Study On The New Technology Of Rice Husk-based High Value-Added Products

Fossil resources are the material foundation and source of energy for the survivalof people, all human activities and the steady development of society are inseparablefrom the use of fossil resources. However, with rapid economic development in theworld, over-exploitation and over-utilization of fossil resources caused very seriousconsequences to the living environment of people. Therefore, the growing shortage ofresources, environmental degradation, political and economic disputes andcompetition for resources, and even the frequency of armed conflicts and wars, theworld will develop new energy and renewable resources as part of a long-termdevelopment of important strategic decisions.Over-consumption of fossil resources make people face the risk of depletion ofcarbon source which is human beings depend to live, then how to find a new carbonsource is the primary task of the protection of human society and sustainabledevelopment. Biomass (narrow biomass) as a renewable carbon source is widelyfound in nature. Thus how to use biomass carbon resource and preparation ofchemical products are the problems that scientific researchers have to solve. Biomasshas many kinds of advantages, such as multiple types, large production, renewable,etc, which can be used as carbon source alternatives to alleviate the world energycrisis. The rice husk as a part of biomass, because of its large production (40milliontons one year), thus it occupies an important position in the development andutilization of biomass in China.The purpose of this paper is to make full use of the rice husk and do not releaseany residue, then prepare a variety of rice husk-based value-added products.The first part, under the premise that does not affect the rice husk four components, two extraction method is used to extract flavonoids in rice husk with theorganic solvent. The results are as follows:1. The optimum extraction conditions of the rice hull flavonoids:40mesh of ricehusk,75°C,4h, solid-liquid ratio of1:15, the ethanol concentration of85%. Theproduct yield was3%, including the flavonoids content of13%.2. Rice husk flavonoids have well OH scavenging activity, IC50reach889.385μg/mL. Rice husk flavonoids can be used as an antioxidant added to foodsinstead of BHT (2,6-di-tert-butyl4-methyl phenol).The innovation of this part lies in the fact that:(a) rice husk as an agriculturalby-products can replace the raw materials extraction of flavonoids——food crops(soybean, buckwheat) and herbal medicines (ginkgo, etc.). Because of its large mass,low cost and other advantages, which is in line with our sustainable developmentadvocated by the strategic thinking;(b) extraction of rice husk flavonoid in this studyis one part of the rice husk-based high value-added products, and the other ingredientsin the rice husk is not damaged, do not affect the extraction and preparation of otherproducts. It facilitates the implementation of the utilization of rice husk, and iseconomically feasibility.The second part, with inorganic acid as catalyst, rice husk hemicellulose is usedto prepare xylose. This part discusses the hemicellulose hydrolysis kinetics at middlepressure conditions, and does some basic researches about the main problems in thexylose industry. The results are as follows:1. Discuss the selective reaction of hemicellulose under middle pressureconditions with inorganic acid as catalyst, xylose and furfural yield was calculated togenerate xylose rate constant k₁, furfural rate constant k2and the activation energy.2. Examine effluent COD values of the xylose production, and compare watertreatment and alkali neutralize treatment, investigate which is more efficient. Oneproblem of xylose industrial production is high extraction rate but low yield. Theexperimental results show that the neutralize process of sugar purification processesin sugar loss rate is small, activated carbon used to decolorize xylose solution in sugarloss rate can reach about16%, ion exchange resin can also retent small amount of sugar. All processes above cause the xylose products output to decline.The meaning of this section is:(a) dynamics study to provide data support for theactual production process, and can provide theoretical guidance for the actualoperation;(b) xylose industry is facing the problem of high extraction rate but lowyield, find out the crux of the problem and give the resolved plan.After the above two steps, a major component of the rice husk residue (I) iscellulose, lignin and ash. This paper gives three routes to give further utilization ofrice husk residue, and prepare high value-added products of activated carbon,nano-silica and carboxymethyl cellulose. Three types of process route are introducedand the material balance of rice husk is given below.The third part (Route One): directional etching is used as theory in preparation ofactivated carbon with acid, this activated carbon obtained is used as adsorbent todecolorize xylose mother liquor, and give good decolorization ability. After activatedcarbon used, it is directly burning to receive amorphous nano-silica products. Theresults are as follows:1. Use rice husk residue (I) as raw material and phosphoric acid as activationagent to prepare activated carbon. The best conditions are: activation temperature of500°C, activation time of0.5h, H₃PO₄concentration of50%, impregnated ratio of5:1(g/g). At this time the surface area of activated carbon is1763m2/g, pore volume is1.98mL/g.2. Activated carbon prepared above on the adsorption efficiency of xylose motherliquor pigment is high, and the adsorption of xylose molecules is low.3. Activated carbon after pigment adsoption used is directly burning to receivenano-SiO₂. Make full use of rice husk. Through route one, receive four kinds of rice husk-based value-added products:rice husk flavonoids, xylose, activated carbon and silica. The yield of the rice huskflavonoids accounting for3%of the rice husk,the yield of xylose is about17%of therice husk,activated carbon yield accounted for about38%of the rice husk,and silicayield about6%.The innovation of this part lies in the fact that:(a) the production ofhigh-value-added products of activated carbon and silica are used the residues of ricehusk after the production of rice husk flavonoids and xylose. The process is simple,easy to industrialization;(b) activated carbon obtained gives good pigment adsorptionefficiency in xylose mother liquor, and low adsorption rate of xylose. Solve theproblem of the xylose industry in decolorization process making xylose yield decline;(c) abandon the traditional idea of the activated carbon regeneration, but use directheat treatment to obtain nano-silica after the use of activated carbon;(d) theutilization of rice husk is over60%, and no waste emissions.The fourth part (Route Two): directional etching is used as theory in preparationof high surface area of activated carbon with alkali, and simultaneously extractedsilica;1. Use rice husk residue (I) as raw material and KOH as activation agent toprepare activated carbon. Rice husk residue (I) is first carbonized1h at450°C, thecarbonized precursor and KOH ratio is1:3(g/g), pre-activation of0.5hours at400°C,increased activation temperature to800°C for1h, the specific surface area reach up to2905m2/g, pore volume is1.1mL/g. This activated carbon gives good pigment adsorption efficiency in xylose mother liquor, and low adsorption rate of xylose,which is an excellent pigment adsorbent.2. The filtrate received in the process of preparation of activated carbon is uesedto obtain nano-SiO₂.Rice husk utilization rate is more than40%in route two, and four kinds of ricehusk-based value-added products is produced: rice husk flavonoids, xylose, activatedcarbon and silica. The yield of the rice husk flavonoids accounting for3%of the ricehusk,the yield of xylose is about17%of the rice husk,activated carbon yieldaccounted for about7%of the rice husk,and silica yield about16%.Its significance of this route lies in:(a) use simple method to prepare highvalue-added products of activated carbon and silica with rice husk residue, and theeconomic effect is significant;(b) activated carbon gives high specific surface area,which makes it with a wide range of applications; the entire process release no waste,thus makes no environmental pollution.The fifth part (Route Three): Further removal of lignin and ash content in ricehusk, then the major components of residue is cellulose, organic solvent is used toprepared carboxymethyl cellulose.1. Rice husk residue (I) is used to prepare carboxymethyl cellulose, the optimumconditions: first, rice husk residue (I) further removal of the lignin and siliconcompounds; second, decolorize the rice husk residue to obtain cellulose; cellulose:NaOH: ClCH2COOH=1:1.2:1.2(g/g/g), ethanol concentration of85%, alkalizationof1h at30°C, etherification of3h at70-80°C, the product received gives theultimate substitution degree of1.24. 2. Rice husk-based carboxymethyl cellulose has good suspension and dispersionproperties, can significantly improve the dispersion of SiO₂.Three kinds of rice husk-based value-added products in route three are prepared:rice husk flavonoids, xylose and rice husk-based carboxymethyl cellulose. The yieldof the rice husk flavonoids accounting for3%of the rice husk,the yield of xylose isabout17%of the rice husk,the yield of rice husk-based carboxymethyl cellulose isabout38%。The innovation of this part lies in the fact that:(a) the use of rice husk which is alarge quantity of biomass production in China to prepare carboxymethyl cellulose,extends the limitations of the past that its raw material is only refined cotton, thusreducing material costs and enhance market competitiveness;(b) the entire route onthe utilization of rice husk is as high as60%;(c) the substitution degree is high, thusgive more wide range of applications;(d) the whole process is simple and easy tooperate, which is suitable for industrial production.The foundation of several different process routes make full utilization of ricehusk, and prepare a variety of high value-added products. The establishments of thethree process routes save the consumption of other non-renewable resources, reducingenvironmental pollution, low cost and simple operation. The establishments of threeprocess routes are also suitable for other similar biomass such as bagasse, corn cobsand straw. Provide broad prospects of these agricultural wastes with comprehensiveutilization.