Recovery Of Ethylene Dichloride & Benzene from Wastewater Effluents Of Vinylchloride Monomer & Poly Butadiene Rubber Plant

Abstract

Effluent of Vinyl chloride monomer (VCM) contains about 2000 ppm of EDC. EDC causes increase in COD of effluent water. The EDC needs to be segregated from water as incineration of EDC leads to formation of hydrochloric acid which is highly corrosive. The level of EDC in water is generally brought down fron 2000 ppm to 500 ppm using steam stripper. This is a continuous process. However, it is not possible to bring it down to < 500 ppm using this process. Adsorption based method is only suitable to remove the EDC from water. EDC can be concentrated using adsorption method and can be separated and knocked off by condensation. Activated carbon is best suited for this application. Hence sorption of EDC on carbon was measured using equilibrium method in vapour phase. Carbon possess very high capacity to adsorb EDC. Also, since carbon is hydrophobic it selectively pick up only EDC from effluent water. The dynamic capacity of carbon was measured at three different concns. 500, 1000 and 2000 ppm. Higher the concn. of EDC, higher is the adsorption capacity of carbon. Also, the measurements were made at 3 different temperatures 30, 40 and 50oC. This was done to study the effect of temperature on adsorption. As during the summer months, the temperature is almost above 40oC this measurement was very much needed. Though carbon possess certain advantages in terms of high sorption capacity and lower cost and regeneration is possible using steam at 150oC, it has certain disadvantages in terms of decreased adsorption capacity after certain cycles. Generally, inhomogenities hinder the convection transport of the heat released by adsorption and result in hot spots and when this exceeds the carbon ignition temperature can cause fire. Zeolite with higher silica alumina ratio which has hydrophobicity can also be used for this application. However, the sorption capacity of zeolites is much lower as compared to activated carbon. Also, the cost of zeolite is much higher and in the range of 4 – 5 times higher as compared carbon. In terms of advantages, causes of fire in the bed can be completely eliminated as it is highly thermally stable. Also, these can be regenerated iv with a swing in temperature. These give a longer life as compared to carbon. Hence, sorption of EDC at three different concns. were measured on zeolites. Benzene is used as solvent in manufacturing PBR at Vadodara Manufacturing Division. As benzene is classified as carcinogenic even at very low concentration it poses a serious environmental issue. The effluent water of this plant contains about 2000 ppm of benzene and it needs to be brought down to < 1ppm. At present, this is being done using steam stripper as it is a continuous process. Using this process benzene at the outlet is controlled to about 10 ppm. However, a higher amount of steam is required to control the concentration of benzene. Hence, an adsorption based process using activated carbon as adsorbent was carried out to replace the existing steam stripper process.