Commercial Ethanol Production Research Articles

Xylooligosaccharides from lignocellulosic biomass and their applications as nutraceuticals: a review on their production, purification, and characterization.

Xylooligosaccharides (XOS) are considered a potent source of prebiotics for humans. The global prebiotic market is expanding in size, was valued at USD 6.05 billion in 2021, and is expected to grow at a 14.9% compound annual growth rate between 2022 and 2030, indicating a huge demand. These XOS are non-digestible pentose sugar oligomers comprising mainly xylose. Xylose is naturally present in the lignocellulosic biomass (LCB), fruits and vegetables. Apart from the prebiotic effect, these XOS have been reported to reduce blood cholesterol, possess antioxidant effects, increase calcium absorption, reduce colon cancer risk, and benefit diabetic patients. The primary use of XOS is reported in the feed industry followed by health, medical use, food and drinks. LCB mainly contains glucan, xylan and lignin. After glucan, xylan is the second-highest available sugar on the globe composed of xylose. Therefore, the xylan fraction of LCB has great significance in producing food, feed and energy. Glucan has been exploited for the commercial production of ethanol, xylitol, furfural, hydroxymethyl furfural and glucose. As of now, xylan has limited applications. Therefore, xylan can be exploited to convert to XOS. The production of XOS from LCB fraction not only helps to produce these at a very low price, but also helps in the reduction of greenhouse gases. Its use in food and drinks is increasing as it can be derived from the abundantly and cheaply available LCB. The article provides a review on the production, purification and characterization of XOS in view of their use as nutraceuticals. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Kluyveromyces marxianus MTCC 1389 Augments Multi-stress Tolerance After Adaptation to Ethanol Stress.

During fermentation, yeast cells undergo various stresses that inhibit cell growth and ethanol production. Therefore, the ability to tolerate multiple stresses during fermentation is one of the important characteristics for yeast cells that can be used for commercial ethanol production. In the present study, we evaluated the multi-stress tolerance of parent and ethanol adapted Kluyveromyces marxianus MTCC1389 and their relative gene expression analysis. Multi-stress tolerance was confirmed by determining its cell viability, growth, and spot assay under oxidative, osmotic, thermal, and ethanol stress. During oxidative (0.8% H2O2) and osmotic stress (2M NaCl), there was significant cell viability of 90% and 50%, respectively, by adapted strain. On the other hand, under 45°C of thermal stress, the adapted strain was 80% viable while the parent strain was 60%. In gene expression analysis, the ethanol stress responsive gene ETP1 was significantly upregulated by 3.5 folds, the osmotic stress gene SLN1 was expressed by 3 folds, and the thermal stress responsive gene MSN2 was expressed by 7 folds. This study shows adaptive evolution for ethanol stress can develop other stress tolerances by changing relative gene expression of osmotic, oxidative, and thermal stress responsive genes.

Technoeconomic analysis of a fungal pretreatment-based cellulosic ethanol production

Cellulosic biomass shows great potential as feedstock for bioethanol production. Despite clear benefits in terms of greenhouse gas mitigation and bioproduct potential, the commercial production of cellulosic ethanol remains economically challenging at the current state of technology. This paper presents a technoeconomic analysis of a fungal pretreatment-based cellulosic ethanol plant with a processing capacity of 2000 tonnes of switchgrass per day. The production process model was designed and simulated using SuperPro Designer. The plant's ethanol yield, capital investment per unit capacity, and unit ethanol production cost were estimated to be 211.90 L/t of switchgrass, $ 3.60/L, and $ 1.44/L of ethanol, respectively. Fungal pretreatment was the major contributor (72%) to the total capital investment, mainly due to the large quantity of equipment required in the process. A positive net present value (NPV) was generated for the baseline model at ethanol selling price of $ 1.50/L, which increased by 5-fold for 80% glucose yield. Glucose yield was the most sensitive to NPV for all the process parameters evaluated.

Optimization Conditions for Ethanol Production from Sweet Sorghum Juice by Thermotolerant Yeast Saccharomyces cerevisiae: Using a Statistical Experimental Design

The optimum fermentation conditions for ethanol production from sweet sorghum juice (SSJ) by the thermotolerant yeast Saccharomyces cerevisiae DBKKUY-53 were determined using a statistical experimental design. Based on the Plackett–Burman design (PBD), yeast cell concentration, sugar concentration, and yeast extract were the significant independent fermentation factors affecting the ethanol production from SSJ at 37 °C by S. cerevisiae DBKKUY-53. These significant factors were optimized using response surface methodology (RSM) based on a central composite design (CCD). The result revealed that the optimum conditions for ethanol fermentation were 7.85 × 107 cells/mL yeast cell concentration, 247 g/L sugar concentration, and 9.99 g/L yeast extract. Verification of the ethanol production using the optimum conditions revealed that the maximum ethanol concentration of 99.75 g/L and the productivity of 2.77 g/L/h were achieved. When the ethanol production was carried out in a 2 L fermentor under optimum conditions, the ethanol concentration was 101.81 g/L and the productivity was 2.83 g/L/h. This finding suggested that the thermotolerant yeast S. cerevisiae DBKKUY-53 has excellent potential for commercial ethanol production at high temperatures.

Bioethanol Production from Lignocellulosic Biomass-Challenges and Solutions.

Regarding the limited resources for fossil fuels and increasing global energy demands, greenhouse gas emissions, and climate change, there is a need to find alternative energy sources that are sustainable, environmentally friendly, renewable, and economically viable. In the last several decades, interest in second-generation bioethanol production from non-food lignocellulosic biomass in the form of organic residues rapidly increased because of its abundance, renewability, and low cost. Bioethanol production fits into the strategy of a circular economy and zero waste plans, and using ethanol as an alternative fuel gives the world economy a chance to become independent of the petrochemical industry, providing energy security and environmental safety. However, the conversion of biomass into ethanol is a challenging and multi-stage process because of the variation in the biochemical composition of biomass and the recalcitrance of lignin, the aromatic component of lignocellulose. Therefore, the commercial production of cellulosic ethanol has not yet become well-received commercially, being hampered by high research and production costs, and substantial effort is needed to make it more widespread and profitable. This review summarises the state of the art in bioethanol production from lignocellulosic biomass, highlights the most challenging steps of the process, including pretreatment stages required to fragment biomass components and further enzymatic hydrolysis and fermentation, presents the most recent technological advances to overcome the challenges and high costs, and discusses future perspectives of second-generation biorefineries.

Process schemes of ethanol coupling to C4 olefins based on a genetic algorithm for back propagation neural network optimization

C4 olefin is an important feedstock for the chemical industry. Designing an effective and stable industrial process for preparing C4 olefin from renewable ethanol is crucial for further sustainable chemical production. In this study, a comprehensive evaluation system of an experimental scheme was constructed based on the Analytic Hierarchy Process/Entropy Weight Method-Technique for Order Preference by Similarity to Ideal Solution (AHP/EWM-TOPSIS) and Chemical production indicators. Using this evaluation system, a Back Propagation Neural Network (BPNN) based on a Genetic Algorithm (GA) was constructed after simulating C4 olefin production conditions using the Improved Mixed Congruential method. Subsequently, the production scheme with the highest evaluation score was determined when the temperature was not limited and when the temperature was lower than 350°C through a series of mathematical models. Overall, our mathematical models provide guidance for the commercial production of ethanol to butene and effectively reduce the risk of scaling up the chemical process to pilot or industrial scale.

Statistical optimization of enzymatic saccharification of sodium hydroxide pretreated parthenium hysterophorus biomass using response surface methodology

The biomass of the lignocellulosic weed P. hysterophorus is abundant and wasteful in India. This study aimed to investigate the lignocellulosic weed P. hysterophorus for reducing sugar production. Therefore, several pretreatment methods, physical (Steam and Microwave), and chemical (alkalis and acids) were investigated to determine the statistically best conditions for enzymatic hydrolysis. The results revealed that alkali pretreatment (sodium hydroxide, 1.0% w/v) had the greatest impact on the production of reducing sugar (110.36 ± 0.05 mg/g substrate) from P. hysterophorus. The decrease in the lignin content and increase in carbohydrates from pretreated biomass was further validated using an ultrastructural technique (Fourier-transform infrared spectroscopy and X-ray diffraction). The quantity of reducing sugars released was optimized using a response surface methodology, and the experimental results with optimized process variables gave 385.44 mg/g substrate reducing sugar. The investigations showed that P. hysterophorus can be utilized as a promising and low-cost biomass source for commercial ethanol production.

Clostridium autoethanogenum isopropanol production via native plasmid pCA replicon.

Clostridium autoethanogenum is a model gas-fermenting acetogen for commercial ethanol production. It is also a platform organism being developed for the carbon-negative production of acetone and isopropanol by gas fermentation. We have assembled a 5.5 kb pCA plasmid for type strain DSM10061 (JA1-1) using three genome sequence datasets. pCA is predicted to encode seven open-reading frames and estimated to be a low-copy number plasmid present at approximately 12 copies per chromosome. RNA-seq analyses indicate that pCA genes are transcribed at low levels and two proteins, CAETHG_05090 (putative replication protein) and CAETHG_05115 (hypothetical, a possible Mob protein), were detected at low levels during batch gas fermentations. Thiolase (thlA), CoA-transferase (ctfAB), and acetoacetate decarboxylase (adc) genes were introduced into a vector for isopropanol production in C. autoethanogenum using the native plasmid origin of replication. The availability of the pCA sequence will facilitate studies into its physiological role and could form the basis for genetic tool optimization.

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.

DLCA (ch) pretreatment brings economic benefits to both biomass logistics and biomass conversion for low cost cellulosic ethanol production

Densifying lignocellulosic biomass with chemicals (calcium hydroxide) (DLC(ch)) followed by regular steam autoclave treatment (DLCA(ch)) is a novel pretreatment method, which unlocks highly fermentable sugars and showed great potential. This study investigated the economics of DLCA(ch) based biorefinery for cellulosic ethanol production and studied the effects of solid loading, enzyme dosage, enzyme price and biorefinery scale on the economics. Compared with dilute acid pretreatment based biorefinery, DLCA(ch) based biorefinery showed much lower feedstock logistics cost, and the savings in feedstock logistics almost offset the DLC(ch) pretreatment cost. DLCA(ch) based biorefinery exhibited higher ethanol yield and lower pretreatment costs. When the biorefinery scale was 2000 Mg rice straw per day, the total capital investment and minimum ethanol selling price of DLCA(ch) based biorefinery were 17.9% and 30.0% lower, respectively, compared to dilute acid pretreatment based biorefinery. This work demonstrated the great potential of DLCA(ch) pretreatment for the commercial production of cellulosic ethanol.

Study on consolidated bioprocessing of pre-treated Nannochloropsis gaditana biomass into ethanol under optimal strategy

Nannochloropsis gaditana is a microalga, constituting cellulose 33 ± 1.3% and hemicellulose 18.2 ± 0.8%; used for the biofuel production. The cellulose in microalgal biomass would contribute to protecting the environment and constitute an attractive renewable raw material for bioethanol production. Ethanol production from N. gaditana microalgal biomass was investigated through Consolidated Bioprocessing (CBP) using Hangateiclostridium thermocellum KSMK1203 bacterial isolate. Screening and optimization of biomass pretreatment with different acids in different dosages, various hydrolysis time at 100 °C were performed and statistically validated using one-way ANOVA for efficient hemicellulose removal from NaClO2-treated N. gaditana biomass. Medium components and process parameters were statistically optimized by Response Surface Methodology. The maximum cellulase of 13.96 ± 1.354 IU/mL and ethanol of 12.90 ± 0.987 g/L were obtained in pretreated N.gaditana biomass. This study demonstrates that N. gaditana is a substitution for vegetal cellulose and these optimized conditions could be successfully used for commercial ethanol production using H. thermocellum KSMK1203.

Resiliency considerations in designing commercial scale systems for lignocellulosic ethanol production

An optimization model for designing a resilient biomass to energy system is applied to study commercial scale ethanol production. Uncertainty in biomass availability due to drought is calculated using historical rainfall data. The probability of drought is region-specific, whereas the magnitude of loss is specific to the feedstock. The supply system includes collection sites, Regional Biomass Pre-processing Depots (RBPD), and biorefineries. The design decisions include locations and capacities of biorefineries and RPBDs, while the operational decisions include feedstock selection and material flow. The probability-weighted expected cost of production is minimized considering ideal and disruption scenarios. The problem is solved for the state of Maharashtra in India with 33 districts and five types of biomass. The results show up to 4.1% benefit due to the proposed approach over a conventional approach that ignores drought. Crop specific scenarios showed that drought affected the facility locations, capacities as well as procurement strategies.

Virginiamycin Thermal Degradation Kinetics in a Model Matrix Simulating Distillation Conditions within a Commercial Fuel Ethanol Production Facility

The current knowledge of virginiamycin (VM) degradation kinetics at processing conditions observed in commercial ethanol production facilities is very limited. This knowledge is critical for assessing the feed and animal-derived food safety risk of the presence of VM residues in dried distillers grains with solubles (DDGS). A bioassay method was optimized to quantify the VM residues in a matrix sample obtained from distillation at an ethanol production facility. There were no significant differences on the VM degradation kinetics among the pH values of the distillation matrix sample used in the DDGS production (P=0.98). Increasing the distillation temperature enhanced the reduction of VM (P<0.01) reaching 70% degradation at 95°C. The log-linear model was able to characterize the VM degradation kinetics with D-values ranging from 19.4 to 43.3min at 70–95°C. The M1 subunit was less heat-resistant with D-values ranging from 10.4 to 23.6min. Distillation temperature conditions commonly used during the DDGS production process significantly degrades VM providing vital information for ethanol and food animal producers on the potential risk of the presence of antimicrobial residues in the final DDGS product.

Using straw as a bio-ethanol source to promote anaerobic digestion of waste activated sludge

Commercial ethanol production from straw is a series of complex processes that are energy-intensive and uneconomical. Corn straw was used as a bioethanol source to mix with waste activated sludge for improving anaerobic co-digestion (AcoD) in this study. Ethanol production from the straw after yeast fermentation was 1400–2200 mg COD/L, accounting for about 0.1% of the fermentative effluent, but methane production of the yeast-group increased by 36% compared to that of control-group with no ethanol production in advance. Volatile suspended solid removal achieved 60%, obviously higher than common anaerobic digestion (AD). Multiple lines of evidence including sludge conductance, effects of activated carbon on methanogenesis and microbial community demonstrated that ethanol from the straw fermentation stimulated direct interspecies electron transfer to be established in the digesters. The results suggested that using ethanol produced from straw was a cost-effective novel way for energy recovery from disposal of agricultural and municipal wastes.

Identification of soil bacteria capable of utilizing a corn ethanol fermentation byproduct.

A commercial corn ethanol production byproduct (syrup) was used as a bacterial growth medium with the long-term aim to repurpose the resulting microbial biomass as a protein supplement in aquaculture feeds. Anaerobic batch reactors were used to enrich for soil bacteria metabolizing the syrup as the sole nutrient source over an eight-day period with the goal of obtaining pure cultures of facultative organisms from the reactors. Amplification of the V4 variable region of the 16S rRNA gene was performed using barcoded primers to track the succession of microbes enriched for during growth on the syrup. The resulting PCR products were sequenced using Illumina MiSeq protocols, analyzed via the program QIIME, and the alpha-diversity was calculated. Seven bacterial families were the most prevalent in the bioreactor community after eight days of enrichment: Clostridiaceae, Alicyclobacillaceae, Ruminococcaceae, Burkholderiaceae, Bacillaceae, Veillonellaceae, and Enterobacteriaceae. Pure culture isolates obtained from the reactors, and additional laboratory stock strains, capable of facultative growth, were grown aerobically in microtiter plates with the syrup substrate to monitor growth yield. Reactor isolates of interest were identified at a species level using the full 16S rRNA gene and other biomarkers. Bacillus species, commonly used as probiotics in aquaculture, showed the highest biomass yield of the monocultures examined. Binary combinations of monocultures yielded no apparent synergism between organisms, suggesting competition for nutrients instead of cooperative metabolite conversion.

Systematic optimization of gene expression of pentose phosphate pathway enhances ethanol production from a glucose/xylose mixed medium in a recombinant Saccharomyces cerevisiae

The pentose phosphate pathway (PPP) plays an important role in the synthesis of ribonucleotides and aromatic amino acids. During bioethanol production from cellulosic biomass composed mainly of d-glucose and d-xylose, the PPP is also involved in xylose metabolism by engineered Saccharomyces cerevisiae. Although the activities and thermostabilities of the four PPP enzymes (transaldolase: TAL1, transketolase: TKL1, ribose-5-phosphate ketol-isomerase: RKI1 and d-ribulose-5-phosphate 3-epimerase: RPE1) can affect the efficiency of cellulosic ethanol production at high temperatures, little is known about the suitable expression levels of these PPP genes. Here, we overexpressed PPP genes from S. cerevisiae and the thermotolerant yeast Kluyveromyces marxianus either singly or in combination in recombinant yeast strains harboring a mutant of xylose isomerase (XI) and evaluated xylose consumption and ethanol production of these yeast transformants in glucose/xylose mixed media at 36 °C. Among the PPP genes examined, we found that: (1) strains that overexpressed S. cerevisiae TKL1 exhibited the highest rate of xylose consumption relative to strains that overexpressed other PPP genes alone; (2) overexpression of RKI1 and TAL1 derived from K. marxianus with S. cerevisiae TKL1 increased the xylose consumption rate by 1.87-fold at 24 h relative to the control strain (from 0.55 to 1.03 g/L/h); (3) the strains with XI showed higher ethanol yield than strains with xylose reductase and xylitol dehydrogenase and (4) PHO13 disruption did not improve xylose assimilation under the experimental conditions. Together these results indicated that optimization of PPP activity improves xylose metabolism in genetically engineered yeast strains, which could be useful for commercial production of ethanol from cellulosic material.

Optimization of Corn Steep Liquor Dosage and Other Fermentation Parameters for Ethanol Production by Saccharomyces cerevisiae Type 1 and Anchor Instant Yeast

Bioethanol production has seen an increasing trend in research recently, with a focus on increasing its economic viability. The aim of this study is to develop a low-cost fermentation medium with a minimum of redundant nutritional supplements, thereby minimizing the costs associated with nutritional supplements and seed production. Corn steep liquor (CSL) in glucose fermentation by Saccharomyces Type 1 (ST1) strain and Anchor Instant Yeast (AIY), which are low-cost media, is used as a replacement for yeast extract (YE). The fermentation process parameters were optimized using artificial neural networks (ANN) and the response surface method (RSM). The study shows that for CSL, maximum average ethanol concentrations of 41.92 and 45.16 g/L, representing 82% and 88% of the theoretical yield, were obtained after 36 h of fermentation in a shake flask for ST1 and AIY, respectively. For YE, ethanol concentrations equivalent to 86% and 88% of theoretical yield were obtained with ST1 and AIY, respectively after 48 h. Although ANN better predicted the responses compared to RSM, optimum conditions were better predicted by RSM. This study shows that corn steep liquor is an inexpensive potential nutrient that may have significant cost implications for commercial ethanol production.

Ethanol from maize: an entrepreneurial opportunity in agrobusiness

ABSTRACTIndia is a developing economy, and an energy-hungry state. With its ever increasing demand for fuel, India is the fourth largest consumer of crude oil in the world and imports 70% of its total demand. Also, to reduce the carbon footprint, the search is on for eco-friendly and renewable sources of energy. In India, one such unconventional fuel is ethanol produced from sugarcane molasses and blended with gasoline for use as biofuel. In this paper, the authors propose an entrepreneurial project to produce ethanol from maize, with an objective to develop a clean & green source of energy and to give a boost to the agricultural economy. Maize is the third most important crop in India, with approximate 85% of areal coverage. It has applications in adhesives, food industry, beverages and breweries for producing ethanol. Ethanol produced from maize has advantages over sugarcane, as the fibrous byproduct makes an excellent animal feedstock and can be further processed for the production of corn starch and syrup, to maximize the profit. The present paper suggests an entrepreneurial opportunity for commercial production of ethanol from maize directly purchased from farmers, creating a win–win scenario for farmers as well as the enterprise.

Optimization of Process Parameters for Efficient Bioconversion of Thermo-chemo Pretreated Manihot esculenta Crantz YTP1 Stem to Ethanol

The production of value-added products from lignocellulosic waste has been of great interest for economic as well as environmental concerns. Also, lignocellulosic waste constitutes an attractive renewable feedstock for bioethanol production due to their abundance, availability and low cost. Ethanol production from Manihot esculenta Crantz YTP1 stem was investigated through consolidated bioprocessing (CBP) using Cellulomonas fimi MTCC 24 and Zymomonas mobilis MTCC 92. CBP integrates enzyme production, saccharification (of pre-treated biomass) and fermentation in a single reactor. Screening and optimization of pre-treatment with different acids namely CH3COOH, HNO3, and combined acids (CH3COOH + HNO3) in different dosages, temperature and hydrolysis time, were evaluated for efficient de-lignification of 85.0 ± 3.2% and maximum cellulose release of 87.45 ± 2.2% of biomass. The pre-treatment data obtained were statistically validated using one-way ANOVA. Process parameters such as pH, temperature, agitation and time on the co-production of cellulase and ethanol were statistically optimized by response surface methodology (RSM) and artificial neural network (ANN). The maximum cellulase of 11.63 ± 1.23 IU/mL and ethanol of 9.39 ± 0.33 g/L were obtained in pre-treated biomass. This study demonstrates that M. esculenta Crantz YTP1 stem is an alternative feedstock, and these optimized conditions could be successfully used for commercial production of ethanol using C. fimi MTCC 24 and Z. mobilis MTCC 92 through CBP.

Process intensification of cellulosic ethanol production by waste heat integration

Lignocellulosic biomass is a promising feedstock for bioethanol production. However, techno-economic feasibility of commercial cellulosic ethanol production is still one of the dominant challenges. In this work, a novel cellulosic ethanol production process was simulated by PRO/II v9.3, and energy efficiency was optimized via vapor recompression and waste sensible and latent heat integration. In hydrolysis stage, the waste sensible heat of hydrolysis products is recovered by heat exchanger to preheat the feedstock. In ethanol purification stage, heat pump assisted distillation is used to elevate and recover the waste condensation heat of the overhead products. The compressed sensible and latent heat is paired with the bottom stream (latent and sensible) and the distillation feedstock (sensible heat), respectively. To assist the efficiency of heat integration, the influence of vapor compression on heat exchange performance is analyzed. Meanwhile, the detail properties (i.e. temperature and pressure) and composition variation of distillation stage are also studied. The investigation results indicated that 11.6MW and 32MW can be recovered from hydrolysis product and distillation overhead stream by using heat integration technology. The total energy consumption could be reduced to 23.9MJ/kg-ethanol, which demonstrated that around 42.8% external energy was avoided compared with the process without heat integration. Thus, waste heat integration could be a promising alternative to reduce external heat utility for cellulose ethanol production.