ACRYLONITRILE MALEIMIDES SOLUTION COMPOSITION OF IMPROVED SHELF LIFE AND METHOD FOR PRODUCTION THEREOF

Abstract: The present invention is directed to an acrylonitrile maleimides solution composition of highly desirable shelf life, having the acid component in said acrylonitrile maleimides solution adjusted to a level of no more than 0.1% by weight based on the amount of said maleimides contained in said solution and having a polymerization inhibitor in said solution adjusted to a level in the range of 0.0001 to 1% by weight based on the amount of said solution, and a method for the production thereof.

Description: This invention relates to an acrylonitrile maleimides solution composition of improved shelf life and a method for the production thereof. Maleimides are compounds useful as raw materials for synthetic resins, medicines, and agricultural pesticides. They are solid at normal room temperature and have previously been handled generally in various forms such as powder, flakes, and tablets. Maleimides in these forms contain minute maleimide particles. While these maleimides in the solid state are in transit, they undergo gradual comminution and give rise to large amounts of minute particles. These maleimides have undesirable qualities; they stimulate the human body. Particularly when minute particles are inhaled, they stimulate nasal cavities and throats and incite coughs and sneezes. When their minute particles are caused to adhere to the skin and remain there, they cause inflammation. When a person happens to handle maleimides containing such minute particles, he is required to take elaborate precautions to keep his skin from contacting the maleimides. In the circumstances, immense labour is expended in preventing the maleimides from shedding minute particles during the course of transportation or for removing minute particles from the maleimides after transportation. In most cases, solid substances are transported as stowed in paper bags, drums and containers. Persons engaging in any of the work involved are inevitably exposed to the maleimides, with the natural result that minute particles of the maleimides adhere to their bodies. Any attempt at conveying the solid substances by pipeline for the purpose of contact with human bodies is basically difficult. The solid substances in transit through the pipeline are apt to clog the interior of the pipeline. For the solid substances to be stably conveyed by the pipeline, harsh restrictions are imposed on the shape, size, specific gravity, etc. of the solid substances to be conveyed. It is only safe to conclude that methods employed for the transportation or conveyance of maleimides which are solid at room temperature entail various difficult problems. Similar problems are also encountered by methods to be employed for the storage of the maleimides. A method for conveying, transporting, or storing maleimides as a solution in acrylonitrile has been disclosed in Japanese Patent Laid-Open SHO 62(1987)-126,167. This method may well be considered highly satisfactory in the sense that it can solve the problems mentioned above in the handling of maleimides. However, the acrylonitrile maleimides solution in common use manifests heavy corrosiveness to metals. The phenomenon that such materials as carbon steel and stainless steel which are popularly used in industries are rapidly corroded by the acrylonitrile maleimides solution is observed frequently. Moreover, this solution in storage generates an insoluble component resulting in a blackish tint. This phenomenon of tarnishing entails a disadvantage that the maleimides are appreciably degenerated and consequently deprived of commercial value. The desirability of developing an acrylonitrile maleimide solution relieved of heavy corrosiveness and improved in stability has been finding enthusiastic approval in the industry. As one way of producing an acrylonitrile maleimides solution comprises preparing a tank provided with a heating coil or a heating jacket and a stirrer, filling the tank with acrylonitrile to capacity, adding solid maleimides in the form of flakes, granules, or particles to the acrylonitrile, and then heating the resultant mixture by means of the heating coil or the heating jacket thereby dissolving the maleimides thoroughly in the acrylonitrile. The solid maleimides assume various forms such as flakes, tablets, granules, and minute particles as described above. However, maleimides possess a quality such that, while the solid maleimides are in storage, their individual particles coalesce and form very hard lumps. When such lumps of solid maleimides are to be dissolved in acrylonitrile, they are conveyed from their containers to a maleimides dissolving tank (hereinafter referred to simply as "dissolving tank") where they tend to clog the injection nozzles and consequently disrupt the operation of dissolution. Further, the dissolution of the solid maleimides in acrylonitrile is highly endothermic and therefore requires the contents of the dissolving tank to be heated to ensure safe dissolution. The inevitable formation of such large lumps impedes effective control of the introduction of the solid maleimides into the dissolving tank. When the feed rate of the solid maleimides into the dissolving tank is unduly lowered, the liquid temperature inside the dissolving tank fluctuates considerably. Owing to this heavy fluctuation of the inner temperature of the dissolving tank, the acrylonitrile maleimides solution once formed tends to suffer from the precipitation of crystals of maleimides in large volumes. If the lumps of maleimides happen to enter the dissolving tank in large amounts all at once, the heat imparted to the solution by the heating system falls short of the level required for dissolving the maleimides, with the result that the lumps of solid maleimides remain intact within the dissolving tank. When this situation arises, the dissolving tank is no longer capable of continuing the operation of stirring which is indispensable to dissolution. Thus, the lumps cannot be dissolved. There are also times when the failure to stir the liquid in the dissolving tank results in local heating of the liquid near the heating surfaces and brings about serious consequences such as, for example, polymerisation of the solution. The dissolution operation is generally carried out at a high temperature close to the boiling point of acrylonitrile. As is widely known, acrylonitrile is an extremely flammable compound and the acrylonitrile vapour, on mixture with air, readily produces an explosive gas. As mentioned above, the solid maleimides are stowed in returnable containers, drums, paper bags, and plastic bags. These containers do not easily permit thorough displacement of the air entrapped therein with an inert gas. When the solid maleimides are released from such containers and introduced into the dissolving tank to be dissolved in acrylonitrile, the air in the gaps between the individual particles of the solid maleimides is inevitably entrained by the solid maleimides and mixes with acrylonitrile giving rise to an explosive gas. Thus, existing methods for the dissolution of solid maleimides in acrylonitrile cannot be considered perfect in the strict sense of the word. The circumstances call for the development of a method which produces an acrylonitrile maleimides solution without entailing any of the drawbacks mentioned above. An object of this invention, therefore, is to provide an acrylonitrile maleimides solution of improved shelf life and a method for its production thereof. Another object of this invention is to provide a method for producing an acrylonitrile maleimides solution easily without exposing human bodies to minute particles of maleimides. A further object of this invention is to provide a method for producing an acrylonitrile maleimides solution even from solid maleimides which have coalesced into coarse lumps during storage. According to the invention there is provided an acrylonitrile maleimides solution composition, characterised by an acid component adjusted to a level of not more than 0.3% by weight based on the amount of the maleimides present in the solution, and a polymerisation inhibitor adjusted to a level in the range of 0.0001 to 1% by weight based on the amount of the solution. According to another aspect of the invention, there is provided a method for the production of an acrylonitrile maleimide solution which comprises adjusting the acid component in the acrylonitrile maleimides solution to a level of no more than 0.3% by weight based on the amount of the maleimides present in the solution, and adjusting a polymerisation inhibitor in the solution to a level in the range of 0.0001 to 1% by weight based on the amount of the solution. According to a further aspect of the invention, there is provided a method for the production of an acrylonitrile maleimides solution characterised by placing solid maleimides in a substantially airtight closed container provided with a liquid circulating nozzle and circulating heated acrylonitrile in the presence of a polymerisation inhibitor through the solid maleimides via the nozzle, thereby dissolving the maleimides. According to a still further object of the invention, there is provided a method for the production of an acrylonitrile maleimides solution, characterised by either placing preliminarily loose solid maleimides blocked particles in an airtight container or crushing solid maleimides in the airtight container and then, while retaining a substantially inert atmosphere, continuously or intermittently introducing the maleimides from the container to a dissolving tank, thereby dissolving the maleimides in acrylonitrile in the tank. Figure 1 is a schematic diagram illustrating a typical maleimides dissolving apparatus to be used in working the method for the production of an acrylonitrile solution according to the present invention. The applicants have discovered that acrylonitrile itself and an acrylonitrile maleimides solution of high purity possess no corrosiveness to metals. After a study on various corrosive impurities present in maleimides, it was found that the acid component in the maleimides is the cause for the corrosion of metals. It has been found quite unexpectedly that the stability of the acrylonitrile maleimides solution is significantly affected by the amount of the acid component in the maleimides. It has also been found that maleimides having a small acid component content can exist very stably in the presence of a polymerisation inhibitor. The present invention has been perfected as the result. Specifically, this invention is directed to an acrylonitrile maleimides solution composition highly satisfactory in shelf life, having the acid component in the acrylonitrile maleimides solution adjusted to a level of no more than 0.3% by weight based on the amount of the maleimides contained in the solution and having a polymerisation inhibitor incorporated in the solution in an amount in the range of 0.0001 to 1% by weight based on the amount of the solution. The maleimides to which the transferring and storaging method of this invention can be effectively applied are the compounds represented by the general formula I: wherein R stands for one member selected from the class consisting of hydrogen atom, an alkyl group of 1 to 20 carbon atoms, phenyl group, benzyl group, cyclohexyl group, pyridyl group, quinolyl group, and the groups mentioned above severally having a halogen substitution, a carboxyl group substitution, or nitro group substitution, preferably an alkyl group or a phenyl group. Typical examples of these compounds include maleimide, N-methyl maleimide, N-ethyl maleimide, N-hexyl maleimide, N-octyl maleimide, N-dodecyl maleimide, N-benzyl maleimide, N-cyclohexyl maleimide, N-phenyl maleimide, N-nitrophenyl maleimide, N-methoxyphenyl maleimide, N-methylphenyl maleimide, N-carboxyphenyl maleimide, N-hydroxyphenyl maleimide, N-chlorophenyl maleimide, N-dimethylphenyl maleimide, N-dichlorophenyl maleimide, N-bromophenyl maleimide, N-dibromophenyl maleimide, N-trichlorophenyl maleimide, and N-tribromophenyl maleimide. The acid component present in the maleimides may be an acid catalyst used in the production of maleimides or an impurity or by-product from the production of the maleimides. Examples of the acid catalyst are inorganic or organic acids such as sulphuric acid, p-toluenesulphonic acid, benzenesulphonic acid, orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, and trichloroacetic acid and examples of the impurities are maleic acid, fumaric acid, maleinamic acid, and fumaramic acid. When the maleimides are produced by the dehydroimidation of maleinamic acid by the use of a carboxylic anhydride such as acetic anhydride, the acetic acid which is by-produced by the reaction with the formed water is also contained in the produced maleimides. Though the amount of the acid component will vary depending upon the method used for purification of maleimides, it normally falls in the range of 0.01 to 5% by weight based on the amount of maleimides produced. To prevent the acrylonitrile maleimides solution from corroding metals and to improve the acid component level in the maleimides must be lowered to no more than 0.3% by weight, preferably no more than 0.2% by weight. The reduction in the acid component in the maleimides may be attained, for example, by a method which purges the maleimides of the acid component by thorough washing with water or a method which curbs the by-production of acidic impurities by selection of the reaction conditions in the production of maleimides. For the production of maleimides, a method which effects dehydroimidation of maleinamic acids by the use of acetic anhydride and a method which effects dehydroimidation of maleinamic acid in acrylonitrile by the use of acetic anhydride are available, for example. By any of these methods which involve the use of acetic anhydride, it is extremely difficult to lower the acid component in the maleimides produced to a level of no more than 0.3% by weight even when the product is thoroughly washed with water or an alkali. For the product by any of these methods to be stably stored on a commercial scale, there are problems yet to be solved. Maleimides which are produced by a synthesis in an organic solvent in the presence of an acid catalyst are more desirable in the sense that the removal of the acid component is easy to make. A more desirable solution might be a method which refines the maleimides produced as described above to a high level of purity by washing them with water and further distilling the washed maleimides may be cited. These are not the only methods available for the removal of the acid component. The polymerisation inhibitors which can be used in the dissolution of solid maleimides in acrylonitrile include methoxybenzoquinone; p-methoxyphenol; phenothiazine; hydroquinone; alkylated diphenylamines; methylene blue; tert-butyl acatechol; tert-butylhydroquinone; dialkyl dithiocarbamates such as zinc dimethyldithiocarbamate, copper dimethyldithiocarbamate, and copper dibutyldithiocarbamate; thiodipropionic esters; mercaptobenzimidazole; triphenyl phosphites; alkylphenols; and hindered phenols such as 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine; 2,2'-thiobis-(4-methyl-6-t-butylphenol) and triethylene glycol bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate], for example. The amount of the polymerisation inhibitor to be used is in the range of 0.0001 to 1% by weight, preferably 0.001 to 0.5% by weight, based on the amount of the acrylonitrile maleimides solution. The particular kind of the polymerisation inhibitor to be used is selected in due consideration of the kind of the polymer to be produced, the method of polymerisation, and the initiator to be used. Particularly when the finished product of a styrene type resin such as ABS resin or an AS resin is desired to be a polymer which is white in colour, hindered phenols are preferred as polymerisation inhibitors. The addition of the polymerisation inhibitor may be effected by its being dissolved in advance in acrylonitrile or by being directly mixed with solid maleimides. The polymerisation inhibitor is believed effectively to curb the occurrence of colouring impurities in the finished product in the acrylonitrile maleimides solution or during the course of polymerisation. The concentration of maleimides in the acrylonitrile maleimides solution is selected in dependence upon the nature of the final polymer to be obtained by use of the acrylonitrile maleimides solution, the method of polymerisation, and the conditions of polymerisation. Generally, this concentration is in the range of 30 to 90% by weight, preferably 40 to 70% by weight. The dissolution of maleimides in acrylonitrile can be attained basically by any of the conventional methods available for the purpose. It may be effected by throwing acrylonitrile into maleimides or allowing maleimides to dissolve an acrylonitrile. The maleimides to be used in this case may be in a solid state or in a molten liquid state. The temperature of the solution thus obtained by the dissolution is generally in the range of 10° to 70°C, though it is variable with the concentration of maleimides in the solution. During the course of this dissolution, the vapour phase in the reaction system is preferably displaced with nitrogen and may be maintained under normal pressure. This invention also extends to a method for the production of an acrylonitrile maleimides solution, which comprises placing solid maleimides in a substantially airtightly closed container provided with liquid circulating nozzles and circulating heated acrylonitrile solution through the solid maleimides in the presence of a polymerisation inhibitor via the liquid circulating nozzles thereby dissolving the maleimides. The solid maleimides may be in the form of flakes, granules, or minute particles. Preferably, they are in the form of flakes. It has been found that the minute particles in maleimides which poses problems as mentioned above are preferentially dissolved in acrylonitrile in accordance with the method of the present invention. Common sense might lead one to infer that when a solid substance is brought into contact with a solvent, the solid substance may not easily be dissolved in the solvent where the individual particles of the solid substance coalesce face to face and form large lumps or are shed from the solid substance and find their way to the intervening spaces and so interfere with the passage of the solvent through the spaces. It is surprising to note that in the case of the combination of maleimides and acrylonitrile, the acrylonitrile solution can pass easily through the spaces between the individual particles and, therefore, the solid maleimides are very easily dissolved. The maleimides are highly susceptible to polymerisation and, even during their dissolution in acrylonitrile, polymerisation is readily induced. It has been found, however, that this polymerisation can be effectively prevented by the presence of the polymerisation inhibitor in the reaction system. It is therefore very surprising indeed that by the method of this invention, an acrylonitrile maleimides solution can be economically produced perfectly and easily without entailing the occurrence of minute particles of maleimides. It is only proper to conclude that the present invention itself constitutes a remarkable advance in the production of the solution. The airtight container to be used for the purpose of the dissolution has no particular restriction but is preferably provided with liquid-circulating nozzles. To be specific, either a stationary tank such as, for example, a tank provided with an internal heating coil or a jacketed tank, or a mobile tank such as, for example, a tank car, a tank lorry, or a bulk container may be used. The density to which the container is packed with the maleimides may be in the range of 0.2 to 0.8 ton/m³, preferably 0.3 to 0.7 ton/m³. The application of heat to the acrylonitrile in circulation may be attained by means of a heat exchanger to be disposed on the outside of the container or a heating jacket or a heating coil to be attached as an accessory to the container, for example. The temperature of the acrylonitrile solution to be circulated during the course of dissolution is generally set at a level about 10° to 30°C higher than the saturated solution temperature corresponding to the concentration of maleimides in the solution, though it is variable more or less with the concentration of maleimides in the acrylonitrile maleimides solution. The amount of the solution to be circulated during the dissolution of maleimides is generally set at a level such that the contents of the dissolution tank are wholly renewed 0.1 to 10 times per hour, though it is variable with such factor as the diameter of the pipe and the capacity of the liquid circulating pump. Any suitable concentration of the acrylonitrile maleimides solution to be produced may be selected. It is not particularly limited for the purpose of this invention. For the sake of the transportation or storage of maleimides in the form of a solution in acrylonitrile, this concentration is desired to be high. In this case, the concentration may be in the range of 30 to 90% by weight. In a preferred embodiment of this invention, the production of an acrylonitrile maleimides solution is achieved by packing a mobile tank such as a tank lorry or a bulk container with maleimides in the form of flakes, transporting the solid maleimides to a given destination, filling the container with acrylonitrile and a polymerisation inhibitor, and then heating and circulating the acrylonitrile through the interior of the tank. By this method, the tank lorry or bulk container is not required to be provided with any special heat insulating device adapted to prevent the maleimides from being precipitated in the acrylonitrile maleimides solution. Furthermore, the maleimides in transit are precluded from deterioration and the transportation and the handling of the maleimides are attained easily and economically. This method proves to be advantageous in many respects. This invention is also directed to a method for the production of an acrylonitrile maleimides solution, which comprises placing solid maleimides in a substantially airtight closed container provided with liquid circulating nozzles one each in its upper and lower parts, adding acrylonitrile to the solid maleimides in the presence of a polymerisation inhibitor, and then withdrawing acrylonitrile solution from the container via the upper nozzle and heating the acrylonitrile solution and, at the same time, circulating the heated acrylonitrile through the container interior via the lower nozzle thereby dissolving the maleimides. Alternatively, the maleimides may be dissolved by withdrawing the acrylonitrile solution from the container via the lower nozzle and circulating heated acrylonitrile solution into the container via the upper nozzle. The acrylonitrile maleimides solution which is retained inside the container, however, has a widely differing concentration in its upper and lower layers and forms a supersaturated solution in the lower layer. When the solution in the lower layer region is withdrawn via the lower nozzle, therefore, the maleimides are precipitated in the form of crystals near the lower nozzle and tend to clog the lower nozzle and consequently prevent its function of releasing the liquid. In accordance with the method of this invention which effects the circulation of the solution by withdrawing this solution from the upper layer region via the upper nozzle and returning the heated solution to the lower layer region via the lower nozzle, the occurrence of crystals of maleimides near the nozzles is not observed at all and the clogging of the nozzles with precipitated crystals avoided is because the solution withdrawn via the upper nozzle is an unsaturated solution. Advantageously, the possibility of crystals being precipitated in the regions adjacent to the nozzles is wholly avoided since the inflow of the solution via the lower nozzle dilutes the dense supersaturated solution present in the proximity of the lower nozzle and giving rise locally to an unsaturated solution. It has been found consequently that an acrylonitrile maleimides solution can be easily produced by withdrawing the solution from the upper layer region, heating the solution from the upper layer region, heating the solution for example by passage through a heat exchanger and circulating the heated solution into the container interior via the lower nozzle. The maleimides are highly susceptible to polymerisation and readily polymerise even during their dissolution in acrylonitrile. It has been found, however, that polymerisation of the maleimides can be effectively prevented by carrying out the dissolution in the presence of a polymerisation inhibitor. Generally when a solid substance is brought into contact with a solvent, the individual particles of the solid substance coalesce and form large lumps or the minute particles shed from the solid substance collect in the intervening gaps between the individual particles possibly to an extent of impeding the passage of the solvent through the intervening gaps. There is also a possibility that crystals precipitated near out outlet nozzle might clog the nozzle and render the release of liquid difficult. Thus, it is very difficult to dissolve a solid substance and obtain a solution thereof by causing a solvent to be circulated through a packed bed of the solid substance. Moreover, in the case of the maleimides which are a polymerising substance, polymerisation possibly induced during the course of dissolution is a potential cause of difficulties. A method which produces a solution of a polymerising solid substance by packing the substance in a container and circulating a solvent through this container has not been accepted as a useful method. It is therefore most surprising that by the method of this invention, the acrylonitrile maleimides solution can be produced economically and safely by enabling the solid maleimides, a substance highly susceptible to polymerisation, to be dissolved very easily in acrylonitrile without entailing the occurrence of minute maleimide particles. The closed airtight tank to be used for the dissolution is not required to be in any special form but is only required to be provided with liquid circulating nozzles, one each in its upper part and lower part. To be specific, either a stationary tank such as, for example, a tank provided with an internal heating coil or a tank provided with a heating jacket or a mobile tank such as, for example, a tank car, a tank lorry, a bulk container may be used. The density of the packing of the maleimides in the container, the method for heating the acrylonitrile in process of circulation, the temperature of the acrylonitrile solution, the amount of the solution to be circulated for the dissolution of the maleimides, and the concentration of maleimides in the acrylonitrile maleimides in the acrylonitrile maleimides solution may be as described above. This invention also extends to a method for the production of an acrylonitrile maleimides solution which comprises either placing pre-prepared loosened solid maleimides crushed particles in an airtightly closed container or crushing solid maleimides inside the airtightly closed container and then, while retaining a substantially inert atmosphere, continuously or intermittently introducing the maleimides from the container into a dissolving tank to be dissolved in acrylonitrile therein. After study, it has been found that though the solid maleimides in storage have a property such that individual particles coalesce and form a large lumps, this transformation into the large lumps proceeds very slowly and that. Therefore, when the large lumps of the loosened solid maleimides crushed particles mentioned above are crushed and transformed into ordinary flakes, tablets, or granules, they can be easily handled, though over a short span of time. It has also been found that the atmosphere surrounding the loosened particles can be readily displaced with an inert gas such as nitrogen and that when the maleimides are dissolved in acrylonitrile or after dissolution, the composition of the gaseous phase over the solution can be easily adjusted to fall outside explosive limits. This discovery has also been incorporated in the present invention. The present invention will now be described by way of example with reference to Figure 1 which illustrates an apparatus for the dissolution of maleimides in accordance with the invention. The solid maleimides which are stored in paper bags, plastic bags, or returnable containers are loosened and crushed to particles and then packed in an an airtight closed container 1 annexed to the dissolving tank 6, prior to their introduction into the dissolving tank 6. Alternatively, the solid maleimides are loosened and crushed to particles within the airtight closed container and then introduced into the dissolving tank 6. This crushing of the solid maleimides can be accomplished by any of conventional method available for the purpose. After the solid maleimides have been transferred from their original container to the airtight closed container 1, the air entrapped in the closed container 1 is displaced with an inert gas such as nitrogen, carbon dioxide, or argon through the nozzles 2 and 3 associated with the closed container 1. After the operation mentioned above, the crushed maleimides particles are delivered continuously or intermittently from the airtight closed container 1 into the dissolving tank 6. Thus, by the method of this invention, the acrylonitrile solution can be produced quite safely, without the risk of lumps of solid maleimides clogging the maleimides discharge outlet 5 and without the danger of the acrylonitrile mixing with air to give rise to an explosive gas. The dissolving tank 6 used for the dissolution of solid maleimides is provided with a heating coil or a heating jacket 10 and a stirrer 11. It is also provided with a solid maleimides inlet nozzle 9 and an acrylonitrile maleimides solution outlet 8. The airtight closed container 1 attached to the dissolving tank 6 is provided with a solid maleimides inlet 4 and a solid maleimides discharge outlet 5 at its underside. It is further provided with an inert gas inlet nozzle 2 and an outlet nozzle 3 since the airtight closed container requires the air entrapped to be displaced with an inert gas. In order that displacement of the entrapped gas in the airtight closed container 1 by an inert gas might be carried out easily, the container must be constructed so as to retain the necessary airtightness. Specifically, the airtightness is ensured by providing each of the solid maleimides inlet 4 and discharge outlet 5, and the inert gas nozzles 2,3 with a stop valve. It is provided, when necessary, at the solid maleimides inlet 4 with a device for crushing large lumps of solid maleimides (not shown). Where the feed rate of the solid maleimides is required to be controlled rigidly, the airtight closed container may be provided at the solid maleimides discharge outlet 5 with a rotary valve (not shown). The airtight closed container may be made of any material which is capable of withstanding the action of acrylonitrile vapour and maleimides. Desirably, it is made of aluminium, stainless steel, or carbon steel, for example. The dissolution is desired to be be accomplished by filling the dissolving tank in advance with heated acrylonitrile and then introducing the solid maleimides into the acrylonitrile held in the tank. Of course, this particular sequence of procedure is not critical. The temperature of the contents of the dissolving tank during the course of dissolution is generally set in the range of 10° to 70°C, preferably 20° to 60°C, though it is variable with the concentration of the acrylonitrile maleimides solution. The rate of the introduction of solid maleimides into acrylonitrile is generally in the range of 1 to 1,000 kg of solid maleimides per ton of acrylonitrile per minute, though this is variable with the amount of heat applied to the solution. It is selected in due consideration of the inner volume of the dissolving tank, the diameter of the inlet, the inner volume of the hopper, etc. The present invention, as described above, concerns an acrylonitrile maleimides solution which as the acid component in a acrylonitrile maleimides solution adjusted to a level of no more than 0.3% by weight based on the amount of the maleimides contained in the solution and has the polymerisation inhibitor adjusted to a level in the range of 0.0001 to 1% by weight based on the amount of the solution. Since carbon steel or stainless steel, a general purpose industry grade material, can be used as the material for the storing container, the apparatus for handling is not expensive. The tank lorry, tank car, or bulk container which is used for transportation of the solution is not required to be made of any special material but may be made of a general-purpose ordinary material. Thus, the solution can be carried out inexpensively. Particularly since the acrylonitrile maleimides solution can be stably handled and prevented from deterioration during storage, the final polymer produced from the maleimides enjoys a high quality. As described above, by the method of this invention, the maleimides can be produced and supplied inexpensively and safely. Further, since the method of this invention is as described above, it enjoys the following advantages. The acrylonitrile maleimides solution can be produced safely and easily without entailing the occurrence of harmful minute particles of maleimides or the exposure of human bodies to the maleimides. Since acrylonitrile maleimides solution can be produced with a very simple apparatus, the acrylonitrile maleimides solution produced is not expensive. The acrylonitrile maleimides solution can be prepared immediately before its actual use by the procedure which comprises transporting the maleimides to the destination stowed in a mobile tank such as a tank lorry or a bulk container and dissolving the maleimides in acrylonitrile there. Since the problems due to the otherwise inevitable precipitation of maleimides in transit can be precluded, the acrylonitrile maleimides solution can be obtained inexpensively and simply. The acrylonitrile maleimides solution can be easily produced from the solid maleimides which have been transformed into large lumps during storage. The solid maleimides to be effectively used in the present invention are never discriminated on account of the type of the storing container to be used. The operation of dissolving the solid maleimides in acrylonitriles performed very easily because the rate of introduction of the solid maleimides into the dissolving tank can be freely controlled. The solution can be produced with great safety because the acrylonitrile is not allowed to mix with air and form an explosive gas. The acrylonitrile maleimides solution can be produced inexpensively with a simple apparatus. The invention will now be described more specifically below with reference to the following examples. Example 1 A flask having an inner volume of 500 ml and provided with a stirrer and a condenser was charged with 200 g of N-phenyl maleimide adjusted to the following composition, 100 g of acrylonitrile, and 10 mg of p-methoxy phenol. N-phenyl maleimide composition N-phenyl maleimide 99.9% by weight N-phenyl maleinamic acid (molecular weight 191) 0.1% " Total acid component (only N-phenyl maleinamic acid) 0.1% " When the inner temperature of the flask was set to 50°C by adjusting the temperature of the bath, the maleimides were immediately dissolved to give rise to a perfectly clear yellow acrylonitrile maleimides solution. With the temperature of the water bath further adjusted, a test piece of carbon steel measuring 20 mm x 40 mm x 2 mm was left standing in the solution at a temperature of 50°C for 30 days. At the end of this time, the solution was found to have retained its original clarity and contained absolutely no foreign matter. The test piece of carbon steel showed absolutely no discernible sign of corrosion. When the solution was subjected to distillation under vacuum to expel acrylonitrile, there remained bright yellow crystals. By liquid chromatography, the crystals were found to have a purity of 99.9% by weight and absolutely no sign of deterioration. Control 1 The procedure of Example 1 was faithfully repeated, except that N-phenyl maleimide adjusted to the following composition was used instead. When this solution was left standing similarly at 50°C for 30 days, it turned brown, formed insolubles in large amounts, and completely lost its clarity. The surface of the test piece of carbon steel lost its initial metallic gloss and showed clear signs of corrosion. When the solution was distilled to expel acrylonitrile, there remained a yellowish brown solid substance. By liquid chromatography, this solid substance was found to have a purity of 95.3% by weight and clear signs of deterioration. Control 1 The procedure of Example 1 was faithfully repeated, except that N-phenyl maleimide adjusted to the following composition was used instead. When this solution was left standing similarly at 50°C for 30 days, it turned brown, formed insolubles in large amounts, and completely lost its clarity. The surface of the test piece of carbon steel lost its initial metallic gloss and showed clear signs of corrosion. When this solution was distilled to expel acrylonitrile, there remained a light yellowish brown solid substance. By liquid chromatography, this solid substance was found to have a purity of 97.2% by weight and clear signs of deterioration. Examples 2 to 14 and Control 3 The procedure of Example 1 was repeated, except that N-phenyl maleimide adjusted to the following composition was used instead, the kind and amount of a polymerisation inhibitor were changed as indicated in Table 1 and the inner temperature of the flask was changed to 70°C. The results are shown in Table 1. N-phenyl maleimide composition N-phenyl maleimide 99.8% by weight N-phenyl maleinamic acid 0.1% " Maleic acid 0.1% " Examples 15 to 17 Solutions were prepared using in each case N-phenyl maleimide adjusted to the following composition and respectively using triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], and p-methoxphenol as a polymerisation inhibitor. They were left standing at 70°C for 30 days by way of a test for stability. The results are shown in Table 2. Example 18 A cylindrical tank measuring 5.6 m in length and 2.2 m in inside diameter, having an inner volume of 20 m³, and provided with nozzles 3 inches (7.6cm) in inside diameter, one each in the central part of the upper side and at the lower end was charged with 8 tons of N-phenyl maleimide adjusted to the following properties and 0.4 kg of p-methoxyphenol. The n-phenyl maleimide used was the same as that of Example 1. Attributes of N-phenyl maleimide (1) Shape Flakes (2) Particle diameter distribution No more than 1mm 10% 1 to 4mm 90% (3) Average particle diameter 2mm The packing density of the tank was 0.5 ton/m³ and the void space inside the tank was about 3 m³. To the contents of the tank, 8 tons of acrylonitrile heated to 60°C was added via the liquid inlet nozzle disposed in the upper part of the tank. Then, after 30 minutes following this addition, the solution was disposed at the lower end of the tank. At this time, the liquid temperature of the tank was 23°C. Subsequently, the acrylonitrile solution was heated to 50°C with a heat exchanger possessing a heat transfer area of 30 m² and circulated back into the tank interior via the lower nozzle of the tank. The amount of circulation of this solution was 40 tons/hr, indicating that the solution was circulated through the tank interior at a rate of 2.5 times per hour. When N-phenyl maleimide fed to the tank was thoroughly dissolved, the saturated solution temperature of this solution was 26°C. When this operation was continued for 2 hours, the N-phenyl maleimides was in a thoroughly dissolved state. Thus, a clear yellow acrylonitrile N-phenyl maleimide solution was obtained. By ultraviolet absorption spectrometry, this solution was found to have a concentration of 50% by weight, indicating that the N-phenyl maleimide was thoroughly dissolved. During the dissolution of the N-phenyl maleimide, the occurrence of minute particles of N-phenyl was not observed at all. Example 19 A cylindrical tank measuring 5.6 m in length and 2.2 m inside diameter, having an inner volume of 20 m³, and provided with nozzles 3 inches (7.6cm) in inside diameter, one each in one upper and lower ends, was charged with 8 tons of N-phenyl maleimide adjusted to the following properties and 0.4 kg of p-methoxy phenol. The N-phenyl maleimide used here was the same as that of Example 2. Attributes of N-phenyl maleimide (1) Shape Flakes (2) Particle diameter distribution No more than 1 mm 10% 1 to 4 mm 90% (3) Average particle diameter 2 mm The packing density of the tank was 0.5 ton/m³ and the void spaced of the tank was about 4 m³. To the interior of the tank, 8 tons of acrylonitrile heated to 60°C was introduced via the lower liquid inlet nozzle. Then, after 30 minutes following the addition of the heated acrylonitrile, the solution was withdrawn from the tank via the upper liquid discharge nozzle. Then, after 30 minutes following the addition of the heated acrylonitrile, the solution was withdrawn from the tank via the upper liquid discharge nozzle. At this time, the liquid temperature of the tank was 23°C. Subsequently, the acrylonitrile solution was heated to 50°C with a heat exchanger having a heat transfer area of 30 m² and circulated back into the tank via the lower liquid inlet nozzle. The amount of the circulation was 40 tons/hr, indicating that the solution was circulated through the interior of the tank at a rate of 2.5 times per hour. When the N-phenyl maleimide was thoroughly dissolved, the saturated solution was 26°C. When this operation was continued for 2 hours, the N-phenyl maleimide was in a thoroughly dissolved state. Consequently, there was obtained a yellow clear acrylonitrile N-phenyl maleimide solution. By ultraviolet adsorption spectrometry, this solution was found to have a concentration of 50% by weight, indicating that the N-phenyl maleimide was thoroughly dissolved. During the course of dissolution of N-phenyl maleimide, the occurrence of minute particles of N-phenyl maleimide was not observed at all.

Claims: An acrylonitrile maleimides solution composition, characterised by an acid component adjusted to a level of not more than 0.3% by weight based on the amount of the maleimides present in the solution, and a polymerisation inhibitor adjusted to a level in the range of 0.0001 to 1% by weight based on the amount of the solution. A composition as claimed in Claim 1, characterised in that the concentration of the maleimides is in the range of 30 to 90% by weight. A composition as claimed in Claim 1 or Claim 2, characterised in that the amount of the acid component is no more than 0.2% by weight based on the amount of the maleimides in the solution. A composition as claimed in any preceding claim, characterised in that the polymerisation inhibitor is at least one member selected from the group consisting of methoxybenzoquinone, p-methoxyphenol, phenothiazine, hydroquinone, alkylated diphenylamines, methylene blue, tert-butyl catechol, tert-butyl hydroquinone, dialkyldithiocarbamates, copper salicylate, thiodipropionic esters, mercaptobenzimidazole, triphenyl phosphites, alkyl phenols, alkyl bisphenols, 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, 2,2'-thiobis-(4-methyl-6-t-butylphenol), and triethylene glycolbis-[3-(-t-butyl-5-methyl-4-hydroxyphenyl) propionate]. A composition as claimed in any preceding claim characterised in that the polymerisation inhibitor is present in an amount in the range of 0.001 to 0.5% by weight based on the amount of the solution. A method for the production of an acrylonitrile maleimides solution as claimed in any preceding claim which comprises adjusting the acid component in the acrylonitrile maleimides solution to a level of no more than 0.3% by weight based on the amount of the maleimides present in the solution, and adjusting a polymerisation inhibitor in the solution to a level in the range of 0.0001 to 1% by weight based on the amount of the solution. A method for the production of an acrylonitrile maleimides solution characterised by placing solid maleimides in a substantially airtight closed container provided with a liquid circulating nozzle and circulating heated acrylonitrile in the presence of a polymerisation inhibitor through the solid maleimides via the nozzle, thereby dissolving the maleimides. A method as claimed in Claim 7, characterised in that the container is provided with liquid circulating nozzles, one in each of its upper and lower parts, the acrylonitrile is added to the solid maleimides in the presence of a polymerisation inhibitor, the acrylonitrile solution is then withdrawn from the container via the upper nozzle, the acrylonitrile solution is heated and circulated through the container via the lower nozzle thereby dissolving the said maleimides. A method as claimed in Claim 7 or Claim 8 characterised in that the polymerisation inhibitor is incorporated in the solution in the range of 0.0001 to 1% by weight based on the amount of the maleimides. A method as claimed in any of Claims 7 to 9 characterised in that the concentration of the maleimides is in the range of 30 to 90% by weight. A method as claimed in any of Claims 7 to 10 characterised in that the polymerisation inhibitor is at least one member selected from the group consisting of methoxybenzoquinone, p-methoxyphenol, phenothiazine, hydroquinone, alkylated diphenylamines, methylene blue, tert-butyl catechol, tert-butyl hydroquinone, dialkyldithiocarbamates, copper salicylate, thiodipropionic esters, mercaptobenzimidazole, triphenyl phosphites, alkyl phenols, alkyl bisphenols, 2,4-bis(n-oxtylthio)-6-(4-hydroxy-3,5-di-butylanilino)-1,3,5-triazine, 2,2'-thiobis-(4-methyl-6-t-butylphenol), and triethylene glycolbis-[3,(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate]. A method for the production of an acrylonitrile maleimides solution, characterised by either placing prediminarily loosed solid maleimides blocked particles in an airtight container or crushing solid maleimides in the airtight container and then, while retaining a substantially inert atmosphere, continuously or intermittently introducing the maleimides from the container to a dissolving tank, thereby dissolving the maleimides in acrylonitrile in the tank. A method as claimed in Claim 12 characterised in that the airtight container is a hopper type container provided with inlet and outlet nozzles for an inert gas and inlet and discharge outlet for maleimides. A method as claimed in Claim 12 or Claim 13, characterised in that the rate at which the maleimides are introduced into the acrylonitrile is in the range of 1 to 1,000 kg/min per ton of acrylonitrile. A method as claimed in any of Claims 12 to 14 characterised in that the inert atmosphere is formed by the introduction of nitrogen, carbon dioxide and/or argon. A method as claimed in Claims 7 to 15 characterised in that the meleimides are dissolved in the acrylonitrile at a temperature in the range to 10° to 70°C.

Inventors: KANEI, HITOSHI, KISHINO, KAZUO, KITA, YUICHI, NAKAGAWA, MASAKAZU, OKUNO, TAKESHI, SAKAMOTO, KENTARO
Applicants: NIPPON SHOKUBAI CO., LTD.
Application year: 1988
Main classification: C07D207
IPC codes: C07D207