Valorization of lignocellulosic rice husk producing biosilica and biofuels—a review

Abstract

Lignocellulosic biomass is an agricultural waste material abundantly produced in large quantities on earth. Rice husk (RH) is one of the lignocellulosic biomass and a huge byproduct of rice milling. Notably, the rice plant collects silica from the soil and stores the collected silica in the form of silicic acid inside the cellulose micro-compartments of the plant. Therefore, RH obtained from rice milling contains a significant quantity of amorphous silica, which can further be used for several other purposes. Furthermore, Silica-rich RH can be employed as raw material for the production of biofuels and biochars instantaneously via thermochemical processes like pyrolysis, gasification. This article thoroughly explored the prospective method of rice husk use to produce bio silica and energy at the same time, which is currently under investigation. Moreover, this study also discussed current improvements in the synthesis of RH silica materials and their long-term uses, particularly in energy and environmental functional materials. In terms of the environment, RH-silica materials may remove heavy metals and organic pollutants in soil amendment, wastewater treatment, and gas purification via adsorption, catalysis, and integrative methods. In essence, there are numerous research and development obstacles to the production of bio silica and biofuels, respectively, from RH to overcome, and this review article highlights all of them.

A review on thermochemical based biorefinery catalyst development progress

“…[16][17][18] However, the selection of a suitable catalyst, which is cheap and can work for a long time, is the main challenge of this process. [19][20][21][22][23][24][25][26][27] In addition, gasication occurs at high temperature (>700 °C), which requires a high source of heat and also special materials for the reactor. These lead to the high cost of operation.…”

Thermochemical Characterization of Rice-Derived Residues for Fuel Use and Its Potential for Slagging Tendency

“…It was estimated that the mass ratios of rice straw and rice husk to rice production were approximately 100% and 20%, respectively [10]. Due to its richness in lignocellulosic constituents and other nutrients, the biomass is currently reused as a variety of by-products or application fields [4,7,8,10,[18][19][20][21]. Their industrial/agricultural reuses include surface retention (as mulch), soil amendment, poultry/livestock feed, composting, biofuel and so on.…”

Extractability of Rice Husk Waste Using Green Gamma Radiation for Dye Elimination in Laboratory-Scale Sorption System: Equilibrium Isotherm and Kinetic Analysis

“…Since RH results from the milling process of paddies, therefore, from the paddy milling process, approximately 22% of paddy weight results as RH [9]. A small amount of resultant RH is used for power generation and as fuel during the paddy milling process [10]. Meanwhile, RH has a negative impact on the environment, especially in developing countries, since RH is produced in massive amounts, which causes difficulties in its management as well as its costly disposal.…”

“…As a result, RH is usually left unused after the milling process in farmlands or burned in situ in open air. The result of such a burning technique is extreme environmental damage as well as the waste of a valuable source of nutrients [10,11]. Moreover, burning RH in open air causes greenhouse gas emissions which result from the conversion of elements such as C, O and H into flammable gases and ash [11].…”

“…Silica causes strong environmental pollution since it is a non-biodegradable product. Given that 25% of RH weight is converted into RHA due to burning [10], 20% of RH is in the form of complex silica while RHA contains 95% amorphous silica [12]. RH chemically comprises cellulose, hemicellulose in high proportions, lignin in medium proportions, silica in small proportions and very small traces of metal oxides such as CaO, MgO, Al 2 O 3 and Fe 2 O 3 [9,13,14].…”