GB1574572A - Production of polyvinyl cloride by polymerization in suspension - Google Patents

Description

(54) PRODUCTION OF POLYVINYL CHLORIDE BY POLYMER1IZAON IN SUSPENSION (71) We, HOESCEIT AKTIENGESELL SCHAFT, a body corporate organised under the laws of the Federal Republic of Germany, of D6230 Frankfurt am Main 80, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for making polyvinyl chloride by suspension polymerization.

It is known in the discontinuous suspension polymerization of vinyl chloride to use a oil-soluble low temperature initiator, e.g.

acetylcyclohexane sulfonyl peroxide or diisopropyl peroxydicarbonate, which is dissolved in a suitable organic solvent and introduced together with the vinyl chloride into a polymerization reactor.

According to Germany Patent Specification ("Offenlegungsschrift") No. 2,442,574, it is necessary to observe certain requirements to prevent undesirable premature polymerization in the single pipe through which the initiator solution and monomer are introduced into the polymerization reactor. That specification describes more particularly a process for making polyvinyl chloride substantially without emission of vinyl chloride by discontinuous polymerization in an aqueous suspension in contact with an initiator comprising a monomersoluble catalyst and an ordinary suspension stabilizer in a polymerization reactor having a capacity of at least 40 m3. This process comprises introducing the catalyst through a vessel disposed inside the vinyl chloride supply line, and, prior to introducing the catalyst into this vessel, filling with water the space between this vessel and a valve.

Between individual polymerization procedures, the polymerization reactor may be hydrodynamically cleaned automatically in known manner, the polymerization reactor remaining closed between the said prb cedures, i.e. during these cleaning operations.

A preferred feature of the process just described provides for any hollow space which may be present downstream of the sealing surface of the valve to be filled with water at a pressure higher than that which prevails in the polymerization reactor and in the vinyl chloride supply line.

This process, however, is not fully satisfaotory, in the following respect. When the initiator solution passes from the above mentioned vessel into the polymerization reactor, the catalyst, which is usually unstable at room temperature, is liable to rise quickly to a high concentration in the vinyl chloride, and to cause it to undergo premature polymerization. As a result of this, the outlet of the above-mentioned vessel is liable to become clogged. In the event of the vinyl chloride supply unforeseeably being ob structed or interrupted, it is even possible for spontaneous reactions to occur which culminate in explosive disturbances in the above-mentioned vessel. This is very hazardous, especially for the operation of a high capacity polymerization reactor.

The undesirable premature formation of polymer is liable not only to affect adversely the degree of safety with which the polymerization unit can be operated, but also to lead to the formation of fisheyes, as they are called, in subsequent polymerization batches.

The reason for this is that the premature polymers are formed at room temperature and therefore have a high molecular weight; also, the cross-linking of polymer nuclei is favoured by the high concentration of initiator in the outlet of the above-mentioned vessel.

The above-mentioned German Specification also contemplates the polymerization reactor being supplied with the organic initiator solution by a manual method. To this end, it is naturally necessary to open the polymerization reactor; however, this causes delay, and is invariably associated with considerable emission of vinyl chloride.

We have now found, in accordance with our present invention, that adverse effects of the character described above can be obviated by supplying the vinyl chloride and organic initiation solution to the polymerization reactor separately from one another, i.e. through separate supply lines.

According to the present invention, therefore, we provide a process for making polyvinyl chloride by polymerizing vinyl chloride in an aqueous suspension in the presence of a monomer-soluble initiator and a suspension stabilizer, at elevated temperature and with agitation, and separating the resulting polymer, in which process: the vinyl chloride, the suspension stabilizer, and demineralized water for suspending the vinyl chloride are introduced into a polymerization reactor which has been freed from oxygen or air, through a supply line separate from a supply line for the initiator, and mixed therein, and a gauge pressure of 0.5 to 6, preferably 1 to 5, atmospheres is established in the reactor; at least one initiator is conveyed to the reactor, by means of demineralized water at a pressure higher than that in the reactor, from a valved container which is kept free from oxygen or air and which is disposed in the initiator supply line leading to the reactor, vinyl chloride gas or vapour being prevented from passing into the portion of the initiator supply line running between the reactor and valved container; the introduction of water into the valved container is stopped; and the polymerization of the vinyl chloride is initiated by heating the contents of the polymerization reactor.

A preferred feature of the present process provides for one or more initiators to be dissolved or suspended in an organic solvent which is immiscible with water an inert with respect to the vinyl chloride and suspension stabilizer.

Specific examples of initiators which are useful in the process of this invention are: acetylcyclohexanesulfonyl peroxide; din so propyl peroxydicarbonate; tertiary butyl perpivalate; tertiary butyl perneodecanoate.

These should preferably be used in a proportion of about 0.01 to 0.03 weight %, based on the weight of vinyl chloride. A further useful initiator is dilauryl peroxide, which should Ipreferably be used in a proportion of 0.05 to 0.15 weight %, based on the weight of vinyl chloride.

Examples of solvents which are useful for dissolving the initiator(s) are: aliphatic or aromatic hydrocarbons, phthalates; alkyl halides and other halogen-substituted alkanes. Typical representatives are, for example, iso-dodecane, butyl phthalate, and carbon tetrachloride.

A further preferred feature of the present process provides for the quantity of water supplied by way of the valved container to be 5 to 15%, preferably 7 to 12%, by volume, of the quantity of water introduced into the polymerization reactor.

A still further preferred feature of the present process provides for a single valved container to be used for supplying the initiator(s) to a plurality of polymerization reactors connected thereto by supply lines disposed in parallel.

The use of one or more protective colloids, e.g. polyvinyl alcohol, partially saponified (hydrolysed) polyvinyl acetate, polyglycol ether, cellulose mixed ethers, sorbitan esters or mixtures thereof, is optional in the process of this invention. The protective colloids, if employed, are usually employed in a proportion of 0.03 to OA, e.g. 0.05 to 0.3,weight %, based on the weight of vinyl chloride.

The present process may be effected in an apparatus as shown in the accompanying drawing, the single Figure of which is a diagrammatic side view of the appraatus concerned, showing a valved initiator supply line and a valved vinyl chloride supply line which are separately connected to a polymerization reactor.

The apparatus shown in the drawing comprises a polymerization reactor 1 having a domed head into which opens a vinyl chloride supply line 3 provided with a check valve 2, and into which opens also an initiator supply line 4. This line 4 is provided with a first check valve 5 and a second check valve 6, and is connected to a valved container 7 which acts as a lock. The container 7 is furthermore provided with an inlet 8 comprising a rapidly closable trap for the introduction of initiator, and is additionally connected to a line 9, provided with a check valve 10, for the supply of demineralized water.

The present process compares favorably with prior processes which provide for a polymerization reactor to be supplied with initiator by a manual method, in respect of the following points: The emission of vinyl chloride is obviated by the fact that all components which contain vinyl chloride, or through which vinyl chloride is passed, are hermetically sealed or closed off during each phase of the present process. In comparison with the process disclosed in the abovementioned German Specification, the present process offers a greater degree of safety during operation, as it definitely prevents vinyl chloride from coming into contact with the initiator outside the polymerization reactor, so that premature polymerization is not liable to occur. Thus the present process avoids any need for the spraying with water under pressure of check valves in vinyl chloride supply lines, which is required in certain prior processes.

It would appear totally unobvious to introduce initiators into a polymerization reactor in the particular manner of this invention, inasmuch as it has long been assumed by those skilled in the art that the use of water would not permit waterinsoluble initiators to be introduced completely into a polymerization reactor, but would entail phase separation and residue formation in the interior of whatever valved initiator container or initiator supply line was employed.

In the process of the present invention we have been able, by repudiating this preconception, to use considerably simplified testing and control methods for the programmed controlled supply of a polymerization reactor with feed material. In particular, as stated earlier, the present invention enables use to be made of a single valved container for the supply of initiator(s) to a plurality of polymerization reactors.

The following Examples illustrate the invention, which is not, however, limited thereto.

EXAMPLE I A reactor 1 comprising a stainless steel autoclave was free from oxygen and air; this autoclave, which was provided with an adjustable impeller mixer and a flow interrupter, was fed with the following feed materials, which were mixed together: 1400 parts by weight of water, 1.1 part by weight of a partially saponified polyvinyl acetate with an ester content of 20 weight %, and 675 parts by weight of vinyl chloride.

The vinyl chloride was introduced into the autoclave through the line 3, and gauge pressure of 3 atmospheres was found to have been established therein. Next, the valved container 7, free from oxygen and air, was fed through the inlet 8, while the check valves 6, 5 and 10 were closed, with 0.2 part by weight of dissopropyl peroxydicarbonate, which was in the form of a 40 weight % solution in butyl phthalate, and 0.05 part by weight of acetylcyclohexanesulfonyl peroxide, which was in the form of a 30 weight % solution in butyl phthalate; the inlet 8 was then closed by means of its rapidly closable trap. Next, the check valves 10, 5 and 6 were opened, and 100 parts by weight of demineralized water under a pressure of 6 atmospheres gauge was introduced through the line 9, to convey the initiator solution from the container 7 to the autoclave. After this had been done, the check valve 5 was closed, and then, after the line 4 was found to be empty, the check valves 10 and 6 were closed. The autoclave was heated to 55 CC, with agitation of the material therein at a peripheral speed of 6 m per second, to initiate the polymerization, which was complete after the pressure in the autoclave had dropped to 5 atmospheres gauge.

The container 7, which, after the initiator had been introduced into the autoclave, was still full of water, was freed therefrom by the introduction of nitrogen under pressure.

After the discontinuous polymerizatian of altogether 40 vinyl chloride batches, the interiors of the container 7 and of all the check valves were found to have remained free from residues and deposits.

The polyvinyl chloride so made had a K-value of 70.2 and an apparent density of 480 g/l. The number of fisheyes was determined on a 100 cm2 PVC sheet 0.2 mm thick, which was rolled at temperatures of 1400C and 1600C, for periods of 15 and 10 minutes, respectively. There were found to be six fisheyes at 1400C and zero at 1600C.

EXAMPLE 2 The procedure was as in Example 1, but 0.4 part by weight, based on the weight of vinyl chloride, of di(2-ethylhexyl) peroxydicarbonate was used as the initiator in the form of a;65 weight % solution in isododecane.

After 10 polymerizations under the conditions described in Example 1, the inside wall of the container 7 was completely clean, the check valves were free from polymer.

The polymer obtained had a K-value of 70, and an apparent density of 485 g/l. The number of fisheyes at 140 and 1600C were 4 and zero, respectively.

EXAMPLE 3 The procedure was as in Example 1, but 0.23- part by weight of tertiary butyl peroxypivalate, which was in the form of a 75 weight % solution in iso-octane, and 0.1 part by weight of diisopropyl peroxydicarbonate, which ias in the form of a 40 weight % solution in carbon tetrachioride, were used as the initiators. The polymerization temperature was 580C.

After the initiators had been introduced into the autoclave, the inside wall of the container 7 was inspected. The result was the same as in Example 1.

EXAMPLE 4 The procedure was as in Example 1, but 0.5 part by weight of dilauryl peroxide and 0.15 part by weight of tertiary butyl tperoxy- pivalate were used as the initiators; the polymerization was effected at 640C. Thereafter the inside of the container 7 was inspected; the result was the same as in Example.

EXAMPLE 5 (Comparative Example) The conditions described in Example 1 were modified as follows: The autoclave was supplied with 1500 parts by weight of water, and the entire quantity of vinyl chloride, together with the initiator, was delivered to the reactor 1 from the container 7. After the introduction of the monomer, the check valve 10 was closed, the pressures in the container 7 and the reactor 1 were equalized, and the check valves 5 and 6 were closed so that the container 7 and line 4 were definitely free from liquid vinyl chloride. The tank 7 was evacuated, and then filled with nitrogen; its interior was inspected.

After polymerization of not more than 3 batches, a grey-brown polyvinyl chloride layer several mm thick was found to have been formed in the container 7, which layer became thicker and thicker after each operation. The valves 5 and 6 associated with the container 7 were so difficult to actuate that it was necessary for them to be replaced.

One of the polymerization tests was marred by an explosive disturbance in the container 7, accompanied by an enormous evolution of heat. This occurred, early in the vinyl chloride introduction, at a stage at which the delivery of vinyl chloride could not be kept up, due to operational difficulties, and the bulk of the activator or initiator which was still mixed with monomer could not flow off.

The number of fisheyes was found to increase from batch to batch, as follows: Roll teselperature and railing period Batch 1400C 1600C No. 15 minutes 10 minutes 1 .. 15 fisheyes . . 1 fisheye 2 . 25 ,, 2 fisheyes 3 . 70 ,, ... 2 4 . . 110 " 4 5 . . 180 ,, . 6 EXAMPLE 6 (Comparative Example) The conditions described in Example 1 were modified as follows: 1500 parts by weight of water and dispersant were introduced into the reactor. Next, the initiator was introduced into the still open reactor.

The atmospheric oxygen present therein was expelled by means of nitrogen, the reactor was evacuated, and vinyl chloride was introduced thereinto in metered quantities through the line 3; the container 7 was kept empty and the check valves 6, 5 and 10 remained closed.

Apart from the fact that one more hour was needed for the termination of the polymerization reaction, which was indicated by a pressure drop, the resulting polymer was found to have a much higher number of fisheyes than the product of Example 1. This was evidently due to initiator inactivation in the water phase and to increased cross-linking with the dispersant.

The number of fisheyes was 300 at 1400C and 15 minutes, and 20 at 1600 and 10 minutes.

A comparison of the present process as described in Examples 1 to 4 with prior processes as described in comparative Examples 5 and 6 shows that the invention compares favourably with these prior processes in the following respects. Firstly, the formerly hazardous introduction of initiator into the polymerization reactor has been made safe, and in addition to this the formation of fisheyes in the resulting polymer is reduced significantly.

WHAT WE CLAIM IS: 1. A process for making polyvinyl chloride by polymerizing vinyl chloride in an aqueous suspension in the presence of a monomer-soluble initiator and a suspension stabilizer, at elevated temperature and with agitation, and separating the resulting polymer, in which process: the vinyl chloride, the suspension stabilizer, and demineralized water for suspending the vinyl chloride are introduced into a polymerization reactor which has been freed from oxygen or air, through a supply line separate from a supply line for the initiator, and mixed therein, and a gauge pressure of 0.5 to 6 atmospheres is established in the reactor; at least one initiator is conveyed to the reactor, by means of demineralized water at a pressure higher than that in the reactor, from a valved container which is kept free from oxygen or air and which is disposed in the initiator supply line leading to the reactor, vinyl chloride gas or vapour being prevented from passing into the portion of the initiator supply line running between the reactor and valved container; the introduction of water into the valved container is stopped, and the polymerization of the vinyl chloride is initiated by heating the contents of the polymerization reactor.

2. A process as claimed in claim 1, employing one or more initiators dissolved or suspended in an organic solvent which is immiscible with water and inert with respect to the vinyl chloride and suspension stabilizer.

3. A process as claimed in claim 1 or 2, employing one or more of the following

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. pivalate were used as the initiators; the polymerization was effected at 640C. Thereafter the inside of the container 7 was inspected; the result was the same as in Example. EXAMPLE 5 (Comparative Example) The conditions described in Example 1 were modified as follows: The autoclave was supplied with 1500 parts by weight of water, and the entire quantity of vinyl chloride, together with the initiator, was delivered to the reactor 1 from the container 7. After the introduction of the monomer, the check valve 10 was closed, the pressures in the container 7 and the reactor 1 were equalized, and the check valves 5 and 6 were closed so that the container 7 and line 4 were definitely free from liquid vinyl chloride. The tank 7 was evacuated, and then filled with nitrogen; its interior was inspected. After polymerization of not more than 3 batches, a grey-brown polyvinyl chloride layer several mm thick was found to have been formed in the container 7, which layer became thicker and thicker after each operation. The valves 5 and 6 associated with the container 7 were so difficult to actuate that it was necessary for them to be replaced. One of the polymerization tests was marred by an explosive disturbance in the container 7, accompanied by an enormous evolution of heat. This occurred, early in the vinyl chloride introduction, at a stage at which the delivery of vinyl chloride could not be kept up, due to operational difficulties, and the bulk of the activator or initiator which was still mixed with monomer could not flow off. The number of fisheyes was found to increase from batch to batch, as follows: Roll teselperature and railing period Batch 1400C 1600C No. 15 minutes 10 minutes 1 .. 15 fisheyes . . 1 fisheye 2 . 25 ,, 2 fisheyes 3 . 70 ,, ... 2 4 . . 110 " 4 5 . . 180 ,, . 6 EXAMPLE 6 (Comparative Example) The conditions described in Example 1 were modified as follows: 1500 parts by weight of water and dispersant were introduced into the reactor. Next, the initiator was introduced into the still open reactor. The atmospheric oxygen present therein was expelled by means of nitrogen, the reactor was evacuated, and vinyl chloride was introduced thereinto in metered quantities through the line 3; the container 7 was kept empty and the check valves 6, 5 and 10 remained closed. Apart from the fact that one more hour was needed for the termination of the polymerization reaction, which was indicated by a pressure drop, the resulting polymer was found to have a much higher number of fisheyes than the product of Example 1. This was evidently due to initiator inactivation in the water phase and to increased cross-linking with the dispersant. The number of fisheyes was 300 at 1400C and 15 minutes, and 20 at 1600 and 10 minutes. A comparison of the present process as described in Examples 1 to 4 with prior processes as described in comparative Examples 5 and 6 shows that the invention compares favourably with these prior processes in the following respects. Firstly, the formerly hazardous introduction of initiator into the polymerization reactor has been made safe, and in addition to this the formation of fisheyes in the resulting polymer is reduced significantly. WHAT WE CLAIM IS:

1. A process for making polyvinyl chloride by polymerizing vinyl chloride in an aqueous suspension in the presence of a monomer-soluble initiator and a suspension stabilizer, at elevated temperature and with agitation, and separating the resulting polymer, in which process: the vinyl chloride, the suspension stabilizer, and demineralized water for suspending the vinyl chloride are introduced into a polymerization reactor which has been freed from oxygen or air, through a supply line separate from a supply line for the initiator, and mixed therein, and a gauge pressure of 0.5 to 6 atmospheres is established in the reactor; at least one initiator is conveyed to the reactor, by means of demineralized water at a pressure higher than that in the reactor, from a valved container which is kept free from oxygen or air and which is disposed in the initiator supply line leading to the reactor, vinyl chloride gas or vapour being prevented from passing into the portion of the initiator supply line running between the reactor and valved container; the introduction of water into the valved container is stopped, and the polymerization of the vinyl chloride is initiated by heating the contents of the polymerization reactor.

2. A process as claimed in claim 1, employing one or more initiators dissolved or suspended in an organic solvent which is immiscible with water and inert with respect to the vinyl chloride and suspension stabilizer.

3. A process as claimed in claim 1 or 2, employing one or more of the following

initiators: acetylcyclohexane sulfonyl peroxide; diisopropyl peroxydicarbonate; tertiary butyl perpivalate; tertiary butyl perneo- deconoate.

4. A process as claimed in any of claims 1 to 3, employing the initiator(s) in the form of a solution in an aliphatic or aromatic hydrocarbon, a phthalate or an alkyl halide or other halogen-substituted alkane.

5. A process as claimed in any of claims 1 to 4, wherein the quantity of water supplied by way of the valved container is 5 to 15% by volume, of the quantity of water introduced into the polymerization reactor.

6. A process as claimed in any of claims 1 to 5, wherein a single valved container is used for supplying the initiator(s) to a plurality of polymerization reactors con- necked thereto by supply lines disposed in parallel.

7. A process for making polyvinyl chloride substantially as described in any of Examples 1 to 4 herein.

8. A polyvinyl chloride obtained by a process as claimed in any of claims 1 to 7.