TREATMENT OF THE EFFLUENTS FROM THE PRODUCTION OF EPOXY RESINS

Abstract: Process for the treatment of aqueous effluents from the production of epoxy resins, which effluents contain as their main impurities chlorohydrins, glycidol, isopropyl alcohol and sodium chloride, which process comprises the following steps: (a) hydrolytic treatmnent of the effluent under alcaline conditions, until the effluent's content of epichlorohydrin in reduced down to values of about 75 ppm, and the effluent's glycidol content is reduced to values lower than about 4,000 ppm; (b) removal of about 90% of sodium chloride from the hydrolysed effluent;; and (c) anaerobic digestion of the hydrolysed, sodium chloride-deprived effluent, after preliminary dilution, neutralization and integration with nitrogen and phosphorus sources. The (b) step can be carried out by means of a process of concentration of the effluent, in order to cause sodium chloride to precipitate, or by submitting the same effluent to a treatment of electrodialysis.

Description: This invention relates to a process for purifying an aqueous effluent stream exiting an epoxy-resin production plant and containing chlorohydrins, glycidol, isopropanol and sodium chloride as impurities. Such an aqueous effluent has a pH in the neighbourhood of 10 and a COD, that is the oxygen demand for oxidizing the organic substances which are present in the aqueous medium, of from 80 g/l to 90 g/l. Due to its particular composition, the effluent in question is toxic to both the anaerobic and the aerobic bacteria, so that it cannot be disposed off, as such, by an aerobic oxidation facility. DE-A1-1 517 653 suggested, for an effluent exiting petrochemical plants, an alkaline hydrolysis at 70°C-100°C at a pH over 6, to convert the organic chlorine into NaCl, and the organic carbon into biodegradable compounds, without any previous dilution. With this approach, however, the problem of disposing of NaCl remains unsolved. The Applicants have ascertained that the effluent in question can be anaerobically digested, thus abating the COD to a negligible value, after a preliminary treatment intended to significantly decrease, if not to eliminate, organic chlorine and NaCl. Consequentially, the particular effluent referred to above can be directly disposed off in the usual aerobic waste treatment facilities, once that the anaerobic digestion step has been completed. In order to solve the technical problem outined above, this invention provides: A process for purifying an aqueous effluent stream exiting an epoxy-resin production plant and containing chlorohydrins, glycidol, isopropanol and sodium chloride as impurities, comprising the steps of: (a) hydrolyzing the effluent by adding thereto aqueous sodium hydroxide at a concentration of from 5 g/l to 10 g/l, a pH of from 11 to 13, a temperature of from 50°C to 100°C, and for a time of from 1 to 10 h, whereby, in the hydrolyzed effluent, the epichlorohydrin content is reduced to 75 parts per million (ppm), and the glycidol content is reduced to less than 4,000 ppm; (b) removing at least 90% of sodium chloride from said hydrolyzed effluent, and (c) diluting, neutralizing, and integrating with N and P sources the thus partially purified effluent, and anaerobically digesting it on an inoculated anaerobic filter which has been started up with a synthetic substrate. A typical effluent which can be submitted to the process according to the present invention is an aqueous effluent with a pH value of about 10, a COD value of 80-90 g/litre, with densities of 1.18-1.20 g/litre, which contains from 4 to 5 g/litre of epichlorohydrin, from 16 to 22 g/litre of isopropyl alcohol, from 5 to 10 g/litre of glycidol, from 7 to 9 g/litre of 3-chloro-1,2-propane-diol, from 0.5 to 1.5 g/litre of 1,1-dichlorohydrin, from 0.1 to 0.5 g/litre of 1,2-dichlorohydrin and from 270 to 290 g/litre of sodium chloride. During the treatment of hydrolysis, the isopropyl alcohol can be at least partially removed from the reaction medium, and the same alcohol can be recovered as an aqueous solution. This latter, if desired, can be recycled to the (c) step of the process. By operating within the range of the above stated conditions, the content of epichlorohydrin in the waste liquors is reduced down to values tower than 75 ppm (parts per million by weight) and preferably to values lower than 10 ppm and the contents of glycidol is reduced to values lower than 4,000 ppm, and preferably lower than 3,000 ppm. Furthermore, the contents of 3-chloro-1,2-propane-diol, 1,1-dichlorohydrin and 1,2-dichlorohydrin are reduced down to values of a few ppm. In the (b) step of the process, the hydrolysed effluent is submitted to a treatment capable of eliminating at least about 90% of sodium chloride. For that purpose, the process can be carried out by concentrating the solution, preferably under a reduced pressure, or by submitting the same solution to a treatment of electrodialysis. This latter treatment is preferably carried out inside a modified cell, which makes it possible for sodium to be separated as aqueous sodium hydroxide, and for chlorine to be separated as aqueous hydrochloric acid. This cell, which is described in greater detail in the following experimental examples, prevents any development of chlorine gas and reduces the problems of corrosion and the chemical attack of the membranes by the same chlorine. The so obtained desalted effluent, after the preliminary addition of the aqueous solution of isopropyl alcohol separated in the (a) step and of water separated in the (b) step, is diluted down to a value of COD of the order of from 15 to 20 g/litre, and is submitted to anaerobic digestion in the (c) step of the process according to the present invention. After the dilution, the concentration of epichlorohydrin, of glycidol and of sodium chloride respectively decreases down to values lower than about 5, 1,200 and 20,000 ppm. The operation of digestion can be carried out by using an anaerobic filter suitably inoculated and previously started up with a synthetic substrate, until microbial flora is acclimated. Finally, the diluted waste liquors are submitted to anaerobic digestion, after a preliminary neutralization down to a pH value of about 7, and addition of nitrogen and phosphorus sources. By means of this treatment, the value of COD of the anaerobically-digested waste waters is decreased by an extent of more than 80%, and the resulting waste liquors can be directly discharged into the normal facilities used for the aerobic digestion of wastes. The following experimental examples are illustrative of the process according to the present invention. Example 1 A) To the treatment according to the present invention an effluent is submitted, which is constituted by a byproduct deriving from the production of epoxy resins from bisphenol A and epichlorohydrin, having the following average composition: - epichlorohydrin 4,1 g/litre - isopropyl alcohol 17,0 g/litre - glycidol 9.6 g/litre - glycerol 6.3 g/litre - 3-chloro-1,2-propane-diol 8.0 g/litre - 1,1-dichlorohydrin 1.0 g/litre - 1,2-dichlorohydrin 0.35 g/litre - sodium chloride 280.0 g/litre Said effluent additionally has a pH value of 10.0, a COD value of 83.0 g/litre and a density value of 1.19 g/ml. B) To this effluent, sodium hydroxide is added up to a concentration of sodium hydroxide of 8.0 g/litre, and the effluent is heated up to 95°C, and is kept at this temperature for 5.5. hours, by operating inside a laboratory-size rotary evaporator. The vapour released during the treatment are collected and condensed at a temperature of 4°C. Five litres of effluent are treated, and about 430 ml of condensate are collected. The condensate contains a concentration of 19.8% of isopropyl alcohol. In this way, about 95% of alcohol is recovered. C) The residue obtained from the above treatment is concentrated by operating at about 70°C and under a pressure of 400 mbar (300 torr), until 3.0 litres of condensate is obtained. The crystals of sodium chloride formed during the concentration are filtered off under vacuum, with about 1.15 kg of dry sodium chloride and 600 ml of mother liquors being obtained. The solution of isopropyl alcohol collected during the hydrolysis of epichlorohydrin, the condensate obtained during the concentration step and the mother liquors are combined and the volume of the combined liquors is adjusted at 5 litre by means of the addition of water. A solution is thus obtained, which has a practically unchanged COD concentration as compared to the pristine waste waters. This solution is diluted with a dilution ratio of about 1:4, and a waste liquor is obtained, which has the following composition: - epichlorohydrin <5 ppm - isopropyl alcohol 4.1 g/litre - glycidol 0.8 g/litre - glycerol 8.5 g/litre - 3-chloro-1,2-propane-diol 20 ppm - 1,1-dichlorohydrin 20 ppm - 1,2-dichlorohydrin 20 ppm - sodium chloride 12.5 g/litre The solution , which additionally has a pH value of 12.0 and a COD value of 19.8 g/litre, is submitted to anaerobic digestion, after the preliminary integration with about 1.1 ml of a solution of concentrated ammonium hydroxide per each litre of waste liquor, and neutralization with about 2.2 ml of a solution of concentrated phosphoric acid per each litre of waste liquor. D) The anaerobic digestion is carried out by using an anaerobic filter constituted by a cylindrical reactor of 35 litres of total volume (D = 15 cm; H = 2 m); packed with river pebbles having an average diameter of about 5 cm (empty room degree of the reactor = 0.5), and with the operating temperature being maintained at about 35°C. The filter is inoculated with 4.5 litres of a suspension containing a mixed, non-specific, anaerobic flora and started up with a synthetic substrate at a pH value of 7.0 and with a COD value of 25.0 g/litre, having the following composition: - sodium acetate 1.2 g/litre - KH₂PO₄ 1.2 g/litre - NaCl 4.8 g/litre - Glycerol 4.8 g/litre - IPA (isopropyl alcohol) 7.2 g/litre - H₃PO₄ 2.2 ml/litre - NH₄Cl 1.1 ml/litre During the start-up step, the anaerobic filter is fed with progressively increasing organic loads until about 4 kg of COD/mc per day is reached. On the 28th day, the process of acclimation of the flora to the synthetic substrate can be regarded as concluded, and the synthetic substrate is replaced by the treated effluent, obtained as disclosed under (C). The change of substrate involves initially a considerable decrease in the performance of the anaerobic filter, with a decrease in biogas production of about 60%. After about 10 days, the microbial flora is acclimated and on the 46th day a production of biogas is reached, which is similar to the reduction obtained with the synthetic substrate (decrease of COD by an extent of about 80%). During the anaerobic treatment, no appreciable changes are observed in pH, whose values remain within the range of from 6.3 to 7.0. Example 2 320 ml of the effluent having the same composition as reported under (A) in Example 1 is allowed to decant for 48 hours. The supernatent (about 300 ml), having a COD value of 80 g/litre, is submitted to a first filtration through sintered filters of 3 µm, in order to separate any traces of material in corpuscular form, potentially capable of damaging the membranes of the electrodialyser device. The filtrate, having a nearly unchanged COD value as compared to the starting material, is submitted to the hydrolysis of epichlorohydrin under the same conditions as disclosed under (B), Example 1. The hydrolysed solution is diluted 1:4, is filtered again through a membrane filter (pore diameter 0.2 µm), and is then electrodialysed. The process of electrodialysis is carried out inside a cell inside which, between the anion-exchange membranes and the anode, a second cation-exchange membrane is installed. Between this latter and the anode, a fourth compartment is therefore obtained, into which a solution of sulfuric acid is fed. With this arrangement, the chlorine ions passing through the anion-exchange membrane cannot reach the anode, with the formation of free chlorine being thus prevented. At the anode, only the development of oxygen and the migration of hydrogen ions through the cation-exchange membrane take hence place. Inside the third compartment of the cell, the above said hydrogen ions and chlorine ions form hydrochloric acid. The conditions of electrodialysis are the following: At the end of the treatment, removed sodium chloride is of about 87% of total sodium chloride (i.e., a removed amount of 74 g over the fed amount of 85 g), with about 47 g of sodium hydroxide being produced in an aqueous solution at 11.7% by weight, and 33 g of hydrochloric acid being produced in an aqueous solution at 2.8% by weight. A solution, depleted of sodium chloride, is obtained, whose pH value is of 12.0, and whose COD value is of 14.0 g/litre, which solution has the following composition: - epichlorohydrin <5 ppm - isopropyl alcohol 3.95 g/litre - glycidol 2.3 g/litre - glycerol 2.8 g/litre - 3-chloro-1,2-propane-diol 20 ppm - 1,1-dochlorohydrin 20 ppm - 1,2-dochlorohydrin 20 ppm - sodium chloride 10 g/litre The anaerobic digestion is carried out in the same way as in above Example 1. In this case too, the acclimation of the bacterial flora to the synthetic substrate takes place within about 30 days. After this time, increasing amounts of the waste liquors having the hereinabove reported composition, at pH 7.0 and to which the nitrogen and phosphorus sources are added as shown under (C) of the above Example 1, are fed in mixture with the synthetic substrate (from 15% up to 100% over a time of about three months). The total organic load is maintained around about 5 kg of COD/m³ per each day. Values of COD decrease higher than about 80% are reached after 70-80 operating days.

Claims: A process for purifying an aqueous effluent stream existing an epoxy-resin production plant and containing chlorohydrins, glycidol, isopropanol and sodium chloride as impurities, comprising the steps of: (a) hydrolyzing the effluent by adding thereto aqueous sodium hydroxide at a concentration of from 5 g/l to 10 g/l, a pH of from 11 to 13, a temperature of from 50°C to 100°C, and for a time of from 1 to 10 h, whereby, in the hydrolyzed effluent, the epichlorohydrin content is reduced to 75 parts per million (ppm), and the glycidol content is reduced to less than 4,000 ppm; (b) removing at least 90% of sodium chloride from said hydrolyzed effluent, and (c) diluting, neutralizing, and integrating with N and P sources the thus partially purified effluent, and anaerobically digesting it on an inoculated anaerobic filter which has been started up with a synthetic substrate. Process according to Claim 1, wherein step (a) is carried out at a temperature of from 80°C to 90°C and for a time of from 5 to 6 h. Process according to Claim 1, wherein step (b) is carried out by concentrating the hydrolyzed effluent under a subatmospherical pressure. Process according to Claim 1, wherein step (b) is carried out by electrodialysis.

Inventors: BARADEL, AGOSTINO, DELLA PENNA, GINO, GULINELLI, SILVIO, ROBERTIELLO, ANDREA, VALDISERRI, MARIO
Applicants: ENIRICERCHE S.P.A.
Application year: 1989
Main classification: C02F9
IPC codes: C02F3, C02F1, C02F9