Effects of Stepwise Microwave Synergistic Process Water Recirculation During Hydrothermal Carbonization on Properties of Wheat Straw

Abstract

In this study, wheat straw (WS) was treated using two-step synergistic techniques, which were process water recirculation (PWR) during hydrothermal carbonization (HTC) and microwave energy activation (MEA). The physicochemical properties of solid and liquid products during the process of HTC PWR were characterized. The temperature-rising properties, yields, and fuel properties of hydrochar after MEA were explored. Then the optimal technique conditions were explored. When HTC PWR was twice, the carbon content (55.59%) and higher heating value (21.72 MJ/kg) were the highest, and the ash content (1.93%) and the O/C and H/C ratios were the lowest. When HTC PWR was three times, the fixed carbon content, mass yield, and energy yield were the highest: 18.53%, 58.25%, and 71.84%, respectively. Many more carbon microspheres and pores appeared on the surface of hydrochar after PWR, which could improve the fuel characteristics and mass yield. After HTC PWR, the concentration of organic acids and HMF in liquid by-products increased, which was conducive to the increase of carbon content and mass yield. The best effect was HTC PWR twice or three times. With the increase of microwave power or the extension of microwave activation duration, the temperature-rising properties of hydrochar significantly increased, and the mass and energy yields decreased. The volatile contents of hydrochar decreased and their fixed carbon contents and HHV increased with the increase of microwave power. The properties of hydrochar could be improved when MEA was 900 W or 1000 W for 4 min. Therefore, MEA had significant effects on the properties of hydrochar after different PWR conditions.

Two-Step Preparation of Hierarchical Porous Carbon Materials Derived from Tannin for Use as an Electrode Material for Supercapacitors

“…During hydrothermal carbonization, the surface of carbon materials can be given rich oxygen-containing functional groups as a result of the appropriate temperature and pressure conditions, without the need to add additional reagents. Furthermore, as a result of hydrothermal treatment, biomass materials will form abundant carbon microspheres, resulting in a substantial increase in the SSA of the carbon materials [20,21]. There is, however, a drawback to the traditional hydrothermal synthetic method, which is that it takes a long time, resulting in low efficiency.…”

Alkali Etching Hydrochar-Based Adsorbent Preparation Using Chinese Medicine Industry Waste and Its Application in Efficient Removal of Multiple Pollutants

“…HTC is a thermochemical process in a wet medium that can effectively treat organic solid waste with high moisture content, such as CMIW [8,9]. Studies have shown that HTC is a promising technique for converting organic solid waste into hydrochar, which can be used as a fuel, adsorbent, catalyst, and others [10][11][12]. Hydrochar has porous structures and abundant surface functional groups, which also depend on the feed-stock and treatment conditions [13,14].…”