Lignocellulosic Feedstocks For Biofuels

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02 Nov 2017

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Introduction

Biomass is considered as one of the most suitable resource available to address some of the current issues including environmental degradation, carbon management, energy security, rural development, and unemployment [Demirbas et al. 2007]. Biomass has been using from the pre-historic periods for energy and materials [Agbor et al. 2011]. During the course of time we have shifted our dependence on fresh biomass to fossilized biomass for energy and materials. Overdependence on the fossilized biomass led to the disruption in the global climate patterns and degradation in the environmental quality [Jyoce and Stewart 2011]. Utilization of biomass as a renewable resource also poses the challenge to find the methods to use it efficiently [US Interagency Strategic Plan 2001]. Biomass requires some form of pre-treatment before used to produce energy and materials and is dependent on the choice of the technology and the products. Pre-treatment has to be done at various stages of the utilization of biomass, from the field to the end product formation. Harvesting, handling, transporting, and storing are considered as the initial processes applied with all biomass types irrespective of the final product [Hesse et al. 2007].

The conventional biomass to biofuel conversion process is depicted in Figure 1. In this approach, biomass has been harvested and collected from different locations and then transported to the centralized processing industries where it will be stored before the pretreatment and the final production processes. The products formed will be then transported back and to various end-users for its utilization. The low density (70-150 kg/m3) of biomass reduces the economical transportation distances. The conventional approach is to reduce the transportation cost is the compaction of the biomass to increase its density before transportation. Alternate approaches to the road transport of biomass for bioenergy production are transportation through pipeline and rail transport [Short 2009]. But these methods are suitable only for the bulk handling and processing of the biomass and the role of biomass producers is very limited in these approaches.

Figure 1. The model of existing biofuel production process [courtesy: Prof. Mark Holtzapple, Texas A&M university].

In the present scenario, most of the industries are utilizing only specific component of the biomass and the remaining components are not used effectively by them [Hamelinck et al. 2005]. For example, for an industry producing bioethanol from glucose, components like pentoses, lignin and minerals are not important and they need separate systems to handle these high value components. An alternative approach of biomass handling and valorization would facilitate the efficient use of biomass than the current practice of bulk handling and processing. Direct involvement of the biomass producers, mainly the farmers, in the biomass processing would create more job opportunities and thereby facilitating the rural development and youth employment [Hesse et al. 200].

An industry processing biomass to fuels and materials requires a continuous supply of raw materials and it would be practically difficult to obtain the same type of biomass throughout the year from an area where the crops and other sources of biomass varies from fields to fields as in the case of most of the developing countries. Even in the large scale cultivation of same type of biomass, it would be profitable for the producers to process the raw material and sell the component separately to different industries at higher prices.

There are many researchers around the world working to develop low cost biomass pre-treatment processes having minimum input in energy and chemicals [Yang 2007]. The objective of the pretreatment process is to make biomass amenable to the enzymes or other catalysts to be broken down to its components before the production of final products from it. Most of the pretreatment processes developed so far can only be used at an industrial site having facilities for enzymatic treatment and fermentation. A few of the industries and researchers have been thinking on the decentralized mode of biomass pre-treatment and processing to address the issue of biomass availability and its transportation [Hess et al. 2007, Richard 2010, Xu et al. 2011]. But the real solution is yet to be developed.

The objective of this work is to develop a process to pre-treat biomass at its site of production itself to separate it into its components thus produce specific raw materials for the production of biofuels and biomaterials. This work envisages developing a market pathway where the farmers would treat available biomass at their own facilities or the facilities owned in groups, to isolate the component polymers in its pure and compact form and the industries would collect it from these producers and convert it to the final products depending on their interest and expertise. The processed materials can be purchased by a biorefinery also where they can substantially reduce the cost of pre-treatment processes.

Literature review

2.1 Lignocellulosic feedstocks for biofuels

The selection of lignocellulosic feedstock is important for the biofuel production as it contributes to 30-50% of the final product price depends on the location, handling and the processing methods [Hess et al. 2007].

The biomass raw materials should have the following characteristics to be a suitable feedstock for the production of bioenergy and biomaterials.

It should not affect the food security of the people. Utilization of the biomass, which has been used as a food resource, for bioenergy production would compromise the food security of the people.

It should be easily and continuously available and easy to handle.

It should have well developed root system to reduce the water and nutrient input and hold soil and fix more atmospheric carbon.

Lignocellulosic feedstocks available in the biomass supply system are from wood, grasses, agricultural residues and other wastes. The systems and processes to collect and process the feedstocks are designed based on the type of feedstock selected [Hesse et al. 2007]. The main constituents of these feedstocks are cellulose (40-50%), hemicellulose (20-30%), and lignin (20-30%) and the recalcitrance of the feedstock depends on the concentration of these components in it [Agbor et al. 2011].

Switchgrass is perennial grass native to the North America suitable to the marginal lands and grow with minimum inputs and it protects the soil from eroding [McLaughlin and Walsh 1998]. This high yielding (3-15 Mg per hectare) grass has been selected as a feedstock for the biofuel production as it would not compete with the food security and sequester more amounts of atmospheric carbon in its roots (1-12 Mg per hectare) [Lal 2008]. The estimated cost of production of switchgrass is about 66 $ per ton and it can grow in a wide geographical range [Duffy and Nanhou 2000]. Switchgrass contains about 45% cellulose, 31% hemicellulose and 12-20% lignin [Sun and Cheng 2002].

2.2 Lignocellulosic biomass pretreatment options

Pre-treatment of lignocellulosic biomass has been under research and development for more than a century and the initial pre-treatment methods developed were acid hydrolysis and were followed by steam based hydrolysis methods. Even though there are different pretreatment options available for lignocellulosic biomass there is no consensus in the classification of them. All the pretreatment processes have some aspects of physical and chemical factors in it. The chemical factors can be of purely non-biological or biological in nature. Some of these chemicals are formed during the pretreatment processes that add up to the chemical reactions and make the general classification a difficult one [Saville 2011]. In general, the pretreatment processes can be classified into physicochemical, thermochemical and biochemical processes [FAO 2010].

Biomass pretreatment processes are required to have the following characteristics for its commercial viability;

Low capital and operational cost,

Applicable to a wide range of lignocellulosic feedstocks,

Maximum recovery of the different components of the feedstock in its useable and pure form,

Minimum requirement of pre- and post- pretreatment processes,

Minimum degradation of sugars and no or minimal inhibition to the enzymes or microorganisms used in the succeeding processes of the pretreatment, and

Low energy requirement and maximum energy recovery [Chandra et al. 2007, Saville 2011].

There are many pretreatment processes been studied and it is difficult to evaluate and compare them completely, since they involve both upstream and downstream capital investment, operational cost, chemical recovery and waste treatment operations [Agbor et al. 2007]. The following sections are a general review of pretreatment processes for lignocellulosic biomass for the production of liquid biofuels through the biochemical route. It does not deal with the themochemical routes of biofuel production.

2.2.1 Physical and physicochemical pretreatment processes

Physical methods of lignocellulosic biomass pretreatment include mechanical, thermal, and the electromagnetic ones. Main mechanical pretreatment methods for lignocellulosic biomass include chopping, shredding, grinding, and milling [Agbor et al. 2007]. These treatments increase the surface area and reduce the degree of polymerization of cellulose and its crystallinity [Sun and Cheng 2002]. Among these mechanical methods milling is used to reduce the size of the biomass to particles of about 0.2-2 mm and is the most effective one to increase the surface area and reduce the crystallinity of cellulose [Zhua et al. 2009]. Milling methods include ball milling, compression milling, hammer milling, Szego milling, and disc refining. The required energy input is in the range of 100 kWh per ton of wood and 20 to 40 kWh per ton of agricultural residues [Saville 2011].

A method of biomass pretreatment is known as hot water treatment and in which water at high temperatures (180-2000C) pass through the biomass that facilitates the breakdown of the bonds in and between the polymeric compounds in biomass so as to release some of the carbohydrates as its monomers. This treatment makes biomass amenable for the enzymes to act on the cellulose during the enzymatic hydrolysis. The solids loading of this process is about 30-40% (w/w) which is an important pre-requisite for an industrial pre-treatment process. The Inbicon group in Denmark is producing bio-ethanol from agricultural wastes based on this technology [www.inbicon.com].

Steam explosion is one of the most studied physicochemical pretreatment options for the lignocellulosic biomass. In steam explosion treatment, biomass is subjected to high pressure steam at 160-2400C with 0.7 to 4.8 MPa for a short duration of time of about1to 2 minutes. The developed pressure released rapidly to facilitate the internal expansion of the biomass and breakdown of the bonds between the polymers. Hemicellulose fractions get hydrolyzed and solubilised and the lignin fractions get transformed during the steam treatment. The acidity due to the acetic acid generated from the acetyl groups of the hemicellulose combines with pressure and the following rapid expansion makes the biomass amenable to the hydrolysing enzymes [Agbor et al. 2007]. The efficiency of steam explosion pretreatment can be increased by adding acidic catalysts like H2SO4 or CO2 and it reduces the retention time while increasing the hemicellulose hydrolysis and reduces the formation of fermentation inhibitory compounds [Balat 2011]. Some of the industries using this technology for the production of bio-ethanol include the Finn sugar in Finland using oat hulls and birch fins, the Chinese Oil and Foodstuffs Company (COFC), ZhaoDong, China using corn stover, and the Verenium Corporation in USA using sugar cane bagasse [Saville 2011]. This process can handle higher solids loading (85-90%, w/w) which is highest of the pre-treatment processes available. The main disadvantage of this pre-treatment process is that it requires high safety precautions and expertise for operation.

Pre-treatment using microwave in presence of alkali has also been studied as lignocellulosic pretreatment process and was shown enhancing the digestibility of the pretreated materials by the enzymes [Kim et al. 2006, McKone et al. 2011]. Keshwani et al. (2007) have studied the effect of microwave treatment with other pretreatment options like acid hydrolysis, alkaline hydrolysis and autohydrolysis and has shown that microwave irradiation at 250 watts for 10 minutes during the alkali treatment highly enhanced the enzymatic digestibility of switchgrass. Similar results have reported on rice straw by Zhu et al. (2005) also. During microwave treatment, the internal heating due to the vibrations of the polar bonds in biomass and its surrounding aqueous environment causes the reactions in biomass. The heating of biomass in an aqueous medium releases the acetic acid from it that create an acidic environment for the autohydrolysis [Keshwani et al. 2007].

2.2.2 Chemical and thermochemical pretreatment processes

Chemicals like acids, alkalis, organic solvents and ionic liquids have effects on the structure of the lignocellulosic biomass and have been used in the pretreatment of biomass, with the external supplementation of them, for biofuel production [Agbor et al. 2007, Saville 2011]. Generally the chemical pretreatment processes for biomass can be classified based on the pH of the medium as neutral, acidic and alkaline. Some of the major pretreatment processes for lignocellulosic biomass are discussed below;

Neutral treatment processes: These treatment processes are classified as neutral because there is no acidic or alkaline reagents other than water or steam are added into the systems during treatment, but the treatment conditions are mostly acidic in nature due to the property of water to act as acid at high temperatures. The acidity also increased by the release of acidic compounds which are formed from the biomass at high temperatures. These processes are also known as autohydrolysis treatments. The main advantage of these treatment processes is that they are more environment-friendly and the capital investment would be less than that for systems with addition of external chemicals.

Acidic treatment processes: There are two types of acid treatment processes available depend on the concentration of acid using for the hydrolysis of biomass. Dilute acid treatment is one of the most developed biomass pretreatment process for biofuel production and it completely hydrolyse the hemicellulose fraction of biomass and also partially hydrolyse the cellulose component of it. Acid concentration varies from 0.75% (w/w) to 5% (w/w) depending on the temperature (120-2000C) and time (30-120 min.) selected for the pretreatment. Sulphuric acid is the most widely used acid but acids like HCl, H3PO4, CH3COOH, CO2, SO2 have also been used to study the process. The resulting hydrolysate requires neutralization and detoxification using lime and it results in gypsum formation [Saville 2011]. The main disadvantage of this process is the presence of sugar degradation products that impose difficulty in fermentation of the sugars released through hydrolysis. Another disadvantage is the requirement of corrosion resistant facilities for this pretreatment method [Agbor et al. 2011].

Carbon dioxide explosion treatment: It is also known as supercritical carbon dioxide explosion and in this treatment carbon dioxide at high pressure (1000-4000 psi) and temperature (usually at 2000C) is applied to the biomass for pre-fixed duration of time. CO2 penetrates the biomass and act as carbonic acid to facilitate the hydrolysis and release of this high pressure results in the disruption of the internal structure of biomass that increases the total accessible surface area for enzymes and further hydrolysis. The high cost of the equipment acts as the major hindrance to the scaling up of this process [Agbor et al. 2011].

Solvent based processes: Organic solvents like ethanol, methanol, acetone, and glycols in presence of acids or alkalis are being used to dissolve the lignin in the lignocellulosic biomass but the main concern in applying this processes are the recovery of the solvent and presence of the residual solvents in biomass that is inhibitory to the preceding enzymatic hydrolysis and fermentation processes.

Ozonolysis treatment: Ozonolysis is a delignification process carried out at room temperatures. It uses ozone gas to remove lignin and hemicellulose without affecting cellulose in the biomass. Studies have shown that ozonolysis removes lignin from corn stover, wheat and rye straws and increases the enzymatic digestibility of the pretreated material. The major drawback of ozonolysis is the large quantity of ozone required and the resulting higher expense of the process [Balat 2011].

Ionic liquid pretreatment: Ionic salts are salts with low melting point (< 1000C), high thermal stability, minimal vapour pressure, and high polarities. Ionic liquids of imidazonium salts are generally used to dissolve lignocellulosic biomass and the possible reaction is the competition between the ions of these salts and the carbohydrate components for the hydrogen bonding. This competition results in the disruption of the internal structure of biomass. The cellulose fraction dissolved in the ionic liquid can be recovered using water, ethanol or acetone. The solvents are then recovered through evaporation and are reused in the process [Agbor et al. 2011]. The main disadvantage of this pretreatment process is the high cost of ionic salts.

Alkaline treatment processes: Alkaline pretreatment uses NaOH, Ca(OH)2, or NH3. Among these NH3 is the most widely employed alkali for the pretreatment of agricultural residues at pilot and commercial levels. Alkaline treatments have longer retention times (48 hours ??? 4 weeks) than acidic treatment methods and it is considered as a disadvantage due to the reason that sugars starts degrade at 600C in presence of alkalis [Saville 2011]. Alkaline treatment disrupts the ester bonds between xylan and lignin with removal of hemicellulose and lignin from the solid residue of cellulose. The crystallinity of the cellulose also decreases during the alkaline treatment. The retention times can be reduced if the pressure and temperature increased to 100-1500C.

Pretreatment with alkalis causes swelling of the biomass which leads to increase in the internal surface area, decrease in degree of polymerization and crystallinity of cellulose. It breaks the bonds between lignin and other carbohydrate components by disrupting the structure of the lignin. Alkali treatments also remove the acetyl and uronic acid substitutions on hemicelluloses that limit the access of the enzymes to the cellulose surface [Chandra et al. 2007].

Delignification occurs during the treatment of lignocellulosic biomass with alkali in three steps such as initial, bulk and residual. In the initial delignification stage, the phenolic linkages like ??-O-4 and ??-O-4 in the lignin get cleaved. In the bulk delignification stage, the non-phenolic ??-O-4 bonds get cleaved. During the final residual stage, the carbon-carbon bonds in the lignin get broken with the degradation of the carbohydrates. The activation energies for the bulk and residual delignification of the corn stover were 50.15 and 54.21 kJ/mol respectively [Kim and Holtzapple 2006]. Alkali treatment is effective only for the low lignin containing biomass like agricultural residues and is found less effective for biomass with high lignin content [Agbor et al. 2007].

Ammonia Fiber Expansion treatment: Ammonia Fiber Expansion (AFEX) is one of the most studied alkaline pretreatment processes that use liquid ammonia of 1-2 kilogram per kilogram of biomass and then treated at 90-1000C and 1-3 MPa for 30-60 minutes. The ammonia is then released and collected completely to be reused in the next cycle of operation. This treatment fractionates the biomass into its components without the solubilisation. This treatment is best suited for biomass with low lignin content but the main impediment is the requirement of highly sophisticated systems to handle and recover ammonia without leakage into the atmosphere. The smaller amount of residual ammonia in the biomass would be used up in the following fermentation stages. Higher temperatures (1800C) resulted in good fractionation results with woody biomass [Saville 2011].

Lime pretreatment: Lime pretreatment is a proven method to remove the lignin from the biomass without affecting the carbohydrate portion of it. It uses the calcium hydroxide in presence of water at different temperature and pressure with or without the addition of air or oxygen for different duration of time. The conditions vary depend on the raw materials and the process option selected. The oxidative conditions are applied for biomass with higher lignin content in it, such as with about 18% or more [Sierra et al. 2009]. The lime treatment required to be followed by a neutralization step to remove the excess of the lime from the treated biomass.

The lime pretreatment causes the deacetylation and partial delignification in biomass and oxygen improves the delignification under high pressure. It has been shown that lime pretreatment of wheat straw at 850C for 3 hours with oxygen resulted in better yield than without oxygen. Lime pretreatment removes about 80% of the lignin in the lignocellulosic biomass [Agbor et al. 2011].

The advantages of lime pretreatment include the safety and low cost of the reagent and also the unused lime can be recovered as calcium carbonate to reuse in the next cycle of treatment. Lime treatment can be performed under mild temperatures (<1000C) compared to other chemical pretreatment processes and does not require much sophisticated equipments. The main disadvantages of lime pretreatment are that, it is not as effective as ammonia treatment and also the requirement of huge amount of water for the washing and neutralization of the residue [Agbor et al. 2011].

2.2.3 Biological pretreatment

In biological pre-treatment processes microorganisms are used to treat the lignocellulosic biomass. Brown-, white-, and soft-rot fungi are the commonly used microorganisms to degrade lignin and hemicellulose [Bisaria et al. 1981]. These microorganisms produce enzymes such as lignin peroxidases, polyphenol oxidases, manganese-dependent peroxidases, and laccases to degrade lignin [Agbor et al. 2007]. The main drawback of the biological pre-treatment is the long retention time with low hydrolysis rate [Sun 2002]. The residence time for biological treatment is 10-14 days and it requires careful growth conditions and large amount space. These factors are considered to be disadvantageous for an industrial biomass treatment process [Agbor et al. 2007]. The consolidated bioprocessing (CBP) using microorganisms capable of converting biomass to sugars or biofuels is under the investigation and have the potential to reduce the overall processing cost [Agbor et al. 2011].

2.3 Post-pre-treatment processes

The pretreatment of lignocellulosic biomass results in dissolved and undissolved materials. The dissolved materials include the monomers and oligomers of the carbohydrates in the biomass and the degraded products of them and lignin which are inhibitory to the enzymatic digestion as well as fermentation. To separate the dissolved components from the undissolved materials, the slurry would be passed through a filter system and the solid residue will be washed to remove the traces of the degraded products on it. The pH of the materials after pretreatment has to be adjusted before the next hydrolysis or fermentation process. The catalysts will be recovered through precipitation or absorption [Hamelinck et al. 2005].

2.4 Techno-economic and ecological analyses

Biomass pretreatments have conventionally been assessed based on i) the quantity of sugars released during the pretreatment and the recoverable carbohydrates in the insoluble residue, ii) the sugar released through the enzymatic hydrolysis of the insoluble residue, iii) product formation through the fermentation of sugars released in other stages of the pretreatment, and iv) additional products from the feedstock. Another parameter that is being used to assess the pretreatment is the ???severity factor???, which is the combined effect of temperature, acidity, and duration of the pretreatment. But these methods are not accurate and are giving only a rough estimate of the pretreatment merits and demerits [Agbor et al. 2011].

Biomass pretreatment processes have also undergone the life cycle analysis (LCA) study which analyzes the information collected on the contributions of the developed process to climate change, release of pollutants and their impact, effects on water resources, changes in land-use, nutrients needs, human and ecological health effects, and social and economic changes. LCA study starts with the biofuel feedstock, its production, and the land-use practices. Then it considers the transportation and storing with the aspects of investments in treatment facilities and operation. The LCA study of process of pretreatment of lignocellulosic biomass for liquid biofuel production remains unstudied until now [McKone et al. 2011].

2.5 Limitations of current biofuel production processes

Even though there are many advances in the research and development of biofuel production, the cost of the products needs to be further reduced. The cost of the pretreatment and the low density of the biomass make the process and resulting products less accessible in the market [Cheng and Timilsina 2011]. There are many differences in terms of technology and outcomes among the pretreatment processes studied in lab scales and demonstration or the commercial scales. So, it would be difficult to conclude on the merits and demerits of pretreatment processes based on these studies. However, technologies that have high capital and utility costs and low outputs have economical disadvantages over the pretreatment processes that uses less chemicals and provide high outputs in terms of products [Saville 2011]. It is also unlikely that a method would be developed for all the feedstocks, and the pretreatment of mixed feedstocks is yet to be studied with any selected pretreatment process [Agbor et al. 2011].

The supply chain infrastructure is required to be changed to meet the increasing demand for lignocellulosic bioenergy and efficient supply chains are possible by decentralized conversion process with business models that rewards the biomass producers. Transport of low density biomass to meet the demand for bioenergy through a centralized processing method would add up to the current traffic of commodity movement that include about 2.75 billion m3 of agricultural produce, 6.2 billion m3 of coal and 5.7 billion m3 of oil. This additional traffic would give stress on the traffic infrastructures especially in rural areas around the world. But this additional demand for the movement of lignocellulosic materials would provide an opportunity for the improvement of rural transportation infrastructure [Richard 2010].

The current practise of large scale cultivation of bioenergy feedstocks through the contract farming, which is being used today by many of the biofuel companies throughout the world, created problems with the land access, appropriation and employee rights [Richard 2010]. Based on the insight from these experiences it would be important to have more direct involvement of the biomass producers in the production and processing of bioenergy feedstocks for the centralized biorefineries.

There are many questions unanswered about the suitability of second generation biofuel production technologies to the developing countries which are claimed to be in the pilot or demonstration scales in the industrialized countries. The processes developed in developed countries are capital intensive, labour-minimizing, and are designed for large scale operation and economical benefits. Bioenergy feedstocks selected by the industrialized countries may not be the best feedstock option for the developing countries. At present the scenario expect the developing countries become only as the producers of the biomass rather than the exporters of the surplus biofuels produced by them [UNCTAD 2008].

Figure 1: The Schematic representation of the industrial use of biomass for biofuels and bioproducts.

2.6 The concept of decentralized biomass pretreatment

Based on the analysis of the current biofuel production process, it is clear that there is a need for more sustainable approaches for the handling and pretreatment of biomass. The alternate approach to the practise of bulk handling and processing of biomass is a process to pre-treat the biomass at the site of production itself to separate it into its components and each industry buying the component or components of interest from these centres. The separated components would be easy to handle, as in its pure and compact form, and would reduce the cost of transport and the final processing by the industries [Hesse et al. 2007]. One of the industrial companies for the bioenergy production has already started to pretreat the lignocellulosic biomass at the site of production itself and the processed materials are then transported to their centralized facilities for further processing and biofuel production [www.atlanticbiomassconversions.com]. But the industry???s approach of pretreating the biomass to produce fermentable sugars out of it using their proprietary process using advanced biochemicals and sophisticated facilities that require trained human resource and high capital investment would not benefit the biomass producers very much.

Study hypothesis

Development of a process for the on-site pre-treatment of biomass will enable the farmers to directly participate and contribute in and thereby benefit from the emerging bio-economy which has the potential to solve the problem of unemployment and lead to the rural development. This process will also ensure a continuous supply of the pre-processed raw materials for the biomass processing industries.

Research objectives

The overall objective of this research work is to develop a process for the decentralized and onsite pre-treatment of biomass for the centralized bio-refinery operations. It would be achieved through the following sub-objectives;

i) The process parameters such as concentration of substrate and chemicals, particle size, moisture content, temperature and retention time would be optimized.

ii) Post-treatment processes for the purification, handling and storage of the treated materials for further transport and processing at the centralized facilities would be studied and developed.

iii) It also aims to carry out the technical, economical and environmental analyses of the developed process in a foreseeable manner.

Rationale of the study

In the context of utilizing lignocellulosic biomass for biofuels and biomaterials there should be more involvement and participation by the farmers in the production and processing of the feedstocks that are produced by them. The value addition of the raw lignocellulosic materials by processing it into its components would generate more employment opportunities with livelihood enhancement and rural development. The fractionated materials would help the industries to collect in their purer and dense form that would reduce the cost of production and also ensure continuous supply of the raw materials.

Figure 2: The Schematic representation of the concept of decentralized pretreatment of biomass for the centralized biorefinery operations.

Materials and methods

Feedstock: Switchgrass, which is a promising bio-energy crop, would be selected as the feedstock for this study. Alternate feedstocks that have similar structural and compositional features would be selected if switchgrass is not available for the study.

Chemicals: Calcium hydroxide (Ca(OH)2) and Calcium oxide (CaO) would be used as catalysts to pretreat the feedstock in the presence of water and air. Other chemicals and reagents required for the biomass analyses are given in the Appendix.

Biomass / Sweet sorghum bagasse

Collection, size reduction, storing

Pre-treatment (Lime, Energy, Water)

Black liquor (Lignin, Hemicellulose, minerals, remaining chemicals)

Cellulose

Washing, filtering and storing

Lignin and minerals

Lignin isolation using CO2

Hemicelluloses or sugars in the liquor

For industries or local use

Drying

For Energy + CO2

Concentration

Minerals

Figure 3: Schematic representation of the process to be developed

Pretreatment reactor: Conical flasks or stainless steel pipes or PVC (Poly-Vinyl Chloride) tubing that can withstand temperature up to 1200C and pressure of about 1.5 kg/cm2 would be used as pretreatment reactor. The total reaction volume of the reactor would be 100 mL.

Heating source: A convective oven with temperature range of 00C to 2000C with temperature controls would be used as a heating source. This oven would also be used to dry the pretreated biomass for analyses.

Analytical methods: The analysis of the biomass materials for the composition will be done using the Laboratory Analytical Procedures (LAPs) developed by the National Renewable Energy Laboratory (NREL) available at their website http://www.nrel.gov/biomass/analytical_procedures.html. An alternate approach is analysing the biomass composition using Near Infrared (NIR) spectroscopy as described by Hames et al. (2003). The materials required under each analytical procedure are given in the Appendix.

Experimental design: All the pretreatment studies would be designed and analysed using the required statistical methods and softwares for them, like Design Expert 6.0.2. The design of experiment prepared using Design Expert 6.0.2 is given in the Appendix.

Work plan and timeline

i) Fresh switchgrass would be collected from the fields to avoid any compositional changes due to handling or storage. The collected switchgrass would then chopped and reduced in size to particles of different sizes (0.2-5 cm). The different sized particles will be used to find out the effect of size of raw material on the product quality. Chopped switchgrass would be treated in the pretreatment reactor using lime at different concentrations at room temperature to moderately high temperatures (??? 1200C), to fractionate it into cellulose, hemicellulose, and lignin. The exact form of lime, among Ca(OH)2 and CaO, would be selected based on preliminary analyses. The lime pretreatment protocol developed by Sierra et al. (2009) would be used with modifications to conduct the experimental studies. The lime pretreatment protocol is given in the Appendices section of this proposal. As mentioned earlier all the experiments would de designed using software (Design Expert 6.0.2) to find out the optimum pre-treatment conditions. The substrate concentration (10-50% (w/w)), substrate size (0.2-5 cm), moisture content (10-50% (w/w)), processing time (30-240 min.), processing methods (the sequence of addition of substrate and reagents and mixing methods), temperature (25-1200C), and chemical loadings (0.5 ??? 10% (w/w)) would vary in the experiments and analyse using response surface methodology (RSM) to find out the optimum conditions favouring the maximum yield in terms of quantity and purity of the products. The effectiveness of the treatment would be assayed by analyzing the composition of the resulting residue and different process streams using the standard analytical procedures.

ii) The resulting streams would be further treated under mild processing conditions to purify each component. These steps are known as post-pre-treatment processes. The cellulose containing solid residue will be washed to remove the remaining lime and the solubilised lignin and other components. The washed residue will be filtered and stored to study further handling and transporting mechanisms. The solid residue and the liquor parts will be analysed for their composition.

iii) Detailed technical, economical, and environmental evaluation of the process would be done for thorough understanding and future scale up of the process. Technical analysis would be done to assess the mass and energy balance of the process. It would also include a comparison with other pretreatment options; using the literature data available on pretreatment of switchgrass for biofuel production. Economical analysis would be done to estimate the scope for future scaling up and dissemination of the process. The developed process would also be subjected to an assessment in terms of its impacts on the surrounding environment and life. The latter study would be performed in the format of a life cycle analysis (LCA).

Activity

Timeline (tentative)

1.

Literature review, experimental design, work plan

0-3 months

2.

Lime pretreatment of switchgrass to optimize the treatment conditions and publication of the results

4-18 months

3.

Studies on post-pretreatment processes and publication of the results

19-24 months

4.

Comparative techno-economic and ecological studies of the developed process with other biomass pretreatment processes and publication of the results

25-30 months

5.

Preparation and submission of thesis

31-36 months

Table 1. Experimental plan of activities versus tentative timeline of the project.

Expected outcome and contribution to the knowledge

The proposed project would contribute to the advance of knowledge on pre-treatment of ligno-cellulosic biomass especially on the concept of decentralized pre-treatment for the centralized bio-refinery operations.

Pre-treatment process for the fractionation of biomass rather than hydrolyzing it would advance the knowledge in this area. It would also provide data on the different process parameters of lime pretreatment of biomass include size of the substrate, moisture content required in the substrate and the reacting mixture, type and concentration of the reagents, temperature, treatment time, and post pre-treatment processes, etc.

The proposed study would advance the knowledge on technical, economical, and ecological aspects of pre-treatment and fractionation of ligno-cellulosic biomass to its components using lime.

The outcome of the project would also give some insight into the goal of rural development and livelihood enhancement achieved through the onsite value addition of biomass and ensuring sustainable supply of raw materials for the biorefinery operations.

Study limitations

The present study focuses only on the switchgrass as the substrate for the pre-treatment studies. The study should extend to agricultural residues and hardwood substrates also. Another limitation is the range of pretreatment options to be tested in this study, processes using microorganisms and chemicals other than lime also have to be studied. The designing of the integrated biomass handling and pretreatment systems with provisions for the heat and chemicals recovery also has to be carried out before the dissemination of the study results. The new approach has to be convinced to both the biomass producers and biomass industries for the easier dissemination of the developed process. Further research works has to be conducted to produce biofuels and biomaterials at the site of biomass production and pretreatment itself.



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