Increasing dry grind ethanol yield through fiber pretreatment after liquefaction

Concentrations of starch and fiber in corn grain are 72 and 10% on a dry basis (db), respectively. In the conventional dry grind process, starch is converted to ethanol; whereas, corn fiber remains unconverted. Corn fiber contains 12 to 18% cellulose and 11 to 23% starch which can be hydrolyzed and fermented into ethanol. Conversion of corn fiber into ethanol would lead to an increase in ethanol yield, decrease in downstream processing costs, improvement in DDGS quality and D3 RIN generation for dry grind plants. Recalcitrance towards enzyme hydrolysis is a major challenge associated with the conversion of corn fiber into ethanol. Objectives of this study were to study the effects of hot water pretreatment, disk milling and cellulase dose on conversion of corn fiber into ethanol and to modify the conventional dry grind process for converting corn fiber into ethanol. Mash obtained after liquefaction was filtered and retentate (referred to as fiber) was used to study effects of pretreatments on ethanol yield. Fiber contained 23.5% db structural carbohydrates and 62.1% db extractives which were mostly soluble sugars. Fiber was pretreated using hot water at 20% solids at 160°C for 5, 10 and 20 min residence times and 3 cycles of disk milling at 20 and 45% solids. SSF was performed at a 10% db fiber concentration with the addition of commercially available glucoamylase, cellulase (30 FPU/g fiber) and hemicellulase enzymes and ethanol red yeast. SSF of untreated biomass was performed with 120 FPU/g fiber cellulase dose to understand effects of excess cellulase addition on ethanol yields. Conversion for hot water pretreated fiber was higher than that of untreated biomass (69.4%), with highest increase using a 5 min residence time at 160°C (76.6%). Disk milling had no effect on conversion. Use of excess cellulase (120 FPU/g fiber) resulted in higher conversion (92.5%) than that at normal cellulase (30 FPU/g fiber) (69.8%). Corn fiber could be converted to ethanol in the conventional dry grind process through the addition of cellulolytic enzymes during SSF. Conventional dry grind process was modified for converting corn fiber into ethanol. These modifications included addition of 30 or 120 FPU/g fiber cellulase during SSF, disk milling (3 cycles) slurry and combination of disk milling and cellulase (30 FPU/g fiber) addition during SSF. Cellulase addition (30 FPU/g fiber) during SSF resulted in higher conversion (85.3%) compared to the conventional dry grind process (81.1%). Disk milling corn slurry had no effect on ethanol yield compared to the conventional process. Cellulase addition (120 FPU/g fiber) at the SSF stage and combination of disk milling with cellulase addition (30 FPU/g fiber) achieved lower ethanol yields compared to conventional dry grind process. Residual glucose was observed at the end of fermentation in all experiments with cellulase addition. Cellulase addition in the conventional dry grind process might lead to yeast inhibition. Cellulase addition at the SSF stage can increase ethanol yields in the conventional dry grind process by 0.14 gal/bushel corn.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Agricultural & Biological Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2018

Author dc:creator

• Kurambhatti, Chinmay

Contributors dc:contributor

• Singh, Vijay
• Rausch, Kent
• Tumbleson, Mike

• dry grind
• corn fiber
• cellulosic ethanol
• ethanol yield

Statement dc:rights

• Copyright 2018 Chinmay Kurambhatti

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/101518

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/101518