Purification of carbohydrate-containing effluents

Abstract

The aim of the present work was to develop a method for purifying the viscous syrupy carbohydratecontaining effluents formed after the isolation of the desired products when their additional extraction from the mother solutions is economically undesirable. Industrial methods of utilizing carbohydrates by their acid'splitting and the production from them of furfural, 5-hydroxymethylf urfural [1], and levulinic acid [2] are known. However, these methods of utilizing carbohydrate-con taining raw material, which are of independent interest for the whole industrial sector, cannot be applied to the local purification of specific smallvolume intermittent effluents of some intermediates of the medicinal industry. The object of the investigation was effluents, especially mother liquors, containing carbohydrates and their derivatives and characterized by a high value (about 1 kg of O2/liter) of the chemical oxygen demand (CGD). At the present time, such concentrated effluents are, as a rule, dilutedwith a large amount of water before being passed into the drainage network, which leads both to an increase in the water-consumptio n levels per unit of production and also to the additional consumption of oxygen in biological purification plants. ~e have established that when the acid degradation of the carbohydrates present in the effluents is performed under certain conditions, the degree of purification of the effluents reaches 60-100% with respect to the COD. This process is performed by the autoclaving of the carbonate-contai ning effluents in the presence of a mineral acid at 120-150~ and a pressure of 1.5-1 arm gauge. The consumption of concentrated mineral acid amounts to 1-5 vol. % of the initial amount of initial solution to be rendered harmless, and the optimum concentration of mineral acid depends primarily on ~he nature of the carbohydrates present in [he effluents (see Table 1). As a result of the degradation of the carbohydrates, a solid black carbonaceous precipitate is formed which is practically the only reaction product. Table 1 gives the capacity for acid degradation of various hydrocarbons that may be present in the effluents from the production of vitamins, in particular, the production of vitamins C and B 2. As can be seen from the table, all the carbohydrates readily undergo degradation and the ketoses (sorbose and fructose) are converted almost completely into a carbonaceous mass. The carbonaceous mass obtained possesses a good adsorption capacity and has the following average composition: C 40-45%, H 3-5%, residue after ignition 5-8%. When the dehydration of the carbohydrate is incomplete, in addition to the carbonaceous precipitate, a superna~ant liquid remains which is readily separated by decantation or filtration and has better sanitary and chemical indices than the initial solution. The carbonaceous precipitate is sent to the waste dump and the supernatant liquid to the drainage system. Table 1 also gives results on the decontamination of the intermittent effluents from the production of ascorbie acid by the method of acid hydration: the mother solutions after the isolation of L-sorbose and ascorbic acid. These mother solutions, which are dark-brown viscous paste-like masses with a COD of from 0.2 to 1 kg of O2/liter, amount in absolute magnitude of the COD to 8-10% of all the organic pollutants passing into the effluents in the production of ascorbic acid. With the optimum amount of mineral acid (see Table 1) the purification effect, judged by the COD, amounts to 81 and 100%, respectively, for the mother solutions after the isolation ef the L-sorbose and the ascorbic acid; i.e., the passage of these effluents into the total effluent from the production of ascorbic acid is practically eliminated.