Volume 6 Issue 2

A reaction route accounting for the formation of levulinic acid from 5-hydroxymethylfuran-2-carbaldehyde was deduced on the basis of the mechanism previously offered by Horvat, to match the steps with more details. A newly deduced reaction route was proposed between two intermediate products within this mechanism, and the probabilities of the two mechanisms were compared by Gaussian 03 software. It was found that the conversion from the intermediate 2,3-dihydroxy-5-methyl-2,3-dihydro-furan-2-carbaldehyde (DMDFC) to 2,5-dioxo-hex-3-enal (DOHE) in the original mechanism has a lower net energy barrier than that in the newly deduced mechanism, and thus should be more preferred. The mechanism indicates that DMDFC is first protonized, followed by a proton shift process, and thereafter an OH- ion is added, completing the hydration process. Thereafter, an intramolecular H-shift reaction proceeds, leading to conversion to the intended intermediate product DOHE by the consecutive processes of isomerization and dehydration.

This study has demonstrated a rapid spectroscopic method for the determination of chlorine dioxide and hypochlorous acid concentrations in the pulp bleaching processes. It was found that chlorine dioxide and hypochlorous acid have an isosbestic wavelength of 295 nm. The soluble lignin in such a system is the main interference, but can be corrected by determining the absorbances at 295 nm, 380 nm, and 480 nm. Thus, based on the spectroscopic measurements at 295 nm (the isosbestic point wavelength for chlorine dioxide and hypochlorous acid), 380 nm (absorbance wavelength of chlorine dioxide) and 480 nm (the acid soluble lignin absorbance wavelength), the chlorine dioxide and hypochlorous acid concentrations in the bleaching process can be quantified. However, hypochlorous acid was not detected in the real bleaching effluent for its low content. The present method is simple, rapid, accurate, and has the potential for on-line monitoring of the chlorine dioxide bleaching process.

Properties of heat-treated wood have been studied extensively in recent years. However, study on wood that has been treated in pressurized steam is limited, as most wood heat treatments are carried out in atmospheric steam. The main purpose of this study was to explore the influence of steam pressure on chemical changes of heat-treated wood. Wet chemical analysis, elemental analysis, and FTIR analysis were performed to investigate the changes of cell wall components of Mongolian pine wood. Samples treated in pressurized steam had lower percentages of polysaccharides and higher percentages of lignin compared to those treated in atmospheric steam, indicating greater chemical changes during the treatment. It was also found that thermal degradation of both samples was modest at the treatment temperature of 205 °C. These results help to explain the better dimensional stability and limited strength deterioration of wood treated in pressurized steam.

The amount of residual lignin in birch wood after a hot water extraction in a batch reactor was investigated as a function of extraction temperature and time. A kinetic model fitting the experimental data was then developed to explain delignification of wood during a hot water treatment. Results showed that delignification kinetics involves simultaneous degradation and condensation reactions, with degradation of lignin being much faster than its condensation. Native lignin in wood was successfully modeled as the sum of two fractions with different degradation rates. The rates of degradation and condensation increased along with increasing extraction temperature. The proportion of acid-soluble lignin to acid-insoluble (Klason) lignin in the wood residue decreased with increasing extraction temperature and time, probably due to chemical and structural changes in the lignin during the hot water treatment. Condensed lignin was predominantly determined as Klason lignin. On the other hand, the amount of soluble lignin in the extraction liquor increased slightly with temperature, but remained mostly constant after any extraction time. An insoluble fraction in the liquor that originated from precipitated lignin fragments is believed to contain traces of degradation products from carbohydrates or other degradation compounds.

The decolourisation of reactive and cationic dyes by physical and chemical modified esparto fibers was investigated. Previously the decolourisation of reactive dyes only had been tested and optimized using untreated esparto fibers and those reinforced by zeolite. Non-treated cellulosic esparto fibers can absorb an important amount of dyes. In order to improve absorption properties of esparto fibers, chemical graft copolymerization with acrylic acid (AA), itaconic acid (IA), and a mixture of acrylamide and IA was performed using potassium persulfate as initiator. The effect of physical modification by zeolite was investigated. Reinforced zeolite esparto fibers were obtained from cellulose esparto fibers pre-treated with NaOH, and preformed zeolite powders. The IR spectroscopy, X-ray diffraction, thermal behavior, as well as the surface morphology of the treated fibers were also studied. The results showed that zeolite treated esparto fibers (the first time application of this kind) are more efficient adsorbents than luffa fibers.

In this study a cationic talc was applied to deinked pulp for control of sticky contaminants. Effects of the cationic talc on stickies and dissolved and colloid substances were investigated and compared with those of a conventional talc. Characteristics of wet-end chemistry were examined for the pulp with addition of both kinds of talc samples. Furthermore, influences on paper properties were also compared. The results showed that the addition of cationic talc can effectively decrease the content of stickies and DCS, while reducing the cationic demand of the pulp, and the turbidity of the filtrate. Deposition of stickies can be reduced by about 63% with the addition of 2.0% cationic talc into the pulp, and the DCS was reduced from 1989 mg/L to 1927 mg/L. Addition of cationic talc significantly increased the ash content of the paper, but it negatively influenced the paper strength properties.

Novel starch solutions were prepared by dissolving starch in NaOH/ thiourea/ urea aqueous solution, and they were further used as a surface sizing agent at high solids content in papermaking to improve the surface strength of papers. Two methods were adopted to dissolve the starch. In method A dry starch granules were directly added into the prepared solution. In method B a starch slurry was mixed with the prepared solution. The results revealed that method B was more effective than method A to achieve a lower viscosity of the starch solution. Dissolving temperature played an important role in dissolution of the starch. The viscosity values decreased with a decrease in the temperature of sample preparation. The starch dissolved in 4 wt% NaOH – 3 wt% urea – 3 wt% thiourea aqueous solution at -10°C were optimized to do the further application experiments. This kind of starch solution had lower viscosity and reached better viscosity-temperature stability, the viscosity was stable over a broad range of temperatures, and it also can be stored for over one month under room temperature. The surface sized papers with them had outstanding surface strength. Moreover, the prepared starch solutions were investigated by infrared spectroscopic analysis and scanning electron microscope, respectively, showing the structure of the starch solution.

Current ethanol production processes using crops such as corn and sugar cane have been well established. However, the utilization of cheaper lignocellulosic biomass could make bioethanol more competitive with fossil fuels while avoiding the ethical concerns associated with using potential food resources. In this study, Miscanthus, a lignocellulosic biomass, was pretreated using NaOH to produce bioethanol. The pretreatment and enzymatic hydrolysis conditions were evaluated by response surface methodology (RSM). The optimal conditions were found to be 145.29 °C, 28.97 min, and 1.49 M for temperature, reaction time, and NaOH concentration, respectively. Enzymatic digestibility of pretreated Miscanthus was examined at various enzyme loadings (10 to 70 FPU/g cellulose of cellulase and 30 CbU/g of β-glucosidase). Regarding enzymatic digestibility, 50 FPU/g cellulose of cellulase and 30 CbU/g of β-glucosidase were selected as the test concentrations, resulting in a total glucose conversion rate of 83.92%. Fermentation of hydrolyzed Miscanthus using Saccharomyces cerevisiae resulted in an ethanol concentration of 59.20 g/L at 20% pretreated biomass loading. The results presented here constitute a significant contribution to the production of bioethanol from Miscanthus.

shell (), a abundant and inexpensive material, is currently being investigated as an adsorbent to remove cobalt(II) from water. Before the adsorption experiments, QCS was subjected to chemical treatment to provide maximum surface area. Then, the kinetics and adsorption mechanism of Co(II) ions on QCS were studied using different parameters such as adsorbent dosage, initial concentration, temperature, contact time, and solution pH. The loaded metals could be desorbed effectively with dilute hydrochloric acid, nitric acid, and 0.1 M EDTA. The Langmuir and Freundlich models were used to describe the uptake of cobalt on QCS. The equilibrium adsorption data were better fitted to Langmuir adsorption isotherm model. The maximum adsorption capacity (qm) of QCS for Co(II) was 33 mg g-1. Various kinetic models were used to describe the adsorption process. The adsorption followed pseudo second-order kinetic model. The intraparticle diffusion was found to be the rate-limiting step in the adsorption process. The diffusion coefficients were calculated and found to be in the range of 3.11×10−6 to 168.78×10−6 cm2s-1. The negative DH* value indicated exothermic nature of the adsorption.

Magnesium aluminum hydroxides (MAH) of nitrate and carbonate forms were prepared by co-precipitation, dried at different temperatures, and employed as an adsorbent for pitch and stickies in papermaking. Results indicated that MAH that had been heat-treated had higher adsorption capacity to model pitch and stickies at neutral pH. Low-temperature-dried magnesium aluminum hydroxides of nitrate form (MAH-NO3) had higher adsorption capacity to model pitch and model stickies than those of the carbonate form (MAH-CO3). Increasing the drying temperature of MAH reduced the difference of adsorption capacity between MAH-NO3 and MAH-CO3. Higher-temperature-dried magnesium aluminum hydroxides also showed higher adsorption capacity to model pitch and stickies when the drying temperature was lower than 550 oC. MAH displayed higher adsorption capacity while a lower initial adsorption rate of model stickies than of model pitch. The model pitch and stickies were adsorbed on MAH significantly by charge neutralization and distributed mainly on the surface of the platelets of magnesium aluminum hydroxides. The experimental isothermal adsorption data of model pitch and stickies on MAH dried at 500 oC fit well to the Freundlich and Dubinin–Radushkevich isotherm equations.