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engineering (Htting out the last traces of VCM Tenneco process uses activated carbon to remove vinyl chloride monomer from PVC plant gas streams. It's one of several methods producers are licensing More than a year's experience with its carbon adsorption method of controlling \inyl chloride emissions from polyvinyl chloride plants has convinced Tenneco Chemicals (Saddle Brook, N.J.) that it lias tound the best route. So it is setting mt to license the method to others. When the cancer-causing properties of m\l chloride monomer became known, explains Robert S. Miller, manager of polvmers research, the firm had to de velop its own technology to control emisaons. Now it is marketing the know-how in the U.S, and in European countries that are following the U.S. lead in setting stringent emission standards. The firm is just one of a number of U S, producers that have developed li censing packages in an effort to recoup part of the millions they have spent to de velop the new technology. Goodrich is licensing its steamst^Htg process, which removes VCM from PVC suspension resins. Diamond Shamrock has developed a proprietary technique for removing residual VCM from PVC dispersion resins. Monsanto has been licensing its PVC reactor clean ing know-how for more than a year. Lon/u (Basle. Switzerland) is offering a procedure for preventing suspension resin polvmer buildup on reactor walls. And several others have developed instrumentation to monitor the amount of VCM m the air and in PVC. Thirsty Carbon: Tenneeo's develop ment is aimed at recovering the residual VCM in vent gas streams (Ok, Sept. IS, 1974. p t>6). A unit built by Chemical De sign (Lockport. NY.) was installed at Tenneeo's PVC plant in Pasadena, Tex., in early 1975. A year's experience with the equip ment, says Roy T Gottesman, associate director of research and development, shows that less than 4 ppm of vinyl chlo ride monomer is escaping in the adsorber effluent stream. During that time, the ac tivated carbon in the unit has undergone n^^^thun 1.300 adsorption and regenera^^KvcIes That makes it good enough to meet the proposed Environmental Pro tection Agency standard ol 10 ppm. Moreover, alter 10 months ol contin uous service, samples ol carbon with drawn Irom the adsorber showed that it retained 'Ml', ol its otisimal adsoiplivc ca pacity. Further, there was no evidence of vinyl chloride polymerization in the ad sorption unit or within the carbon. Trouble Spots: Aside from leaks, which manufacturers try to keep to a minimum, there are several points where VCM can escape to the atmosphere: at the reactor, the slurry tanks, and equip ment purge streams. PVC is made primarily by either sus pension or emulsion polymerization tech niques. Generally, in these processes VCM and the polymerization initiator are dispersed in water by the use of sus pending or emulsifying agents. The poly merization temperature is selected to ob tain the desired molecular weight. But not all of the vinyl chloride is converted into PVC. Usually 17-20% of monomer that does not react remains at the end of the polymerization cycle. Much of that can be recovered and recycled to the front end of the process. But as much as TENNECO'S GOTTESMAN: New process cuts PVC plants' VCM loss to below 4 ppm. 4'4 VCM can remain in the PVC slurry Irom the teactor. That can be removed by specialized stripping techniques, such .is the ones Goodnch, Diamond Shamrock and 1 cuncco now oiler. Residual VCM horn that cleanup phase is one ol the potential sources of teed loi ilie c.uhon adsorption step Miothci source is the slurry tanks, wheie operators Hash air oi miroeen through the vapor space of the tank to l^eep VCM concentrations down and pre vent a flammable mixture from forming. Depending on the level of stripping of the slurry downstream, VCM concentra tions in the nitrogen purged may reach 15 mol percent. Various equipment in the process is also purged with inert gar to reduce the explosion hazard and to remove the last traces of VCM. These off-gas purge streams generally contain 10-30 mol per cent vinyl chloride. New Twist: Vinyl chloride has been around a long time and so has activated carbon. But up to now, researchers have worked with pure monomer, Tenneeo's^ s contribution has been to make the pro cess work with recovered vinyl chloride, says Gottesman. He explains that this material can contain residual initiators, catalyst fragments, and suspending agents, so that it is prone to polymerize and foul the carbon system. Making the process work is a matter of selecting the right operating conditions and the right type of activated carbon. Another method of scrubbing VCM from stack gas, called oxyphotolysis, has been investigated by Robintech of Fort Worth, Tex. (CW Technology Newsletter, July 9, 1975). The firm says it is still eval uating the economics of installing the unit, which so far has not been used com mercially. Although carbon adsorption is the pro cess that Gottesman believes will attract the widest interest., the company is arm ing itself with a variety of other tech nology. "We have filed 13 patent appli cations on widely ditiering subjects," savs Gottesman. "They include a spray appa ratus for cleaning PVC reactors, processes for removing VCM from suspension and emulsion processes, the destruction of VCM by ozonolvsts and the removal of monomer from dispersion latex bv spar ging." If others' experience is anv indication, there is a big demand lor the know-how B.F. Goodrich Chemical says it has signed agreements with six corporations in Sweden. Italy, Japan and the U S. lor iIs suspension-resin stripping technology Diamond Shamrock became a licensor in Match, ollering its proprietary t eehmque lot removing residual VCM Irom BOR I Ii 01491 A , e, l I I O 7 Cl i r It A If' IJDCTI/ > =