REVIEW OF SAWDUST PRETREATMENT PROCESSES FOR BIOFUEL PRODUCTION Ayoade Kuye Onuora Okorie Edem Utibe Benedict Department of Chemical Engineering, University of Port Harcourt, PMB 5323, Port Harcourt, Nigeria ayokuye@yahoo.com November 14, 2013

Presentation Outline Introduction Efficacy of Pretreatment Classification of Pretreatment Methods Biochemical Pretreatment Methods Thermochemical Pretreatment Methods Conclusion Acknowledgement November 14, 2013

Introduction Sawdust contains three major constituents; Cellulose Hemi-cellulose Lignin Bio-fuel products can be obtained from sawdust through several biochemical and thermochemical conversion processes. The cellulose component of the sawdust is recalcitrant to biochemical conversion Processes. The 30-60wt. % moisture content of raw sawdust feedstock coupled with problem of size specification often results in poor or unacceptable values in various properties of the desired bio-fuel products. November 14, 2013

Introduction Contd To render the sawdust feedstock liable to biochemical or thermochemical conversion processes it is subjected ab initio to a variety of pretreatment technology. The pretreatment technologies for converting sawdust feedstock into bio-fuel products are broadly classified as biochemical and thermochemical. The goal of this presentation is to give the participants a good understanding of the basic pretreatment methods involved in the conversion of sawdust to biofuel. November 14, 2013

Efficacy of Pretreatment Mass balance analysis can validate the pretreatment efficacy of the conversion process . This necessitates thorough economic analysis to determine the best pretreatment method suitable for a particular genre of sawdust. Ultimately, the chosen pretreatment process should have a low capital and operational cost. November 14, 2013

Classification of Pretreatment Methods November 14, 2013

Biochemical Pretreatment Methods Biochemical pretreatments employs the use of enzyme-producing fungi and chemicals to degrade or effectively disrupt linked lignin and crystalline cellulose of the sawdust feedstock thus making it liable to biochemical conversion processes. Typical methods include Acid hydrolysis Alkaline wet oxidation Steam Explosion and Ammonia Fiber Explosion (AFEX) Ozonolysis November 14, 2013

Biochemical Pretreatment Methods Contd Acid hydrolysis Acid hydrolysis is the most commonly adopted technique It is an effective method used for sawdust feedstock pretreatment in saccharification which could further change into ethanol. Diluted acid hydrolysis especially sulfuric acid has been successfully developed for pretreatment of sawdust Handling higher concentrations of acid requires reactors that are resistant to erosion in sawdust pretreatment. November 14, 2013

Biochemical Pretreatment Methods Contd Alkaline Wet Oxidation Wet oxidation refers to the oxidation of dissolved or suspended components in water using oxygen as the oxidizer. It is referred to as Wet Air Oxidation (WAO) when air is used. Alkaline addition reduces the production of furfurals while increasing the convertibility of the cellulose fraction. November 14, 2013

Biochemical Pretreatment Methods Contd Steam Explosion and Ammonia Fiber Explosion (AFEX) Steam Explosion involves pretreating the sawdust with high-pressure saturated steam and then swiftly reducing the pressure, resulting in an explosive decompression of the sawdust. Ammonia Fiber Explosion (AFEX) Ammonia fiber explosion (AFEX) is another biochemical pretreatment process very similar to steam explosion AFEX involves exposing the sawdust to liquid ammonia at high temperature and pressure for a period of time, followed by a sudden reduction in pressure. November 14, 2013

Biochemical Pretreatment Methods Contd Ozonolysis It involves the use of ozone to change the structure of sawdust feedstock. It is carried out at room temperature and normal pressure. It can effectively remove the lignin without producing any toxic residues. The main restriction to this process is the large amount of ozone utilization making it expensive. November 14, 2013

Thermochemical Pretreatment Methods Thermochemical pretreatment methods involve the combined use of heat and chemical catalyst to prepare the sawdust feedstock for thermochemical conversion processes. Typical methods include Drying Torrefaction Fast pyrolysis pelletization November 14, 2013

Thermochemical Pretreatment Methods Contd Drying It is a major step in the pretreatment of sawdust. It is performed mainly to increase sawdust energy input and minimize the risk of microbial decomposition It aims to reduce the moisture to values below 15wt. %. This in turn insulates the desired biofuel from the adverse effects of water on its stability, viscosity, pH, corrosiveness etc. The drying process sometimes can be problematic resulting from sizing specifications and poor sawdust grindability. November 14, 2013

Thermochemical Pretreatment Methods Contd Torrefaction It is a thermolysis process that subjects the sawdust feedstock to thermal treatment at relatively low temperatures of 200–3000C in the absence of oxygen. It is commonly associated with roasting, mild pyrolysis, slow pyrolysis and thermal pretreatment, according to its utilization. Early research work on torrefaction was mainly on wood based material such as woodchips and sawdust In recent years, more studies have incorporated agricultural crops and agro-forestry residue. November 14, 2013

Thermochemical Pretreatment Methods Contd Fast pyrolysis It is a thermal process which involves the rapid heating of organic material to a high temperature in the absence of an oxidizing agent which then vaporizes and condenses to bio-oil. There are four essential features of a fast pyrolysis process: Very high heating and heat transfer rates of >10000C usually requires finely grounded sawdust feed. November 14, 2013

Thermochemical Pretreatment Methods Contd 2. Controlled pyrolysis reaction temperature of about 5000C and vapour phase temperature of 400-4500C. 3. Short vapor residence time (typically <2s). 4. Rapid quenching of the pyrolysis vapors to freeze the pyrolytic products and avoid secondary cracking. fast pyrolysis is the least developed and most promising for converting sawdust to liquid fuels. November 14, 2013

Thermochemical Pretreatment Methods Contd Pelletization It can be defined as drying and pressing of biomass under high pressure to produce cylindrical pieces of compressed and extruded biomass. Pellets have a smaller volume and a higher volumetric energy density compared to wood chips and hence more efficient to store, ship and convert into energy. The production of pellets requires small feedstock particles, maximum 3–20mm. November 14, 2013

Thermochemical Pretreatment Methods Contd Pelletization is performed at a temperature of around 150oC. Water plays an important role in densification of the feedstock. If the feedstock is either too dry or too wet, the pressure required for densification increases dramatically. A moisture content of 10–25% is considered optimal. To obtain the desired moisture content the feedstock is heated to 50–100oC and at approximately 150oC mechanical densification is applied. November 14, 2013

Conclusion Pretreatment is an initial and crucial step in the conversion of sawdust feedstock to biofuel. It consist of both biochemical and thermochemical methods. This presentation has reviewed several of these pretreatment methods. November 14, 2013

Acknowledgement The presenters gratefully acknowledge the Petroleum Technology Development Fund (PTDF) for funding this work. November 14, 2013

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