, and with complete retention of the catalytic effect without any interruption of the Overall process, In addition, the working solution - even with long-term circulation - is not damaged

The invention is explained using the following examples:

example 1

A working solution, consisting of 150 g / l Ethy'sinthraquinone and 150 g / l tetrahydroethyl anthraquinone in

in a mixture of 60 parts by volume of tributyl phosphate and 40 parts by volume of methylnaphthalene (- technical mixture of isomers 1 and 2), at 60 ° C over a fixed bed contact (0.3% Pd on pebbles) was accordingly a hydrogen peroxide content of 30 g / l hydrogenated and

r> after fine filtration with air at 60 ° C in one Oxidation tower to anthraquinone / tetrahydroanthraquinone and hydrogen peroxide re-oxidizes that Hydrogen peroxide was desorbed with butyl acetate. The working solution freed from hydrogen peroxide, the

- ¹ O either a residual content of 0.3 g / l of hydrogen peroxide containing or which had been brought by means of a side stream from the oxidation or with the aid of hydrogen peroxide in butyl acetate lOgewichtsprozentigem to a content of 03 g / l of hydrogen peroxide was

2ί returned to the hydrogenation tower After 1200 hours the hydrogenation contact showed no decrease in activity

Example 2

A working solution according to Example 1 was freed from hydrogen peroxide to a residual content of 0.001 g / l hydrogen peroxide. After 12 hours, the degree of hydrogenation had fallen so far that it only corresponded to 20 g / l hydrogen peroxide. The working solution was then desorbed to a residual content of 0.5 to 0 g hydrogen peroxide per liter of working solution and the working solution was returned to the hydrogenation. After a further 12 hours, full hydrogenation activity was achieved again.

Claims (1)

Claim: Process for the production of hydrogen peroxide by the anthraquinone process in the presence of hydrogenation catalysts on support materials from the platinum metal group of the periodic System, preferably palladium - optionally mixed with other metals Platinum group - and regeneration of the hydrogenation catalyst, with the working solution at their Re-entry into the hydrogenation stage still has a content of reactive hydrogen peroxide of at least 250 mg / 1 working solution possesses, thereby characterized in that the noble metal catalysts with full performance of the hydrogenation stage the working solution coming from the extraction or desorption stage without separate separation regenerated during the hydrogenation.