GB595407A - Production of pure glycol solutions - Google Patents

Abstract

Aqueous glycol solutions containing acidic impurities including acids and salts are purified by passing the solutions through a bed of anion-exchange material A1, thence through a bed of cation-exchange material C1 and thence through an anion-exchange material A2. In modifications, the effluent from bed C1 or A2 may pass through a bed of anion-exchange material A3 which has been buffered so that the fluid flowing therefrom will have a neutral or other desired pH, or the effluent from the bed A2 may be passed through another bed of cation-exchange material C2 and thence through a bed of anion-exchange material A4 which may be buffered as in the case of bed A3, and, if desired, one or more series of beds of anion- and cation-exchange materials may be inserted between beds C2 and A4. Preferably, when using a bed of buffered anion-exchange material, the effluent flowing thereto should contain a low content of ionizable solids, preferably less than 20 p.p.m. The anion-exchange material may be activated by means of aqueous alkali and then buffered by treatment with carbon dioxide or an aqueous solution of sodium hydroxide or carbonate to give the desired pH. Suitable anion-exchange materials include the aldehyde-condensation products of m-phenylene diamine, biguanide guanyl urea, methyl guanidine, phenyl biguanide and polyamines such as the polyethylene polyamines; they may be formed from formaldehyde, furfural, acrolein and benzaldehyde. When the products are insufficiently insoluble they may be rendered insoluble by treatment with formaldehyde reactive materials such as urea, thiourea, the aminotriazines, especially melamine and guanamines. The methods of preparation described in Specifications 561,896 and 562,402 may be used. Suitable cation-exchange materials are catechol tannin-formaldehyde condensation products, aromatic sulphonic acid-formaldehyde condensation products as described in U.S.A. Specification 2,204,539 and carbonaceous zeolites such as sulphated or sulphonated coal, peat, or lignite. In an example, an aqueous solution containing a mixture of ethylene glycol, diethylene glycol and propylene glycol, acid and some salt is passed through a bed of activated anion-exchange resin, for example, that prepared according to example 1 of Specification 561,896, then through a cation-exchange material, for example a bed of resin (C) prepared as described hereinafter and acid activated, and thence through a second bed of anion-exchange material whereby the ash content of the solution is reduced from 0.075 to 0.0002 grams per 100 c.cs. Resin (C) is prepared by reacting acetone and furfural in aqueous caustic soda, then refluxing with sodium bisulphite and thereafter heating the product with additional furfural and aqueous sulphuric acid; the resin obtained on gelling is granulated and dried. Specifications 569,661 and 572,915 also are referred to.