RESIDUE TREATMENT

Abstract: Degradation of acetone cyanohydrin residues by dilution and pH modification to give an aqueous solution containing acetone and cyanide ions followed by treatment with a cyanide degrading micro-organism in which cyanide hydra­ tase has been induced.

Description: Residue treatment This invention relates to the treatment of residues and in pasticulas to the treatment of residual quantities of acetone cyanobydrin remaining in tanks or other containers. Acetone cyanobydrin, which is used in the manufactnre 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 cyanobydrin 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 snail 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. bypo- chlorite. Such bypochlorite 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 bypochiorite: 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 that the enzyme cyanide hydratase (otherwise termed formamide hydrolyase) which can be induced in certain micro-organisms, particularly fungi, can degrade cyanide, even at relatively high cyanide ion concentrations. 3ecause 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 contwining 1% by weight of cyanide ions will also contain about 2.2 by weight of acetone0 It is surprising however that, when treating such high concentrations of cyanide derived from acetone cyanohydrin decom- position, the acetone does not affect the activity of the microorganism: 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 con tailing 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 con- taining a cyanide-degrading micro-organism, in which the enzyme cyanide bydratase 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 350C until the cyanide ion concentration is below 10 ppm by weight. Micro-organisms that may be used include Stenmhylium loti, e.g. ATCC 11718; Mycoleptodiscus terrest-is, e.g. C3S 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 C3S 161.82; Helminthosporium sorghicola, otherwise known as Drechslera sorghicola, e.g. C3S 245.49; Periconia circinata, e.g. C3S 263.37; and Glomerella tucamanensis, e.g. CBS 132037. (MCC No. refers to the- number desigaated by the Bmerican Rype Culture Collection, 12301 Park Lawn Drive, Rockville, Maryland 20852, USB, while CBS No. refers to the number designated by the Central Bureau Voor Schimmelcultures, Baaxn, Netherlands)0 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, E. 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, particul- arly the following parameters: pH, nitrogen source (nature and amount), carbon source (nature and amount), amount of phosphorus source, will enable the mycelial form to be obtained. Thus with any particular micro-organism, simple experimentation varying the above parameters will enable the mycelial form to be obtained. The preferred carbon sources are carbohydrates, particularly glucose. 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, e0 g. 0.05 to 5, preferably 0.1 to 1 I 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. Alternstively 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 pE modification in order to convert the acetone cyanohydrin to cyanide and acetone, and then a biological degradation step. The dilution and pH modification may canveniently 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 cos centrated, alkali added to give the requisite pit. In such a case the water nsed. 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 pit between 6 and 10, preferably between 7 and 9, and in particular at about pH 8. We have found that there is some buf fearing action so that a pit 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 aaueous 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 nE) 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 ions0 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 regul actions into waterways, e.g. rivers or the sea, or into a CQnven- tional 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 I Fusarium moniliforme (CBS 161.82) was aerobically grown in an aqueous nutrient medium containing, per litre KH2PO4 5 g MgSO4#7H2O 1 g KCl 0.5 g yeast extract 1 g casitone 2 g glucose 30 g trace elements solution 1 ml deionised water balance, The trace element solution had the following composition, per litre FeSO4#7H2O 1 g CuSO4#5H2O 0.15 g ZnSO47H2O 1 g MnSO4#4H2O 0.1 g E2NoO4 0.1 g The oultivation was conducted at 28 C and pH 5.5 to give a culture containing 20 g/l 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 280C for 12 hours. To sfrmilate the treatment of a typical quantity of acetone cyanobydrin residue in a tank after discharge of acetone cyanohydrin therefrom, 1.15 ml of commercial grade acetone cyanohydrin (containing 98. &commat;A 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 (2O0C). The acetone cyanohydrin was diluted by adding 50 ml of water. 3.5 M sodium hydroxide solution was then added until the pR was 7.8. The resultant solution contained 0.8% by weight of cyanide ions0 1 ml of the Ftisarium 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. EMPIRE 2 250 litres of tap water was charged to a mild steel vessel of nominal 400 litres capacity. The water, pR 6.8, was heated to 200C. 6370 g of commercial grade acetone cyanobydrin (as used in Example 1) was then charged to the vessel0 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. EMI8.1 <tb> <SEP> Cyanide <SEP> ion <SEP> concentration <SEP> (ppm) <tb> <SEP> Time <SEP> pH <SEP> temperature <tb> (min) <SEP> ( C) <SEP> Top <SEP> Bottom <tb> <SEP> 0 <SEP> 7.8 <SEP> 20 <SEP> 8081 <SEP> 8159 <tb> <SEP> 15 <SEP> 8.0 <SEP> 18.5 <SEP> 4092 <SEP> 3600 <tb> <SEP> 30 <SEP> 8.0 <SEP> 19.0 <SEP> 2253 <SEP> 1968 <tb> <SEP> 105 <SEP> 8.5 <SEP> 18.5 <SEP> 258 <SEP> 129 <tb> <SEP> 135 <SEP> 8.4 <SEP> 18.5 <SEP> 110 <SEP> 92 <tb> <SEP> 190 <SEP> 8.2 <SEP> 18.0 <SEP> 44 <SEP> 46 <tb> <SEP> 245 <SEP> 8.4 <SEP> 17.5 <SEP> 20 <SEP> 17 <tb> <SEP> 305 <SEP> 8.5 <SEP> 17.0 <SEP> 13 <SEP> 9 <tb> <SEP> 1320 <SEP> 8.5 <SEP> 11.0 <SEP> 1 <SEP> 1 <tb>

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 cyaside-degraiing micro-orgasism, 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 oyanide 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 microorganism is a fmtgal mycelium. 3. A process according to claim 1 or claim 2 wherein said acetone cyanobydrin residue is diluted with such an amount of water and alkali that the solution contains 0.1 to 1% by weight of cyanide ions0 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 300C 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.

Inventors: NAYLOR, THOMAS WILLIAM, RODGER, WILLIAM RHODES
Applicants: IMPERIAL CHEMICAL INDUSTRIES PLC
Application year: 1984
Main classification: A62D3
IPC codes: A62D3, A62D101