First-generation ethanol production (1G) is based on yeast fermentation using corn starch, but when cellulase is added at the beginning of the 1G fermentation, the processing turns into in situ 1.5G ethanol production, where the coproduction of corn starch and cellulosic ethanol can occur. It is critical to use accurate analytical methods to quantify the starch and cellulose content in the pre-conversion samples (liquefied corn mash), and post-conversion samples (dried final beer at low temperature). Ethanol producers must demonstrate to the U.S. EPA what fraction of the total ethanol produced is cellulosic, made as a result of the in situ 1.5G processing. The cellulosic ethanol production from corn flour is eligible for D3 Renewable Identification Numbers (RINs), financially benefiting the ethanol producer.Analytical Testing&nbsp; The major carbohydrates in corn matrix are starch, cellulose and hemicellulose, with both starch and cellulose being naturally occurring glucose-containing polymers with different linked structure. Traditionally, the analytical assays to quantify each polymer involve converting them to glucose, making it extremely challenging to accurately identify whether the converted glucose came from starch or cellulose. Therefore, it is hard to obtain accurate data on starch and cellulose contents in corn matrix.The National Corn-to-Ethanol Research Center of Southern Illinois University Edwardsville (NCERC) tackled this challenge by optimizing the total starch testing method first. NCERC modified the AOAC 996.11 method for the measurement of total starch in cereal matrix by improving the conversion of starch in the corn matrix to glucose. Another modification was implementing strict quality control criteria for data quality, such as using high quality calibration standards, in-house check standards, and a recovery acceptance range for those check standards. The method was validated for precision and accuracy in various sample formats, such as pre- and post-conversion samples, as well as corn flour.Next, NCERC developed the total cellulose method based on the method of NREL LAP on cellulose in biomass, but with modification. Through acid hydrolysis, NCERC can convert both starch, cellulose and yeast cell wall (for post-conversion samples) to glucose. By using two check standards made freshly with each batch—one with starch only in corn matrix and the other with both starch and cellulose—its possible to monitor both starch and cellulose conversion rates and calculate the total cellulose level (within acceptable error bar) after the consideration of the contribution from total starch. In addition, the yeast cell wall contribution in the post-conversion samples can be estimated by testing the cellulose level in fermented yeast biomass and assuming 15% yeast biomass in the sample. The accuracy of the total cellulose method is between 85% to 115% recovery with a spiked standard in the corn matrix, and the precision is lower than 10% relative standard deviation.After the validation of the total starch and total cellulose methods in corn matrix, NCERC used the methods to build sound scientific data for various contractual projects and self-initiated projects. The success of each project provides the best testimonial for the high quality of the NCERC starch and cellulose methods:1. We built mass balance within a single bioreactor, from flask to 1,000 L size, between the production of ethanol, carbon dioxide, and the conversion of starch and cellulose from feedstock to DDGS. The independent lines of evidence related to mass balance from the in situ 1.5G trials have demonstrated the accuracy of the analytical methods within acceptable error bar.2. NCERC worked with multiple ethanol plants on samples related to in situ 1.5G processes and observed an average of 1% total ethanol production increase. Of that percentage, 50% was cellulosic ethanol, however, less than 20% of the cellulose in the corn flour was used in the conversion.Yield Optimization&nbsp; Optimizing the in situ 1.5G processing can help increase cellulosic ethanol yields. In order to increase the cellulose conversion from less than 20% through the in situ 1.5G, NCERC has modified the front-end processing by adding one liquefaction tank and other processing steps. As a result, with minimal investment on CAPEX, NCERC is able to double the cellulose conversion from 20% to 40%, which leads to 2% total ethanol increase and more than 50% of the ethanol increase belongs to cellulosic ethanol. NCERC’s Boost in situ 1.5G Technology has been validated using a 1,000 L bioreactor with accurate mass balance data.Author: Yanhong Zhang,&nbsp;&nbsp; Interim Executive Director/&nbsp; Director of Research at NCERC&nbsp; YZhang@ethanolresearch.com

2024-08-06 - Cellulosic Coproduction (Ethanol Producer Magazine)

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With minimal investment, NCERC’s validated process doubles the conversion of corn fiber cellulose in the feedstock from 20% to 40%, delivering a 2% total ethanol increase.

Cellulosic Coproduction

Cellulosic Coproduction

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