Process of preparing polyolefin with the discontinuous addition of a thermal runaway reducing agent

A process for the continuous preparation of a polyolefin from one or more α-olefin monomers in a reactor system, the reactor system comprising:

• a reactor having a wall comprising:
• a lower part, comprising a distribution plate and an inlet for a recycle stream below the distribution plate;
• a middle part above said lower part, said middle part comprising a fluidized bed, an inlet for a polymerization catalyst, an outlet for polyolefin;
• and
• an upper part above said middle part, said upper part comprising an outlet for fluids;
• a heat exchanger;
• first connection means for fluids connecting the outlet for fluids to the heat exchanger;
• and
• second connection means for fluids connecting the heat exchanger to the inlet for a recycle stream;
• the process for the continuous preparation of the polyolefin comprising the steps of:
• feeding a polymerization catalyst to the fluidized bed through the inlet for a polymerization catalyst;
• feeding the one or more monomers to the reactor,
• polymerizing the one or more monomers in the fluidized bed at a polymerization temperature to prepare the polyolefin;
• withdrawing the polyolefin that is formed from the reactor through the outlet for polyolefin;
• withdrawing fluids from the reactor through the outlet for fluids and transporting the fluids through the first connection means and the heat exchanger to cool the fluids, to produce a cooled recycle stream, and through the second connection means and through the inlet for the recycle stream back into the reactor;
• wherein the temperature of the reactor wall is measured at a plurality of positions by a plurality of temperature sensing means and wherein a thermal run away reducing agent (TRRA) is added to the reactor when at least one of a plurality of the temperature sensing means measures a temperature that is at least 2° C. above the average temperature of the plurality of temperature sensing means;
• and/or
• wherein the static voltage is measured by one or more static voltage indicators and wherein a thermal run away reducing agent (TRRA) is added to the reactor when the static voltage is above 200 Volt;
• and/or
• wherein the polymerization temperature is measured and wherein a thermal run away reducing agent (TRRA) is added to the reactor when the polymerization temperature is at least 5° C. above a predetermined value for the polymerization temperature, wherein a titanium-comprising polymerization catalyst is used and wherein the molar ratio of the TRRA to titanium in the polymerization catalyst (TRRA/Ti) is at least 1.0;
• and/or
• wherein the polyolefin withdrawn from the reactor is analyzed to determine the percentage of fines and wherein a thermal run away reducing agent (TRRA) is added to the reactor when the polyolefin comprises more than 2 wt. % fines based on the weight of the polyolefin;
• and/or
• wherein the polyolefin withdrawn from the reactor is analyzed to determine the presence of one or more agglomerates and wherein a thermal run away reducing agent (TRRA) is added to the reactor when one or more agglomerates are observed;
• and/or
• wherein the flow of fluids through the heat exchanger, first connection means and/or second connection means is measured using fluid flow measuring means and wherein a thermal run away reducing agent (TRRA) is added to the reactor when the flow decreases by at least 20% per unit of time;
• and
• further wherein
• the addition of TRRA is performed for a period of at most 20 minutes;
• and/or
• the TRRA is selected from the group consisting of ethyl acrylate, methyl methacrylate, di-methyl carbonate, ethyl cyclohexanoate, propyl pivalate, ethylbenzoate, methylbenzoate, p-methoxy ethylbenzoate, p-ethoxy ethylbenzoate, methylbenzoate, dimethyloxalate, p-chloroethylbenzoate, p-amino hexylbenzoate, isopropyl naphthanate, n-amyl toluate, 1,2,4-trimethyl piperazine, 2,3,4,5-tetraethyl piperidine, dimethyl phthalate, diethyl phthalate, di-n-propyl phthalate, diisopropyl phthalate, di-n-butyl phthalate, diisobutyl phthalate, di-tert-butyl phthalate, diisoamyl phthalate, di-tert-amyl phthalate, dineopentyl phthalate, di-2-ethylhexyl phthalate, and di-2-ethyldecyl phthalate, trimethyl acetonitrile, and N,N-dimethyl benzamide.