Techno-economic evaluation of integrated first- and second-generation ethanol production from grain and straw

Abstract

BackgroundIntegration of first- and second-generation ethanol production can facilitate the introduction of second-generation lignocellulosic ethanol production. Consolidation of the second-generation with the first-generation process can potentially reduce the downstream processing cost for the second-generation process as well as providing the first-generation process with energy. This study presents novel experimental results from integrated first- and second-generation ethanol production from grain and wheat straw in a process development unit. The results were used in techno-economic evaluations to investigate the feasibility of the plant, in which the main co-products were distiller’s dried grains with solubles and biogas.ResultsAn overall glucose to ethanol yield, of 81 % of the theoretical, based on glucose available in the raw material, was achieved in the experiments. A positive net present value was found for all the base case scenarios and the minimal ethanol selling price varied between 0.45 and 0.53 EUR/L ethanol. The revenue increased with combined xylose and glucose fermentation and biogas upgrading to vehicle fuel quality. A decrease in the biogas yield from 80 to 60 % also largely affects the net present value. The energy efficiency for the energy content in products available for sale compared with the incoming energy content varied from 74 to 80 %.ConclusionsOne of the two main configurations can be chosen when designing an integrated first- and second-generation ethanol production plant from grain and straw: that producing biogas or that producing distiller’s dried grains with solubles from the xylose sugars. The choice depends mainly on the local market and prices for distiller’s dried grains with solubles and biogas, since the prices for both co-products have fluctuated a great deal in recent years. In the current study, however, distiller’s dried grains with solubles were found to be a more promising co-product than biogas, if the biogas was not upgraded to vehicle fuel quality. It was also concluded that additional experimental data from biogas production using first- and second-generation substrates are required to obtain improved economic evaluations.

Fatty alcohol production in Lipomyces starkeyi and Yarrowia lipolytica

“…Analyzing the cell pellets and supernatant separately showed that 97% of the produced fatty alcohol was associated with or trapped in the cells while only 3% was secreted (Table 2). This result is consistent with the recent research about Y. lipolytica that most of the fatty alcohols were retained intracellularly when TaFAR1 gene was expressed in Y. lipolytica [31]. Using a 10% (v/v) dodecane overlay during growth, 92.5% of the produced fatty alcohols were extracted into the dodecane phase, while only 5% remained associated with cells (Table 2).…”

“…In addition to the “pull” strategy, blocking TAG synthesis, i.e., disruption of the dga gene which encodes for diacylglycerol acyltransferase, the final enzyme for TAG synthesis, is another strategy for further enhancing fatty alcohol production. Also, as demonstrated in recent research [31], eliminating fatty alcohol degradation pathway, might be another strategy deserving a try. However, considering the complex nature of this species and for other unknown genetic reasons, the subsequent knocking out genes is very challenging.…”

“…However, despite of this advantage, the fatty alcohol titers in the engineered S. cerevisiae , which co-expressed the far gene, the fatty acid synthesis pathway genes as well as the regulatory genes in lipid metabolism, were relative low, i.e., 93.4 mg/L [24] for the mouse far gene expression, 84 mg/L for the bird far gene expression [29] and 330 mg/L for barn owl far gene expression in shake flasks [30]. In a recent report, expressing barn owl far gene in Y. lipolytica together with dga1 and fao1 knock out led to production of 636.89 mg/L intracellular and 53.32 mg/L extracellular fatty alcohols [31]. In contrast to the low lipid content in Y. lipolytica , some oleaginous yeasts are capable of accumulating up to 60% of lipid intracellularly, which implicates abundant metabolic flux to fatty acyl-CoA.…”

REVIEW OF BIOFUEL PRODUCTION – FEEDSTOCK, PROCESSES AND MARKETS — Review Article

“…In addition the production of ethanol from agricultural wastes (e.g. straw, bagasse) gains more importance (Sarkar et al, 2012;Joelsson et al, 2016).…”

Efficient production of second generation ethanol and xylitol by yeasts from Amazonian beetles (Coleoptera) and their galleries

“…When production occurs from easily accessible sugars, it is referred to as first generation (1G) production, whereas, if lignocellulosic materials such as agricultural residues, forest materials and dedicated crops are used, they are called second-generation (2G) production (Joelsson et al, 2016).…”