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AssigneeBasell Polyolefine GmbH
InventorsGiuseppe Penzo, Cyrus Ahmadzade-Youssefi, Rainer Karer, Ulrich Nieken
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Process for the polymerization of ethylene or of ethylene with further 1-olefins, in which the ethylene is polymerized in the presence of a catalyst in a gas-phase reactor and reaction gas comprising propane and unpolymerized ethylene is circulated to remove the heat of polymerization, wherein the polymer particles are discharged continuously or discontinuously from the reactor, the polymer particles are separated from the major part of the concomitantly discharged gas and the polymer particles are degassed, the gas is freed of entrained fine particles and is separated from a low-boiling fraction comprising ethylene or from a high boiling fraction containing further 1-olefins or alkanes having from 4 to 12 carbon atoms in a first separation stage, a propane fraction is separated off in a second separation stage and this propane fraction is used for degassing the polymer particles discharged from the reactor, with the proportion of ethylene in the propane fraction being less than 1 mol % and the proportion of 1-olefins and alkanes having from 4 to 12 carbon atoms in the propane fraction being less than 4 mol %, in each case based on the total propane fraction. Furthermore, an apparatus for carrying out the process. In this way, a high heat discharge from the reactor, satisfactory degassing of the discharged polymer particles and recovery of the reaction gas discharged together with the polymer particles and also the gas used for degassing the polymer particles are made possible.
A process for the polymerization of ethylene or of ethylene with further 1-olefins, in which the ethylene is polymerized in the presence of a catalyst in a gas-phase reactor (1) to form polymer particles and reaction gas comprising propane and unpolymerized ethylene is circulated to remove the heat of polymerization, wherein
The process according to either of the preceding claims, wherein the proportion of ethylene in the propane fraction is less than 0.5 mol %, in particular less than 0.2 mol %.
The process according to either of the preceding claims, wherein the partial pressure of ethylene in the propane fraction is less than 750 Pa, in particular less than 300 Pa.
The process according to any of the preceding claims, wherein the proportion of 1-olefins and alkanes having from 4 to 12 carbon atoms in the propane fraction is less than 0.1 mol %, in particular less than 0.01 mol %.
The process according to any of the preceding claims, wherein the vapour pressure of 1-olefins and alkanes having from 4 to 12 carbon atoms in the propane fraction is less than 150 Pa, in particular less than 15 Pa.
The process according to any of the preceding claims, wherein the circulated gas comprises propane in an amount of at least 20, in particular at least 30 mol %.
The process according to any of the preceding claims, wherein a maximum of 10 mol %, preferably a maximum of 5 mol %, of other gases or liquids are present in addition to ethylene, further 1-olefins, hydrogen and propane in the reactor (1).
The process according to any of the preceding claims, wherein the degassing of the polymer particles by means of the propane fraction and the separation of the polymer particles from the major part of the discharged gas is carried out simultaneously and/or in the same place.
The process according to any of the preceding claims, wherein the reaction gas is taken from the reactor (1), part of the reaction gas is condensed and is recirculated together with or separately from the uncondensed gas to the reactor.
The process according to any of the preceding claims, wherein the low-boiling fraction separated off in the first separation stage is recirculated to the reactor (1).
The process according to any of the preceding claims, wherein a high boiling fraction containing further 1-olefins or alkanes having from 4 to 12 carbon atoms leaving the second separation stage is recirculated to the reactor (1).
The process according to any of the preceding claims, wherein at least part of the ethane separated off in the first separation stage is discharged.
The process according to any of the preceding claims, wherein the propane fraction is used for the metered addition of the catalyst or catalysts.
An apparatus for carrying out the process according to any of the preceding claims comprising
The use of propane which has a proportion of ethylene of less than 1 mol % and a proportion of 1-olefins and alkanes having from 4 to 12 carbon atoms of less than 4 mol %, in each case based on the total amount of gas, and has been obtained from the gas discharged from a gas-phase polymerization reactor together with the polymer particles for degassing ethylene homopolymers or ethylene copolymers.
Dependencies are inferred from the claim text.