Acid Pretreatment Process Research Articles

Dilute acid pretreatment for cellulosic alcohol production

Dilute acid pretreatment can be an effective and traditional method to make raw biomass feedstock more suitable for biomass-to-ethanol conversion. Four types of biomass feedstock including switchgrass, sorghum, prairie cordgrass, and rice straw were tested by applying dilute sulfuric acid pretreatment under controlled conditions for degrading the lignin component. This research studied the kinetic rates and activation energy for both heat degradation and acid degradation. Simple kinetic expressions have been proposed and rate constants determined from the tests in order to describe and predict the biomass weight loss during the heated dilute acid pretreatment process. It was found that a zero-order heat degradation rate coupled with a first-order acid degradation rate can adequately predict the overall biomass degradation process.

Research on Pretreatment Process and Product Detection in Enzymatic Hydrolysis of Lignocellulosic Biomass

Sulfite pretreatment was explored in enzymatic hydrolysis of bagasse for the first time, and was compared with dilute acid pretreatment. The results showed that enzymatic hydrolysis yield of bagasse after sulfite treatment was lower than that of the bagasse pretreated with dilute acid. Meanwhile, complexity of sulfite pretreatment and its high cost made it infeasible for industrialized production. Results also showed positive correlation of bagasse pretreatment weight loss to enzymatic hydrolysis yield in dilute acid pretreatment processes, which made substrate weight loss a plausible parameter in pretreatment evaluation.

Sugar recovery from rice straw by dilute acid pretreatment

Rice straw was pretreated with dilute sulfuric acid in order to decrease the amorphous portion and enhance enzyme accessibility. Dilute acid pretreatment process was optimized using a statistical method, and the relationships between each factor were investigated. Saccharification of pretreated rice straw was then performed, followed by fermentation of glucose, the hydrolysate of the saccharification process. The optimal dilute acid pretreatment process was as follows: temperature 110 °C, reaction time 14.02 min, and acid concentration 1.2%. Following dilute acid pretreatment, the solid weight was decreased by about 20% and 73.14% of the theoretical maximum content of xylose was solubilized. Glucose was recovered at a rate of about 90% at 24 h after rice straw was treated with dilute acid. Qualitative analysis such as SEM, XRD, and FT-IR were conducted after the pretreatment process, and the results supported the pretreatment process.

Evaluation of an adapted inhibitor-tolerant yeast strain for ethanol production from combined hydrolysate of softwood

In order to evaluate the potential of an adapted inhibitor-tolerant yeast strain developed in our lab to produce ethanol from softwood, the effect of furfural and HMF presented in defined medium and pretreatment hydrolysate on cell growth was investigated. And the efficiency of ethanol production from enzymatic hydrolysate mixed with pretreatment hydrolysate of softwood by bisulfite and sulfuric acid pretreatment process was reported. The results showed that in the combined treatments of the two inhibitors, cell growth was not affected at 1 g/L each of furfural and HMF. When 3 g/L each of furfural and HMF was applied, the adapted strain responded with an extended lag phase of 24 h. Both in batch and fed-batch runs of combined hydrolysate fermentation, the final ethanol concentrations were above 20.0 g/L and the ethanol yields ( Y p/s) on the total amount of fermentable sugar presented in the pretreated materials were above 0.40 g/g. It implies the great promise of the yeast strain for improving ethanol production from softwood due to its high ability of metabolizing inhibitor compounds of furfural and HMF.

Effects of Biodiesel Blending with Fossil Fuel on Flow Properties of Biodiesel Produced From Non-Edible Oils

The cold flow properties of biodiesel from various feedstocks have been a challenge in adapting the use of biodiesel in diesel engines, especially in cold regions. The use of cold flow improvers for biodiesel helps using biodiesel in a wide range of temperature conditions. In this study, cold flow properties of biodiesel produced from non-edible feedstocks such as croton megalocarpus, jatropha curcas, and moringa oleifera oils were investigated. The evaluated properties were kinematic viscosity, cloud point, and pour point. Different transesterification methods were used to produce biodiesel from these feedstocks due to their difference in the level of free fatty acids (FFA). Croton and moringa oils were found with FFA levels of 1.68% and 0.6%, respectively; thus, one-step transesterification method was chosen for their methyl esters conversion. Jatropha oil was found with FFA level of 8.14% making a two-step acid-base transesterification method to be employed for its methyl esters conversion. The effect of water in the two-step acid-base transesterification process was also investigated for jatropha biodiesel production. The presence of water after acid pretreatment process of jatropha oil was found to reduce both product and methyl esters yield, the best option was to preheat the pretreated jatropha oil to 110°C for 10 min to evaporate water that remain during gravity separation of methanol–water phase. Blending of biodiesels from these three feedstocks with kerosene improved their cold flow properties. The reduction of cloud and pour points from −4°C and −9°C to −11°C and −15°C, respectively, of croton biodiesel was observed when blended with 20% kerosene while cloud and pour points reduction from 1°C and −2°C to −7°C and −12°C, respectively, of jatropha biodiesel was observed when blended with 20% kerosene. Similarly, the reduction of cloud and pour points from 10°C and 3°C to −3°C and −7°C, respectively, of moringa biodiesel was observed when blended with 20% kerosene.

Comparison of dilute acid and ionic liquid pretreatment of switchgrass: Biomass recalcitrance, delignification and enzymatic saccharification

The efficiency of two biomass pretreatment technologies, dilute acid hydrolysis and dissolution in an ionic liquid, are compared in terms of delignification, saccharification efficiency and saccharide yields with switchgrass serving as a model bioenergy crop. When subject to ionic liquid pretreatment (dissolution and precipitation of cellulose by anti-solvent) switchgrass exhibited reduced cellulose crystallinity, increased surface area, and decreased lignin content compared to dilute acid pretreatment. Pretreated material was characterized by powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and chemistry methods. Ionic liquid pretreatment enabled a significant enhancement in the rate of enzyme hydrolysis of the cellulose component of switchgrass, with a rate increase of 16.7-fold, and a glucan yield of 96.0% obtained in 24h. These results indicate that ionic liquid pretreatment may offer unique advantages when compared to the dilute acid pretreatment process for switchgrass. However, the cost of the ionic liquid process must also be taken into consideration.

Variation due to Growth Environment in Alfalfa Yield, Cellulosic Ethanol Traits, and Paper Pulp Characteristics

Alfalfa (Medicago sativa L.) is a promising bioenergy and bioproduct feedstock because of its high yield, N-fixation capacity, potential for planting in rotation with corn (Zea mays L.), and valuable protein co-product (leaf meal). Our objective was to examine the effect of growth environment on biomass yield, cellulosic ethanol traits, and paper pulp fiber characteristics of alfalfa stems. Landscape position (summit and mild slope), season of harvest (four harvests per season), and multiple years (2005 and 2006) provided environmental variation. Alfalfa stem samples were analyzed for cell wall carbohydrate and lignin concentration. Stems were subjected to dilute acid pre-treatment, enzymatic saccharification, and pulping processes to measure relevant cellulosic ethanol and paper production traits. Landscape position was not a significant source of variation for yield or any biomass quality trait. Yields varied among harvests in 2005 (1,410–3,265 kg ha−1) and 2006 (1,610–3,795 kg ha−1). All cell wall, conversion test, and paper production traits exhibited year by harvest interactions with no clear pattern. Total carbohydrates and lignin ranged from 440 to 531 g kg−1 DM and from 113 to 161 g kg-1 DM, respectively. Release of cell wall sugars by the conversion test ranged widely (419 to 962 g kg−1 DM). Fiber traits were similarly variable with length and fine content ranging from 1.24 to 1.59 mm and from 15.2% to 21.9%, respectively. Utilizing alfalfa biomass for cellulosic ethanol and paper pulp production will involve dealing with significant feedstock quality variation due to growth environment.

Initial design of a dilute sulfuric acid pretreatment process for aspen wood chips

A preliminary process design for dilute sulfuric acid pretreatment of aspen wood chips in order to obtain fermentable sugars has been prepared and subjected to an economic evaluation. The process design was prepared according to experimental data on the kinetics of dilute sulfuric acid prehydrolysis and particle size effects obtained in this study and our previous work. The initial economic evaluation shows woodchips are 56% of the cost of production, whereas the reactor is only 4%, and the comminution operation is just under 10%, indicating that the process economics are extremely vulnerable to feedstock costs and are thus yield-sensitive. Although chances for major cost improvements by modification of the reactor design and finding alternatives to dry milling of aspen chips to small (20–80 mesh) particles needed for acid penetration and enzymatic saccharification are not great, design improvements of the process will necessitate development of a cheaper acid resistant pretreatment reactor and a less energy intensive comminution system. Experimental results on effects of particle size on the dilute acid pretreatment design are presented.