Design of a Polystyrene Plant for Differing Single Pass Conversions
Design of a Polystyrene Plant for Differing Single-Pass Conversions
November 25, 2013
Introduction
Polystyrene is one of the most widely used plastics, with applications ranging from food packaging to appliances to manufacturing (Maier). On an industrial scale, polystyrene is derived from its monomer, styrene. This is achieved by free-radical polymerization of a solution of monomer, polymer, and initiator. This reaction is a multistep radical reaction that includes initiation, propagation, and termination (Eq.B.1 through Eq.B.5).
Figure A.1 shows a process that produces 1000 kg/hr of polystyrene in an isothermal plug flow reactor at a styrene conversion of lower than 80%. Azobisisobutyronitrile (AIBN) initiator is fed into the reactor at a concentration of 0.022 mol/L. The stream exiting the reactor is fed into an evaporator that perfectly separates unreacted styrene from the mixture. Unreacted styrene is recycled back into the reactor feed at a recycle ratio of 1 (in reference to fresh styrene feed). Costs associated with operating the plant increase with the size of the reactor ($200 per m3), with the rate styrene is fed into the reactor ($70 per kg/hr), and with the power required to pump the viscous mixture through the length of the reactor ($15×10-5 per W). We will determine the optimal single-pass conversion for a polystyrene plant described above.
Design Approach
Qualitatively, to achieve a larger single-pass monomer conversion, a larger reactor volume is need, necessitating more power to pump the reaction mixture through the length of the reactor. Both of these factors will contribute an increase in overall cost. In return, however,, less fresh styrene feed is needed, contributing to a decrease in overall cost. There is a single pass conversion that best balances these cost contributing factors. To determine the single-pass conversion that minimizes plant-operating costs, the following design approach was
November 25, 2013
Introduction
Polystyrene is one of the most widely used plastics, with applications ranging from food packaging to appliances to manufacturing (Maier). On an industrial scale, polystyrene is derived from its monomer, styrene. This is achieved by free-radical polymerization of a solution of monomer, polymer, and initiator. This reaction is a multistep radical reaction that includes initiation, propagation, and termination (Eq.B.1 through Eq.B.5).
Figure A.1 shows a process that produces 1000 kg/hr of polystyrene in an isothermal plug flow reactor at a styrene conversion of lower than 80%. Azobisisobutyronitrile (AIBN) initiator is fed into the reactor at a concentration of 0.022 mol/L. The stream exiting the reactor is fed into an evaporator that perfectly separates unreacted styrene from the mixture. Unreacted styrene is recycled back into the reactor feed at a recycle ratio of 1 (in reference to fresh styrene feed). Costs associated with operating the plant increase with the size of the reactor ($200 per m3), with the rate styrene is fed into the reactor ($70 per kg/hr), and with the power required to pump the viscous mixture through the length of the reactor ($15×10-5 per W). We will determine the optimal single-pass conversion for a polystyrene plant described above.
Design Approach
Qualitatively, to achieve a larger single-pass monomer conversion, a larger reactor volume is need, necessitating more power to pump the reaction mixture through the length of the reactor. Both of these factors will contribute an increase in overall cost. In return, however,, less fresh styrene feed is needed, contributing to a decrease in overall cost. There is a single pass conversion that best balances these cost contributing factors. To determine the single-pass conversion that minimizes plant-operating costs, the following design approach was
References: Maier, Karyn. "What Is Polystyrene?" WiseGEEK. Ed. Bronwyn Harris. Conjecture Corporation, 07 Nov. 2013. Web. 25 Nov. 2013. "Polystyrene FAQ | Polystyrene Recycling | Polystyrene Products." Polystyrene FAQ | Polystyrene Recycling | Polystyrene Products. Polystyrene Packaging Council, n.d. Web. 25 Nov. 2013. Sanoja, Gabriel. "Design - Updated - 112113." BSpace. N.p., 22 Nov. 2013. Web. 25 Nov. 2013. Sanoja, Gabriel. "Design - PFR." BSpace. N.p., 18 Nov. 2013. Web. 25 Nov. 2013. Sanoja, Gabriel. "Polymerization_PFR." BSpace. N.p., 10 Nov. 2013. Web. 25 Nov. 2013. Radke, Clayton. "140 Report Writing." BSpace. N.p., 14 Nov. 2013. Web. 25 Nov. 2013.