Rice husk (RH), an agricultural waste, is abundantly available in rice producing countries like China, India, Bangladesh, Brazil, US, Cambodia, Vietnam, Myanmar, and South East Asia. Despite the massive amount of annual production worldwide, so far RHs have been recycled only for low-value applications. In recent years, many rice mills in rice producing countries have started using RH for the energy production for mill operations as well as household lighting in rural regions. Burning of RHs produces the rice husk ash (RHA). The disposal in landfills or open fields can be problematic and may cause a serious environmental and human health related problems due to the low bulk density of RHA. Several ways are being thought of for disposing RHA by making its commercial use. The amorphous silica forms the main component (83–90%) of RHA. The amorphous silica rich RHA has wide range of applications. High-value applications and current research investigations such as the use of RHA in manufacturing of silica gels, silicon chip, synthesis of activated carbon and silica, production of light weight construction materials and insulation, catalysts, zeolites, ingredients for lithium ion batteries, graphene, energy storage/capacitor, carbon capture, and in drug delivery vehicles are presented. Use of RHA in potential future applications is also discussed. It is suggested that the amorphous silica rich RHA could become a potential resource of low cost precursor for the production of value-added silica based materials for practical applications.

Potential applications of rice husk ash waste from rice husk biomass power plant

This paper describes the application results of a previous and current EU-project on super insulating glazing based on monolithic silica aerogel. Prototypes measuring approx. 55×55 cm 2 have been made with 15 mm evacuated aerogel between two layers of low-iron glass. Anti-reflective treatment of the glass and a heat-treatment of the aerogel increases the visible quality and the solar energy transmittance. A low-conductive rim seal solution with the required vacuum barrier properties has been developed along with a reliable assembly and evacuation process. The prototypes have a centre heat loss coefficient below 0.7 W/m 2  K and a solar transmittance of 76%.

Super insulating aerogel glazing

Biogenerated silica nanoparticles synthesized from sticky, red, and brown rice husk ashes by a chemical method

Upgrading the rice husk char obtained by flash pyrolysis for the production of amorphous silica and high quality activated carbon.

A study has been performed on the production of high quality activated carbon from rice husk char obtained by flash pyrolysis in a conical spouted bed reactor. In order to enhance both the quality of the adsorbents obtained and the economy of the process, the amorphous silica contained in the char has been recovered with Na2CO3. Subsequently, the resulting carbonaceous material has been subjected to physical activation at 800 °C using steam and carbon dioxide as activating agents. Although the maximum BET surface areas obtained with carbon dioxide and steam are similar, 1514 and 1365 m2 g–1, respectively, significant differences are observed in the performance of the two oxidizers. Thus, steam gasification kinetics is faster than that of carbon dioxide. The carbons produced by activation using both steam and carbon dioxide have a wide pore size distribution, with microporous structure being more developed when the latter is used.

Physical Activation of Rice Husk Pyrolysis Char for the Production of High Surface Area Activated Carbons

In recent years, silica gels have developed a lot of interest due to their extraordinary properties and their existing and potential applications in science and technology. Silica gel has a wide range of applications such as a desiccant, as a preservation tool to control humidity, as an adsorbent, as a catalyst and as a cata-lyst support. Silica gel is a rigid three-dimensional network of colloidal silica, and is classified as: aqua-gel, alco-gel, xero-gel and aero-gel. Out of all known solid porous materials, aero-gels are particularly known for their high specific surface area, high porosity, low bulk density, high thermal insulation value, ultra low dielectric constant and low index of refraction. Because of these extraordinary properties silica aero-gel has many commercial applications such as thermal window insulation, acoustic barriers, super-capacitors and catalytic supports. However, monolithic silica aero-gel has been used extensively in high energy physics in Cherenkov radiation detectors and in shock wave studies at high pressures, inertial confinement fusion (ICF) radio-luminescent and micrometeorites. Silica gel can be prepared by using various sol gel precursors but the rice husk (RH) is considered as the cheapest source for silica gel production. Rice husk is a waste product abundantly available in rice producing countries during milling of rice. This review article aims at summarizing the developments carried out so far in synthesis, properties, characterization and method of determination of silica, silica gel, silica aero-gel and silica xero-gel. The effect of synthesis parameters such as pH, temperature of burning the rice husk, acid leaching prior to formation of rice husk ash (RHA) on the properties of final product are also described. The attention is also paid on the application of RH, RHA, sil-ica, silica aero-gel and silica xero-gel. Development of economically viable processes for getting rice husk silica with specific properties assumes importance at this juncture. Copyright © 2012 by BCREC UNDIP. All rights reserved. Received: 23th November 2011, Revised: 09th January 2012, Accepted: 10th January 2012 [How to Cite : R. Prasad, and M. Pandey. (2012). Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview. Bulletin of Chemical Reaction Engineering & Catalysis , 7 (1): 1-25. doi:10.9767/bcrec.7.1.1216.1-25 ] [How to Link / DOI : http://dx.doi.org/10.9767/bcrec.7.1.1216.1-25 ]

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Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview

IL-6: An endogenous activator of MMP-9 in preterm birth.

To assess the association of TLR4 (rs4986790 and rs4986791) and TNF-α (rs1800629) genes polymorphisms and TLR4mRNA levels with preterm birth Hospital-based case-control study on women of Caucasoid morphological subtype ethnicity in Northern India Inclusion criteria for cases: women aged between 18–40 years with preterm birth (<37 weeks gestation), and for controls: women who delivered a term neonate consecutive to an enrolled case Three polymorphisms TLR4 (Asp299 Gly, Thr399 Ill) and TNF-a (-308G/A) and TLR4 mRNA levels were compared between cases and controls From 2012–2015, 559 cases and 559 controls were recruited TLR4 mRNA levels were found to be higher (P<0001) in cases [(07 (004)] than in controls [(05 (004)] No association was found between TLR4 Asp299 Gly, TLR4 Thr399 Ill and TNF-α (-308G/A) with preterm birth Increased TLR4 mRNA levels seem to be associated with preterm birth, and can be investigated further as a potential biomarker for identifying women at risk

Monika Pandey

Papers

Rice Husk Ash as a Renewable Source for the Production of Value Added Silica Gel and its Application: An Overview

IL-6: An endogenous activator of MMP-9 in preterm birth.

Association of TLR4 and TNF-α Gene Polymorphisms and TLR4 mRNA Levels in Preterm Birth in a Northern Indian Population