DE1542031B1 - Process for the regeneration of exhausted activated carbon catalysts containing nickel or cobalt - Google Patents

Description

From this prior art it is known that catalysts, which by initial impregnation of activated carbon with a cobalt or nickel salt 15 of an oxygen-containing mineral acid, for example Nitric acid, generally give the best efficacy. The U.S. Patent 2,380,358 describes that although the effective life of the catalyst is quite long, nickel reduces the surface area of the resulting material its effectiveness nonetheless when using material somewhat, and the surface of an exhausted one

The activated charcoal is preferably an activated vegetable charcoal, such as. B. Coconut shell charcoal or other charcoal.

The isolated catalyst can then be activated in a known manner, such as. B. by heating in a nitrogen atmosphere.

Activated carbon is very porous and has a very large surface. The decomposition of cobalt or

decreases. For example, if a cobalt consisting of reduced cobalt deposited on active coal Catalyst for a relatively long time for that Conversion of ethylene to polymers in which butylene predominates is used, the rate of conversion begins decrease, so that over time the process became uneconomical because of the low rate of conversion. This rubbish the effectiveness is evident on the adsorption of ethylene polymers by the catalyst traced back. In order to regenerate the catalyst, it was therefore necessary to adsorbed this organic Remove substances. This was done by heating the partially exhausted catalyst to a temperature causes sufficient to evaporate the impurities.

It has now been found that this process is relatively good for ethylene polymerization acts, its application to catalysts that are responsible for the Polymerization of propylene and other olefins have been used, but of limited effect is. In these cases the regeneration is only partial and the catalyst activity drops much faster than in the case of a freshly prepared catalyst. If the catalyst continues beforehand for a long period of time (1000 hours) was used with very pure starting material, is that by this technique effected degree of regeneration very small.

Comparatively speaking, the catalyst is very small. For example, steam activated coconut shell charcoal can initially have a surface area of about 1200 m ² / g, and after impregnation with 18% cobalt this surface area can ^{decrease to 850 to 900 m 2} / g. The surface area of a spent catalyst containing adsorbed polymer can be about 80 m ² / g.

It has already been stated that the precipitate Blocking the activity caused by polymer is not the only cause of the decline in the Catalytic effect is. Nonetheless, the greater the restoration of the initial surface of the The more efficient the regeneration process becomes be. That is the purpose of the initial heat treatment.

It is expedient to heat the exhausted or partially exhausted catalyst in the presence a carrier gas to facilitate removal of the adsorbed polymer. Suitable Carrier gases are nitrogen, steam and hydrogen.

If nitrogen or steam is used as the carrier gas, the treatment temperature is suitably lie at 600 to 800 ⁰ C. If hydrogen is used, the required temperature is not so high, for example between 200 and 400 ° C. This is because hydrogen converts the adsorbed olefinic polymers into paraffinic polymers.

It can be assumed that when the catalyst converts, the less strongly the catalyst absorbs Used for very long periods of time, this surface will be adsorbed. The following table shows

Surface areas obtained by treating exhausted catalyst with hydrogen and nitrogen at different temperatures. Hydrogen at 400 ⁰ C is just as effective as nitrogen

is not only deactivated by adsorption of olefin polymers, which can be easily removed, but that it is also deactivated by a chemical change, the nature of which in the case of cobalt or Nickel deposits on coal could not yet be fully clarified; a chemical change that not just by simply heating either in the presence or absence of an inert gas or Hydrogen can be reversed.

It is an object of the present invention to provide a regeneration process for regeneration to bring such exhausted catalysts in proposal, in which a chemical change of the Cobalt or nickel component has gone on.

The present invention therefore relates to a process for the regeneration of an exhausted or partially exhausted, cobalt or nickel in connection material at 600 ⁰ C.

60 Carrier gas temperature Time Scored Ober
area size ° C m ² / g hydrogen 270 4th 250 65 hydrogen 300 4th 654 hydrogen 340 2 840 hydrogen 400 4th 906

Continuation of the table

Carrier gas temperature
⁰ C Time Scored Ober
area size
mVg nitrogen
nitrogen 400
500 1
1 603, 650
(two separate
Experiments)
734 nitrogen 500 4th 770 nitrogen 600 4th 870

Suitably the treated in the heat substance is impregnated with an aqueous acid solution of the cobalt or nickel salt at an elevated temperature, in particular at a temperature between 50 and 110 ⁰ C. The mixture is preferably left to ^{stand for 1} _1/2 hours or more. The mixture can then be filtered and the impregnated catalyst ψ dried, for example by allowing it to stand in the air.

The concentrations of acid and cobalt or nickel salts in the impregnation solution become appropriate chosen so that the total amount of cobalt or nickel in the catalyst and in the solution remain essentially unchanged during the process; it can also regenerate one the same or lesser degree can be achieved when using solutions of different strengths, what leads to an overall exchange of cobalt or nickel between the solution and the catalyst. The final cobalt or nickel content is expediently in the range from 12 to 30 percent by weight.

The salts which decompose when exposed to heat are preferably used are the nitrates of cobalt or Nickel. Other suitable salts are formates and acetates.

Other cobalt compounds that yield cobalt nitrate with nitric acid, such as e.g. B. the different Cobalt oxides and cobalt carbonates can also be used. A limited regeneration is also available when using cobalt salts such as cobalt chloride, which is soluble in nitric acid, but not is decomposed by them. The effectiveness of the impregnation stage consists primarily in the implementation of the deactivated cobalt or nickel coating, which is already present in the catalyst, into a potential effective form, more than in the manufacture of a new additional coating, albeit the manufacture of the latter can occur to some extent.

The aqueous acidic solution of the heat-decomposable salt preferably contains nitric acid, in particular in concentrations of 8 to 40 percent by weight.

The regeneration process is preferably suitable for the regeneration of a cobalt-on-charcoal catalyst, that was used in the dimerization of propylene and that initially in its absence activated by hydrogen.

The regeneration process can be carried out repeatedly when the regenerated catalyst itself loses its effect.

The invention is illustrated in the following examples:

example 1

An effective cobalt-on-charcoal catalyst with a cobalt content of about 18 percent by weight and a surface area of 850 m ^a / g and an effectiveness (in a 5 hour autoclave test) of about 4.5 g / g / h was used for the dimerization of propylene in a fixed bed reactor used until its effectiveness was less than 0.1 g / g / h. The catalyst produced over 300 grams of dimer per gram of catalyst.

The exhausted catalyst was ^{heated in nitrogen at 300 °} C. for 4 hours and was found to have an effective surface area of only 86 m ² / g and only 13.9 percent by weight cobalt corresponding to a high concentration of polymer precipitate in its pores.

Its propylene dimerization activity after this treatment was less than 0.1 g / g / h. 100 g of the treated spent catalyst were placed in a tube furnace in a stream of dry oxygen-free nitrogen heated to 600 ° C and held at disser temperature for 4 hours.

A weight loss of 22.7% was found. The remaining material contained 18.8 percent by weight cobalt and had a surface area of 809 m ² / g, while its propylene dimerization activity was less than 0.1 g / g / h.

This example clearly shows that removal of polymer alone is not enough to remove the catalyst to reactivate.

Example 2

72 g of the treated with nitrogen the catalyst from Example 1 were immersed in a solution of 100 g of cobalt nitrate hexahydrate in 100 ml of 30 ° / _o nitric acid. The mixture was stirred while the temperature was kept at 80 ^° C. for 24 hours. The catalyst was filtered off and activated with nitrogen in the usual way. The product had a surface area of 676 m ² / g and contained 19.4 percent by weight cobalt.

10.34 g of the catalyst were placed under nitrogen in a 1-1 shaking autoclave, which was fed with liquid propylene to 600 psi, and held at this pressure at 40 ^° C. for 5 hours. The reaction products were then drained into vessels cooled by carbon dioxide and acetone. After evaporation of excess propylene at room temperature, the residue was distilled. 187.4 grams of hexenes were recovered containing 52.2% linear hexenes and less than 0.5% 2-methylpentene-2-pentene. 18.5 grams of higher boiling material was also recovered. This corresponds to a catalyst activity of 3.98 g / g / h.

This shows that the initial activity of the catalyst has almost been restored. It it should also be noted that the increase in activity compared with the non-impregnated, nitrogen treated material, with a very small change in the cobalt content of the catalyst became.

Claims (2)

Patent claims: 1. Process for regenerating an exhausted or partially exhausted, cobalt or Nickel in connection with activated carbon containing catalyst, which is used in the conversion of low Geren olefins was used to form essentially linear polymers and the adsorbed Contains polymer, the catalyst optionally in the presence of a carrier gas at high Temperature is heated, thereby marked ζ e i c h η e t that the heating is carried out at 200 to 1000 ° C, after which the catalyst is cooled, with an aqueous acidic solution of a thermally decomposable cobalt or nickel salt is impregnated, separated and activated in a known manner. 2. The method according to claim 1, characterized in that that an aqueous nitric acid solution of the cobalt or nickel salts is used in which the nitric acid is present in a concentration of 8 to 40 percent by weight.