Method of removing volatiles from raw polymerizate

 

(57) Abstract:

Usage: in the chemical industry to remove unreacted monomer upon receipt of polymethylmethacrylate. The inventive method of removing volatiles from the raw polymerize containing less than 50 wt.% methyl methacrylate) or a copolymer of 80-99 wt.% of methyl acrylate and/or ethyl acrylate, by single-stage heating to 200-270°C and evaporation under a pressure of 10-150 mm RT.article 1 Il.

The invention relates to the chemistry of macromolecular compounds, namely, the processes of obtaining polymethylmethacrylate or copolymers. At the stage of removal of unreacted monomers.

There are various ways to remove volatile components upon receipt of polyvinyl products.

The closest to the technical nature of the proposed method is a method of removing volatiles from raw polymerizate upon receipt of polystyrene [1]. Polymerizate contains less than 50 wt.% by weight of polymerizate polystyrene, organic solvent and unreacted monomer. According to the way raw polymerizat multi-stage heated under reduced atmospheric pressure with subsequent evaporation of polymerizate volatile and separation shall provide for re-heating polymerizate cannot be used for polymethacrylate raw polymerizaton.

The aim of the invention is to simplify technology for the removal of volatile crude polymetylmetacrylate of polymerizaton.

This goal is achieved by heating the raw polymerizate containing less than 50 wt.% by weight of polymerizate poly (methyl methacrylate) or a copolymer of 80-99 wt.% of methyl methacrylate and 1 to 20 wt.% of methyl acrylate and/or ethyl acrylate. Crude polymerizate heated at one stage to 200-270aboutC at a pressure below atmospheric and evaporated under a pressure of 10-150 mm RT.article Crude polymerizate may contain an amount of solvent sufficient to maintain below 50% concentration of the solid phase, preferably below 40%. You can use any solvent with a low boiling point, for example, saturated or aromatic hydrocarbons, in particular, hexane, heptane, octane, benzene, xylene, cyclohexane, cyclodecane, isooctane, and mixtures thereof, such as nafta, etc. Typically use solvents having a boiling point at atmospheric pressure of about 40-225aboutWith, preferably, about 60 to 150aboutC. it is Recommended to use a solvent having a boiling point close to the boiling point of the main monomer of methyl methacrylate, to avoid the need for intermediate francioni range of boiling points, that reduces the likelihood of contaminants in the recycled mixture.

The invention is well applicable to copolymers of methyl methacrylate and ethyl acrylate or methyl acrylate.

The drawing shows a circuit for implementing the method.

Crude polymerizate drawn from polymerizate 1, is transferred by pump 2 through the transmission line 3 in the heater 4 devolatilization. Crude polymerizate recommended to pass through a tube shell-tube heat exchanger to raise the temperature of the load approximately in the range 220-260aboutWith this heat exchanger the heat transfer of the heating fluid, for example, the flow of hot oil, which is introduced into the shell portion of the heat exchanger through line 5. Crude polymerizate heated in the heat exchanger 4, is passed through the transmission line 6 in the rapid evaporation tank 7 in section devolatilization. Transmission line 6 has a reverse pressure regulating valve 8, responsive to the output pressure from the gear pump 2. The pressure that is maintained in a damp polymerizate, enough to sustain a mixed two-phase system of liquid and vapor. In practice, a significant portion of the solvent is maintained in liquid phase in the heater 4 heat transfer in the heater of devolatilization. When the heat exchanger is excessive evaporation, the crude polymer can be cooled to a temperature evaporation or below this temperature, which leads to the formation of a solid phase, which quickly forms a crust on the surfaces of heat transfer. This is eliminated by maintaining sufficient back pressure in the raw polymerizate in the heater 4.

The necessary pressure for raw polymerizate can be determined experimentally by heating the sample raw polymerizate to the temperature at the inlet of the heater in a laboratory pressure vessel while maintaining sufficient pressure in the sample to exclude significant evaporation. Then the pressure is slowly reduced in the sample by observing the liquid phase of the sample to determine the pressure at which it starts curing. This pressure is the minimum pressure that must be maintained at the input of the heater 4.

You should ensure that raw polymerizat not heated to a temperature above 270aboutC, since higher temperatures discolor the product. However, for effective devolatilization need to crude polymerizate was heated to about 240-250aboutWith and, therefore, LASS="ptx2">

Crude polymerizate subjected to rapid evaporation in the tank devolatilization 7, which is maintained at a pressure below atmospheric sufficient to deformirovaniya almost all of the solvent, unreacted monomer and by-polymeric product with a low boiling point from the finished polymer product. It is recommended to use the spray to ensure effective devolatilization. As a rule, devolatilization is maintained at an absolute pressure of from about 10 to 150 mm RT.art., preferably at 50 mm RT.article The pair is removed from the vessel 7 through the pipe at its upper dome, pass them on line 9 recirculation distillation apparatus 10, which represents a column having two zones of the nozzle 11 and 12 and located beneath the evaporator 13. Hot couples enter into the lower zone 12 of the nozzle and partially condensed by contact with recycled condensate from lines 14 and 15. The velocity obtained by counterflow cooling condensate line 14 regulate by means of the valve 16 to maintain a predetermined liquid level in the evaporator 13. The solvent, some Monomeric products and polymer products with a low boiling point are collected in the evaporator 13 and a flow condenser 19. A counter-current condenser 19 is a shell-tube heat exchanger, and solvent vapours condense and collect in counterflow fluid vessel 20. Non-condensable components is passed through line 21 into the vacuum system 22 via the control valve 23. Part of the condensed solvent is returned to the recirculation distillation apparatus as a reverse flow in the line 14, and the rest of the condensed solvent is recycled to the process through line 24, closing the cycle of solvent in the process. The finished polymer, which typically contains residual monomer and solvent in a quantity of less than 1.0 wt.%, preferably less than 0.1 wt.%, out through the bottom of the reservoir 7 devolatilization through the pump 25 and sent for final processing.

P R I m m e R. example illustrates the method used for installation, with a capacity of 12000 tons of polymethylmethacrylate in the year. Raw material is a mixture with the following composition, wt.%:

The monomers 39,6

The solvent 60,0

Supplements 0,4

The monomers are a mixture of methyl methacrylate (97%) and methyl acrylate (3%). The raw material is produced by mixing fresh monomers of the present composition with recycle volatile received from desolately ereset, remote after polymerization from the reactor has the following composition, wt.%:

The monomers of 6.6

The solvent 60,0

Supplements 0,4

The polymer 33,0

The conversion of monomer in the process, on the basis of supply of raw materials (including recycling), is 83.8 percent.

Crude polymerizate transferred from the reactor to the heat exchanger of devolatilization. To the shell of the heat exchanger serves hot oil at a temperature of 270aboutC and extracted with 260aboutC. the temperature of the raw polymerizate increase from 95 to 260aboutWith, and the pressure of raw polymerizate inside of the heat exchanger is maintained at a level between 300 and 600 mm RT.art., which is sufficient to prevent evaporation and the formation of the foam crusts in the heat exchanger.

Heated polymerizat miss in one vacuum chamber, in which its pressure is reduced to 60-80 mm RT.art., and the solvent and unreacted monomers are subjected to instantaneous evaporation, leaving a polymer product having the following composition, %:

The polymer 99,82

The monomers 0,10

The solvent 0,08

The polymer is passed through a static mixer, which adds traditional additives such as UV stabilizers, internal lubricants, plasticizers, and so forth, depending(l loss of mass at 300aboutWITH

for 1/2 h in nitrogen)

The content of residual

monomers 0,1

Ash content Not found

The melt index (ASTM D-1238): 2,5

Light transmission

(ASTM D-1003): 92,7

Teplosnabjenie (ASTM D-648

at 264 lb/in2): 90aboutWITH

Impact strength Izod 2,2

(ASTM D-256): kg-cm/snakes

METHOD of REMOVING VOLATILES FROM RAW POLYMERIZATE containing less than 50% by weight of polymerizate vinyl polymer, an organic solvent and unreacted monomer by heating raw polymerizate at a pressure below atmospheric, with subsequent evaporation of polymerizate volatile and selection of a polymer melt with a volatile content less than 1%, characterized in that the vinyl polymer used poly (methyl methacrylate) or a copolymer of 80 to 99 wt. % of methyl methacrylate and 1 to 20 wt.% of methyl acrylate and/or ethyl acrylate, crude polymerizate single-stage heated to 200 - 270oC at a pressure sufficient to maintain liquid phase during heating and evaporated under a pressure of 10 to 150 mm RT.article

 

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