Process optimization for bioethanol production from cassava starch using novel eco-friendly enzymes

Although cassava (Manihot esculenta Crantz) is a potential bioethanol crop, high operational costs resulted in a negative energy balance in the earlier processes. The present study aimed at optimizing the bioethanol production from cassava starch using new enzymes like Spezyme^® Xtra and Stargen™ 001. The liquefying enzyme Spezyme was optimally active at 90 °C and pH 5.5 on a 10% (w/v) starch slurry at levels of 20.0 mg (280 Amylase Activity Units) for 30 min. Stargen levels of 100 mg (45.6 Granular Starch Hydrolyzing Units) were sufficient to almost completely hydrolyze 10% (w/v) starch at room temperature (30 ± 1 °C). Ethanol yield and fermentation efficiency were very high (533 g/kg and 94.0% respectively) in the Stargen + yeast process with 10% (w/v) starch for 48 h. Raising Spezyme and Stargen levels to 560 AAU and 91.2 GSHU respectively for a two step loading [initial 20% (w/v) followed by 20% starch after Spezyme thinning]/initial higher loading of starch (40% w/v) resulted in poor fermentation efficiency. Upscaling experiments using 1.0 kg starch showed that Stargen to starch ratio of 1:100 (w/w) could yield around 558 g ethanol/kg starch, with a high fermentation efficiency of 98.4%. The study showed that Spezyme level beyond 20.0 mg for a 10% (w/v) starch slurry was not critical for optimizing bioethanol yield from cassava starch, although an initial thinning of starch for 30 min by Spezyme facilitated rapid saccharification-fermentation by Stargen + yeast system. The specific advantage of the new process was that the reaction could be completed within 48.5 h at 30 ± 1 °C.     

Consumer choice between ethanol and gasoline: Lessons from Brazil and Sweden

The introduction of flex-fuel vehicles since 2003 has made possible for Brazilian drivers to choose between high ethanol blends or gasoline depending on relative prices and fuel economies. In Sweden, flex-fuel fleets were introduced in 2005. Prices and demand data were examined for both Brazil and Sweden. Bioethanol has been generally the most cost-efficient fuel in Brazil, but not for all states. In any case, consumers in Brazil have opted for ethanol even when this was not the optimal economic choice. In Sweden, a different behavior was observed when falling gasoline prices made E85 uneconomical in late 2008. In a context of international biofuels expansion, the example of E85 in Sweden indicates that new markets could experience different consumer behavior than Brazil: demand falls rapidly with reduced price differences between ethanol and gasoline. At the same time, rising ethanol demand and lack of an international market with multiple biofuel producers could lead to higher domestic prices in Brazil. Once the limit curve is crossed, the consumer might react by shifting back to the usage of gasoline.     

Dynamic impacts of high oil prices on the bioethanol and feedstock markets

This study investigates the impacts of high international oil prices on the bioethanol and corn markets in the US. Between 2007 and 2008, the prices of major grain crops had increased sharply, reflecting the rise in international oil prices. These dual price shocks had caused substantial harm to the global economy. Employing a structural vector auto-regression model (SVAR), we analyze how increases in international oil prices could impact the prices of and demand for corn, which is used as a major bioethanol feedstock in the US. The results indicate that an increase in the oil price would increase bioethanol demand for corn and corn prices in the short run and that corn prices would stabilize in the long run as corn exports and feedstock demand for corn decline. Consequently, policies supporting biofuels should encourage the use of bioethanol co-products for feed and the development of marginal land to mitigate increases in the feedstock price.     

Pretreatment and hydrolysis of cellulosic agricultural wastes with a cellulase-producing Streptomyces for bioethanol production

Production of reducing sugar by hydrolysis of corncob material with Streptomyces sp. cellulase and ethanol fermentation of cellulosic hydrolysate was investigated. Cultures of Streptomyces sp. T3-1 improved reducing sugar yields with the production of CMCase, Avicelase and ??-glucosidase activity of 3.8, 3.9 and 3.8 IU/ml, respectively. CMCase, Avicelase, and ??-glucosidase produced by the Streptomyces sp. T3-1 favored the conversion of cellulose to glucose. It was recognized that the synergistic interaction of endoglucanase, exoglucanase and ??-glucosidase resulted in efficient hydrolysis of cellulosic substrate. After 5 d of incubation, the overall reducing sugar yield reached 53.1 g/100 g dried substrate. Further fermentation of cellulosic hydrolysate containing 40.5 g/l glucose was performed using Saccharomyces cerevisiae BCRC 21812, 14.6 g/l biomass and 24.6 g/l ethanol was obtained within 3 d. The results have significant implications and future applications regarding to production of fuel ethanol from agricultural cellulosic waste.     

Influence of impregnation with lactic acid on sugar yields from steam pretreatment of sugarcane bagasse and spruce, for bioethanol production

Lignocellulosic biomass can be utilized to produce ethanol, a promising alternative energy source produced through fermentation of sugars. However, in order to achieve high sugar and ethanol yields, the lignocellulosic material must be pretreated before the enzymatic hydrolysis and fermentation. Dilute acid pretreatment, using SO₂, is one of the most promising methods of pretreatment for softwood and agricultural residues. However, handling the high acidity of the slurry obtained from pretreatment and difficulty in recycling/degradation of the impregnating agent are some of the drawbacks of the dilute acid processes. In the present study the influence of utilization of a weak organic acid (lactic acid), as impregnating agent, on the sugar yield from pretreatment, with and without addition of SO₂, was investigated. The efficiency of pretreatment was assessed by enzymatic hydrolysis of the slurry obtained by pretreatment, using sugarcane bagasse and spruce, stored for one and two months in the presence of lactic acid separately, as feedstocks. Pretreatment of bagasse after storage with 0.5% lactic acid resulted in an overall glucose yield, i.e. after enzymatic hydrolysis, of 79% of theoretical based on the amount available in the raw material. This was as good as pretreatment using SO₂ as impregnating agent. However, storage of spruce with lactic acid before pretreatment, with and without addition of SO₂, was not efficient and resulted in lower sugar yields than pretreatment using SO₂ only.     

The impact of a growing bioethanol industry on food production in Brazil

The Brazilian production of major food commodities increased fivefold between 1961 and 2008. In the same time, the area cropped with sugar cane increased with high growth rates, currently covering 3% of the area dedicated to agricultural production in Brazil. In order to assess a possible competition between biofuel and food production, the development of agricultural productivity and area expansion in the past was analysed. Furthermore, the future situation of land resources for agricultural production was illustrated. The findings of this study indicated that area resources of more than 20 million hectare would be available for agricultural production in the upcoming years. A current constraint of food production throughout land dedicated to biofuels was not found. Three scenarios were investigated, simulating possibilities of future changes in Brazilian agriculture. The results demonstrated that primary food production could be enhanced by 1.5 times while bioethanol production was enhanced simultaneously by 1.8 times over the years 2007/2008 and 2020. The generated bioethanol volumes would meet 38% of the total energy demand in Brazilian transport sector, applied to the year 2007. The second scenario evaluated an agricultural development with a higher focus on biofuels. It was projected that the production of bioethanol could be increased by 3.0 times to 76.7 million m³ of bioethanol, while increasing at the same time primary food production with the factor 1.4 aligned to the projected population growth. This bioethanol volume represents 67% of the total energy demand in Brazilian transport sector in the year 2007. A third scenario demonstrated that food production could be increased even with no area expansion higher than the projected population growth, due to a continued increase of productivity. At the same time bioethanol production would rise to 32 million m³ without occupying more area.     

The productive potentials of sweet sorghum ethanol in China

As one of the important non-grain energy crops, sweet sorghum has attracted the attention of scientific community and decision makers of the world since decades. But insufficient study has been done about the spatial suitability distribution and ethanol potential of sweet sorghum in China. This paper attempts to probe into the spatial distribution and ethanol potential of sweet sorghum in China by ArcGIS methods. Data used for the analysis include the spatial data of climate, soil, topography and land use, and literatures relevant for sweet sorghum studies. The results show that although sweet sorghum can be planted in the majority of lands in China, the suitable unused lands for large-scale planting (unit area not less than 100 hm²) are only as much as 78.6 × 10⁴ hm²; and the productive potentials of ethanol from these lands are 157.1 × 10⁴–294.6 × 10⁴ t/year, which can only meet 24.8–46.4% of current demand for E10 (gasoline mixed with 10% ethanol) in China (assumption of the energy efficiency of E10 is equivalent to that of pure petroleum). If all the common grain sorghum at present were replaced by sweet sorghum, the average ethanol yield of 244.0 × 10⁴ t/year can be added, and thus the productive potentials of sweet sorghum ethanol can satisfy 63.2–84.9% of current demand for E10 of China. In general, Heilongjiang, Jilin, Inner Mongolia and Liaoning rank the highest in productive potentials of sweet sorghum ethanol, followed by Hebei, Shanxi, Sichuan, and some other provinces. It is suggested that these regions should be regarded as the priority development zones for sweet sorghum ethanol in China.     

The substitutive effect of biofuels on fossil fuels in the lower and higher crude oil price periods

Various biofuels, including bioethanol and biodiesel are technologically being considered replacements for fossil fuels, such as the conventional gasoline and diesel. This paper aims to measure whether economic substitutability can be generated during periods of higher and/or lower prices of crude oil. The empirical results of the bivariate EGARCH model prove that this substitutive effect was occurred during the higher crude oil price period due to the significant price spillover effects from crude oil futures to corn and soybean futures, indicating that the increase in food prices can be attributed to more consumption of biofuels. We suggest more extensive research in the search for fuel alternatives from inedible feedstock such as pongamia, jojoba, jatropha, especially the 2nd generation biofuel technologies such as algae-based biofuels.     

Feasibility assessment,process design and dynamic simulation for cogeneration of heat and power by steam reforming of diluted bioethanol

A bioethanol reforming system, capable of converting a diluted water-ethanol mixture into hydrogen, is sized and set up to produce 5 kW of electric power via a polymer electrolyte membrane fuel cells (PEMFC). A part of the produced hydrogen supplies heat for the reforming reaction without impairing the power generation, then no additional fuel is required. According to the different configurations of the control variables, the heat released from the system is distributed between two different temperature ranges and coupled to a standard house-scale combined heat and power (CHP) cogeneration apparatus. Hot water can be produced continuously at a high enough temperature to cover the need of a F-class home in the moderately cold Northern Italy winter climate. With a micro-accumulation solution and a careful choice of the set-points, also the sanitary hot water demand (DHW) of a 4-members family might be fulfilled with 2–3 daily cycles of the same system.     

Comparative study of fuel gas production for SOFC from steam and supercritical-water reforming of bioethanol

Theoretical study of fuel gas (H₂ + CO) production for SOFC from bioethanol was carried out to compare performances between two reforming technologies, including steam reforming (SR) and supercritical-water reforming (SCWR). It demonstrates that the fuel gas productions are comparable among the two reforming systems; however, SCWR requires the operation at much higher temperature and pressure than SR. The maximum hydrogen yield can be obtained at 850 K, atmospheric pressure, ethanol to water molar feed ratio of 1:20 for SR system and at 1300 K, 22.1 MPa, and ethanol to water feed ratio of 1:20 for SCWR. The use of a distillation column to purify the bioethanol feed was proven to improve the fuel conversion efficiency of both systems. The analysis reveals that SCWR is a promising system for fuel production for SOFC when a gas turbine is incorporated to the system for energy recovery. Further, it is not necessary to distil bioethanol to obtain too high ethanol recovery (i.e. >90%) as higher energy consumption at the distillation column could lead to lower overall thermal efficiency.