Process and system for product recovery and cell recycle

Abstract

The invention is directed to a method for recovering at least one product from a fermentation broth. The invention relates to the use of a vacuum distillation vessel to recover products, such as ethanol, from a fermentation broth, where the fermentation broth comprises viable microbial biomass, and where the recovery of the product is completed in such a manner to ensure the viability of the microbial biomass. The invention provides for product recovery at an effective rate so as to prevent the accumulation of product in the fermentation broth. To ensure the viability of the microbial biomass, the invention is designed to reduce the amount of stress on the microbial biomass. By ensuring the viability of the microbial biomass, the microbial biomass may be recycled and reused in the fermentation process, which may result in an increased efficiency of the fermentation process.

1 . A process for removing a product from a fermentation broth, the process comprising:
 a. flowing a fermentation broth comprising microbial biomass and product from a bioreactor to a broth stripper comprising a top, a bottom;   b. partially vaporizing the fermentation broth in the broth stripper to produce product rich vapor stream, and product depleted liquid stream comprising live microbial biomass;   c. passing the product depleted liquid stream back to the bioreactor and passing the product rich vapor stream to a trim condenser to generate a condensed product stream;   d. passing the condensed product stream to a rectification column comprising a top and a bottom, to separate a rectification column overhead stream comprising product and a rectification column bottoms stream; and   e. passing the rectification column bottoms stream to the bottom of the broth stripper and directly transferring heat from the bottom of the rectification column to the bottom of the broth stripper.   
     
     
         2 . The process of  claim 1  wherein the condensing of the product vapor stream is incomplete and a secondary condenser is used to condense remaining vapor. 
     
     
         3 . The process of  claim 2  wherein the secondary condenser provides cooling through indirect contact with cooling water or chilled water. 
     
     
         4 . The process of  claim 1  further comprising transferring heat, indirectly, by heat exchanging the rectification column bottoms stream with the condensed product stream. 
     
     
         5 . The process of  claim 1 , wherein the fermentation broth is partially vaporised in the broth stripper at a temperature between 37° C. and 50° C. and a pressure between 40 mbar and 100 mbar. 
     
     
         6 . The process of  claim 1 , wherein a viability of the microbial biomass in the product depleted liquid stream is greater than 85%. 
     
     
         7 . The process of  claim 1 , further comprising storing the product depleted liquid stream from the broth stripper in a cooled tank prior to passing to the bioreactor wherein where the cooled tank is temperature controlled to between 30° C. and 37° C. and wherein the temperature control results in maintenance of cell viability greater than 85%. 
     
     
         8 . The process of  claim 1  wherein the broth stripper comprises an associated broth stripper liquid reboiler, and the process further comprises
 a. compressing the product rich vapor stream; 
 b. passing a liquid stream from the broth stripper to the broth stripper liquid reboiler and back to the broth stripper; and 
 c. transferring heat, indirectly, from the compressed product rich vapor to the liquid in the broth stripper liquid reboiler. 
 
     
     
         9 . The process of  claim 2  wherein the product rich vapor stream is compressed to a pressure of between 200 mbar to 300 mbar. 
     
     
         10 . The process of  claim 2  wherein the compressing is performed by multistage turbofans. 
     
     
         11 . The process of  claim 4  wherein between 2 and 4 turbofan stages are provided. 
     
     
         12 . The process of  claim 2  wherein the broth stripper liquid reboiler is positioned below theoretical distillation stages of the vessel which are separated from an upper portion of the vessel by a total trap-out tray. 
     
     
         13 . The process of  claim 2 , wherein the transferring heat is a process in which the product rich vapor stream is indirectly contacted with liquid in the broth stripper liquid reboiler, resulting in condensation of the product rich vapor stream and evaporation of the liquid in the liquid reboiler. 
     
     
         14 . The process of  claim 1  wherein the rectification column comprises an associated rectification column liquid reboiler, and the process further comprises:
 a. compressing the rectification column overhead stream; 
 b. passing a liquid stream from the rectification column to the rectification column liquid reboiler and back to the rectification column; and 
 c. transferring heat, indirectly, from the compressed rectification column overhead stream to the liquid in the rectification column liquid reboiler. 
 
     
     
         15 . The process of  claim 1  further comprising passing the rectification column overhead stream to a dehydration system. 
     
     
         16 . A system for removing a product from a fermentation broth, the system comprising:
 a. a stripper vessel comprising a feed inlet, a vapor outlet, a liquid outlet, a bottoms recycle inlet, a reboiler liquid outlet, and a reboiler return inlet, wherein the feed inlet is in fluid communication with a bioreactor;   b. a stripper reboiler in fluid communication with the reboiler liquid outlet and the reboiler return inlet;   c. a first multistage mechanical recompression unit in fluid communication with the vapor outlet of the stripper vessel and the stripper reboiler;   d. a trim condenser in fluid communication with the stripper reboiler;   e. a rectification column in fluid communication with the trim condenser via a rectification column inlet conduit, the rectification column comprising an overhead outlet, a bottoms outlet, a heat exchange outlet, and a heat exchange return inlet;   f. a heat exchanger in fluid communication with the heat exchange outlet and the heat exchange return inlet;   g. a second multistage mechanical recompression unit in fluid communication with the overhead outlet of the rectification column and the heat exchanger; and   h. a bottoms conduit in fluid communication with the bottoms outlet of the rectification column and the bottoms recycle inlet of the stripper vessel.   
     
     
         17 . The system of  claim 16  further comprising a dehydration system in fluid communication with the heat exchanger and the second multistage mechanical recompression unit. 
     
     
         18 . The system of  claim 16  further comprising a bottoms stream heat exchanger in thermal communication with the bottoms conduit and the rectification column inlet conduit. 
     
     
         19 . The system of  claim 16  further comprising a degasser in fluid communication with the bioreactor and the feed inlet of the stripper vessel. 
     
     
         20 . The system of  claim 16  further comprising a cooling tank in fluid communication with the liquid outlet of the stripper vessel.