Suzana Yusup, Murni Melati Ahmad, Yoshimitsu Uemura,

Razol Mahari Ali, Azlin Suhaida Azmi, Mas Fatiha Mohamad and Sean Lim Lay

Abstract Various renewable energy technologies are under considerable interest due to the projected depletion of our primary sources of energy and global warming associated with their utilizations. One of the alternatives under focus is renewable fuels produced from agricultural wastes. Malaysia, being one of the largest producers of palm oil, generates abundant agricultural wastes such as fibers, shells, fronds, and trunks with the potential to be converted to biofuels. However, prior to conversion of these materials to useful products, pre-treatment of biomass is essential as it influences the energy utilization in the conversion process and feedstock quality. This chapter focuses on pre-treatment technology of palm-based agriculture waste prior to conversion to solid, liquid, and gas fuel. Pre-treatment methods can be classified into physical, thermal, biological, and chemicals or any combination of these methods. Selecting the most suitable pre-treatment method could be very challenging due to complexities of biomass properties. Physical treatment involves grinding and sieving of biomass into various particle sizes whereas thermal treatment consists of pyrolysis

S. Yusup (H) • M. M. Ahmad • Y. Uemura

Chemical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia e-mail: drsuzana_yusuf@petronas. com. my

R. M. Ali

Management and Humanities Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia

A. S. Azmi

Department of Biotechnology Engineering, Faculty of Engineering, International Islamic University Malaysia,

Jalan Gombak, 53100 Kuala Lumpur, Malaysia

M. F. Mohamad

Biomass Processing Laboratory, Green Technology MOR,

Universiti Teknologi PETRONAS, Bandar Seri Iskandar,

31750 Tronoh, Perak, Malaysia

S. L. Lay

Kawasan Institusi Bangi, PETRONAS Research Sdn. Bhd.,

Lot 3288 & 3289, Off Jalan Ayer Itam, 43000 Kajang, Selangor, Malaysia

Z. Fang (ed.), Pretreatment Techniques for Biofuels and Biorefineries,

Green Energy and Technology,

DOI 10.1007/978-3-642-32735-3_17, © Springer-Verlag Berlin Heidelberg 2013 and torrefaction processes. Additionally biological and chemical treatment using enzymes and chemicals to derive lignin from biomass are also discussed.

Keywords Pre-treatment ■ Palm waste ■ Physical ■ Thermal ■ Biological ■ Chemical

17.1 Introduction

Energy from biomass sources accounts for 11 % of the total world energy supply [1]. Biomass of forestry, agricultural, and municipal wastes has become an alternative source for renewable energy to fulfill global energy demand which currently is sus­tained by the depleting fossil-based fuels, due to its abundance amount. As the world’s largest producer of palm oil, the availability of biomass from the palm oil industry provides an excellent opportunity for Malaysia to produce biofuels [2]. There are more than 3 million hectares of oil palm plantations in Malaysia and each year, about 90 million metric ton of renewable biomass in the form of trunks, fronds, shells, palm press fiber, and the empty fruit bunch (EFB) are produced [2]. Biomass is character­ized as a low energy density material, thus converting biomass into gaseous, liquid or solid-derived fuels and chemicals can be challenging. In general, biomass are characterized using several important properties such as calorific value (CV), bulk density, moisture content, ash content, and volatile and fixed carbon (FC) content. A lot of difficulties need to be overcome in order to utilize the biomass as fuel feed­stock; one of them is the limitations associated with the biomass fuel characteristics. Pre-treatment can enhance the properties of biomass prior to its effective conver­sion into fuels and chemicals. In this chapter, four pre-treatment methods including physical, thermal, biological, and chemical treatment are reviewed.

For example, direct comparison of solid biomass with coal, which is still the leading solid fuel for electricity and heat generation, frequently discloses inferior properties of biomass [3]. Typically, biomass has low-energy densities and high moisture content and is more tenacious (due to its fibrous nature). These properties give drawbacks such as lower combustion efficiencies and gasifier design limitations. Compared to coal, biomass varies in many properties; such as heating values, ultimate analysis (amounts of carbon, hydrogen, nitrogen, sulphur, and other impurities), and proximate analysis (FC, volatile material, ash content, and moisture content) [4]. Properties of biomass such as moisture and ash contents, volatile compounds, and particle size impose significant effect on the performance of a gasifier [5, 6]. Thus pre-treatment of biomass is crucial to increase its potentials for subsequent utilization as a solid fuel.

Biomass can be converted to liquid fuel through thermochemical or pyrolysis process. The liquid product is known as bio-oil. Bio-oil is a complex mixture of highly oxygenated compounds [7] and can be burnt efficiently in standard or slightly modified boilers [8, 9] and internal combustion engines [10, 11] at rates similar to those of commercial fuels. However, the combustion occurs at compromised heating values, that is, 40-50 % of that for hydrocarbon fuels. This is due to high water content (15-25 wt%) and high oxygen content (35-40 wt% on dry basis) that is detrimental for ignition. In addition, organic acids, mostly acetic and formic acid, in bio-oil are corrosive to common construction materials [12, 13]. The corrosiveness becomes severe at elevated temperature and with the increase of water content [14]. Moreover, solids (char) in bio-oil can cause clogging in injectors or corrode turbine blades. Over time, physicochemical changes will occur that further degrade the quality of the bio-oil. Presence of moistures will also decrease the biomass heating value. The density and viscosity of the liquid oil increase as the high molecular mass lignin fraction content increases. The increase in viscosity increases the pour point. The decrease in volatile aldehydes and ketones increases the flash point of the liquids.

Fermentation of biomass that is composed of cellulose, hemicellulose, lignin, and proteins, into bioalcohols quite often requires pre-treatment of biomass to break away the sugars contained within the matrix of cellulose fibers in plant cell walls. Pre­treatment also removes lignin from biomass, making it more digestable for enzymatic and microbial hydrolysis of lignocollulosic biomass [15]. Degradation of the lignin and hemicelluloses by the action of white-rot fungi is an aerobic process but there are some bacteria like Entrobacter lignoluticus SCF1 and rumen microorganisms with the lignin degradating capability under anaerobic condition [16, 17].

Pretreatment of the biomass feedstock is the first step in the gasification process. It is essential in some cases due to the process characteristics, but it generally helps to improve the quality of the fuel by homogenizing its size, moisture content, and density. For the operation of continuous processes, biomass storage is required, yet it may lead to issues related to decomposition and self-heating. Pretreatment can help solve or minimize the impact of these issues. It includes several processes, such as size reduction (milling, grinding, and pulverization), screening, drying, torrefaction, pelletization, and pyrolysis.

The major assumptions regarding the moving bed (updraft gasifier) model are as follows:

• There is no temperature or concentration distribution radially.

• The solid hydrodynamic is considered as a plug flow flowing downward.

• The gas flows upward as a plug flow.

• The mass transfer between two phases takes place by diffusion [14].

The mass balance equation ofjth-gas species can be written as (10.6):

Also, the energy balance of the gasifier in the z direction is expressed as follows:

These equations will be solved simultaneously with the appropriate kinetics discussed in section 3.

In entrained-flow reactors, free-falling particles are entrained downwards by a gas flow. For gasification, entrained-flow reactors are a promising technology as demon­strated in 2002-2003 by Shell and BTG with woody biomass as feedstock [58]. Preliminary tests for biomass pyrolysis applications have shown very high non­condensable yields [59]. It is believed that the geometry of this type of reactor technology promotes important bio-oil thermal cracking. Since the purpose ofpyroly — sis for biorefineries is to produce higher molecular-weight chemicals, this technology will not be covered.

Table 13.4 shows the results of the calculation of the process potential in terms of GHG reduction per year and the amount of GHGs reduced by the BGUS. The follow­ing GWP (Global Warming Potential) ratios were used: CO2:1; CH4:25; N2O:298 [16]. The total carbon load of the shared portion of the previous biogas plant was 271 t-CO2eq ((219,260 kg-CO2eq (gas flare) + 6,042 kg-CO2eq (Buying electricity for Biogas Plant) + 45,215 kg-CO2eq (volatilization)).

Against this value, CO2 reduction in the total carbon load of common portions from the biogas plant that introduced the BGUS was counted as being produced by ~6.3 % of Town A’s households to which biogas was sent (which did not include the farm in Town A with the biogas plant installation) and by farm trucks and kitchen equipment that used refined biogas as substitute energy source in the biogas plant, besides the livestock waste treatment system that existed in the previous biogas plant.

The results of analysis show that the total carbon load of the common portions of the BGUS was 102 t-CO2eq. Compared with the carbon load of the common portion of the biogas plant before introduction of the BGUS and of the gas-utilizing equipment inside and outside the farm production system (209 t-CO2eq), a reduction of 107 t-CO2eq was achieved.

13.3 Conclusion

In this chapter, a biogas refining-compressing-filling facility that uses surplus biogas produced by a privately owned biogas plant was devised and constructed, field tests of biogas utilization systems made up of equipment using purified gas obtained from the facilities were performed, and the possibility of a regional purified biogas system in rural areas of Japan was validated. Consequently, the refining-compressing-filling facility was able to reach the biogas Wobbe Index (WI) of 49.2-53.8 and com­bustion rate of 34-47 m/s (town gas 12A specification) in production volumes of high-pressure gas that qualified for class 2 producer status under the specifications of Japan’s “High-pressure Gas Safety Act” (<100 Nm3/day).

Additionally, the budget analysis results of a biogas utilization system modeled after Town A in Northern Japan showed a distribution of the purified gas such that

0. 3 % of the purified gas produced by the biogas plant (approximately 35,000 Nm3/yr) was used for running consumption and 98.3 % was distributed to the town’s gas infrastructure, thereby satisfying the gas needs of 219 (6 %) of the 3,661 residences of Town A.

Fig. 13.4 Biogas utilization system (BGUS)

The results of analysis show that the total carbon load of the common portions of the BGUS was 102 t-CO2eq. Compared with the carbon load of the common portion of the biogas plant before introduction of the BGUS and of the gas-utilizing equipment inside and outside the farm production system (209 t-CO2eq), a reduction of 107 t-CO2eq was achieved.

The results show that the area’s carbon dioxide emissions can be reduced through the standardization of Town Gas 12A and that refining biogas allows for the export of biogas outside of the system to be used by common gas appliances. Purified gas is locally produced and consumed as a source of carbon-neutral energy in dairy farming areas. Packing the purified gas into tanks and supplying it to the town makes possible the reduction of the area’s carbon emissions.

Solid acid catalysts are promising for the conversion of cellulosic materials into soluble sugars and have the characteristics that they are environment-friendly and recoverable. However, the existing catalytic systems showed low efficiency, leading to high-energy consumption and generation of by-products. Nano-catalysts can be used to improve many aspects of solid acid catalysts. Nano-catalysts are defined as solid catalysts with particle size in the nanometer level (usually ~100nm), and mainly used in acid-catalyzed organic reactions, such as hydrogenation, oxidation, alkylation, transesterification, condensation, and polymerization. Nano-catalysts can be used for most of the reactions catalyzed by traditional solid acid catalysts. Com­pared with traditional solid acid catalysts, nano-catalysts usually showed improved structural and textural properties in terms of high active site loading, small crystalline size, high surface area and pore volume, and high catalytic activity and selectivity. Moreover, most traditional solid acid catalysts can be used for synthesizing nano­catalysts by supporting acidic sites on nano-carriers or directly preparing nano-scale particles. Up to now, nano oxides are mostly studied supports.

The feedstock constitutes 70-95 % of the biodiesel’s production costs [16]. The price of biodiesel in the open market stands approximately at $1,300/ton. This means the lower the cost of feedstock which contains higher %FFAs, the bigger the margins and the more profit is made on biodiesel from lower value feedstock. When choos­ing feedstock, there are several important factors to consider such as quality, price, availability, and ability to meet product specifications “ASTM and EN specs” which can be achieved by choosing proper pretreatment and to some extent post-treatment methods [6]. Understandably, higher quality feedstocks which don’t need pretreat­ment typically are much more costly. Refined, bleached, and deodorized (RBD) vegetable oils are more expensive than crude vegetable oils, both vegetable oils are more expensive than tallow and waste-cooking oil (yellow grease), yellow grease is more expensive than fat trap (brown grease), and so on. However, soybean oil which is very abundant is also more expensive than palm oil simply because of its
process ability and inherent characteristics that impacts cloud point (CP) and cold filter plugging point (CFPP) of the biodiesel product [17, 18].

Crude corn oil which is available as byproduct of the ethanol industry typically contains 10-15 % FFAs and is reddish in color, requires pretreatment process. The purification needed is to minimize the sterol, glycosides, waxes, and FFAs to ASTM acceptable levels in the oil in order to make an acceptable transesterification feedstock [19]. The ability to convert FFAs into methyl esters instead of soap increases product yield and reduces feedstock cost per gallon of biodiesel. The high-FFAs crude corn oil is 20 cents cheaper than the soybean oil, and it has a -3 °C CP, nearly 5 °C better than soybean [20]. This is great to the biodiesel consumers, especially since there will be at least twice as much crude corn oil in the market in 2012 compared to 2011 which will also yield biodiesel suitable for cold winters [20].

The development of the SPORL process is based on the fundamental understandings of sulfite pulping [109]. Usually the SPORL pretreats the woodchips in an aque­ous sulfite solution at 160-180 °C and pH 2-4 for about 30 min. The woodchips are then fiberized (size-reduced) using a disk mill to generate fibrous substrate for subsequent saccharification and fermentation. With low pretreatment cost, excel­lent substrate digestibility, along with sulfite pulping and chemical recovery, and disk refining technologies that have long been practiced in the pulp and paper in­dustry, and existing industry infrastructure and commercial markets for high-value co-products from pretreatment-dissolved hemicellulose sugars and lignin, SPORL has low environmental and technological barriers and risks [112].

8.3.4.1 Mode of Action

Since the SPORL process is based on the sulfite pulping, this pretreatment chemistry is also similar to sulfite pulping. The major chemistry related to hemicellulose, cellulose, and lignin can be summarized as follows:

• A considerable amount of hemicellulose degradation and removal takes place during the pretreatment, as evidenced by the predominant Xyl content in pretreated effluent [113].

• Thedegrees of polymerization of xylan [114-117] and cellulose [118] are reduced.

• Sulfonation of lignin increases the hydrophilicity of lignin, which may promote the aqueous enzyme process.

• The degrees of dissolution of hemicellulose, degradation of cellulose, and sul­fonation and condensation of lignin are increased as reaction time and temperature increases, and pH decreases [111, 119].

It should be noted that the production of fermentation inhibitors HMF and furfural in the SPORL is significantly lower than those in dilute acid, which is favorable to the fermentation of pretreatment-dissolved sugars from cellulose and hemicellulose. Excellent performance of the SPORL with different wood species indicates that this process may be tree species independent [109].

Popular catalysts in this group are Ni-based catalysts. A wide variety of Ni-based steam reforming catalysts are commercially available, and they are widely applied in the petrochemical industry. The literature contains numerous studies reporting the use of commercial Ni-based catalysts for tar cracking, which has been shown to be very effective in increasing synthesis gas yield. However, the use of the Ni catalyst in the gasifier is limited due to its fast deactivation caused by coke, chlorine, and alkali metals that may be present in the gasifier (from biomass ash). So far, the use of a nickel catalyst as an additive to the gasifier has had little success.

All these catalysts, when used in-situ, are not promising due to the combination of coking and friability. Using them in secondary beds is more effective. The duration of most-reported catalyst tests has been quite short, especially considering the long activity requirements for expensive catalysts, such as Ni, to be economical. Although downstream gas cleaning methods are reported to be very effective in tar reduction; catalyst deactivation due to impurities in the gas outlet of the gasifier makes catalytic tar cracking economically unfeasible.

For particle size reduction, it is preferable to process biomass with low moisture content (after a drying pre-treatment) since its brittleness is increased and higher

shear forces are promoted. Taking that into consideration, the most common size reduction techniques are dry shredding and hammermilling. Dry shredding relies on rotating cutters: A geared roll is mounted with sharp designed metal cutters, which are regularly disposed on its surface. Larger wood pieces can this way be converted into wood chips. As smaller pieces will simply bypass the cutters, there is no need to separate the biomass feed before this step. Dry shredding can easily reduce biomass size down to wood chips-like particulate [10].

If a powder-like feedstock (<500 ц-m) is required for pyrolysis, further size re­duction can be achieved with hammermills [10]. The principle is to grind a material until it reaches a minimal particle size. It is designed to limit particle size by the use of perforated plate outlet whose holes size determines the final average particle diameter. In a small drum, solid metal hammers are mounted on a central shaft. The metal hammers are rotated and the biomass material comes under the action of cen­trifugal force: the biomass is crushed between the hammers and the drum wall. The drum wall has grooves oriented perpendicular to those of the hammers extremities to maximize shear forces. By gravity, the fine particles percolate at the bottom of the drum where the perforated plate controls their exit in the outlet duct.