Integrated Leaching and Thermochemical Technologies for Producing High-Value Products from Rice Husk: Leaching of Rice Husk with the Aqueous Phases of Bioliquids

Abstract

It remains challenging to develop a techno-economically feasible method to remove alkali and alkaline earth metal species (AAEMs) from rice husk (RH), which is a widely available bioresource across the world. In this study, the AAEMs leaching effect of aqueous phases of both bio-crude prepared by hydrothermal liquefaction (AP-HT) and bio-oil prepared by pyrolysis (AP-Pyro) of RH were systematically investigated. The results indicated that although the acidity of AP-HT and AP-Pyro are much lower than that of HCl, they performed a comparable removal efficiency on AAEMs (Na: 56.2%, K: 96.7%, Mg: 91.0%, Ca: 46.1% for AP-HT, while Na: 58.9%, K: 96.9%, Mg: 94.0%, Ca: 86.3% for AP-Pyro) with HCl. The presence of phenolics in bio-oil could facilitate the penetration of water and organic acids into the inner area of RH cells, thus enhancing the AAEMs removal via chelate reactions. The thermal stability of leached RH during thermochemical conversions was studied via TG and Py-GC-MS. The results showed that the heat conduction efficiency in leached RH was enhanced with a high pyrolysis rate, resulting in a narrow carbon chain distribution (C5–C10) of derived chemical compounds.

Quest for the Co-Pyrolysis Behavior of Rice Husk and Cresol Distillation Residue: Interaction, Gas Evolution and Kinetics

“…Thermogravimetric (TG) and differential thermal gravity (DTG) curves showed a difference in thermal behaviors between RH and CDR (Figure 1). RH consists of (hemi)cellulose, lignin and other organic minorities [36,37] so that the weight loss of RH can be divided into three main stages (Figure 1a). The release of adsorbed gases and water vapor occurred from 50 to 218 • C, followed by the thermal decomposition of volatiles from (hemi)cellulose with the range of 218 to 409 • C (weight loss = 57.3%).…”

Heavy bio‐oils as bio‐binders for rice husk densification: Parameter optimization, binding mechanisms and subsequent pyrolysis and combustion performances

“…The hydrothermal liquefaction of RH was carried out using a 100 mL stirred autoclave as detailed elsewhere. 18 In brief, 3 g of RH and 50 mL of deionized water were loaded into the autoclave for each run, then degassed using N 2 (30 min). 22 After degassing, the reactor was pressurized to 1 MPa with N 2 , followed by heating to 280 °C (5 °C min −1 , holding for 10 min) and the stirring speed was constant at 175 rpm.…”

“…The slow pyrolysis of RH samples (HBO-SP) was carried out in a tubular furnace system as illustrated in a previous paper. 18 Samples of RH (30 g) were pre-loaded into the reactor, then heated to 110 °C (10 °C min −1 ) and held for 30 min, followed by heating to 500 °C with the same heating rate (holding for 60 min). The bio-oil was collected and placed in an ice bath for cooling.…”

“…Recently, the leaching performance of RH-derived aqueous bio-oils to remove ash content from RH was investigated and achieved a considerable removal of alkali and alkaline earth metal species. 18 However, utilization of the HBOs has not been studied. This study co-densified HBOs and RH to produce a solid biofuel.…”

Exploration of mechanisms of lignin extraction by different methods

“…Lignin contains phenolic hydroxyl groups, phenol alcohol groups, carboxylic acid groups and carbonyl groups 24 . Lignin is a typical multi‐group ligand which has the ability to form lignin chelate soluble salts with metal cations under alkaline conditions, 25 hence lignin can be dissolved in alkaline solution. In alkaline media, the bonds between carbohydrates and lignin are easy to break.…”