HU180652B - Process and equipment for the polymerisation of vinylchloride in suspension - Google Patents

Abstract

A process for the suspension polymerization of vinyl chloride is disclosed, according to which the suspension is withdrawn from the reactor prior to attaining 70% conversion, and is recycled to the reactor via an external tube which is externally cooled. By suitably modifying the internal profile of the tube, the results can be improved. The apparatus including a tube with a suitably modified internal profile constitutes another aspect of the invention.

Description

The present invention relates to a process and apparatus for high yield polymerization of vinyl chloride.

In particular, the present invention is directed to increasing the specific production capacity of reactors most commonly used in slurry polymerization of vinyl chloride.

The rate of polymerization of vinyl chloride is known to increase significantly as the reaction proceeds, and it is also known that decomposition of initiators is slow (at temperatures generally in the range of 50-60 ° C). Thus, the maximum reaction rate is almost always 50% higher than the average rates.

Due to this specific kinetic property and the time-worsening of the heat transfer coefficient (due to the deposition on the reactor walls and the increase in reactant viscosity), the full heat exchanger capacity of the reactor cannot be fully utilized in less than three quarters of the average reaction time.

Use of initiators such as. acetylcyclohexane sulfonyl peroxide and peroxodicarbonates having a conversion half-life of one hour or less and the development of anti-deposition methods and dilution of the reactant with water 25 alleviate these problems and thus kinetic characteristics and heat exchange capacity can be maintained at about the same level in time.

The current effort to polymerize in large reactors (over 100 cm ⁵ ) has been made possible by the combined application of these measures. It also contributed to the improvement of heat exchange with reflux condensers, the installation of cooled buffers and deep-temperature coolants. Thus, the cost per 5 lm ³ reactor space is more favorable for large reactors compared to a 20 m ³ reactor with a specific production capacity of 250 t / m ³ , even if, for example, a specific production capacity of a 130 m ³ reactor is still 190 t / m ³ .

However, the transition to large reactors is hampered by several difficulties, namely:

For plants designed for large reactors, it is usually only at an additional investment cost that the quality of batch products will be nearly constant and to minimize the possibility of failure in the automatic washing and distillation of vinyl chloride, automatic control of individual production stages and refrigeration and other systems. .

The development of such polymerization processes requires considerable investment of time and money, since it is almost impossible to theoretically determine the morphological properties of the product, and therefore experiments are usually carried out on industrial equipment equipped with, for example, variable blade and speed mixers, movable stops. .

Operating costs are overburdened with vinyl chloride treatment, cooling of coolants, and operation of reflux condensers.

The possibility of more flexible production for large reactors 30 is more limited.

From the foregoing, it is obvious that it is of great importance to significantly increase the specific production capacity of widely used smaller reactors (25-70 cm ³ ) and thus approach the annual yield of large reactors without the above difficulties occurring.

It is also known that in the case of slurry polymerization of polyvinyl chloride, i.e. PVC, the stirring in the reactor must not exceed a certain limit (depending on the geometry of the stirrer), otherwise an uncontrolled lump formation process will be initiated. On the other hand, it is particularly difficult to achieve rapid and complete solubilization of the components (e.g., dispersing the catalyst in vinyl chloride) so that both phases and heat are uniformly distributed over the course of the reaction, the physical properties of the phases change constantly. Particularly when the conversion has reached 70%, local overheating of the material can occur and thus the gel and degraded particles can be incorporated into the product and greatly impair its quality. This effect occurs mainly when the reaction time is shortened, so that in the case of a reaction of less than 8 hours, the quality of the final product is inadequate, even if an increase in yield is achieved.

Also known from U.S. Patent No. 2,128,799. A disclosure in the Federal Republic of Germany discloses that the reactor is provided with a cooling device, i.e. a pipe located outside the reactor. The reaction mixture is circulated in this tube under laminar flow conditions to stop the polymerization reaction. As a result, deposits are formed on the inner walls of the tube and heat exchange is impaired.

It has been found, and it is an object of the present invention, that the production capacity of a reactor capable of slurry polymerization of vinyl chloride can be significantly increased (by at least 20%) and at the same time a product is obtained which is completely free of particles and visible in it). According to the process of the invention, before reaching the 70% conversion, the suspension is passed through an outer tube with a cooling jacket under turbulent flow conditions.

In addition to turbulence, the formation of tube deposits and tube clogging are prevented by known methods or compositions, by passivation and curing or other treatment of stainless tubes, by an anti-caking enamel coating or by other appropriate means, and by moving the suspension at in the tube.

Vinyl chloride may be present in the composition of the inlet material at any concentration from 100% to 5%, i.e. flow in the outer rain may be initiated at any time during the polymerization, provided that the degree of conversion has not yet reached 70%. . The flow was continued until the reaction was complete. Said outer tube may also be used to feed a previously prepared aqueous vinyl chloride suspension into a reactor in a suitable container, as well as to feed partially prepolymerized suspensions.

It has further been found that if the flow rate of the flow back material is such that the residence time in the reactor is reduced to less than 30 minutes, the mixing flow rate can be reduced or even stopped without any appreciable effect. however, the suspending agent must be slightly enriched in the starting material.

The present invention also relates to a device for slurry polymerization comprising a reactor for vinyl chloride polymerization and an associated cylindrical tube for circulating the slurry, a circuit connected to the reactor and a pump for transferring the slurry.

The modified pipe profile shown in Figure 1 is particularly advantageous in unmixed systems as it provides better heat transfer and slower suspending agent consumption than smooth pipes at steady flow and average speeds.

The inner profile modification of the tube is achieved by placing a plurality of elements on the inner wall of the tube which are conical and whose conical top is intersected by a plane and the surface of the tube 20, the intersection plane is at an angle equal to or greater than 3a ', where' is half the opening angle of the cone. The axis of the cone is parallel to the axis of the tube and is located inside or outside the tube wall. These elements are placed one after the other in a spi25 shape along the tube, diagonally in the opposite direction.

In the drawing shown in the figure, the pipe wall 1 shows the conical surface 2 of the element and the intersecting plane 3 which closes the angle with the radius of the element. Particularly advantageous is the design of the following additive dependencies:

& 3α α '; α '^ 10 °; b ^ D _T / 6; DIL:

where 'a is the half angle of the taper, D _{T is} the inside diameter of the tube, L is the length of the member which modifies the cylinder surface of the tube, d is the distance between two consecutive members, R is the maximum radius of bending .

The aqueous vinyl chloride suspension can be prepared in a manner well known to those skilled in the art. For example, the suspension may be added:

Primary suspending agents, such as water-soluble cellulose ethers and hydroxy ethers, polyvinyl alcohols with a saponification number below 270, polyvinylpyrrally ralidone, maleic anhydride copolymers, gelatin and the like. among others.

Secondary suspending agents, e.g. sulfonate and long chain alkyl sulfate type ionic surfactants, nonionic surfactants of the polyethylene oxide derivative group 50, potivinyl alcohols having a saponification number of 270-550 and others.

Buffers such as sodium bicarbonate.

Additives with specific anti-cortical activity, such as natural substances of the clay and bentonite type, hydroxides of alkali and alkaline earth metals, monocarboxylic and polycarboxylic acids and their salts (citric acid, oxalic acid, etc.), inorganic oxidizing agents such as permanganates, bicarbonate. , highly polar organic compounds such as aniline and others.

Peroxide initiators such as alkyl peresters, diacyl peroxides, peroxydicarbonates, alkyl or cycloalkylsulfonyl acyl peroxides and dtazos injectors. These initiators can be readily added to the polymerization reactor 65 and can be prepared in situ.

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Molecular weight regulators such as alpha-olefins, chlorinated alkyl or alkene derivatives, mercaptans and other substances.

The present invention relates to the preparation of vinyl chloride homopolymers in powder form or to vinyl chloride copolymerates having up to 20% by weight of any initial comonomer that can be polymerized with vinyl chloride, such as vinylidene chloride, vinyl acetate and butyrate, methyl, butyl. - and isooctyl acrylate, methyl and hexyl methacrylate, diethyl maleate, dipropyl fumarate, diallyl phthalate, diallyl maleate, styrene, ethylene, propylene, butene, acrylonitrile, methacrylonitrile, vinyl ethyl ether and the like.

The examples in Tables 1 and 2 illustrate the possibilities of using an external heat exchanger without limiting the scope of application.

Table 1 shows the conditions of use of the external heat exchanger, the conditions required for polymerization and the annual yield per cubic meter of equipment.

Table 2 shows composition data, powder morphological properties and analytical data for gels and impurities.

The experiments were carried out in reactors with an actual volume of 25-30 m ³ , the inner wall surface of which was stainless steel coated and enamelled.

Comparative studies were conducted with each reactor type under the conditions required for polymerization without a heat exchanger tube (Experiments 1, 2 and 22) and with a heat exchanger tube.

Part of the heat was removed by injecting 5 ° C water directly into the reaction mixture as soon as the other heat exchange systems reached their performance limits.

Experiment # 2 was performed with a reflux condenser to achieve a shorter reaction time. The minimum temperature of the coolant (water from the water tower) was 25 ° C and the polymerization temperature was maintained at 54 ° C to obtain a K = 70. eluted with 100 g of cyclohexane in 1 g of polyvinyl chloride at 25 ° C.

In some experiments, the stirring was either reduced or needles completely stopped during operation of the heat exchanger (Experiments 6, 7, 8, 9 and 10). Table 1 provides information on the extent of conversion at the beginning of the reflux and on the time of residence in the reactor at the time of mixing change. Experiments Nos. 1, 2 and 3 were carried out without the presence of an anti-barking agent, so that at the end of the reaction, the autoclave and tube were coated with a highly adherent PVC film, so starting from Experiment 4, barking agent was added so that the tube could be reused for the next polymerization after a short wash with clean water and distilled water.

In our experiments, we have found that in the presence of a bark-forming additive, the heat exchanger can be used for a very large number of 20 (more than 100) experiments without any purification. In the series described, only in Experiment # 5, local PVC deposition was observed due to the low reflux rate of the suspension.

In our experiments with reactors with 50 m ³ usable space, enameled tubes gave similar results to stainless steel coated tubes, even if no bark inhibitor was added.

In experiment 10, the angle α is greater than 3a ', more particularly its value is 6.66a'. At this time, the material structure is uneven, the product contains unclear and clearly visible inclusions.

In Experiment 10B, the reactor is too high (h = D / 3). 35 Due to excessive mixing, the structure of the material is inadequate.

In the 10 C experiment, it is > 10 °, more precisely 30 °. The same shortcomings were observed as for the 10 A experiment.

Table 1

The number of the example 1 2 3 4 5 6 7 pipe Type I I I I I Pipe diameter, mm 200 200 200 100 100 Pipe length, m 50 50 50 150 100 Flow rate, m ³ / h 230 140 90 30 40 u tZ) Flow rate, m / s 2 1.2 0.8 1.1 1.4 reactor E.g E.g E.g E.g E.g E.g E.g Reactor volume, m ³ 23 23 23 23 23 23 23 Stirring, rpm Transformation from the beginning of the backflow- 120 120 120 120 120 120/0 120/60 age,% It was time to change the stirring 11.3 11.7 12.7 13 11.3 time, min 36 32 Volume of water injected, m ³ 3.8 6 2.8 6 7.4 7.5 4.6 y · ** g 6 Feed water, t 11.5 10.6 11.5 11.1 10.3 10.0 11.5 Feed vinyl chloride, vol 9.2 8.5 9.2 8.9 8.2 8.0 9.2 .§ ^: 2 Final conversion,% 90 91 89 88 91 90 92 Reaction time, h 10 6.8 5 4.8 5 4.9 5.2 Duration of the cycle, h 12 9 7 6.9 7 7 7.3 Specific annual output, t / m ⁸ 215 265 365 355 333 321 362

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The number of the example 8 9 10 11 12 13 pipe Type I I PM / I S S Pipe diameter, mm 100 100 200 300 200 Pipe length, m 150 150 50 100 100 Flow rate, m ³ / h 50 60 140 500 120 <Z> Flow rate, m / s 1.8 2.1 1.3 * 2 1.1 •SHE reactor E.g E.g E.g s S S Reactor volume, m ³ 23 23 23 50 50 50 Stirring, rpm Transformation from the beginning of the backflow- 120/0 120/0 120/0 100 100 100 age,% It was time to change the stirring 11.3 11.3 11.8 8.7 6.9 8.7 time, min 25 22 9 '5 Volume of water injected, m ³ 5 2.8 5.6 17 15.7 20.2 'G3 s? N in the UK Feed water, t 11.5 11.5 11.1 20.3 25.5 20.3 Uh Feed vinyl chloride, vol 9.2 9.2 8.8 16.2 20.4 16.2 1 ^: 2 Final transformation, /, 88 87 91 90 88 90 Reaction time, h 5 5 4.8 9.9 5 5.1 Duration of the cycle, h 7.1 7 6.9 11.8 7 7.1 Specific annual output, t / m ³ 356 357 362 175 364 291

Notes to Table 1: 1 = Stainless steel

Pl = Stainless steel coated

S = enameled

PM = Modified Profile * = Average values along the pipe

Example 2 with reflux condenser

Continue Table 1 (Compare)

The number of the example 10 10A 10B 10C pipe Type PM / 11 as in Example 10 υ Pipe diameter, mm 200 as in Example 10 She 'SHE Pipe length, m 50 as in Example 10 Flow rate, m ³ / h 140 as in Example 10 Flow rate, m / s 1.3 1.3 1.4 1.3 of reactor E.g as in Example 10 A4 £ Reactor volume, m ³ 23 as in Example 10 the Stirring, rpm 120/0 as in Example 10 E Transformation at start of reflux, ° / 11.8 12 11.6 11.8 s- Time between mixing changes, min 9 9 9 9 give Volume of water injected, m ³ 5.6 6.5 5 5.2 Feed water, t 11.1 11.1 11.1 11.1 Q 'n Feed vinyl chloride, vol 8.8 8.8 8.9 8.8 'C Final transformation, ° / 91 89 90 89 Reaction time, h 4.8 4.9 4.6 4.8 * 6 Duration of the cycle, h 6.9 7 6.8 6.8 Specific annual output, t / m ³ 362 350 363 359

Table 2

The number of the example 2 3 4 5 6 7 <Z> Methyl cellulose 0.082 0.082 0.082 0.09 0.1 0.1 0.18 · - · < SHE N.S. 450 polyvinyl alcohol 0,094 0,094 0,094 0.1 0.12 0.12 0.18 give NaHCO ₃ 0.02 0.02 0.02 - - - - CD Mg (OH) ₂ - - - - 0.12 0.12 - < Bentons (Ultragel 300) - - - 0,045 - - 0,045

The number of the example 1 2 3 4 5 6 7 C / R She Initiator 1 (space, butyl perneo decanoate) 0,035 0.06 0.088 0.088 0.088 0.088 0.088 Initiator 2 (dilauroyl peroxide) 0,012 0,015 0.02 0.02 0.02 0.02 0.02 Ό Apparent density, g / cm ³ 0,048 0.490 .487 0.471 0.493 0.480 0.515 Above 315 μιη,% Above 250 μιη,% Above 200 μιη,% 0.4 0.8 0.2 9.4 5.2 6.7 ε E 0.4 4.6 sin * · « Above 160 μιη, ° / _o 8.6 7.4 10.2 6.4 10.4 Λ 15.8 Above 100 μη »,% 70.3 68.4 65.1 75.3 52.8 c 44.6 cü C 71 μη »above,% 15.4 18.2 17.0 16.1 15.8 I- 4> 20.6 % Sediment 5.3 6.0 6.9 2.0 5.7 14.0 Eye Softening absorption rate PVC 100 / DOP 50 (min and s) 2 ', 55 3 ', 20' 3 ', 00 3 ', 05 3 ', 45 4 ', 00' Visible inclusions, * 10 / cm ² 1 => 100 5 2 1 > 100 30

Remarks: Addition refers to parts by weight per 100 parts by weight of vinyl chloride.

* Addition with softening and carbon black. Transparent grains are counted on a 10 cm ² plate after 5 minutes of mixing on a rolling mill.

The number of the example 8 9 10 11 12 13 Methyl cellulose 0.12 0.13 0.09 0.09 0.08 0.09 N.S. 450 polyvinyl alcohol 0.14 0.14 0.1 0.10 0.09 0.10 VI NaHCO - - - 0.02 0.02 0.02 She Mg (OH) ₂ 0.12 0.12 - - - - Bentons (Ultragel 300) - - 0,045 - - - 'Ctf Ό Initiator 1 (hi, butyl pemeo deca- BENZENEPROPANOATE) 0.088 0.088 0.088 0.088 0,085 0,085 Initiator 2 (dilauroyl peroxide) 0.02 0.02 0.02 0.01 0.02 0.02 Apparent density, g / cm ³ 0.490 0,485 .479 0.465 0.480 0,484 Above 315 μιη,% Above 250 μπι,% 0.2 Above 200 μπι,% 0.8 0.6 0.8 0.2 0.6 0.4 bo 'C0 Above 160 μπι,% 12.3 11.4 10.7 3.4 7.4 8.2 co Above 100 μπι,% 71.8 69.3 70.8 68.8 65.3 70.2 CÖ e Above 71 μιη, ° / ₀ 12.4 15.8 15.4 22.0 18.5 15.0 particle Sediment Softening absorption rate 2.7 2.7 2.3 5.6 8.2 6.2 PVC 100 / DOP 50 (min and s) 3 ', 10 3 ', 05' 3 ', 00 2 ', 50' 3 ', 00 3 ', 05' Visible inclusions, * 10 / cm ² 1 2 1 5 1 3

Continue to Table 2 (Compare)

The number of the example 10 10A 10B toc Methyl cellulose 0.09 as in Example 10 V) N.S. 450 polyvinyl alcohol 0.1 as in Example 10 'She NaHCOj - - - - -SHE Mg (0H) ₂ - - - - ce Concrete (Ultragel 300) 0,045 < Initiator 1 (space, butyl pemeo decanoate) 0.088 Initiator 2 (dilauroyl peroxide) 0.02 Apparent density, g / cm ³ .479 0.490 0.502 0,485 Above 315 μπι,% - 0.3 9.8 0.4 Above 250 μιη,% - 0.5 15.8 0.6 Above 200 μπι,% 0.8 0.5 25.4 3.2 Above 160 μιη,% 10.7 5.0 30.8 10.0

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The number of the example 10 10A 103 ¹ 10C wj Above 100 µm,% 70.8 72.3 12.7 64.3 & Above 71 μιη,% 15.4 18 5.2 14 CD s co Q Sediment Softener absorption rate PVC 100 / DOP 50 2.3 3.4 0.3 7.5 E (min and s) 3 '00 3 '10 2 '45 3 '15 N Visible inclusions *, 10 / cm ² 1 more than 100 10 more than 100

Table 3

The number of the example 10 10A 10B 10C b D _T / 5 (40mm) D _T / 5 (40mm) D _r / 3 (67mm) D _T / 5 (40mm) R D _T / 5 (40mm) D _r / 5 (40mm) D _T / 3 (67mm) D _T / 5 (40mm) d 200 mm 150mm 300mm 50mm L 236 mm 195 mm 395 mm 69 mm the' 12 ° 12 ° 12 ° 30 ° the 40 ° 80 ° 40 ° 90 °

Patent claims

Claims (2)

A process for slurry polymerization of vinyl chloride, characterized in that a slurry containing 5 to 100% by weight of vinyl chloride introduced into the polymerization reactor is passed through a turbulent flow through an outer tube section with a cooling system prior to 70% of the polymerization reaction. then returning the mixture to the reactor and, if the flow rate of the recycled material is adjusted so that the residence time of the mixture in the reactor is not more than 30 minutes, the mixture is discontinued; optionally a prepolymerized vinyl chloride suspension is used as the starting mixture. 2. A reactor for slurry polymerization of vinyl chloride, an associated cylindrical tube for circulating the slurry, a circumferential circuit connected to the reactor, and a pump for transferring the suspension, characterized in that the inner wall of the cylindrical tube connected to the reactor has a conical arrangement. having a conic surface intersected by a plane and a tubular surface, the intersection plane is at an angle to the axis of the cone, and this angle is equal to or greater than 3a ', where' the half of the cone opening angle, the cone axis is parallel to the tube axis and located on or outside the pipe wall and the conical members are successively disposed in a spiral shape on the pipe wall with an opposite elevation.