Polymerization Of Vinyl Chloride Monomer Research Articles

Improvements in protective measures in factories with acetylene hydrochlorination and ethylene oxychlorination techniques declined risk assessment levels and affected liver health status.

Acetylene hydrochlorination and ethylene oxychlorination are the two most common methods of producing vinyl chloride monomer (VCM), which has been linked to liver impairment, hepatocellular carcinoma (HCC), and angiosarcoma of the liver (ASL) in occupational settings. However, whether and how these impairments could be effectively improved from workplace root causes has yet to be discovered. This study aimed to evaluate whether improvements in protective measures in groups Y (408 subjects) and Z (349 subjects) could have an influential impact on the alleviation of liver impairment by comparing risk assessment levels under several semi-quantitative models and results from liver ultrasound detection and liver function tests before and after the improvement. Importantly, significant differences in constituent ratio involved in parameters among age, length of employment, weekly exposure time, smoking status, alcohol consumption, and sleeping quality were found between Y and Z before improvement took place in 2020 (P < 0.05 or P < 0.001), and population distribution by gender between Y and Z was in a large homogeneity with differences in age and length of employment. CSTE involves ore breaking, acetylene generation, steam stripping, outward processing, and welding maintenance, was disqualified in 2020 compared to OEL, and was said to have declined to meet OEL requirements by 2021. Further, a negative correction of fresh air requirement and ventilation air changing rate with ambient concentration toward hazards in Y was stronger in 2021 than in 2020. Significant differences in risk levels in Y between 2020 and 2021 were found as ore breaking, acetylene generation, steam stripping, outward processing, VCM polymerization, welding, and repairing, decreasing to relatively lower risk levels in 2021 from the original ones in 2020 only under the semi-quantitative comprehensive index model. Abnormal rates toward other hepatic symptoms decreased in the majority of positions after the improvement, as referred to by alterations such as ALT, AST, and GGT. Overall, the effect of improvements on protective measures effectively reduced positions' risk assessment levels through ventilation enhancement and airtight strengthening, which further affected abnormal rates toward other hepatic symptoms, and alterations such as ALT, AST, and GGT were much more significant in Y than effect in Z.

Preparation of Ultralow Molecular Weight Poly(vinyl chloride) with Submicrometer Particles via Precipitation Polymerization

Poly(vinyl chloride), with ultralow molecular weight, produced by free radical polymerization either at high temperature or in the presence of chain transfer agents, is widely used as special resins and polymer process additives. This paper reports a new process, called self-stabilized precipitation polymerization, in which the polymerization of vinyl chloride monomer (VCM) is conducted in hydrocarbon diluents without addition of any suspending agent or emulsifier. The merits of this novel strategy include: (1) PVC resins with ultra-low number-average molecular weight (Mn) from 4000 to 15000, which is much lower than Mn of those prepared by conventional suspension and emulsion polymerizations, (2) sub-micrometer PVC particles with near spherical morphology, and (3) the very simple post-polymerization separation process. Under mild stirring, polymerization proceeds stably and smoothly. The influences of main process factors, such as solvents, initiator and monomer concentrations, polymerization time, and temperature on both particle morphology and Mn of the polymer products are investigated systematically. The molar ratio of -CH2-CHCl-/-CH=CH-CH2CHCl, a good indicator of structural defects, is about 1000/0.1 which means the low molecular weights do not result from chain transfer to the monomers. Then the mechanism of this polymerization is proposed. In summary, this novel polymerization technology provides a straightforward method for preparing PVC particulate products with low Mn.

EFFECT OF STIRRING SPEED ON CONVERSION AND TIME TO PARTICLE STABILIZATION OF POLY (VINYL CHLORIDE) PRODUCED BY SUSPENSION POLYMERIZATION PROCESS AT THE BEGINNING OF REACTION

Abstract The effect of changes in the stirring speed during suspension polymerization of vinyl chloride monomer (VCM) was investigated near the particle stabilization. Preliminary tests were conducted to check the highest conversion and information regarding the porosity and particle stabilization of two formulations, which are based on different concentrations of initiators and dispersing agents. The influence of stirring speed during the first 2 h of reaction was investigated for the best formulation, indicating that there was a proportional relationship between the increase in speed and the increase in conversion. The results presented suggest that the highest stirring speeds (900 and 1000 rpm) tended to achieve the same conversion with increasing reaction time. This was also observed with the lower stirring speeds (600 and 700 rpm); however, the conversions obtained were lower than those found with higher stirring speeds. The conversions achieved in 20 to 30 min of reaction were similar for all stirring speeds studied (20 min: 4.8% ± 1.3%; 30 min: 7.5% ±1.4%). However, there was greater variation in conversion for longer reaction times (60 min: 15.9 ± 2.8%; 120 min 36.5 ± 2.4%). Stability of the particles was achieved for 6-8% conversion for all stirring speeds used when breakage and coalescence processes stop. The conversion interval obtained in this work was smaller than the values found in the literature (between 15 and 20%). The effect of stirred conditions on particle size distribution showed that better stability of the particle size occurred at 900 rpm for the system studied. In this case, variations in the particle size decreased when the conversion increased.

Mechanism of synthesis of vinyl chloride catalyzed by carbon load bivalent metal catalyst RCl&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;/C: a density functional theoretical study

Polyvinyl chloride is widely used in industry due to its many properties, and polyvinyl chloride is produced by the polymerization of vinyl chloride monomer. The process of production of vinyl chloride is related to catalyst activity, catalyst carrier and catalyst poisoning effect. In this paper, by using graphene to simulate the surface of activated carbon structure surface, the catalytic mechanism and the feasible reaction channels of synthesis for vinyl chloride catalyzed by RCl2/C (R=Hg2 +, Pt2 +, Cu2 +, Pd2 +, Mg2 +, Cd2+) were theoretically studied under the carbon load conditions. By comparing the activation energy of the velocity control steps of different paths, the optimal reaction channel was determined, and the new reaction channels have been found. Furthermore, the relationship between the catalytic activity of each catalyst and its microscopic properties was analyzed, and the relationship between the reaction activation energy and energy gap of catalyst was also discussed. At the same time, we have studied the poisoning effect of the series of catalysts, and the synthesis catalyst of vinyl chloride was optimized by comparing the characteristics of series catalysts. The results of some experiments are well explained from this work, and our results also provide useful information for the production of vinyl chloride industry.

Enhancement of poly(vinyl chloride) productivity by continuous initiator injection

Polymerization of vinyl chloride monomer with continuous initiator dosage at constant temperature was modeled. Initiators with a half‐life shorter than 0.4 hour at the reaction temperature are suitable for continuous injection. Using a suitable initiator dosage regime, it is possible to keep the reaction rate at its maximum permissible value until critical conversion. It is found that a suitable dosage regime allows the total polymerization time to be reduced by as much as 38.6%, while the final conversion remains unchanged from standard isothermal polymerization. Also, addition of initiators with a half‐life greater than 0.47 hour, preferably from 0.47 hour to the time needed to reach the critical conversion, at the polymerization temperature at the beginning of the reaction are required to achieve a high conversion. The injection of initiators during polymerization into the reactor causes the weight‐averaged molecular weight and corresponding K value of the product to decrease. The drop in K value can be compensated by a decrease in reaction temperature. Initiator dosage shows no significant effect on the structural chemical defects in the PVC chains. Dispersibility and persistent gels (fisheyes) were not measured. J. VINYL ADDIT. TECHNOL., 23:248–258, 2017. © 2015 Society of Plastics Engineers

A combinatorial approach to evaluation of monomer conversion and particle size distribution in vinyl chloride emulsion polymerization

This work is targeted to study emulsion polymerization of vinyl chloride monomer (VCM) using experimental and mathematical methods. To fulfill this goal, a computer code was developed on the basis of zero–one population balance by which the effects of initiator and emulsifier concentration on the evolution of VCM conversion were investigated in the course of polymerization. The model was also trained to capture the coagulation of the particles. This enabled to adopt a reliable way of evaluating the particle size distribution (PSD). In particular, the rates of homogeneous and micellar nucleation mechanisms were simulated and reasonably predicted alterations in the PSD and the number of polymer particles under the influence of aforementioned parameters. The results from modeling were satisfactorily consistent with the experimental outputs and obviously visualized the impact of initiator and surfactant concentration on the PSD of the prepared PVC latexes.

Failure Analysis of Process Equipment Used in the Production of Polyvinyl Chloride

Polyvinyl chloride (PVC) is produced in petrochemical plants by polymerization of vinyl chloride monomer prepared by cracking of ethylene dichloride, which takes place at 500 °C in furnace tubes made of 347 stainless steel. Hydrochloric acid resulting from the cracking process is recycled in the gaseous state and used in an oxychlorination process. However, after less than half the life expectancy, gas leakage has been detected due to a crack in a furnace tube. Another problem has been encountered in the dewatering and drying unit of PVC where the outlet gas at a temperature of 40–60 °C contains 110 ppm of hydrogen. In this case, a dryer support made of 304 stainless steel has fractured. Various electron-optical techniques and x-ray diffraction have been used to characterize the microstructure of damaged materials. The mechanical strength has been evaluated by microhardness measurements. It is concluded that the furnace tube has been damaged by chloride stress corrosion cracking, which is correlated with precipitation of Cr-rich phases including M23C6 carbide and sigma phase due to long-term exposure at elevated temperatures as well as the presence of chloride ions in the environment due to un-cycled HCl. However, the dryer support is found to be damaged by hydrogen-assisted quasi-cleavage.

Adsorption of PVA on Stainless Steel During the PVC Synthesis

The formation of scale on the inner part of reactors during suspension polymerization of Vinyl Chloride Monomer (VCM) has always been a technical and economical problem for PolyVinyl Chloride (PVC) producers. This process leads to the presence of a thick and large polymer build-up, which is stuck to the surface of the autoclaves. This phenomenon will affect among others the properties of the final product at the end of the polymerization and the reactor productivity. The aim of this study was to investigate the physical and chemical origins of this scale formation and to determine the factors responsible for this process. Stainless steel plates (to simulate the reactor's walls) were immersed in the polymerization reactor and analyzed as a function of the immersion time. Infrared Reflection Absorption Spectroscopy (IRRAS) and optical microscopy were used in this study to follow the crust formation during the polymerization process in order to propose a mechanism for the formation of scale.

On‐line acoustic attenuation spectroscopy of emulsions stabilized by vinyl alcohol–vinyl acetate copolymers: a model system for the suspension polymerization of vinyl chloride

AbstractBACKGROUND: Poly[(vinyl alcohol)‐co‐(vinyl acetate)] (PVA) copolymers obtained by partial hydrolysis of poly(vinyl acetate) are currently used as industrial stabilizers in the suspension polymerization of vinyl chloride monomer (VCM). Their molecular characteristics, mainly the average degree of hydrolysis (DH) and average degree of polymerization (DPw), have a major influence on the monomer droplet size and the properties of the final poly(vinyl chloride) resin.RESULTS: The average droplet size and size distribution of chlorobutane/water emulsions, as a model system for VCM/water emulsions, were studied using acoustic attenuation spectroscopy on‐line with an agitated laboratory reactor. The emulsions were stabilized by PVA with DH values between 73 and 88 mol% and DPw values between 450 and 2500. The effects of agitation speed, stirring time and concentration of the PVA copolymers were investigated. An attempt was made to correlate the interfacial tension and the droplet size.CONCLUSION: On‐line acoustic spectroscopy appears to be a suitable technique for the real‐time control of the droplet size of monomer suspensions. The advantages and limitations of the technique are outlined. The validity and the application limits of the commonly cited correlation between the droplet size and the Weber number are established for polymeric surfactant‐stabilized emulsions. Copyright © 2009 Society of Chemical Industry

Particle Formation in Vinyl Chloride Emulsion Polymerization: Reaction Modeling

A mathematical model is developed to help quantify and improve our understanding of the formation of particles and the evolution of the particle size distribution (PSD) in the emulsion polymerization of vinyl chloride monomer (VCM). A special feature of the model is the computation of the coupled radical number and particle size distributions by means of the zero−one−two population balance equations. This approach is shown to be necessary when modeling processes that involve particle nucleation. Preliminary results are presented to illustrate the ability of the model in interpreting experimental data.

Preparation of poly(vinyl chloride) latexes using a dual surfactant system: The effect in the particle size distribution

AbstractThe control of the average particle size and size distribution in the emulsion polymerization of vinyl chloride monomer is an important parameter to determine, not only the latex characteristics, but also the properties of the final dispersion powder in several industrial applications. It is possible to manipulate the particle size distribution (PSD) by applying a mixture of an anionic surfactant‐fatty alcohol before the start of the free radical polymerization. Contrary to the procedures of the miniemulsion and the derivative diffusional swelling techniques, no kind of high shear is applied to the monomer and/or surfactant mixtures. In fact, the concentration and selection of the anionic surfactant, together with the fatty‐alcohol, can play an interesting role on the final PSD of the polymer's particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Preparation and characterization of poly(vinyl chloride)/layered double hydroxides nanocomposite via in situ suspension polymerization

AbstractPoly(vinyl chloride)/layered double hydroxides (PVC/LDHs) composite resins were prepared by in situ suspension polymerization of vinyl chloride monomer in the presence of LDHs intercalated with dodecyl sulfate anions (LDH‐DS), and were further processed to obtain PVC/LDH‐DS nanocomposites. It was found that the mean particle size of PVC composite resins decreased as LDH‐DS was added in the polymerization system. The 5 and 10% weight loss temperatures of PVC resins significantly increased with the increase of LDH‐DS weight fraction in the composite resins. The transmission electron microscopy images showed that LDH‐DS particles were partially intercalated and partially exfoliated, and well distributed in the PVC nanocomposites. The storage modulus below the glass transition region and the glass temperature of the PVC/LDH‐DS nanocomposites are greater than that of the pristine PVC. The mechanical properties of PVC/LDH‐DS nanocomposites indicate that LDH‐DS nanoparticles stiffen and toughen PVC. The tensile strength, Young's modulus, and Charpy notched impact strength of the PVC/LDH‐DS nanocomposites are greater than those of the pristine PVC and PVC/LDH‐DS composites prepared by the melt blending. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1471–1477, 2006

Particle features of poly(vinyl chloride) resins prepared by a new heterogeneous polymerization process

AbstractThe heterogeneous polymerization of vinyl chloride monomer (VCM), with n‐butane as the reaction medium, was used to prepare poly(vinyl chloride) (PVC) resins. The particle features of the resulting resins and the particle formation mechanism of the polymerization process were investigated. The PVC resins prepared by the new polymerization process had a volume‐average particle size comparable to that of suspension PVC resins and a lower number‐average particle size. From scanning electron micrographs, it could be seen that the new PVC resins had a regular particle shape and a smooth surface with no obvious skin. They also had a high porosity. The new PVC resins were composed of individual and loosely aggregated primary particles. The diameter of the primary particles in the top layer of the grains was smaller than that of the primary particles in the center part of the grains. On the basis of the particle features of these PVC resins, a particle formation mechanism for the new polymerization process was proposed. PVC chains precipitate from a VCM/n‐butane mixed medium to form primary aggregates at a very low conversion, and the primary aggregates of the PVC chains aggregate to form primary particles, which further aggregate to form grains. The primary particles and grains grow by the capture of newly formed PVC chains and their primary aggregates and by polymerization occurring inside the aggregates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 954–958, 2003

Bulk and suspension polymerization of vinyl chloride: the two-phase model

An in-depth investigation into the validity of the two-phase model in describing the bulk and suspension polymerization of vinyl chloride monomer is carried out, in the light of the latest theoretical and experimental works that have appeared in the literature. Particular attention is paid to the influence upon the reaction of the transfer of free radicals and of the distribution of the chemical initiators between the two phases. Equations giving, respectively, the kinetic chain length and the degree of polymerization of the polymer, as a function of conversion, are calculated. A good agreement between these theoretical models and the experimental data is observed. Methods for the detemination of the kinetic parameters, and numerical values of some of them are also given.

Calculation and Applications of VCM Distribution in Vapor/Water/Solid Phases during VCM Polymerization

Abstract The distribution of vinyl chloride monomer (VCM) in vapor, water, swollen polymer, and free monomer phases as a function of conversion of VCM can be calculated from the related partition coefficients. It was found that the amount of monomer in the vapor and water phases is particularly significant, being 20% (at 60°C) of that in the polymer phase at the peak exotherm. Neglecting the VCM dissolved in water and that in the head space of the reactor would seriously overestimate the polymerization rate and overdesign the required cooling capacity of the reactor. From the distribution the relation between conversion (x) vs pressure (P) after the pressure starts to drop can be developed and used to determine conversion at termination by pressure measurement. The results of ×vs P from our partition coefficient approach are consistent with those derived from Flory-Huggin's equation. Also the knowledge of VCM distribution at termination of the polymerization will assist VCM accountability and stripper design.

Compatibility of polyacrylates and polymethacrylates with poly(vinyl chloride): 1. Compatibility and temperature variation

Mixtures of a series of polymethacrylates and polyacrylates with PVC were prepared by solvent casting from methyl ethyl ketone. Some mixtures were also prepared by mechanical mixing and in situ polymerization (polymerization of vinyl chloride monomer in the presence of the other polymer). The mixtures were assessed for compatibility by dynamic mechanical measurements and optical clarity. It was found that all polymethacrylates from poly(methyl methacrylate) to poly(n-hexyl methacrylate) were compatible with PVC as were poly(n-propyl acrylate) and poly(n-butyl acrylate). Higher chain polyacrylates are incompatible. Poly(methyl acrylate) and poly(ethyl acrylate) appear incompatible with PVC when mixtures are prepared by solvent casting, but compatible when prepared by in situ polymerization, and mechanical mixtures show some sign of compatibility. It seems possible that in this case the solvent interferes with the compatibility. Mixtures of PVC with poly(n-hexyl methacrylate), poly(n-butyl acrylate) and poly(n-propyl acrylate) phase separate when heated in the region between 100°C and 160°C indicating the existence of a lower critical solution temperature.

Studies on poly(vinyl chloride). III. The role of the precipitated polymer in the kinetics of polymerization of vinyl chloride

AbstractIn polymerization of vinyl chloride monomer, free radicals precipitate on or within aggregates of partially swollen dead polymer. Polymerization on the solid polymer is characterized by autoaccelerating rates due to a progressive reduction in termination rate. This reduction in termination rate is due to the fact that as the reaction progresses and more polymer accumulates there is a decrease in probability that chain transfer of polymer radicals to monomer will generate a mobile radical, which can readily terminate an occluded or stuck free radical. From the appearance of the particles of solid polymer in the system, it has been concluded that free radicals precipitate both on polymer particle surface and inside the open structure of polymer particles.