Emulsion Copolymerization of Acrylonitrile and Butadiene in a Train of CSTRs. Intermediate Addition Policies for Improving the Product Quality

MINARI, ROQUE J; GUGLIOTTA, LUIS M; VEGA, JORGE R; MEIRA, GREGORIO R

Costa Verde – Rio de Janeiro (Brasil)

Congreso; II Mercosur Congress on Chemical Engineering and IV MERCOSUR Congress on Process System Engineering; 2005

A continuous industrial emulsion copolymerization of acrylonitrile (A) and butadiene (B) carried out in a train of 8 continuous stirred-tank reactors (CSTRs) at 10 °C is theoretically investigated, with the aim of producing nitrile rubber (NBR) of a quality similar to that obtained in an equivalent batch process. The rubber quality is specified by the latex characteristics (number particle concentration and number-average particle diameter), and by the molecular parameters (average values of the copolymer composition, the molecular weights, and the degree of branching). Compared with the batch product, the continuous process produces a deteriorated rubber (of a higher polydispersity and a higher degree of branching). These undesirable effects were corrected through intermediate additions of comonomers and/or chain transfer agent (CTA) along the continuous train operating in the steady-state. A mathematical model of the industrial batch process (Vega et al., Ind. Eng. Chem. Res., 36, 1997) is here extended for simulating the steady-state operation of the CSTR train. Two NBR grades of a different chemical composition are investigated. The following optimization problems are solved: a) the addition of A and CTA along the train for producing a polymer of the same final properties as in the batch operations; b) a split of comonomers feed between the first and intermediate reactors, for increasing the rubber productivity without affecting the latex characteristics; and c) the addition of A, B, and CTA along the train, for increasing productivity while simultaneously producing prespecified profiles of the copolymer composition and the average molecular weights along the train.