Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in tubular or loop reactor
Reexamination Certificate
2000-01-07
2002-04-30
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in tubular or loop reactor
C526S088000, C526S918000
Reexamination Certificate
active
06380324
ABSTRACT:
This invention relates to a continuous process for preparing polymers, in particular to the reduction of polymer fouling on reactor surfaces in a continuous process for preparing polymers.
Polymers are typically commercially prepared in batch processes. Batch processes require several hours, in some cases greater than eight hours, to feed the reactants, including monomer or monomers into the reactor, conduct the polymerization reaction, cool the resulting polymer, remove the polymer, and clean the reactor. The equipment required for batch processes typically includes reactors which can hold up to 75,000 liters and may cost more than $1,000,000 per reactor.
To improve the deficiencies of the batch processes, continuous polymerization processes have been developed. Continuous polymerization processes are potentially more efficient than a batch process. In a continuous process, monomer and other reactants are continuously fed into and through the reactor while, at the same time, polymer is continuously removed from the reactor. A continuous process may produce more product per day, utilizing smaller, less expensive reactors. Continuous processes utilizing continuous stirred tank reactors or tubular reactors are two types of continuous processes. Both processes are susceptible to polymer fouling on the reactor surfaces. This polymer fouling results in having to shut the reactors down and clean the reactor surfaces. The cleaning process may be costly due to reduction of production time.
Co-pending U.S. patent application Ser. No. 60/068,177 discloses a continuous process for preparing polymers including continuously feeding a reaction mixture containing at least one monomer to at least one non- cylindrical channel, continuously controlling the temperature of the non-cylindrical channel by exposing the surface of the non-cylindrical channel not exposed to the reaction mixture containing at least one monomer to a temperature control medium, polymerizing the monomer in at least one non-cylindrical channel and continuously removing polymer from at least one non-cylindrical channel. The use of non-cylindrical channels reduces polymer fouling on the reactor surfaces, as compared with continuous stirred tank reactors or tubular reactors. Even though the use of non-cylindrical channels reduces polymer fouling, it does not eliminate polymer fouling.
Therefore, there is a need for an improved continuous process of preparing polymers whereby polymer fouling on the reactor surfaces is reduced.
We have discovered that controlling the ratio of the monomer fed to a reactor which contains polymer reduces the formation of polymer fouling on the reactor surfaces.
The present invention provides a continuous process for preparing polymers including: continuously feeding at least one reaction mixture containing at least one monomer to at least one non-cylindrical channel; continuously controlling the temperature of the non-cylindrical channel by exposing the surface of the non-cylindrical channel not exposed to the reactant to a temperature control medium; polymerizing the monomer in at least one non-cylindrical channel; and continuously removing the polymer from at least one non-cylindrical channel; wherein the rate at which the at least one reaction mixture containing at least one monomer is fed to at least one non-cylindrical channel containing polymer is controlled, such that the amount of monomer in the at least one non-cylindrical channel does not exceed the amount that can be swollen into the polymer in the at least one non-cylindrical channel.
By “non-cylindrical” it is meant any shape whereby the reactant is exposed to a greater surface area for a given length than a cylindrical shape. Suitable non-cylindrical shapes of the channel are for example, oval, ellipse, square, triangular, and flat.
The surface of the one or more non-cylindrical channels not exposed to the reaction mixture containing at least one monomer can be exposed to a temperature control medium. The temperature control medium may be a solid, gas or liquid. A typical gas medium may be applied by simply exposing the non-cylindrical channel to air. Liquid medium may be for example, water, brine, or glycol solvents such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and the like. Solid medium may be for example an electrically heated metal plate. It is preferable that the temperature control medium be a liquid.
The process may be operated at any temperature. The temperature typically ranges from 0 to 350° C., preferably 1 to 200° C., more preferably 3 to 100° C. The process may be operated under vacuum as low as 25 mm Hg, or at pressures up to 5,000 psi. The flow rate through the channel for the process may range from 50 ml/min to 750 L/min.
The non-cylindrical channels can be immersed in the temperature control medium by methods known in the art such as simply exposing to air, placing them in a forced air oven or placing them in a bath containing liquid or solid temperature control medium. However, it is preferable that the temperature control medium flows through separate, alternating channels to the non-cylindrical channels in which the reaction mixture containing at least one monomer flows. By alternating, it is meant that the channel next to a non-cylindrical channel in which the reaction mixture containing at least one monomer flows, contains temperature control medium. The non-cylindrical channels may share a common wall, or the non-cylindrical channels may have separate walls so long as the non-cylindrical channels are close enough together to provide sufficient temperature control to polymerize the monomer. It is further preferable that the flow of the temperature control medium be opposite to the flow of the reaction mixture containing at least one monomer to accomplish maximum heat transfer.
When at least two non-cylindrical channels are connected in a series or in parallel, and at least two reaction mixtures are fed to the separate non-cylindrical channels, it may be necessary to set the temperature of the first non-cylindrical channel at a different temperature than subsequent non-cylindrical channels. The temperature control media and methods described above may also be utilized in this case.
It may also be necessary to heat the reaction mixture containing at least one monomer prior to feeding the reaction mixture containing at least one monomer to the at least one non-cylindrical channel. The temperature control media described above may also be utilized to heat the reaction mixture containing at least one monomer. Generally, the reaction mixture containing at least one monomer would be stored in a heated vessel and fed to the at least one non-cylindrical channel. A problem associated with storing the reaction mixture containing at least one monomer in a heated vessel is that polymerization may begin to occur in the heated vessel rather than in the at least one non-cylindrical channel.
We have discovered that steam or inductive heating may be used to heat a reaction mixture containing at least one monomer being fed to one or more non-cylindrical channels. This is particularly useful in a multi-stage reactor, where a first reaction mixture containing at least one monomer is fed to a first non-cylindrical channel. The first reaction mixture exits the first non-cylindrical channel and enters a line which feeds the subsequent non-cylindrical channel. A subsequent reaction mixture containing at least one monomer may be fed into the line between the first non-cylindrical channel and the subsequent non-cylindrical channel. The subsequent reaction mixture is heated in the line between the first non-cylindrical channel and the subsequent non-cylindrical channel. This is known as interstage heating.
Many methods of imparting heat to a system rely on transferring the energy through the system wall, creating a situation where the system walls are at a higher temperature than the processing material. This may lead to fouling of the system. We have discovered that inter stage heating of the subsequen
McFadden Dawn Marie
Wu Richard Shu-Hua
Egwim Kelechi C.
Rohm and Haas Company
Wu David W.
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