Preparation of low-molecular-weight and high-sulfate-content chitosans under microwave radiation and their potential antioxidant activity in vitro

In the present paper microwave radiation has been used to introduce N-sulfo and O-sulfo groups into chitosan with a thigh degree of substitution and low-molecular weight. The sulfation of chitosan was performed in microwave ovens. It was found that microwave heating is a convenient way to obtain a wide range of products of different degrees of substitution and molecular weight only by changing reaction time or/and radiation power. Moreover, microwave radiation accelerated the degradation of sulfated chitosan, and the molecular weight of sulfated chitosan was considerably lower than that obtained by traditional heating. There are no differences in the chemical structure of sulfated chitosan obtained by microwave and by conventional technology. FTIR and C-13 NMR spectral analyses demonstrated that a significantly shorter time is required to obtain a satisfactory degree of substitution and molecular weight by microwave radiation than by conventional technology. In this present paper, we also determined antioxidant activity of low-molecular-weight and high-sulfate-content chitosans (LCTS). The results showed LCTS could scavenge superoxide and hydroxyl radical. Its IC50 is 0.025 and 1.32mg/mL, respectively. It is a potential antioxidant in vitro. (C) 2004 Published by Elsevier Ltd.

Effect of microwave treatment on chemical composition and in sacco digestibility of wheat straw in yak cow

Wheat straw was treated with microwave for 4 min and 8 min at a power of 750 W and frequency of 2,450 MHz. Chemical compositions of untreated, 4 min treated and 8 min treated Straws were analyzed and in sacco degradabilities of all these straws in yak rumens were measured. Microwave treatment didn't significantly (p > 0.05) affect the chemical composition of the straw. In sacco dry matter (DM) degradability of the straw after 18 h incubation in rumen was significantly (p < 0.01) improved by microwave treatment. In sacco crude protein (CP) degradability of the straw was not (p > 0.05) affected by microwave treatment. In sacco organic matter (OM) degradability of the straw was increased (p < 0.01) by around 20% for both the 4 min and 8 min microwave treatment, that of acid detergent fibre (ADF) was increased (p < 0.01) by 61.6% and 62.8%, and that of ash free ADF was enhanced by 72.1% and 69.6% for the 4 min and 8 min microwave treatment respectively. No significant difference was observed between the 4 min and 8 min microwave treatment on the degradability of DM, OM, CP, ADF and ash-free ADF of the straw.

Microwave effects on the selective reduction of NO by CH4 over an In-Fe2O3/HZSM-5 catalyst

Microwave effects have been shown to promote the activation of NOx molecules in the process of selective reduction of NO by CH4 over an In-Fe2O3/HZSM-5 catalyst and to enhance the water tolerance of this catalyst for NO reduction.

Removal of NO by microwave discharge with the addition of CH4

Removal of NO by a continuous microwave discharge at atmospheric pressure with the addition of CH4 is reported. The conversion of NO to N-2 is approximately 80%, and the energy efficiency is up to 0.55 g-NO/kWh. The effects of CH4 addition and three discharge modes on NO conversion and energy efficiency are investigated. The dependence of NO conversion on experimental time is also observed.

Fast formation of NaA zeolite membrane in the microwave field

NaA zeolite membrane was successfully synthesized on the porous alpha-Al2O3 support by microwave heating. The synthesis of NaA zeolite membrane in the microwave field only needs 15 min and the synthesis time is 10 times shorter than that by conventional heating. SEM characterization indicates that the zeolite crystals in the NaA zeolite membrane synthesized by microwave heating are uniform in size; the membrane thickness is about 4 mu m and is thinner than that of the NaA zeolite membrane synthesized by conventional heating. Gas permeation studies indicate that the permeances of the NaA zeolite membrane synthesized by microwave heating are 3-4 times higher than those of the NaA zeolite membrane synthesized by conventional heating, while their permselectivities are comparable.

Synthesis of a high-permeance NaA zeolite membrane by microwave heating

Zeolite membranes with high permeance and separation factors are highly desirable for practical applications. Although, in the past, very good separation factors have been obtained, it has proved difficult to achieve a high permeance. Ken a comparative study of microwave versus conventional heating in the hydrothermal synthesis of NaA zeolite membranes is made. It is demonstrated that membranes prepared by microwave heating have not only a higher permeance but also a considerably shorter synthesis time. These observations are rationalized by examining the mechanism of membrane formation.

Synthesis of NaA zeolite membrane by microwave heating

The synthesis of NaA zeolite membrane on a porous alpha -Al2O3 support by microwave heating (MH) was investigated. The formation of a NaA zeolite membrane was drastically promoted by MH. The synthesis time was reduced from 3 h for conventional heating (CH) to 15 min for MH. Surface seeding cannot only promote the formation of NaA zeolite on the support, but also inhibit the transformation of NaA zeolite into other types of zeolites. The thickness of the NaA zeolite membrane synthesized by MH was about 4 mum, thinner than that of NaA zeolite membrane synthesized by CH. The permeance of NaA zeolite membrane synthesized by MH was four times higher than that of the NaA zeolite membrane synthesized by CH, while their permselectivities were comparable. Multi-stage synthesis resulted in the transformation of NaA zeolite into other types of zeolites, and the perfection of the as-synthesized membrane decreased.