Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Effecting a change in a polymerization process in response...
Patent
1991-10-04
1992-10-13
Schofer, Joseph L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Effecting a change in a polymerization process in response...
364499, 526352, 5263486, 5263484, C08S 200
Patent
active
051551845
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process and an apparatus for the manufacture of polymers, which manufacture is controlled by means of a control system. This process makes it possible to manufacture polymers having physical, rheological or mechanical properties which are set in advance and which are controlled during the polymerization reaction.
There is a known polymerization process, according to U.S. Pat. No. 4,469,853, making it possible to prepare, in particular, polyolefins having one or more properties which are kept substantially constant during the polymerization, this or these properties corresponding to values which are set in advance. These polyolefins are generally prepared in a reactor by polymerization of the olefins in the presence of hydrogen and with the aid of a catalyst of the Ziegler-Natta type in suspension in a liquid hydrocarbon medium. Above the liquid, the polymerization reactor contains a gaseous phase comprising the olefins to be polymerized and hydrogen. The composition of this gaseous phase is determined by means of a gas phase chromatography apparatus connected directly to a process computer provided with a program designed to control the rates of feed of olefins and of hydrogen to the reactor, and the reactor purge rate, so that the composition of the gaseous phase may be continually close to a composition which is set in advance. This program also makes it possible to control the rate of catalyst feed to the reactor and the pressure in the polymerization reactor. However, this process has the disadvantage of controlling a restricted number of properties such as the relative density and/or the flow index of the polyolefin manufactured. It does not make it possible to simultaneously control a large number of physical, rheological and/or mechanical properties which would therefore require that these properties be evaluated only by conventional analytical tests during the quality control of the polyolefin produced. When these conventional tests find the properties to be different from the set values, it would then be necessary to modify the composition of the gaseous reaction phase with a delay which is relatively long. A result of this process is that polymers of unsatisfactory quality may be produced in relatively large quantities.
Generally, it is known to manufacture polyolefins having one or more properties which are kept substantially constant during their preparation. The polyolefins can be for instance manufactured in a reactor containing a gaseous phase consisting of the olefins to be polymerized and optionally an inert gas and/or hydrogen. In that case, the property or properties of the polyolefin manufactured are periodically evaluated during the reaction by means of conventional and specific analyses for each of these properties and the values thus measured are introduced manually into a process computer. The latter is provided with a program comprising, for each of the various qualities of polyolefins manufactured, relationships between the properties of the polyolefin and the composition of the gaseous phase in the polymerization reactor. Depending on the measured values, the computer controls the composition of the gaseous phase by means of its program, so that these measured values may be as close as possible to the set values. The control of the composition of the gaseous phase is carried out with the aid of the feed rates of the various constituents of the gaseous phase in the reactor, and with the aid of the purge rate of this gaseous phase. However, this process involves a separate and specific measurement of each of the properties of the polyolefins which it is desired to keep at substantially constant values during the polymerization. In fact, each of these properties requires the use of a specific apparatus and analytical method. Furthermore, the measurement of each of these properties requires a relatively long time, and this results in a major delay in the correction of the composition of the gaseous phase in the reactor and of the quality of the poly
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Laurent Joseph
Martens Andre
Vidal Jean-Louis
BP Chemicals Ltd.
Schofer Joseph L.
Weber Tom
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