(509i) On the Injection of Initiator as Bubbles in Helical Ribbon Agitated Cstr during Continuous Mass Polymerization of Abs

Polybutadiene was dissolved in a feed stream of styrene, acrylonitrile, and methyl ethyl ketone to form a feed mixture. The mixture was polymerized in a continuous process under agitation using the Monsanto two continuous stirred tank reactor in series process. The polymerization occurred in a two stage reactor system over an increasing temperature profile. During the polymerization process, some of the forming copolymer grafts to the rubber particles while some of it does not graft, but, instead, forms matrix copolymer. The resulting polymerization product was then devolatilized, extruded, and pelletized. The peroxy initiators are used to initiate the free radical chain polymerization reactions. These have been found to yield better results in terms of the degree of grafting and desired molecular weight etc. The first reactor is agitated using a close clearance helical ribbon agitator. For the same power draw the HRA provides a better degree of agitation and flow throughput with a circulation pattern with flow of fluid down the wall and up at the central axis. The mixing time in this reactor is given as a constant times the agitator RPM. For a CSTR at 35 RPM the mixing time can be taken as 4 minutes. The half-life of the initiators can be less than the mixing time can cause non-uniform grafting. So initiators with higher half-lives are selected. In any case the initiator can be introduced in the reactor as a bubble train at a frequency of 2.5 Hz. For example whtn the bubble diameter is 2 cm. and for a initiator half-life of 7 minutes the interfacial area of the bubbles at the half-way point was calculated. At a feed rate of 45.5 kg/hr with a monomer concentration of 20 kg/hr and a conversion level of 15% what the mass transfer rate of the initiator to the graft phase was foudn to be 0.21 mol/m^2/s.