Method of Recovering Aqueous N-methylmorpholine-N-Oxide Solution Used in Production of Lyocell Fiber

Abstract

A method of recovering an aqueous N-methylmorpholine-N-oxide (NMMO) solution used in production of Lyocell fiber includes: decoloring the aqueous NMMO solution by mixing the same with activated carbon using an agitation blower and by alternately energizing and de-energizing the agitation blower to contact the activated carbon with the aqueous NMMO solution thoroughly in an energy-efficient manner; filtering the aqueous NMMO solution which has been decolored through coarse filtration followed by ultrafiltration to remove the activated carbon and impurities from the aqueous NMMO solution; and concentrating the aqueous NMMO solution which has been filtered using one of a mechanical vapor recompression evaporator and a triple effect evaporator to remove water from the aqueous NMMO solution.

1 . A method of recovering an aqueous N-methylmorpholine-N-oxide (NMMO) solution used in production of Lyocell fiber, comprising:
 decoloring the aqueous NMMO solution by mixing the same with activated carbon using an agitation blower and by alternately energizing and de-energizing the agitation blower;   filtering the aqueous NMMO solution which has been decolored through coarse filtration followed by ultrafiltration to remove the activated carbon and impurities from the aqueous NMMO solution; and   concentrating the aqueous NMMO solution which has been filtered using one of a mechanical vapor recompression evaporator and a triple effect evaporator to remove water from the aqueous NMMO solution.   
     
     
         2 . The method of  claim 1 , further comprising adding an oxidizing agent to the aqueous NMMO solution which has been concentrated to oxidize N-methylmorpholine contained in the aqueous NMMO solution to N-methylmorpholine N-oxide; and adding a neutralizing agent to the concentrated aqueous NMMO solution to neutralize the oxidizing agent remaining in the concentrated aqueous NMMO solution. 
     
     
         3 . The method of  claim 1 , wherein a ratio of a duration to energize the agitation blower to a duration to de-energize the agitation blower ranges from 1:3 to 1:6, and a total time of the decoloring of the aqueous NMMO solution is not longer than 8 hours. 
     
     
         4 . The method of  claim 1 , wherein the amount of the activated carbon is 0.05 wt %-0.10 wt % based on the total weight of the aqueous NMMO solution. 
     
     
         5 . The method of  claim 1 , wherein the coarse filtration is conducted by using a cartridge filter that includes a cartridge having a surface coated with a filter aid, and by adding the filter aid to the decolored aqueous NMMO solution, the filter aid being made from diatomaceous earth and cellulose. 
     
     
         6 . The method of  claim 5 , wherein the amount of the filter aid is 0.03 wt %-0.05 wt % based on the total weight of the decolored aqueous NMMO solution, and a weight ratio of the diatomaceous earth to the cellulose is 4:1. 
     
     
         7 . The method of  claim 5 , further comprising centrifugally drying a sludge resulting from the coarse filtration. 
     
     
         8 . The method of  claim 1 , wherein the coarse filtration is conducted using a filter material that has a pore size ranging from 1 μm to 100 μm, and the ultrafiltration is conducted using a filter material that has a pore size ranging from 0.01 μm to 1 μm. 
     
     
         9 . The method of  claim 1 , wherein, after the concentrating step, the amount of N-methylmorpholine N-oxide in the aqueous NMMO solution ranges from 50 wt % to 55 wt % based on the total weight of the aqueous NMMO solution. 
     
     
         10 . The method of  claim 2 , wherein the oxidizing agent is H 2 O 2 , and the neutralizing agent is N 2 H 4 ·H 2 O. 
     
     
         11 . The method of  claim 10 , wherein N-methylmorpholine in the concentrated aqueous NMMO solution is oxidized by the oxidizing agent at a temperature of 80±2° C.