• Energy Research

Abstract This work deals with the production of fuel ethanol from olive tree pruning. This raw material is a renewable, low cost, largely available, and lacking of economic alternatives agricultural residue. Olive tree pruning was submitted to steam explosion pre-treatment in the temperature range 190–240 °C, with or without previous impregnation by water or sulphuric acid solutions. The influence of both pre-treatment temperature and impregnation conditions on sugar and ethanol yields was investigated by enzymatic hydrolysis and simultaneous saccharification and fermentation on the pretreated solids. Results show that the maximum ethanol yield (7.2 g ethanol/100 g raw material) is obtained from water impregnated, steam pretreated residue at 240 °C. Nevertheless if all sugars solubilized during pre-treatment are taken into account, up to 15.9 g ethanol/100 g raw material may be obtained (pre-treatment conditions: 230 °C and impregnation with 1% w/w sulphuric acid concentration), assuming theoretical conversion of these sugars to ethanol.

Abstract The use of pretreated sugarcane bagasse for ethanol production was investigated by comparing three process configurations, separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF) and presacchararification followed by simultaneous saccharification and fermentation (PSSF). Design of experiments was applied to the different configurations. Glucose concentration and glucose yield were selected as response parameters for the saccharification step, while ethanol concentration and amount of bagasse per liter of ethanol were taken as comparison parameters among the three process configurations. Best values for ethanol yield of 81.6, 59.4 and 68.4% of theoretical yield based on glucose content in raw material were achieved for SHF, SSF and PSSF, respectively. From one ton of sugarcane bagasse it is possible to obtain, under these experimental conditions, 192, 172 and 198 L of ethanol, respectively. PSSF is the best process configuration based on ethanol yield and on volume of ethanol that can be produced from one tone of sugarcane bagasse. Further studies will be focused on increasing working scale.

AbstractBACKGROUND: The organosolv pretreatment followed by enzymatic hydrolysis of the pretreated material and subsequent fermentation of the hydrolysate produced, was the strategy used for ethanol production from sugarcane bagasse. The effect of different operational variables affecting the pretreatment (the catalyst type and its concentration, and the pretreatment time) and enzymatic hydrolysis stage (substrate concentration, cellulase loading, addition of xylanase and Tween 20, and the cellulase/β‐glucosidase ratio), were investigated.RESULTS: The best values of glucose concentration (28.8 g L−1) and yield (25.1 g per 100 g dry matter) were obtained when the material was pretreated with 1.25% (w/w) H2SO4 for 60 min, and subsequently hydrolyzed using 10% (w/v) substrate concentration in a reaction medium supplemented with xylanase (300 UI g−1) and Tween 20 (2.5% w/w). Fermentation of the broth obtained under these optimum conditions by Saccharomyces cerevisiae resulted in an ethanol yield of 92.8% based on the theoretical yield, after 24 h.CONCLUSION: Organosolv pretreatment of sugarcane bagasse under soft conditions, and subsequent enzymatic hydrolysis of the pretreated material with a cellulolytic system supplemented with xylanase and Tween 20, is a suitable procedure to obtain a glucose rich hydrolysate efficiently fermentable to ethanol by Sacharomyces cerevisiae yeasts. Copyright © 2010 Society of Chemical Industry

The production of fermentable sugars from olive tree biomass was studied by dilute acid pretreatment and further saccharification of the pretreated solid residues. Pretreatment was performed at 0.2%, 0.6%, 1.0% and 1.4% (w/w) sulphuric acid concentrations while temperature was in the range 170-210 degrees C. Attention is paid to sugar recovery both in the liquid fraction issued from pretreatment (prehydrolysate) and that in the water-insoluble solid (WIS). As a maximum, 83% of hemicellulosic sugars in the raw material were recovered in the prehydrolysate obtained at 170 degrees C, 1% sulphuric acid concentration, but the enzyme accessibility of the corresponding pretreated solid was not very high. In turn, the maximum enzymatic hydrolysis yield (76.5%) was attained from a pretreated solid (at 210 degrees C, 1.4% acid concentration) in which cellulose solubilization was detected; moreover, sugar recovery in the prehydrolysate was the poorest one among all the experiments performed. To take account of fermentable sugars generated by pretreatment and the glucose released by enzymatic hydrolysis, an overall sugar yield was calculated. The maximum value (36.3 g sugar/100 g raw material) was obtained when pretreating olive tree biomass at 180 degrees C and 1% sulphuric acid concentration, representing 75% of all sugars in the raw material. Dilute acid pretreatment improves results compared to water pretreatment.

Abstract Several strategies based on a two steps organosolv pretreatment followed by enzymatic hydrolysis of sugarcane bagasse (SCB) were evaluated with the objective of selecting operational conditions suitable to promote an efficient and low cost production of ethanol. Initially, the influence of six variables used for the organosolv pretreatment was studied. The variables included the time of the first organosolv pretreatment step, the use of 45% ethanol as pulping solution, solid-to-liquid ratio of the ethanol solution used during the first pretreatment step, time of second organosolv pretreatment, concentration of ethanol and concentration of NaOH solution used in the second pretreatment step. Further assays of enzymatic hydrolysis were carried out to promote additional reduction in the costs of the process and improve the results of cellulose conversion to glucose. Eliminating the milling step of the pretreated SCB, using a commercial tensoactive (composed of esters and several surfactants), and recycling 50% of the slurry obtained during the second step of organosolv pretreatment as reaction medium proved to be feasible for use during the enzymatic hydrolysis. Fermentation of the glucose medium produced under the selected pretreatment conditions to ethanol by Saccharomyces cerevisiae occurred with 81% efficiency and a cost of 102.88 $/hL of ethanol.

The growing interest on rape oil as raw material for biodiesel production has resulted in an increasing availability of rape straw, an agricultural residue that is an attractive renewable source for the production of second-generation bioethanol. Pretreatment is one of the key steps in such a conversion process. In this work, a sequential two-stage pretreatment with dilute sulfuric acid (130 °C, 60 min, 2% w/v H2SO4) followed by H2O2 (1-5% w/v) in alkaline medium (NaOH) at low temperature (60, 90 °C) and at different pretreatment times (30-90 min) was investigated. The first-acid stage allows the solubilisation of hemicellulose fraction into fermentable sugars. The second-alkaline peroxide stage allows the delignification of the solid material whilst the cellulose remaining in rape straw turned highly digestible by cellulases. Simultaneous saccharification and fermentation with 15% (w/v) delignified substrate at 90 °C, 5% H2O2 for 60 min, led to a maximum ethanol production of 53 g/L and a yield of 85% of the theoretical.

Abstract Sugar cane bagasse was submitted to ethanol organosolv pre-treatment using a 50 L pilot scale reactor. The influence of catalyst type (H2SO4 or NaOH), catalyst concentration (1.25–1.50% w/w on dry fiber) and process time (60–90 min) on total solid recovery and solid composition (glucan, xylan and lignin contents) was evaluated by performing a 23 full factorial experimental design. Pretreated sugar cane bagasse was further submitted to enzymatic hydrolysis using a commercial enzyme complex formed by cellulases and β-glucosidases. Glucose concentration in the hydrolysates and glucose yield referred to initial raw material (g glucose/100 g sugar cane bagasse) were used to select the best operational conditions. Concerning the enzymatic hydrolysis, the resulting glucose concentration was found to be dependent on xylan contents of the pretreated material. The modelling equations for glucose concentration and glucose yield as a function of the pre-treatment variables and the statistical analysis are also discussed in this work.

Sugarcane bagasse pretreated with dilute-acid was submitted to an organosolv ethanol process with NaOH under different operational conditions (pretreatment time, temperature, and ethanol concentra- tion) aiming to maximize the glucose yield in the subsequent enzymatic hydrolysis stage. The different pretreatment conditions resulted in variations in the chemical composition of the solid residue as well as in the glucose recovered by enzymatic hydrolysis. All the studied variables presented significant (p < 0.05) influence on the process. The optimum organosolv pretreatment conditions consisted in using 30% (v/v) ethanol at 195 ◦C, during 60 min. Enzymatic hydrolysis of the residue then obtained produced 18.1 g/l glucose, correspondent to a yield of 29.1 g glucose/100 g sugarcane bagasse. The scale-up of this process, by performing the acid pretreatment in a 10-l semi-pilot reactor fed with direct steam, was success- fully performed, being obtained a glucose yield similar to that found when the acid pretreatment was performed in autoclave. © 2011 Elsevier B.V. All rights reserved.