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

Abstract

The present invention relates to a process for preparing PVC, and particularly provides a process for preparing PVC by polymerizing vinyl chloride, comprising: (a) reacting an acid halide with a peroxide in a reactor to form a diacyl peroxide, (b) reacting an acid halide with a peroxide in the same reactor without removing the diacyl peroxide formed in step (a), the present invention relates to a method for polymerizing vinyl chloride, comprising (a) reacting an alkyl haloformate with a peroxide to form a dialkyl peroxydicarbonate, and preparing a mixture comprising a diacyl peroxide and a dialkyl peroxydicarbonate, and (c) using the mixture comprising a diacyl peroxide and a dialkyl peroxydicarbonate as an initiator mixture for polymerizing vinyl chloride.

Description

[0001] The present invention relates to a process for preparing PVC and in particular to a process comprising the use of a mixture of initiators to polymerize vinyl chloride.

[0002] Polyvinyl chloride (PVC) is one of the most important thermoplastic materials on the market today. Due to its very good mechanical and physical properties, it is used in a large number of applications.

[0003] Several methods are known for producing PVC. For example, PVC can be produced by suspension polymerization of vinyl chloride in a suspending liquid in the presence of a suspending agent. This produces a slurry (or suspension) of PVC particles, typically having a particle size of approximately 100-200 microns. The resulting PVC slurry is then dried (typically by centrifugation followed by fluidized bed drying) to provide porous (i.e., adsorbent) PVC. PVC produced by the suspension method is known as "S-PVC." S-PVC can absorb plasticizers to provide a dry blend.

[0004] PVC can also be produced by a process commonly referred to as a paste polymerization process. The paste process can be characterized in that the polymerization produces a latex of polymer particles of relatively small size (typically 0.2-5 microns) compared to the S-PVC process. The latex can be dried (e.g., by spray drying) to produce PVC particles in the form of agglomerates. The dried PVC polymer particles are generally much smaller than the dried particles produced by the suspension PVC process.

[0005] Regardless of whether the preparation is by a suspension method or a paste method, the general method for polymerization involves polymerization in a solvent (usually water) and the use of one or more initiators, which are usually peroxides or other compounds that decompose to provide free radicals that can initiate polymerization. The half-life of the initiator at the polymerization temperature can be on the order of seconds to several hours, and the initiator can be added to start the polymerization and can be added during the polymerization to provide additional polymerization activity.

[0006] The polymerization of vinyl chloride is an exothermic reaction, and cooling (especially cooling water in the reactor jacket) is usually used to keep the reaction at the desired temperature. In a preferred operation, the reactor is operated as close as possible to the maximum cooling capacity of the reactor, because this maximizes the reaction rate / reactivity and therefore the output of the method. A common problem is to control the amount of initiator to obtain a largely stable polymerization rate that is as close as possible to the available cooling capacity. For example, if an initiator with a relatively long half-life is used, the reaction may take some time to reach a desired preparation rate, and there is also a time lag between adding more initiator and the increase in reactivity. On the other hand, the use of an initiator with a relatively short half-life can provide a faster increase in reactivity, but the effect is not lasting, and therefore initiator must be constantly added or at least regularly added to maintain reactivity.

[0007] In order to try and overcome such problems, it is known to use mixtures of initiators. For example, EP 1618137 describes a process using a mixture of initiators of different half-lives, wherein the initiator with the shorter half-life is dosed into the reactor over at least the initial period of polymerization to provide reactivity in the initial stage.

[0008] Although this allows for some control over reactivity, initiators with short half-lives are relatively unstable by nature. Therefore, such initiators are typically cooled during transportation and storage and are therefore typically stored in solutions containing alcohol. This increases the chemical oxygen demand of the initiator solution. For example, diisobutyryl peroxide is provided in a solution of water and alcohol and is recommended to be stored at -20°C. When dosed continuously or intermittently over a period of time, the initiator may also be present in the pipeline or injection system for the reactor at ambient temperature or a temperature far above ambient temperature for a relatively significant period of time. Therefore, it may be necessary to provide cooling for the pipeline or adopt other methods to mitigate the risk of initiator decomposition in the pipeline.

[0009] Another problem about initiator mixture is that the additive that can be used to control the reactivity of a kind of initiator may be invalid to another kind of initiator.Especially, suitable reagent (" initiator " or " activity control agent ") is usually used in the method, and it can reduce reaction rate by termination reaction.The example of known activity control agent comprises alkali metal halide, nitrogen monoxide and alkali metal nitrite.For example, alkali metal halide can be used to terminate and therefore control the reactivity of initiator such as peroxydicarbonate.Yet many such activity control agents are invalid when used together with the peroxide such as diisobutyryl peroxide.

[0010] It is therefore still desirable to provide a process for the preparation of PVC which enables the high reactivity of the process to be maintained throughout the polymerization in a safe manner. It is also desirable to simplify the provision and use of initiators in such processes.

[0011] Thus, in a first aspect, the present invention provides a process for polymerizing PVC comprising: a. reacting an acyl halide with a peroxide in a reactor to form a diacyl peroxide, b. in the same reactor, and without removing the diacyl peroxide formed in step (a), reacting an alkyl haloformate with a peroxide to form a dialkyl peroxydicarbonate and preparing a mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate, and c. Use of a mixture comprising diacyl peroxide and dialkyl peroxydicarbonate as an initiator mixture for the polymerization of vinyl chloride.

[0012] A particular advantage of the method of the first aspect of the invention is its simplicity. In particular, the mixture of initiators can be prepared just before it is needed and can be used in its formed state. In particular, no steps need to be performed to purify the mixture obtained in step (b), and in this case no storage is required.

[0013] Thus, in a preferred embodiment, the mixture prepared in step (b) after the reaction of the alkyl haloformate with the peroxide to form dialkyl peroxydicarbonate is not purified and is used for the vinyl chloride polymerization in step (c) within 24 hours of starting step (a) of the process. Preferably, the mixture is used within 12 hours, more preferably within 6 hours, for example within 4 hours or even within 1 hour of starting step (a) of the process. Although in this embodiment it is not stored for a long period of time before use, it is preferably kept cooled, for example in the range of 1°C to 10°C or in the range of 1°C to 5°C, until use.

[0014] In some embodiments, as further described below, the mixture prepared in step (b) following the reaction of the alkyl haloformate with the peroxide to form dialkyl peroxydicarbonate can comprise an aqueous phase and an organic phase, and the organic phase can be separated from the aqueous phase to provide a mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate for use in step (c).

[0015] Although not generally preferred, it is also possible to prepare a mixture according to steps (a) and (b) for subsequent use in the polymerization according to step (c). Thus, the mixture prepared in step (b) after the reaction of the alkyl haloformate with the peroxide to form the dialkyl peroxydicarbonate can be removed from the reactor and stored. In such embodiments, the mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate can be stored for 24 hours or more (e.g., 48 hours or more) before use in step (c). To achieve storage for such periods, The mixture should be cooled during storage, for example, to below 10° C., such as below 5° C. In embodiments where the mixture prepared in step (b) after the reaction of the alkyl haloformate with the peroxide to form dialkyl peroxydicarbonate comprises an aqueous phase and an organic phase, it is preferred that the organic phase be separated from the aqueous phase to provide a mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate for storage (and thereafter for subsequent use in step (c)). This allows the mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate (i.e., the organic phase) to cool and be stored below 0° C.

[0016] The reaction of step (a) comprises making acyl halide and superoxide react in reactor, to form diacyl peroxide.Can add reactant in any suitable order, but preferably this reaction comprises in one or more initial steps, adding water, alkali and superoxide in reactor.In a preferred embodiment, organic solvent is also added in this stage.In some embodiments, especially when also using organic solvent, water can be salt solution, that is, the water that comprises sodium chloride.This has increased the density of water and can improve phase separation when needed.

[0017] The acyl halide is then added, whereupon an exothermic reaction occurs to produce the diacyl peroxide. The reactor is typically cooled, and particularly, even under the exotherm of the acyl halide reaction, the reaction is maintained at a temperature below 20°C. For example, the reaction may be carried out at a temperature in the range of 1-15°C. The rate of introduction of the acyl halide may be such that the exotherm does not cause the temperature to exceed 20°C, preferably 15°C. The reaction may be carried out at any suitable pressure, but is most typically carried out at atmospheric pressure.

[0018] The acyl halide is preferably an acyl chloride. Suitable acyl chlorides are defined by the desired diacyl peroxide. For example, if diisobutyryl peroxide is desired, isobutyryl halide, preferably isobutyryl chloride, is used. In a preferred embodiment of this first aspect, the diacyl peroxide is a diacyl peroxide wherein the acyl group has 2 to 8 carbon atoms.

[0019] The preferred base for this step is an alkali metal hydroxide, with sodium hydroxide being preferred.

[0020] The preferred peroxide for use as a reactant is hydrogen peroxide.

[0021] Typical organic solvents that can be used include any organic solvent that is immiscible with water. This allows the aqueous and organic phases to be separated when necessary. Suitable examples of organic solvents include alkanes (e.g., pentane) and diesters. Preferred organic solvents have a freezing point below 0° C., e.g., below -5° C., especially 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.

[0022] The reaction of step (b) comprises making alkyl haloformate and peroxide reaction, to form dialkyl peroxydicarbonate.This reaction generally comprises adding extra peroxide and alkyl haloformate to the solution in the reactor from step (a).Add other alkali then, exothermic reaction this moment, to prepare dialkyl peroxydicarbonate.

[0023] As with step (a), the reactor is typically cooled during this step. (And, in fact, the reactor is typically cooled throughout steps (a) and (b) of the synthesis, as well as between these steps, and also at the end of the synthesis.) In particular, during this step, the reaction is maintained at a temperature below 20°C, even under the exotherm from the reaction of the alkyl haloformate. For example, the reaction in this step can be carried out at a temperature in the range of 1-15°C. The rate of introduction of the alkyl haloformate can be such that the exotherm does not cause the temperature to exceed 20°C, preferably not exceed 15°C.

[0024] Similarly, the reaction may also 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 may be carried out at the same pressure, most preferably at atmospheric pressure.

[0025] Alkyl haloformate is preferably alkyl chloroformate.Suitable alkyl haloformate is limited by required dialkyl peroxydicarbonate.For example, if need diethyl peroxydicarbonate, then use ethyl haloformate, preferred ethyl chloroformate.In the preferred embodiment of this first aspect, dialkyl peroxydicarbonate is a dialkyl peroxydicarbonate in which said alkyl has 1-4 carbon atom.

[0026] Preferred bases for this step are alkali metal hydroxides, with sodium hydroxide being again preferred.

[0027] The preferred peroxide for use as a reactant is hydrogen peroxide.

[0028] Additional water can be added at this step if needed.

[0029] Sodium chloride may be added in this step (especially if it was not added in the first step).

[0030] An organic solvent may be added in this step if desired (especially if it was not added in the first step).

[0031] In the present invention, the formation of the diacyl peroxide and the formation of the dialkyl peroxydicarbonate are carried out in sequence. This has the following advantages: (by using appropriate amounts of reactants in each step) the relative amounts of the diacyl peroxide and the dialkyl peroxydicarbonate in the formed mixture can be easily controlled and "mixed" products can be avoided.

[0032] With respect to 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 and dialkyl peroxydicarbonate. The weight ratio of diacyl peroxide to dialkyl peroxydicarbonate is typically from 1:4 to 4:1, more preferably from 1:3 to 3:1, e.g., from 1:3 to 2:1, and most preferably from 1:3 to 1:1.

[0033] About " mixing " product, in some known prior art methods, by making acyl chlorides and alkyl chloroformate and hydrogen peroxide react in a single step to form the mixture of diacyl peroxide and dialkyl peroxydicarbonate.Formed like this the mixture of required diacyl peroxide (having the acyl group based on the chloride reactant) and dialkyl peroxydicarbonate (having the alkyl based on the chloroformate reactant), and formed " mixing " reaction product (it is acyl peroxycarbonate) that is generally significant amount.Wherein making the method for dialkyl pyrocarbonate, acyl anhydride and hydrogen peroxide reaction also is known, and has produced superoxide and peroxydicarbonate equally, and has produced the acyl peroxycarbonate of mixing.Under the contrast, the inventive method can provide the mixture that does not contain this type of compound.

[0034] 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).

[0035] Although it is generally preferred that no acyl peroxycarbonate is present in the mixture obtained at the end of step (b), small amounts of "mixed" products can be tolerated. Thus, it is preferred that the composition contains no acyl peroxycarbonate or contains less than 20% by weight of acyl peroxycarbonate relative to the total weight of diacyl peroxide and dialkyl peroxydicarbonate in the mixture. More preferably, the composition contains no acyl peroxycarbonate or contains less than 10% by weight, for example less than 5% by weight, relative to the total weight of diacyl peroxide and dialkyl peroxydicarbonate in the mixture.

[0036] In step (c) of the first aspect, a mixture comprising a diacyl peroxide and a dialkyl peroxydicarbonate is used as an initiator mixture for the polymerization of vinyl chloride.

[0037] The polymerization of vinyl chloride can be carried out under any suitable conditions for such reactions (some of which are further described below). In a particularly preferred option, the polymerization occurs in the presence of an activity control agent. Suitable activity control agents are well known in the art, but in the present invention preferably include alkali metal halides, nitric oxide, or alkali metal nitrites. The activity control agent is preferably an alkali metal halide, and more preferably an alkali metal iodide, such as sodium iodide or potassium iodide. Most preferably, it is potassium iodide.

[0038] In a further preferred embodiment of this first aspect, the diacyl peroxide is a diacyl peroxide wherein the acyl group has 2-8 carbon atoms, and the dialkyl peroxydicarbonate is a dialkyl peroxydicarbonate wherein the alkyl group has 1-4 carbon atoms.

[0039] In the present invention, it has been found that particularly preferred polymerisation can be obtained by using a selected activity control agent with a defined mixture of a diacyl peroxide and a dialkyl peroxydicarbonate.

[0040] Thus, in a second aspect, there is provided a process for preparing PVC comprising polymerizing vinyl chloride in suspension in an aqueous medium using a mixture of initiators and using an activity control agent, wherein the activity control agent comprises an alkali metal halide, nitric oxide or an alkali metal nitrite, and wherein the mixture of initiators comprises: a. a first initiator which is a diacyl peroxide, the acyl group having 2 to 8 carbon atoms, and b. A second initiator which is a dialkyl peroxydicarbonate, the alkyl group having 1 to 4 carbon atoms.

[0041] In particular, while the defined activity control agents are generally ineffective when used with the first initiator / diacyl peroxide alone, it has been found that when used with a mixture of a diacyl peroxide and a dialkyl peroxydicarbonate, as in the second aspect, wherein the alkyl group of the dialkyl peroxydicarbonate has 1 to 4 carbon atoms, the activity control agents are effective in controlling polymerization. In particular, it has been found that, with this particular combination, the selected activity control agent is also effective in capping the free radicals obtained from the diacyl peroxide initiator.

[0042] In this second aspect, the activity control agent is preferably an alkali metal halide, and more preferably an alkali metal iodide, such as sodium iodide or potassium iodide. It is most preferably potassium iodide.

[0043] In a preferred embodiment of the second aspect, the mixture of initiators in the process is obtained by adding a mixture comprising the first initiator and the second initiator to the process, ie the initiators are added together rather than separately to the process.

[0044] In a preferred embodiment of this second aspect, the mixture containing the initiator is added to the process only at the start of polymerization. This is particularly advantageous because the entire initiator mixture can then be removed from the feed pipe and injection device on the reactor. The pipe / injection device can be rinsed, for example, with a solvent (typically water) to remove any residual initiator. This provides a safe process that does not require cooling of the pipe or injection device.

[0045] Preferred features of the mixture of initiators (diacyl peroxide and dialkyl peroxydicarbonate) used in the process of this second aspect are generally as set out for the first aspect. For example, the mixture may comprise any suitable relative ratio of diacyl peroxide and dialkyl peroxydicarbonate, but the weight ratio of diacyl peroxide to dialkyl peroxydicarbonate is preferably from 1:4 to 4:1, more preferably from 1:3 to 3:1, for example from 1:3 to 2:1, and most preferably from 1:3 to 1:1.

[0046] Similarly, it is generally preferred that no acyl peroxycarbonate is present in the mixture of initiators (or more generally in the polymerization), although small amounts of "mixed" products can be tolerated. Preferably, the process contains no acyl peroxycarbonate, or contains less than 20% by weight of acyl peroxycarbonate relative to the total weight of diacyl peroxide and dialkyl peroxydicarbonate in the mixture. More preferably, the composition contains no acyl peroxycarbonate, or contains less than 10% by weight, for example less than 5% by weight, relative to the total weight of diacyl peroxide and dialkyl peroxydicarbonate in the mixture.

[0047] In a most preferred embodiment, the method is operated according to both the first and second aspects of the invention. In particular, the mixture of initiators of the second aspect is formed by the method of the first aspect.

[0048] In preferred embodiments of both the first and second aspects of the present invention, the diacyl peroxide may be one in which the acyl group has 2 to 5 carbon atoms (e.g. 2 to 4 carbon atoms). The most preferred diacyl peroxide is diisobutyryl peroxide.

[0049] 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 group has 1 to 3 carbon atoms (and more preferably 1 to 2 carbon atoms). A preferred dialkyl peroxydicarbonate is diethyl peroxydicarbonate.

[0050] Turning more generally to the polymerisation process step, the polymerisation process may be carried out as any suitable polymerisation process, but is preferably carried out as a suspension polymerisation process. The polymerisation step may then be suitably carried out in any suitable apparatus known for suspension polymerisation processes.

[0051] Typically, polymerization occurs in an aqueous suspension in the presence of a suitable suspending agent. Any suitable suspending agent may be used for the polymerization, but particularly preferred suspending agents are polyvinyl acetates and water-soluble cellulose esters having various degrees of hydrolysis. These suspending agents may be used with auxiliary suspending agents as needed. The amount employed may vary widely and is generally between 0.05% and 1.5% by weight, calculated on the vinyl chloride used. Other additives conventionally known for use in suspension polymerization of vinyl chloride to produce PVC may also be present, including buffers and chain transfer agents.

[0052] One or more chain transfer agents may be used in the polymerization process. Chain transfer agents are known to control the molecular weight in vinyl chloride polymerizations, particularly in polymerizations carried out at higher temperatures and higher pressures. Most preferably, at least one chain transfer agent is present in the polymerization reaction during initiation. Suitable chain transfer agents are well known in the art. They typically have at least one weak chemical bond that promotes the chain transfer reaction. Common chain transfer agents include mercaptans and halogenated hydrocarbons, such as carbon tetrachloride. In the present invention, it has been found that mercaptans (particularly alkanethiols, such as mercaptans (methyl mercaptan), and most preferably 1-dodecyl mercaptan) provide particularly good results.

[0053] The polymerization may be carried out at any suitable temperature. Typically, the polymerization is carried out at a temperature in the range of 30-80°C. In some embodiments, the temperature may be varied, for example increased, during the polymerization.

[0054] The polymerization can be carried out at any suitable pressure. Typically, the polymerization is carried out at a pressure in the range of 2-20 bar (200-2000 kPa), for example 6-12 bar (600-1200 kPa). (Unless otherwise indicated, all pressures used herein are absolute pressures.)

[0055] The polymerization process may produce homopolymers or, by adding one or more monomers other than vinyl chloride, copolymers may be produced. Typical comonomers include, for example, alkyl acrylates and alkyl methacrylates; and acetates, such as vinyl acetate.

[0056] The polymerization is usually initiated by introducing a mixture of initiators after the required solvent, vinyl chloride and other reactants are charged to the reactor. The initiator may be used in conventional amounts - generally 0.01 to 1 weight percent calculated on the vinyl chloride.

[0057] While it is generally preferred to add the entire initiator mixture at the beginning of the process, in some embodiments, a portion of the initiator mixture may be added during the polymerization.

[0058] When used, the activity control agent is present in any suitable amount to provide the desired inhibition. Generally, the activity control agent is added as needed during the polymerization to control the exotherm / polymerization temperature and maintain control over the reaction rate. In a preferred embodiment, the activity control agent is added continuously at an addition rate adjusted as needed to control the exotherm of polymerization.

[0059] The polymerization is continued until the desired monomer conversion is achieved.

[0060] Optionally, an inhibitor (or in particular an additional inhibitor or an additional amount of an existing inhibitor) may be added to terminate the polymerization. Any suitable inhibitor may be used. Examples of suitable initiators include, for example, bases such as alkali metal hydroxides and amines (including diethylhydroxylamine), 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 inhibitor and activity control agent. Most preferably, potassium iodide is used. However, in general, since the purpose of this step is to permanently stop the polymerization, a larger amount is used in this step.

[0061] Optionally, a defoamer is added at the end of the polymerization. Any unreacted monomer can be removed by decompressing the reactor, and the polymer solids can then be recovered. The polymer solids are typically subjected to a stripping step followed by filtration and drying. The polymer can be dried by any suitable method (e.g., in a fluidized bed dryer).

[0062] As already pointed out, the method for first aspect of the present invention can provide the mixture of diacyl peroxide and dialkyl peroxydicarbonate, and it does not comprise " mixing " product or only comprises relatively small amount of " mixing " product.In addition, many " original position " initiator synthesis methods need to use anhydride precursor.Yet, produce carboxylic acid or carboxylate by product like this.For example, the reaction of isobutyric anhydride and hydrogen peroxide under the presence of alkali in order to prepare diisobutyryl peroxide causes also formed two molecular isobutyrates for formed every molecule diisobutyryl peroxide.Increased the COD (" chemical oxygen demand ") of reaction mixture like this, and this is disadvantageous.

[0063] The present invention avoids these problems and, in particular, provides compositions that are free of, or contain lower amounts of, undesirable by-products.

[0064] Thus, in a third aspect, the present invention provides a composition comprising at least a first initiator and a second initiator, wherein: a. The first initiator is a diacyl peroxide, the acyl group having 2 to 8 carbon atoms, and b. The second initiator is a dialkyl peroxydicarbonate, wherein the alkyl group has 1 to 4 carbon atoms, Its characteristics are: - the composition does not contain acyl peroxycarbonate or contains acyl peroxycarbonate in an amount of less than 20% by weight relative to the total weight of the first initiator and the second initiator, and The composition does not contain carboxylic acid or carboxylate salts, or contains carboxylic acid or carboxylate salts in an amount of less than 20% by weight relative to the total weight of the first initiator and the second initiator.

[0065] Preferred features of the composition, and in particular preferred features for the first and second initiators, have been described with respect to the first and / or second aspects. For example, the weight ratio of diacyl peroxide to dialkyl peroxydicarbonate is preferably 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.

[0066] In the most preferred composition according to this third aspect, the diacyl peroxide is diisobutyryl peroxide and the dialkyl peroxydicarbonate is diethyl peroxydicarbonate.

[0067] With respect to acyl peroxycarbonates, the composition contains no acyl peroxycarbonates or contains acyl peroxycarbonates in an amount of less than 20% by weight relative to the total weight of the first and second initiators (diacyl peroxides and dialkyl peroxydicarbonates) present. More preferably, the composition contains no acyl peroxycarbonates or contains acyl peroxycarbonates in an amount of less than 10% by weight, for example less than 5% by weight, relative to the total weight of the first and second initiators.

[0068] With respect to carboxylic acids or carboxylates, the composition contains no carboxylic acids or carboxylates, or contains carboxylic acids or carboxylates in an amount of less than 20% by weight relative to the total weight of the first and second initiators (diacyl peroxides and dialkyl peroxydicarbonates) present. More preferably, the composition contains no carboxylic acids or carboxylates, or contains carboxylic acids or carboxylates in an amount of less than 10% by weight, for example less than 5% by weight, relative to the total weight of the first and second initiators.

[0069] Notice that the existence of carboxylic acid or carboxylate by-product is normally the result of " original position " initiator synthesis method using anhydride precursor.Because the method for first aspect of the present invention does not involve anhydride precursor or at least does not need to involve anhydride precursor, therefore in the initiator mixture obtained and used in the first aspect and corresponding preferred embodiment of the second aspect usually do not have carboxylic acid or carboxylate by-product.But, for fear of doubt, the usually preferred feature of the method for the first aspect and the second aspect also is that there is not carboxylic acid or carboxylate in initiator mixture or the method, or is that when they exist, relative to the gross weight meter of existing first initiator and the second initiator (diacyl peroxide and dialkyl peroxydicarbonate), the amount of any carboxylic acid or carboxylate is less than 20 % by weight.More preferably, composition does not comprise carboxylic acid or carboxylate, or relative to the gross weight meter of the first initiator and the second initiator, comprises its amount and is less than 10 % by weight, for example, is less than the carboxylic acid or carboxylate of 5 % by weight.

[0070] 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 less than 20 wt%, preferably less than 10 wt% and more preferably less than 5 wt%, relative to the total weight of the first and second initiators present. Example Synthesis of initiator 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.

[0071] In the first step, 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) are added to the reactor. To this mixture is added 494 g of isobutyryl chloride (purity 970 g / kg). An exothermic reaction occurs to produce a solution of diisobutyryl peroxide. The isobutyryl chloride is added at a rate that ensures that the temperature does not exceed 7°C.

[0072] In the second step, to the same reactor still cooled below 7° C. and to the solution obtained from the first step, another 432 g of hydrogen peroxide solution (concentration 350 g / kg) and 1.1 kg of ethyl chloroformate (purity 970 g / kg) are added. Then another 1.8 kg of sodium hydroxide solution (concentration 220 g / kg) is added thereto. An exothermic reaction occurs to prepare a mixture of diethyl peroxydicarbonate and in particular diisobutyryl peroxide and diethyl peroxydicarbonate. Sodium hydroxide is added at a rate such that, for example, the temperature does not exceed 7° C.

[0073] The solution was allowed to separate into an aqueous phase and an organic (dioctyl adipate) phase, and the organic phase was separated. The solution contained diisobutyryl peroxide and diethyl peroxydicarbonate, and in particular, the weight ratio of diisobutyryl peroxide / diethyl peroxydicarbonate in the dioctyl adipate solution was approximately 30 / 70, and the initiator concentration was 282 g / kg solution. The total yield of the two initiators was 86%.

[0074] The resulting 3.2 kg solution was used for subsequent polymerization (discussed below).

[0075] Initiator 2 The synthesis of Initiator 2 was carried out in a similar manner to that of Initiator 1, except that no sodium chloride was added and the amounts reacted were changed as follows: Step 1: 10.3kg water, 942g sodium hydroxide solution (concentration 220g / kg), 168g hydrogen peroxide solution (concentration 350g / kg), 2.4 kg dioctyl adipate (DOA) (purity 1000 g / kg). 432 g isobutyryl chloride (purity 970 g / kg).

[0076] Step 2: 392g hydrogen peroxide solution (concentration 350g / kg), 975 g of ethyl chloroformate (purity 970 g / kg). 1.6 kg sodium hydroxide solution (concentration 220 g / kg).

[0077] In addition, separation of the aqueous and organic (dioctyl adipate) phases was not performed. As with Initiator 1, the resulting solution contained a weight ratio of approximately 30 / 70 diisobutyryl peroxide / diethyl peroxydicarbonate, but in this example, all of the resulting solution (comprising both the organic and aqueous phases) was used in the subsequent polymerization (discussed below).

[0078] Comparative Initiator 1 Comparative initiator 1 comprises only diethyl peroxydicarbonate. It was synthesized in a conventional manner and in a manner similar to the second step of the preparation described above by first mixing ethyl chloroformate and hydrogen peroxide in a solution comprising water and dioctyl adipate, and then adding sodium hydroxide to induce the reaction.

[0079] The reaction is carried out in a stirred autoclave reactor of 50 liter capacity, also at atmospheric pressure, and cooled to below 7°C, and sodium hydroxide is added at a rate such as to ensure that the temperature does not exceed 7°C.

[0080] The resulting solution contained diethyl peroxydicarbonate and both organic and aqueous phases and was used in this form (ie, without phase separation) for the subsequent polymerization (discussed below).

[0081] Polymerization reaction Example A In a polymerization reactor having a capacity of 3800 L and equipped with a stirrer, 794 kg of water, 18,850 kg of an aqueous solution of polyvinyl alcohol having a hydrolysis degree of 72.5% (30 g / kg), 14,437 kg of an aqueous solution of polyvinyl alcohol having a hydrolysis degree of 88% (30 g / kg) and an initiator 1 solution were added.

[0082] Once the reactor was closed and the stirring speed was set to 37 rpm, vacuum was applied. The stirring speed was then set to 120 rpm and 1203 kg of vinyl chloride was added. Once the vinyl chloride was added, 553 kg of 180°C water was added and the reaction mixture was heated to 57°C using a double jacket.

[0083] One hour after the polymerization temperature reached 57°C, 4.8 kg of an aqueous solution of polyvinyl alcohol with a degree of hydrolysis of 72.5% (30 g / kg) and 16 kg of an aqueous solution of polyvinyl alcohol with a degree of hydrolysis of 88% (30 g / kg) were added to the polymerization reactor. 75 kg of water was used to wash the pipes and then added to the polymerization reactor.

[0084] 1 h 30 min to 3 h 30 min after the polymerization temperature reached 57° C., 397 kg of water was charged into the polymerization reactor.

[0085] Potassium iodide activity control agent was added to the polymerization reactor as needed to slow down the polymerization kinetics and to control the polymerization temperature once the maximum cooling capacity of the double jacket was reached.

[0086] Once the pressure drop occurred, 3 kg of initiator solution (245 g / kg) were introduced to stop the polymerization reaction, and the product was recovered.

[0087] The reaction was stopped after approximately 3 hours and 40 minutes. Figure 1 Shows the percentage of available cooling capacity used vs. time during this time period.

[0088] Example B Example A was repeated, but using a solution containing Initiator 2.

[0089] In this case, the reaction was stopped after approximately 4 hours (as soon as a pressure drop occurred), and Figure 2 Shows the percentage of available cooling capacity used vs. time during this time period.

[0090] Comparative Example A Example A was repeated, but using a solution containing Comparative Initiator 1.

[0091] In this case, the reaction took about 4 hours and 20 minutes. Figure 3 Shows the percentage of available cooling capacity used vs. time during this time period.

[0092] Summary of results Comparison of Example A and Example B with Comparative Example A shows improved utilization of the available cooling capacity. In particular, it can be seen that the reactor cooling capacity is better utilized, especially during the initial phase of the process. This results in higher polymerization rates and shorter polymerization process times.

Claims

1. A method for preparing PVC by polymerizing vinyl chloride, comprising: a. reacting an acyl halide with a peroxide in a reactor to form a diacyl peroxide, b. in the same reactor, and without removing the diacyl peroxide formed in step (a), reacting an alkyl haloformate with a peroxide to form a dialkyl peroxydicarbonate, and preparing 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.

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

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

4. The process according to any one of the preceding claims, wherein the dialkyl peroxydicarbonate is a dialkyl peroxydicarbonate in which the alkyl group has 1 to 4 carbon atoms.

5. A process according to any one of the preceding claims, wherein the mixture prepared in step (b) after the reaction of the alkyl haloformate with the peroxide to form dialkyl peroxydicarbonate is not purified and is used for the polymerization of vinyl chloride in step (c) within 24 hours of starting step (a) of the process.

6. A process according to any one of claims 1 to 4, wherein the mixture prepared in step (b) after the reaction of the alkyl haloformate with the peroxide to form dialkyl peroxydicarbonate comprises an aqueous phase and an organic phase, and the organic phase is separated from the aqueous phase to provide the mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate for use in step (c).

7. The method according to claim 6, wherein the mixture comprising the diacyl peroxide and the dialkyl peroxydicarbonate is stored for 24 hours or more and then used in step (c).

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

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

10. The process according to claim 9, wherein the mixture comprising 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, and preferably potassium iodide.

12. The process according to any one of the preceding claims, 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, wherein: a. The first initiator is a diacyl peroxide, the acyl group having 2-8 carbon atoms, and b. The second initiator is a dialkyl peroxydicarbonate, wherein the alkyl group has 1 to 4 carbon atoms, Its characteristics are: - the composition does not contain acyl peroxycarbonate or contains acyl peroxycarbonate in an amount of less than 20% by weight relative to the total weight of the first initiator and the second initiator, and The composition does not contain carboxylic acid or carboxylate salts, or contains carboxylic acid or carboxylate salts in an amount of less than 20% by weight relative to the total weight of the first initiator and the second initiator.

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

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

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