DE3508902A1 - Process for the recovery of molybdenum and/or vanadium from used catalysts - Google Patents

Abstract

The application relates to a process for the recovery of molybdenum and/or vanadium from used catalysts or oxide residues of such catalysts, by a selective leaching of the ground catalysts with solutions of aqueous oxalic acid at 50 to 150 DEG C, in particular at 90 to 120 DEG C. The leaching and grinding can also be performed simultaneously in an intensively stirred and heated container using grinding bodies.

Description

Process for the recovery of molybdenum and / or vanadium from used Catalysts It is known to use molybdenum- and / or vanadium-containing catalysts To regenerate use or decrease in their activity or if this is not the case it is more possible to work it up for the recovery of molybdenum and / or vanadium. Because of the high raw material price of the molybdenum used for catalyst production and vanadium compounds, there is great interest in as complete as possible Recovery of the metals from the used catalysts. In the old catalytic converters Oxide mixtures are usually present, often together with a catalyst support such as aluminum oxide or silicon dioxide. In case the used catalyst with sulfur, carbon or organic residues are contaminated, roasting is usually carried out beforehand.

For the reprocessing of old catalysts containing molybdenum is already a number of procedures are described, some of which are practiced. The known Depending on the treatment, procedures can be subdivided into procedures involving a treatment with alkali or ammonia, or a treatment with acids, or a chlorinating one Roasting or an extraction process is carried out.

The choice of the process to be used depends on the composition of the old catalyst and the possible uses for the work-up products. The individual procedures differ greatly in terms of the technical required Effort and the selectivity of separating the usable from the rest Metals and from the catalyst carrier.

The treatment with alkalis allows a selective separation of the Anion-forming metals e.g. molybdates, vanadates and tungstates. Disadvantageous is the formation of the alkali compounds, as these are usually not directly used for the new production of catalysts can be used.

Complex formation with ammonia also causes copper, cobalt and and nickel oxide in solution, so that additional separation steps are then required. These processes are e.g. in DE-OS 23 16 837, DE-OS 26 31 089 or FR-PS 2 472 030 described.

Acid treatment gives high metal yields, but mostly will catalyst carrier also dissolved. A selective molybdenum recovery is after these Processes that are described, for example, in DE-OS 21 37 817, are not yet known.

Likewise high yields, but only low selectivity is through the chlorinating detent is achieved (see e.g. JA patent application 7 917 368/79 and 7 917 369/79). In this known process, the volatile chlorides become the transition elements Mo, .Bi, Co, Ni, V, W, Fe, Mn, Cu, Cr, etc.

formed in the stream of chlorine or hydrogen chloride and at high temperatures evaporates. The mixture of chlorides then has to be separated.

The extraction methods are a complement to the above Is a digestion process for separating the dissolved valuable metals.

Molybdenum separated from hydrochloric acid solutions using tributyl phosphate will.

It was therefore the task to use a simple procedure, Molybdenum and / or vanadium from used catalysts as much as possible in to regain them in a form in which these substances can be produced without further processing for the production of catalysts can be reused. It was of particular importance to have a procedure to develop that can be carried out in standard apparatus without any special effort and the use of highly corrosive, toxic and environmentally harmful substances avoids.

The known processes for the recovery of molybdenum and vanadium do not meet these demands. Both alkalis and chlorine are in in many cases catalyst poisons and must therefore be avoided during catalyst production will.

It has now been found that molybdenum and / or vanadium were used Catalysts or other oxidic residues of such catalysts in reusable Form can be gained if one has a selective leaching with solutions of aqueous Oxalic acid performs.

The selective leaching can be done with pre-ground material at 50 to 1500C, preferably at 90 to 1200C. But you can also use leaching and grinding simultaneously using an intensely stirred and heated one Make the container with grinding media. In this case, the separation of the catalyst sludge and grinding media are carried out by a separation system with backwashing built into the container. In this embodiment, it is advantageous to add the starting materials and the removal of the digested sludge from the intensely stirred container to be carried out continuously.

The molybdenum or molybdenum normally used for catalyst production. Vanadium compounds are compounds that turn into oxides and when heated decompose volatile compounds. Furthermore, these links in a purity of over 90 7. can be made available for reuse there is no impairment from disturbing elements.

It was found that most metal oxides in'inorganic acids, like z.ß. Nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid and in formic acid are more soluble than molybdenum and vanadium oxide and therefore a selective leaching out of molybdenum and vanadium from the old catalyst was not possible. Other organic Acids, such as acetic acid, on the other hand, only have poor dissolving power for old catalysts. It was therefore surprising that when using oxalic acid as the solvent selective leaching of molybdenum and vanadium or their compounds with very good results are possible.

It was found that molybdenum and vanadium were obtained with good yield Old catalytic converters can be leached out while most of the others turn into catalytic converters Existing metal oxides remain undissolved because they form poorly soluble oxalates or are not attacked by oxalic acid.

The good selectivity of molybdenum or vanadium leaching with oxalic acid is surprising because oxalato complexes are known to be readily soluble in numerous metals are. Under the conditions according to the invention, only the oxalic acid compounds have des Mo and V the desired solubility.

Very good results are obtained when separating molybdenum and / or Vanadium from mixtures with metal oxides or carrier materials such as e.g.

CuO, CoO, NiO, ZnO, CdO, SiO2, MnO, alkaline earths, bs203 and Sb203.

Metal oxides of tungsten and iron, e.g. WO3 and Fe203, as they also form soluble compounds with oxalic acid.

When leaching or preparing the solution, it is advisable to use an excess of oxalic acid, advantageously in a ratio of 5: 1 to 1: 1. the The best yields were achieved, for example, with a weight ratio of oxalic acid: MoO3 or oxalic acid: V205 of about 1.50: 1. This corresponds to a molar ratio of oxalic acid: MoO3 as 2.4: 1 and oxalic acid: V205 as 3.0: 1. When working up catalysts containing molybdenum a dark blue to green solution with about 10 to 20% by weight of MoO3 is obtained. From vanadium catalysts VOC204, which is very soluble in water, is formed with oxalic acid.

To carry out the process you can use a stirred tank or Use a container that is subject to intense mechanical movement and smashing the catalyst grains is possible. To the process of mechanical Crushing To intensify, you can use grinding media, e.g. porcelain or aluminum oxide balls, from the old catalyst add. In some cases, a sufficient crushing effect can also be achieved due to the mutual abrasion of the catalyst particles (autogenous comminution).

If you have the grinding process with grinding bodies during leaching performs, the yield of MoO3 or V205 compared to the use of pre-ground Old catalyst without grinding media in one-stage operation from about 60 Z to over 90 Z can be increased. In addition, an operation, namely the grinding of the Old catalyst saved before leaching.

The process can be generally pressureless or at moderately increased Pressure e.g. at 1.5 to 3 bar and at temperatures from 60 to 1300C e.g. at approx 900C are executed. The dissolution time is 1 to 3, generally about 2 hours. The yield often falls below 1 hour to values below 85%.

By installing a sieve at the outlet you can put the grinding balls in the container hold back while solution and catalyst sludge are removed and placed on a filter press can be pumped. The solution obtained can be used in different ways further processing. The metal solution obtained can be used directly for the production of the catalyst can be used, e.g. for impregnating catalyst carriers or as a component for kneading pastes. But you can also dry a powder, e.g. spray drying with a loss on ignition of about 25 to 50 Z z.8. 35 Z. This powder In addition to the components of value, it contains Mo undi or V and minor metallic elements Contaminants only organic constituents that are used in the production of the catalyst disappear by burning. For most catalytic uses this powder can be used without further work-up. Finally can the dried material is subjected to tempering at about 5000C in a stream of air. This burns the organic material, leaving only the oxides of the recovered Metals lag behind.

By using the wet milling process described, the process steps Crushing, loosing and classifying can be carried out in a single device. Compared to dry shredding with subsequent loosening and separation of Grinding balls can be combined into 3 process steps in one step. From it procedural simplifications, shorter processing times and The cost of setting up a catalyst processing plant is reduced by around half.

Example 1 100 parts by weight of old catalyst, containing about 50 parts by weight of molybdenum oxide, in 75 parts by weight of oxalic acid, 250 parts by weight Water and 30 parts by weight of ceramic grinding media subjected to an intensive stirring treatment. The contents of the boiler are heated to 909C, the exposure time is approx 2 hours. The resulting sludge is placed in the bottom outlet of the container by means of a sieve separated from the grinding media, pumped onto a filter press and washed out. The filtrate contains the soluble oxalates of molybdenum and is spray-dried subjected. By subsequent decomposition in a rotary kiln, MoO3 is obtained a yield of about 90%.

Example 2 The catalyst is continuously worked up in one System consisting of a wet rotor mill, pump, agitator mill and downstream agitator tank.

The starting materials are used in the wet rotor mill in the same proportion as in example 1 and pre-shredded there. The material is pumped out conveyed into the agitator mill and with an average residence time of 1 hour subjected to grinding stress at 900C. The discharge takes place via a bottom sieve with retention of the grinding balls and filtration on continuous rotary filters. The drying and decomposition are carried out according to Example 1.

The yields achieved are 90% of the amount of MoO3 used.

Example 3 100 parts by weight of a 7.5 wt Catalyst containing V2Os together with 15 parts by weight of oxalic acid and 250 parts by weight Water introduced, and with intensive mixing for one hour at 90 to 950C treated. The resulting suspension is pumped onto a frame filter press, the filtrate separated, spray-dried and decomposed at 5000C. Based on the yield on inserted V205 is 89 1.

Claims (5)

Patent claims 9 method for the recovery of molybdenum and / or Vanadium from used catalysts or oxidic residues of such catalysts, characterized in that a selective leaching with solutions of aqueous Oxalic acid performs. 2. The method according to claim 1, characterized in that the selective leaching of ground material at 50 to 1500C, especially at 90 up to 1200C. 3. The method according to claim 1 and 2, characterized in that one Leaching and grinding simultaneously using a vigorously stirred and heated container with grinding media. 4. The method according to claim 1 to 3, characterized in that the Separation of catalyst sludge and grinding media by a built-in container Separation system with backwash takes place. 5. The method according to claim 1 to 4, characterized in that the Addition of the starting materials and the removal of the digested sludge from the intensively stirred container takes place continuously, «?