FR2484420A1 - IMPROVED PROCESS FOR THE SUSPENSION POLYMERIZATION OF VINYL CHLORIDE - Google Patents

Abstract

THE INVENTION RELATES TO AN IMPROVED PROCESS FOR THE SUSPENSION POLYMERIZATION OF VINYL CHLORIDE OR OF A MIXTURE OF MONOMERS OF WHICH THE MAJOR PART IS VINYL CHLORIDE, IN AN AQUEOUS MEDIUM CONTAINING A SUSPENSION AGENT, IN A REUSPENSIONER, OF POLYMERIZATION, IN THE PRESNECE OF A POLYMERIZATION INITIATOR AT THE PRESCRIBED HIGH POLYMERIZATION TEMPERATURE, CHARACTERIZED IN THAT THE MONOMER OR THE MIXTURE OF MONOMERS AND THE POLYMERIZATION INITIATOR ARE INTRODUCED UNDER THE POLYMERIZATION REACTOR ARE INTRODUCED UNDER THE POLYMERIZATION REACTER HOMOGENEOUS AT THE SAME TIME AS PREHEATED WATER, TO OBTAIN A POLYMERISABLE MIXTURE, IN WHICH THE POLYMERIZATION REACTION CAN BEGIN, THE TEMPERATURE OF THE POLYMERISABLE MIXTURE DURING AND AT THE END OF THE INTRODUCTION OF THE HOMOGENOUS MIXTURE OF THE MONOMER AND OF THE HOMOGENOUS MIXTURE OF POLYMERIZATION, AND PREHEATED WATER BEING ABOUT THE PRESCRIBED POLYMERIZATION TEMPERATURE.

Description

The present invention relates to an improved process for

  polymerization in an aqueous medium of vinyl chloride.

  As is well known, the polymerization of the chlorinated monomer

  vinyl chloride is usually done in a batch process. se-

  In this conventional method of suspension polymerization of

  vinyl, water is introduced as a reaction medium, a dispersing agent

  suspending or suspending a polymerization initiator and vinyl chloride in the polymerization reactor by adding further optional additives to form the polymerizable mixture which is then heated to

  the temperature prescribed to ensure the start of. the reaction of poly-

  merization. The polymerization temperature is usually kept constant for the duration of the reaction required to complete a cycle

of polymerization.

  When trying to increase the productivity of the polymerization

  By reducing the duration of a polymerization cycle, it is necessary to reduce the time required for the introduction of the ingredients of the polymerizable mixture into the reactor, the duration of the reaction and also the time.

  necessary to raise the temperature of the cold polymerisable mixture

  than at the prescribed polymerization temperature. Since the increase

  the temperature of the polymerizable mixture contained in the reactor is usually carried out only by means of a heating jacket

  surrounding the reactor, such a large reactor has some

  sometimes insufficient heating capacity because the surrounding surface, ie the surface for the transfer of heat, of such a reactor is small in relation to its volume, which gave rise to the desire to develop

  more efficient means of raising the temperature of the polymer blend.

sand in a big reactor.

  Another solution to the problem mentioned above is the introduction

  preheated water or vinyl chloride. However, in the case where the initiator

  The polymerization reactor is introduced with water at a high temperature,

  the initiator is rapidly decomposed before the introduction of the chloride of

  which makes the control of the polymerization reaction difficult.

  on the other hand, if the vinyl chloride and the polymerization initiator are introduced

  in the reactor already containing the preheated water, the polymerization of the

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  The name begins during its introduction, which leads to significant polymer deposits on the walls of the polymerization reactor, decreasing

  the quality of the polymerized product obtained, which has a very large

Tyeux depoisson ".

  In addition, the amount of fish eyes is increased during the polymerization by adding the polymerization initiator after the introduction.

  preheated water and vinyl chloride in the reactor. Problems

  similar circumstances are inevitable in the event of the introduction of the pre-

  heated. It is therefore an object of the present invention to provide a

  new process for increasing the productivity of the polymerization by

  vinyl chloride pension, by reducing the overall time required to

  the completion of a polymerization cycle.

  The present process, developed after extensive research, is based on the premise that the most effective way to reduce the onset time of the polymerization reaction is the simultaneous introduction of preheated water and a homogeneous mixture. vinyl chloride compound

  monomer and polymerization initiators in the polymer reactor.

  to obtain a hot polymerizable mixture in which the polymerization reaction can begin immediately. It is desirable that the

  polymerizable mixture formed in the reactor during and at the end of the

  of preheated water and the homogeneous mixture of monomer and

  temperature, at a temperature substantially equal to the prescribed polymerization temperature. More specifically, the temperature of the polymerizable mixture should not exceed the polymerization temperature

prescribed ZOC or more.

  In practice, the application of the present invention is to first mix the vinyl chloride and the polymerization initiator for

  to obtain a uniform mixture, before introducing them into the reactor of

  lymérisation. There are several ways to obtain in advance a homogeneous mixture of monomer and initiator. For example, they are mixed together in a separate container to form a uniform mixture and this mixture is then introduced into the polymerization reactor. According to another

  variant they are mixed together on the way to the poly-

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  merging in an online mixer working continuously, so that they

  arrive in the reactor in the form of a uniform mixture.

  The need to introduce the monomer and the polymer initiator

  in the reactor in the form of a homogeneous mixture, of course requires that the initiator be selected from those which are soluble in the

  number. In this respect, any of the conventional initiators can be used.

  for suspension polymerization belonging either to peroxides

  such as diisopropyl peroxydicarbonate, peroxydicarboxylic acid,

  diethoxyethyl nate, tert-butyl peroxyneodecanoate, peroxynodeodene

  O -cyloyl canoate, tert-butyl peroxyneodecanoate, peroxide

  acetylcyclohexylsulfonyl, 2,4,4-trimethyl-2-peroxyphenoxyacetate

  pentyl and the like, or azure compounds such as azobis-2, 4di-

  methylvaleronitrile, azobis (4-methoxy-2,4-dimethylvaleronitrile) and

  milaires. These initiators may be used singly or in combinations of two or more, as needed. The amount of polymerization initiator

  relative to the monomer is determined in the usual way.

  In the case where the monomer and the initiator are mixed together to form a homogeneous mixture and are introduced simultaneously into the preheated water, the temperature of the mixture must be sufficiently low not to cause premature decomposition of the initiator before

  that the polymerization mixture is formed in the reactor. We have

  stated in this regard that the temperature of the monomer and initiator mixture should be such that the monomer conversion rate in the mixture is equal to or less than 5% or, preferably, equal to or less than 3%, after having been maintained for Z hours at this temperature. If this condition

  the quantity of polymer deposits on the walls of the reactor is not

  increases significantly and the resulting polymer contains a large number of

of fish eyes.

  When the homogeneous mixture of monomer and star initiator

  polymerization is introduced into the polymerization reactor,

  water preheated in the reactor to form a mixture of

  polymerizable high temperature, so that the reaction of

  lymerization begins immediately. In such a case it is essential that the

  the temperature of the polymerizable mixture thus formed is at the moment when the

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  both the monomer-initiator mixture and the preheated water are

  finished, substantially equal, or as close as possible to the temperature

  prescribed polymerization level. More specifically, the temperature of the

  polymerisable mixture must not be greater than the temperature of

  2VC or more merger, because an excessively high temperature of the polymerizable mixture can cause the dangerous triggering of a violent polymerization reaction, difficult to control. On the other hand, a temperature of the polymerizable mixture lower than the polymerization temperature does not pose any problems in terms of safety, but the

  advantages of the present invention with regard to improved productivity.

  lessen directly with the temperature difference, because the temperature

  of the polymerizable mixture must then be increased by

  outside, which differs the start of the polymerization reaction.

  A temperature difference of 50C or less is acceptable in the practice.

  Although this is not a limiting condition, it is advantageous in practice to maintain the temperature of the monomer initiator mixture and that of the preheated water both constant during their introduction into the reactor. This introduction begins simultaneously for the two ingredients, and is continued according to the flow rates of the one and the other ingredient which are proportional to the ratio of their total quantities to be added, so that their introduction ends approximately at the same time.

  moment. In this way the polymerization temperature is maintained practically

  constant during and at the end of the introduction of the mono-

  mother-initiator, and preheated water.

  The simultaneous introduction of the monomer-initiator mixture and the preheated water must be carried out with stirring and terminated in an interval

  as short as possible, usually 30 minutes or less.

  An extension of this gap causes an increase in polymer deposits on the walls of the reactor which lowers the quality of the resin

  PVC obtained with a significantly higher fish eye ratio.

  It is understood that suspension polymerization of vinyl chloride is carried out by dispersing the monomer in an aqueous medium using a dispersing agent or a suspending agent. If the agent

  dispersant is soluble in the monomer, it can be introduced into the reaction

  at the same time as the monomer in the form of a solution. On the other hand, if the dispersing agent is soluble in water, it may be introduced into the reactor together with the preheated water, in the form of a solution, or it may be introduced into the reactor separately in the form of an aqueous solution. relatively high concentration, preferably at the very beginning, or before the introduction of the preheated water. If the introduction of the dispersing agent is carried out too late the amount of the polymer deposits increases and leads to a lowering of the quality of the polymer

  obtained, which has a higher rate of fish eyes.

  The above-mentioned dispersing agent or suspending agent may be of the type usually employed for the polymerization

  in suspension of vinyl chloride and is for example a hydro-

  soluble, such as water-soluble cellulose ethers, for example methyl-

  cellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropyl-

  methylcellulose and the like, the partially saponized polyvinyl alcohols

  acrylic acid polymers, gelatin and the like, monomer-soluble emulsifying agents, such as sorbitan monolaurate, sorbitan trioleate, oxide block copolymers

  of ethylene and propylene oxide, as well as hydrous emulsifiers

  soluble such as polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerine oleate, sodium laurate and the like. These suspending agents can be used alone or in combinations of two

types or more.

  In addition, suspension polymerization according to the present invention

  may be carried out under the addition of various types of additives

  employed in the known processes for the polymerization of the chloride of

  such as polymerization control agents, chain transfer agents, gel promoters, antistatic agents and

pH control.

  The present method applies not only to the homopolymerization

  vinyl chloride, but also to the copolymerization of a mixture of

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  monomers whose major component, ie 50% or more, is vinyl chloride. The comonomers copolymerizable with vinyl chloride are, for example, vinyl esters, such as vinyl acetate,

  vinyl propionate and the like, esters of acrylic and

  such as methyl and ethyl acrylate, methacrylate

  and the like, olefins such as ethylene, propylene and the like.

  derivatives, maleic anhydride, acrylonitrile, styrene and vinylidene chloride. For the implementation of the present process the ratios by weight

  different ingredients, the polymerization temperature and other conditions

  may be determined in a manner analogous to the usual conditions

  in the known processes for the suspension polymerization

  vinyl chloride, without there being any special restrictions to ob-

server.

  According to the present method the advantage is obtained that the time required

  to achieve a polymerization cycle can be considerably reduced, so that the method of the invention is particularly effective

  high productivity, especially in cases where the poly-

  The merization is carried out in a large polymerization reactor having a relatively low heating capacity relative to its volume capacity, which, according to conventional methods, would require a prolonged delay for raising the temperature of the cold polymerizable mixture to

  the prescribed polymerization temperature.

  The invention will be described in more detail in the non-limiting examples.

mitatives below.

  Example 1 (Tests Nos. 1 to 8) During each test, the polymerization of the vinyl chloride is carried out in a polymerization reactor with a capacity of 1.2 m

  equipped with an agitator and provided with a heating envelope.

  First, a mixture of the monomer and the initiator of

  polymerization by cold dissolving 200 g of di-2-ethyl peroxydicarbonate

  hexyl in 350 kg of vinyl chloride. The temperature of this mixture

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  in each cycle before its introduction into the reactor is recorded in Table I appended, together with the conversion rate to polymer evaluated

  in% after maintaining the mixture for 2 hours at this temperature.

  Separately an aqueous solution of a suspending agent is prepared by dissolving 150 g of a partially polyvinyl alcohol.

  saponified and 50 g of a hydroxypropyl methylcellulose in 480 kg of water pre-

  heated. The temperature of the aqueous solution thus prepared is recorded

in table I.

  The cold mixture of monomer and polymerization initiator prepared above and the preheated aqueous solution of the suspending agent are separately introduced but simultaneously at constant flow rates into the polymerization reactor, through separate inlets to form a hot polymerization mixture with continuous stirring. The temperatures of the polymerizable mixture during and at the end of the introduction of the monomer-initiator mixture and the aqueous solution into the reactor are shown in Table I.

  In cases where at the end of the introduction of the monomer mixture

  initiator and aqueous solution the temperature of the polymerizable mixture

  given above is below the polymerization temperature

  570 ° C, the temperature of the polymerizable mixture is increased

  the heat envelope for the time recorded in Table I in minutes, and the reaction

  polymerization without continuous stirring.

  When the polymerization reaction approaches its end and the

  pressure inside the reactor has fallen to 7 bar, the lemon

  mother who has not reacted and the polymerized aqueous slurry is dehydrated

  and dried after discharge and thus gives the polyvinyl chloride resin.

  In test 8, recorded in table r. the monomer-initiator mixture is introduced into the polymerization reactor simultaneously with the preheated water containing no suspending agent, and then this agent is added in the form of an aqueous solution of a concentration

relatively high.

  In each test, the rate of polymer deposition on the walls of the

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  reiterated and the "" "" "e" "of fish y-them in the polymer are evaluated

  according to the methods and criteria given below.

  Conversion of the monomer to polymer in the monomer mixture

  initiator after 2 hours (in): 20 ml of the homogeneous mixture of the monomer and the polymerization initiator are sealed in a glass ampoule

  and we evaluate the conversion after a stay of the bulb of Z hours at the time of

room temperature.

  Number of fish eyes: a resinous composition is prepared by mixing 100 parts by weight of the resin, 1 part by weight of tribasic lead sulphate, 1.5 parts by weight of lead stearate, 0.2 parts by weight of

  weight of titanium dioxide, 0.1 part by weight of carbon black and 50 parts by weight of

  By weight of dioctyl phthalate, 25 g of this composition are worked in a roll mill at 145 ° C. for 5 minutes and a sheet of 0.2 mm thick is made. The number of translucent points on 100 cm of this

  leaf is counted and recorded as number of fish eyes.

  Polymer deposit rate A ..... practically no deposit B ..... polymer deposit in the vapor-liquid interface area

  C ..... polymer deposit all over the walls of the reaction

  Example Z. (Tests 9 to 13) In a polymerization reactor having a capacity of 40 m, equipped with a condenser whose heat transfer surface reaches 40 m, 13 tonnes of vinyl chloride are simultaneously introduced and 18 m3 of preheated water at constant flow rates of 0.65 tonnes / min and

  0.9 m3 / min, with stirring, duration of the introduction 20 min.

  On the path of the conduit for the transfer of vinyl chloride to

  14 kg of a 50% solution in toluene deperoxydi-

  di (ethoxyethyl) carbonate in the monomer stream at a flow rate of

  0.7 kg / min with stirring by means of a static mixer, so that the initial

  The reactor is uniformly mixed with the monomer upon arrival at the reactor.

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  Similarly, 100 liters of an aqueous solution containing

  3 kg of a partially saponified polyvinyl alcohol and 2.5 kg of a hydroxypropyl methylcellulose in the preheated water during its

the conduit, at a rate of 5 1 / min.

  In the case where the temperature of the polymerizable mixture thus formed in the polymerization reactor is less than 570.degree. C., this is increased to 57.degree. C. by means of a heating jacket and the reaction of

  polymerization begins with continuous stirring.

  The polymerization reaction is stopped when the pressure at

  The reactor interior dropped to 7 bar, evacuating the poly-

  merited reactor. After dehydration and drying this slurry provides

PVC resin.

  In annexed Table II are recorded for each test the temperature

  of the monomer-initiator mixture at the reactor inlet, the rate. of con-

  in the monomer-initiator mixture at this temperature after 2 hours, the temperature of the water preheated at the inlet of the reactor after the addition of the solution of the suspending agents, the temperature of the polymerizable mixture at the end of end of the introduction of monomer and water

  preheated, the time required for raising the temperature of the

  polymerizable mixture up to 57 ° C. and the duration of the polymerization as well as the rate of polymer deposits on the reactor walls and the number of fish eyes in the polymer. The test shown in Table II is a comparative test according to a usual method in which the polymerization medium

  that is to say, water, containing the agents suspended in suspension, the nitrate-

  polymerization and vinyl chloride are introduced into the reaction

  separately and successively.

  For a second comparison we proceed for the most part. corn-

  in test 9, except that the vinyl chloride and the talunic solution of the polymerization initiator are not introduced into the reactor under

  the form of a homogeneous solution, but separately by the separate entries

  the static mixer in the conduit path has been removed.

  The higher number of fish eyes in the softwood product obtained in this test and recorded in Table II clearly indicates the significance

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  of the introduction of the monomer and the initiator in the form of a mixture

homogeneous (test 13).

Table I

Test No. 1 2 3 4 5 6 7 8

Monomer mixture.

  initiator Temperature, C Conversion of the monomer after 2 hours,% Temperature of the aqueous solution, C

Charge duration-

The temperature of the

polymeric mixture

riseable, C

During the

ment

At the end of

ment

Time for students

the temperature

at 57 C, half

  n 1, 5, 6-57 (1 -57 -57 1.5 61.3 52-53 1, -5, 3 48-49 62, 5 - -57 4, 5 -56 1, 5 -5 / Number of fish eyes 9 12> 500 23> 500> 500 28> 500

Deposit of poly-

mother A A C A C C B C

Table II

  Test No. 9-101 12 Monomer-Initiator Mixture Temperature; C 18 8 16 22 18 Conversion of monomer after 2 hours,% 1 I 1 - 1 Preheated water temperature,

 C 67 67.5 19 25 67

Temperature of the polymer mixture

  sand at the end of loading, C 57 55 18 24 57 Time to raise the temperature to 57 C, minutes -0 10 55 50 O Duration of polymerization, hours 4.8 5, O 5, 7 6.2 4, 8 Number of fish eyes 8 9 5 8> 500

Polymer deposit A A A A A-

|:. ,.

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Claims (6)

  1 - Improved process for the suspension polymerization of vinyl chloride or a mixture of monomers, most of which is vinyl chloride, in an aqueous medium containing a suspending agent, in a polymerization reactor, in the presence of a polymerization initiator at the prescribed high polymerization temperature, characterized in that the monomer or mixture of monomers and the polymerization initiator are introduced into the polymerization reactor in the form of a homogeneous mixture together with preheated water,   to obtain a polymerizable mixture, wherein the polymerization reaction   The temperature of the polymerizable mixture can be started during and at the end of the introduction of the homogeneous mixture of the monomer and the initiator.   of polymerization, and the preheated water being substantially equal to the temperature   prescribed polymerization temperature.   2 - Process according to claim 1, characterized in that, at the end of the introduction of the homogeneous mixture of the monomer and the initiator of   polymerization, and the preheated water, the temperature of the polymer mixture   risable is greater than the prescribed polymerization temperature only 2OC or less.   3 - Process according to claim 1, characterized in that the   homogeneous mixture of monomer and polymerization initiators is maintained prior to introduction into the polymerization reactor at a temperature such that the conversion rate of monomer to polymer does not exceed 5% after 2 hours.   4 - Process according to claim 1, characterized in that the introduction   duction of the homogeneous mixture of monomer and polymerization initiator   is completed in a time interval of not more than 30 minutes.   - Method according to claim 1, characterized in that the suspending agent is dissolved in the preheated water before introduction   preheated water in the polymerization reactor.   6 - Process according to claim 1, characterized in that the suspending agent is introduced into the polymerization reactor under 14 2484420   the form drutme soIutioa aqtteuse before the introduction of the homogeneous mixture of monotnre and dmnritiatetr s of polymerization, and water'préchauffée in the polymerization reactor.   7 - Method according to claim 1, characterized in that the introduction   the homogeneous mixture of the monomer and the polymerization initiator   preheated water is introduced at constant flow rates.   and begin and end at about the same time.