Hydrotropic Pretreatment Research Articles

Changes in various lignocellulose biomasses structure after microwave-assisted hydrotropic pretreatment

Effective pretreatment of lignocellulosic biomass combined with delignification is a condition for effective enzymatic hydrolysis of cellulose, which is of key significance for the efficiency of the process of production of cellulosic ethanol. Becoming aware of the full range of changes in the structure of lignocellulose as a result of biomass pretreatment is important in view of the necessity to optimise the process of technological production of bioethanol. Our research was aimed at a comprehensive analysis of changes in structure of pine chip (softwood), beech chip (hardwood) and wheat straw (non-wood) biomasses resulting from a newly developed pretreatment method combining the use of hydrotrope in the form of sodium cumene sulfonate and microwave radiation. The performed analyses of the biomass composition indicate a high effectiveness of the proposed pretreatment method in the area of biomass delignification and hemicellulose removal. An effective removal of amorphous substances, i.e. lignin and hemicellulose, led to an increase in the crystallinity of pine chip biomass to 55%, and beech chips and wheat straw biomasses to 61%.

Cellulose hydrolysis and bioethanol production from various types of lignocellulosic biomass after microwave-assisted hydrotropic pretreatment

This study examined the impact of microwave-assisted hydrotropic pretreatment using sodium cumene sulfonate on the enzymatic hydrolysis of cellulose contained in pine chips, beech chips and wheat straw biomasses as well as the effectiveness of the production of bioethanol from the obtained hydrolysates. The effectiveness of enzymatic hydrolysis of cellulose contained in beech chips and wheat straw subjected to pretreatment in optimised process conditions amounted to ca. 55–60%. As a result of this, hydrolysates containing glucose in the concentration of 76–84 g/L were acquired, which is a significant achievement in the case of cellulosic hydrolysates. A lower efficiency of the process was recorded when cellulose from pine chips was used (maximum hydrolysis efficiency was 17.21 ± 0.09%), which confirms a higher resistance of softwood biomass to the process of biodegradation. The highest concentration of ethanol, at the level of 41.44 ± 0.55 g/L, was achieved through the fermentation of the medium being a hydrolysate of wheat straw after microwave-assisted hydrotropic pretreatment. The developed raw material and hydrolysate preparation method indicates the possibility of using wheat straw after microwave-assisted hydrotropic pretreatment for efficient cellulosic ethanol production using high-gravity (HG) technology.

Fractionation of poplar using hydrothermal and acid hydrotropic pretreatments for co-producing xylooligosaccharides, fermentable sugars, and lignin nanoparticles

In the present study, an integrated process involving hydrothermal pretreatment (HP) and acid hydrotropic pretreatment (AHP) was proposed for co-producing high value-added xylooligosaccharides (XOS), fermentable sugars, and lignin nanoparticles (LNPs) from poplar (Populus spp.). Approximately 36.2% of XOS (X2-X6) was obtained from raw xylan after HP at 170 °C for 50 min. Moreover, LNPs with an average size of 44.8 nm were produced from the HP-AHP pretreated poplar, using p-toluenesulfonic acid at a concentration of 55% (w/v) at 90 °C for 120 min. A mild alkaline incubation adopted to reduce the surface lignin of HP-AHP pretreated poplar significantly improved the enzymatic hydrolysis yield from 69.2% to 97.3%. The mass balance results showed that 1000 g of poplar generated 66.4 g of XOS, 468.0 g of fermentable sugars (442.0 g of glucose and 26.0 g of xylose), and 103.5 g of LNPs.

Delignification efficiency of various types of biomass using microwave-assisted hydrotropic pretreatment

The use of a method of an effective delignification of lignocellulosic biomass is a key stage of designing processes of its microbiological conversion e.g. for the purposes of the production of cellulosic ethanol. The study was aimed at evaluating the effectiveness of microwave-assisted hydrotropic pretreatment using sodium cumene sulfonate (NaCS) for the delignification of pine and beech chips and wheat straw. Research results presenting the impact of process parameters of microwave-assisted hydrotropic delignification confirm a high effectiveness of this method of pretreatment of lignocellulosic biomass. The observed effects included changes in the composition of the biomass and an increased susceptibility of cellulose to the subsequent enzymatic hydrolysis. The use of microwave heating combined with an addition of hydrotrope of 40% w/v NaCS and 117 PSI for 60 min enabled a reduction of the absolute concentration of lignins by 36.58% in pine chips, by 57.68% in beech chips, and by 74.08% in wheat straw. After enzymatic hydrolysis was conducted, the highest concentration of glucose: 463.27 ± 11.25 mg glucose/g (hydrolysis yield 46.76 ± 1.14%) was obtained from the wheat straw, while 327.70 ± 22.15 mg glucose/g (hydrolysis yield 35.13 ± 2.37%) was acquired from the beech chips, and only 50.77 ± 0.75 mg glucose/g (hydrolysis yield 6.63 ± 0.10%) was obtained from the pine chips. Microwave-assisted hydrotropic delignification in the optimum process conditions additionally allows a complete removal of hemicellulose from biomass, which improves the effectiveness of enzymatic hydrolysis. Due to a significant reduction of lignin and hemicellulose concentration in biomass, cellulose—which is susceptible to enzymatic hydrolysis and a source of carbon in biosynthesis processes—becomes the main biomass component.

Microwave-Assisted Urea-Based-Hydrotropic Pretreatment of Rice Straw: Experimental Data and Mechanistic Kinetic Models.

The three major lignocellulose components can be transformed into various biomass-derived platform fuels, chemicals, and materials upon pretreatment and chemical upgrading. Lignocellulose pretreatment is an important step to obtain an eco-friendly, economical, and effective biomass utilization process. The combination of microwave heating and hydrotropic pretreatment is considered as a green method of lignocellulose pretreatment. Experimental data and two mechanistic kinetic models of microwave-assisted pretreatment of rice straw are presented. Here, the use of urea solution as the hydrotropic agent was examined to facilitate the degradation of three major lignocellulose components. The first kinetic model assumes that the soluble lignin does not undergo condensation, while the second one assumes that part of the soluble lignin condenses to a solid product. The mechanistic models were validated with a series of experimental data obtained from microwave-assisted hydrotropic pretreatment of rice straw. The results show that both models could generally describe the experimental data well. However, based on the evaluation of the results of the kinetic models, it turned out that the rate of lignin condensation was relatively slow compared to the rate of lignin degradation to soluble lignin (the value of kc is relatively small compared to the value of kl1). Hence, the kinetic model with exclusion of lignin condensation is suggested more since it is mathematically simpler. The proposed mechanistic model can also predict the cellulose and hemicellulose dissolution and thereby can be used as a process optimization tool. The microwave-assisted urea-based hydrotropic pretreatment conducted at a solid–liquid ratio of 1:35, a urea concentration of 36.8%, a reaction temperature of 90 °C, and a pretreatment duration of 73.6 min is predicted to give a solid residue with low lignin content and high cellulose content which resulted in a cellulose to lignin ratio of 5.53. Cellulosic biomass characterization revealed that microwave-assisted hydrotropic pretreatment was able to produce higher crystallinity and thermally stable cellulosic biomass.

Microwave-assisted hydrotropic pretreatment as a new and highly efficient way to cellulosic ethanol production from maize distillery stillage

Aim of the study was to assess the suitability of the combined use of microwave radiation and sodium cumene sulfonate under optimized process conditions for the preparation of maize stillage biomass as a raw material for the production of cellulosic ethanol. The key parameter guaranteeing a high level of lignin removal from biomass (ca. 44%) was concentration of hydrotrope. Even at high biomass concentration (16% w/v) and a cellulase enzyme dose of about 4 filter-paper units/g, maize stillage biomass subjected to microwave-assisted hydrotropic pretreatment was highly susceptible to enzymatic degradation, which resulted in 80% hydrolysis yield. It is possible to obtain a fermentation medium with a very high glucose concentration (up to 80 g/L), without fermentation inhibitors and, as a consequence, to reach a very high level of sugar conversion to ethanol (concentration above 40 g/L), even as much as 95% of theoretical yield. Microwave hydrotropic treatment with sodium cumene sulfonate is a very effective way to prepare waste maize stillage biomass for the production of cellulosic ethanol. The degradation of the lignocellulose structure by the simultaneous use of microwaves and hydrotropes ensured a high degree of conversion of structural polysaccharides to bioethanol. The method provides a high level of enzymatic degradation of cellulose, leading to a medium with high content of released sugars suitable for bioconversion, which is in line with assumptions of the second-generation ethanol production technology.Key points• Microwave-assisted hydrotropic pretreatment is a new way to cellulosic ethanol production.• Microwave-assisted hydrotropic delignification removes 44% of lignin from biomass.• No fermentation inhibitors are obtained after microwave-assisted hydrotropic pretreatment.• High ethanol concentration (above 40 g/L) and fermentation yield (95% of theoretical yield) from biomass after microwave-assisted hydrotropic pretreatment.

Valorization of Alkaline Peroxide Mechanical Pulp by Metal Chloride-Assisted Hydrotropic Pretreatment for Enzymatic Saccharification and Cellulose Nanofibrillation.

Developing economical and sustainable fractionation technology of lignocellulose cell walls is the key to reaping the full benefits of lignocellulosic biomass. This study evaluated the potential of metal chloride-assisted p-toluenesulfonic acid (p-TsOH) hydrolysis at low temperatures and under acid concentration for the co-production of sugars and lignocellulosic nanofibrils (LCNF). The results indicated that three metal chlorides obviously facilitated lignin solubilization, thereby enhancing the enzymatic hydrolysis efficiency and subsequent cellulose nanofibrillation. The CuCl2-assisted hydrotropic pretreatment was most suitable for delignification, resulting in a relatively higher enzymatic hydrolysis efficiency of 53.2%. It was observed that the higher residual lignin absorbed on the fiber surface, which exerted inhibitory effects on the enzymatic hydrolysis, while the lower lignin content substrates resulted in less entangled LCNF with thinner diameters. The metal chloride-assisted rapid and low-temperature fractionation process has a significant potential in achieving the energy-efficient and cost-effective valorization of lignocellulosic biomass.

Hydrotropic pretreatment on wheat straw for efficient biobutanol production

Pretreatment is an important upstream process that affects the economics of biofuels production from lignocellulose. Hydrotropic reagent sodium xylene sulfonate (SXS) was used in this study to treat wheat straw for efficient butanol production. Effects of temperature, time, SXS concentration on pretreatment were evaluated. In addition, a modified SXS pretreatment method with pH adjusted to 3.5 by formic acid was also conducted for efficient wheat straw conversion by removing hemicellulose fraction. Composition analysis, structure characterization, enzymatic hydrolysis and fermentation tests were conducted. The results showed that modified SXS pretreatment can be considered as an efficient method for improving wheat straw conversion efficiency for ABE production. The hexoses and pentoses in the enzymatic hydrolysates can be used by C. acetobutylicum for butanol production with 12.41 g L−1 ABE produced, and the overall ABE yield of 100 g ABE/kg wheat straw was obtained. This study revealed that hydrotropic pretreatment provides an alternative potential to the conventional pretreatment processes for butanol production.

Modified Hydrotropic Pretreatment of Eucalyptus under Alkali and Acid Conditions for Lignin Removal and Enhancing Enzymatic Hydrolysis

Hydrotropic pretreatment is an environmentally friendly technology that can be applied for lignin isolation from lignocellulosic biomass to enhance enzymatic hydrolysis. In this study, conventional hydrotropic pretreatment was modified with additional alkali and acid to investigate the lignin removal mechanism. Lignin recovered from the hydrotropic solution was analyzed by Heteronuclear Single Quantum Coherence-Nuclear Magnetic Resonance (HSQC-NMR). It was found that the amounts of β-O-4 linkages in the different types of hydrotropic lignin were more than 50%. Alkali-hydrotropic lignin particularly contained 74.9% of β-O-4 linkages. Also, the cleavage of α-O-4 formed more phenolic groups in alkali-hydrotropic lignin. The addition of acid in the hydrotropic treatment could reinforce the broken β-O-4 bond. Modified hydrotropic pretreatments more easily displaced the lignin from the fiber surface and improved the enzymatic accessibility of the pretreated substrates. Considering other impact factors including the fiber structure and total lignin content, enzymatic hydrolysis was heavily influenced and facilitated by the acid-hydrotropic method.

Comparison of hydrothermal, hydrotropic and organosolv pretreatment for improving the enzymatic digestibility of bamboo

Pretreatment is the crucial step to disrupt the recalcitrant structure of lignocellulosic biomass for improving the enzymatic hydrolysis efficiency. Typically, hydrothermal, organosolv and hydrotropic pretreatments are environmentally benign and effective methods. In this work, effects of hydrothermal, organosolv and hydrotropic pretreatments on improving enzymatic hydrolysis of bamboo were comprehensively compared. Hydrotropic pretreatment was more effective in removal lignin and xylose from bamboo fiber cell wall. However, the surface coverage by lignin and extractives were dramatically displaced during organosolv pretreatment as investigation by X-ray photoelectron spectroscopy. After pretreatments, the crystallinity of cellulose in pretreated substrates has a significant reduction, and pores were exposed on fiber surface. The residual content of acetyl and phenolic groups in hydrotropic pretreated substrates is lower than organosolv pretreated substrates. In order to deeply assess the delignification of pretreatments, the isolated lignins obtaining from pretreatments process were characterized by Fourier transform infrared spectroscopy also. It was revealed that hydrotropic lignin contained more phenolic hydroxyl group and syringyl units than organosolv lignin. Compared to hydrothermal and organosolv pretreatment, cellulase adsorption capacity of pretreated substrates was notably improved by hydrotropic pretreatment, which indicating the better enzyme accessibility of cellulose. Eventually, the maximum glucose yield was obtained from hydrotropic pretreated substrates.

Comparison of organosolv and hydrotropic pretreatments of eucalyptus for enhancing enzymatic saccharification

The objective of this study was to investigate the effects of organosolv and hydrotropic pretreatments on improving enzymatic hydrolysis of eucalyptus. The chemical composition of the fiber surface was analyzed using X-ray photoelectron spectroscopy (XPS) to determine the surface characteristics of pretreated eucalyptus. Other than the significant decrease of surface coverage by lignin, hydrotropic pretreatment was more effective in removing the lignin and xylose from fiber cell walls than organosolv pretreatment. The restriction of acetyl and phenolic groups in pretreated substrates was typically eliminated by hydrotropic pretreatments. Moreover, fiber structure and morphology after pretreatments were more suitable for enzymatic hydrolysis. Cellulase adsorption capacity was notably improved by hydrotropic pretreatment, which indicating the better enzyme accessibility of cellulose in pretreated substrates. Eventually, higher glucose yield was obtained with hydrotropic pretreatment. In addition, the precipitated lignin as an important by-product of pretreatments was characterized by Fourier transforms infrared spectroscopy (FTIR) also.

RETRACTED: Evaluation of hydrotropic pretreatment on lignocellulosic biomass

The production of cellulosic ethanol from biomass is considered as a promising alternative to fossil fuels, providing a sustainable option for fuels production in an environmentally compatible manner. The presence of lignin poses a significant challenge for obtaining biofuels and bioproducts from biomass. Part of that problem involves understanding fundamental aspects of lignin structure which can provide a pathway for the development of improved technologies for biomass conversion. Hydrotropic pretreatment has several attractive features that make it an attractive alternative for biofuel production. This review highlights the recent developments on hydrotropic pretreatment processes for lignocellulosic biomass on a molecular structure basis for recalcitrance, with emphasis on lignin concerning chemical structure, transformation and recalcitrance. The review also evaluates the hydrotropic delignification in comparison to alkaline delignification on lignin reduction and surface coverage by lignin. The effect of hydrotrope pretreatment on enzymatic saccharification has also been discussed.

Hydrotropic pretreatment on rice straw for bioethanol production

The aim of this study was to investigate the effect of hydrotrope as a pretreatment process on rice straw for bioethanol production. Sodium cumene sulfonate and sodium xylene sulfonate (Na–X) were used as hydrotropes to delignify rice straw. Effects of biomass loading, time, temperature and hydrotrope concentration were studied for both the hydrotropes. There was no loss of cellulose & hemicellulose in the hydrotrope solution. Sodium cumene sulfonate could remove more than 50% of lignin from rice straw with 5% biomass loading at 121 °C for 1 h. Reusability of aqueous hydrotrope solution was demonstrated. Enzymatic digestibility of the hydrotrope pretreated rice straw was studied and evaluated for subsequent bioethanol production. The use of the hydrotrope for biomass pretreatment has the potential to mitigate the environmental impact of chemical pretreatment.

Topochemistry of Environmentally Friendly Pretreatments To Enhance Enzymatic Hydrolysis of Sugar Cane Bagasse to Fermentable Sugar

In this work, dilute alkaline and alkaline peroxide pretreatments were conducted in comparison with hydrotropic pretreatment to improve the delignification of bagasse prior to enzymatic hydrolysis. The surface chemical composition of bagasse after pretreatments was investigated by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The surface distribution of lignin and extractives on the bagasse fiber was significantly changed by dilute alkaline, alkaline peroxide, and hydrotropic pretreatments. Hydrotropic pretreatment typically showed, other than the decrease of surface coverage by lignin and extractives, dramatic removal of xylan, thereby leading to more cellulose exposed on the fiber surface after pretreatment. Fiber morphology after pretreatments was more favorable for enzyme hydrolysis as well. However, the hydrotropic treatment had clear advantages because the enzymatic hydrolysis yields of glucan and xylan of pretreated bagasse were 83.9 and 14.3%, respectively.

Pretreatment of Corn Stover with the Modified Hydrotropic Method To Enhance Enzymatic Hydrolysis

Hydrotropic pretreatment using sodium xylene sulfonate (SXS) could remove lignin and xylan from corn stover to enhance enzymatic saccharification. Peracetic acid (PAA) treatment prior to the hydrotropic process [so-called modified hydrotropic pretreatment (MHP)] could double the delignification efficiency and remarkably increase glucan conversion. After pretreatment, samples were treated by PFI refining for comparison. With the supplement of PFI refining before enzymatic hydrolysis of the MHP-treated corn stover, 87.6% of the glucan yield could be achieved and the corresponding xylan yield was 43.7%. In addition, the pretreated corn stover was analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD), and scanning electron microscopy (SEM). The lignin precipitate from the spend liquor was also investigated by FTIR. The cleavage of the lignin structure could be observed from FTIR results. The crystallinity index (CrI) of corn stover after MHP was increased according to XRD analysis, while the reduction of total CrI of cellulose between pretreatment samples was analyzed by FTIR. SEM analysis demonstrated that PAA treatment affected the morphology of corn stover fiber by generating pores and allowing for better contact of the enzyme to polysaccharides.

Topochemistry of alkaline, alkaline-peroxide and hydrotropic pretreatments of common reed to enhance enzymatic hydrolysis efficiency

Common reed was studied as raw material for sugar bioconversion. The low temperature alkaline, alkaline-peroxide and hydrotropic pretreatments were employed to overcome the recalcitrance of reed before enzymatic hydrolysis. After pretreatments, lignin was efficiently decreased from the fiber cell wall. Xylan was significantly reduced by hydrotropic pretreatment as well. The surface chemical compositions of reed before and after pretreatments were investigated by X-ray spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). Reed had a high surface coverage by lignin. Hydrotropic pretreatment was outstanding to decrease the surface coverage by lignin and expose the polysaccharides to fiber surface. The surface lignin reduction was also supported by attenuated total reflectance (ATR)-FTIR results. Furthermore, the topochemical modification of the fiber wall by hydrotropic pretreatment could improve the fiber digestibility, and thus the maximum glucan and xylan yields with the cellulase dosage of 20 FPU/g raised to 93.1% and 25.5%, respectively.

Topochemical pretreatment of wood biomass to enhance enzymatic hydrolysis of polysaccharides to sugars

The surface chemistry of milled birch and pine wood pretreated by ionic liquid, hydrothermal and hydrotropic methods, followed by enzymatic hydrolysis was studied in this work. Surface coverage by lignin was measured by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to describe the surface chemical composition after pretreatment in detail, and the morphology after pretreatment was investigated by FE-SEM. Ionic liquid (1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride) pretreatment at room temperature made the samples swell but did not dissolve the wood. Comparing the surface coverage by lignin, both in the case of birch and pine wood, hydrotropic worked best to remove the lignin hampering enzymatic hydrolysis. ToF-SIMS supported this finding, and showed that in birch, the carbohydrates were degraded more than in pine after hydrotropic pretreatment. The glucose yield of birch was improved by hydrotropic pretreatment from 5.1% to 83.9%, more significantly than in case of pine.