| There were a lot of lignite dehydration technology at home and abroad, the main problem is easy re-adsorption moisture after dehydration upgrading and waste a large number of dehydration energy. Many reports thought that the main reason of drying lignite re-adsorption moisture is there is a strong interaction between oxygen containing functional groups and water. At present, study on lignite focus on the effect of drying on physicochemical properties of lignite, there is little to study how to passivate surface oxygen groups from the essence of lignite so as to suppress moisture re-adsorption. The research group members’ study results on microwave drying of lignite showed that microwave had removal effect on surface oxygen groups, but in terms of low value lignite, high-quality microwave energy is used only for lignite dehydration uneconomical. Therefore, based on the member research of the project group, in order to suppress moisture re-adsorption and prevent dehydration energy waste, we should combine the conventional dehydration technology with microwave to passivate the surface oxygen groups of lignite.This paper mainly studied the passivation effect of microwave irradiation on surface oxygen groups during lignite hot air and hot vacuum dehydration process. By experimental data changes of surface oxygen groups, water vapor adsorption, contact angle and Zeta potential reflect the passivation role of microwave so as to provide the theoretical basis for the passivation of surface hydrophilic oxygen containing functional groups during dehydration process and the combination between conventional lignite drying technology and microwave irradiation passivation.Experimental results of lignite dehydration have shown that hot vacuum dehydration is better than hot air before dewatering rate of 50% and microwave dehydration is obvious better than hot air and hot vacuum throughout the dehydration process. The results of oxygen-containing groups have shown that there are main hydroxyl, carbonyl, carboxyl in lignite. Oxygen containing functional groups content of upgraded coal after microwave irradiation changes, the total oxygen containing groups first increased and then decreased again after the increase for different dehydration degree hot air drying samples after microwave irradiation, the total oxygen containing groups of different dehydration degree hot vacuum drying samples after microwave irradiation after the first increase and then decrease increase decrease again. For hot air and hot vacuum dehydration, introduction of microwave energy when the dehydration rate of about 50% for surface hydrophilic groups passivation is more suitable.Adsorption results of water vapor have shown that balance readsorption moisture of microwave dehydration samples under the same conditions of dehydration rate is much less than hot air samples balance readsorption moisture, slightly less than hot vacuum samples balance readsorption moisture. The total moisture content of microwave dehydration samples is less than the total moisture content of hot air and hot vacuum samples. Readsorption moisture change trends of dehydration sample after microwave irradiation and its oxygen containing groups change trends are basically consistent. Contact angle of microwave dehydration samples under the same dehydration rate is much larger than hot air and hot vacuum samples contact angle. Research of pore structure showed that microwave have expanded effect on pore of hot air drying lignite samples, this expand action make some micropore converted into mesopore, combined with water vapor adsorption data showed that pore structure has little effect on lignite readsorption moisture and its water-holding capacity. Zeta potential of the absolute value of upgraded coal after microwave irradiation becomes small.Comprehensive analysis of oxygen containing group, water vapor adsorption, contact angle and Zeta potential can be drawn: microwave can play better passivation action when the dehydration rate of about 50~65%microwave joined. |
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