Biofuels are a potential candidate for enhancing the energy security of countries that are currently dependent on petroleum imports. The most abundant bioenergy feedstocks are lignocellulosic materials. Bioethanol is one of the biofuels that can be produced from lignocellulosic feedstocks and can be blended with gasoline. The lignocellulosic materials can be grouped into three main categories; agricultural, forestry and recycled materials. Agricultural and forestry materials includes material left in fields after the crop has been harvested, such as corn stover, wheat stalks and bagasse from sugar cane, dedicated energy crops such as switch grass, and trees. Recycled materials include waste office paper, newspapers and other mixed papers. Collectively, they are called lignocellulosic biomass and consist of two basic constituents: carbohydrate polymers (called cellulose and hemicelluloses) that can be converted to sugars, and a non-fermentable fraction called lignin that can be burned for production of electricity and/or heat. The key steps in lignocellulosic bioethanol production are pretreatment, enzymatic hydrolysis, fermentation and recovery of the non-fermentable fraction (e.g. lignin).

Of the various available lignocellulosic feedstocks some have been considered to be less tractable because the pretreatment required to make them usable includes acid hydrolysis or steam explosion with an acid catalyst. These pretreatments may lead to negative impacts on downstream processing and may lower ethanol yield or lower the value of recoverable by-products. Also, the acidic reactants may cause corrosion and require expensive materials for the processing equipment. Another technology for producing bioethanol from woody materials is gasification, followed by fermentation to ethanol using anaerobic bacteria. This eliminates the need for hydrolysis to break up the cellulose and hemicellulose fractions of the biomass. In this process, the lignin fraction can also be converted into ethanol. The choice of best conversion method is based on the properties of the feedstock. The presence of more sugars and starch makes a feedstock much desirable for ethanol production because sugars and starch are much easier to convert to ethanol than cellulose and hemicellulose. Fibrous materials may contain more cellulose, hemicellulose, lignin and lesser sugars than non-fibrous materials. Furthermore, the amount of lignin, moisture, ash and silica also affects the conversion process.

Ethanol industry is primarily based on relatively expensive starch feedstocks such as corn, although some potato processing residuals are also used. Integration of new lignocellulosic feedstocks that are regionally available into these facilities has not been demonstrated at a sufficiently meaningful scale to evaluate the technical and cost implications. This study will categorize and compare lignocellulosic feedstock options for a bioethanol plant. If successful, this work will enable the utilization of lignocellulosic feedstocks for the production of fuel-ethanol, and will lower the production cost of ethanol.

Conversion of biomass to ethanol is based on the chemical properties of the feedstock. For example, fibrous materials may contain more cellulose, hemicellulose, lignin and less sugars, than non-fibrous materials. The presence of more sugars and starch makes a feedstock more desirable for ethanol production, because sugars and starch are easier to convert to ethanol than cellulose and hemicellulose. Furthermore, the amount of lignin, moisture, ash and silica also affects the conversion process. Table 1 shows the composition of various biomass feedstocks and table 2 shows the ultimate and proximate analysis of biomass feedstocks.

Table 3 shows estimates of the operating cost to produce alternate fuels taken from Wright and Brown [1]. The figure for the operating cost of a grain ethanol plant and for a cellulosic ethanol plant can be considered to reflect the relative difficulty of conversion of cellulosic material to ethanol compared with grain-based ethanol. For grain ethanol and cellulosic ethanol, these operating cost estimates convert to $170/metric ton and $245/metric ton, respectively.

The quantity of ethanol is based on the composition of the feedstock. For example, some materials may contain more cellulose, hemicellulose, and less lignin and other materials. Since the lignin cannot be converted to sugars and fermented to ethanol it reduces the yield of ethanol per ton of biomass. Table 1 shows the theoretical ethanol yield of various feedstocks. The amount of fermentable sugars in a lignocellulosic material is one of the important parameter in selecting feedstock for lignocellulosic ethanol production. Therefore the percentage of lignin and sugar content in feedstock determine the best feedstock for ethanol production. Experiments were done on regionally available feedstocks kenaf, douglas fir and black locust. The sugar and lignin content were determined to demonstrate their potential of as feedstock for bioethanol plant.

Among the various available woody biomass feedstocks Kenaf, Douglas Fir and Black Locust samples were used. The Kenaf samples were given by Pacific Northwest National Laboratory, Richland, WA. The lignin and sugar content were compared. The samples were milled and were classified to pass a 0.5 mm-mesh screen.

The average lignin content of Kenaf₁, Kenaf₂, Douglas fir and Black locust is 10.96%, 8.99%, 20.49% and 20.89% respectively, and average total sugar content is 59.64%, 80.43%, 56.54% and 55.68% respectively. Table 4 shows the determined values for lignin and sugar content of the various samples. Figure 1 is the bar chart showing the comparison of the experimental results. The difference in lignin content of Kenaf₁ and Kenaf₂ is due to difference in working conditions and environment parameters.

The percentage of sugar content in Kenaf is more and lignin content is less than other species (refer Table 4). As ethanol yield is directly related to amount of sugars in the feedstock and inversely related to amount of lignin. Therefore we may say that among selected samples, Kenaf is a better lignocellulosic feedstock for ethanol production. The next step is to produce ethanol by fermentation of the produced sugars and compare ethanol yield. The experimental yield will be compared with the theoretical yield (Table 1).

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