Bioethanol Production Process Research Articles

Emulsion Stabilization by Cationic Lignin Surfactants Derived from Bioethanol Production and Kraft Pulping Processes.

Oil-in-water bitumen emulsions stabilized by biobased surfactants such as lignin are in line with the current sustainable approaches of the asphalt industry involving bitumen emulsions for reduced temperature asphalt technologies. With this aim, three lignins, derived from the kraft pulping and bioethanol industries, were chemically modified via the Mannich reaction to be used as cationic emulsifiers. A comprehensive chemical characterization was conducted on raw lignin-rich products, showing that the kraft sample presents a higher lignin concentration and lower molecular weight. Instead, bioethanol-derived samples, with characteristics of non-woody lignins, present a high concentration of carbohydrate residues and ashes. Lignin amination was performed at pH = 10 and 13, using tetraethylene pentamine and formaldehyde as reagents at three different stoichiometric molar ratios. The emulsification ability of such cationic surfactants was firstly studied on prototype silicone oil-in-water emulsions, attending to their droplet size distribution and viscous behavior. Among the synthetized surfactants, cationic kraft lignin has shown the best emulsification performance, being used for the development of bitumen emulsions. In this regard, cationic kraft lignin has successfully stabilized oil-in-water emulsions containing 60% bitumen using small surfactant concentrations, between 0.25 and 0.75%, which was obtained at pH = 13 and reagent molar ratios between 1/7/7 and 1/28/28 (lignin/tetraethylene pentamine/formaldehyde).

The possibility of aquatic weeds serving as a source of feedstock for bioethanol production: a review

Anaerobic digestion is recognized as an attractive option for the effective management and treatment of lignocellulosic biomass as well as waste recovery of resources for bioethanol production. Long enough testing has been done on bioethanol production using lignocellulosic biomass. This helps to reduce stress and global energy problems. Global wide has a variety of environmental impacts due to its use of fossil fuels. Bioethanol might be produced in Asian locations from many types of biomasses, including agricultural waste, forest waste, and wood biomass. This would be an environmentally friendly process. Unfortunately, there is very little research into the production of ethanol from rice field weeds. This makes it difficult to develop bioethanol production. This review is aimed at developing bioethanol production and the trend towards organic products that began nowadays. Unwanted weed growth is a major problem in rice cultivation. This review demonstrated the waste-to-energy aspect of the bioethanol production process using two weeds, gooseweed (Sphenoclea Zeylanica), and small-flowered nutsedge (Cyperus difformis). 

Understanding the Dynamics of the Saccharomyces cerevisiae and Scheffersomyces stipitis Abundance in Co-culturing Process for Bioethanol Production from Corn Stover

Understanding the Dynamics of the Saccharomyces cerevisiae and Scheffersomyces stipitis Abundance in Co-culturing Process for Bioethanol Production from Corn Stover

The ability of Pichia kudriavzevii to tolerate multiple stresses makes it promising for developing improved bioethanol production processes.

Thermotolerant ethanol fermenting yeasts have been extensively used in industrial bioethanol production. However, little is known about yeast physiology under stress during bioethanol processing. This study investigated the physiological characteristics of the thermotolerant yeast Pichia kudriavzevii, strains NUNS-4, NUNS-5 and NUNS-6, under the multiple stresses of heat, ethanol and sodium chloride. Results showed that NUNS-4, NUNS-5 and NUNS-6 displayed higher growth rates under each stress condition than the reference strain, Saccharomyces cerevisiae TISTR5606. Maximum specific growth rates under stresses of heat (45°C), 15% v/v ethanol and 1·0 M sodium chloride were 0·23 ± 0·04 (NUNS-4), 0·11 ± 0·01 (NUNS-5) and 0·15 ± 0·01 h-1 (NUNS-5), respectively. Morphological features of all yeast studied changed distinctly with the production of granules and vacuoles when exposed to ethanol, and cells were elongated under increased sodium chloride concentration. This study suggests that the three P. kudriavzevii strains are potential candidates to use in industrial-scale fermentation due to a high specific growth rate under multiple stress conditions. Multiple stress-tolerant P. kudriavzevii NUNS strains have received much attention not only for improving large-scale fuel ethanol production, but also for utilizing these strains in other biotechnological industries.

Sustainable Production of Bioethanol Using Levulinic Acid Pretreated Sawdust.

The sustainability and economic viability of the bioethanol production process from lignocellulosic biomass depend on efficient and effective pretreatment of biomass. Traditional pretreatment strategies implicating the use of mineral acids, alkalis, and organic solvents release toxic effluents and the formation of inhibitory compounds posing detrimental effects on the environment and interfering with the enzymatic saccharification process, respectively. Ionic liquids (ILs) as green solvents were used to overcome this issue, but the deep eutectic solvent as an emerging class of ionic liquids performed better in terms of making the process environmentally and economically viable. The green solvent-based pretreatment strategy applied in the current research was levulinic, acid-based natural deep eutectic solvent (NADES). Three different hydrogen bond acceptors (HBAs)—acetamide, betaine, and choline chloride—in combination with levulinic acid as hydrogen bond donor (HBD) in (HBD: HBA) molar ratio 2:1, were screened for biomass pretreatment. The best deep eutectic solvent was levulinic acid: choline chloride in an optimized molar ratio of 1:0.5, resulting in 91% delignification. The physicochemical parametric optimization of saccharification exhibited maximum enzymatic hydrolysis of 25.87% with 125 mg of pretreated sawdust via simultaneous addition of three thermostable cellulases [i.e., endo-1,4-β-D-glucanase (240 U), exo-1,4-β-D-glucanase (180 U), and β-glucosidase (320 U)] for 5 h of incubation at 75°C. The reducing sugar slurry obtained from the saccharified biomass was then added to a fermentation medium for bioethanol production, and a maximum of 11.82% of production was obtained at 30°C, 72 h, and 180 rpm using a 2.5% 24 h old Saccharomyces cerevisiae seed culture. The current study revealed that the levulinic-based deep eutectic solvent exhibited remarkable delignification, which led to the efficient enzymatic hydrolysis of sawdust and hence bioethanol production. Furthermore, it will prospect new avenues in bioethanol production using a deep eutectic solvent. Deep eutectic solvent overcame the issues posed by ionic liquids: toxicity, expensive and complex preparation, and non-biodegradability.

Continuous Bioethanol Production by Fungi and Yeast Working in Tandem

Biofuel is considered one of the most viable alternatives to fossil fuels derived from the dwindling petroleum resources that damage the environment. Bioethanol could be manufactured from agricultural wastes, thus providing inexpensive natural resources. Several strategies have been utilized to convert lignocellulosic hydrolysate to bioethanol with various suspended microorganisms. In this study, we alternatively propose to encapsulate these microorganisms in bioreactor setups. An immobilized cell system can provide resistance to the inhibitors present in hydrolysates, enhance productivity, facilitate the separation process, and improve microorganism recycling. Herein, we developed a continuous bioethanol production process by encapsulating three types of micro-organisms: T. reesei, S. cerevisiae, and P. stipitis. These microorganisms were encapsulated in SBP (“Small Bioreactor Platform”) capsules and tested for their viability post encapsulation, biological activity, and bioethanol production. Encapsulating microorganisms in SBP capsules provided a confined protective environment for the microorganisms, facilitated their acclimation, and ensured their long-term prosperity and activity. An additional significant benefit of utilizing SBP capsules was the simultaneous availability of saccharification and fermentation over a very long time—about 2.5–3 months—with no need to renew the cells or encapsulating matrices. Two different configurations were tested. The first one consisted of columns packed with fungal cells and specific yeast cells together. In the second configuration, the fungal cells were separated from the yeast cells into two columns in series. The presented systems achieved an efficiency of 60–70%, suggesting the long-term prosperity and uninterrupted metabolic activity of the microorganisms.

Isolation and characterization of lignin-rich particles as byproducts of bioethanol production from wheat straw to reinforce starch composite films

Bioethanol was produced from wheat straw by a concentrated alkali pretreatment at specific conditions with a yield of 88 g ethanol per 1 kg of dry straw. To economically improve the bioethanol production process and valorize residual waste, the lignin-rich solid waste particles were isolated from the pretreatment waste liquid and characterized, and finally employed to reinforce starch-based biodegradable film. The solid waste particles were characterized by chemical analysis, dynamic light scattering (DLS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). As bioethanol byproducts, they have mainly contained 88 wt% lignin. The average diameter of the uniform spherical shape extracted particles was determined to be 160 nm by DLS and FESEM. The presence of syringyl and guaiacyl rings were conducted by FTIR. Due to their suitable mechanical performance and thermal resistance, the lignin nanoparticles were employed as reinforcement for green biodegradable starch films. To prepare films, suspensions containing starch, glycerol, and different concentrations of lignin (0–30 wt%) were molded by the solution casting process. The starch-lignin composite films were analyzed by mechanical tensile tests, crystallinity analysis, FESEM, and thermal analysis. From the results, it was found that by adding 20 wt% lignin particles, the tensile strength and modulus of the pure starch film were increased from 4.8 and 0.9–8 and 2.4 MPa which can be partially explained due to crystallinity enhancement of film from 29 % to 48.3 %. In addition, the thermal resistance and the hydrophilic property of the composite films were enhanced due to lignin nanoparticle presence. It can be concluded that the isolation of lignin nanoparticles as waste solid in bioethanol production could be considered as a promising stage in the sustainability of second-generation products from the bioethanol production process.

Process Simulation-based Net Energy Analysis for Future Bioethanol Production as Commercial Biofuel from Waste Rice Straw in Sri Lanka

As the staple food crop in Sri Lanka, paddy rice occupies around 34% (over 0.87 million hectares of land) of the total arable area in the country, corresponding to an average rice production of 3,774,344 t/year. Rice straw is the major biomass waste from rice cultivation, which approximates to an average of 2,830,758 t/year generation at a theoretical straw/grain ratio of 0.75. Open burning of rice straw in paddy fields is the common practice, which could result in an average GHG emissions of 92 kg CO2 eq/t of dry rice straw and other harmful airborne emissions. Application of rice straw into soil as an organic fertiliser is also an inefficient practice, compared to bioenergy generation using rice straw. The average composition of the Sri Lankan rice straw (i.e. 30.0 wt.% cellulose, 3.9 wt.% hemicellulose, 38.2% lignin, 16.1 wt.% wax, and 12.3 wt.% silica) shows the possibility to be used as a second-generation bioethanol feedstock. Existing studies indicate that bioethanol production from rice straw is more environmentally-benign, compared to alternative options, such as gasification for combined heat and power and dimethyl ether (DME) production. This study analyses the net energy indicators of a possible bioethanol production process from rice straw in Sri Lanka. Chemical process simulations using Aspen Plus software were utilised to evaluate the bioethanol production process from rice straw, with a plant output capacity of 1,000 litres/hr of dehydrated bioethanol (99.7 vol.% ethanol) that can be blended with gasoline as a commercial fuel (e.g. E10: 10% bioethanol+gasoline) without any vehicle engine modification. The cradle to gate bioethanol production process from waste rice straw, considered for net energy analysis consists of three major stages: 1. Rice straw preparation, 2. Rice straw transportation, and 3. Bioethanol conversion. The results show that the considered bioethanol production process has a positive net energy gain and increased renewability factor. Detailed analysis indicates that only around 8% of the total process energy consumption is utilised for the bioethanol dehydration operation that is favourable for converting any existing rice straw ethanol plant into commercial gasohol production plant. The sensitivity of bioethanol yield and process energy parameters for the net energy indicator results are further analysed and discussed. The findings from this study can support decision making for a future waste-to-biofuel plant using waste rice straw in Sri Lanka.Keywords: Rice straw, Bioethanol production, Net energy analysis, Process simulation, Waste-to-biofuel

Delignification of Cassava Peel as Bioethanol Raw Material using Combined Alkali and Microwave Heating Methods

Indonesia is ranked fourth as the largest cassava producing country with a total production of around 20 million tons per year. As much as 15-20% per kilogram of cassava is waste in the form of cassava peel which contains starch and allows it to be converted into alternative energy such as bioethanol. The bioethanol production process is carried out through the stages of pretreatment (delignification) to obtain cellulose used in the hydrolysis process, hydrolysis, fermentation, and purification. This paper discussed the use of combined alkali and microwave heating methods to increase the cellulose content and reduce the lignin content of cassava peel. Delignification was carried out by varying the NaOH concentration of 0.5, 0.75, and 1 M and microwave exposure of 5, 10, and 15 min. The data of the pretreatment variation were statistically tested using a completely randomized design. The results shows that combined alkali and microwave heating methods was able to increase cellulose content from 39.78 to 59.01 %, decrease hemicellulose content from 24.75 to 12.79 %, and decrease lignin content from 23.28 to 14.66 %. The combination of 1 M NaOH and 15 min microwave exposure showed the best results.

Evaluation of water footprint in sugar industries and bioethanol distilleries in two different water basins toward water sustainability.

Sugarcane farming and bioethanol production are water-intensive activities that result in high water competition. The competition, in turn, can exacerbate water scarcity. Therefore, this study aims to evaluate the water footprint (WF) of the sugar and bioethanol production at the Finchaa and Metehara sugarcane farms, which are located in different river basins in Ethiopia. The climatic data (minimal and maximum temperature, relative humidity, wind speed, and sunshine duration), meteorological data (rainfall), CROPWAT 8.0 model, nitrogen fertilizer application rates, sugarcane yield, and sugar and bioethanol production over 12 years (2008–2019) were used. Penman–Monteith method-based sugarcane water requirements of Finchaa and Metehara were found to be 2021.1 and 3605.4 mm/growing period, respectively. The sugarcane WF of Finchaa was 188.01 m3/t, which was composed of green (67.45 m3/t), blue (113.42 m3/t), and grey (7.14 m3/t) components, whereas the WF of Metehara was 239.11 m3/t consisting of green (29.42 m3/t), blue (204.13 m3/t), and grey (5.56 m3/t). The low sugarcane WF recorded was attributed to the high yield of sugarcane that was harvested in the study areas. Hence, the irrigation (blue WF) requirement is the major concern of water management in the basins. Similarly, the WF of bioethanol at the Finchaa distillery (2067.62 L/L) was much higher than that of the Metehara distillery (1441.54 L/L). However, both WFs were within the global range. Significant differences were observed between the two water basins. The sugarcane estate farm and bioethanol production processes require water management intervention to reduce the impact of WF in the basins.

Bioethanol production from seaweed solid waste biomass of agar processing

This paper describes about the potential application of renewable energy sources from biomass (seaweed waste) to replace fossil fuels combustion which produced CO2 emission and heavy metal pollution. The objective of the research is to utilize the seaweed solid waste from agar production industry for bioethanol feedstock. The enzymatic method was carried out for glucose production with the addition 1% of surfactant Tween 20 during the saccharification process of three kinds of substrate concentration (20, 25, 30% dw) and 10 FPU/g substrate for the cellulose concentration and used S. cerevisae as yeast in the fermentation process for bioethanol production. The result showed that the highest reducing sugar value (122.4 mg/mL) and 2.86% for the bioethanol content were from 30% dw treatment of substrate concentration of solid agar waste. Therefore, the waste from agar industry is a potential raw material to be used as biofuel and could reduce the heavy metal problems.

Technoeconomic Analysis of Integrated Bioethanol from Elephant Grass (Pennisetum purpureum) with Utilization of Its Residue and Lignin

Bioethanol has been developed as an alternative biofuel. Elephant grass is one of the lignocelluloses that can be used as a source of bioethanol. The bioethanol fermentation process should be improved along with its economic competitiveness to promote its wider application. This study aims to investigate and to evaluate the best scheme of biethanol (standalone) and the combination of bioethanol and its by-products through technoeconomic analysis. The method used is collecting data from several previous studies and simulating it with SuperPro Designer. Data from flowsheeting simulation is used as economic simulation data using Microsoft Excel. The results of this study indicate that the processing of biogas and lignin waste as fuel and lignosulfonates can increase the economic value of the bioethanol production process. The best economic value is the bioethanol production process using biogas and lignin as fuel for a Biomass Power Plant which is called Pembangkit Listrik Tenaga Biomassa (PLTBm) with a Net Present Value (NPV) of IDR 364,358,976,036, Internal Rate of Return (IRR) 11.32%, Pay Back Period (PBP) 7.2 years, and Profitability Index (PI) 1.08

Sensitivity Analysis of Bioethanol Simulation from Microalgae with Pressure Swing Distillation Process

Energy is an important parameter in the social and economic development of a country. Thus, it is necessary to seek renewable energy to supply energy needs in Indonesia. The production of bioethanol from microalgae as a biofuel is one way to reduce the use of fossil fuels. Microalgae has an advantage over other types of biomass sources due to its high biomass productivity and do not compete with agricultural crops for land and water resources. In the bioethanol production process, the ethanol and water form an azeotrope mixture of 95.6% of ethanol at 1 atm and 78.15°C. The objective of this research was to analyse and determine the operating conditions and the optimum distillation column configuration which results in high ethanol purity according to fuel specifications (fuel grade ethanol). The method of pressure-swing distillation was applied to separate the azeotrope of ethanol-water and obtain high purity ethanol. A simulation model of bioethanol production with pressure-swing distillation system was conducted by using Aspen Plus V10. In this research, the influence of process parameters such as distillation column pressure, reflux ratio, feed stage location, and the number of theoretical stages was analysed by using model analysis tools. The results showed that the obtained bioethanol purity of 99.9% with the condenser and reboiler duty of the LP column -79.931 kW and 667.651 kW, respectively; while the HP column is -47.627 kW and 57.698 kW.

Enzymatic digestibility of pretreated dewaxed bamboo residues as feedstock for bioethanol production

Due to abundant availability, biofuel production from bamboo residues is gaining popularity. Bamboo biomass and its residues are widely available in the north-eastern part of India, which can be sustainably exploited for green energy production. The aim of the present study was to evaluate the pretreatments of dewaxed bamboo residues with dilute alkali (NaOH), and dilute acid, and the effect of pretreatment on biomass hydrolysis was performed with a commercial enzyme (Zytex). Results showed that maximum fermentable sugars were 490 mg/g obtained from 10% biomass with 0.6% (w/v) of alkali, and acid pretreated biomass produced 320 mg/g of sugars from 2% (w/v) acid with 10% biomass. Changes in biomass structure during the pretreatment process are correlated with FTIR, SEM, and component analysis for lignin, cellulose, and hemicelluloses. Fermentation studies of the hydrolysate showed that the yield of ethanol was 77% of the theoretical maximum at 36 h. Results indicate the scope of utilization of bamboo residues as substrates for biofuels, and alkaline pretreatment is an effective pretreatment process for bioethanol production.

Bioethanol Production from Spent Sugar Beet Pulp—Process Modeling and Cost Analysis

Global economic development has led to the widespread use of fossil fuels, and their extensive use has resulted in increased environmental pollution. As a result, significantly more attention is being paid to environmental issues and alternative renewable energy sources. Bioethanol production from agro-industrial byproducts, residues, and wastes is one example of sustainable energy production. This research aims to develop a process and cost model of bioethanol production from spent sugar beet pulp. The model was developed using SuperPro Designer® v.11 (Intelligen Inc., Scotch Plains, NJ, USA) software, and determines the capital and production costs for a bioethanol-producing plant processing about 17,000 tons of spent sugar beet pulp per year. In addition, the developed model predicts the process and economic indicators of the analyzed biotechnological process, determines the share of major components in bioethanol production costs, and compares different model scenarios for process co-products. Based on the obtained results, the proposed model is viable and represents a base case for further bioprocess development.

Bio-upgrading of ethanol to fatty acid ethyl esters by metabolic engineering of Pseudomonas putida KT2440

Fatty acid ethyl esters (FAEEs) have gained increasing attention as a replacement for traditional fossil fuels in the recent years. Here, we report the efficient upgrading of ethanol to FAEEs from Pseudomonas putida KT2440, using ethanol as the sole carbon source. First, the wax synthase (WS) encoded by the atfA gene from Acinetobacter baylyi ADP1 was expressed in P. putida KT2440. Second, the flux from ethanol towards acetyl-CoA was increased by expression of the acetaldehyde dehydrogenase (ada) from Dickeya zeae. By using dodecane overlay to capture FAEEs, 1.2 g/L of FAEEs with a yield of 152.09 mg FAEEs/g ethanol were produced. Culture optimization enhanced the FAEEs contents up to 1.6 g/L in shake flask and 4.3 g/L in a fed-batch fermenter. In summary, our study provides a basis for combining the bioethanol production process with the efficient upgrading of ethanol to biodiesel.

Semi-supervised learning for data-driven soft-sensing of biological and chemical processes

Continuously operated (bio-) chemical processes increasingly suffer from external disturbances, such as feed fluctuations or changes in market conditions. Product quality often hinges on control of rarely measured concentrations, which are expensive to measure. Semi-supervised regression is a possible building block and method from machine learning to construct soft-sensors for such infrequently measured states. Using two case studies, i.e., the Williams-Otto process and a bioethanol production process, semi-supervised regression is compared against standard regression to evaluate its merits and its possible scope of application for process control in the (bio-) chemical industry. The case studies show that semi-supervised regression can serve as a valuable building block in construction of a soft sensor to reliably predict steady state data even in case of very few quality measurements (hourly or daily measurements). However, no reliable prediction of process dynamics can be ensured in case of common measurement frequencies for offline quality measurements.

Partial energy integration between biofuels production processes: Effect on costs, CO2 emissions and process safety

Energy integration is a tool which allows reducing the heating and cooling requirements for production processes. This is particularly important in the processes for production of biofuels, since such processes are expected to have low environmental impact, which can be achieved by reducing the need for steam and cooling water. It is common to perform energy integration by making use of all the available streams. This approach may allow reducing as much as possible utilities’ requirements, but other indicators may be affected, such as capital costs, since the number of required equipment is increased. Thus, in this work the effect of performing partial integration is assessed, i.e., selecting only a few streams to perform the energy integration. The effect of increasing the number of integrated streams is assessed in terms of sustainability indicators based on the green chemistry principles. The studied indicators are utilities’ requirements, total annual cost, environmental impact (assessed through CO2 emissions) and safety (assessed through the HPSI index). The study is applied to the energy integration of a supercritical biodiesel production process and a lignocellulosic bioethanol production process.

Modeling and optimization of bioethanol production planning under hybrid uncertainty: A heuristic multi-stage stochastic programming approach

When making planning decisions, fluctuation in both product demand and yield for the bioethanol plant denotes an important factor to affect the results. In this paper, a mixed multi-stage stochastic optimization model is proposed to solve the production planning problem of a bioethanol plant with multiple raw materials simultaneously considering uncertain demand and yield. The multi-source uncertainty is described as a multi-layer hybrid scenario tree model according to the historical statistics. Due to the diversity of pretreatment approach in the bioethanol production process, the yield of saccharification liquid is different. At each node of the scenario tree, the uncertainty of demand is expressed by probability. The uncertain scenarios of the yield are integrated at each node of demand to form a mixed scenario tree. To improve the solution efficiency, a heuristic algorithm based on fast forward selection is designed to simplify the decomposition of the large-scale hybrid scenario tree in the mixed multi-stage stochastic programming problem. The effectiveness of the proposed model is verified by a practical case. The results show that the proposed approach performs better than the two-stage stochastic programming and the deterministic approaches, and the algorithm can significantly reduce the computational efforts.

Insights into cell robustness against lignocellulosic inhibitors and insoluble solids in bioethanol production processes

Increasing yeast robustness against lignocellulosic-derived inhibitors and insoluble solids in bioethanol production is essential for the transition to a bio-based economy. This work evaluates the effect exerted by insoluble solids on yeast tolerance to inhibitory compounds, which is crucial in high gravity processes. Adaptive laboratory evolution (ALE) was applied on a xylose-fermenting Saccharomyces cerevisiae strain to simultaneously increase the tolerance to lignocellulosic inhibitors and insoluble solids. The evolved strain gave rise to a fivefold increase in bioethanol yield in fermentation experiments with high concentration of inhibitors and 10% (w/v) of water insoluble solids. This strain also produced 5% (P > 0.01) more ethanol than the parental in simultaneous saccharification and fermentation of steam-exploded wheat straw, mainly due to an increased xylose consumption. In response to the stress conditions (solids and inhibitors) imposed in ALE, cells induced the expression of genes related to cell wall integrity (SRL1, CWP2, WSC2 and WSC4) and general stress response (e.g., CDC5, DUN1, CTT1, GRE1), simultaneously repressing genes related to protein synthesis and iron transport and homeostasis (e.g., FTR1, ARN1, FRE1), ultimately leading to the improved phenotype. These results contribute towards understanding molecular mechanisms that cells might use to convert lignocellulosic substrates effectively.