Measuring and testing – Sampler – sample handling – etc. – Analyzer supplier
Patent
1996-02-12
1997-02-11
Raevis, Robert
Measuring and testing
Sampler, sample handling, etc.
Analyzer supplier
73 191, B01F 304
Patent
active
056023480
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method and an equipment for taking a sample in slurry polymerization.
Various methods have been developed for the preparation of solid and semisolid polymers out of hydrocarbons, such as 1-olefins. In one such method, olefins, such as ethylene, propylene, butylene, or pentenes, are polymerized in the presence of catalysts in hydrocarbon diluents or while the monomers themselves act as diluents. In such a case, the reaction agents are kept in the solution phase by maintaining a suitable pressure in the polymerization reactor. When the polymer that is formed is insoluble or poorly soluble in said diluent, the polymer product is formed as particles and, thus, the product flow comprises a suspension composed of polymer particles, diluents, and monomers. This product flow is usually passed into a polymer separation tank, in which the solid materials and the liquid and gaseous constituents are separated from one another.
One reactor type that is applied in such methods is a continuous pipe reactor that forms a loop, the polymerization taking place in a turbulent flow circulating in the loop. The product, which contains a polymer, diluents and monomers, is taken out of the loop reactor either continuously or, more commonly, periodically through an exhaust valve, being passed into a separator, in which the polymer is separated by lowering the pressure.
In view of regulation of the polymerization reaction, samples can be taken from the product flow of the reactor continuously or periodically. A normal way is to take a sample from the gas flow departing from the polymer separation tank and to analyze this gas sample by various methods, for example by means of gas chromatography. Such an arrangement is described, e.g., in the U.S. Pat. No. 3,556,730.
In this prior-art procedure, the period of delay that occurs from the departure of the product from the polymerization reactor until the time of start of the analysis is often considerably long, and during that period essential changes may take place in the process. Thus, the sample is not representative at all times. Therefore, it would be preferable to make said period of delay of analysis shorter.
In the FI Patent No. 85,191, a method is described by whose means a substantial shortening of the sampling delay is achieved. In said method, the sample is taken from the product pipe through a closing valve of the on/off type, which valve is closed for the time of the pressure swing produced on opening of the exhaust valve, and which valve is opened after said pressure swing.
In a polymerization plant, the process delay related to the analysis is, as a rule, of an order of about 10 minutes. When a sampling system in accordance with the FI Patent 85,191 is used, the process delay related to the analysis is shortened to about one minute under equivalent conditions.
For the regulation of the properties of the polymer in slurry polymerization, precise regulation of the concentration is required. Conventionally this has been carried out by analyzing the input concentration, in mixing-tank reactors the gas-phase concentrations or the concentrations of the gas phase separated from the product. These measurements do, however, not give sufficiently precise information on the liquid-phase concentrations in the reactor.
When the input concentration is analyzed, the factual concentrations in the reactor are not known. When the gas-phase concentrations in a mixing-tank reactor are analyzed, the factual liquid-phase concentrations are not known. Further, problems are produced by the adhesion of polymer particles in the sampling system. When the taking of samples takes place from the gas flow after the product pipe of the reactor (after the separation tank), adhering of polymer particles in the sampling line causes problems. Further, possible return-blow gases in the product filters may interfere with the analyzing, and there may be a long time delay until the analysis of concentration has been carried out. Also, analyzing from the gas space is impossible if the p
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Nyfors Klaus
Takakarhu Jouni
Borealis Polymers OY
Raevis Robert
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