Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in tubular or loop reactor
Reexamination Certificate
2002-02-19
2004-12-21
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in tubular or loop reactor
C526S068000, C528S480000
Reexamination Certificate
active
06833415
ABSTRACT:
FIELD OF 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 a slurry polymerization process. In particular, the present 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 the polymerization process. In another aspect, the invention relates to a method for continuously separating polymer solids from a liquid medium. In particular, 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 the polymerization process.
The present invention also relates to a process for producing polymer in a continuous slurry loop reactor comprising feeding catalyst, monomer, and, optionally, at least one of co-monomer, co-catalyst, diluent, polymer modifier, or mixtures thereof into the reactor; wherein catalyst is fed into the reactor from multiple catalyst inlets; and recovering polymer from the reactor.
The present invention also relates to a process for producing polymer in a continuous slurry loop reactor which comprises: reacting a monomer in a hydrocarbon diluent to form a polymerization slurry of polymer solids in a liquid medium; discharging a portion of the polymerization slurry as slurry effluent which comprises a slurry of discharged polymer solids in a discharged liquid medium through at least two discharge conduits; combining the effluent from at least two of the discharge conduits; flashing the combined effluent in a first flash to form a first flash vapor and a first flash slurry; and condensing at least a portion of the first flash vapor without compression.
The present invention also relates to a slurry loop reactor which comprises: multiple catalyst inlets; at least one feed inlet; at least one discharge conduit; and at least one circulator in the reactor; wherein the catalyst inlets are located within 45% of the points of symmetry of the loop reactor.
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 liquified 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 liquify 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 a process for producing polymer in a continuous slurry loop reactor comprising feeding catalyst, monomer, and, optionally, at least one of co-monomer, co-catalyst, diluent, polymer modifier, or mixtures thereof into the reactor; wherein catalyst is fed into the reactor from multiple catalyst inlets; and recovering polymer from the reactor.
In one embodiment in accordance with the present invention, the process also comprises at least one feed inlet for at least one of monomer, co-monomer, co-catalyst, diluent, polymer modifier, process additive, or mixtures thereof. Preferably, the process comprises multiple feed inlets.
In another embodiment in accordance with the invention, the process also comprises at least one circulator in the reactor. Preferably, the at least one circulator comprises a pump. Also preferably, the at least one circulator comprises a motor driven device to increase the pressure of the circulating slurry in the loop reactor.
In one embodiment in accordance with the invention, at least one of the catalyst inlets is located at the suction end of at least one circulator. In another embodiment in accordance with the present invention, at least one feed inlet is located at the discharge end of at least one circulator. Preferably, at least one catalyst inlet and at least one feed inlet are located at the suction end and discharge end, respectively, of the same circulator.
Generally, the catalyst inlets are located within 45% of the points of symmetry of the loop reactor. Preferably, the catalyst inlets are located within 25% of the points of symmetry of the loop reactor. More preferably, the catalyst inlets are located within 10% of the points of symmetry of the loop reactor. Most preferably, the catalyst inlets are located at the points of symmetry of the loop reactor.
Generally, the circulators are located within 45% of the points of symmetry of the loop reactor. Preferably, the circulators are located within 25% of the points of symmetry of the loop reactor. More preferably, the circulators are located within 10% of the points of symmetry of the loop reactor. Most preferably, the circulators are located at the points of symmetry of the loop reactor.
Also generally, the feed inlets are located within 45% of the points of symmetry of the loop reactor. Preferably, the feed inlets are located within 25% of the points of symmetry of the loop reactor. More preferably, the feed inlets are located within 10% of the points of symmetry of the loop reactor. Most preferably, the feed inlets are located at the
Kendrick James Austin
Roger Scott Thomas
Towles Thomas W.
Boykin Terressa M.
ExxonMobil Chemical Patents Inc.
Reid Frank E.
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