SI7611588A8 - Process for the elimination of the residual monomer from a polyvinyl chloride polymer - Google Patents

Description

The invention relates to a process by which both a homopolymer or a copolymer of polyvinyl chloride, which is in suspension form with a high percentage of residual vinyl chloride monomer, removes the residual monomer by contacting the polymer with hot gas, such as saturated water vapor, in atmospheric pressure or greater than atmospheric pressure. Quite low values of residual vinyl chloride monomer (less than 1 ppm) can be achieved.

Polyvinyl chloride (PVC) polymer, whether homopolymer or copolymer, in which copolymerized units of vinyl chloride monomers predominate, is known in the loom as a multilayer plastic. PVC is obtained in a number of ways, which include polymerization in emulsion (latex), solution, suspension or polymerization in mass. No matter which method is used, however, complete conversion of the vinyl chloride monomer to the polymer is not achieved. The consequence is that the vinyl chloride (VCN) monomer, which is often dissolved or enveloped in the polymer of PVC, lags behind. · One method for eliminating the backlog. The VCN and in the polymer consists in heating the PVC to about 82 ° C to allow the VCN to evaporate and evaporate. The procedure is performed under reduced pressure (vacuum) to facilitate removal of the VCM. As an example of a condition in the area of VCM removal, a typical striping operation would be performed at about 77 ° C and at 532 to 598 mbar. Significantly higher temperatures are not applied because of the fear of PVC breakdown. A recent patent from Solvay and Company (Belgium Patent 793,505 of June 29, 1973) provides a technique for removing VCM from PVC by a stripping process consisting of condensation of water vapor per polymer of PVC whereby the PVC is heated above its glass transition temperature and then applying a vacuum to water and VCM would evaporate. Evaporation of water and VCM cools the PVC below its glass transition temperature. Here again the removal of the VCM striping process takes place under vacuum.

According to the present invention, the method for reducing the residual amount of VCM in PVC polymers consists in frictions bringing the PVC polymer containing unacceptably large amounts of VCM into contact with hot gas such as water vapor at a temperature of from about 93 ° C to about 132 ° C and at atmospheric pressure or higher than atmospheric pressure. The mixture of hot gas and VCM is drained and the VCM regenerated for reuse.

Copolymers or copolymers of polyvinyl chloride (hereinafter referred to as PVC) can be obtained by applying the known polymerisation processes in emulsion, suspension, solution or mass, unfortunately, no technique or method translates the total amount of vinyl chloride monomer (hereinafter VCM) into Polymer A lot of unreacted VCM dissolves or fits into a PVC polymer. VCM, if not removed, will be released later in further poultry or use of polymers. According to the new pollution and toxicity standards proposed by the Environmental Protection Agency and prescribed by the Occupational Safety and Health Act Board, an amount of one hundred ppm. the residual VCM is unacceptably high. PVC must be subsequently treated to remove VCM to a small content (below 10 ppm, preferably less than 1 ppm).

One known method for removing residual VCM from PVC polymers is heating the polymer to about 77 ° C under vacuum to release and evaporate the VCM.

It has surprisingly been found that the remaining VCM can be practically and successfully removed from the PVC polymer by contacting the polymer with a single hot gas at a temperature of about 95 ° C to about 132 ° C and at atmospheric pressure iii, greater than atmospheric pressure. Using the new procedure, residual amounts of VCM were obtained for PVC as low as 0.5 ppm. The PVC polymer does not decompose during the process.

Any PVC polymer, whether hopolymer or copolymer or higher polymer, can be used in the process of the invention. It is understood that the use of low-stability PVC polymers iii with a melting point or a softening point below 93 ° C is not advantageous. The molecular weight of PVC polymers is not crucial. Most preferably, the PVC polymer used is porous, and the executive results are achieved using a PVC polymer in which the porosity is uniform. Polymers of polymerized units of vinyl chloride monomers with copolymerizing vinylidene monomers, such as vinyl bromide, vinyldenchloride, Z -olefins such as ethylene and propylene, acrylic and methacrylic acid, acrylates and methacrylates such as ethyl acrylate and methyl methacrylate, , and the like, as well as mixtures of these monomers, are known in the art or are obtainable. Some or all of these PVC polymers may contain unacceptably large amounts of VCM. According to the invention, the new process of the present invention can be used. to remove residual VCM.

The PVC polymer can be obtained using a method or technological process known in the art. Polymerization processes in emulsion, suspension, solution, and in mass may be applied. The process according to the invention is responsible for PVC in the form of particles containing residual amounts of VCM, and the manner in which polymerization is obtained by PVC is immaterial. However, if the PVC polymer is not obtained by polymerization which gives the PVC polymer completely in the particles, then the polymer should be separated and obtained in the form, particle, before the VCM removal process by contact with the hot gas is used. The right particle size is not crucial as the VCM removal process takes place in all cases. However, removal of VCM through gas contact is faster if the PVC particle size is below 200 micrometers. Characteristically, the PVC polymer used for contact removal has an amount of residual VCM over 1000 ppm by weight in the polymer, and may contain up to 1000,000 ppm VCM and more.

The temperature ranges used in the process according to the invention are from about 93 ° C to about 132 ° C, most preferably from 100 ° C to about 118 ° C. The removal procedure by contact with the gas is carried out at atmospheric pressure or more than atmospheric pressure. Normal overpressure ranges from 0 to 1.72 bar. The PVC polymer is brought into contact with the hot-gas gas, which serves both to heat the PVC and as a carrier for the VCM. Gas is primarily an inert gas such as nitrogen or helium, and is not a gas that can cause oxidation of polymers such as oxygen. Warm air is preferred if it contains most of the inert gases. Saturated water vapor is most advantageous. The temperature and pressures of saturated water vapor are known and can be found in tables for saturated steam (see Chemical Engineers' Handbook, 3rd Ed., McGram-Hill Book., Inc. (1950), pages 277-278). The use of saturated water vapor as a hot gas results in the heating of the PVC polymer, gives positive pressure in the contact area, and acts as a carrier of the VCM.

PVC polymer is used in the form of a suspension of OVC polymer particles in a liquid carrier. Sus— 39 043 - pension facilitates pumping and starting of particles. The liquid carrier may be any that is not a solvent of PVC polymer 'and which has a relatively high boiling point (above 70 ° C). Examples of carrier cancers include ethanol, butanol, cyclohexane, water and the like. Water is the most convenient liquid carrier. The total solids content of the PVC suspension can range from a very low weight percentage to that of the solids content where the suspension can barely be pumped. In practice, the total amount of particulate matter of the PVC slurry is contained in eye sacks. 5% by weight to about 80% by weight of PVC polymers., In suspension PVC polymer in suspension can; is brought into contact with hot gas in various ways. The PVC suspension and the hot gas can be mixed together in a closed boiler, the PVC suspension and the hot gas can be mixed together and released together into a low pressure space, or the PVC suspension and the hot gas can be brought into touching each other in a counterflow process.

As one way of performing the new procedure, the PVC suspension can be brought into contact with the gas in the boiler. The PVC polymer in water, suspension, is placed in a sealed container which can be a polymerization boiler or tank, and hot gas is introduced into the vessel. To ensure good contact between PVC and hot gases, hot gas is generally introduced at the bottom of the pan. PVC blending aids this contact. The pressure in the vessel is atmospheric or above atmospheric, and is usually up to 1.37 bar. The temperature of the vessel and the PVC polymer is in the range of about 93 ° C to about 121 ° C, most preferably from about 93 ° C to about 104 ° C. The duration of contact depends on the capacity of the court and ranges from about 5 minutes to 60 minutes or more. The stability of PVC at elevated temperatures is a phenomenon dependent on the duration of the temperature. Therefore, a shorter contact duration should be applied if the temperature is elevated. Warm gas and VCM are drawn from the steam space in the vessel, and the VCM is regenerated. The PVC is pumped from the vessel into the tank or directly into the drying unit. The amount of residual VCM can be reduced to 4 ppm and below. It was unexpectedly found that not only the residual VCM was successfully and conveniently removed from the PVC polymer, but also that the PVC polymer product did not significantly undergo decomposition by the process. Prior to this discovery, it was widely believed that any operation in the process of heating the PVC to above 82 ° C should have a strong destructive effect on the PVC and its stability. Under the most favorable conditions of the procedure, little or no harmful decomposition of PVC was observed.

Another embodiment of the new process according to the invention is to mix the PVC polymer suspension with warm gas at a temperature and pressure within the specified limits, so that the mixture is injected into a space (such as a boiler) with less pressure (but not vacuum). 'Only rapid touch removal can be applied to the process, then quick removal can be recycled whereby hot gas and VCM are removed from the boiler steam room after injection into the boiler and the PVC is then pumped back to the hot gas mixing room. , and multi-stage rapid removal can be applied by contacting the suspension of PVC to be mixed with hot gas and the mixture injected into the first boiler and then repeated in the following boilers. Temperatures over 121 ° C were also tested using this rapid removal operation. The hot gas and the suspension of PVC were rapidly pressurized into the boiler under atmospheric pressure.

A suspension of PVC with about 35% solids was used.

The most advantageous embodiment of the process according to the invention is when the PVC suspension and the hot gas are brought into contact in the flow column. The hot gas used is saturated water vapor. In contrast to the periodic procedure performed in one boiler, here the PVC polymer, in the form of a suspension, is pumped into the removal column at the top or near the top of the column. The introduction rate may vary, depending on the column capacity, the amount of residual VCM and PVC, the particle dimensions and the porosity of the PVC polymer, and together with the operating temperatures and pressures. The rate of introduction of raw materials into production can range from about 45360 gr of artificial resin per hour to 200 x 45360 gr of artificial weight per hour and more. Water vapor is introduced at the bottom or near the bottom of the column. Therefore PVC and water vapor ~ p'rdt against each other by opposite currents. Pressure and temperature inside the column can be controlled using known methods such as external heating or double wall cooling _± internal heating pipes, using compressed gases. However, it is both advantageous and advantageous to use saturated water vapor in the column which can withstand pressure to warm and to the PVC pressure in the column. For example, saturated water vapor at a pressure of 1.37 bar has a temperature of 109 ° C and below 1.72 bar has a temperature of 116 ° C. The amount of water vapor introduced into the column varies according to the rate of «introduction of the PVC suspension and from the construction of the column.

Water vapor and PVC polymer come into contact in the removal column. It is best that the removal column be a floor column to facilitate flow control and promote evenness of touch. The height and width of the column, the number of floors and its volume and construction are all variable values that can easily be calculated if the flow rates and suspension properties of PVC are known.

According to one advantageous method of carrying out the column removal process, the PVC polymer is pumped from the raw material reservoir into a column with floors near the top of the column. Saturated vapor at about 113 ° C is introduced into the column near the bottom. The pressure in the column is about 1.52 bar. The duration of contact in the column changes according to the feed rate and the capacity of the column. When working with a column having an outer diameter of 76.2 cm and having 17 floors and a PVC feed rate of 2268 kg / hour, the column retention lasts from about 3 minutes to about 15 minutes. The PVC polymer is discharged from the bottom of the column and pumped into the tank or into the dryer. Water vapor with the VCM monomer exits the top of the column and goes to the receiving condenser where the water is then condensed and the VCM regenerated. The PVC polymer entering the column averages about 20,000 ppm of residual VCM. The PVC polymer at the outlet of the column averages about 10 ppm of residual VCM in the polymer. A residual VCM content in a PVC polymer of less than 1 ppm may also be obtained.

The amounts of residual VCM and PVC polymer were determined by analysis of the gas chromatography of the PVC particles, using a given calibration. Stability of PVC mass before and after surgery VCM removal in a column can be determined by comparative aging speeds with a control sample, or by a thermal stability test with a capillary viscometer where the artificial mass mixed with a certain amount of stabilizer (if desired) is placed in the cylinder of the capillary viscometer, heated to 210 ° C and slowly extruded. Obtaining a dark artificial color after - 39 043 - extrusion indicates decomposition of the PVC polymer. Comparative trials between PVC polymer not subjected to the new VCM and PVC stripping process purified by this process show each and every slight discoloration (tanning).

The invention will be illustrated by the following examples.

Examples

Examples in which the suspension of PVC polymer is mixed with hot gas (water vapor) in a boiler type apparatus demonstrate the practicality of this method for removing residual VCM from PVC polymer at temperatures above 93 ° C and at pressures which are atmospheric or greater than atmospheric, without decomposition 'of the polymer. It can be achieved that the residual VCM in PVC is less than 10 ppm. However, it has been verified that more successful removal of VCM can be achieved with a counter current during the suspension of PVC and hot gas, thereby maximizing VCM diffusion. Continuous removal operations require smaller volume capacities and higher productivity as opposed to periodic operation in a boiler type appliance. Therefore, the experiments are directed to the use of a contact removal column to guide a new process of the invention. These experiments were isolated at the laboratory level and at the semi-factory level.

At the laboratory level, the apparatus used was a column with a diameter of 15.24 cm, with 8 floors. Various types of floors were accommodated to the columns, and six different types of floors were assessed (one column dome and five variants of sieve plates with permeable surfaces from 1 to about 10 percent ^{1 with} certain dimensions of the opening and number). The fluid level on all floors, regardless of type, was about 3.81 cm for all experimental cycles. A suspension of PVC with 25% solids in water as a liquid carrier was used. The PVC suspension was pumped in a column above the first floor with an introduction rate of about 0.9 to about 20.4 kg / h. Raw material feed rate determines the length of stay 'in the column. The capacity of the column was about 5.30 liters, based on the rates of introduction of the raw material mentioned above, the duration of stay in the column ranged from about 2 minutes to about 45 minutes. In the PVC polymer, there was initially a residual VCM of about 100 to 2000 ppm. In purified PVC fasting ·· the reduction of residual VCM to 10 ppm was driven. The amount of VCM was determined using gas chromatography analysis.

Experiment A

One series of duty cycles was performed in the contact removal column using the conventional sieve floor type. The duty cycles are separated at about 102 ° C and at about 1.11 bar. The PVC used was a suspension of PVC homopolymers with an average particle size of 130 micrometers and a porosity of 0.14 cc / gr. PVC suspension introduction rates from about 5.44 to about 19.9 kg / h, column residence time from 2 minutes to about 8 minutes. The efficiency of VCM removal at different flow rates was evaluated by measuring the VCM content before entering the column and after leaving the column. The percentage of residual VCM removal varies from 60% to about 98% by weight (relative to the original VCM content of the PVC polymer). Higher removal efficiency is achieved with a longer column stay (6 to 8 minutes) indicating that there is a balance between feed rates and working conditions for optimal VCM removal through gas contact.

Experiment B

One set of duty cycles was performed in the contact removal column using the usual sieve floor and the same feed rate for all duty cycles. The PVC polymer and suspension used in Experiment A were also used in these experiments. The purpose of this series of duty cycles was to examine the effect of temperature and pressure on the removal of VCM from PVC polymers. Saturated water vapor was used as the hot gas. Again, the VCM lagged behind the PVC mcren at the entrance and after leaving the column. The results of the work cycles are summarized in the following table.

Temperature (° C) Pressure fmbara) Percentage removal of residual VCM Duration of stay 4 minutes 77 399 20 94 837,9 55 100 1011 75 109 1463 97.5 110 1529 98.5

Duration of stay 12 minutes

77 399 50 94 837,9 85 100 1011 93 109 1463 over 99 110 1529 over 99

The data show an unanticipated result, that much more favorable and efficient removal of residual VCM is achieved by subconditions and higher temperature and higher pressure. Prior to this discovery, it was believed that removal of the VCM by contact was carried out under reduced pressure (vacuum) in order to conveniently remove the residual monomer in the polymer. Operating conditions, from about 93 ° C to about 132 ° C and pressures from atmospheric to 2.76 bar were checked and evaluated? In these GRANIĆ is ^- sapaža very little iii nikakvo interpretation of the PVC polymer.

Semi-factory process

Based on the favorable results obtained from experiments in the laboratory column for VCM removal, experiments have been performed and I classify to evaluate the feasibility of using the method on a larger scale. Again, the column in which the new procedure will be conducted and evaluated? The column was 76.2 cm in diameter with 18 floors (perforated type). The capacity of the column is limited by its flooding, which is 189 liters / minute of liquid raw material. A suspension of 30% by weight of particulate matter in water was used. - PVC polymer injection rates were from about 771 kilograms / hour to about 2293.7 kg / hour. The rate of introduction of water vapor ranged from 453.6 kg / h to about 2041 kg / h. The stay in the column varied from 1 minute to about 10 minutes (based on the stay in the column about 370 liters). Significant and extensive experiments were carried out with different speeds of PVC polymers (suspensions) and / or saturated water vapor, which are introduced into the column, as well as with different operating temperatures and pressures?

Example I

A PVC homopolymer containing 30% by weight of suspensions — 30043 - ran n water was introduced into the removal column by contact which operated under atmospheric pressure at 100 ° C. The polymer has a particle size of about 100 micrometers and a porosity of about 0.12 cc / g. The results of the experiment show that 80% to 90% of the residual VCM is removed.

Action cycle PVC suspension lit / min Water vapor induction rate (kg / h) Retention time (min) Content inbound raw materials (PPm) Exit VCM (ppm) 1 94,635 1020,6 4 460 45 2 117.35 1632,9 3 520 90 3 143.85 1927,8 2.5 490 80

Example II

The slurry of PVC hopolymer used in Example 1 was introduced into a column with an introduction rate of 56.78 lit / min (1134 kg / h PVC). The rate of introduction of water vapor was 680 kg / h and the residence time was about 6.5 minutes. The operating conditions were 102 ° C and about 1.03 bar. The initial VCM content of the PVC polymer was 2460 ppm, and the final residual VCM content after removal was 330 ppm, indicating yesterday that 86% mass VCM was eliminated.

Example III

The hopolymer slurry used in the previous examples was used in a series of duty cycles with changes in temperature, pressure, PVC slurry introduction rate, and water vapor introduction rate. The results of the work cycles are given in the following table. In all cases, up to 90% VCM was removed up to duty cycle 5, where the PVC suspension injection rate was close to 151 liters per minute.

Working cycle Tempera tour (° C) Push- sak (bars) (PVC suspension introduction rate (1 / min) Water vapor induction rate (kg / h) Holding time, min. VCM ppm content Percentage removals entrance exit 1 104.99 1,24 56.78 680,4 6.5 2810 130 95 2 107.22 1.38 56.78 680,4 6.5 2210 130 94 3 110.54 1,516 th most common 37,85 680,4 8 2600 120 ' 96 4 113,32 1,585 th most common 94.63 907,2 4 1550 100 94 5 113,86 1.65 143.85 1474,2 2.5 950 140 86 1- near the bottom columns. PVC and water vapor varied are from 37,8 lit / min

Example IV

The PVC homopolymer purified at various temperatures and pressures was tested for stability using a thermal stability test using a capillary viscometer. One sample of the same type of PVC homopolymer, which was not purified by the new process, was used for comparison purposes. The data indicate that the purification process has little or no effect on the thermal stability of PVC polymers.

(748.43 kg / h) to 181.8 lit / min (2993.7 kg / h), and the vapor velocities introduced were from 680.39 to 1995.8 kg / h. The residence time varied inversely to the rate of introduction of the suspension and ranged from 2.5 minutes to 10 minutes. The removal percentage of residual VCM monomer varied from 86% to 99.8% by weight. Under conditions of introduction rate of PVC suspension of 94.63 lit / min (1859.7 kg / hour PVC) and introduction rate of water vapor of 907 kg / hour, a residual VCM content of 3 ppm was obtained from a polymer of PVC which had a starting content of VCM from 1500 ppm.

Purification conditions Min. to color changes Temperature ° C Pressure bars Comparative sample purified sample

101,7 1,033 th most common 18 18 111,2 1.45 19 18 113,9 1.59 19 19

Example V

A series of duty cycles were performed using a PVC homopolymer with a porosity of about 0.15 cc / g and an average particle size of 130 micrometers. All duty cycles were run at 103 ° C and at 1,033 to 1,102 bar. Introduction rates of polymer suspension

Example VI

Using the same PVC homopolymer as in Example V, operating at 112 ° C and 1.59 bar, with a suspension introduction rate of 94.6 lit / min and a water vapor introduction rate of 907.2 kg / h, the content was reduced VCM of polymers from 3020 ppm to 25 ppm, 99.2%.

Example VII

The series of experimental duty cycles performed in Example V was substantially repeated, but using a PVC homopolymer with a porosity of about - 39 043 -

0.25 cc / g and an average particle size of about 130 micrometers. PVC is more porous than that used in Example I (0.12 cc / g) and Example V (0.15 cc / g). The particle sizes of the three types of PVC homopolymers are roughly equal, averaging about 100 to 130 micrometers. At temperature limits from 102 ° C to 113 ° C, at atmospheric pressures of 1.59 bar, PVC suspension introduction rates from 56.78 to 132.5 lit / min (1134 to 2631 kg / h), residual VCM content in PVC the refining polymer was below 1 ppm in all duty cycles except one of the fourteen cycles. In this duty cycle the percentage of VCM recovered was still 99% by mass.

After a number of favorable results obtained from the experiments, it has been successfully evaluated that the procedure for the removal of vinyl chloride monomers from polyvinyl chloride polymers has been applied on a larger scale.

A periodic boiler can be used to perform the procedure periodically.

However, it is more successful to remove the monomers by the anti-poisonous Jock suspension of polymer and hot gas with a continuous working process) and with higher productivity. For this method, a sieve-floor column is used whereby a suspension of polymer particles is introduced at the top of the column and saturated water vapor is introduced near the bottom of the column. The anti-current contact occurs at a temperature of about 102 ° C to about 116 ° C and at an elevated pressure of J, 03 to 1.58 bar. A mixture of water vapor and vinyl chloride monomer is drained near the top of the column. The percentage of removed monomer reaches over 99% without decomposition of PVC polymer.

Claims (1)

PATENT APPLICATION A process for removing residual vinyl chloride monomer from a polyvinyl chloride polymer, characterized in that the polymer of polyvinyl chloride having an average particle size of 200 micrometers and a porosity of 0.1 to 0.25 cc / gram as a suspension of particles in water with 5 to 80 weight percent solids particle ₁ contacts 93.3 ° to 132.2 ° C, preferably 100 ° to U5.6 ° C, with warm gas, preferably with saturated water vapor at a pressure of 1.03 to 2.76 bar . Publisher: Federal Patent Office, Belgrade, Uzun Mirkova 1. Print: IPP »Banat« OOUR »Gr Mrka« Kikinda, Boris Kidric 54.