CS248977B1 - The production of emulsion polyvinyl chloride - Google Patents

Abstract

The essence of the solution lies in the fact that the latex with a surface tension that is 1 to 2 times, preferably 1 to 1.2 times the surface tension of the emulsifier used at its critical micellar concentration, is first demonomerized to a vinyl chloride content below 3,000 ppm, preferably below 1,000 ppm, and then subjected to ultrafiltration at latex flow rates over the membrane of 0.3 m/s to 3 m/s.

Description

It is an object of the present invention to provide a process for the production of emulsion polyvinyl chloride with improved qualitative properties and reduced energy consumption during manufacture.

According to the prior art, emulsion polyvinyl chloride is prepared by polymerizing vinyl chloride in an aqueous emulsion in the presence of surfactants, water-soluble radical initiators, buffering agents that maintain the environment during the polymerization reaction, and any other substances such as activators, molecular weight modifiers, and the like.

The polymerization is carried out under pressure at elevated temperature in polymerization autoclaves in a batch or continuous manner. After a sufficient conversion of vinyl chloride, usually above 90%, has been achieved, an aqueous dispersion is obtained as a result of the polymerization which:. it comprises 2 to 10% by weight of unreacted monomer, 40 to 55% by weight of polyvinyl chloride particles and 45 to 55% by weight. a dispersion phase consisting of water and the components of the polymerization system dissolved therein; j. emulsifier, initiator residues and decomposition products thereof, the buffer system used, water-soluble organic or inorganic substances introduced into the system as a monomer impurity, further monomer or polymer decomposition products formed during the polymerization by the polymerization temperature, especially chloride ions. The aqueous dispersion prepared by polymerization is dried in a further process for the production of polyvinyl chloride, usually in spray driers, in which the dispersion is rotated by a rotating disc, single or two-component nozzle, sprayed into a stream of hot air. The drying is carried out at temperatures of usually 60 to 80 ° C in a drying tower, for which a temperature of 150 to 190 ° C of inlet air is required.

The cost of drying the polyvinyl chloride dispersion is inversely proportional to its concentration. It is therefore an attempt to obtain dispersions from the polymerization process with the highest possible concentration. However, the concentration is limited by several factors, such as:

- level of technology - level of polymerization equipment used - quality of raw materials used, especially emulsifier and vinyl chloride - possibilities of heat removal - required qualitative indicators of final polyvinyl chloride.

Usually, on a technical scale by polymerization, dispersions with a concentration of 45-55% by weight are prepared. The preparation of some special types, such as paste-forming types of polyvinyl chloride, sometimes require working below the lower limit, i. j.

below 45 wt. Ensuring stringent requirements for the residual vinyl chloride content in the final product is in some cases technologically solved. by desorption of vinyl chloride by introducing steam into the polyvinyl chloride dispersion, resulting in a reduction of its concentration before drying. The evaporation of all the water from the polymer dispersions thus prepared imposes considerable energy consumption and increases the cost of producing the final polyvinyl chloride powder.

To increase the concentration of latexes, ultrafiltration processes are known in which a semipermeable membrane separates a portion of the water present from the latex prior to its actual spray drying. Due to the high (relatively) solid phase concentration in the polyvinyl chloride latexes, the ultrafiltration process is not easy and the formation of a layer of solids on the filter membranes reduces the ultrafiltration performance and therefore it is necessary to repeat or regenerate the membrane regeneration cycles frequently. In addition to the actual solid phase concentration in the latex, the clogging intensity of the membranes is also influenced by other qualities of the latex, such as the residual vinyl chloride content, the surface tension value and the size and particle size distribution of the polymer.

The issue of self-clogging ultrafilter partially solves the pat. DAS 2,420,922, however, with the need to include a further operation, which is the treatment of membranes prior to ultrafiltration with an emulsifier solution, which imposes increased material and labor time requirements.

These drawbacks are overcome by the invention wherein the polymerization of vinyl chloride is carried out under conditions such that the surface tension of the latex at the end of the polymerization is 1 to 2 times, preferably 1 to 1.2 times the surface tension achieved with the emulsifier used at critical micellar emulsifier concentration. The latex thus prepared is subjected to demonomerization to reduce the vinyl chloride content below 3000 ppm, preferably below 1000 ppm, and only after this operation the latex is subjected to ultrafiltration. In ultrafiltration, the aqueous dispersion of polyvinyl chloride is circulated under a pressure of 0.1 to 1.0 MPa, preferably 0.2 to 0.5 MPa, in an ultrafilter equipped with semipermeable membranes of a suitable type, for example cellulose acetate membranes, cellulose nitrate or polysulfone, polyamide, polypropylene and the like membranes. The ultrafiltration is carried out at a temperature of 10 to 60 ° C, preferably 20 to 40 ° C and at a dispersion flow rate above the membrane of 0.3 m / s to 3 m / s.

In this process, the clogging of the ultrafilter is minimal and the regeneration cycles, respectively. membrane changes are prolonged to 1 to 6 months.

The following examples illustrate the invention, examples 1 to 3 are comparative and examples 4 and 5 illustrate the advantages of the invention.

Example 1

In a 501 liter autoclave equipped with a tempering jacket. at 48 ° C and a pressure of 0.7 to 0.8 MPa polymerized under stirring

800 g demineralized water g potassium persulfate g Na2HPO4. 12 HzO

500 g of a 20% aqueous emulsifier solution with a surface tension at a critical micellar concentration of 24,0 mNm ¹ (sodium 2-ethylhexyl sulfosuccinate)

500 g vinyl chloride.

The raw materials were fed into the autoclave at the beginning of the polymerization and after heating to the polymerization temperature the temperature was maintained by cooling. After the pressure dropped to 0.3 MPa, the unreacted vinyl chloride from the autoclave was slowly degassed with stirring and the autoclave content was cooled. A polyvinyl chloride dispersion having a content of 43.6% by weight was obtained. dry surface, the surface tension of which was 50 µm ^-1 and the residual vinyl chloride content was 9,500 ppm.

1 of the dispersion thus prepared was circulated at a pressure of 0.2 MPa and a temperature of 26 ° C through an ultrafilter fitted with cellulose acetate membranes with a total filtration area of 0.125 square meters. The filtration rate, which was 0.42 cm ^{3 of} filtrate / cm ² h at the start of the experiment, decreased by 25% after 108 minutes. After 2 hours, a concentrate containing 53.2% solids and 825 ml of filtrate was obtained.

Example 2

Part of the dispersion prepared according to Example 1, containing 43.6 wt. The solids content of the vinyl chloride was reduced to 2500 ppm by stirring at 55 ° C. The latex had a surface tension of 49 mNm ^-1 after repeated demonomerization.

1 of the dispersion thus treated was subjected to ultrafiltration under the conditions of Example 1. After 2 hours, a concentrate was obtained containing 54.1 wt. solids. The ultrafilter performance decreased during the ultrafiltering similar to Example 1. After opening the ultrafilter, a deposit of precipitated polyvinyl chloride was visible on the membranes.

Example 3

In a 501 liter autoclave, equipped with a 7 mashing jacket, polymerized at 48 ° C and a pressure of 0.7 to 0.8 MPa with stirring

600 g demineralized water 20 g potassium persulfate 60 g NaHPCh. 12 HZO, total

000 g of a 20% aqueous emulsifier solution with a surface tension at a critical micellar concentration of 24,0 inNni ¹ (sodium 2-ethylhexylsulphosuccinate) and a total

000 g vinyl chloride.

Vinyl chloride and sodium sulfosuccinate were added sequentially in six portions, each time a pressure drop of the previous portion was noted. After the addition of the last emulsifier and vinyl chloride and the pressure drop to 0.3 MPa, the unreacted vinyl chloride from the autoclave was slowly degassed with stirring and the autoclave content was cooled. A polyvinyl chloride dispersion having a content of 44.9% by weight was obtained. solids. The surface tension of the dispersion was 35 mNm ¹ and the residual vinyl chloride content was 10,200 ppm.

1 of the dispersion thus prepared was subjected to ultrafiltration under the same conditions as in Example 1. Filter performance hol at the beginning of 0.39 cm ^{3 of} filtrate / cm ² . hao decreased by 25% after 142 minutes of ultrafiltration. The deposition of the precipitated polymer on the membranes was of the character of Example 2.

Example 4

The latex routes prepared in Example 3 were subjected to repeated demonomerization by heating to 70 ° C for 2 hours while stirring and evacuating the vapors of vinyl chloride vapor. A latex having a surface tension of 32 mNm ¹ and a vinyl chloride content of 950 ppm was obtained.

1 of the dispersion thus prepared was circulated at a pressure of 0.3 MPa and a temperature of 28 ° C through an ultrafilter equipped with polymeric semipermeable membranes with a total filtration area of 0.125 m ² . After one hour, a concentrate was obtained having a content of 54.6% by weight. dry matter and 410 cm ^{3 of} filtrate. Inspection of the filter after ultrafiltration revealed no polymer deposits on the membranes, and no decrease in ultrafiltration rate was found after 1 hour.

The 54.6% concentrate was spray dried in a hot air stream with an inlet temperature of 175 ° C and a temperature of 75 ° C in the drying chamber. Polyvinyl chloride powder was obtained in which the content of 0.91% by weight was determined. % sulphated ash versus 1.09 wt. sulphated ash, as determined for the powder obtained by drying the original 44.9% dispersion. Example 5

A 40 liter polyvinyl chloride dispersion was charged into a 501 liter autoclave equipped with a stirrer and tempering jacket.

48% S77 with 45 wt. dry matter and after heating to 48 ° C, the autoclave was further charged with 2.0 L / h of the aqueous phase containing per liter

25.0 g of an emulsifier whose surface tension at a critical micellar concentration is 26 mNm ^-1 (sodium alkylsultonate with C12-C18 alkyls)

1.5 g NaHCO3

1.0 g K2S2O8 a

1.9 L / h vinyl chloride.

The contents of the autoclave were maintained at 48 ° C and at a pressure of 0.58 to 0.65 MPa. The polyvinyl chloride dispersion was periodically discharged from the autoclave at a rate such that the volume in the autoclave was maintained at 40-45 L. After 48 hours of continuous operation, a dispersion of 45.2 wt. dry matter, a surface tension value of 26 mNnr ¹ and a residual vinyl chloride content of 1200 ppm.

1 of the dispersion thus prepared was circulated at a rate of 300 l / h through an ultrafilter fitted with cellulose acetate membranes with a total area of 0.125 m ² , at a pressure of 0.2 to 0.3 MPa and a temperature of 26 to 30 ° C. After increasing the dry matter of the concentrate from 45.2 wt. to 58 percent by weight. an aqueous dispersion having a dry matter content of 45.2% by weight was continuously added to the circulating solution. at a rate of 1400 cm ³ / h and at the same time the concentrate was discharged at a rate of 350 + 20 cm ³ / h. The average dry matter of the collected concentrate was maintained at 58 + 1% by weight.

The ultrafiltration rate after 100 hours of continuous operation was reduced by an average of only 5% and the filter control showed only minimal clogging of the membranes by the polymer.

The obtained concentrated latex was spray dried in a hot air jet at an inlet temperature of 175 ° C and at a temperature of 75 ° C in the drying chamber. Drying was performed at a 1.25-fold speed compared to drying the unconcentrated latex. The obtained polymer had better thermal stability, lower ash content, and lower water-methanol content compared to the polymer prepared by drying unconcentrated latex.

Claims (1)

7,445,577 containing 45 wt. and after heating to 48 ° C, the autoclave duty was further added to a 2.0 L / hr aqueous phase containing 25.0 g of emulsifier in one liter, the surface tension value at critical microsphere of 26 mNm -1 (al Sodium alkylsulfonate with C12-C18 alkyls 1.5 g NaHCO3 1.0 g K2S2O8 and 1.9 1 / h vinyl chloride The autoclave content was maintained at 48 DEG C. and at a pressure of 0.58 to 0.65 MPa. The polyvinyl chloride dispersion was periodically discharged from the autoclave at such a rate as to maintain the autoclave volume within the range of 40 to 45 ° C. The dispersed dispersion was fed with vinyl chloride in a 65 ° C blended and aspirated duplicator and the degassed latex was collected in a latex reservoir. 48 hours of continuous operation was obtained with a dispersion of 45.2 wt% dry matter, a surface tension value of 26 mNnr1 and residual vinyl chloride of 1200 ppm, 5 liters of the dispersion thus prepared was circulated at 300 l / h through ultrafilteradated acetate with lullo membranes at a total area of 0.125 m 2, at a pressure of 0.2 to 0.3 MPa and a temperature of 26 to 30 ° C. After increasing the dryness of the concentrate from 45.2 wt. to 58 Percent Mass bare to the circulating solution continuously added flood dispersion with a dry matter content of 45.2% by weight. at a rate of 1400 cm 3 / h, while concen- trating the concentrate at 350 + 20 cm 3 / h. The average dry matter of the concentrate collected was maintained at 58 + 1% by weight. The ultrafiltration rate after 100 hours continuous operation was reduced by an average of 5% and the filter control showed only minimal membrane fouling by the polymer. The obtained concentrated latex was dried on a spray drier with a flow of hot air with an inlet temperature of 175 ° C at 75 ° C in a drying chamber. Drying took place at a 1.25-fold rate compared to that of non-concentrated latex. The polymer obtained had a better thermal stability, a lower ash content, a lower water-methanol content than the polymer prepared by drying the non-concentrated latex. SUBSTITUTE A method for producing emulsion polyvinyl chloride by known discontinuous or continuous polymerization processes of vinyl chloride using ultrafiltration of latex and subsequent drying, characterized in that the latex having a surface tension of 1 to 2 times, preferably 1- to 1.2 times the surface area. The invention relates to the emulsifier used at its critical micellar concentration, first monomerized to a vinyl chloride content below 3000 ppm, preferably below 1000 ppm, and then subjected to ultrafiltration at a latex flow rate of 0.3 m / s to 3 m /with. Severografia, n. P., Závod 7, Most 'Price 2,40 Kcs