Rice hull as a renewable raw material and its processing routes

Abstract

It was shown that rice hull has a unique composition and can be used as a renewable raw material. A method for rice hull conversion into polyfunctional materials was proposed, which gives a solid product, a liquid organic product, and a mixture of noncondensable gases. The solid product is suitable as a filler for elastomers, fodder supplement for farm poultry, and sorbent for noble and rare metal recovery. The liquid product acts as a highly selective collector of lead minerals in beneficiation of complex rebellious ores, plant growth stimulant, and antiseptic agent. The mixture of noncondensable gases can be used for carbon black production or as a high-calorific fuel.Rice hull, a unique large-tonnage waste material from cultivation and processing of crops, is dissimilar in the composition and properties to some other plant wastes. Specifically, rice hull contains lignin, carbohydrates, nitrogenous substances, vitamins, organic acids, and mineral components, whose content depends on the rice variety and is affected by the geographical location and agronomic method of rice cultivation. The carbohydrate components of rice hull include cellulose (the main component) and hemicelluloses (contained in a slightly lesser amount) dominated by pentosans. Depending on the technique applied, crude or purified lignin can be recovered from rice hull. Crude lignin contains cellulose and ash; nitrogenous substances are represented primarily by proteins, with a small amount of nitrogen comprised by the vitamins contained in rice hull. Organic acids contained in rice hull include acetic, citric, fumaric, oxalic, and succinic acids, as well as some aromatic acids.The predominant mineral component of rice hull, responsible for its high ash content, is silica. The ash also contains potassium, sodium, magnesium, calcium, iron, and phosphorus, as well as considerably smaller quantities of copper, iron, manganese, etc. The content of rice hull components, wt %, varies extensively as follows [1]: water 2.4-11.35, crude protein 1.7-7.26, crude fat 0.38-2.98, nitrogen-free extractive substances 24.7-38.79, raw cellulose 31.71-49.92 (34.34-43.8, according to other sources), pentosans 16.94-21.95, ash 13.16-29.04; other substances (lignin) 21.4-46.97. It should be noted that data reported by different researchers can differ considerably.

Rice Husk Research: From Environmental Pollutant to a Promising Source of Organo-Mineral Raw Materials

“…It is known that the performance characteristics of finished materials and the scope of their application largely depend on the technological parameters of processing of raw materials. Hence, as it was revealed by an earlier review of the literature [ 5 ], the studies of rice husk are mainly devoted to the research of conditions and operating parameters of processes of its refining. There are positive results of approbation of rice husk and products of its processing in different areas of practical use [ 5 , 6 ].…”

“…Hence, as it was revealed by an earlier review of the literature [ 5 ], the studies of rice husk are mainly devoted to the research of conditions and operating parameters of processes of its refining. There are positive results of approbation of rice husk and products of its processing in different areas of practical use [ 5 , 6 ]. The two most common of them are the production of activated carbon [ 4 , 7 , 8 , 9 , 10 ] and the extraction of silicon dioxide as a source of silicon for the production of pure metal and its compounds, concrete, cement, and refractory ceramics [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ].…”

Synthesis and Electrochemical Behavior of the Molybdenum- Modified Electrode Based on Rice Husk

“…C, Fe, Cu, Zn, Mn, Cr, Ca, K, Ti, Cl, S, Ni, Si were found. This fact corresponds to the reference data [10][11][12][13][14][15][16][17][18][19]. Unmodified BS samples and composite materials obtained on its base were investigated by EDAX method in order to establish their elemental composition.…”

“…Such adsorptive materials consisting of two active components (SiO 2 |C) are called bisorbents (BS). RH is a high-ash biomass, which is the most suitable precursor for a preparation of porous carbon materials, since it allows to control porosity by mineral part [19][20][21][22][23][24][25]. The ions of modifying agent were adsorbed on these carbon-silica materials.…”

Rice Husk Hydrolytic Lignin Transformation in Carbonization Process

“…While the scale of rice production in Kazakhstan is significantly less compared to China or India for example, the problem of rice husk processing is relevant as in these countries. The number of methods of rice husk processing developed is huge [15]. However, rice husk up to now has not found an effective industrial application, because of economic and ecological factors, and is sent to dumps.…”