TREATMENT OF INORGANIC SALTS CONTAMINATED WITH ORGANIC COMPOUNDS

Abstract: Inorganic salts contaminated with relatively high boiling organic chemical contaminants are removed by washing the contaminated salt with a solvent which has a boiling point below the organic chemical contaminant, removing the salt from the wash solvent and drying the thus treated inorganic salt. This method is particularly suitable in the treatment of the alkali metal halide produced in the manufacture of epoxy resins.

Description: The present invention pertains to the treatment of inorganic salts contaminated with organic compounds. Various processes for the production of organic compounds such as the production of epoxy resins from a hydroxyl-containing compound and an epihalohydrin and an alkali metal or alkaline earth metal hydroxide or carbonate and the like also produce large quantities of an inorganic salt which must be disposed in an environmentally acceptable manner. In many of these organic processes such as the production of epoxy resins, this inorganic salt is contaminated with not only the organic reactant materials, but are also contaminated with high boiling organic by-product compounds. One method for disposal of contaminated salts is by land-fill which is not only expensive but a less desirable method of disposal. In the process for the production of epoxy resins, this salt contaminated with epihalohydrin and high boiling by-product compounds is treated by dissolving the contaminated salt in water and sending the resulting brine to treatment ponds. While this method is acceptable, it nevertheless results in a salt-water solution, brine, which contains significant amounts of relatively high boiling organic chemical contaminants. This salt-water solution contains significantly high quantities of total organic carbon, TOC, resulting in high total oxygen demand, TOD, biological oxygen demand, BOD or chemical oxygen demand, COD. These significantly high quantities of TOC, TOD, BOD or COD places a huge load on organic waste treatment ponds. Not only is this expensive, but the salt is lost which if treated such that there were insignificant quantities of organic contaminants present it could be used as a raw material for subsequent processes employing such salts. It would be highly desirable to have a method whereby an inorganic salt contaminated with relatively high boiling point organic chemical contaminants could be treated so as to remove a significant amount of the organic chemical contaminants from the inorganic salt so that it could be employed in subsequent useful purposes for which said inorganic salt is known. US-A-4,662,948 discloses a method for removing polychlorinated biphenyls and dioxins from soil, landfill, gravel, sand, clay or a mixture thereof by washing the material with halogenated hydrocarbons, comprising fluorinated hydrocarbons, and/or polar organic solvents including lower alcohols and ketones. The liquid is separated from the material after the washing process. It is the object of the present invention to provide a method for removing relatively high boiling chemical contaminants from a contaminated material. This object is attained by (A) washing said contaminated material with a solvent or a mixture of solvents selected from the group of ketones, alcohols in which the organic chemical contaminant(s) is (are) soluble at the treatment temperature, thereby forming a liquor containing the solvent(s) and the contaminant(s) and separating the liquor and said material by any suitable means, characterized in that the contaminated material is an inorganic salt contaminated with reaction products of epihalohydrin and water and the group of solvents comprising furthermore epihalohydrins, aromatic hydrocarbons and glycolethers and (B) excess liquor is removed from the thus treated salt such that the resultant inorganic salt composition contains not more than 60 percent liquor by weight; (C) the thus treated inorganic salt composition is subjected to drying at conditions of temperature and pressure sufficient to remove the residual solvent or solvent mixture remaining in the inorganic salt composition after step (B), thereby producing an inorganic salt containing on a dry basis not more than 700 parts per million parts by weight total organic carbon. The contaminated inorganic salt composition can be removed from the mother liquor which contains such contaminated inorganic salts by first subjecting the composition to drying, if it contains water, such that the water content of the composition is suitably not more than 2, more suitably not more than 1, most suitably not more than 0.2, percent by weight. This can be accomplished, for example, by drying at any suitable temperature and pressure, such as, for example, at a temperature suitably from 40°C to 150°C, more suitably from 50°C to 100°C, most suitably from 60°C to 70°C; and at pressures suitably from 13.79 kPa (2 psia) to 206.84 kPa (30 psia,) more suitably from 20.68 kPa (3 psia) to 137.90 kPa (20 psia), most suitably from 27.58 kPa (4 psia) to 103.42 kPa (15 psia); for a time sufficient to reduce the non-chemically bound water content to the desired level. The inorganic salt contaminated by the relatively high boiling chemical contaminants can be removed from the product stream containing the contaminated inorganic salt and the product and any unreacted reactants by any suitable means such as, for example, filtration, centrifugation, precipitation, decantation, or the like. The resultant contaminated inorganic salt composition is then washed one or more times with an organic solvent or mixture of organic solvents in an amount suitably from 0.76 to 18.93 l (from 0.2 to 5 gallons), more suitably from 1.14 to 11.36 l (from 0.3 to 3 gallons), most suitably from 1.89 to 3.79 l (from 0.5 to 1 gallon[s]) of solvent per pound of inorganic salt being treated. Suitable solvents include, for example, halogenated hydrocarbons; ketones, aliphatic alcohols, aromatic hydrocarbons, glycol ethers, and combinations thereof. Particularly suitable solvents include, for example, epichlorohydrin, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, benzene, methanol, ethanol, isopropanol, propylene glycol methyl ether, and combinations thereof. The temperature at which the solvent(s) is (are) employed to wash the contaminated inorganic salt is not critical. However, suitable temperatures are from 5°C to 100°C, more suitably from 10°C to 60°C, most suitably from 20°C to 40°C. After washing the contaminated inorganic salt with the solvent or solvent mixture, the thus treated inorganic salt composition is then deliquored by filtration, centrifugation, precipitation, decantation, or the like to the extent that the inorganic salt composition suitably contains not more than 60, more suitably not more than 40, most suitably not more than 20 percent by weight of the volatile organic components. Upon completion of the deliquoring, the inorganic salt composition is then dried in a suitable drier to remove the organic solvents. The drying can be conducted at temperatures suitably from 40°C to 600°C, more suitably from 50°C to 300°C, most suitably from 60°C to 150°C. This drying step can be conducted in any drying equipment which is suitable for this purpose. Particularly suitable drying equipment include, for example, Torus Disc driers, fluid bed driers, and the like. This drying step is suitably conducted at pressures of from 1.38 to 310.28 kPa (from 0.2 to 45 psia), more suitably from 27.58 to 206.85 kPa (from 4 to 30 psia), most suitably from 55.16 to 137.90 kPa (from 8 to 20 psia). The method of the present invention produces, after the drying step, an inorganic salt which contains on a dry weight basis not more than 700, suitably not more than 285, more suitably not more than 140, most suitably not more than 70, parts per million parts by weight (ppm) total organic carbon (TOC). The chemical contaminants can be removed from the solvent(s) by distillation, if the difference between the boiling points of the solvent(s) and the organic chemical contaminant(s) will permit it, otherwise, they can be removed by water washing and subsequently disposed of by burning. This method for removing relatively high boiling organic chemical contaminants is particularly suitable in the treatment of the alkali metal halide produced in the manufacture of epoxy resins by dehydrohalogenating the reaction product of an aliphatic hydroxyl-containing compound with an epihalohydrin. In this case, the relatively high boiling organic chemical contaminants are reaction products of epihalohydrin and water, i.e., glycerine (B.P.:290°C) and glycerine monochlorohydrin (B.P.:213°C) or any reactive organics that tend, through polymerization or intercomponent reaction followed by polymerization to form compounds having vapor pressures so low as to require temperatures equal to or greater than the thermal decomposition temperature of said products or the melt point of the salt components for effective removal by conventional distillation methods. Examples of the reactive organics are glycidyl derivatives of aromatic compounds containing an active hydrogen atom reacted with an epihalohydrin. Other processes include, for example, cleaning and recovering the salt from the manufacture of glycerine from epichlorohydrin and the like. The following example is illustrative of the invention. Example One hundred thirty-six (136) kg (300 lbs.) of sodium chloride from an epoxy resin process containing 30 percent by weight (pbw) of epichlorohydrin, 0.5 to 1.5 pbw of a mixture of glycerine monochlorohydrin and glycerine dichlorohydrin and 10 pbw of epoxy resin was washed with 290 gallons (1089.9 l) of a 90/10 weight percent mixture of epichlorohydrin/propylene glycol methyl ether (1-methoxy-2-propanol) in a basket centrifuge at a temperature of 35°C for 30 minutes at 300 rpm. This was followed by washing the salt with 107 gallons (405 l) of epichlorohydrin at a temperature of 30°C for 11 minutes in the centrifuge running at 300 rpm. The salt was then deliquored in the basket centrifuge running at 800 rpm for 2 to 4 minutes resulting in a sodium chloride cake containing 17-23 percent residual volatiles by weight based on dry salt weight. The salt was then dried in a Torus Disc drier at a temperature of 90°C to 120°C for 15 to 20 minutes. After this time, the sodium chloride contained 303 ppm by weight of epichlorohydrin and 47 ppm by weight of propylene glycol methyl ether (1-methoxy-2-propanol). A sample of this salt was dissolved in deionized water to make an 18 percent brine solution. A total organic carbon (TOC) analysis revealed 40-50 ppm TOC in the brine solution. On a dry basis, the treated, dried salt contained 222-278 ppm TOC.

Claims: A method for removing relatively high boiling chemical contaminants from a contaminated material by (A) washing said contaminated material with a solvent or a mixture of solvents selected from the group of ketones, alcohols in which the organic chemical contaminant(s) is (are) soluble at the treatment temperature, thereby forming a liquor containing the solvent(s) and the contaminant(s) and separating the liquor and said material by any suitable means, characterized in that the contaminated material is an inorganic salt contaminated with reaction products of epihalohydrin and water and the group of solvents comprising furthermore epihalohydrins, aromatic hydrocarbons and glycolethers and (B) excess liquor is removed from the thus treated salt such that the resultant inorganic salt composition contains not more than 60 percent liquor by weight; (C) the thus treated inorganic salt composition is subjected to drying at conditions of temperature and pressure sufficient to remove the residual solvent or solvent mixture remaining in the inorganic salt composition after step (B), thereby producing an inorganic salt containing on a dry basis not more than 700 parts per million parts by weight total organic carbon. The method of Claim 1 wherein (a) the contaminated inorganic salt is washed with from 0.76 to 18.93 l (0.2 to 5 gallon(s)) of solvent per 453,59 g (pound) of inorganic salt being treated at a temperature of from 5°C to 100°C; (b) the product resulting from step (B) has a volatiles content of not more than 60 percent by weight based upon the weight of dry inorganic salt; (c) the drying step (C) is conducted at a temperature of from 40°C to 600°C; and (d) the resulting product contains not more than 285 ppm total organic carbon. The method of Claim 1 wherein (a) the contaminated inorganic salt is washed with from 1,14 l to 11.36 l (0.3 to 3 gallon(s)) of solvent per 453,59 g (pound) of inorganic salt being treated at a temperature of from 10°C to 60°C; (b) the product resulting from step (B) has a volatiles content of not more than 40 percent by weight based upon the weight of dry inorganic salt; (c) the drying step (C) is conducted at a temperature of from 50°C to 300°C; and (d) the resultant product contains not more than 140 ppm total organaic carbon. The method of Claim 1 wherein (a) The contaminated inorganic salt is washed with from 1.89 l to 3.79 l (0.5 to 1 gallon(s)) of solvent per 453,59 g (pound) of inorganic salt being treated at a temperature of from 10°C to 60°C; (b) the product resulting from step (B) has a volatiles content of not more than 20 percent by weight based upon the weight of dry inorganic salt; (c) the drying step (C) is conducted at a temperature of from 60°C to 150°C; and (d) the resultant product contains not more than 70 ppm total organic carbon. The method of Claim 1 wherein the contaminated inorganic salt being treated is an alkali metal halide. The method of Claim 5 wherein (a) the contaminated inorganic salt being treated is sodium or potassium chloride; and (b) the solvent employed in step (A) is selected from epichlorohydrin, methyl ethyl ketone, methyl isobutyl ketone, toluene, methanol, ethanol, isopropanol, propylene glycol methyl ether or any combination thereof. The method of Claim 6 wherein (a) the contaminated inorganic salt being treated is sodium chloride; and (b) the solvent employed in step (A) is selected from epichlorohydrin, methyl isobutyl ketone, or any combination thereof.

Inventors: GAMMILL, BENNY B., SAWA, HIROSHI, SUZUKI, TAMIO
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1989
Main classification: C01D3
IPC codes: C01D17, B01D11, C01D3