Patent ID: 8706665

Claim:
A method comprising: selecting operating conditions in a double loop slurry reactor to produce a polymer of a pre-determined density and a pre-determined melt flow index prior to polymerization of the polymer, by: selecting n input variables that are linked to operating conditions; defining a constrained neural network model of the general form: ƒ 1 =1/(1+exp(−( a 11 *X 1 +a 12 *X 2 +a 13 *X 3 + . . . +b 1 ))) ƒ 2 =1/(1+exp(−( a 21 *X 1 +a 22 *X 2 +a 23 *X 3 + . . . +b 2 ))) ƒ 3 =1/(1+exp(−( a 31 *X 1 +a 32 *X 2 +a 33 *X 3 + . . . +b 3 ))) . . . Res= 1/(1+exp(−( a (n+1)1 *ƒ 1 +a (n+1)2 *ƒ 2 +a (n+1)3 *ƒ 3 + . . . +b (n+1) ))) wherein the X i 's are n normalised input variables, the a ij 's and b i 's are numerical coefficients, the f i 's are intermediate functions, and Res is a resulting scaled polymer property estimate; separately for the specified density and the specified melt flow index, adjusting numerical coefficients in the constrained neural network model to minimise error on Res under constraints, such constraints being imposed by equalities or inequalities on X i 's, a ij 's, b i 's, f i 's, Res, any partial derivative X i 's of any order, any partial derivative a ij 's of any order, any partial derivative b i 's of any order, any partial derivative f i 's of any order, any partial derivative Res of any order, or combinations thereof, wherein the partial derivatives measure variations of results derived from the constrained neural network model when only one of the input variables is changed by an infinitesimal step; predicting a density and a melt flow index resulting from the operating conditions using the constrained neural network model; inferring values for any combination of two input variables X i and X j , knowing the other (n−2) input variables, the specified density, and the specified melt flow index; calculating an average amount of the polymer product in each reactor in order to use the constrained neural network model to infer estimates of a density and a melt flow index of the polymer product leaving each reactor of the double loop slurry reactor resulting from the operating conditions; wherein the polymer product in each reactor includes polymer product that is synthesized within that reactor, or a combination of the polymer product that is synthesized within that reactor and polymer product that is admitted into that reactor from an upstream reactor; wherein the input variables are determined before polymerisation is started to simultaneously obtain the pre-determined density and the pre-determined melt flow index for the polymer.