Enhanced conversion of α-cellulose to 5-HMF in aqueous biphasic system catalyzed by FeCl_3-CuCl_2

This study was to investigate the optimal additions of the cellulose decomposition reaction to obtain the most yield of 5-HMF and other furan derivatives in various biphasic systems with FeCl_3-CuCl_2 mixed catalysts,and explore its depolymerization kinetics.A series of controllable reactions have been performed under mild environmentally friendly atmosphere.The experiment results showed that49.13 wt% of 5-HMF was the maximum production along with 2.98 wt% other furan derivatives catalyzed by mixed Lewis acid FeCl_3-CuCl_2 under the two phases which included high concentration NaCl aqueous phase and n-butanol organic phase at 190℃ for 45 min.The conclusion suggested that two-phase systems benefited the yield of 5-HMF,furan derivatives via extracting the target products from reaction phase to organic phase to avoid rehydration of 5-HMF.The kinetic calculation revealed the conversion with mixed catalysts had lower reaction apparent activation energy(21.65 kJ/mol,190-230℃) and the reaction rate was faster than that with acid-based catalysts.Based on experiment exploration,the probable mechanism of cellulose decomposition with FeCl_3-CuCl_2 was proposed.     

Combined use of H2SO4 and SO2 impregnation for steam pretreatment of spruce in ethanol production

Fuel ethanol can be produced from softwood through hydrolysis in an enzymatic process. Prior to enzymatic hydrolysis of the softwood, pretreatment is necessary. In this study, two-step steam pretreatment employing dilute H₂SO₄ impregnation in the first step and SO₂ impregnation in the second step, to improve the overall sugar and ethanol yield, was investigated. The first pretreatment step was performed under conditions of low severity (180°C, 10 min, 0.5% H₂SO₄) to optimize the amount of hydrolyzed hemicellulose. In the second step, the washed solid material from the first pretreatment step was impregnated with SO₂ and pretreated under conditions of higher severity to make the cellulose more accessible to enzymatic attack, as well as to hydrolyze a portion of the cellulose. A wide range of conditions was used in the second step to determine the most favorable combination. The temperatures investigated were between 190 and 230°C, the residence times were 2, 5, and 10 min; and the SO₂ concentration was 3%. The effect of pretreatment was assessed by both enzymatic hydrolysis of the solids and by simultaneous saccharification and fermentation (SSF) of the whole slurry, after the second pretreatment step. For each set of pretreatment conditions, the liquid fraction was also fermented to determine any inhibitory effects. Ethanol yield using the SSF configuration reached 66% of the theoretical value for pretreatment conditions in the second step of 210°C and 5 min. The sugar yield using the separate hydrolysis and fermentation configuration reached 71% for pretreatment conditions of 220°C and 5 min.     

Effects of temperature and moisture on dilute-acid steam explosion pretreatment of corn stover and cellulase enzyme digestibility

Corn stover is emerging as a viable feedstock for producing bioethanol from renewable resources. Dilute-acid pretreatment of corn stover can solubilize a significant portion of the hemicellulosic component and enhance the enzymatic digestibility of the remaining cellulose for fermentation into ethanol. In this study, dilute H₂SO₄ pretreatment of corn stover was performed in a steam explosion reactor at 160°C, 180°C, and 190°C, approx 1 wt% H₂SO₄, and 70-s to 840-s residence times. The combined severity (Log₁₀ [R _o ] - pH), an expression relating pH, temperature, and residence time of pretreatment, ranged from 1.8 to 2.4. Soluble xylose yields varied from 63 to 77% of theoretical from pretreatments of corn stover at 160 and 180°C. However, yields >90% of theoretical were found with dilute-acid pretreatments at 190°C. A narrower range of higher combined severities was required for pretreatment to obtain high soluble xylose yields when the moisture content of the acid-impregnated feedstock was increased from 55 to 63 wt%. Simultaneous saccharification and fermentation (SSF) of washed solids from corn stover pretreated at 190°C, using an enzyme loading of 15 filter paper units (FPU)/g of cellulose, gave ethanol yields in excess of 85%. Similar SSF ethanol yields were found using washed solid residues from 160 and 180°C pretreatments at similar combined severities but required a higher enzyme loading of approx 25 FPU/g of cellulose.     

Accessibility and size of <Emphasis Type="Italic">Valonia</Emphasis> cellulose microfibril studied by combined deuteration/rehydrogenation and FTIR technique

We report an FTIR method to measure the accessibility and the size of cellulose microfibrils from the cell wall of Valonia ventricosa. This method is similar to the conventional deuteration technique for measuring the accessibility of cellulosic materials; however, the difference in our method is that the hydroxyl groups O2H, O3H, and O6H in the crystalline region were initially completely deuterated. The sample was then rehydrogenated by soaking in water at 25 °C, so that the OD groups on the surface were rehydrogenated. The ratio of OH to OD absorbance was used to calculate the number of surface vs. core cellulose chains in a microfibril. The obtained experimental ratio of 0.934 was consistent with the value calculated for a previously published 33 × 38 chain Valonia model (Sugiyama et al. 1984). The rehydrogenation process was further investigated by immersing the sample in water at elevated temperatures. At temperatures above 120 °C, rehydrogenation was more efficient, and the efficiency plots vs. rehydrogenation temperature showed two inflection. These points may correspond to the temperature where the cleavage of inter-chain hydrogen bonds and/or crystalline-phase transition would have been occurred.     

Optimization of steam pretreatment of corn stover to enhance enzymatic digestibility

Among the available agricultural byproducts, corn stover, with its yearly production of 10 million t (dry basis), is the most abundant promising raw material for fuel ethanol production in Hungary. In the United States, more than 216 million to fcorn stover is produced annually, of which a portion also could possibly be collected for conversion to ethanol. However, a network of lignin and hemicellulose protects cellulose, which is the major source of fermentable sugars in corn stover (approx 40% of the dry matter [DM]). Steam pretreatment removes the major part of the hemicellulose from the solid material and makes the cellulose more susceptible to enzymatic digestion. We studied 12 different combinations of reaction temperature, time, and pH during steam pretreatment. The best conditions (200°C, 5 min, 2% H₂SO₄) increased the enzymatic conversion (from cellulose to glucose) of corn stover more then four times, compared to untreated material. However, steam pretreatment at 190°C for 5 min with 2% sulfuric acid resulted in the highest overall yield of sugars, 56.1 g from 100 g of untreated material (DM), corresponding to 73% of the theoretical. The liquor following steam explosion was fermented using Saccharomyces cerevisiae to investigate the inhibitory effect of the pretreatment. The achieved ethanol yield was slightly higher than that obtained with a reference sugar solution. This demonstrates that baker's yeast could adapt to the pretreated liquor and ferment the glucose to ethanol efficiently.     

Elastic modulus of the crystalline regions of chitin and chitosan

The elastic moduli E_l of the crystalline regions of α‐chitin and chitosan in the direction parallel to the chain axis were measured by X‐ray diffraction. The E_l values were 41 GPa for α‐chitin, and 65 GPa for chitosan, respectively, at 20°C. The contracted skeletons of α‐chitin and chitosan are the key factor for the low E_l values compared with that (138 GPa) of cellulose I. The E_l value of α‐chitin was constant at 41 GPa both at −190°C and 150°C, which indicates that the molecular chain of α‐chitin is stable against heat within the temperature and stress range studied. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1191–1196, 1999     

Poly(phenylene) and m‐Terphenyl as Powerful Protecting Groups for the Preparation of Stable Organic Hydroxides

Four benzimidazolium hydroxide compounds, in which the C2‐position is attached to a phenyl group possessing hydrogen, bromine, methyl groups, or phenyl groups at the ortho positions, are prepared and investigated for stability in a quantitative alkaline stability test. The differences between the stability of the various protecting groups in caustic solutions are rationalized on the basis of their crystal structures and DFT calculations. The highest stability was observed for the m‐terphenyl‐protected benzimidazolium, showing a half‐life in 3 m NaOD/CD₃OD/D₂O at 80 °C of 3240 h. A high‐molecular‐weight polymer analogue of this model compound is prepared that exhibits excellent mechanical properties, high ionic conductivity and ion‐exchange capacity, as well as remarkable hydroxide stability in alkaline solutions: only 5 % degradation after 168 h in 2 m KOH at 80 °C. This is the most stable hydroxide‐conducting benzimidazolium polymer to date.     

Rapid dissolution of spruce cellulose in H<Subscript>2</Subscript>SO<Subscript>4</Subscript> aqueous solution at low temperature

Dissolution of cellulose is the key challenge in its applications. It has been discovered that spruce cellulose with high molecular weight (4.10 × 10⁵ g mol^?1) can be dissolved in 64 wt% H₂SO₄ aqueous solution at low temperature within 2 min, and the cellulose concentration in solution can reach as high as 5 % (w/v). FT-IR spectra and XRD spectra proved that it is a direct solvent for cellulose rather than a derivative aqueous solution system. The cold H₂SO₄ aqueous solution broke the hydrogen bonds among cellulose molecules and the low temperature dramatically slowed down the hydrolysis, which led to the dissolution of cellulose. The resultant cellulose solution was relatively stable, and the molecular weight of cellulose only slightly decreased after storage at ?20 °C for 1 h. Due to the high molecular weight of cellulose, cellulose solution could form regenerated films with good mechanical properties and transparency at low concentration (2 % w/v). This work has not only provided the new evidence of cellulose dissolution which facilitated the development of cellulose solvent, but also suggested a convenient way to directly transfer cellulose with high molecular weight into materials without structure modifications.     

Properties of cellulose films prepared from NaOH/urea/zincate aqueous solution at low temperature

Cellulose films were successfully prepared from NaOH/urea/zincate aqueous solution pre-cooled to −13 °C by coagulating with 5% H₂SO₄. The cellulose solution and regenerated cellulose films were characterized with dynamic rheology, ultraviolet–visible spectroscope, scanning electron microscopy, wide angle X-ray diffraction, Fourier transform infrared (FT-IR) spectrometer, thermogravimetry and tensile testing. The results indicated that at higher temperature (above 65 °C) or lower temperature (below −10 °C) or for longer storage time, gels could form in the cellulose dope. However, the cellulose solution remained a liquid state for a long time at 0–10 °C. Moreover, there was an irreversible gelation in the cellulose solution system. The films with cellulose II exhibited better optical transmittance, high thermal stability and tensile strength than that prepared by NaOH/urea aqueous solution without zincate. Therefore, the addition of zincate in the NaOH/urea aqueous system could enhance the cellulose solubility and improve the structure and properties of the regenerated cellulose films.     

Influence of cation on the cellulose dissolution investigated by MD simulation and experiments

Cellulose is the most abundant natural polymer on the earth, and effective solvents are essential for its wide application. Among various solvents such as alkali/urea or ionic liquids, cations all play a very important role on the cellulose dissolution. In this work, the influence of cation on the cellulose dissolution in alkali/urea via a cooling process was investigated with a combination of MD simulation and experiments, including differential scanning calorimetry (DSC) and NMR diffusometry (PFG-SE NMR). The results of DSC proved that the dissolution of cellulose in both solvents was a process within a temperature range, starting at above 0 °C and completing at low temperature (?5 °C for LiOH/urea and ?20 °C for NaOH/urea), indicating the necessity of low temperature for the cellulose dissolution. Molecular dynamic (MD) simulation suggested that the electrostatic force between OH^? and cellulose dominated the inter-molecular interactions. In our findings, Li⁺ could penetrate closer to cellulose, and displayed stronger electrostatic interaction with the biomacromolecule than Na⁺, thus possessed a greater “stabilizing” effect on the OH^?/cellulose interaction. PFG-SE NMR demonstrated a more significant binding fraction of Li⁺ than Na⁺ to cellulose, which was consistent with MD. These results indicated that the direct interactions existed between the cations and cellulose, and Li⁺ exhibited stronger interaction with cellulose, leading to stronger dissolving power.     

Steam pretreatment of acid-sprayed and acid-soaked barley straw for production of ethanol

Barley is an abundant crop in Europe, which makes its straw residues an interesting cellulose source for ethanol production. Steam pretreatment of the straw followed by enzymatic hydrolysis converts the cellulose to fermentable sugars. Prior to pretreatment the material is impregnated with a catalyst, for example, H₂SO₄, to enhance enzymatic digestibility of the pretreated straw. Different impregnation techniques can be applied. In this study, soaking and spraying were investigated and compared at the same pretreatment condition in terms of overall yield of glucose and xylose. The overall yield includes the soluble sugars in the liquid from pretreatment, including soluble oligomers, and monomer sugars obtained in the enzymatic hydrolysis. The yields obtained differed for the impregnation techniques. Acid-soaked barley straw gave the highest overall yield of glucose, regardless of impregnation time (10 or 30 min) or acid concentration (0.2 or 1.0 wt%). For xylose, soaking gave the highest overall yield at 0.2 wt% H₂SO₄. An increase in acid concentration resulted in a decrease in xylose yield for both acid-soaked and acid-sprayed barley straw. Optimization of the pretreatment conditions for acid-sprayed barley straw was performed to obtain yields using spraying that were as high as those with soaking. For acid-sprayed barley straw the optimum pretreatment condition for glucose, 1.0 wt% H₂SO₄ and 220°C for 5 min, gave an overall glucose yield of 92% of theoretical based on the composition of the raw material. Pretreatment with 0.2wt% H₂SO₄ at 190°C for 5 min resulted in the highest overall xylose yield, 67% of theoretical based on the composition of the raw material.     

Catalytic effects of copper(II) chloride and aluminum chloride on the pyrolytic behavior of cellulose

The cellulose without and with catalyst (CuCl₂, AlCl₃) was subjected to pyrolysis at temperatures from 350 to 500 °C with different heating rate (10 °C/min, 100 °C/s) to produce bio-oil and selected chemicals with high yield. The pyrolytic oil yield was in the range of 37–84 wt% depending on the temperature, the heating rate and the amount of metal chloride. The non-catalytic fast pyrolysis at 500 °C gives the highest yield of bio-oil. The mixing cellulose with both metal chlorides results with a significant decrease of the liquid product. The non-catalytic pyrolysis of cellulose gives the highest mass yield of levoglucosan (up to 11.69 wt%). The great influence of metal chloride amount on the distribution of bio-oil components was observed. The copper(II) chloride and aluminum chloride addition to cellulose clearly promotes the formation of levoglucosenone (up to 3.61 wt%), 1,4:3,6-dianhydro-α-d-glucopyranose (up to 3.37 wt%) and unidentified dianhydrosugar (MW = 144; up to 1.64 wt%). Additionally, several other compounds have been identified but in minor quantities. Based on the results of the GC–MS, the effect of pyrolysis process conditions on the productivity of selected chemicals was discussed. These results allowed to create a general model of reactions during the catalytic pyrolysis of cellulose in the presence of copper(II) chloride and aluminum chloride.     

Microwave Induced Synthesis of 3,4-Dihydro-2H-pyran-2-carboxaldehyde: A Versatile Linker for Solid Phase Combinatorial Library

Procedures for the dimerization of acrolein to form 3,4-dihydro-2H-pyran-2-carboxaldehyde by microwave induced synthesis have been developed. Significant rate-enhancement and yield increase were observed. 3,4-Dihydro-2H-pyran-2-carboxaldehyde was obtained in 91% yield under microwave irradiation for 5 minutes instead of 39% yield by reacting at 190 °C for 40 min or at 160 °C for 4 hr.     

Ethanol production from steam-explosion pretreated wheat straw

Bioconversion of cereal straw to bioethanol is becoming an attractive alternative to conventional fuel ethanol production from grains. In this work, the best operational conditions for steam-explosion pretreatment of wheat straw for ethanol production by a simultaneous saccharification and fermentation process were studied, using diluted acid [H₂SO₄ 0.9% (w/w)] and water as preimpregnation agents. Acid-or water-impregnated biomass was steam-exploded at different temperatures (160–200°C) and residence times (5, 10, and 20 min). Composition of solid and filtrate obtained after pretreatment, enzymatic digestibility and ethanol production of pretreated wheat straw at different experimental conditions was analyzed. The best pretreatment conditions to obtain high conversion yield to ethanol (approx 80% of theoretical) of cellulose-rich residue after steam-explosion were 190°C and 10 min or 200°C and 5 min, in acid-impregnated straw. However, 180°C for 10 min in acid-impregnated biomass provided the highest ethanol yield referred to raw material (140 L/t wheat straw), and sugars recovery yield in the filtrate (300 g/kg wheat straw).     

Effect of chip size on steam explosion pretreatment of softwood

Although considerable progress has been made in technology for converting lignocellulosic biomass into ethanol, substantial opportunities still exist toreduce production costs. In biomass pretreatment, reducing milling power is a technological improvement that will substantially lower production costs for ethanol. Improving sugar yield from hemicellulose hydrolysis would also reduce ethanol production costs. Thus, it would be desirable to test innovative pretreatment conditions to improve the economics by reducing electrical power of the milling stage and by optimizing pretreatment recovery of hemicellulose, as well as to enhance cellulose hydrolysis. The objective of this study was to evaluate the effect of chip size (2–5, 5–8, and 8–12 mm) on steam-explosion pretreatment (190 and 210°C, 4 and 8 min) of softwood (Pinus pinater).     

Evaluation of the sealed‐tube low‐temperature combustion method for the 13C/12C and 2H/1H ratio determinations of cellulose nitrate

Traditionally‐suggested combustion time of 1 h at 550°C) with the sealed‐tube combustion method for determining the ¹³C/ ¹²C ratio of cellulose nitrate or other nitrogen‐containing components could produce large negative deviation up to 1°. Three types of cellulose are used to ascertain possible causes. The presence of nitrous oxide (N₂O) formed during combustion is most likely responsible for this deviation. Prolongation of the combustion time (at least 5 h at 550°C) and intimate contact between copper oxide and organic matter can greatly improve the analysis precision and effectively reduce this deviation to an acceptable level. Regardless of scattered carbon isotope data, hydrogen isotope data are all reproducible within 2° when this method is coupled with the high temperature uranium reduction method. Thus, care should be taken for determining carbon and nitrogen isotope compositions of nitrogen‐containing substances using the low temperature sealed‐tube combustion method.     

To understand the superior hydrolytic activity after polymorphic conversion from cellulose I to II from the adsorption behaviors of enzymes

The role of the cellulose ultrastructure on the relationship between cellulase binding and activity is not clear yet. In this article, a quartz crystal microbalance with dissipation (QCM-D) was employed to monitor the interactions between a given cellulase and the cellulose substrates with varied polymorphs of pure cellulose I and II and the intermediate state (I/II). Initially, cellulose nanocrystals (CNCs) with polymorphs of cellulose I, I/II and II were prepared and spin-coated on QCM sensors. The cellulose substrates’ crystallinity degree was examined by XRD, and morphology was detected by AFM. Then, a commercial cellulase from Trichoderma reesei was used to test the adsorption and hydrolysis of cellulose substrates with polymorphs of I, I/II and II, respectively. The results revealed that in the enzyme adsorption and desorption process at a temperature of 15 °C, CNC-II had the lowest adsorption capacity with a total adsorption mass of 179 ng cm^?2 but the highest reversible binding ratio of 33.7%; for comparison, the values were 235 ng cm^?2 versus 25.6% and 207 ng cm^?2 versus 26.9% for CNC-I and -I/II, respectively. And the conformation of adlayers on CNC-I, -I/II and -II derived from the QCM data became softer and softer in turn. On the other hand, CNC-II exhibited the best enzymatic hydrolytic ability among three substrates when enzymatic hydrolysis experiments were conducted at 45 °C. The results indicated that polymorphic conversion from I to II changes the affinity between the enzyme and cellulose surface; CNC-II has the lowest affinity to the enzyme, but the softer conformation of the adsorbed enzyme layer, and the more reversible adsorption may facilitate its hydrolytic activity. This article gives a perspective from the adsorption dynamics and conformation of the adsorbed enzyme layer, helping to understand the superior hydrolytic activity of cellulose with polymorph II. Thus, there is a potential of polymorphic conversion in the reduction of enzyme dosage and cost in the enzymatic hydrolysis process.     

X‐ray diffraction study of the thermal expansion behavior of cellulose triacetate I

Highly crystalline samples of cellulose triacetate I (CTA I) were prepared from highly crystalline algal cellulose by heterogeneous acetylation. X‐ray diffraction of the prepared samples was carried out in a helium atmosphere at temperatures ranging from 20 to 250 °C. Changes in seven d‐spacings were observed with increasing temperature due to thermal expansion of the CTA I crystals. Unit cell parameters at specific temperatures were determined from these d‐spacings by the least squares method, and then thermal expansion coefficients (TECs) were calculated. The linear TECs of the a, b, and c axes were α_a = 19.3 × 10^?5 °C^?1, α_b = 0.3 × 10^?5 °C^?1 (T < 130 °C), α_b = ?2.5 × 10^?5 °C^?1 (T > 130 °C), and α_c = ?1.9 × 10^?5 °C^?1, respectively. The volume TEC was β = 15.6 × 10^?5 °C^?1, which is about 1.4 and 2.2 times greater than that of cellulose I_β and cellulose III_I, respectively. This large thermal expansion could occur because no hydrogen bonding exists in CTA I. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 517–523, 2009     

Kinetic study of the annealing of fission tracks in a Fe2O3KPO3 glass containing 100 ppm of uranium

The kinetics of the annealing of fission tracks in an artificial glass were studied using an optical microscope. The annealing experiments were performed in an electric furnace at 160–230°C for 15–160 min. The measurement of the fission tracks through an optical microscope was carried out after etching the annealed tracks with 10 N NaOH aqueous solution at 40°C. All reactions were found to be of first order within the annealing temperatures. An activation energy of 0.66 eV for the annealing reaction was obtained from the Arrhenius plot of the rate constants determined at 160, 190, 210, and 230°C.     

Novel hybrid process for the conversion of microcrystalline cellulose to value-added chemicals: part 1: process optimization

In this paper, a novel hybrid process for the treatment of microcrystalline cellulose (MCC) under hot-compressed water was investigated by applying constant direct current on the reaction medium. Constant current range from 1A to 2A was applied through a cylindrical anode made of titanium to the reactor wall. Reactions were conducted using a specially designed batch reactor (450 mL) made of SUS 316 stainless steel for 30–120 min of reaction time at temperature range of 170–230 °C. As a proton donor H₂SO₄ was used at concentrations of 1–50 mM. Main hydrolysis products of MCC degradation in HCW were detected as glucose, fructose, levulinic acid, 5-HMF, and furfural. For the quantification of these products, High Performance Liquid Chromatography (HPLC) and Gas Chromatography with Mass Spectroscopy (GC–MS) were used. A ½ fractional factorial design with 2-level of four factors; reaction time, temperature, H₂SO₄ concentration and applied current with 3 center points were built and responses were statistically analyzed. Response surface methodology was used for process optimization and it was found that introduction of 1A current at 200 °C to the reaction medium increased Total Organic Carbon (TOC) and cellulose conversions to 62 and 81 %, respectively. Moreover, application of current diminished the necessary reaction temperature and time to obtain high TOC and cellulose conversion values and hence decreased the energy required for cellulose hydrolysis to value added chemicals. Applied current had diverse effect on levulinic acid concentration (29.9 %) in the liquid product (230 °C, 120 min., 2 A, 50 mM H₂SO₄).