EP0116423B1

EP0116423B1 - Residue treatment

Info

Publication number: EP0116423B1
Application number: EP19840300445
Authority: EP
Inventors: William Rhodes Rodger; Thomas William Naylor
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1983-02-11
Filing date: 1984-01-25
Publication date: 1986-07-30
Also published as: EP0116423A1; DE3460363D1; JPS59155272A; GB8303818D0

Description

This invention relates to the treatment of residues and in particular to the treatment of residual quantities of acetone cyanohydrin remaining in tanks or other containers. Acetone cyanohydrin, which is used in the manufacture of methacrylic acid esters, is often transported in bulk, for example by road, rail, or ship, tanker. After discharge of the acetone cyanohydrin from the tank, generally a small residual amount thereof remains in the tank. It is often necessary to dispose of this residual amount of acetone cyanohydrin before the tank can be returned for refilling or for use with another material.
Acetone cyanohydrin not only is itself toxic but readily decomposes, especially in conditions that are not highly acidic, to acetone and hydrogen cyanide which presents an even greater toxicity hazard. To reduce the hazard, acetone cyanohydrin is usually stabilised by a small amount of a suitable acid, e.g. sulphuric acid.
To render the acetone cyanohydrin residues safe for disposal the residue is usually treated . with an excess of an aqueous alkali to produce the corresponding cyanide and acetone, and then the cyanide is decomposed by treatment with, e.g. hypochlorite. Such hypochlorite treatment represents a considerable expense. The treatment may be performed inside the original tank, but frequently this is not convenient because of the corrosive nature of hypochlorite: the transfer of the residues to a suitable treatment tank may itself present a hazard. It is generally required that the effluent contains less than 10 ppm (by weight) of cyanide ions, and often a concentration of less than 1 ppm is required.
We have found that the cyanide degradation can more conveniently be carried out biologically. It is known from EP-A-0061249 that the enzyme cyanide hydratase (otherwise termed formamide hydrolyase) which can be induced in certain micro-organisms, particularly fungi, can degrade inorganic cyanide, even at relatively high cyanide ion concentrations.
Because of volume limitations, it is generally necessary to perform the treatment of the cyanide-containing solution at relatively high cyanide ion concentrations, e.g. containing 0.1 to 2% by weight of cyanide ions. Such solutions will also have a relatively high acetone concentration: thus a solution containing 1% by weight of cyanide ions will also contain about 2.2% by weight of acetone.
It is surprising however that, when treating such high concentrations of cyanide derived from acetone cyanohydrin decomposition, the acetone does not affect the activity of the micro-organism: acetone is a powerful solvent for micro-organism cell constituents.
According to the present invention we provide a process for the treatment of acetone cyanohydrin residues comprising adding sufficient water and alkali to the residues to give a solution containing between 0.1 and 2% by weight of cyanide ions and having a pH within the range 6 to 10, adding to the solution a culture containing a cyanide-degrading micro-organism, in which the enzyme cyanide hydratase has been induced, in an amount of at least 0.005 g of micro-organism (dry weight) per g of cyanide ions, and maintaining the resultant mixture at between 5 and 35°C until the cyanide ion concentration is below 10 ppm by weight.
Micro-organisms that may be used include Stemphylium loti, e.g. ATCC 11718; Mycolep- todiscus terrestris, e.g. CBS 231.53; Fusarium moniliforme, e.g. No. 3104.SA.49a available from the Canadian Department of Agriculture, Culture Collection, Ottawa, and which has also been deposited as CBS 161.82; Helminthosporium sorghicola, otherwise known as Drechslera sorghicola, e.g. CBS 249.49; Periconia circinata, e.g. CBS 263.37; and Glomerella tucamanensis, e.g. CBS 132.37. (ATCC No. refers to the number designated by the American Type Culture Collection, 12301 Park Lawn Drive, Rockville, Maryland 20852, USA, while CBS No. refers to the number designated by the Central Bureau voor Schimmel- cultures, Baarn, Netherlands). Other fungi that may be used and which have been described in the literature as producing the enzyme include Collectotrichum graminicola, Gloeocercospora sorghi, Helminthosphorium turcicum, H. maydis, H. carbonum, H. victoriae, and Phoma.
Fungi can be made to grow in two distinct forms, namely a ball or pellet form or in a mycelial form where the fungal cells are diffuse filamentous strands dispersed in the growth medium. It is desirable, though not essential, that the fungus is grown in the mycelial, as opposed to ball or pellet, form since, with the fungus in pellet or ball form, diffusion into, and out of the fungal pellet or ball, may be restricted, thereby preventing efficient utilisation of the active enzyme within the ball or pellet.
Often when growing fungi, the ball or pellet form is obtained: however adjustment of the growth conditions, particularly the following parameters:

pH,
nitrogen source (nature and amount),
carbon source (nature and amount),
amount of phosphorus source,

The preferred carbon sources are carbohydrates, particularly gluclose.
When the desired concentration of micro-organism has been achieved, the enzyme cyanide hydratase may be induced by adding to the culture a low concentration of cyanide ions, e.g. 0.05 to 5, preferably 0.1 to 1 mM per gram of cells (dry weight) and continuing culturing for 1 to 24, preferably about 12 hours, at 20 to 40°C.
The culture may then be concentrated if desired in readiness for use. Alternatively the micro-organism may be harvested and stored, e.g. by freeze drying.
The acetone cyanohydrin treatment process comprises a first step involving dilution and pH modification in order to convert the acetone cyanohydrin to cyanide and acetone, and then a biological degradation step.
The dilution and pH modification may conveniently be performed by adding a dilute aqueous alkali, for example sodium hydroxide, to the acetone cyanohydrin residue: where residues remain in several tanks it may be convenient to wash all the residues into a single tank wherein the treatment process is performed. The aqueous alkali may be added as such or the acetone cyanohydrin first diluted with water and then solid, or more concentrated, alkali added to give the requisite pH. In such a case the water used may be mains water or sea water if a supply thereof is available. However, the degradation process may take longer if sea water is utilised.
The cyanide degradation process should be carried out at a pH between 6 and 10, preferably between 7 and 9, and in particular at about pH 8. We have found that there is some buffering action so that a pH of about 8 can be achieved even with a significant excess of alkali.
The amount of water and alkali required will of course depend on the amount of acetone cyanohydrin residue present: the acetone cyanohydrin residues normally comprise in excess of 95% by weight acetone cyanohydrin and should be diluted with the aqueous alkali so that the solution contains 0.1 to 2% by weight of cyanide ions. This corresponds approximately to dilution of the acetone cyanohydrin by at least 15 times its volume. Preferably the acetone cyanohydrin is diluted until the solution contains 0.1 to 1% by weight (1000-10,000 ppm, i.e. approx. 40-400 mM) of cyanide ions.
The culture, in which the cyanide hydratase has been induced, is then added, e.g. as a slurry or as dried cells. The amount of culture should be at least 0.005 g of micro-organism dry weight per g of cyanide ions. This corresponds approximately to at least 1.5 g of micro-organism dry weight per litre of acetone cyanohydrin residue. If smaller amounts of the culture are employed, we have found that there will probably be insufficient cyanide degradation even if the mixture is left for 24 hours or more. Preferably the amount of culture is at least 0.02 g of micro-organism dry weight per g of cyanide ions.
After adding the culture, the mixture is left for sufficient time for the cyanide ions to be degraded to the desired level, below 10, preferably below 1 ppm. Preferably the mixture is agitated during the cyanide degradation, e.g. by sparging with compressed air. The time taken for the cyanide degradation will depend on the proportion of cells to cyanide ions, the desired degree of treatment, the pH, the temperature, and, as mentioned hereinbefore, the type of water employed.
The temperature employed may range between 5 and 35°C and is preferably between 10 and 30°C, and in particular is above 20°C. If necessary the mixture can be heated, for example by injecting steam to achieve the desired temperature, prior to addition of the culture.
After treatment in some cases it may be desirable to add a fungicide as an insurance against release of biologically active spores upon discharge of the aqueous mixture. However generally the addition of such a fungicide is not necessary.
The invention is of particular utility in the cleaning of vessels used to transport acetone cyanohydrin: after discharge of the bulk of the transported acetone cyanohydrin, the acetone cyanohydrin residues in the vessel are treated by the method described hereinbefore and then the aqueous mixture having a cyanide ion concentration below 10 ppm by weight is discharged. The aqueous mixture can be discharged, depending on local regulations into waterways, e.g. rivers or the sea, or into a conventional sewage treatment plant. Discharge of the diluted acetone cyanohydrin residues before microbiological degradation of the cyanide ions into a conventional sewage treatment plant would not normally be possible since the latter can not normally tolerate influents containing such large concentrations of cyanide.
The invention is illustrated by the following examples.

Example 1

Fusarium moniliforme (CBS 161.82) was aerobically grown in an aqueous nutrient medium containing, per litre
The trace element solution had the following composition, per litre
The cultivation was conducted at 28°C and pH 5.5 to give a culture containing 20 g/I of cells. The pH was then raised to 7.8 and cyanide hydratase induced by adding 0.2 m moles of cyanide ions (as acetone cyanohydrin) per gram of cell dry weight and incubating at 28°C for 12 hours.
To simulate the treatment of a typical quantity of acetone cyanohydrin residue in a tank after discharge of acetone cyanohydrin therefrom, 1.15 ml of commercial grade acetone cyanohydrin (containing 98.6% by weight of acetone cyanohydrin and stabilised with 0.12% by weight of sulphuric acid) was charged to a 500 ml flask at ambient temperature (20°C). The acetone cyanohydrin was diluted by adding 50 ml of water. 3.5 M sodium hydroxide solution was then added until the pH was 7.8. The resultant solution contained 0.8% by weight of cyanide ions. 1 ml of the Fusarium moniliforme culture in which cyanide hydratase had been induced was then added and the mixture gently agitated. After 6 hours the cyanide ion concentration was less than 1 ppm by weight.

Example 2

250 litres of tap water was charged to a mild steel vessel of nominal 400 litres capacity. The water, pH 6.8, was heated to 20°C. 6370 g of commercial grade acetone cyanohydrin (as used in Example 1) was then charged to the vessel. The pH was then 5.2. The solution was stirred while 180 ml of 10 N sodium hydroxide solution was added to raise the pH to 7.8.
A slurry containing 45 g of Fusarium moniliforme (CBS 181.82) in which cyanide hydratase had been induced as described in Example 1 was then added.
At intervals 500 ml samples were removed from the top and bottom of the vessel for analysis.
The results are shown in the following Table.

Claims

1. A process for the treatment of acetone cyanohydrin residues comprising adding sufficient water and alkali to said residues to give a solution containing between 0.1 and 2% by weight of cyanide ions and having a pH within the range 6 to 10, adding to the solution a culture containing a cyanide-degrading micro-organism, in which the enzyme cyanide hydratase has been induced, in an amount of at least 0.005 g of micro-organism (dry weight) per g of cyanide ions, and maintaining the resultant mixture at between 5 and 35°C until the cyanide ion concentration is below 10 ppm by weight.

2. A process according to claim 1 wherein said micro-organism is a fungal mycelium.

3. A process according to claim 1 or claim 2 wherein said acetone cyanohydrin residue is diluted with such an amount of water and alkali that the solution contains 0.1 to 1% by weight of cyanide ions.

4. A process according to any one of claims 1 to 3 wherein the amount of culture of said micro-organism employed is at least 0.02 g of micro-organisms dry weight per g of cyanide ions.

5. A process according to any one of claims 1 to 4 wherein the mixture of the diluted acetone. cyanohydrin residues and culture is maintained at between 10 and 30°C to effect degradation of the cyanide ions.

6. A method of cleaning a vessel used to transport acetone cyanohydrin wherein, after discharge of the bulk of the transported acetone cyanohydrin from said vessel, residual acetone cyanohydrin in said vessel is treated by a process as claimed in any one of claims 1 to 5 to produce an aqueous mixture containing less than 10 ppm by weight of cyanide ions and then discharging said aqueous mixture from said vessel.