A comparison of liquid hot water and steam pretreatments of sugar cane bagasse for bioconversion to ethanol

Sugar cane bagasse was pretreated with either liquid hot water (LHW) or ste am using the same 251 reactor. Solids concentration ranged from 1% to 8% fo r LHW pretreatment and was greater than or equal to 50% for steam pretreatm ent. Reaction temperature and time ranged from 170 to 230 degreesC and 1 to 46 min, respectively. Key performance metrics included fiber reactivity, x ylan recovery, and the extent to which pretreatment hydrolyzate inhibited g lucose fermentation. In four cases, LHW pretreatment achieved greater than or equal to 80% conversion by simultaneous saccharification and fermentatio n (SSF), greater than or equal to 80% xylan recovery, and no hydrolyzate in hibition of glucose fermentation yield. Combined effectiveness was not as g ood for steam pretreatment due to low xylan recovery. SSF conversion increa sed and xylan recovery decreased as xylan dissolution increased for both mo des. SSF conversion, xylan dissolution, hydrolyzate furfural concentration, and hydrolyzate inhibition increased, while xylan recovery and hydrolyzate pH decreased, as a function of increasing LHW pretreatment solids concentr ation (14%). These results are consistent with the notion that autohydrolys is. plays an important, if not exclusive, role in batch hydrothermal pretre atment. Achieving concurrently high (greater than 90%) SSF conversion and x ylan recovery will likely require a modified reactor configuration (e.g. co ntinuous percolation or base addition) that better preserves dissolved xyla n. (C) 2001 Elsevier Science Ltd. All rights reserved.