Impacts of utilization patterns of cellulosic C5 sugar from cassava straw on bioethanol production through life cycle assessment.

Integrated processes of whole plant cassava bioethanol production using full components including cellulosic C5 sugar are proposed. The impacts of different utilization patterns of cellulosic C5 sugar on bioethanol production are investigated by life cycle assessment. Results show that for cassava straw bioethanol, process using cellulosic C5 sugar performs better, and the NER, renewability and GWP (global warming potential) are 0.94, 1.09 and 2929 kg CO2 eq. The integrated process WPC-2 that the cellulosic C5 sugar mash is fermented together with the cassava starch, is a better cellulosic C5 sugar utilization pattern with NER 1.49, renewability 2.20 and GWP 1579 kg CO2 eq. The process WPC-2 shows the potential to approach cassava bioethanol in terms of energy and environmental emissions. The downstream products are investigated and the E85 fuel from WPC-2 has higher application potential.

Exploring the reaction mechanism of ethanol synthesis from acetic acid over a Ni2In(100) surface.

A low-cost and high-efficiency nickel-indium bimetallic catalyst is designed to improve the activity of acetic acid hydrogenation to ethanol, which can make full use of the overproduced acetic acid. In this work, density functional theory (DFT) calculations are carried out to explore the mechanism of ethanol synthesis from acetic acid on the Ni2In(100) surface and tailor the catalyst to acquire enhanced properties. The results show that the most feasible pathway is CH3COOH → CH3CO → CH3CHO → CH3CHOH → CH3CH2OH, and the rate-determining step is the hydrogenation of CH3CHOH* to CH3CH2OH, with an activation barrier of 1.20 eV and an endothermic energy of 0.15 eV. Compared with the Cu2In(100) surface, the Ni2In(100) surface converts the reaction pathway to the acetyl species direction, which shows great advantages for the following CH3CHO* formation. Furthermore, the effects of indium doping in the nickel catalyst on the side reaction is also discussed by comparing with the monometallic Ni(111) surface. The addition of indium turns out to cause a significant inhibition on the C-C bond breaking and is beneficial for promoting the acetic acid hydrogenation to ethanol. Electronic analysis proves that the role of In is to donate electrons, which can increase the electron density of Ni and enhance the catalytic activity.

The synergistic effects of Cu clusters and In2O3 on ethanol synthesis from acetic acid hydrogenation.

The development of high efficiency catalysts for acetic acid hydrogenation to ethanol could ameliorate the petroleum crisis and acetic acid overproduction. Cu and In2O3 catalysts both show catalytic activity for acetic acid hydrogenation. However, monometallic Cu catalysts are less active in the dissociative adsorption of acetic acid through C-O bond breaking, while the H2 adsorption and dissociation ability of In2O3 is weak. In this work, Cu4/In2O3 is designed to enhance the dissociation of both acetic acid and H2. The detailed mechanism of acetic acid hydrogenation to ethanol on Cu4/In2O3 is explored using periodic density functional theory (DFT). The results show that the H2 adsorption and dissociation are enhanced by the Cu cluster, while the H atom spillover from Cu to In2O3 is favorable on the Cu4/In2O3(110) surface. Additionally, a synergistic effect exists between the Cu cluster and In2O3 surface: H2 adsorbs on the Cu cluster and the dissociated H atoms react with acetic acid activated by the In2O3 oxygen vacancy. Finally, compared with a Cu2In(100) surface, the Cu4/In2O3(110) surface possesses higher catalytic activity owing to the reduced energy barriers of acetic acid dissociation and hydrogenation of the intermediates (CH3COO*, CH3CHO*, and CH3CH2O*). The Cu4/In2O3 catalyst proposed in this work can provide promising guidance for related catalyst design.

The byproduct-organic acids strengthened pretreatment of cassava straw: Optimization and kinetic study.

The subcritical liquid hot water (SLHW) pretreatment could be strengthened by its byproduct-organic acids, such as acetic acid (AA), lactic acid (LA) and formic acid (FA). The effects of these three acids on the pretreatment were investigated by the yield of fermentable sugars. The results showed that the addition of acids could effectively catalyze the hydrolysis of hemicellulose to C5 sugars and contribute to the subsequent enzymatic hydrolysis of cellulose. It was found that all three organic acids promote xylose production, and the copresence of AA + LA could limit the content of the fermentation inhibitor. The optimum proportion of three organic acids were 0.33 wt%AA + 0.45 wt%LA + 0.20 wt%FA, and the yield of C5 sugars after pretreatment and C6 sugar after enzymatic hydrolysis were 89.06% and 78.56%, respectively. The kinetic studies proved that byproduct-organic acids could promote xylose production and inhibit its further degradation and explained that xylose would accumulate at lower temperatures.

Exploration and optimization of mixed acid synergistic catalysis pretreatment for maximum C5 sugars.

The liquid hot water (LHW) pretreatment could be strengthened by acetic and lactic acids produced from the process. The synergistic effect of the mixed acid catalyst of lactic acid and acetic acid was investigated for the purpose of maximization of the overall C5 sugars yield. Individual acids (acetic and lactic acid) and mixed acid were used to strengthen the LHW pretreatment at different conditions. The results showed that the suitable conditions of mixed acid synergistic catalysis was at 180 °C for 60 min and 3 wt% mixed acid where the ratio of 40% (i.e. 0.40 in mass fraction of lactic acid in mixed acid). Response surface methodology (RSM) was applied to further optimize this process. The highest yield of C5 sugars of 93.83% according to theoretical predicted model, was close to the experiment value of 92.53% at 177 °C for 67 min and with the ratio of mixed acid of 40%.

Effect of surface oxygen vacancy sites on ethanol synthesis from acetic acid hydrogenation on a defective In2O3(110) surface.

Developing a new type of low-cost and high-efficiency non-noble metal catalyst is beneficial for industrially massive synthesis of alcohols from carboxylic acids which can be obtained from renewable biomass. In this work, the effect of active oxygen vacancies on ethanol synthesis from acetic acid hydrogenation over defective In2O3(110) surfaces has been studied using periodic density functional theory (DFT) calculations. The relative stabilities of six surface oxygen vacancies from Ov1 to Ov6 on the In2O3(110) surface were compared. D1 and D4 surfaces with respective Ov1 and Ov4 oxygen vacancies were chosen to map out the reaction paths from acetic acid to ethanol. A reaction cycle mechanism between the perfect and defective states of the In2O3 surface was found to catalyze the formation of ethanol from acetic acid hydrogenation. By H2 reduction the oxygen vacancies on the In2O3 surface play key roles in promoting CH3COO* hydrogenation and C-O bond breaking in acetic acid hydrogenation. The acetic acid, in turn, benefits the creation of oxygen vacancies, while the C-O bond breaking of acetic acid refills the oxygen vacancy and, thereby, sustains the catalytic cycle. The In2O3 based catalysts were shown to be advantageous over traditional noble metal catalysts in this paper by theoretical analysis.

Insights into the mechanism of ethanol synthesis and ethyl acetate inhibition from acetic acid hydrogenation over Cu2In(100): a DFT study.

Developing low-cost and high-efficiency non-noble metal catalysts is beneficial for industrially massive synthesis of ethanol from acetic acid, which can be obtained from renewable biomass. Understanding the detailed mechanism of the reaction from a molecular level provides insights that can be used to tailor catalysts to improve their performance. In this study, alternative mechanisms for ethanol synthesis from acetic acid hydrogenation over Cu2In(100) have been investigated using periodic density functional theory (DFT) calculations. The pathway of CH3COOH → CH3COO → CH3CHOO → CH3CHO → CH3CH2O → CH3CH2OH was found to be most favorable. The high activation barriers for CH3COO hydrogenation to CH3CHOO (1.33 eV) and CH3CH2O hydrogenation to CH3CH2OH (1.04 eV) indicate that these two steps are the rate-limiting steps. In addition, the results also show that there are probably two more active intermediate species of CH3CO and CH3CH(OH)O besides CH3COO. Furthermore, the synergy and the role of copper and indium in the Cu-In bimetallic catalyst were discussed. The adsorption strength of copper will be improved by indium. Indium, however, has high chemical inertness in Cu2In. They evenly divided the surface into small reaction areas which could significantly inhibit ethyl acetate formation through the hindrance effect.

Kinetic studies of the strengthening effect on liquid hot water pretreatments by organic acids.

The liquid hot water (LHW) pretreatments would be accelerated by the organic acids produced from the process. In the study, the organic acids included not only acetic acid but also lactic acid during LHW hydrolysis of reeds, at 180-220°C and for 15-135min. The lactic acid was presumably produced from xylose degradation in the pretreatment process. The different organic acids, such as acetic acid, lactic acid and acetic-lactic acids, were used to strengthen the LHW pretreatments for increasing xylose production. Moreover, the work presented kinetic models of xylose and hemicellulose at different conditions, considering the generation of lactic acid. The experimental and kinetic results both indicated that acetic-lactic acids had synergistic catalytic effect on the reaction, which could not only inhibit the degradation of xylose, but also promote the hydrolysis of hemicellulose. Besides, the highest concentration of xylose of 7.323g/L was obtained at 200°C, for 45min and with 1wt% acetic-lactic acids.