Fuel Ethanol Production Research Articles

A Coupling Process of Distillation with Vapor Permeation and Adsorption for Production of Fuel Ethanol: A Comparative Analysis on Energy Consumption

To efficiently produce fuel ethanol from fermentation broth, the distillation column was coupled with vapor permeation (VP) of a NaA zeolite membrane instead of using the adsorption technique to remove solvent water. The comparative analysis indicated that the energy efficiency was consistently higher for distillation-VP coupling, using a single-column distillation and three-column distillation, respectively. The best performance was obtained for the VP membrane coupling with a three-column distillation technique, where only 2.7 tons of steam per ton of fuel ethanol were consumed to produce fuel ethanol using a 3.0 wt % ethanol broth. This saved 0.25 tons of steam per ton of fuel ethanol in comparison with the results for the coupling with adsorption technique. The effect of ethanol content in broth on the energy efficiency was also investigated, which indicated that the ethanol content was a decisive factor to determine the energy consumption in the coupling techniques. The operation pressures were crucial to balance the energy consumption between columns coupled with the VP membrane. It was found that the operation pressure of the low-pressure column was the decisive factor to the whole energy efficiency, while the pressure of the high-pressure column was preferably adjusted according to practical production due to fewer disturbances in the system. This work benefits the process design for production of fuel ethanol from fermentation broth.

Recent Developments and Current Status of Commercial Production of Fuel Ethanol

Ethanol produced from various biobased sources (bioethanol) has been gaining high attention lately due to its potential to cut down net emissions of carbon dioxide while reducing burgeoning world dependence on fossil fuels. Global ethanol production has increased more than six-fold from 18 billion liters at the turn of the century to 110 billion liters in 2019, only to fall to 98.6 billion liters in 2020 due to the pandemic. Sugar cane and corn have been used as the major feedstocks for ethanol production. Lignocellulosic biomass has recently been considered as another potential feedstock due to its non-food competing status and its availability in very large quantities. This paper reviews recent developments and current status of commercial production of ethanol across the world with a focus on the technological aspects. The review includes the ethanol production processes used for each type of feedstock, both currently practiced at commercial scale and still under developments, and current production trends in various regions and countries in the world.

Ethanol yield calculations in biorefineries.

The ethanol yield on sugar during alcoholic fermentation allows for diverse interpretation in academia and industry. There are several different ways to calculate this parameter, which is the most important one in this industrial bioprocess and the one that should be maximized, as reported by Pereira, Rodrigues, Sonego, Cruz and Badino (A new methodology to calculate the ethanol fermentation efficiency at bench and industrial scales. Ind Eng Chem Res 2018; 57: 16182-91). On the one hand, the various methods currently employed in industry provide dissimilar results, and recent evidence shows that yield has been consistently overestimated in Brazilian sugarcane biorefineries. On the other hand, in academia, researchers often lack information on all the intricate aspects involved in calculating the ethanol yield in industry. Here, we comment on these two aspects, using fuel ethanol production from sugarcane in Brazilian biorefineries as an example, and taking the work of Pereira, Rodrigues, Sonego, Cruz and Badino (A new methodology to calculate the ethanol fermentation efficiency at bench and industrial scales. Ind Eng Chem Res 2018; 57: 16182-91.) as a starting point. Our work is an attempt to demystify some common beliefs and to foster closer interaction between academic and industrial professionals from the fermentation sector. Pereira, Rodrigues, Sonego, Cruz and Badino (A new methodology to calculate the ethanol fermentation efficiency at bench and industrial scales. Ind Eng Chem Res 2018; 57: 16182-91).

Potentials of multi-stress tolerant yeasts, Saccharomyces cerevisiae and Pichia kudriavzevii for fuel ethanol production from industrial cassava wastes

Cassava processing wastes are suitable substrates for bioethanol production due to their high starch contents. However, these cassava wastes often contain various substances that inhibit cell growth and ethanol production. The abilities of multi-stress tolerant Saccharomyces cerevisiae LC269108 and Pichia kudriavzevii LC375240 to produce ethanol from cassava industrial wastes were evaluated. Analysis of cassava peels and pulps from two cassava starch factories showed that the cassava peels contained high cyanide (KCN) concentrations while cassava pulps contained high concentrations of sodium dodecyl benzene sulfonate (SDBS) used to improve starch extraction in the factory. Although S. cerevisiae LC269108 produced ethanol efficiently from the cassava peel, its growth and ethanol production were inhibited in the cassava pulp. On the other hand, the growth and ethanol production by P. kudriavzevii LC375240 were inhibited slightly in the cassava peel but not in the cassava pulp. Based on the intracellular pyruvate concentrations in the presence of KCN and SDBS, it was inferred that their inhibition site is on the pyruvate synthetic pathways. With a co-culture of the two strains, ethanol production from the cassava peel increased significantly but there was no significant improvement in ethanol production from the cassava pulp.

Toward an Understanding of Physical and Biological Properties of Corn-Based Whole Stillage, Thin Stillage, and Condensed Distillers Solubles and Changes Thereof During Storage

The production of bio-based ethanol has been one of the fastest growing industries in the United States during the past decade. Thus, wider exploration of ethanol coproduct uses is necessary in the ethanol plant. Currently, process steams such as whole stillage, thin stillage, and syrup are processed into distiller dried grains with solubles and fed to livestock. The storability of whole stillage, thin stillage, and syrup influences the economic and energetic balances of fuel ethanol production. However, there are few investigations of the shelf life for these products or how to measure these quantities. The objectives of this research were to test physical and biological properties of whole stillage, thin stillage, and syrup and determine storability and allowable shelf life for these materials as influenced by storage temperature levels. Using standard laboratory methods, several properties were determined, including moisture content, water activity, thermal properties (conductivity, resistivity, volumetric heat capacity, and diffusivity), color, mold development, and CO2 production. Also, the separation processes due to settling were observed over 72 h. The thin stillage and whole stillage had relative high average moisture contents of 92% (w.b.) and 87% (w.b.), respectively, and a mean water activity of 0.99; the high water content marked samples easily susceptible to rapid spoilage. Time had a significant effect (p < 0.05) on properties of coproducts. Both thin stillage and whole stillage samples got mold growth after 5 days incubation at 32°C. Thin stillage had the greatest separation rate in the settling experiment. However, syrup had a relative low average moisture content of 62% and an average water activity of 0.92. No mold growth and settling separation happened in syrup samples. There was no evidence showing that a linear relationship exists between Hunter L*, a* and b*, and mold growth. The Solvita® test showed that high-temperature treatment caused high CO2 production in all samples. The exponential models described the relationship between storage time (from 0 to 5 days at 25 and 35°C) and CO2 concentration for the three coproducts. This study is a first step to explore opportunities for utilizing valuable components from these coproducts. Follow-up study should work on separation processes to concentrate the valuable components of these coproducts. Exploring the potential value of ethanol coproducts could maintain and improve the profitability of the ethanol industry.

Overexpression of NtAGPase small subunit gene increases leaf starch content and tobacco biomass

Production of biofuels such as ethanol from non-grain crops may contribute to alleviating the global energy crisis and reducing the potential threat to food security. Tobacco (Nicotiana tabacum) is a commercial crop with high biomass yield. Breeding of starch-rich tobacco plants may provide alternative raw materials for the production of fuel ethanol. We cloned the small subunit gene NtSSU of ADP-glucose pyrophosphorylase (NtAGPase), which controls starch biosynthesis in tobacco, and constructed a plant expression vector pCAMBIA1303-NtSSU. The NtSSU gene was overexpressed in tobacco upon Agrobacterium-mediated leaf disc transformation. Phenotypic analysis showed that overexpression of NtSSU gene promoted the accumulation of starch in tobacco leaves, and the content of starch in tobacco leaves increased from 17.5% to 41.7%. The growth rate and biomass yield of the transgenic tobacco with NtSSU gene were also significantly increased. The results revealed that overexpression of NtSSU gene could effectively redirect more photosynthesis carbon flux into starch biosynthesis pathway, which led to an increased biomass yield but did not generate negative effects on other agronomic traits. Therefore, NtSSU gene can be used as an excellent target gene in plant breeding to enrich starch accumulation in vegetative organs to develop new germplasm dedicated to fuel ethanol production.

Saccharomyces cerevisiae strains used industrially for bioethanol production.

Fuel ethanol is produced by the yeast Saccharomyces cerevisiae mainly from corn starch in the United States and from sugarcane sucrose in Brazil, which together manufacture ∼85% of a global yearly production of 109.8 million m3 (in 2019). While in North America genetically engineered (GE) strains account for ∼80% of the ethanol produced, including strains that express amylases and are engineered to produce higher ethanol yields; in South America, mostly (>90%) non-GE strains are used in ethanol production, primarily as starters in non-aseptic fermentation systems with cell recycling. In spite of intensive research exploring lignocellulosic ethanol (or second generation ethanol), this option still accounts for <1% of global ethanol production. In this mini-review, we describe the main aspects of fuel ethanol production, emphasizing bioprocesses operating in North America and Brazil. We list and describe the main properties of several commercial yeast products (i.e., yeast strains) that are available worldwide to bioethanol producers, including GE strains with their respective genetic modifications. We also discuss recent studies that have started to shed light on the genes and traits that are important for the persistence and dominance of yeast strains in the non-aseptic process in Brazil. While Brazilian bioethanol yeast strains originated from a historical process of domestication for sugarcane fermentation, leading to a unique group with significant economic applications, in U.S.A., guided selection, breeding and genetic engineering approaches have driven the generation of new yeast products for the market.

The impact of transcription factors Znf1, Sip4, Adr1, Tup1, and Hap4 on xylose alcoholic fermentation in the engineered yeast Saccharomyces cerevisiae.

Lignocellulosic biomass is an attractive sustainable platform for fuel ethanol production. Xylose is a second after glucose most abounded sugar in lignocellulosic hydrolysates. Effective conversion of xylose to ethanol is one of key prerequisite for the development of an efficient conversion of biomass to ethanol. Engineered Saccharomyces cerevisiae strains are able to xylose fermentation. However, the yield and productivities of xylose fermentation remains lower in comparison with glucose fermentation. In this work, we studied impact of transcription factors Znf1, Sip4, Adr1, Tup1, and Hap4 on xylose catabolism. We have isolated znf1Δ, adr1Δ, tup1Δ and hap4Δ mutants, and strains overexpressing SIP4, ADR1 and HAP4 genes on the background of xylose-fermenting strain of S. cerevisiae aiming to explore involvement of these transcription factors in regulation of xylose growth and fermentation. It was shown that hap4Δ reveal 1.8-fold increase of ethanol production from xylose as compared to that of parental strain. The hap4Δ mutant accumulates 10.38gl-1 of ethanol with an overall ethanol yield reaching 0.41gg-1 of consumed xylose. While the other constructed strains revealed a decrease in ethanol production from this pentose.

Mixed fermentation of corn and pretreated corn stover for fuel ethanol production

AbstractBackground and objectivesFuel ethanol is almost exclusively produced from corn with minor contributions from other cereal grains. Cellulosic ethanol production has significant potential as well as serious limitations. This study proposed that pretreated corn stover could be simultaneously converted and fermented with corn in existing ethanol facilities.FindingsMixed fermentation ethanol yields increased significantly relative to the control fermentations. Incorporation of 5% pretreated corn stover increased ethanol yields by 12.7% with 10% corn mash and 11.9% with 20% corn mash over corn only control fermentations. Using 20% corn, residual xylose and arabinose were 0.072 and 0.023 grams/gram biomass, respectively, indicating addition ethanol potential with a C5 fermenting yeast. DDGS color and lipid contents were negatively impacted; however, the nutrient value of the corn portion is unlikely to be altered.ConclusionsDirect incorporation of pretreated corn stover into the corn ethanol process can be done with little or no reduction in corn or stover conversion efficiency.Significance and noveltyThis study demonstrates clearly that pretreated biomass can be efficiently co‐fermented with corn to produce cellulosic ethanol in yields approximating those from biomass alone and eliminates many of the significant economic and processing issues that stand‐alone cellulosic ethanol facilities face.

Comparative Genomics Supports That Brazilian Bioethanol Saccharomyces cerevisiae Comprise a Unified Group of Domesticated Strains Related to Cachaça Spirit Yeasts.

Ethanol production from sugarcane is a key renewable fuel industry in Brazil. Major drivers of this alcoholic fermentation are Saccharomyces cerevisiae strains that originally were contaminants to the system and yet prevail in the industrial process. Here we present newly sequenced genomes (using Illumina short-read and PacBio long-read data) of two monosporic isolates (H3 and H4) of the S. cerevisiae PE-2, a predominant bioethanol strain in Brazil. The assembled genomes of H3 and H4, together with 42 draft genomes of sugarcane-fermenting (fuel ethanol plus cachaça) strains, were compared against those of the reference S288C and diverse S. cerevisiae. All genomes of bioethanol yeasts have amplified SNO2(3)/SNZ2(3) gene clusters for vitamin B1/B6 biosynthesis, and display ubiquitous presence of a particular family of SAM-dependent methyl transferases, rare in S. cerevisiae. Widespread amplifications of quinone oxidoreductases YCR102C/YLR460C/YNL134C, and the structural or punctual variations among aquaporins and components of the iron homeostasis system, likely represent adaptations to industrial fermentation. Interesting is the pervasive presence among the bioethanol/cachaça strains of a five-gene cluster (Region B) that is a known phylogenetic signature of European wine yeasts. Combining genomes of H3, H4, and 195 yeast strains, we comprehensively assessed whole-genome phylogeny of these taxa using an alignment-free approach. The 197-genome phylogeny substantiates that bioethanol yeasts are monophyletic and closely related to the cachaça and wine strains. Our results support the hypothesis that biofuel-producing yeasts in Brazil may have been co-opted from a pool of yeasts that were pre-adapted to alcoholic fermentation of sugarcane for the distillation of cachaça spirit, which historically is a much older industry than the large-scale fuel ethanol production.

Optimization of saccharification prospective from starch of sweet potato roots through acid-enzyme hydrolysis: structural, chemical and elemental profiling

The sweet potato root, a potent source of starch which is being considered as an efficient alternative for fuel ethanol production in recent times. The starchy substrate needs to be subsequently dextrinized and saccharified so as to enhance the utilization of its carbohydrates for ethanol production. In the present investigation, acid-enzyme process was conducted for the dextrinization and saccharification of sweet potato root flour (SPRF). The best optimized condition for dextrinization was achieved with an incubation period of 60 min, temperature 100 ºC and 1M HCl. However, for saccharification, the best result was obtained with an incubation of 18 h, pH 4, temperature 65 ºC and 1000 U concentration of Palkodex®. After the dextrinization process, maximum concentrations of total sugar and hydroxymethylfurfural (HMF) [380.44 ± 3.17 g/kg and 13.28 ± 0.25 mg/g, respectively] were released. Nevertheless, after saccharification, 658.80 ± 7.83 g/kg of total sugar was obtained which was about 73% more than that of dextrinization. After successful dextrinization and saccharification, the structural, chemical and elemental analysis were investigated using techniques such as scanning electron microscopy (SEM), Fourier-transforms infrared spectroscopy (FTIR) and energy-dispersive X-ray fluorescence spectrophotometer (EDXRF), respectively. Effective hydrolysis was demonstrated in thin layer chromatography (TLC) where the HCl was able to generate monomeric sugar such as glucose and maltose. On the other hand, only glucose is synthesized on the mutual effect of HCl and Palkodex®. The SEM findings indicate that the rough structure of both dextrinized and saccharified sample was gained due to the vigorous effect of both acid and enzyme subsequently. The saccharified SPRF when subjected to fermentation with Saccharomyces cerevisiae and Zymomonas mobilis separately, it was observed that Z. mobilis produced more stretching vibration of –OH than S. cerevisiae, which evidenced the better production of bioethanol. Additionally, evaluation of the influence of S. cerevisiae and Z. mobilis through elemental analysis revealed upsurge in the concentrations of S, Cl, Ca, Mn, Fe and Zn and decline in the concentrations of P, K and Cu in the fermented residue of S. cerevisiae and Z. mobilis, however, Z. mobilis showed little more variation than that of S. cerevisiae.

What’s the Role Of Corn Ethanol Fuel in China: From the Life Cycle Cost View

China originally planned to use fuel ethanol gasoline nationwide in 2020, and taking corn as an important raw material of ethanol gasoline, this paper analyzed the life cycle cost model of corn fuel ethanol gasoline and traditional gasoline from production to consumption, including internal and external cost calculations. The internal cost is the actual cost of the industry chain, while the external cost is converted into the cost value by examining the environmental impact of pollutant emission levels in each stage of the life cycle of ethanol gasoline production. Based on this model, by selecting the project data of specific regions and manufacturers in China, it can be calculated as follows: The main links affecting the internal cost of ethanol gasoline production are crude oil procurement cost, refinery and ethanol plant construction cost; The main influencing link of external cost is the emission of ethanol gasoline combustion, including the fuel, power and other energy consumption factors in the production of ethanol and gasoline; The cost can be optimized from the perspective of production technology, technological process, energy material consumption and various labor costs. Assuming E10 is used in the whole Chinese market, the empirical results are as follows: among the pollutants produced by the use of ethanol-added gasoline in the whole region, CO2 emission reduction is the largest, exceeding 53 million tons, followed by CO and wastewater emission reduction of 1.78 million tons and 1.58 million tons respectively. In terms of the conventional gasoline, the CO emission reduction of about 20% is the largest, followed by about 17% reduction of HC, about 15% reduction of SO2 and about 9% reduction of CO2 respectively. These results show that the promotion of ethanol gasoline (E10) usage in China has a considerable reduction effect of emission if the availability of raw materials are sufficient. The life cycle external cost of ethanol gasoline is 11.45%, lower than that of conventional gasoline. In 2019, China’s fuel ethanol production capacity was 4.15 million tons, and the actual production was about 3 million tons. Assuming that all of it were used to produce E10 ethanol gasoline, compared with traditional gasoline consumption, the emission reduction benefit of E10 gasoline would be nearly $84.7 million.

Bioeconomy and biofuels: the case of sugarcane ethanol in Brazil

AbstractBrazilian bioethanol is one of the most prominent biofuels produced on a large scale, representing 30% of the global fuel ethanol production share. Around 8.6 billion gallons were produced in 2019, second only to the US fuel ethanol production in the same period (15.8 billion gallons). Obtained from sugarcane in a highly energy‐efficient process, the biofuel, which can be used in Brazil as 100% ethanol (hydrated, minimum mass content of 92.5%) or in a volume proportion of 27% (anhydrous ethanol) in common gasoline, has contributed to the reduction of oil dependency and CO2 emissions, as well as to the development of an important economic sector. Pioneer biofuel policies and important advances in science and technology led to the establishment of a 46% renewable energy matrix. In this manuscript, an overview of the impacts of ethanol production and utilization will be given, with respect to environmental and socio‐economic concerns. The public policies and some technical aspects of sugarcane and ethanol production and energy cogeneration will be reviewed and discussed. © 2021 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

From baker's yeast to genetically modified budding yeasts: the scientific evolution of bioethanol industry from sugarcane.

The peculiarities of Brazilian fuel ethanol fermentation allow the entry of native yeasts that may dominate over the starter strains of Saccharomyces cerevisiae and persist throughout the sugarcane harvest. The switch from the use of baker's yeast as starter to selected budding yeasts obtained by a selective pressure strategy was followed by a wealth of genomic information that enabled the understanding of the superiority of selected yeast strains. This review describes how the process of yeast selection evolved in the sugarcane-based bioethanol industry, the selection criteria and recent advances in genomics that could advance the fermentation process. The prospective use of genetically modified yeast strains, specially designed for increased robustness and product yield, with special emphasis on those obtained by the CRISPR (clustered regularly interspaced palindromic repeats)-Cas9 (CRISPR-associated protein 9) genome-editing approach, is discussed as a possible solution to confer higher performance and stability to the fermentation process for fuel ethanol production.

Condensed Phase Guerbet Reactions of Ethanol/Isoamyl Alcohol Mixtures

The self-condensation and cross-condensation reactions of ethanol and isoamyl alcohol are examined to better understand the potential routes to value-added byproducts from fuel ethanol production. Reactions have been carried out in both batch autoclave and continuous condensed-phase reactors using a lanthanum-promoted, alumina-supported nickel catalyst at near-critical condensed phase conditions. Analysis of multiple candidate kinetic models led to a Langmuir–Hinshelwood rate expression that is first-order in alcohol with water as the strongly adsorbed species. This model provides the best fit of data from both batch and continuous reactor experiments. Activation energies for primary condensation reactions increase as carbon chain lengths increase. Selectivities to higher alcohols of 94% and 87% for ethanol and isoamyl alcohol, respectively, were observed at different operating conditions.

Advances in Clean Fuel Ethanol Production from Electro-, Photo- and Photoelectro-Catalytic CO2 Reduction

Using renewable energy to convert CO2 to a clean fuel ethanol can not only reduce carbon emission through the utilization of CO2 as feedstock, but also store renewable energy as the widely used chemical and high-energy-density fuel, being considered as a perfect strategy to address current environment and energy issues. Developing efficient electrocatalysts, photocatalysts, and photoelectrocatalysts for CO2 reduction is the most crucial keystone for achieving this goal. Considerable progresses in CO2-based ethanol production have been made over the past decades. This review provides the general principles and summarizes the latest advancements in electrocatalytic, photocatalytic and photoelectrocatalytic CO2 conversion to ethanol. Furthermore, the main challenges and proposed future prospects are illustrated for further developments in clean fuel ethanol production.

Effects of high-amylase corn on performance and carcass quality of finishing beef heifers.

Developed initially for use in fuel ethanol production, Enogen Feed Corn (EFC; Syngenta Crop Protection) is genetically modified to express high concentrations of α-amylase in the corn kernel. Experiments were conducted to evaluate processing characteristics of EFC, in vitro digestion, and effects on feedlot performance, carcass characteristics, and liver abscess incidence. Experiment 1 used a randomized complete block design (3 × 3 × 5 factorial) to evaluate starch availability, in situ dry matter disappearance (ISDMD), in vitro gas production (IVGP), and volatile fatty acid (VFA) profiles of in vitro cultures. Grains (EFC or mill-run control [CON]) were flaked to a density of 360 g/L, and mixtures with 0%, 25%, 50%, 75%, or 100% EFC were prepared. Grains were tempered with added moisture (0%, 3%, or 6%) prior to steam conditioning for 15, 30, or 45 min. No two- or three-way interactions were observed. Adding moisture improved starch availability (linear; P < 0.01), and tended to improve ISDMD (linear, P = 0.06). Steam conditioning for 30 min improved starch availability, IVGP, and production of acetate, propionate, butyrate, valerate, and total VFA (P < 0.01) compared with conditioning for 15 or 45 min. Starch availability, ISDMD, IVGP, acetate, propionate, valerate, and total VFA production increased with an increasing proportion of EFC (linear, P < 0.01). Experiment 2 used 700 beef heifers (394 ± 8.5 kg initial body weight [BW]) fed finishing diets with steam-flaked corn as CON or EFC for 136 d. Targeting similar starch availabilities, grains were processed to 360 g/L (CON) and 390 g/L for CON and EFC, respectively. Heifers were blocked by BW, stratified, and then randomly assigned to 28 dirt-surfaced pens (25 animals per pen). Dry matter intakes were similar between treatments (P = 0.78), but cattle fed EFC had greater average daily gain (P < 0.01), improving feed efficiency by 5% (P < 0.01). Hot carcass weight was 6 kg greater for EFC cattle (P <0.01) than CON. No differences were observed for longissimus muscle area (P = 0.89), 12th-rib fat thickness (P = 0.21), or USDA yield grade (P = 0.13). Cattle fed CON had greater marbling scores than EFC (P = 0.04), but this did not affect the USDA quality grade (P > 0.33). Cattle fed EFC had 23% fewer abscessed livers than CON (P = 0.03). High-amylase corn may be used to improve microbial digestion, mill-throughput, and cattle performance, and it may mitigate liver abscesses.

Development Status and Technical and Economic Analysis of Ethanol Gasoline for Automobile in China

With the shortage of petroleum resources and the aggravation of environmental pollution, the research of alternative fuel for automobile is paid more and more attention. As a relatively clean fuel, ethanol gasoline can significantly reduce the emission of harmful substances in automobile exhaust. Compared with ordinary gasoline, it has the advantages of high octane number, good antiknock performance and high oxygen content. But it also has disadvantages such as low combustion heat value, large latent heat of evaporation, corrosion to metals, poor and compatibility with some engine materials, etc. The three factors affecting the development of ethanol gasoline are resources, technology and economic benefits. Although China is the third largest ethanol production and consumption country in the world, its resource conditions are not as good as those of the United States and Brazil. Under the current market and industrial policy environment, the overall benefits of domestic fuel ethanol production enterprises are poor. Cellulosic ethanol technology is the key technology to restrict the development of ethanol gasoline. Only when the second generation of biofuels pass the economic test, can the use of ethanol gasoline be promoted nationwide.

Production of bioethanol from pumpkin peel wastes: Comparison between response surface methodology (RSM) and artificial neural networks (ANN)

Pumpkin peel wastes are an unutilized source of starch, whose bioethanol production has not been reported by any research work so far. Such bioethanol is believed to show the potential uses of these wastes. Therefore, the present work was conducted to optimize the reducing sugar concentration and bioethanol production from pumpkin peel wastes using two modeling approaches (artificial neural networks and response surface methodology). Actually, a central composite rotatable design was used to optimize bioethanol production to obtain maximum reducing sugar and bioethanol concentrations. ANN proved to be superior to RSM in terms of its estimation and prediction capabilities. Therefore, the optimum conditions were obtained based on predicted ANN-model as follows. Concerning the hydrolysis process, hydrolysis time was 120 min, loading substrate was 17.5 g/L, α-amylase concentration was 7.5 U/g and amyloglucosidase concentration was 56.40 U/mL. As for the fermentation process, the optimal conditions were: fermentation temperature 45 °C, pH 5.06, shaking speed 188.5 rpm, and yeast concentration of 1.95 g/L. Under these conditions, the experimental concentration values of reducing sugar and bioethanol were 50.60 and 84.36 g/L, respectively, which are in good agreement with those predicted by the ANN-model (84.27 and 50.69 g/L, respectively). Besides, the results revealed that substrate loading and fermentation temperature were the most significant factors affecting the reducing sugar and bioethanol concentration, respectively (p < 0.01). Subsequently, the kinetics of yeast growth and bioethanol formation under the optimized conditions were estimated using the Monod, logistic and modified Gompertz models, respectively. Subsequently, the pumpkin peel wastes would offer an energy-saving alternative for fuel-ethanol production.

Chemical variation in cell wall of sugar beet pulp caused by aqueous ammonia pretreatment influence enzymatic digestibility of cellulose

Sugar beet pulp (SBP) is considered to be an important feedstock for the fuel ethanol production. The aim of this study is to investigate the relationship between chemical variation in cell wall caused by aqueous ammonia pretreatment and the enzymatic digestibility of cellulose through imaging techniques coupled with enzymatic hydrolysis kinetics analysis. The results revealed that the partly decreased and redistributed lignin could weaken interactions between lignin and cellulose, expose more hydroxyl groups on cell wall, and lead to more absorbed cellulase on cellulose. The maximum amount of adsorbed cellulase (370.37 FPU/g) was obtained from SBP (at 80 °C), which was 37 % more than that of the control. Additionally, the reducing sugar yield, initial hydrolysis rate, and maximum catalytic efficiency were 121 %, 202 %, and 125 % more than that of the control, respectively. Aqueous ammonia provided a good approach for improving enzymatic digestibility of cellulose through weakening the interactions between lignin and cellulose, which might be a suitable pretreatment in fuel ethanol production from SBP.