United States Patent Office Patented Mar
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3,433,737 United States Patent Office Patented Mar. 18, 1969 holding ponds and the like can kill or injure plant, 3,433,737 METHOD OF REDUCING TOXICITY OF WASTE animal, and vegetative life dependent thereon. STREAMS CONTAINING ORGANIC THIOCYA Various methods have been proposed for elimination NATE COMPOUNDS of the thiocyanate pollutant. For example, conversion Donald Clifford Wehner, Stamford, Conn., assignor to of unrecovered thiocyanate to non-toxic compounds has American Cyanamid Company, Stamford, Conn., a been attempted by treatment of spent mother liquor and corporation of Maine wash liquid with a sodium polysulfide, e.g., Na2S3. Other NoDrawing. Filed Nov. 23, 1965, Ser. No. 509,407 methods include refluxing in water or with 5% sulfuric U.S. C. 210-49 4 Claims acid to hydrolyze to other products, treatment with sodium Int, Cl. B01d 21/01, C02b 1/20 O hypochlorite or chlorine gas to bleach the thiocyanates, and attempted reversal of the synthesis reaction by ad dition of a thiocyanate salt. These methods have proved inoperative, or if somewhat effective, uneconomical. ABSTRACT OF THE DISCLOSURE According to the present invention, it has been dis Waste effluent streams containing spent mother liquor 5 covered that the toxicity of waste streams containing and wash liquid resulting from the synthesis of organic spent mother liquor and wash liquid, due to the presence thiocyanate compounds such as methylene bisthiocyanate of minor amounts of an organic thiocyanate compound, are rendered non-toxic by adding sufficient alkali to raise may be substantially reduced or eliminated by providing their pH to at least 9, followed by separation of the in said water streams a pH sufficient to decompose said resulting decomposition products. 20 organic thiocyanate compound, and thereafter separat ing the resultant decomposition product. The method has the advantages of convenience, economy, and effective This invention relates to pollution abatement and more ness as will become more evident in the following illus particularly to a method of reducing or substantially trative description of the synthesis of a typical highly eliminating the toxicity of waste streams containing spent 25 toxic organic thiocyanate compound, methylene bisthio mother liquor and wash liquid resulting from the Syn cyanate. thesis of organic thiocyanate compounds. Methylene bisthiocyanate is conveniently prepared by By “organic thiocyanate compound(s)" is meant any heating methyl dibromide or diiodide and an alkali metal of the numerous known organic compounds, containing or ammonium thiocyanate at about 60-70 C. in a non one or more thiocyanate (-SCN) or isothiocyanate 30 aqueous solvent medium as follows: (-NCS) radicals attached to carbon, which are toxic in varying degrees to one or more species of micro organism (bacteria, fungi, algae), pest (insects, mites, wherein X is a halogen and M is alkali metal or am nematodes), undesirable plant growth, and the like. monium ion. Typical nonaqueous solvents are alcohols Such thiocyanates may be aliphatic, aromatic, alicyclic, such as methanol or ethanol, acetonitrile, dimethylform heterocyclic and they may be simple organic thiocyanates amide, dimethylsulfoxide, dimethylacetamide, and lower which also contain oxygen, nitrogen, sulfur, chlorine, bro aliphatic ketones such as acetone. When methanol is the mine, iodine, and the like elements. Among Such com solvent, the thiocyanate product is precipitated from the pounds may be mentioned methylene bisthiocyanate, trans mother liquor by addition of water and separated by con dithiocyanoethylene, 1,2-dihalo-1,2 - dithiocyanoethane, 40 ventional means such as filtration, centrifugation, and the mono-, di- and tri-chloro and -bromo thiocyanates; esters like. The thiocyanate product is then repeatedly washed of thiocyanic acid and aliphatic alcohols such as hexyl with large volumes of water. The spent mother liquor thiocyanate, cyclohexyl thiocyanate, stearyl thiocyanate, and wash water is then discarded into Waste streams. oleyl thiocyanate, terpinylthiocyanate, bornylthiocyanate, Alternatively, a solvent reaction medium may be em fenchyl thiocyanate, isobornyl thiocyanate, methylcyclo 45 ployed in which the byproduct salt is insoluble, the thio hexyl thiocyanate, hexyl thiocyanoacetate, cyclohexyl cyanate product being soluble. In this case, the salt thiocyanoacetate, octyl thiocyanoacetate, octyl thiocyano cake is separated, by filtration for example, and re propionate, terpinyl thiocyanoacetate, bornyl thiocyano peatedly washed with the solvent for the thiocyanate acetate, fenchyl thiocyanoacetate, terpinyl thiocyanopro product in order to reduce the amount of the latter on pionate, terpinyl thiocyanobutyrate, beta-thiocyanoethyl 50 the byproduct salt. The solution of thiocyanate may propionate, beta-thiocyanoethyl thiocyanoacetate, beta be concentrated or the product may then be precipitated thiocyanoethyl laurate, beta-thiocyanoethyl stearate, beta with water as desired. thiocyanaoethyl benzoate, butyloxyethyl thiocyanate, In either preparation, it will be evident that minor butyloxyethyl thiocyanoacetate, beta-butoxy-beta-thio amounts of toxic thiocyanate product will remain in the cyanodiethyl ether, glycerol thiocyanate distearate, benzyl 55 spent mother liquor or in the wash water or other wash thiocyanoacetate, styrol dithiocyanoacetate, glycol di liquid used to separate solvent or byproduct from pre thiocyanoacetate, diphenylamine dithiocyanate, furfuryl cipitated organic thiocyanate or byproduct salt cake. thiocyanoacetate, butyl thiocyanate, lauryl thiocyanate, Generally, the pH required to decompose the minor and cetyl thiocyanate; and organo thiocyanoacrylates or trace amounts of organic thiocyanate product in the such as aliphatic esters of thiocyanoacetic acid, c-thio 60 waste stream containing spent mother liquor or wash cyanopropionic acid, g-thiocyanopropionic acid, thiocy liquid will be on the alkaline side and preferably at least anobutyric acid, and the like. These and other thiocy 9. Alkalinity is provided by adding an alkaline material anates are disclosed, including synthesis and use, in the in an amount effective to give an alkaline pH. literature, such as U.S. Patents 2,214,971, 2,486,090, A great variety of alkaline materials are suitable, in 65 cluding individual compounds, mixtures, and buffered 2,572,564, 2,650,240, 3,205,247, 3,212,963, and German solutions or dispersions. Typical alkaline materials are Patent 1,157,603. the alkali and alkaline earth metal hydroxides such as Disposal of spent mother liquor and wash liquid re lithium, sodium, potassium, magnesium, calcium, and sulting from synthesis of thiocyanate compounds is a barium hydroxide; ammonium hydroxide; basic salts such considerable problem, assuming massive proportions in 70 as sodium carbonate and alkyl guanidine acetates and plant scale manufacture, since even minute amounts of carbonates; amines such as butylamine, dibutylamine, unrecovered thiocyanate injected into streams, rivers, ethylhexylamine, diethylhexylamine, ethylenediamine, di 3,433,737 3 4 ethylenetriamine, triethylenetetramine, tetraethylenepen essary to add 36 grams of 25% aqueous sodium hydrox tamine, hydroxyethyl ethylenediamine, propylenediamine, ide solution to neutralize the solution before discharge diethylaminoethanol, morpholine, monoethanolamine, di into the sewage system. ethanolamine, triethanolamine, and the like. From the foregoing it will be evident that the method Buffered alkaline reagents are effective as well. For of the invention affords a convenient and economical example, the aqueous equimolar solution of KHPO4 (pH means for destroying the toxicity of waste streams con about 9) and KH2PO4 (pH about 4.8) will provide an taining spent mother liquors and wash liquids resulting alkaline pH. Preferably, a strongly basic reagent will be from the synthesis of organic thiocyanate compounds as employed, e.g., sodium, potassium or ammonium hydrox compared with known treatments such as the hypochlo ide, in order to provide a pH of at least about 9. 0. rite process described above. The alkaline material is added to the waste stream and EXAMPLE 2 mixed with the spent mother liquor and wash liquid for a time and at a temperature sufficient to cause substan In substantially the same manner as in Example 1, a tially complete decomposition of organic thiocyanate com waste stream containing wash liquid from the synthesis pound. Decomposition will be evident by formation of a 15 of monochloromethyl thiocyanate (preparable as in Ex precipitate and generally also by a mercaptain (garlic-like) ample 1 of German Patent 1,157,603) is treated with an odor. Room temperature or heating at a temperature up amount of an aqueous sodium hydroxide solution suffi to the boiling point of the treated liquid is effective. Time cient to raise the pH above 9. This treatment decomposes of treatment and temperature are therefore not critical. the monochloromethyl thiocyanate, thereby abating the The alkaline material may be added directly or as solu 20 toxicity of the stream caused by the presence of this tions or dispersions, e.g., dilute or concentrated aqueous compound. solutions. I claim: Completeness of decomposition may be determined by 1. A method of reducing the toxicity of waste streams standard analytical procedures and the decomposition of the group consisting of spent mother liquor and wash products may be separated by any convenient means such 25 liquid resulting from the synthesis of an organic thiocy as filtering,