Jiayu Ma

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.

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.

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.

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.

Effect of iron salt type and dosing mode on Fenton-based pretreatment of rice straw for enzymatic hydrolysis

Fenton-based processes with four different iron salts in two different dosing modes were used to pretreat rice straw (RS) samples to increase their enzymatic digestibility. The composition analysis shows that the RS sample pretreated by the dosing mode of iron salt adding into H2O2 has a much lower hemicellulose content than that pretreated by the dosing mode of H2O2 adding into iron salt, and the RS sample pretreated by the chloride salt-based Fenton process has a much lower lignin content and a slightly lower hemicellulose content than that pretreated by the sulphate salt-based Fenton process. The higher concentration of reducing sugar observed on the RS sample with lower lignin and hemicellulose contents justifies that the Fenton-based process could enhance the enzymic hydrolysis of RS by removing hemicellulose and lignin and increasing its accessibility to cellulase. FeCl3·6H2O adding into H2O2 is the most efficient Fenton-based process for RS pretreatment.