Method for producing PVC in aqueous suspension using a mixture of initiator and activity control agent

Abstract

The present invention relates to a method for producing PVC, and in particular provides a method for producing PVC by polymerization of vinyl chloride, comprising the steps of: (a) reacting an acyl halide with a peroxide in a reactor to form a diacyl peroxide; (b) reacting an alkyl haloformate with the peroxide in the same reactor to form a dialkyl peroxydicarbonate without removing the diacyl peroxide formed in step (a), thereby producing a mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate; and (c) using the mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate as an initiator mixture for the polymerization of vinyl chloride.

Description

[Technical Field]

[0001] This invention relates to a process for producing PVC, and in particular to a process which involves polymerizing vinyl chloride using a mixture of initiators. [Background technology]

[0002] Polyvinyl chloride (PVC) is one of the most important thermoplastic materials on the market today. It has excellent mechanical and physical properties, which makes it suitable for a wide variety of applications. Several methods for producing PVC are known. For example, PVC can be produced by suspension polymerization of vinyl chloride in a suspension and in the presence of a suspending agent. This produces a slurry (or suspension) of PVC particles, typically with a particle size of around 100-200 microns. The resulting PVC slurry is typically dried by centrifugation followed by fluidized bed drying to obtain porous (i.e., adsorbent) PVC. PVC produced by the suspension process is referred to as "S-PVC." S-PVC can absorb plasticizers to form a dry blend. PVC can also be produced by a process commonly known as paste polymerization. The paste process can be characterized by the polymerization producing a latex of polymer particles that are relatively small in size, typically 0.2 to 5 microns, compared to the S-PVC process. The latex can be dried, for example, by spray drying, to produce PVC particles in the form of agglomerates. The dried PVC polymer particles are typically much smaller than the dried particles produced by the suspension PVC process. Whether produced by suspension or paste techniques, the general process for polymerization involves polymerization in a solvent, usually water, and the use of one or more initiators, usually peroxides or other compounds that decompose to provide radicals that can initiate polymerization. Initiators can have half-lives on the order of seconds to hours at the polymerization temperature and can be added to not only initiate the polymerization but also to provide additional polymerization activity during the polymerization.

[0003] Vinyl chloride polymerization is an exothermic reaction, and the reaction is typically maintained at the desired temperature by cooling within the reactor jacket, particularly using cooling water. In preferred operation, the reactor is operated as close as possible to the reactor's maximum cooling capacity to maximize reaction rate / reactivity and, therefore, process productivity. A common challenge is controlling the amount of initiator to achieve a fairly steady polymerization rate that is as close as possible to the available cooling capacity. For example, using an initiator with a relatively long half-life can result in a longer reaction time for the reaction to reach the desired production rate, and there is also a lag between adding more initiator and the increase in reactivity. On the other hand, using an initiator with a relatively short half-life can result in a faster increase in reactivity, but the effect is short-lived, requiring continuous, or at least periodic, addition of initiator to maintain reactivity. To overcome this problem, it is known to use a mixture of initiators. For example, EP 1618137 describes a process using a mixture of initiators with different half-lives, where the initiator with the shorter half-life is introduced into the reactor for at least the initial period of polymerization to provide reactivity in the early stages.

[0004] While this allows for some degree of reactivity control, initiators with short half-lives are inherently relatively unstable. Therefore, such initiators are typically refrigerated during transport and storage, and for this reason, they are often stored in solutions containing alcohol. This increases the chemical oxygen demand of the initiator solution. For example, diisobutyryl peroxide is provided as a water and alcohol solution and is recommended for storage at -20°C. When added to a process continuously or intermittently over a period of time, the initiator may reside in the piping or injection system to the reactor at room temperature or temperatures well above room temperature for a relatively long period of time. Therefore, it may be necessary to cool the pipes or take other measures to mitigate the risk of initiator decomposition in the pipes.

[0005] Another problem with initiator mixtures is that additives that can be used to control the reactivity of one initiator may be ineffective with other initiators. In particular, it is common to use suitable agents ("inhibitors" or "activity control agents") in the process that can slow the reaction rate by terminating the reaction. Examples of known activity control agents include alkali metal halides, nitric oxide, and alkali metal nitrites. For example, alkali metal halides can be used to terminate the reaction of initiators such as peroxydicarbonates, thereby controlling their reactivity. However, many of these activity control agents are ineffective when used in combination with peroxides such as diisobutyryl peroxide. Therefore, it remains desirable to provide a process for producing PVC that maintains high reactivity throughout the polymerization process in a safe manner, and it is also desirable to simplify the provision and use of initiators in such processes. Summary of the Invention

[0006] Thus, in a first aspect, the present invention provides a process for polymerizing PVC, comprising the steps of: a. reacting an acyl halide with a peroxide in a reactor to form a diacyl peroxide; b. reacting an alkyl haloformate with a peroxide in the same reactor to form a dialkyl peroxydicarbonate without removing the diacyl peroxide formed in step (a) to produce a mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate; and c. using a mixture comprising a diacyl peroxide and a dialkyl peroxydicarbonate as an initiator mixture for the polymerization of vinyl chloride; The present invention provides a method comprising: A particular advantage of the process of the first aspect of the invention is its simplicity. In particular, the mixture of initiators can be prepared just before it is required for use, and the mixture can be used as formed. In particular, it is not necessary to carry out any steps to purify the mixture obtained in step (b), and in this case no storage is necessary.

[0007] Thus, in a preferred embodiment, the mixture produced after reacting the alkyl haloformate with peroxide to form the dialkyl peroxydicarbonate in step (b) is used without purification to polymerize vinyl chloride in step (c) within 24 hours after the start of step (a) of the process. The mixture is preferably used within 12 hours, more preferably within 6 hours, such as within 4 hours, or even within 1 hour after the start of step (a) of the process. In this embodiment, the mixture is not stored for an extended period of time before use, but preferably is stored refrigerated, such as in the range of 1°C to 10°C, or in the range of 1°C to 5°C, until use. In some embodiments, as further described below, the mixture produced after reacting the alkyl haloformate with peroxide to form the dialkyl peroxydicarbonate in step (b) may comprise an aqueous phase and an organic phase, and the organic phase can be separated from the aqueous phase to provide a mixture comprising a diacyl peroxide and a dialkyl peroxydicarbonate for use in step (c).

[0008] Although not generally preferred, it is also possible to prepare a mixture according to steps (a) and (b) and then use it in polymerization according to step (c). Thus, the mixture produced after reacting the alkyl haloformate with peroxide to form the dialkyl peroxydicarbonate in step (b) can be removed from the reactor and stored. In such embodiments, the mixture comprising the diacyl peroxide and dialkyl peroxydicarbonate can be stored for 24 hours or more, e.g., 48 hours or more, prior to use in step (c). To permit storage for such periods, the mixture must be cooled during storage, e.g., to 10°C or below, e.g., 5°C or below. In embodiments where the mixture produced after reacting the alkyl haloformate with peroxide to form the dialkyl peroxydicarbonate in step (b) comprises an aqueous phase and an organic phase, it is preferred to separate the organic phase from the aqueous phase to provide the mixture comprising the diacyl peroxide and dialkyl peroxydicarbonate for storage (and later for subsequent use in step (c)). This allows the mixture containing the diacyl peroxide and the dialkyl peroxydicarbonate (i.e., the organic phase) to be cooled and stored below 0°C.

[0009] The reaction in step (a) involves reacting an acyl halide with a peroxide in a reactor to form a diacyl peroxide. While the reactants can be added in any suitable order, preferably the reaction involves adding water, a base, and a peroxide to the reactor in a first step or steps. In preferred embodiments, an organic solvent is also added at this stage. In some embodiments, particularly when an organic solvent is also used, the water may be brine, i.e., water containing sodium chloride. This increases the density of the aqueous phase, which may improve phase separation if desired. Next, an acyl halide is added, at which point an exothermic reaction occurs to produce diacyl peroxide. Typically, the reactor is cooled, and the reaction is maintained at a temperature below 20°C, even if the reaction of the acyl halide generates heat. For example, the reaction can be carried out at a temperature range of 1 to 15°C. The acyl halide can be introduced at a rate that does not cause the temperature to rise above 20°C, preferably below 15°C, due to the exothermic reaction. The reaction can be carried out at any suitable pressure, but is usually carried out at atmospheric pressure.

[0010] The acyl halide is preferably an acyl chloride. Suitable acyl chlorides are defined by the required diacyl peroxide. For example, if diisobutyryl peroxide is desired, then an isobutyryl halide, preferably chloride, is used. In a preferred embodiment of this first aspect, the diacyl peroxide is one in which the acyl has 2 to 8 carbon atoms. The preferred base for this step is an alkali metal hydroxide, with sodium hydroxide being preferred. The preferred peroxide (used as a reactant) is hydrogen peroxide. Typical organic solvents that can be used include any that are immiscible with water, allowing for separation of the aqueous and organic phases, if desired. Suitable examples of organic solvents include alkanes such as pentane and diesters. Preferred organic solvents have a freezing point below 0°C, e.g., below -5°C, particularly when the organic phase can be separated for storage of the mixture prior to step (c) of the present invention. A particularly preferred organic solvent is dioctyl adipate.

[0011] The reaction in step (b) involves reacting an alkyl haloformate with peroxide to form a dialkyl peroxydicarbonate. The reaction typically involves adding additional peroxide and alkyl haloformate to the solution in the reactor from step (a). Additional base is then added, at which point an exothermic reaction occurs to produce the dialkyl peroxydicarbonate.

[0012] As with step (a), the reactor is typically cooled in this step. (In practice, the reactor is typically cooled throughout steps (a) and (b) of the synthesis, as well as between steps and at the end of the synthesis.) In particular, in this step, the reaction is maintained at a temperature below 20°C, even if the reaction of the alkyl haloformate generates heat. For example, the reaction in this step can be carried out at a temperature range of 1 to 15°C. The alkyl haloformate can be introduced at a rate such that the temperature does not exceed 20°C, preferably 15°C, due to the exothermic reaction.

[0013] Again, the reaction can be carried out at any suitable pressure, including atmospheric pressure. Typically, step (b) is carried out at the same pressure as step (a), and preferably the entire synthesis is carried out at the same pressure, most preferably atmospheric pressure. The alkyl haloformate is preferably an alkyl chloroformate. The appropriate alkyl haloformate is determined by the required dialkyl peroxydicarbonate. For example, if diethyl peroxydicarbonate is desired, an ethyl haloformate, preferably ethyl chloroformate, is used. In a preferred embodiment of this first aspect, the dialkyl peroxydicarbonate is a dialkyl peroxydicarbonate in which the alkyl has 1 to 4 carbon atoms.

[0014] The preferred base for this step is an alkali metal hydroxide, again preferably sodium hydroxide. The preferred peroxide (used as a reactant) is hydrogen peroxide. Additional water can be added at this step if desired. In particular, if sodium chloride was not added in the first step, it can be added in this step. An organic solvent can be added in this step if desired, especially if one was not added in the first step. In the present invention, the formation of diacyl peroxide and dialkyl peroxydicarbonate are carried out sequentially. The advantage of this method is that the relative amounts of diacyl peroxide and dialkyl peroxydicarbonate in the resulting mixture can be easily controlled (by using appropriate amounts of reactants in each step), and a "mixed" product can be avoided.

[0015] Regarding the first of these points, the mixture of diacyl peroxide and dialkyl peroxydicarbonate formed (and used) may comprise any suitable relative ratio of diacyl peroxide to dialkyl peroxydicarbonate. Typically, the weight ratio of diacyl peroxide to dialkyl peroxydicarbonate is 1:4 to 4:1, more preferably 1:3 to 3:1, for example 1:3 to 2:1, and most preferably 1:3 to 1:1. Regarding "mixed" products, some known prior art processes react acyl chloride and alkyl chloroformate with hydrogen peroxide in a single step to form a mixture of diacyl peroxide and dialkyl peroxydicarbonate. This produces a mixture of the desired diacyl peroxide (containing an acyl group based on the chloride reactant) and dialkyl peroxydicarbonate (containing an alkyl group based on the chloroformate reactant), but typically also produces a significant amount of acyl peroxycarbonate, a "mixed" reaction product. Processes for reacting dialkyl pyrocarbonate, acyl anhydride, and hydrogen peroxide are also known, which also produce peroxide and peroxydicarbonate, but also mixed acyl peroxycarbonates. In contrast, the method of the present invention can provide a mixture free of such compounds. In particular, the presence of mixed products can be avoided by ensuring that the acyl halide is completely reacted in step (a) before adding the alkyl haloformate and further peroxide in step (b).

[0016] Generally, it is preferred that the mixture obtained at the end of step (b) be free of acyl peroxycarbonates, although small amounts of "mixed" product may be tolerated. Thus, preferably, the composition is free of acyl peroxycarbonates or contains less than 20% by weight of acyl peroxycarbonates, based on the total weight of diacyl peroxides and dialkyl peroxydicarbonates in the mixture. More preferably, the composition is free of acyl peroxycarbonates or contains less than 10% by weight, e.g., less than 5% by weight, of acyl peroxycarbonates, based on the total weight of diacyl peroxides and dialkyl peroxydicarbonates in the mixture.

[0017] In step (c) of the first embodiment, a mixture comprising a diacyl peroxide and a dialkyl peroxydicarbonate is used as an initiator mixture for the polymerization of vinyl chloride. The polymerization of vinyl chloride can be carried out under any conditions suitable for such a reaction, some of which are further described below. In a particularly preferred option, the polymerization is carried out in the presence of an activity control agent. Suitable activity control agents are well known in the art, but for the purposes of the present invention, preferably include alkali metal halides, nitric oxide, or alkali metal nitrites. Preferably, the activity control agent is an alkali metal halide, more preferably an alkali metal iodide such as sodium iodide or potassium iodide. Most preferably, it is potassium iodide.

[0018] In a further preferred embodiment of this first aspect, the diacyl peroxide is a diacyl peroxide in which the acyl has from 2 to 8 carbon atoms, and the dialkyl peroxydicarbonate is a dialkyl peroxydicarbonate in which the alkyl has from 1 to 4 carbon atoms. In the present invention, it has been found that the use of selected activity control agents in conjunction with a defined mixture of diacyl peroxide and dialkyl peroxydicarbonate results in particularly favorable polymerizations. Thus, in a second aspect, there is provided a method for producing PVC comprising polymerizing vinyl chloride in suspension in an aqueous medium using a mixture of initiators and an activity control agent, the activity control agent comprising an alkali metal halide, nitric oxide or an alkali metal nitrite, the mixture of initiators comprising: a. a first initiator, wherein the acyl is a diacyl peroxide having 2 to 8 carbon atoms; and b. a second initiator, wherein the alkyl is a dialkyl peroxydicarbonate having 1 to 4 carbon atoms; A method is provided, comprising:

[0019] In particular, it has been found that while a given activity control agent is typically ineffective when used alone with a first initiator / diacyl peroxide, when used in conjunction with a mixture of a diacyl peroxide and a dialkyl peroxydicarbonate, as in this second embodiment, where the alkyl in the dialkyl peroxydicarbonate has 1 to 4 carbon atoms, the activity control agent is effective in controlling polymerization. In particular, in this particular combination, it has been found that the selected activity control agent is also effective in terminating the radicals resulting from the diacyl peroxide initiator. In this second embodiment, preferably the activity control agent is an alkali metal halide, more preferably an alkali metal iodide such as sodium iodide or potassium iodide, most preferably potassium iodide. In a preferred embodiment of this second aspect, the mixture of initiators in the process is obtained by adding a mixture comprising the first and second initiators to the process, i.e., the initiators are not added to the process separately, but are added together.

[0020] In a preferred embodiment of this second aspect, the mixture containing the initiator is added to the process only at the start of the polymerization. This method is particularly advantageous because it allows the initiator mixture to be completely removed from the feed pipes and injection means on the reactor. For example, the pipes / injection means can be flushed with a solvent (usually water) to remove any residual initiator. This provides a safe process without the need to cool the pipes or injection means.

[0021] Preferred features of the mixture of initiators (diacyl peroxide and dialkyl peroxydicarbonate) used in the process of this second embodiment are generally as described for the first embodiment. For example, the mixture may contain diacyl peroxide and dialkyl peroxydicarbonate in any suitable relative ratio, but preferably the weight ratio of diacyl peroxide to dialkyl peroxydicarbonate is 1:4 to 4:1, more preferably 1:3 to 3:1, for example 1:3 to 2:1, and most preferably 1:3 to 1:1. Similarly, the absence of acyl peroxycarbonates in the initiator mixture (or more generally during polymerization) is generally preferred, although small amounts of "mixed" product may still be acceptable. Preferably, the process contains no acyl peroxycarbonates or contains less than 20% by weight of acyl peroxycarbonates, based on the total weight of diacyl peroxides and dialkyl peroxydicarbonates in the mixture. More preferably, the composition contains no acyl peroxycarbonates or contains less than 10% by weight, e.g., less than 5% by weight, of acyl peroxycarbonates, based on the total weight of diacyl peroxides and dialkyl peroxydicarbonates in the mixture.

[0022] In a most preferred embodiment, a process is carried out according to both the first and second aspects of the invention, in particular the initiator mixture of the second aspect is formed by the process of the first aspect. In preferred embodiments of both the first and second aspects of the present invention, the diacyl peroxide may be one in which the acyl has 2 to 5 carbon atoms, for example 2 to 4 carbon atoms. The most preferred diacyl peroxide is diisobutyryl peroxide. In preferred embodiments of both the first and second aspects of the present invention, the dialkyl peroxydicarbonate may be a dialkyl peroxydicarbonate wherein the alkyl has 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms. A preferred dialkyl peroxydicarbonate is diethyl peroxydicarbonate.

[0023] Looking more generally at the steps of the polymerization process, the polymerization process can be carried out as any suitable polymerization process, but is preferably carried out as a suspension polymerization process. The polymerization step can be suitably carried out in any suitable equipment known for suspension polymerization processes. Polymerization typically occurs in aqueous suspension in the presence of a suitable suspending agent. While any suitable suspending agent can be used, particularly preferred suspending agents are polyvinyl acetates and water-soluble cellulose esters of various degrees of hydrolysis. These suspending agents can be used in combination with a secondary suspending agent, if necessary. The amount used can vary widely, but is typically 0.05 to 1.5% by weight, calculated on the vinyl chloride used. Other additives, such as buffers and chain transfer agents, conventionally used in the production of PVC by suspension polymerization of vinyl chloride may also be present.

[0024] One or more chain transfer agents can be used in the polymerization process. Chain transfer agents are known to be used to control molecular weight in the polymerization of vinyl chloride, particularly in polymerizations conducted at elevated temperatures and pressures. Most preferably, at least one chain transfer agent is present at the beginning of the polymerization reaction. Suitable chain transfer agents are known. They typically have at least one weak chemical bond to facilitate the chain transfer reaction. Common chain transfer agents include thiols and halocarbons such as carbon tetrachloride. In the present invention, thiols, particularly alkanethiols, such as mercaptans (methanethiol), most preferably 1-dodecanethiol, have been found to provide particularly good results.

[0025] The polymerization can be carried out at any suitable temperature. Typically, the polymerization is carried out at a temperature of 30 to 80° C. In some embodiments, the temperature may be changed during the polymerization, for example, by increasing the temperature. The polymerization can be carried out at any suitable pressure. Typically, the polymerization is carried out at a pressure in the range of 2 to 20 bar (200 to 2000 kPa), for example, 6 to 12 bar (600 to 1200 kPa). (All pressures used herein are absolute pressures unless otherwise specified.) The polymerization process may produce a homopolymer or may produce a copolymer by adding one or more monomers other than vinyl chloride. Typical comonomers include, for example, alkyl acrylates and methacrylates, and acetates such as vinyl acetate.

[0026] Polymerization is typically initiated by charging the necessary solvent, vinyl chloride, and other reactants to a reactor followed by the introduction of a mixture of initiators, which may be used in conventional amounts, generally speaking, from 0.01 to 1% by weight calculated on the vinyl chloride. It is generally preferred to add all of the initiator mixture at the beginning of the process, although in some embodiments, a portion of the initiator mixture may be added during polymerization. When used, the activity control agent is present in an amount appropriate to provide the necessary inhibition. Generally speaking, it is added during the polymerization as needed to control the exotherm / polymerization temperature and keep the reaction rate under control. In a preferred embodiment, the activity control agent is added continuously, adjusting the addition rate as needed to control the exotherm of the polymerization. The polymerization is continued until the desired conversion of the monomer is achieved.

[0027] If necessary, an inhibitor (or particularly an additional inhibitor or an additional amount of an inhibitor already present) may be added to terminate the polymerization. Any suitable inhibitor may be used. Examples of suitable initiators include bases such as alkali metal hydroxides and amines (including diethylhydroxyamine), and also α-methylstyrene. Preferred inhibitors in the present invention are alkali metal halides, and more preferably, the same alkali metal halide is used as both the inhibitor and the activity control agent. Most preferably, potassium iodide is used. However, larger amounts are generally used in this step, as the purpose of this step is to permanently terminate the polymerization. If necessary, an antifoaming agent may be added at the end of the polymerization. The reactor may be depressurized to remove any unreacted monomers and recover the polymer solids. Typically, the polymer solids undergo a stripping step, followed by filtration and drying. The polymer may be dried by any suitable method, such as a fluidized bed dryer. As previously mentioned, the process of the first aspect of the present invention can provide a mixture of diacyl peroxide and dialkyl peroxydicarbonate that contains no or relatively little "mixed" products. Additionally, many "in situ" initiator synthesis methods require the use of anhydride precursors, which, however, generate carboxylic acid or carboxylate by-products. For example, the reaction of isobutyric anhydride with hydrogen peroxide in the presence of a base to produce diisobutyryl peroxide results in the formation of two molecules of isobutyric acid for every molecule of diisobutyryl peroxide formed. This unfavorably increases the COD ("chemical oxygen demand") of the reaction mixture. The present invention avoids these problems and in particular provides compositions that are free of or have low amounts of undesirable by-products.

[0028] Thus, in a third aspect, the present invention provides a composition comprising at least a first initiator and a second initiator, a. the first initiator is a diacyl peroxide, wherein the acyl has 2 to 8 carbon atoms; and b. a composition in which the second initiator is a dialkyl peroxydicarbonate, the alkyl having 1 to 4 carbon atoms; the composition does not contain an acyl peroxycarbonate or contains an acyl peroxycarbonate in an amount of less than 20% by weight, relative to the total weight of the first and second initiators; The composition is characterized in that it does not contain a carboxylic acid or a carboxylic acid salt, or contains a carboxylic acid or a carboxylic acid salt in an amount of less than 20% by weight, relative to the total weight of the first and second initiators.

[0029] Preferred features of this composition, particularly the first and second initiators, are as already described for the first and / or second aspects, for example, preferably the mass ratio of diacyl peroxide to dialkyl peroxydicarbonate is 1:4 to 4:1, more preferably 1:3 to 3:1, for example 1:3 to 2:1, and most preferably 1:3 to 1:1. In the most preferred compositions according to this third aspect, the diacyl peroxide is diisobutyryl peroxide and the dialkyl peroxydicarbonate is diethyl peroxydicarbonate.

[0030] With respect to acyl peroxycarbonates, the composition is free of acyl peroxycarbonates or contains less than 20% by weight of acyl peroxycarbonates, based on the total weight of the first and second initiators (diacyl peroxide and dialkyl peroxydicarbonate) present. More preferably, the composition is free of acyl peroxycarbonates or contains less than 10% by weight, e.g., less than 5% by weight, of acyl peroxycarbonates, based on the total weight of the first and second initiators. With respect to carboxylic acids or carboxylate salts, the composition is free of carboxylic acids or carboxylate salts or contains less than 20% by weight of carboxylic acids or carboxylate salts, based on the total weight of the first and second initiators (diacyl peroxide and dialkyl peroxydicarbonate) present. More preferably, the composition is free of carboxylic acids or carboxylate salts or contains less than 10% by weight, for example less than 5% by weight, based on the total weight of the first and second initiators.

[0031] It should be noted that the presence of carboxylic acid or carboxylate salt by-products is generally a consequence of the "in situ" initiator synthesis method using anhydride precursors. Because the process of the first aspect of the present invention does not include, or at least does not require, anhydride precursors, typically no carboxylic acid or carboxylate salt by-products are present in the initiator mixture obtained and used in the first aspect, and correspondingly, in preferred embodiments of the second aspect. However, for the avoidance of doubt, a generally preferred feature of the processes of the first and second aspects is that no carboxylic acid or carboxylate salts are present in the initiator mixture or process, or, if present, any carboxylic acid or carboxylate salt is present in an amount of less than 20% by weight, relative to the total weight of the first and second initiators (diacyl peroxide and dialkyl peroxydicarbonate) present. More preferably, the composition is free of carboxylic acid or carboxylate salts, or contains less than 10% by weight, e.g., less than 5% by weight, of carboxylic acid or carboxylate salt, relative to the total weight of the first and second initiators. More generally, in all aspects of the invention, it is preferred that any initiator other than the first and second initiators is present (in the composition or process) in an amount of less than 20% by weight, preferably less than 10% by weight, more preferably less than 5% by weight, based on the total weight of the first and second initiators present. [Brief explanation of the drawings]

[0032] [Figure 1] 1 shows the percentage of available cooling capacity used versus time in Example A. [Figure 2] 1 shows the percentage of available cooling capacity used versus time in Example B. [Figure 3] 1 shows the percentage of available cooling capacity used versus time in Comparative Example A. [Example]

[0033] ( Example ) Initiator synthesis Initiator 1 The synthesis was carried out in a stirred autoclave reactor of 50 liter capacity at atmospheric pressure and cooled to below 7°C. In the first step, a reactor was charged with 23.1 kg of water, 6.9 kg of sodium chloride, 942 g of sodium hydroxide solution (concentration 220 g / kg), 185 g of hydrogen peroxide solution (concentration 350 g / kg), and 2.6 kg of dioctyl adipate (DOA) (purity 1000 g / kg). To this mixture was added 494 g of isobutyryl chloride (purity 970 g / kg). An exothermic reaction ensued, producing a solution of diisobutyryl peroxide. The isobutyryl chloride was added at a rate to ensure the temperature did not exceed 7°C.

[0034] In the second step, to the same reactor, still cooled to below 7°C, an additional 432 g of hydrogen peroxide solution (concentration 350 g / kg) and 1.1 kg of ethyl chloroformate (purity 970 g / kg) were added to the solution obtained in the first step. To this was added an additional 1.8 kg of sodium hydroxide solution (concentration 220 g / kg). An exothermic reaction ensued, producing diethyl peroxydicarbonate, specifically a mixture of diisobutyryl peroxide and diethyl peroxydicarbonate. The sodium hydroxide was added at a rate to ensure that the temperature did not exceed 7°C. The solution was separated into an aqueous phase and an organic (dioctyl adipate) phase, and the organic phase was separated. This solution contained diisobutyryl peroxide and diethyl peroxydicarbonate, specifically, a diisobutyryl peroxide / diethyl peroxydicarbonate mass ratio in dioctyl adipate of approximately 30 / 70, and the initiator concentration was 282 g / kg of the solution. The combined yield of the two initiators was 86%. 3.2 kg of the resulting solution was used in the subsequent polymerization (see below).

[0035] Initiator 2 Initiator 2 was synthesized in the same manner as initiator 1, except that sodium chloride was not added and the reaction volumes were changed as follows: First step: 10.3 kg of water, 942 g of sodium hydroxide solution (concentration 220 g / kg), 168g of hydrogen peroxide solution (concentration 350g / kg), 2.4 kg of dioctyl adipate (DOA) (purity 1000 g / kg), 432 g of isobutyryl chloride (purity 970 g / kg). Second step: 392g of hydrogen peroxide (concentration 350g / kg), 975g of ethyl chloroformate (purity 970g / kg), 1.6 kg of sodium hydroxide solution (concentration 220 g / kg). Furthermore, no separation into aqueous and organic (dioctyl adipate) phases was performed. The resulting solution consisted of approximately 30 / 70 mass ratio diisobutyryl peroxide / diethyl peroxydicarbonate for Initiator 1, but in this example, the entire resulting solution, including both the organic and aqueous phases, was used in the subsequent polymerization (described below).

[0036] Comparative initiator 1 Comparative initiator 1 contained only diethyl peroxydicarbonate. It was synthesized in a conventional manner, similar to the second step of the manufacturing process described above, by first mixing ethyl chloroformate and hydrogen peroxide in a solution containing water and dioctyl adipate, and then adding sodium hydroxide to cause a reaction. The reaction was again carried out at atmospheric pressure in a 50 litre stirred autoclave reactor, cooled to below 7°C and sodium hydroxide added at a rate to ensure that the temperature did not exceed 7°C. The resulting solution, containing diethyl peroxydicarbonate and both organic and aqueous phases, was used in this form (i.e., without phase separation) for subsequent polymerization (described below).

[0037] Polymerization reaction ( Example A ) A polymerization reactor of 3800 L capacity and equipped with a stirrer was charged with 794 kg of water, 18,850 kg of a solution of polyvinyl alcohol in water at 30 g / kg and with a degree of hydrolysis of 72.5%, 14,437 kg of a solution of polyvinyl alcohol in water at 30 g / kg and with a degree of hydrolysis of 88%, and a solution of initiator 1. The reactor was closed, the agitation speed was set to 37 rpm, and a vacuum was applied. The agitation speed was then set to 120 rpm, and 1203 kg of vinyl chloride was charged. After the vinyl chloride addition, 553 kg of water at 180°C was charged, and the reaction mixture was heated to 57°C in the double jacket. One hour after the polymerization temperature reached 57°C, 4.8 kg of a solution of polyvinyl alcohol with a degree of hydrolysis of 72.5% and 30 g / kg in water and 16 kg of a solution of polyvinyl alcohol with a degree of hydrolysis of 88% and 30 g / kg in water were charged into the polymerization reactor. The pipes were washed with 75 kg of water and charged into the polymerization reactor. Between 1 hour 30 minutes and 3 hours 30 minutes after the polymerization temperature reached 57°C, 397 kg of water was added to the polymerization reactor. If necessary, potassium iodide activity control agent was added to the polymerization reactor to slow down the polymerization rate, inhibit the polymerization reaction, and control the polymerization temperature until the maximum cooling capacity was reached by the double jacket. Once the pressure drop occurred, 3 kg of a 245 g / kg inhibitor solution was introduced to stop the polymerization reaction and the product was recovered. The reaction stopped after approximately 3 hours and 40 minutes. Figure 1 shows the percentage of available cooling capacity used over time during this period.

[0038] ( Example B ) Example A was repeated using a solution containing Initiator 2. In this case, the reaction stopped after about 4 hours (after a pressure drop occurred) and Figure 2 shows the percentage of available cooling capacity used over time during this period.

[0039] Comparative example A Example A was repeated, except that a solution containing Comparative Initiator 1 was used. In this case, the reaction took approximately 4 hours and 20 minutes. Figure 3 shows the percentage of available cooling capacity used over time during this period.

[0040] Summary of Results Comparison of Examples A and B with Comparative Example A shows an improved use of the available cooling capacity. It can be seen, inter alia, that the reactor cooling capacity is more efficiently utilized, especially in the early stages of the process. The result is an increased polymerization rate and a shorter polymerization process time.

Claims

1. 1. A method for producing PVC by polymerization of vinyl chloride, comprising: a. reacting an acyl halide with a peroxide in a reactor to form a diacyl peroxide; b. reacting an alkyl haloformate with a peroxide in the same reactor to form a dialkyl peroxydicarbonate without removing the diacyl peroxide formed in step (a) to produce a mixture comprising a diacyl peroxide and a dialkyl peroxydicarbonate; c. using a mixture comprising a diacyl peroxide and a dialkyl peroxydicarbonate as an initiator mixture for the polymerization of vinyl chloride; A method comprising:

2. 10. The process of claim 1, wherein a mixture comprising a diacyl peroxide and a dialkyl peroxydicarbonate is used as an initiator mixture in the presence of an activity control agent for the polymerization of vinyl chloride.

3. 3. The method according to claim 1, wherein the diacyl peroxide is a diacyl peroxide in which the acyl has 2 to 8 carbon atoms.

4. 4. The method according to claim 1, wherein the dialkyl peroxydicarbonate is a dialkyl peroxydicarbonate in which the alkyl has 1 to 4 carbon atoms.

5. 5. The process of any one of claims 1 to 4, wherein the mixture produced after reacting the alkyl haloformate with peroxide to form the dialkyl peroxydicarbonate in step (b) is used in the polymerization of vinyl chloride in step (c) without purification and within 24 hours after the start of step (a) of the process.

6. 5. The method of any one of claims 1 to 4, wherein the mixture produced after reacting the alkyl haloformate with peroxide to form the dialkyl peroxydicarbonate in step (b) comprises an aqueous phase and an organic phase, and the organic phase is separated from the aqueous phase to provide a mixture comprising a diacyl peroxide and a dialkyl peroxydicarbonate for use in step (c).

7. 7. The method of claim 6, wherein the mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate is stored for at least 24 hours before use in step (c).

8. 1. A method for producing PVC comprising polymerizing vinyl chloride in suspension in an aqueous medium using a mixture of initiators and an activity control agent, wherein the activity control agent comprises an alkali metal halide, nitric oxide, or an alkali metal nitrite, and the mixture of initiators comprises: a. a first initiator, wherein the acyl is a diacyl peroxide having 2 to 8 carbon atoms; and b. a second initiator which is a dialkyl peroxydicarbonate, wherein the alkyl has 1 to 4 carbon atoms; A method comprising:

9. 9. The method of claim 8, wherein the mixture of initiators in the method is obtained by adding a mixture comprising the first initiator and the second initiator to the method.

10. 10. The process of claim 9, wherein the mixture containing the initiator is added to the process at the start of the polymerization.

11. A method according to any one of claims 8 to 10, wherein the activity control agent is an alkali metal halide, preferably potassium iodide.

12. 12. The method according to any one of claims 1 to 11, wherein the diacyl peroxide is diisobutyryl peroxide and the dialkyl peroxydicarbonate is diethyl peroxydicarbonate.

13. A composition comprising at least a first initiator and a second initiator, a. the first initiator is a diacyl peroxide, wherein the acyl has 2 to 8 carbon atoms; b. the second initiator is a dialkyl peroxydicarbonate, wherein alkyl has 1 to 4 carbon atoms; the composition does not contain an acyl peroxycarbonate or contains an acyl peroxycarbonate in an amount of less than 20% by weight relative to the total weight of the first and second initiators, the composition does not contain a carboxylic acid or a carboxylic acid salt, or contains a carboxylic acid or a carboxylic acid salt in an amount of less than 20% by weight relative to the total weight of the first and second initiators; A composition characterized by:

14. 14. The composition of claim 13, wherein the diacyl peroxide is diisobutyryl peroxide and the dialkyl peroxydicarbonate is diethyl peroxydicarbonate.

15. 15. The composition of claim 13 or 14, wherein the mixture comprises a diacyl peroxide and a dialkyl peroxydicarbonate in a molar ratio of 1:3 to 1:1.

Images