Nmp distilling apparatus

Abstract

The present invention provides a distillation apparatus for NMP for regenerating a spent NMP recovered from a step of producing an electrode for lithium ion batteries which is capable of purifying the NMP in a simple and safe manner irrespective of variation in concentration of water in a raw material or throughput, and is suitable for conducting an automatic operation on-site. The distillation apparatus for NMP according to the present invention comprises a first distillation column 1 in which the spent NMP as a liquid to be treated is subjected to distillation and separated into a high-concentration NMP and water comprising low-boiling components; and a second distillation column 2 in which bottoms from the first distillation column are further subjected to distillation and separated into a high-purity NMP and the high-concentration NMP comprising high-boiling components, the said distillation apparatus is also provided with an automatic treatment function comprising a start-up function in which the first and second distillation columns are respectively subjected to a reduced pressure operation and then a circulation operation to control the respective distillation columns in a stationary state, and then a continuous treatment operation of the distillation apparatus is initiated; and an operational mode switching function in which upon the continuous treatment operation, an operational mode of the distillation apparatus is switched again to the circulation operation according to a level of the liquid in the raw material tank 41 or a level of the liquid in the product tank 42.

1 . A distillation apparatus for NMP in which a spent NMP comprising low-boiling components and high-boiling components as impurities is purified,
 which distillation apparatus comprises:   a raw material tank for storing the spent NMP as a liquid to be treated;   a first distillation column in which the liquid to be treated which is supplied from the raw material tank is subjected to distillation and separated into a high-concentration NMP having a concentration of not less than 99% and water comprising the low-boiling components as bottoms and a distillate, respectively;   a second distillation column in which the bottoms from the first distillation column are further subjected to distillation and separated into a high-purity NMP having a concentration of not less than 99.9% and the high-concentration NMP comprising the high-boiling components as bottoms and a distillate, respectively; and   a product tank for storing the high-purity NMP obtained as the distillate from the second distillation column, and   which distillation apparatus is provided with an automatic treatment function comprising:   a start-up function in which after previously performing a reduced pressure operation of each of the first and second distillation columns, a circulation operation in which the liquid to be treated is fed from the raw material tank to the first distillation column and the distillate from the second distillation column is fed back to the raw material tank, is preformed to control the respective distillation columns in a stationary state, and then a continuous treatment operation of the distillation apparatus is initiated; and   an operational mode switching function in which upon the continuous treatment operation, an operational mode of the distillation apparatus is switched again to the circulation operation in the case where a level of the liquid in the raw material tank is lowered to a predetermined height during the continuous treatment operation or in the case where a level of the liquid in the product tank is raised to a predetermined height during the continuous treatment operation.   
     
     
         2 . A distillation apparatus according to  claim 1 , further comprising a check drum for recovering the high-purity NMP obtained as the distillate from the second distillation column, wherein the operational mode switching function performs switching an operational mode of the distillation apparatus again to the circulation operation upon the continuous treatment operation in the case where a level of the liquid in the raw material tank is lowered to a predetermined height during the continuous treatment operation, in the case where a level of the liquid in the product tank is raised to a predetermined height during the continuous treatment operation, or in the case where a level of the liquid in the check drum is raised to a predetermined height during the continuous treatment operation. 
     
     
         3 . A distillation apparatus according to  claim 1 , wherein the first distillation column is constructed such that a flow rate of steam through a reboiler is controlled according to an amount of the liquid to be treated which is fed from the raw material tank. 
     
     
         4 . A distillation apparatus according to  claim 1 , wherein the first distillation column is constructed such that the flow rate of steam through the reboiler is controlled such that a temperature of a recovery portion of the first distillation column is adjusted to a temperature corresponding to a boiling point of NMP. 
     
     
         5 . A distillation apparatus according to  claim 1 , wherein the automatic treatment function further comprises an automatic stopping function of stopping, in response to an operation stopping manipulation or an emergent stopping manipulation, operation of the reboiler at each of the first and second distillation columns, supply of the liquid to be treated from the raw material tank, and withdrawal of the distillate and the bottoms from each of the first and second distillation columns, and feeding an inert gas to each of the first and second distillation columns, to thereby equalize a pressure within each of the first and second distillation columns. 
     
     
         6 . A distillation apparatus according to  claim 5 , wherein in the automatic stopping function, when equalizing the pressure within each of the first and second distillation columns, the pressure within a lower pressure side one of the first and second distillation columns is adjusted to be equal to the pressure within a higher pressure side one of the first and second distillation columns, and then the pressures within both of the first and second distillation columns are raised to normal pressures.