Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in tubular or loop reactor
Reexamination Certificate
2000-09-05
2002-04-30
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in tubular or loop reactor
C526S068000, C526S070000, C528S501000
Reexamination Certificate
active
06380325
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
In many polymerization processes for the production of polymer, a polymerization effluent is formed which is a slurry of particulate polymer solids suspended in a liquid medium, ordinarily the reaction diluent and unreacted monomers. A typical example of such processes is disclosed in Hogan and Bank's U.S. Pat. No. 2,285,721, the disclosure of which is incorporated herein by reference. While the polymerization processes described in the Hogan document employs a catalyst comprising chromium oxide and a support, the present invention is applicable to any process producing an effluent comprising a slurry of particulate polymer solids suspended in a liquid medium comprising a diluent and unreacted monomer. Such reaction processes include those which have come to be known in the art as particle form polymerizations.
In most commercial scale operations, it is desirable to separate the polymer and the liquid medium comprising an inert diluent and unreacted monomers in such a manner that the liquid medium is not exposed to contamination so that the liquid medium can be recycled to the polymerization zone with minimal if any purification. A particularly favored technique that has been used heretofore is that disclosed in the Scoggin et al, U.S. Pat. No. 3,152,872, more particularly the embodiment illustrated in conjunction with
FIG. 2
of that patent. In such processes the reaction diluent, dissolved monomers, and catalyst are circulated in a loop reactor wherein the pressure of the polymerization reaction is about 100 to 700 psia. The produced solid polymer is also circulated in the reactor. A slurry of polymer and the liquid medium is collected in one or more settling legs of the slurry loop reactor from which the slurry is periodically discharged to a flash chamber wherein the mixture is flashed to a low pressure such as about 20 psia. While the flashing results in substantially complete removal of the liquid medium from the polymer, it is necessary to recompress the vaporized polymerization diluent (i.e., isobutane) in order to condense the recovered diluent to a liquid form suitable for recycling as liquid diluent to the polymerization zone. The cost of compression equipment and the utilities required for its operation often amounts to a significant portion of the expense involved in producing polymer.
Some polymerization processes distill the liquefied diluent prior to recycling to the reactor. The purpose of distillation is removal of monomers and light-end contaminants. The distilled liquid diluent is then passed through a treater bed to remove catalyst poisons and then on to the reactor. The equipment and utilities costs for distillation and treatment can be a significant portion of the cost of producing the polymer.
In a commercial scale operation, it is desirable to liquefy the diluent vapors at minimum cost. One such technique used heretofore is disclosed in Hanson and Sherk's U.S. Pat. No. 4,424,341 in which an intermediate pressure flash step removes a significant portion of the diluent at such a temperature and at such a pressure that this flashed portion of diluent may be liquified by heat exchange instead of by a more costly compression procedure.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to an apparatus for continuously separating polymer solids from a liquid medium comprising an inert diluent and unreacted monomers. In another aspect, the invention relates to an apparatus for continuously separating polymer solids from a liquid medium, drying the polymer, and recovering the diluent and unreacted monomers with a reduction in compression needed for diluent vapor condensation to liquid diluent for reuse in a polymerization process. In another aspect, the invention relates to a method for continuously separating polymer solids from a liquid medium. In another aspect, the invention relates to a method for continuously separating polymer solids from a liquid medium, drying the polymer, and recovering the inert diluent and unreacted monomers for reuse in a polymerization process.
In accordance with the present invention, there is provided an apparatus for continuously recovering polymer solids from a polymerization effluent comprising a slurry of said polymer solids in a liquid medium comprising an inert diluent and unreacted monomers. The apparatus comprises a discharge valve on a slurry reactor, examples of which include slurry loop reactors and stirred tank slurry reactors, for the continuous discharge of a portion of the slurry reactor contents into a first transfer conduit: a first flash tank having a bottom defined by substantially straight sides inclined at an angle to the horizontal equal to or greater than the angle of slide of the slurry/polymer solids; wherein the pressure of the first flash tank and temperature of the polymerization effluent are such that from about 50% to about 100% of the liquid medium will be vaporized and the inert diluent component of said vapor is condensable, without compression, by heat exchange with a fluid having a temperature in the range of about 65° F. to about 135° F.: a first flash tank exit seal chamber, communicating with said first flash tank, of such a length (l) and diameter (d) as to permit such a level of concentrated polymer solids/slurry to accumulate and form a pressure seal in said first flash tank exit seal chamber: a seal chamber exit reducer providing for a continuous discharge of a plug flow of concentrated polymer solids/slurry to a second transfer conduit which communicates the concentrated polymer solids/slurry into a second flash tank wherein the pressure of said second flash tank and temperature of the concentrated polymer solids/slurry are such that essentially all of any remaining inert diluent and/or unreacted monomer will be vaporized and removed overhead for condensation by compression and heat exchange and the polymer solids are discharged from the bottom of said second flash tank for additional processing or storage.
The invention provides also a method for the continuous removal of a stream of polymerization effluent from a slurry reactor through a discharge valve; increasing the heat content of the polymerization effluent during its transit through said first transfer conduit to a temperature below the fusion point of the polymer while continuously communicating the polymerization effluent to a first flash tank having a bottom defined by substantially straight sides inclined at an angle to the horizontal equal to or greater than the angle of slide of the concentrated polymer solids/slurry; continuously vaporizing from about 50% to about 100% of the liquid medium in said first heated flash tank to yield a concentrated polymer solids/slurry and a vapor stream at such a temperature and pressure that the inert diluent content of said vapor is condensable, without compression, by heat exchange with a fluid having a temperature in the range from about 65° F. to about 135° F.; continuously discharging the concentrated polymer solids/slurry from said first flash tank to a first flash tank exit seal chamber of such a length (l) and diameter (d) that a volume of concentrated polymer solids/slurry is continuously maintained so as to form a pressure seal in said first flash tank exit seal chamber; continuously discharging the concentrated polymer solids/slurry from said first flash tank seal chamber through a seal chamber exit reducer defined by substantially straight sides inclined at an angle to that of horizontal equal to or greater than the angle of slide of the polymer solids which remain after removal of about 50 to 100% of the inert diluent therefrom; communicating a continuous plug flow of concentrated polymer solids/slurry from said first flash tank exit seal chamber through said seal chamber exit reducer to a second transfer conduit which communicates said continuous plug flow of concentrated polymer solids/slurry to a second flash tank; and continuously vaporizing essentially all o
ExxonMobil Chemical Patents Inc.
Henderson Christopher
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