Process simulation of hydrogen production by steam reforming of diluted bioethanol solutions: Effect of operating parameters on electrical and thermal cogeneration by using fuel cells

The possibility to exploit diluted bioethanol streams is discussed for hydrogen production by steam reforming. An integrated unit constituted by a steam reformer, a hydrogen purification section with high- and low-temperature water gas shift, a methanator reactor and a fuel cell were simulated to achieve residential size cogeneration of 5 kW electrical power + 5 kW thermal power as target output.Process simulation allowed to investigate the effect of the reformer temperature, of bioethanol concentration and of catalyst loading on the temperature and concentration profiles in the steam reformer. The net power output was also calculated on the basis of 27 different operating conditions.P_electrical output ranging from 3.3 to 6.0 kW were obtained, whereas the total heat output P_{thermal, total} ranged from 3.9 to 7.2 kW. The highest overall energy output corresponded to P_electrical = 4.8 kW, P_{Thermal, FC} = 3.1 kW, P_{heat recovery} = 4.1 kW, for a total 12 kW energy output. This was achieved by feeding a mixture with water/ethanol ratio = 11 (mol/mol), irrespectively of the catalyst mass, and setting the ref split temperature so to have an average temperature of 635 °C in the ESR reactor.     

Producing bioethanol from cellulosic hydrolyzate via co-immobilized cultivation strategy

Lignocellulose was converted into reducing sugars by using saccharification enzymes from cocultivated Trichoderma reesei and Aspergillus niger and reducing sugars as nutrients for Zymomonas mobilis to produce bioethanol in an immobilization system. After 96 h of cultivation, cocultivated T. reesei and A. niger had enzymatical synergistic effects that enabled a reducing sugar production of 1.29 g/L and a cellulose conversion rate of 23.27%. An 18% total inoculum concentration and a 1/1 inoculation ratio of T. reesei to A. niger obtained a reducing sugar production rate and a cellulose conversion rate of 2.57 g/L and 46.27%, respectively. The co-immobilization cultivation results showed that using polyurethane as a carrier optimized total saccharification enzyme activity at an inoculum ratio of 1/1 and a total inoculum concentration of 6.5×10(6)spores/mL. Based on the experimental results, the bioreactor design was further modified to enhance bioethanol production. The three strains (A. niger, T. reesei and Z. mobilis) were cocultivated with a co-immobilization cultivation system. The experimental results showed that, after 24 h cultivation, bioethanol production reached 0.56 g/L, and reducing sugar conversion rate reached 11.2% when using carboxymethylcellulose (CMC) substrates. The experimental results confirmed that the modified bioreactor enhances bioethanol production. However, further experiments are needed to determine how to prevent multi-stage failure of reducing medium volume.     

Effect of sodium sulfite on acid pretreatment of wheat straw with respect to its final conversion to ethanol

A pretreatment process that combines dilute acid and sodium sulfite has been applied to wheat straw to study the effect of temperature (120–180 °C) and sodium sulfite concentration (0–3%) on the yield of glucose in subsequent enzymatic hydrolysis and ethanol production by fermentation. The results were compared with both dilute acid pretreatment (without Na₂SO₃ addition) and hot water pretreatment. Formation of furfural and hydroxymethylfurural, which can inhibit ethanol-producing microorganisms, were measured and the ethanol yield in a subsequent fermentation was evaluated. The results indicate that a combination of 180 °C, 30 min, 1% H₂SO₄ and 2.4% Na₂SO₃ during pretreatment produced the highest ethanol yield; 17.3 g/100 g dry weight of initial biomass, which corresponds to 75% of the theoretical yield from glucose. 28 mg of furan inhibitors (sum of furfural and hydroxymethylfurfural) per gram dry weight of initial wheat straw were generated under this condition. Increasing sulfite loading up to 2.4% decreased inhibitor formation, leading to increased delignification and preservation of cellulose from dissolution. On the other hand, an elevated temperature in combination with low pH reduced the amount of solid phase after pretreatment, increased the level of inhibitors and reduced the concentration of ethanol produced by fermentation.     

Selection of the best pretreatment for hydrogen and bioethanol production from olive oil waste products

Bioethanol is one of the most promising renewable energy sources, and it can be used as an alternative to petroleum-derived products. Agro-food residues are the substrates most frequently used for bioethanol production through anaerobic fermentation. The cultivation of olive trees and olive oil production are important economic activities throughout all Mediterranean countries. The wastes derived from olive oil production include a liquid waste, known as Olive Mill Wastewater (OMW), and a semi-solid waste, called Olive Pomace (OP), which is rich is lignin and cellulose materials. The aim of this work is to evaluate the quantity of hydrogen and bioethanol that could be extracted from an OMW-OP mixture after Saccharomyces cerevisiae anaerobic fermentation. In addition, different pretreatments (ultrasonic pretreatment, basic pretreatment, and calcium carbonate addition) have been tested to increase the glucose concentration and, consequently, the bioethanol and hydrogen production in the reaction medium and to decrease the content of inhibiting polyphenols which are mainly present in the OMW. All of the pretreatments were shown to have improved the hydrogen and bioethanol concentration at the end of the fermentation. The basic and ultrasonic pretreatments resulted in the best bioethanol and hydrogen production. These two pretreatments contributed to the hydrolysis of the lignin and cellulose and to increasing the soluble sugars (in particular glucose) content in the reaction mixture. Calcium carbonate addition decreased the polyphenol concentration; the polyphenols inhibit the fermentation mediated by S. cerevisiae.     

Corn stover ethanol yield as affected by grain yield,Bt trait,and environment

Literature values for glucose release from corn stover are highly variable which would likely result in tremendous variability in bio-refinery ethanol yield from corn stover feedstock. A relatively recent change in United States corn genetics is the inclusion of the Bacillus thuringiensis (Bt) trait, which now accounts for three-fourths of all US planted corn acreage. The objective of this study was to evaluate the effect of corn grain yield, inclusion of the Bt trait, and location environment on corn stover quality for subsequent ethanol conversion. Two hybrid pairs (each having a Bt and non-Bt near-isoline) were analyzed giving a total of 4 hybrids. In 2010 and 2011, field plots were located in Michigan at four latitudinal differing locations in four replicated plots at each location. Stover composition and enzymatic digestibility was analyzed and estimated ethanol yield (g g⁻¹) was calculated based on hydrolyzable glucan and xylan levels. Analysis showed that there were no significant differences in total glucose or xylose levels nor in enzymatically hydrolyzable glucan and xylan concentrations between Bt corn stover and the non-Bt stover isolines. Regression analyses between corn grain yield (Mg ha⁻¹) and corn stover ethanol yield (g g⁻¹) showed an inverse relationship indicative of a photosynthate source-sink relationship. Nevertheless, the quantity of stover produced was found to be more critical than the quality of stover produced in maximizing potential stover ethanol yield on a land area basis.     

Enhanced ethanol production by removal of cutin and epicuticular waxes of wheat straw by plasma assisted pretreatment

The removal of cutin and epicuticular waxes of wheat straw by PAP (plasma assisted pretreatment) was investigated. Wax removal was observed by Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) as chemical change on the surface of most intensively pretreated samples as well as with Scanning Electron Microscopy (SEM) imaging. Compounds resulting from wax degradation were analyzed in the washing water of PAP wheat straw. The wax removal enhanced enzymatic hydrolysis yield and, consequently, the efficiency of wheat straw conversion into ethanol. In total, PAP increased the conversion rate of the raw material carbohydrate content up to 67%, compared to untreated raw material.     

Recent Advances in Production of Bioethanol from Lignocellulosic Biomass

Ethanol is considered the most potential next generation automotive fuel because it is carbon‐neutral and could be produced from renewable resources like lignocellulosic biomass. There are some technological barriers such as pretreatment, saccharification of cellulose and hemicellulose matrix, and simultaneous fermentation of hexose and pentose sugars which needs to be addressed for efficient conversion of lignocellulosic biomass to bioethanol. This paper reviews the various process options and kinetic models adopted towards resolving the technological challenges to develop a low‐cost commercial process.     

Effect of inlet valve timing and water blending on bioethanol HCCI combustion using forced induction and residual gas trapping

It has been shown previously that applying forced induction to homogeneous charge compression ignition (HCCI) combustion of bioethanol with residual gas trapping, results in a greatly extended engine load range compared to normal aspiration operation. However, at very high boost pressures, very high cylinder pressure rise rates develop. The approach documented here explores two ways that might have an effect on combustion in order to lower the maximum pressure rise rates and further improve the emissions of oxides of nitrogen (NO_x); inlet valve timing and water blending. It was found that there is an optimal inlet valve timing. When the timing was significantly advanced or retarded away from the optimal, the combustion phasing could be retarded for a given lambda (excess air ratio). However, this would result in higher loads and lower lambdas for a given boost pressure, with possibly higher NO_x emissions. Increasing the water content in ethanol gave similar results as the non-optimal inlet valve timing.     

Spatially explicit multi-objective optimisation for design and planning of hybrid first and second generation biorefineries

Climate change mitigation has become a binding driver in biofuels production. First generation bioethanol, initially indicated as the most competitive option, is now incurring in ever increasing discredits forcing the transition towards more sustainable productions (i.e. second and third generation technologies). This paper addresses the strategic design and planning of corn grain- and stover-based bioethanol supply chains through first and second generation technologies. A Mixed Integer Linear Programming framework is proposed to optimise the environmental and financial performances simultaneously. Multi-period, multi-echelon and spatially explicit features are embodied within the formulation to steer decisions and investments through a global approach. A demonstrative case study is proposed involving the future Italian biomass-based ethanol production. Results show the effectiveness of the optimisation tool at providing decision makers with a quantitative analysis assessing the economic and environmental performance of different design configuration and their effect in terms of technologies, plant sizes and location, and raw materials.