1. 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
November 14, 2013

2. Presentation Outline Introduction Efficacy of Pretreatment
Classification of Pretreatment Methods
Biochemical Pretreatment Methods
Thermochemical Pretreatment Methods
Conclusion
Acknowledgement
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3. 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.
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4. 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.
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5. 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.
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6. Classification of Pretreatment Methods
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7. 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
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8. 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.
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9. 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.
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10. 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.
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11. 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.
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12. 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
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13. 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.
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14. 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.
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15. 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.
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16. Thermochemical Pretreatment Methods Contd
2. Controlled pyrolysis reaction temperature of about 5000C and vapour phase temperature of C.
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.
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17. 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.
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18. 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.
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19. 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.
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20. Acknowledgement
The presenters gratefully acknowledge the Petroleum Technology Development Fund (PTDF) for funding this work.
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21. THANK YOU FOR LISTENING
November 14, 2013