Increasing Pretreatment Temperature Research Articles

Alkaline Pretreatment of Banana Stems for Methane Generation: Effects of Temperature and Physicochemical Changes

The effects of NaOH pretreatment temperature on the physicochemical characteristics and methane production of anaerobically digested banana stems were investigated in this paper. With the increase of pretreatment temperature from 0 °C to 100 °C, the chemical oxygen demand (COD) of the soak liquid in the treated biomass approximately linearly increased from 5.9 g/L for the untreated stems to 34.0 g/L. A weight loss of 5.1% was observed for the untreated material, while it was up to 31.2% for the sample treated at 100 °C. The removal of lignin and hemicellulose accounted for the majority of the weight loss. The removal rates of lignin and hemicellulose increased from 15.0% to 41.6% and 1.9% to 23.6% when the treatment temperature increased from 0 °C to 100 °C, respectively. Moreover, the crystalline index (CI) of the banana stems also increased with rising temperature, resulting from the dissolution of amorphous cellulose with increasingly harsher alkaline environments. The optimal pretreatment temperature for banana stems was confirmed at 50 °C. In these conditions, methane was produced via anaerobic digestion with 239.9 mL/g total solid (TS) yield, which represented an increase of 66.7% over untreated banana stems.

Role of Water on the Activity of Magnesium Silicate for Transesterification Reactions

AbstractThis study aims to reveal how water adsorbed on to a solid can influence its catalytic properties for transesterification in liquid phase. A commercial magnesium silicate was subjected to a range of thermal pretreatments and used for the transesterification of ethyl acetate with methanol. Conversion of ethyl acetate decreased with increasing pretreatment temperature, in direct relation to the release of the water content of the magnesium silicate. Thermogravimetric analysis, diffuse reflectance infrared Fourier transform (DRIFT), and 1H NMR spectroscopies revealed that physically adsorbed water had little influence on the reactivity. The water incorporated within the catalysts, however, which desorbs at higher temperatures, played a key role on the conversion. Calorimetry, in situ DRIFT spectroscopy, and 1H NMR characterization indicate that two kinds of active site exist. These are created from the water coordinated to magnesium located on the edge of the clay‐like particles or in the defects present in the silicate layer, respectively. Their role could be to stabilize methanol deprotonated by basic Mg‐OH groups, activate the ester, or help the departure of the alkoxyl moiety.

Hydrothermal and alkaline hydrothermal pretreatments plus anaerobic digestion of sewage sludge for dewatering and biogas production: Bench-scale research and pilot-scale verification

To test the feasibility and practicability of the process combing hydrothermal pretreatment for dewatering with biogas production for full utilization of sewage sludge, hydrothermal/alkaline hydrothermal pretreatments and in turn anaerobic digestion of the filtrates obtained after dewatering the pretreated sludge were performed at bench- and pilot-scales. The hydrothermal temperature fell within the range of 140 °C–220 °C and the pretreatment time varied from 30 min to 120 min. For the alkaline hydrothermal pretreatment the pH value of the sludge was adjusted to 9.0–11.0 by adding Ca(OH)2. The results showed that the dewaterability of the sewage sludge was improved with increasing pretreatment temperature but the impact of the pretreatment time was not significant. The addition of Ca(OH)2 gave better performance on the subsequent mechanical dewatering of the pretreated sludge compared to pure hydrothermal pretreatment, and the higher the pH value was, the better the dewaterability of the pretreated sludge was. The conditions of 180 °C/30 min and 160 °C/60 min/pH = 10.0 (for hydrothermal and alkaline hydrothermal pretreatments, respectively) resulted in relatively good results in the theoretical energy balance, which were verified in the pilot-scale tests. Based on the data from the pilot tests, the alkaline hydrothermal process realized self-sufficiency in energy at the cost of a proper amount of CaO.

2D NMR characterization of wheat straw residual lignin after dilute acid pretreatment with different severities

Abstract The chemical characteristics of wheat straw lignin pretreated under dilute acid conditions were compared. After pretreatment, the lignin content of the solid residue increased as temperature increased (from 160°C to 190°C) and with the amount of acid added (0%, 0.25%, or 1% H2SO4). Pretreatment at 190°C with increasing concentrations of acid catalyst led to a decrease in glucan content, whereas the glucan content remained almost constant at 160°C pretreatment regardless of the acid concentration. The xylan content decreased in proportion with increased acid concentration and pretreatment temperature. The residual lignins were characterized by solution-state, two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy and size-exclusion chromatography (SEC). Results showed that more ether bonds were cleaved with increased pretreatment temperature and lower pH, whereas the levels of carbon-carbon bonded structures (e.g. phenylcoumaran and resinol units) were hardly affected. With a pretreatment of 160°C and 1% H2SO4, the majority of the β-O-4 bonds were cleaved. In addition, lignin depolymerization was more evident than repolymerization at higher pretreatment temperatures and lower pH. Documenting lignin structural changes as a function of pretreatment parameters provides a tool for biorefineries to gain flexibility in processing parameters with full control over the final properties of the products.

Optimizing Phosphoric Acid plus Hydrogen Peroxide (PHP) Pretreatment on Wheat Straw by Response Surface Method for Enzymatic Saccharification.

Wheat straw was pretreated by phosphoric acid plus hydrogen peroxide (PHP), in which temperature, time, and H3PO4 proportion for pretreatment were investigated by using response surface method. Results indicated that hemicellulose and lignin removal positively responded to the increase of pretreatment temperature, H3PO4 proportion, and time. H3PO4 proportion was the most important variable to control cellulose recovery, followed by pretreatment temperature and time. Moreover, these three variables all negatively related to cellulose recovery. Increasing H3PO4 proportion can improve enzymatic hydrolysis; however, reduction on cellulose recovery results in decrease of glucose yield. Extra high temperature or long time for pretreatment was not beneficial to enzymatic hydrolysis and glucose yield. Based on the criterion for minimizing H3PO4 usage and maximizing glucose yield, the optimized pretreatment conditions was 40°C, 2.0h, and H3PO4 proportion of 70.2% (H2O2 proportion of 5.2%), by which glucose yielded 299mg/g wheat straw (946.2mg/g cellulose) after 72-h enzymatic hydrolysis.

Acidified glycerol pretreatment for enhanced ethanol production from rice straw

Rice straw was pretreated using an industrial grade glycerol for ethanol production. The pretreatment was conducted at 130–210 °C for 1–24 h with 5% solid loading. The glucan content in the regenerated rice straw increased with increasing pretreatment temperature and time. The production of fermentable sugars initially increased as the pretreatment temperature and reaction time increased, but then decreased somewhat at the higher temperatures and with longer reaction duration. The highest amount of reducing sugar produced by the enzymatic hydrolysis was achieved at 190 °C for 10 h with 5% solid loading, optimal condition for the glycerol pretreatment of rice straw. Furthermore, it was observed that glycerol pretreatment with the addition of HCl improved the digestibility of fermentable sugars by 4–5 times that of untreated samples. Fermentation of hydrolysates resulted in an ethanol yield of 0.44 g/g sugar, corresponding to a theoretical yield of 84.3%. It was concluded that acidified glycerol is one of the good candidates of the organic solvent for the pretreatment of lignocellulosic biomass.

Kraft GL-ethanol pretreatment on sugarcane bagasse for effective enzymatic hydrolysis

Kraft green liquor (GL) mainly consisting of sodium carbonate and sodium sulfide are available from Kraft mills. Kraft GL combined with ethanol (Kraft GL-ethanol) was chosen to pretreat sugarcane bagasse for effective enzymatic hydrolysis. And the obtained lignins and cellulose rich fractions were characterized in detail. The highest lignin removal of 95.3% was observed at a pretreatment temperature of 160°C, and approximately 70.8% of lignin was removed at the pretreatment temperature of 100°C. The lignin removal with Kraft GL-ethanol pretreatment was higher than that with Soda GL-ethanol pretreatment at 140°C. An FT-IR study of the isolated lignins showed that an increase in pretreatment temperature resulted in the cleavage of ester bonds. GPC results revealed that the molecular weight decreased with increasing pretreatment temperature. The 2D HSQC NMR data showed that the cleavage of β-O-4 became more severe with increasing pretreatment temperature from 80 to 160°C. Fewer condensation reactions between lignin units occurred when the pretreatment temperature was above 100°C. Moreover, the enzymatic hydrolysis efficiency of sugarcane bagasse increasing with increasing pretreatment temperature. The glucose yield reached 65.13% at a pretreatment temperature of 80°C. The maximum glucose yield (98.26%) of sugarcane bagasse after 72h of enzymatic hydrolysis was achieved at a pretreatment temperature of 160°C. When lignin content was low in samples after pretreatment at 140–160°C, the enzymatic hydrolysis efficiency of the substrate increased because the number of crystalline cellulose regions decreased. Scanning electron microscopy showed that the surfaces of Kraft GL-ethanol pretreated sugarcane bagasse were separated into individual fibers. In addition, contact angle analysis showed that the Kraft GL-ethanol pretreated sugarcane bagasse was more hydrophilic than untreated sugarcane bagasse.

Variation of Particle Size and Pretreatment Temperature to the Crystallinity of Leucaena Leucocephala

This study was conducted in order to determine the effect of different particle size and pretreatment temperature to the crystallinity of leucaena leucocephala. The leucaena was pretreated by ionic liquid [1-ethyl-3 methylimidazolium acetate [Emim]Ac. There were three different particle sizes that have been tested in this experiment; less than 0.3 mm, 0.5 mm and 0.7 mm. In the other hand, the pretreatment temperature tested were 30°C, 60°C and 90°C. The effect of particle size and pretreatment temperature to the crystallinity of leucaena was investigated by using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The crystallinity index of the sample represents the percentage of crystalline materials. A lower in the cristallinity index indicated that the material has lower crystillinity, hence give more benefit to the cellulose hydrolysis. From XRD analysis, it shows that the cristallinity index of leucaena decreased with decreasing particle size and increasing pretreatment temperature. SEM analysis also shows that the structure of leucaena has more irregular, porous and destroyed structure with decreasing particle size and increasing pretreatment temperature. Thus, the result from this experiment shows that the smaller particle size and higher pretreatment temperature would provide a more accessible surface area to enhance the cellulose hydrolysis.

Adsorption of Polyvinylpyrrolidone over the Silica Surface: As Affected by Pretreatment of Adsorbent and Molar Mass of Polymer Adsorbate

The adsorption of polyvinylpyrrolidone over the surface of silica has been investigated. The impact of molar mass of the polymer, pH, and pretreatment temperature of silica particles have been evaluated by means of FTIR spectroscopy and electrophoretic measurements. The silica particles used have narrow particle size distribution. The zeta potential of the aqueous silica suspension was decreased with the increase in pH. The amount of polymer adsorbed was increased with the increase in pretreatment temperature, time, concentration, pH, zeta potential, and molar mass of the polymer. The addition of polymer to the system increased the zeta potential due to adsorption of polymer on the surface of the particles. However, the impact increased with the increase in molecular mass of the polymer. The IR spectra obtained before and after adsorption of polymer concluded that, mostly, hydrogen bonding is responsible for the adsorption phenomena; however, hydrophobic interactions also play a significant role. The mechanism has been investigated and established through FTIR spectroscopy.

Influence of pretreatment temperature on catalytic performance of rutile TiO2-supported ruthenium catalyst in CO2 methanation

Catalytic hydrogenation of CO2 to methane was investigated over Ru/rutile TiO2, focusing on the influence of the pretreatment temperature on the activity. Rutile TiO2 stabilized Ru nanoparticles even after pretreatment at 800°C; therefore it was possible to establish the structure–activity relationship without considering the particle size effect. The CO2 turnover frequency initially increased with increasing pretreatment temperature from 300 to 800°C, and reached a maximum value of 1.59s−1 on Ru/rutile TiO2 pretreated at 600°C; it decreased to 1.16s−1 for the sample pretreated at 800°C. The characterization results indicated that the activity depended on both the extent of encapsulation of Ru particles by TiOx layers and the number of hydroxyl groups on the TiOx surface. The mechanism of CO2 methanation was discussed based on in situ diffuse-reflectance infrared Fourier-transform spectroscopy results.

Pretreating Luffa Sponge (Luffa cylindrica L.) with Concentrated Phosphoric Acid and Subsequent Enzymatic Saccharification

Luffa was evaluated as a potential energy crop. A considerable amount of luffa sponge biomass can be grown in a vertical direction with approximately 70% polysaccharide content and low lignin content. When concentrated H3PO4 was employed to pretreat luffa sponge, hemicelluloses were the most sensitive component, followed by cellulose and lignin. Hemicellulose solubilization and cellulose loss positively responded to the elevated temperature, time, H3PO4 concentration, and dosage for pretreatment. However, lignin solubilization was not affected greatly. Although the initial hydrolysis rate was accelerated by increasing pretreatment temperature, the final glucose conversion was reduced as temperature was raised higher than 50 °C. Prolonging pretreatment time was positively correlated to enzymatic digestibility. When H3PO4 concentration was lower than 80%, the final glucose conversion was increased with increasing H3PO4 concentration. Increasing H3PO4 concentration to 84% for pretreatment caused the final glucose conversion to decrease slightly, although the hydrolysis rate was initially accelerated. Additionally, an improvement of glucose conversion was obtained with increasing the substrate-to-phosphoric acid ratio. However, the improvement was not cost-effective, as the ratio was lower than 1-to-8.

Pretreatment of Miscanthus by NaOH/Urea Solution at Room Temperature for Enhancing Enzymatic Hydrolysis

A novel pretreatment process using NaOH/Urea solution at room temperature was developed to overcome recalcitrance of lignocellulose for efficient bioconversion of miscanthus. The process consists of mechanical size reduction, pretreatment with NaOH/Urea solution, and filtration. The results indicated that the substrate enzymatic digestibility (SED) of miscanthus pretreated with 8 wt% NaOH and 12 wt% urea at 21 oC for 30 min was up to 71.99 % at low enzyme loading of 5 filter paper units (FPU)/g glucan after 72 h hydrolysis. NaOH/Urea pretreatment efficiently removed lignin and hemicellulose. And their removal rates increased with the increase of pretreatment temperature, NaOH dosage and urea dosage. With the increase of NaOH dosage, the chemical composition removal rate decreased in the following order: lignin, xylan, araban, galactan. Meanwhile, NaOH/Urea pretreatment could open up the fiber structure, decrease cellulose crystallinity index, and prevent lignin droplets depositing on cellulose. The optimal condition for the NaOH/Urea pretreatment regarding this study was 6 wt% NaOH/12 wt% urea and 21 °C. Approximately 70 % glucose yield was achieved upon this condition.

Characterization of ionic liquid pretreatment and the bioconversion of pretreated mixed softwood biomass

In this study, mixed softwoods were pretreated with an ionic liquid, 1-butyl-3-methylimidazolium chloride ([Bmim]Cl), and the bioconversion efficiencies to fermentable sugars were estimated through the enzymatic hydrolysis. The cellulose crystallinity, surface morphology, structures and compositions of softwood were significantly changed after the ionic liquid pretreatment was carried out under a wide range of temperatures and reaction times. And, biomass digestibility significantly increased with increasing pretreatment temperature and reaction time. The enzymatic degradation of pretreated softwoods was remarkably improved at the pretreatment of high temperatures via the modification of crystalline cellulose I to a mixture of easily digestable cellulose II and amorphous structure, and partial removal of hemicellulose. The conversion of cellulose to glucose reached more than 90% at relevant conditions and the highest glucose yield was measured to about 78%. Through the study, it was clearly shown that ionic liquid pretreatment is one of the effective methods to produce high fermentable sugars without lignin dissolution from lignocellulosic biomass.

Hydrothermal pretreatment for biogas production from anaerobic digestion of antibiotic mycelial residue

This paper aims at investigating the effect of hydrothermal pretreatment on anaerobic digestion of antibiotic mycelial residue (AMR) for biogas production based on batch laboratory experiments. The pretreatment temperature and time varied from 80 to 180°C and from 0 to 60min, respectively. The results show that the hydrothermal pretreatment could degrade the organic particulates in AMR into soluble and even small-molecule substances to significantly improve the anaerobic digestibility of AMR and greatly facilitate biogas production. The biogas yield increased with increasing pretreatment temperature and time when the temperature was not higher than 120°C, and a higher temperature did not significantly facilitate the biogas production and even lead to a lower biogas yield, especially when the pretreatment temperature time was excessively long. The hydrothermal pretreatment at 120°C for 60min gave the best digestion performance, and the corresponding methane and biogas yields reached 290and 446ml/gVS, respectively.

Numerical simulation of biomass fast pyrolysis in an auger reactor

Fast pyrolysis is an effective means of converting solid low-energy density biomass to intermediate energy products, such as bio-oil. In this study, computational fluid dynamics (CFD) simulations of the biomass fast pyrolysis processes in both the fluidized-bed and the auger reactors were conducted. The numerical results were validated by experimental data. Materials of all phases were modeled as interpenetrating continua by use of a multi-fluid model. Chemical reactions were simulated using a multi-step reaction mechanism that considers multiple compounds in biomass and various gaseous species in the reactor. In the study of biomass fast pyrolysis in the fluidized-bed reactor, CFD simulation results were analyzed to obtain the average residence time of materials in the reactor. This residence time was used as the time for chemical reactions in estimating the final product yields. The estimated product yields agreed well with the experimental data. To simulate the complex geometry and fluid dynamics in the auger reactor, a numerical approach based on a rotating reference frame was incorporated into the multi-fluid model to account for the auger rotation. Good levels of agreement between the predicted and measured product yields were obtained. A parametric study was conducted to characterize the effects of operating conditions on product yields. The study shows that the optimal wall temperature for maximum tar production was approximately 823 K. The tar yield decreased with increased pre-treatment temperature of the biomass feedstock. It was also found that increased inlet nitrogen flow rate was beneficial to tar yield, while increased biomass feed rate had a negative effect on tar production.

Homogeneous and heterogeneous cyclopentadienyl-arene titanium catalysts for selective ethylene trimerization to 1-hexene

Cyclopentadienyl-arene complexes [(η5-C5H4CMe2Ph)Ti(OiPr)3] (2) and [(η5-C5H4CMePh(CH2CH2CHCH2))Ti(OiPr)3] (3), where Me = methyl, Ph = phenyl, iPr = isopropyl, were prepared and characterized by spectroscopic methods (NMR, IR, ESI-MS) and elemental analysis (EA). 2 was anchored on two siliceous supports SiO2 and SBA-15 (pre-treated at 200, 700, and 800 °C) predominantly by a covalent Ti–O–Si bond. 3 was grafted onto SiMe2H-modified silica by hydrosilylation at 25 and 90 °C. 3 was attached by a flexible covalent tether –(CH2)4SiMe2– from the ligand to the silica surface. Models for immobilized surface species [(η5-C5H4CMe2Ph)Ti(POSS-O3)] (4) (where POSS-O3 = open silsesquioxane) and [(η5-C5H4{CMePh(CH2)4SiMe2OSi(OtBu)3})Ti(OiPr)3] (6) (where tBu = tertiary butyl) were also prepared and characterized. Comparison of homogenous catalysts 1–4 and 6/MAO (where 1 = [(η5-C5H4CMe2Ph)TiCl3]; MAO = methylaluminoxane) for ethylene trimerization showed that activity was influenced mainly by the σ-ligand. The alkyl (R) substituent of CMePhR had a negligible effect. Activity of the heterogeneous 2/support/MAO catalyst increased with increasing pre-treatment temperature (i.e. decreasing amounts of residual surface silanol groups). However, the leaching test showed, that a significant activity could be attributed to an active species leached from the support. We propose that an easy cleavage (methylation) of Ti–O–Si linkage by an excess of MAO would be the main origin of leaching. The inactivity of 3/support/MAO towards ethylene trimerization was attributed to close contact between the catalytically-active species and the surface.

Understanding changes in cellulose crystalline structure of lignocellulosic biomass during ionic liquid pretreatment by XRD

X-ray diffraction (XRD) was used to understand the interactions of cellulose in lignocellulosic biomass with ionic liquids (ILs). The experiment was designed in such a way that the process of swelling and solubilization of crystalline cellulose in plant cell walls was followed by XRD. Three different feedstocks, switchgrass, corn stover and rice husk, were pretreated using 1-butyl-3-methylimidazolium acetate ([C4mim][OAc]) at temperatures of 50-130°C for 6h. At a 5 wt.% biomass loading, increasing pretreatment temperature led to a drop in biomass crystallinity index (CrI), which was due to swelling of crystalline cellulose. After most of the crystalline cellulose was swollen with IL molecules, a low-order structure was found in the pretreated samples. Upon further increasing temperature, cellulose II structure started to form in the pretreated biomass samples as a result of solubilization of cellulose in [C4mim][OAc] and subsequent regeneration.

Enhancing enzymatic saccharification of water hyacinth through microwave heating with dilute acid pretreatment for biomass energy utilization

Water hyacinth, as waste biomass, can potentially replace fossil fuels and address pressing issues of energy shortage and serious environmental pollution. In this study, microwave-assisted dilute acid pretreatment was proposed to enhance the enzymatic saccharification of water hyacinth for biomass energy utilization. After the pretreatment, a large amount of hemicellulose in the pretreated water hyacinth was hydrolyzed into xylose, galactose, and arabinose, whereas only a small amount of cellulose and lignin was hydrolyzed into glucose and propiolic acid, respectively. Increased pretreatment temperature, reaction time, and H2SO4 concentration generated more hemicellulose, cellulose, and lignin degradation products, including monosaccharides and other hydrolyzates, which were further degraded into smaller acids and aldehydes. In the enzymatic hydrolysis step following the pretreatment, a large amount of cellulose was hydrolyzed into glucose and cellobiose, whereas hemicellulose was completely degraded. When 20 g/l of water hyacinth feedstock was subjected to microwave pretreatment with 1% H2SO4 at 140 °C for 15 min and then enzymatically hydrolyzed using cellulase, a maximum reducing sugar yield of 48.3 g/100 g hyacinth was obtained. This value was 94.6% of the theoretical reducing sugar yield.

Bimetallic RhRe/C catalysts for the production of biomass-derived chemicals

Pretreatment temperature affects the activity of a RhRe/C catalyst for CO hydrogenolysis of 2-(hydroxymethyl)tetrahydropyran and for dehydration of fructose. Catalytic activities for both CO hydrogenolysis and dehydration were observed to decrease with an increase in pretreatment temperature from 393 to 723K, which coincides with a decrease in the number of sites quantified using NH3 temperature-programmed desorption. Results for the characterization of RhRe/C using X-ray absorption spectroscopy (XAS) are consistent with the formation of Rh-rich particles with a shell of metallic Re islands after reduction at 393K, which shows penetration of Re into the nanoparticle with increasing reduction temperature. No evidence of rhenium oxide was found from the Re LIII-edge XAS spectra after reduction at temperatures above 363K or under aqueous operando conditions. The apparent acidity of RhRe/C is suggested to be generated from the activation of water molecules over Re atoms on the surface of metallic RhRe particles.

Titration of Free Hydroxyl and Strained Siloxane Sites on Silicon Dioxide with Fluorescent Probes

A technique enabling the detection and quantification of low density sites on planar SiO2 surfaces is demonstrated. Fluorescent probes are used to titrate free hydroxyl and strained siloxane sites on the surface of amorphous SiO2 substrates in vacuum. The titration of free hydroxyl sites was performed to validate the method and to provide a reference for the measurement of the strained siloxane site density. Perylene derivatives with different functional groups are chemisorbed onto the surface sites, enabling in situ photoluminescence (PL) measurements of the bound fluorophores. An amine functional group is used to selectively titrate strained siloxane sites, while an alcohol group is used for the titration of free hydroxyl sites. Emission intensity was found to be nonlinear with coverage for bound fluorophore densities greater than 0.1 nm(-2), necessitating the removal of molecules from the surface into a solution to obtain accurate density measurements. For lower densities, the coverage of bound fluorophores can be estimated directly from in situ PL measurements. The measured areal densities of bound fluorophores after titrating free hydroxyl sites are in good agreement with literature values for the densities of such sites on high surface area silica. PL measurements of SiO2 surfaces titrated with an amine derivative of perylene indicate that strained siloxane sites exist for vacuum pretreatment temperatures of 300 °C and increase with increasing pretreatment temperature. Densities of strained siloxane sites on the silica surface are estimated at 0.004-0.02 nm(-2) for pretreatment temperatures of 300-700 °C, demonstrating the sensitivity of this technique.