Lower Pretreatment Temperatures Research Articles

Efficient preparation of high-purity cellulose from moso bamboo by p-toluenesulfonic acid pretreatment

This work proposed a promising biorefinery method for the deconstruction of moso bamboo by using p-toluenesulfonic acid (P-TsOH) pretreatment to product high-purity cellulose (dissolving pulp). The cellulose pulp with high α-cellulose content (82.36 %) was successfully prepared for 60 min at low pretreatment temperature (90 °C) and atmospheric pressure. After the simple bleaching and cold caustic extraction (CCE) processes, the properties of cellulose pulp, such as α-cellulose content, polymerization, ISO brightness, all met the standard of dissolving pulp. In general, the cooking method through P-TsOH pretreatment can shorten the preparation time, which can effectively reduce energy consumption and chemical consumption. Therefore, this work may provide a new perspective for the green preparation of dissolving pulp that can be used to produce lyocell fiber after ash and metal ion treatment.

Tuning hydrothermal pretreatment severity of wheat straw to match energy application scenarios

Wheat straw was hydrothermally pretreated over a broad severity range (90–300 °C) to comparatively assess its suitability for energy application scenarios. Although the substrate was not completely deconstructed at the rather low temperature of 120 °C, the biomethane yield through whole slurry anaerobic digestion was 32% higher than that of unpretreated wheat straw. It was proposed that an increasing amount of soluble fractions was released at higher pretreatment temperatures, which consequently limited anaerobic digestion through the acidification or inhibition mechanism; therefore a lower biomethane yield was obtained. In contrast to the profile of anaerobic digestion, increasing the pretreatment temperature significantly facilitated bioethanol production through simultaneous saccharification and fermentation (SSF). When the hydrothermal pretreatment was performed at 210 °C, the ethanol yield was 229.5% higher than that of the untreated wheat straw. The possible reason was that at higher temperatures, the recalcitrant fraction of hemicellulose tended to solubilize through auto acid-catalyzed hydrolysis, which enhanced the accessibility of cellulose to cellulase enzymes. At very high hydrothermal temperatures (≥240 °C), the pretreated substrates were not suitable for biological conversion but were well suited for production of carbons with an ultra-high surface area. In conclusion, lower pretreatment temperatures are recommended for anaerobic digestion, moderate temperatures for SSF, and high temperatures for non-biological conversion to produce supercapacitor carbon electrodes.

Potassium permanganate assisted organosolv pretreatment enhances enzymatic hydrolysis of corn stover

AbstractHigh efficiency enzymatic hydrolysis of lignocellulose to produce fermentable sugar is important for bioconversion of lignocellulosic biomass to liquid fuels and chemicals. In this study, a simple pretreatment with potassium permanganate is used to enhance the efficiency of organosolv pretreatment of corn stover. It is testified that, compared to the single organosolv pretreatment, the KMnO4 assisted organosolv pretreatment significantly increase yields of carbohydrates through decreasing degradation of hemicellulose, decrease formation of inhibitors and enhance enzymatic hydrolysis of corn stover pretreated at a low pretreatment temperature. Process conditions of the KMnO4 assisted organosolv pretreatment are optimized and the conversion of glucan and xylan in pretreated corn stover at 72 h of enzymatic hydrolysis reach to 89.45% and 85.30% respectively when corn stover is firstly treated with 1% (w/w) KMnO4 at 40°C for 60 min prior to ethanol‐water pretreatment with 50% ethanol concentration at 185°C for 90 min. The differences in morphological feature, fiber surface chemical compositions, crystallinity degree and thermostability of pretreated corn stover by ethanol‐water with and without KMnO4 are characterized by scanning electron microscope, X‐ray photoelectron spectroscopy, X‐ray diffraction and thermogravimetry to explore the underlying reasons of KMnO4 strengthening ethanol‐water pretreatment process.

Organosolv Pretreatment of Sorghum Stalks Using Glycerol.

Glycerol is a promising low-cost solvent for biomass pretreatment since a large amount of glycerol is generated as a by-product in the biodiesel industry. Pretreatment is a method of disintegration of the recalcitrant structure of biomass to enhance the accessibility of cellulose and hemicelluloses to enzymes for complete saccharification. During pretreatment, glycerol breaks the lignin carbohydrate complex and selectively solubilizes lignin. Thus, the glycerol pretreatment improves the accessibility of cellulose to cellulases leading to higher sugar yields. The glycerol pretreatment is carried out at high temperature (>190°C) to disintegrate the structure of biomass. The glycerol pretreatment in the presence of acid or base catalyst such as H2SO4 or NaOH results in lower pretreatment temperature and higher glucan hydrolysis. This chapter describes the methodology to carry out glycerol pretreatment of sorghum biomass with or without acid/alkali as catalyst and the basic calculations to determine the efficiency of the pretreatment.

The dynamic change of pore structure for low-rank coal under refined upgrading pretreatment temperatures

Pore structure characteristics are significant factor in the evaluation of the physical characteristics of low-rank coal. In this study, three low-rank coal samples were collected from the Xishanyao Formation, Santanghu Basin, and low-temperature liquid-nitrogen adsorption (LP-N2A) measurements were taken under various pretreatment temperatures. Owing to the continuous loss of water and volatile matter in low-rank coal, the total pore volume assumes a three-step profile with knee temperatures of 150 °C and 240 °C. However, the ash in the coal can protect the coal skeleton. Pore collapse mainly occurs for mesopores with aperture smaller than 20 nm. Mesopores with apertures smaller than 5 nm exhibit a continuous decrease in pore volume, whereas the pore volume of mesopores with apertures ranging from 5 to 10 nm increases at lower pretreatment temperatures (<150 °C) followed by a faint decrease. As for mesopores with apertures larger than 10 nm, the pore volume increases significantly when the pretreatment temperature reaches 300 °C. The pore structure of low-rank coal features a significant heating effect, the pretreatment temperature should not exceed 150 °C when the LP-N2A is used to evaluate the pore structure of low-rank coal to effectively evaluate the reservoir characteristics of low-rank coal.

Chemical Free Two-Step Hydrothermal Pretreatment to Improve Sugar Yields from Energy Cane

Energy cane is an attractive lignocellulosic feedstock for processing into biofuels and bioproducts. A low-severity two-step hydrothermal pretreatment was investigated on energy cane for the production of monomeric sugar. Pretreatment temperature and time, in addition to the effect of disk milling, were observed for the glucose and xylose yields during hydrolysis. At residence times above 5 min in case of pretreatment at 200 °C, all of the hemicellulose was observed to be solubilized. The pretreatment condition of 200 °C for 10 min with disk milling was observed to provide the highest glucose concentration of 5.4%, and 200 °C for 5 min with disk milling provided the highest xylose concentration of 2.15%. The effect of disk milling in improving the sugar concentrations during hydrolysis was significant, especially at lower pretreatment temperatures and times. Low xylose yields at higher temperatures were attributed to the formation of degradation products at increased severity.

Insights into microbial community variability and functional genes of various Candidatus Scalindua-based anammox processes treating nitrogen-rich saline wastewater

Marine anammox bacteria (MAB) has been enriched in four sequencing batch reactors to treat nitrogen-rich saline wastewater. The community variability and cell activity of MAB were studied under different operating conditions. Besides, a novel hydrazine oxidoreductase (Hzo) primer set was designed and used for fast detection of MAB. The results indicated that, independent of operating conditions, Candidatus Scalindua wagneri was the dominant species in nitrogen-rich saline wastewater treatment. Low inoculation pretreatment temperature was a useful operational method to enhance the MAB abundance. Both the enzyme synthesis and cell penetrativity were promoted by Fe(III) addition, which benefited to improve the nitrogen removal performance. High influent NH4+-N and NO2−-N could decrease the synthesis of enzyme and protein which related with nitrogen removal from saline wastewater through MAB. The Hzo gene was an effective functional gene for specific and fast detection of MAB in engineered systems.

Conversion of rubber wood waste to methane by ethanol organosolv pretreatment

The restricted bioavailability of structurally complex carbohydrates for digestion has hitherto resulted in a low methane potential from rubber wood waste (RW). The effects of hydrothermal (HT) and ethanol organosolv (OS) pretreatments on the methane produced by anaerobic digestion of RW were investigated in the study reported. HT with temperatures above 190 °C significantly enhanced the anaerobic digestibility of RW mainly due to the degradation of hemicellulose. On the other hand, OS with 75% ethanol provided a potential methane gas yield of 165.1 L CH4/kg-VS, which was higher than that for HT at 210 and 230 °C by 39 and 7%, respectively. This was due to intensive delignification during OS pretreatment which led to a reduction in the non-productive adsorption of cellulolytic enzymes by lignin. A first-order kinetic model showed that OS had a higher hydrolysis rate (k = 0.073 ± 0.003 day−1) resulting in a higher methane yield when lower pretreatment temperatures were applied. The anaerobic degradation of the pretreated RW in this study was a result of simultaneous CH4 production through the symbiosis of anaerobic bacteria and methanogens using a combination of the aceticlastic and hydrogenothrophic bioconversion pathways. The recovery and use of the phenolic compounds remaining in the process water would be a way of adding value to this process and the feasibility of producing methane from RW should be further investigated.

Comparative evaluation of acid and alkaline sulfite pretreatments for enzymatic saccharification of bagasses from three different sugarcane hybrids.

Sugarcane bagasses from three experimental sugarcane hybrids and a mill-reference sample were used to compare the efficiency and mode of action of acid and alkaline sulfite pretreatment processes. Varied chemical loads and reaction temperatures were used to prepare samples with distinguished characteristics regarding xylan and lignin removals, as well as sulfonation levels of residual lignins. The pretreatment with low sulfite loads (5%) under acidic conditions (pH 2) provided maximum glucose yield of 70% during enzymatic hydrolysis with cellulases (10 FPU/g) and β-glucosidases (20 UI/g bagasse). In this case, glucan enzymatic conversion from pretreated materials was mostly associated with extensive xylan removal (70-100%) and partial delignification occurred during the pretreatment. The use of low sulfite loads under acidic conditions required pretreatment temperatures of 160°C. In contrast, at a lower pretreatment temperature (120°C), alkaline sulfite process achieved similar glucan digestibility, but required a higher sulfite load (7.5%). Residual xylans from acid pretreated materials were almost completely hydrolysed by commercial enzymes, contrasting with relatively lower xylan to xylose conversions observed in alkaline pretreated samples. Efficient xylan removal during acid sulfite pretreatment and during enzymatic digestion can be useful to enhance glucan accessibility and digestibility by cellulases. Alkaline sulfite process also provided substrates with high glucan digestibility, mainly associated with delignification and sulfonation of residual lignins. The results demonstrate that temperature, pH, and sulfite can be combined for reducing lignocellulose recalcitrance and achieve similar glucan conversion rates in the alkaline and acid sulfite pretreated bagasses. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:944-951, 2018.

Impact of thermal pretreatment and MSW origin on composition and hydrolysability in a sugar platform biorefinery

Municipal solid waste (MSW) is a widely available large volume source of lignocellulosic material containing a waste paper/cardboard mixture which can be converted into fermentable sugars via cellulolytic enzyme hydrolysis in a sugar platform biorefinery. Thermal pretreatments are generally applied to MSW to facilitate the extraction of the lignocellulosic material from recyclable materials (plastics, metals etc.) and improve the paper pulp conversion to sugars. Applying high temperature might enhance food waste solubilisation but may collapse cellulose fibre decreasing its hydrolysability. Low temperature pre-treatment will reduce the energy demand but might result in highly contaminated pulp. Preliminary results showed that the enzymatic hydrolysis performances were dependent on the MSW origins. Using 8 different samples, the impact of thermal pretreatment and MSW origin on pulp composition and hydrolysability was assessed in this work. Low pre-treatment temperature produced pulp which contained less lignocellulosic material but which hydrolysed to a higher degree than MSW treated at high temperatures. High temperature pre-treatment could have exposed more of the inhibiting lignin to cellulase. This information would have a significant economic impact on a commercial plant as expensive autoclave could be advantageously replaced by a cheaper process. Glucan conversions were also found to vary depending on the region, the recycling rate possibly because of the lower recycling rate resulting in the use of less paper additive in the material or the difference in paper production technology (chemical VS mechanical pulping). This could also be explained by the differences in paper composition.

Cholinium amino acids-glycerol mixtures: New class of solvents for pretreating wheat straw to facilitate enzymatic hydrolysis

New solvents for pretreating wheat straw, mixtures of cholinium amino acids ionic liquids ([Ch][AA] ILs) and glycerol, were developed. As a typical result, 50% cholinium alanine-glycerol is capable of removing 67.6% lignin while reserving 95.1% cellulose (90°C, L/S mass ratio of 20:1, 6h) and the conversions of cellulose and xylan are 89.7% and 70.9%, respectively, which is comparable to the pretreatment capability of other solvents, while [Ch][AA]-glycerol mixtures have desirable advantages, e.g., biocompatibility, lower cost with adding glycerol than pure IL, much lower pretreatment temperature (typically <100°C) than that by glycerol (typically >200°C). Lignin removal and polysaccharide conversion are dependent on [Ch][AA] content and pH of pretreatment solvents. [Ch][AA] not only remove lignin in wheat straw effectively but also swell cellulose while not remarkably dissolve cellulose with high cellulose reservation, favoring the enzymatic hydrolysis. Such mixtures of ILs and co-solvents are potential solvents for pretreating biomass.

Effects of Low Moisture Anhydrous Ammonia (LMAA) Pretreatment at Controlled Ammoniation Temperatures on Enzymatic Hydrolysis of Corn Stover.

Corn stover was treated using low-moisture anhydrous ammonia (LMAA) at controlled ammoniation temperature. Moisturized corn stover (50% moisture) was contacted with anhydrous ammonia (0.1g NH3/g-biomass) in a batch reactor at various temperatures (ambient to 150°C). After ammoniation at elevated and controlled temperature, ammoniated corn stover was pretreated at various temperatures (60-150°C) for 72-144h. Change in composition was marginal at low pretreatment temperature but was relatively severe with pretreatment at high temperature (130-150°C). The latter resulted in low enzymatic digestibility. It was also observed that extreme levels (either high or low) of residual ammonia affected enzymatic digestibility, while residual ammonia improved by 1.0-1.5%. The LMAA method enhanced enzymatic digestibility compared to untreated corn stover (29.8%). The highest glucan and xylan digestibility (84.1 and 73.6%, respectively) was obtained under the optimal LMAA conditions (i.e., ammoniation at 70°C for 20min, followed by pretreatment at 90°C for 48h).

Factors Governing the Pretreatment Process of Lignocellulosic Biomass in an Acidic Pyrrolidonium Ionic Liquid

Ionic liquid (IL)-assisted pretreatment is an important step in biochemical conversion of lignocellulosic biomass into biofuels. Design for low-cost ILs that efficiently work at a relatively low pretreatment temperature with a short processing time is of great interest. In this work, a functional acidic ionic liquid, 1-H-N-methyl-2-pyrrolidonium chloride ([Hnmp]Cl), was prepared by a simple synthetic procedure in a cost-effective manner and was then investigated for use in the pretreatment of lignocellulosic biomass. Factors including temperature, time, ratio of biomass to ionic liquid, and water content were studied to determine their impact on the pretreatment of lignocellulose; 91.39% of lignin content was recovered when the corn stalk was pretreated by pure [Hnmp]Cl at 100 °C for 45 min with a biomass loading of 5%. The highest glucose yield attained was 93.20% and the highest cellobiose yield was 18.76%, when the ratio of biomass to water was kept at 1:4. The pretreatment efficacy was dependent on the pretreatment temperature and processing time, which was more efficient for pure ionic liquid with respect to lignin recovery from lignocelluloses. However, more efficient enzymatic saccharification of cellulose-rich materials was achieved with aqueous ionic liquid.

Effects of curcumin on cisplatin cytotoxicity in HeLa cells

New solvents for pretreating wheat straw, mixtures of cholinium amino acids ionic liquids ([Ch][AA] ILs) and glycerol, were developed. As a typical result, 50% cholinium alanine-glycerol is capable of removing 67.6% lignin while reserving 95.1% cellulose (90 °C, L/S mass ratio of 20:1, 6 h) and the conversions of cellulose and xylan are 89.7% and 70.9%, respectively, which is comparable to the pretreatment capability of other solvents, while [Ch][AA]-glycerol mixtures have desirable advantages, e.g., biocompatibility, lower cost with adding glycerol than pure IL, much lower pretreatment temperature (typically <100 °C) than that by glycerol (typically >200 °C). Lignin removal and polysaccharide conversion are dependent on [Ch][AA] content and pH of pretreatment solvents. [Ch][AA] not only remove lignin in wheat straw effectively but also swell cellulose while not remarkably dissolve cellulose with high cellulose reservation, favoring the enzymatic hydrolysis. Such mixtures of ILs and co-solvents are potential solvents for pretreating biomass.

Optimizing ethanol and methane production from steam-pretreated, phosphoric acid-impregnated corn stover.

Pretreatment is of vital importance in the production of ethanol and methane from agricultural residues. In this study, the effects of steam pretreatment with phosphoric acid on enzymatic hydrolysis (EH), simultaneous saccharification and fermentation (SSF), anaerobic digestion (AD) and the total energy output at three different temperatures were investigated. The effect of separating the solids for SSF and the liquid for AD was also studied and compared with using the whole slurry first in SSF and then in AD. Furthermore, the phosphoric acid was compared to previous studies using sulphuric acid or no catalyst. Using phosphoric acid resulted in higher yields than when no catalyst was used. However, compared with sulphuric acid, an improved yield was only seen with phosphoric acid in the case of EH. The higher pretreatment temperatures (200 and 210 °C) resulted in the highest yields after EH and SSF, while the highest methane yield was obtained with the lower pretreatment temperature (190 °C). The highest yield in terms of total energy recovery (78 %) was obtained after pretreatment at 190 °C, but a pretreatment temperature of 200 °C is, however, the best alternative since fewer steps are required (whole slurry in SSF and then in AD) and high product yields were obtained (76 %).

Enhancing sugar recovery from sugarcane bagasse by kinetic analysis of a two-step dilute acid pretreatment process

Maximising sugar recovery from pretreatment and enzymatic hydrolysis is a determining factor in the economic viability of bio-refineries using lignocellulose as feedstock. Single-step dilute acid treatment of sugarcane bagasse was investigated at times and temperatures ranging between 12 and 22 min and 422–442 K, respectively. Maximum sugar recovery equalled 78% of the mass fraction polysaccharides (recovered as hydrolysis products xylose and glucose) present in sugarcane bagasse. Preferred operating conditions, as determined by response surface methodology (RSM), included an acid (H2SO4) concentration range of 45–55 mmol.L−1, a time of 14.0 min and temperature of 442 K. Complete recovery of both xylose and glucose could not be achieved through the combination of single-step dilute acid treatment and enzymatic hydrolysis. Whereas a short pretreatment time and low pretreatment temperature process was required for maximum xylose recovery, opposing operating conditions had to be applied to maximise glucose recovery. In order to circumvent some of the limitations associated with the single-step process, the use of a two-step process was tested through RSM simulations. A 4.8% increase in the total sugar recovery yield and a 36.1% reduction in furfural production were calculated for the two - in lieu of the one-stage method. The improvement was attributed to the avoidance of xylose degradation reactions but also the production of low enzymatically-digestible solids.

Structural changes of corn stover lignin during acid pretreatment

In this study, raw corn stover was subjected to dilute acid pretreatments over a range of severities under conditions similar to those identified by the National Renewable Energy Laboratory (NREL) in their techno-economic analysis of biochemical conversion of corn stover to ethanol. The pretreated corn stover then underwent enzymatic hydrolysis with yields above 70 % at moderate enzyme loading conditions. The enzyme exhausted lignin residues were characterized by ³¹P NMR spectroscopy and functional moieties quantified and correlated to enzymatic hydrolysis yields. Results from this study indicated that both xylan solubilization and lignin degradation are important for improving the enzyme accessibility and digestibility of dilute acid pretreated corn stover. At lower pretreatment temperatures, there is a good correlation between xylan solubilization and cellulose accessibility. At higher pretreatment temperatures, lignin degradation correlated better with cellulose accessibility, represented by the increase in phenolic groups. During acid pretreatment, the ratio of syringyl/guaiacyl functional groups also gradually changed from less than 1 to greater than 1 with the increase in pretreatment temperature. This implies that more syringyl units are released from lignin depolymerization of aryl ether linkages than guaiacyl units. The condensed phenolic units are also correlated with the increase in pretreatment temperature up to 180 °C, beyond which point condensation reactions may overtake the hydrolysis of aryl ether linkages as the dominant reactions of lignin, thus leading to decreased cellulose accessibility.

Understanding changes in lignin of Panicum virgatum and Eucalyptus globulus as a function of ionic liquid pretreatment

Ionic liquids (ILs) have shown great potential for the reduction of lignin in biomass after pretreatment. Although dilute acid and base pretreatments have been shown to result in pretreated biomass with substantially different lignin composition, there is scarce information on the composition of lignin of IL pretreated biomass. In this work, temperature dependent compositional changes in lignin after IL pretreatment were studied to develop a mechanistic understanding of the process. Panicum virgatum and Eucalyptus globulus were pretreated with 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]). Measurement of syringyl and guaiacyl ratio using pyrolysis–GC/MS and Kamlet–Taft properties of [C2mim][OAc] at 120°C and 160°C strongly suggest two different modes of IL pretreatment. Preferential breakdown of S-lignin in both eucalyptus and switchgrass at high pretreatment temperature (160°C) and breakdown of G-lignin for eucalyptus and no preferential break down of either S- or G-lignin in switchgrass was observed at lower pretreatment temperatures (120°C).

Low temperature lignocellulose pretreatment: effects and interactions of pretreatment pH are critical for maximizing enzymatic monosaccharide yields from wheat straw.

BackgroundThe recent development of improved enzymes and pentose-using yeast for cellulosic ethanol processes calls for new attention to the lignocellulose pretreatment step. This study assessed the influence of pretreatment pH, temperature, and time, and their interactions on the enzymatic glucose and xylose yields from mildly pretreated wheat straw in multivariate experimental designs of acid and alkaline pretreatments.ResultsThe pretreatment pH was the most significant factor affecting both the enzymatic glucose and xylose yields after mild thermal pretreatments at maximum 140°C for 10 min. The maximal enzymatic glucose and xylose yields from the solid, pretreated wheat straw fraction were obtained after pretreatments at the most extreme pH values (pH 1 or pH 13) at the maximum pretreatment temperature of 140°C. Surface response models revealed significantly correlating interactions of the pretreatment pH and temperature on the enzymatic liberation of both glucose and xylose from pretreated, solid wheat straw. The influence of temperature was most pronounced with the acidic pretreatments, but the highest enzymatic monosaccharide yields were obtained after alkaline pretreatments. Alkaline pretreatments also solubilized most of the lignin.ConclusionsPretreatment pH exerted significant effects and factor interactions on the enzymatic glucose and xylose releases. Quite extreme pH values were necessary with mild thermal pretreatment strategies (T ≤ 140°C, time ≤ 10 min). Alkaline pretreatments generally induced higher enzymatic glucose and xylose release and did so at lower pretreatment temperatures than required with acidic pretreatments.

Investigation on surface molecular conformations and pervaporation performance of the poly(vinyl alcohol) (PVA) membrane

A simple method of changing pre-treatment temperature in the course of film formation was used to tune the surface structures of PVA membranes. Surface structure and property of the resulting membranes were characterized by X-ray photoelectron spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy, and contact angle measurements. The results show that PVA have different molecular conformations at the membrane surface while those membranes were prepared at different pre-treatment temperature. At higher pre-treatment temperatures, polar acetoxyl residues and hydroxyl groups of the PVA chains oriented in a more orderly fashion, as induced by the faster evaporation of water. When the membranes were in air, CH 3 groups adjacent to the acetoxyl groups covered the surface in order to minimize the surface free energy, while backbones of the PVA were rarely observed. These surfaces exhibited a hydrophilic nature upon contact with water due to rapid surface reconstruction. Conversely, at lower pre-treatment temperatures, the backbone CH 2 groups dominated the surface, forming a less hydrophilic surface. When the PVA membranes were employed to separate ethanol/water mixtures, it was found that the PVA membranes with more hydrophilic surface exhibited higher water selectivity. Our investigation indicates that molecular conformations on the membrane surface have considerable influence on pervaporation performance.