Patent ID: 8314197
Filing Date: 2012-11-20
Classification: C08F

Abstract:
1. A process for the production of a degassed polymer powder, which process comprises a) feeding i) a principal monomer, and ii) one or more comonomers fed in an amount of at least 5000 ppmw relative to the principal monomer feed rate, and iii) optionally one or more added alkanes having 2 to 10 carbon atoms, fed in an amount of at least 1000 ppmw relative to the principal monomer feed rate; into a polymerisation reactor wherein the monomer and comonomers react to form a polymer comprising residual hydrocarbons comprising one or more hydrocarbons having 3 to 10 carbon atoms, and b) passing the polymer to a degassing step wherein it is contacted with a purge gas to remove at least some of the residual hydrocarbons, wherein: 1) the G/P ratio in the degassing step is higher than a minimum G/P ratio, G being the purge gas mass flow rate in the degassing step and P being the polymer throughput of the degassing step, and 2) the purge gas has a concentration of critical hydrocarbon component which is lower than a maximum concentration of said critical hydrocarbon component in the purge gas, the critical hydrocarbon component being the heaviest hydrocarbon component selected from (i), (ii) and (iii) fed in step (a), which minimum G/P ratio and maximum concentration of said critical hydrocarbon component in the purge gas have been calculated based on the absorption coefficient, Kh, for the polymer powder to be degassed, and wherein the minimum G/P ratio is 1.25*X, where X=28/Mw/100*Kh*Ptot/Psat(T) and the maximum concentration of said critical hydrocarbon component in the purge gas is Y, where Y=100*(Psat(T)/Ptot/Kh)*Z where: T is the polymer powder temperature at the polymer exit of the degassing step, Mw and Psat(T) are, respectively, the molecular weight and the hydrocarbon saturated vapour pressure above liquid at the temperature T, of the critical hydrocarbon component, Ptot is the pressure measured above the powder to be degassed in the degassing column, and Z is the desired maximum residual hydrocarbon content of the critical component in the degassed polymer powder.