Abstract: This invention discloses a method for producing maleic anhydride comprising an azeotropic distillation step to dehydrate a crude maleic acid-containing aqueous solution, which method is characterized by as an azeotropic solvent (1) using an organic solvent exhibiting a maximum dissolving concentration of the organic solvent in water in the range of 0.1-5% by weight at a temperature of 20° C. According to this invention, it is made possible to prevent the occurrence of a blocking substance, allow a continuous operation for a long time, and remove by-produced acid components by a process of distillation for azeotropic dehydration.

Abstract: An apparatus for the preparation and supply of a polymerization inhibitor which constantly effects stable supply of a polymerization inhibitor solution adjusted to a prescribed concentration and enables a compound handled at the next step to be prevented from polymerization is provided. The apparatus for the preparation and supply of a polymerization inhibitor has at least two tanks and a stirring device, a liquid level detector, a polymerization inhibitor input port, a concentration-adjusting liquid input port, and a polymerization inhibitor solution feed opening, each being installed in at least one of said tanks.

Abstract: A method for starting up a distilling column destined to handle an easily polymerizing compound-containing solution characterized by supplying at the start of the operation of the distilling column a polymerization inhibitor to the bottom liquid of the distilling column having a temperature of not higher than 80° C. Further, by supplying a reflux liquid through the top of the distilling column or the middle stage of the column prior to the start of the temperature elevation of the distilling column, thereby preventing the polymerization of the easily polymerizing compound more effectively.

Abstract: A method for stopping a purifying column handling an easily polymerizing compound-containing solution is disclosed, which method is characterized by lowering the inner oxygen concentration of the column below the limit of oxygen concentration by supplying an inert gas to the column while the concentration of the gas of easily polymerizing compound is in the range of 100% to the lower limit of the flammable range in volume % of the purifying column or by further supplying a reflux liquid thereby cooling the interior of the column at a rate in the range of 0.01-10° C./min. This invention enjoys exceptionally high economic value in respect that it is capable of preventing the easily polymerizing compound from the occurrence of polymerization in the purifying column, precluding the interior of the purifying column from being clogged by adhesion of a polymer, and moreover avoiding the possibility of explosion.

Abstract: According to the present invention, a tank for storing an easily polymerizable compound, the tank fitted with a liquid inlet pipe 3, a liquid draw-off pipe 4 and a liquid recirculating pipe 5, is characterized in that, assuming terminal ends of the individual pipes 3-5 are located at the same height, the apex angle formed by a line joining the central points of the end openings of the pipe 3 and the pipe 4 at the central point of a horizontal cross section of the tank, or the apex angle formed by a line joining the central points of the pipe 5 and the pipe 4 at the central point of the horizontal cross section of the tank, is equal to or larger than 90°. A method of storing an easily polymerizable compound of the invention utilizes the aforementioned tank for storing the polymerizable compound.

Abstract: An apparatus for the preparation and supply of a polymerization inhibitor which constantly effects stable supply of a polymerization inhibitor solution adjusted to a prescribed concentration and enables a compound handled at the next step to be prevented from polymerization is provided. The apparatus for the preparation and supply of a polymerization inhibitor has at least two tanks and a stirring device, a liquid level detector, a polymerization inhibitor input port, a concentration-adjusting liquid input port, and a polymerization inhibitor solution feed opening, each being installed in at least one of said tanks.

Abstract: This invention discloses a method for producing maleic anhydride comprising an azeotropic distillation step to dehydrate a crude maleic acid-containing aqueous solution, which method is characterized by as an azeotropic solvent (1) using an organic solvent exhibiting a maximum dissolving concentration of the organic solvent in water in the range of 0.1-5% by weight at a temperature of 20° C. According to this invention, it is made possible to prevent the occurrence of a blocking substance, allow a continuous operation for a long time, and remove by-produced acid components by a process of distillation for azeotropic dehydration.

Abstract: A solid substance removing device comprising a body provided with a fluid inlet pipe and a fluid outlet pipe and a filtering part disposed between the fluid inlet pipe and the fluid outlet pipe inside said body, the filtering part having (a) a thickness in the range of 5-500 mm, (b) a percentage of voids in the range of 60-99.5 vol. %, and (c) a contact surface area in the range of 100-2000 m2/m3. Owing to the construction described above, it is made possible to facilitate removal of the solid substance and, at the same time, prevent new generation of a polymer during the production of an easily polymerizing substance.

Abstract: A method for stopping a purifying column handling an easily polymerizing compound-containing solution is disclosed, which method is characterized by lowering the inner oxygen concentration of the column below the limit of oxygen concentration by supplying an inert gas to the column while the concentration of the gas of easily polymerizing compound is in the range of 100% to the lower limit of the flammable range in volume % of the purifying column or by further supplying a reflux liquid thereby cooling the interior of the column at a rate in the range of 0.01-10° C./min. This invention enjoys exceptionally high economic value in respect that it is capable of preventing the easily polymerizing compound from the occurrence of polymerization in the purifying column, precluding the interior of the purifying column from being clogged by adhesion of a polymer, and moreover avoiding the possibility of explosion.

Abstract: A solid substance removing device comprising a body provided with a fluid inlet pipe and a fluid outlet pipe and a filtering part disposed between the fluid inlet pipe and the fluid outlet pipe inside said body, the filtering part having (a) a thickness in the range of 5-500 mm, (b) a percentage of voids in the range of 60-99.5 vol. %, and (c) a contact surface area in the range of 100-2000 m2/m3. Owing to the construction described above, it is made possible to facilitate removal of the solid substance and, at the same time, prevent new generation of a polymer during the production of an easily polymerizing substance.

Abstract: A method for starting up a distilling column destined to handle an easily polymerizing compound-containing solution characterized by supplying at the start of the operation of the distilling column a polymerization inhibitor to the bottom liquid of the distilling column having a temperature of not higher than 80° C. Further, by supplying a reflux liquid through the top of the distilling column or the middle stage of the column prior to the start of the temperature elevation of the distilling column, thereby preventing the polymerization of the easily polymerizing compound more effectively.

Abstract: According to the present invention, a tank for storing an easily polymerizable compound, the tank fitted with a liquid inlet pipe 3, a liquid draw-off pipe 4 and a liquid recirculating pipe 5, is characterized in that, assuming terminal ends of the individual pipes 3-5 are located at the same height, the apex angle formed by a line joining the central points of the end openings of the pipe 3 and the pipe 4 at the central point of a horizontal cross section of the tank, or the apex angle formed by a line joining the central points of the pipe 5 and the pipe 4 at the central point of the horizontal cross section of the tank, is equal to or larger than 90°. A method of storing an easily polymerizable compound of the invention utilizes the aforementioned tank for storing the polymerizable compound.