Cunwen Wang

Ultrasound-assisted alkaline pretreatment for enhancing the enzymatic hydrolysis of rice straw by using the heat energy dissipated from ultrasonication

Rice straw samples were exposed to ultrasound-assisted alkaline (NaOH) pretreatment by using the heat energy dissipated from ultrasonication to increase their enzymatic digestibility for saccharification. The characterization shows that the pretreatment could selectively remove lignin and hemicellulose without degrading cellulose, and increase porosity and surface area of rice straw. The porosity, surface area and cellulose content of rice straw increased with the increasing concentration of NaOH used. The rice straw sample pretreated by using the heat energy dissipated from ultrasonication has a higher surface area and a lower crystallinity index value than that pretreated by using the external source of heating, and the amount of reducing sugar released from the former sample at 48h of enzymatic saccharification, which is about 3.5 times as large as that from the untreated rice straw sample (2.91vs. 0.85gL-1), is slightly larger than that from the latter sample (2.91vs. 2.73gL-1). The ultrasound-assisted alkaline pretreatment by using the heat energy dissipated from ultrasonication was proved to be a reliable and effective method for rice straw pretreatment.

Continuous Production of Biodiesel from Soybean Oil Using Supercritical Methanol in a Vertical Tubular Reactor: I. Phase Holdup and Distribution of Intermediate Product along the Axial Direction

Abstract Production of biodiesel with supercritical methanol is a green synthesis process. A study was carried out in a vertical tubular reactor with a length of 3700 mm and a diameter of 20 mm at 275-375 °C, 15 MPa, and molar ratio of methanol to soybean oil of 40?1. The phase holdup, intermediate product, yield and axial distribution of methyl ester (ME) were investigated. Methanol and oil were mixed non-uniformly due to the formation of biodiesel and difference in their densities, even when the reaction system was in the supercritical state. From top to bottom, the phase holdup of methanol increased and that of oil decreased. As temperature increased, the concentrations of monoglyceride and diglyceride decreased gradually and the ME yield increased. When the temperature reached 300 °C, the critical temperature of the system, the ME yield was 50%. Further increase in temperature led to a sharp increase of ME yield. However, at 375 °C after 1200 s of reaction time, the decomposition rate of ME was greater than its formation rate, reducing the ME yield.

Depolymerization of microcrystalline cellulose by the combination of ultrasound and Fenton reagent

In this study, the combined use of Fenton reagent and ultrasound to the pretreatment of microcrystalline cellulose (MCC) for subsequent enzyme hydrolysis was investigated. The morphological analysis showed that the aspect ratio of MCC was greatly reduced after pretreatment. The X-ray diffraction (XRD) and degree of polymerization (DP) analyses showed that Fenton reagent was more efficient in decreasing the crystallinity of MCC while ultrasound was more efficient in decreasing the DP of MCC. The combination of Fenton reaction and ultrasound, which produced the lowest crystallinity (84.8 ± 0.2%) and DP (124.7 ± 0.6) of MCC and the highest yield of reducing sugar (22.9 ± 0.3 g/100 g), provides a promising pretreatment process for MCC depolymerization.

Kinetics of Leaching Flavonoids from Pueraria Lobata with Ethanol

Abstract The kinetics of leaching flavonoids from Pueraria Lobata with ethanol was investigated. The effects of leaching temperature, mechanical agitation rate, concentration of ethanol and feed particle size on leaching kinetics were examined. It is found that the smaller the feed particle size or the higher the leaching temperature, the higher the leaching rate. The leaching process can be described by the shrinking-core model. The apparent activation energy is 10.8kJ·mol −1 , suggesting that the leaching process is controlled by the inner diffusion. An empirical equation relating the flavonoids leaching rate constant to the feed particle size and leaching temperature was expected.

The leaching kinetics of K-feldspar in sulfuric acid with the aid of ultrasound

The leaching kinetics of K-feldspar in H2SO4-CaF2 system with the assistant of ultrasound was investigated. The effects of various factors, such as sulfuric acid concentration, liquid-to-solid ratio, CaF2 dosage and leaching temperature were comprehensively studied. The dissolution fraction of potassium can reach more than 83% under the optimum operation conditions with ultrasound. Because of the cavitation effect, the intensified effect with ultrasound has more obvious at lower temperature than higher temperature. The leaching kinetics of K-feldspar with and without ultrasound was successfully modeled by a classic shrinking core model with the product layer diffusion as the rate-controlling step. The activation energies over the temperature range from 60 to 90°C with and without ultrasound were found to be 55.67kJmol-1 and 72.33kJmol-1, respectively. It was found that the rate constant increases greatly in the presence of ultrasound due to the decreased apparent activation energy, resulting in the improved dissolution fraction of potassium.

Pretreatment of rice straw by ultrasound-assisted Fenton process

Fentons reagent, ultrasound, and the combination of Fentons reagent and ultrasound were used to pretreat rice straw (RS) to increase its enzymatic digestibility for saccharification. The characterization shows that compared with ultrasound, Fentons reagent pretreatment was more efficient in increasing the specific surface area and decreasing the degree of polymerization (DP) of RS. The enzymatic hydrolysis results showed that the RS pretreated by ultrasound-assisted Fentons reagent (U/F-RS), which exhibited the largest specific surface area and the lowest DP value, had the highest enzymatic activity, and the amount of reducing sugar released from U/F-RS at 48h of enzymatic saccharification is about 4 times as large as that from raw RS and 1.5 times as large as that from Fentons reagent pretreated RS. The ultrasound-assisted Fenton process provides a reliable and effective method for RS pretreatment.

Kinetics of Rare Earth Leaching from a Mangnese‐Removed Weathered Rare‐Earth Mud in Hydrochloric Acid Solutions

Abstract The kinetics of leaching rare earth from a manganese‐removed weathered rare earth mud (MRW‐RE mud) in hydrochloric acid solutions was investigated in this study as a function of temperature, particle size, and HCl concentration. It was found that the leaching process can be described by a shrinking‐core model, with the apparent activation energy about 10.17 kJ/M. When the concentration of hydrochloric acid was below 4M, the RE leaching rate was controlled by the diffusion of reactants and leaching products through a porous ore. However, when HCl concentration was higher than 4 M, the leaching process was limited by both chemical reaction and reagent diffusion. Based on the experimental results, an empirical equation relating the rate constant of rare earth leaching to the particle size and leaching temperature was established for the purpose of process deign.

The leaching kinetics and mechanism of potassium from phosphorus-potassium associated ore in hydrochloric acid at low temperature

ABSTRACT The leaching kinetics of potassium from phosphorus-potassium associated ore in hydrochloric acid/fluorite (CaF2) system was studied. HCl concentration, liquor/solid ratio, CaF2 dosage, and temperature were found to be the main factors. The leaching rate of potassium can be reached more than 92% under the optimum operation conditions. A classic shrinking core model with the mixed chemically diffusion as the rate-controlling step was successfully modeled the leaching kinetics of potassium, and the activation energy was found to be 30.7 kJ·mol−1. The leaching mechanism of potassium was also elucidated based on the experimental results.

Optimal Conditions for Preparing Ultra-Fine CeO2 Powders in A Submerged Circulative Impinging Stream Reactor

Abstract Cerium carbonate powders were produced in a submerged circulation impinging stream reactor (SCISR) from Ce(NO 3 ) 3 · 6H 2 O. NH 4 HCO 3 was used as a precipitant in the reaction. Cerium carbonate powders were roasted to produce ultra-fine cerium dioxide (CeO 2 ) powders. The optimal conditions of such production process were obtained by orthogonal and one-factor experiments. The results showed that ultra-fine and narrowly distributed cerium carbonate powders were produced under the optimal flowing conditions. The concentrations of Ce(NO 3 ) 3 and NH 4 HCO 3 solutions were 0.25 and 0.3 mol · L -1 , respectively. The concentration of PEG4000 added in these two solutions was 4 g · L -1 . The stirring ratio, reaction temperature, feeding time, solution pH, reaction time and digestion time were 900 r · min -1 , 80 °C, 20 min, 5∼6, 5 min and 1 h, respectively. The final product, CeO 2 powders, was obtained by roasting the produced cerium carbonate in air for 3 h at 500 °C. The finally produced CeO 2 powders were torispherical particles with a narrow size distribution of 0.8∼2.5 μm. The crystal structure of CeO 2 powders belonged to cubic crystal system and its space point group was O 5 H -F M3M . Under optimal conditions, powders produced by SCISR were finer and more narrowly distributed than that by Stirred Tank Reactor (STR).

Effect of alcohol on cellulose hydrolysis in super/subcritical alcohol-water mixtures

The focus of this work was on investigating the effects of different types of alcohol on the cellulose hydrolysis in supercritical/subcritical alcohol-water mixtures by selecting methanol, ethanol, and isopropanol as co-solvents. The experiments were conducted in a batch reactor under the following conditions: 5% mass ratio, 0.58 min reaction time and stirring speed 600 r/min. The experimental results showed that the reducing sugar yield was very low when the alcohol mole fraction in the alcohol-water mixture was more than 0.8, however, the yield turned very high when the mole fraction was less than 0.6. Critical parameters of alcohol-water mixtures revealed that the alcohol-water mixtures were in the supercritical state when the alcohol mole fraction was above 0.8 at 250°C. As a contrast, the mixtures were in the sub-critical state if the mole fraction turned into 0.6. Therefore, further investigations were carried out in sub-critical alcohol-water mixtures. It was found that ethanol was the best co-solvent among three kinds of co-solvents selected with respect to the yield of reducing sugar and the cost. The cellulose hydrolysis conditions in ethanol-water mixtures were optimized. The reducing sugar yield of cellulose hydrolysis was reached as high as 98.22% under the conditions of 0.22 mole fraction of ethanol, temperature of 260°C, pressure of 5.75MPa, reaction time of 0.58min, stirring speed of 600r/min, and the IR crystallinity index of cellulose was decreased from 0.618 to 0.211.