Comparative economic assessment of ABE fermentation based on cellulosic and non-cellulosic feedstocks

Applied Energy 93 (2012) 193–204

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Comparative economic assessment of ABE fermentation based on cellulosic and non-cellulosic feedstocks Manish Kumar a, Yogesh Goyal a, Abhijit Sarkar b, Kalyan Gayen a,⇑ a b

Department of Chemical Engineering, Indian Institute of Technology Gandhinagar, VGEC Complex, Chandkheda, Ahmedabad 382 424, Gujarat, India Department of Economics and Management, Indian Institute of Technology Gandhinagar, VGEC Complex, Chandkheda, Ahmedabad 382 424, Gujarat, India

a r t i c l e

i n f o

Article history: Received 1 June 2011 Received in revised form 19 December 2011 Accepted 27 December 2011 Available online 24 January 2012 Keywords: Biobutanol Economic feasibility analysis Cellulosic and non-cellulosic material Design and process parameters Future economic trend

a b s t r a c t Biobutanol can become the replacement of petroleum gasoline in near future. However, economic feasibility of biobutanol production from ABE fermentation is suffering due to the unavailability of cheap feedstocks, production inhibition and inefficient product recovery processes. Here, economic analysis of ABE fermentation has been performed based on cellulosic (bagasse, barley straw, wheat straw, corn stover, and switchgrass) and non-cellulosic (glucose, sugarcane, corn, and sago) feedstocks, which are widely and cheaply available in agriculture based countries. Analysis shows that utilization of glucose required 37% lesser total fixed capital cost than the other cellulosic and non-cellulosic feedstocks for the per year production of 10,000 tonnes of butanol. However, the production cost of butanol from glucose was fourfold higher than sugarcane and cellulosic materials because of its (glucose) high cost. The cost of sago also affected threefold production cost of butanol comparative to other feedstocks. Therefore, these two substrates turned the biobutanol production far from being economically feasible. Interestingly, sugarcane and cellulosic materials showed suitability for economically feasible production of butanol with the production cost range of $0.59–$0.75 per kg butanol. Consequently, quantitative variation in the design and process parameters namely fermentor size, plant capacity, production yield using sugarcane and cellulosic materials as raw materials, trigger significant reduction in unitary cost of butanol up to 53%, 19%, and 31% respectively. Therefore, these parameters will play significant role in making the butanol production economical from cheaper feedstocks (sugarcane and cellulosic materials). Further, high sensitivity of production cost from the product yield postulates significant manipulation in genome of butanol producing bacteria for improving the yield of ABE fermentation. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction Inflation of crude petroleum prices (e.g., from $20 per barrel in 2002 to $140 per barrel in 2008 [1]) is one of the key reasons for accelerated search worldwide for energy alternatives. As a result, interest in bioconversion of alcoholic fuels (e.g., bioethanol, biobutanol, and biodiesel) is rapidly emerging as a topic of great interest to academic and industrial organizations [2]. Currently, bioethanol contributes about 20–30% in fuel market in countries like USA and Brazil whereas it is at very early stage for the development in Asia (only 3.5% share of global production of bioethanol) [3–5]. Another biofuel, biodiesel, is also growing at rates similar to bioethanol [6]. However, biobutanol attracts the attention of researchers and investors in present era due its various advantageous properties, like high calorific value, low freezing point, high hydrophobicity, and low heat of vaporization which are closer to gasoline than ⇑ Corresponding author. Present address: Department of Chemical Engineering, National Institute of Technology Agartala, Barjala, Jirania, West Tripura, Tripura 799 055, India. Tel.: +91 79 23972324; fax: +91 79 23972622. E-mail addresses: [email protected], [email protected] (K. Gayen). 0306-2619/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2011.12.079

other biofuels (Table 1) [7–9]. Unfortunately, one time commercialized acetone–butanol–ethanol (ABE) fermentation is facing severe problems due to feedstock cost, product inhibition, low ABE yield (0.28–0.33 g/g), low productivities (<0.3 g l 1 h 1) and low product concentration (<20 g l 1) [10–12]. This low yield has lead to various investigations being carried out for improving the efficiency at process level (fermentation and recovery processes) [13–19] and microorganism level [20,21]. In process development, continuous fermentation with immobilized cells has shown great enhancement leading to productivity levels of 15.8 g l 1 h 1 compared to 0.35–0.4 g 1 l 1 h 1 in batch fermentation, an increase of around 40 times [12]. In addition, such high productivity requires low volume reactors and hence, low capital and operational cost. Also, the byproducts (acetone, ethanol, hydrogen, and carbon dioxide) of ABE fermentation can contribute towards reducing production cost of butanol as their market demand are marked [22]. Fortunately, biobutanol producing organisms are able to co-metabolize multiple sugars which can be hydrolyzed from lignocellulosic materials. Different clostridial strains, namely Clostridium beijerinckii [8,13,14,18,23–30] and Clostridium acetobutylicum [31–36] have been examined for a wide

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Table 1 Comparison between physico-chemical properties of biobutanol, bioethanol, and gasoline as liquid fuel for vehicles. Gasoline and bioethanol are already being used as fuel in pure and blending manner respectively. Properties

Biobutanol

Bioethanol

Gasoline

Caloric value (MJ/l) Air–fuel ratio Heat of vaporization (MJ/kg) Research octane number Motor octane number Solubility in water

29.2 11.2 0.43 96 78 Immiscible

21.2 9 0.92 129 102 Miscible

32.5 14.6 0.36 91–99 81–89 Immiscible

range of non-cellulosic (i.e. sugar, starch [18,27,29,34]), and cellulosic materials [14,15,30,37,38]. The maximum titer of 21 g l 1 of butanol has been achieved in batch fermentation using C. beijerinckii BA101 [39], which is a mutant of C. beijerinckii NCIMB 8052 [20,21]. Before 1950, conventional raw materials for ABE fermentation were molasses and corn [11,40] and these raw materials were being used for ABE fermentation in countries like USA, Japan, India, Australia, and South Africa. Subsequently, increasing cost of traditional raw materials and introduction of cheaper petroleum fuels lead to a decline in butanol fermentation [11]. However, in recent era, biosynthesis of butanol is being motivated by the success of utilizing cost effective lignocellulosic raw materials. The common examples of these raw materials are agriculture wastes (directly from plant) like barley straw, wheat straw, corn stover, corn fibers, bagasse, and switchgrass [41], which are readily available in agriculture based countries. Therefore, the availability and low cost of these raw materials aid to establish industrial level plants. Before developing commercial scale plants for biobutanol production, the proposed techno-economic models should be evaluated for production cost of butanol. The production data for economic evaluation of future biofuel is rarely available and also depends on regional markets. Therefore, these data can be derived from limited assumptions and available detailed techno-economic models for valid comparison of production costs of biobutanol utilizing different feedstocks [1]. The techno-economical evaluations of ABE fermentation using some non-cellulosic materials (corn and molasses) and cellulosic materials (agriculture wastes) have been performed in previous studies [8,22,42–45]. This paper emphasizes on the techno-economic evaluation of ABE fermentation and comparative analysis between costs of butanol production based on various cellulosic and non-cellulosic materials as available feedstocks. Analysis also focuses on sensitivity of biobutanol price with variation of various design and process parameters. Additionally, we analyzed the future status of biobutanol production on the basis of comparison with future trends of petrochemical based butanol prices. 2. Methodologies for process design and economic feasibility analysis 2.1. Process description Clostridial species show promise for ABE fermentation using cellulosic (e.g., bagasse, barley straw, wheat straw, corn stover, and switchgrass) and non-cellulosic (e.g., glucose, corn, sago, and sugarcane) feedstocks [8,13,14,18,23–30,34]. However, in this study, the non-cellulosic feedstocks have been selected for comparative analysis as these materials are not food competitive in present world scenario. ABE fermentation process differs based on raw material availability, namely sugarcane, starchy and lignocellulosic materials as shown in Fig. 1. Here, we represent the three broad processes based on sugarcane, starchy materials (corn and sago) and lignocellulosic feedstocks, which are compatible in ABE fermentation.

2.1.1. Sugarcane The composition of sugarcane is 13.30% sucrose, 4.77% cellulose, 4.53% hemicelluloses, 2.62% lignin, 0.62% reducing sugar, 0.20% minerals, 1.79% impurities, 71.57% water, and 0.60% dirt [46]. On the basis of availability in few countries, sugarcane can be used efficiently for biobutanol production. Key steps involved in sugarcane conversion to biobutanol process are as follows: (i) extraction of sucrose from sugarcane, (ii) fermentation, and (iii) recovery of product and byproducts (Fig. 1a). Filtration is the vital step before fermentation for removing solid residues from sugarcane juice. During the conversion of sugarcane to biobutanol, two byproducts (filtration cake and bagasse) can contribute the credits in economics. Filtration cake can be utilized as fertilizers and bagasse, byproduct of milling section, have potential as substrates for biobutanol production in separate process. Currently, Brazil is the largest producer of sugarcane. Interestingly, from more than 30 years, sugarcane is being used as a feedstock for the production of bioethanol at industrial level in Brazil [46,47]. The sugarcane production has crossed 450 million tonnes per annum in Brazil. Apart from Brazil, sugarcane and its byproducts after processing in sugar industry are available in other countries like Australia, Thailand, India, Vietnam, Cuba, EI Salvador, Guatemala, Honduras, Nicaragua, Costa Rica, Peru, Colombia, Ethiopia, South Africa, and Zimbabwe [48]. However, because of consumption of less energy for pretreatment, sugarcane is more efficient than corn as a raw material for a fermentation process [49]. Along with sucrose, per ton of sugarcane consists 240 kg of bagasse with 50% humidity; nowadays it is used in boiler to generate the electricity and steam [50]. Further, bagasse may be used as a raw material for biofuel production [51] and can add values in the economics of biofuel production. 2.1.2. Corn United States produces largest amount (approximately 280 million tonnes per annum) of corn in the world, whereas china comes on second place with approximately 131 million tonnes per annum [46]. Basically, the composition of corn is 61% starch, 3.8% corn oil, 8.0% protein, 11.2% fiber and 16.0% moisture. It can be used directly and in various other forms, like degermed corn [27], extruded corn [34], and liquefied corn starch (LCS) [29], as feedstock of ABE fermentation (Table 2). Laboratory scale studies have been conducted for these forms of corn as a feedstock. On removing the corn oil through oil extraction from grains, this form of corn is called degermed corn [27]. Continuous extrusion cooking of corn kernel was developed for improving product yield, reduction in energy required, and it was helpful in utilizing mycotoxin-contaminated waste corn [34]. However, LCS is a viscous product of corn processing industry. This cost-effective substrate contains 35–40% dry solids as reducing sugars and dextrin. The concentration of glucose, reducing sugar, and sodium metabisulfite (Na2S2O5) in LCS was found approximately 5.58, 337.5, and 0.71 g l 1 respectively [29]. Corn grains can be milled in dry or wet grind plant. Dry milling includes some advantages like higher yield and low capital cost whereas, wet grinding produces more beneficial byproducts like starch, high fructose corn syrup, corn gluten feed, and corn gluten meal. In wet milling, corn grains are soaked in a mixture of SO2 and water, in a process called ‘steeping’, followed by fine grinding, screening and centrifugation for defibrication and degermination (Fig. 1b). Enzymes (amylase) are added to starch solution for its conversion in sugar and then saccharified sugar can be fermented to butanol and byproducts. 2.1.3. Lignocellulosic feedstocks Sudden rise in the petroleum prices enforced the acceleration in biofuel production from grains, sugarcane, and oilseeds, which is quite beneficial for the countries having suitable resources of

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(b)

(a) Corn Sago

Sugarcane

(c) Bagasse Barley straw Wheat straw Corn stover Switchgrass

Starchy feedstocks

Wet grinding

Wet grinding Milling

Lignocellulosic feedstocks

Bagasse Water Sulphurdioxide

Acids/Enzymes

Steeping

Hydrolysis or saccharification

Pretreatment

Filtration

Inoculum

Fermentation

Germs Fibers

Protein separation

Proteins

Dilute sulfuric acid/Alkaline peroxide

Pretreatment of fermentation inhibitors

Cake

Solid/Liquid Separation

Solid residue

Carbon dioxide, Hydrogen Enzymes

Distillation

Degermination and defiberation

Saccharification Inoculum

Fermentation

Distillation

Recovery

Recovery Inoculum

Dehydration

Fermentation

Carbon dioxide, Hydrogen

Carbon dioxide, Hydrogen

Recovery

Distillation

Dehydration Dehydration Solvent separation Acetone Ethanol

Solvent separation

n-Butanol

n-Butanol

Acetone Ethanol

Solvent separation

Acetone Ethanol

n-Butanol

Fig. 1. Schematic process flow diagram (a) from sugarcane to butanol (b) from starchy feedstocks to butanol (c) from lignocellulosic feedstocks to butanol. For stream data, like flow rate, compositions of products in broth, yield, operating pressure, and bacterial growth conditions can be seen in Table 3 and Appendix Table A.1.

Table 2 Compositions of different raw materials. Raw materials

Composition

Refs.

Sugarcane

13.30% Sucrose, 4.77% cellulose, 4.53% hemicelluloses, 2.62 lignin, 0.62% reducing sugar, 0.20% minerals, 1.79% impurities, 71.57% water, 0.60% dirt 42% Cellulose, 28% hemicellulose , 7% lignin, 11% ash 38% Cellulose, 29% hemicellulose , 24% lignin, 6% ash 20% Starch, 50–60% non-starch polysaccharides 38% Cellulose, 26% hemicellulose, 23% lignin, 6% ash 37% Cellulose, 29% hemicellulose, 19% lignin 73% Starch, 3% ash, 13% proteins 61% Starch, 3.8% corn oil, 8.0% protein, 11.2% fiber 39% Starch, 45% moisture

[48]

Barley straw Wheat straw Corn fiber Corn stover Switchgrass (Panicumvirgatum) Degermed corn Extruded corn Liquefied corn starch

[15] [13,25,38] [26] [37] [37] [27] [34] [29]

feedstocks [52]. In the case of developing countries which encompass insufficient amount of food, revolution of biofuel will enhance the insecurity of food. In this direction, two big enlightenments is being explored, namely expansions in crops cultivating techniques and developing economical strategies of biofuel production from non-food feedstocks such as lignocellulosic materials [52,53]. Lignocellulosic feedstocks, mainly agriculture wastes like sugarcane bagasse [48], barley straw [15], wheat straw [13,25,38], corn stover [37], and switchgrass [37], have potential for the production of future biofuels at commercial scale (Table 2). At the availability point of view, the lignocellulosic materials have been marked as cheaper and abundant feedstock for biofuels [53–55]. The sources of lignocellulosic materials can be wastes of

processing of crops and specifically grown crops for biofuels. Apart from agricultural wastes, crops specific for biofuels can acquire significant part of fertile land, which is being used for cultivation of food related crops. However, another option of non-waste feedstock incorporates herbaceous crops, which can be grown in low potential cropland and woody material of trees, may be from conventional forests [54]. The biocatalysts was not found effective to utilize directly lignocellulosic materials, even most of the biofuel producing microorganisms are unable to consume these feedstocks without pretreatment. The hydrolysis and pretreatment are crucial steps for utilizing lignocellulosic materials as raw material [38]. For hydrolysis, various techniques viz. dilute acid hydrolysis, steam explosion, acid-catalyzed steam explosion, wet oxidation, wet explosion, alkaline hydrolysis, ammonia fiber explosion, and enzymatic hydrolysis are reported [56]. Subsequently, hydrolysate is treated by alkali/enzymatic methods for removing fermentation inhibitors (e.g., 5-hydroxymethylfurfural (HMF), furfural, lignin, and their derivatives) followed by fermentation and recovery processes take place (Fig. 1c). 2.2. Process design and economic analysis Design of ABE fermentation and separation processes have been performed on the basis of experimental data available in literature at laboratory scale. Methodology has been developed with the help of standard chemical engineering books [57,58]. Process and equipment designing data can be seen in Table 3. The industrial data for these processes are not yet available. Therefore, rational assumptions were necessary to design the process and evaluate its economics. The plant design was carried on the basis of 10,000 tonnes butanol production per year with operation on 330 days per year. The prices of raw materials were obtained from local farmers, direct suppliers, and published data based on global

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Table 3 Detailed equipment and process design data for batch plant of biobutanol with capacity of 10,000 tonnes per annum using various feedstocks. Parameters

Value

Fermentation design Capacity of each fermentor (m3) Working volume of each fermentor Length to diameter ratio for fermentor Fermentation time (including turnaround time) (h) Thickness (mm)

500 75% 1.5 8 10

Distillation column and process design Recovery of acetone, butanol, and ethanol form fermentation broth Flow rate to recovery section (kmol/h) Number of total columns used Overall efficiency of tray Thickness (mm) Operating pressure at the top of column (atm) Tray spacing (m) Numbers of holes in tray Diameter of holes (mm) Height of enriching section (percentage of total height of column) Height of stripping section (percentage of total height of column) Column 01 (ethanol–water system) Flow rate (kmol/h) Column 02 (ethanol–acetone system) Flow rate (kmol/h) Column 03 (butanol–water system)a Flow rate (kmol/h) Column 04 (butanol–water system)a Flow rate (kmol/h)

99% 3214.40 04 0.70 10 1 0.90 20,000 2 60 40 3214.40 42.75 3166.184 84.22

a

Two separate columns are required to break an azeotrope, which is formed in butanol and water system.

market (Tables 4 and 5). The cost of building blocks for equipments and basic infrastructure was obtained from available literature of process design and manufactures [58]. It was assumed that separation of acetone, ethanol, hydrogen, carbon dioxide, and biomass will add the values in economics of production. On the completion

Table 4 Market values of various commodities for equipments and byproducts based on global market and baseline data for equipment and process design. The cost of byproducts and equipment commodities has been made on the basis of local market cost, and manufactures and data required for equipment designing have been taken from literature. Parameters

Value

Market prices of byproducts and equipment commodities Ethanol price ($/tonne) Acetone price ($/tonne) Hydrogen and carbon dioxide price ($/tonne) Residual biomass price ($/tonne) Stainless steel price ($/tonne) Carbon steel price ($/tonne)

890 810 13 180 3333.3 1111.1

Baseline for equipment and process design Plant capacity (tonnes per annum) Ratio of ABE (acetone:butanol:ethanol) in fermentation broth Yield of ABE (g/g) Capacity of each fermentor (m3) Working volume of each fermentor Length to diameter ratio for fermentor Fermentation time (including turnaround time) Recovery of acetone, butanol, and ethanol form fermentation broth Flow rate to recovery section (kmol/h) Compositions of products in broth Butanol (g/l) Acetone (g/l) Ethanol (g/l) Growth conditions Temperature (°C) Starting pH Holding pH during fermentation

Table 5 Baseline assumptions for cost of raw materials including transport costs based on global market. For non-cellulosic raw materials like glucose, sugarcane, corn, and sago, the cost was obtained from the market. Cost of cellulosic materials taken from local market survey.

10,000 3:6:1 0.39 500 75% 1.5 80 h 99% 3214.4 20 10 3.3 37 6.5 5.0

Feedstocks

Price ($/kg)

Glucose Sugarcane Corn Sago Bagasse Barley straw Wheat straw Corn stover Switchgrass (Panicumvirgatum)

1.11 0.047 0.19 0.74 0.033 0.061 0.05 0.033 0.04

of batch fermentation, centrifuges, refrigeration, and drying will be carried out for removal of biomass from broth and make it ready as cattle feed. Acetone, ethanol, and water will be separated along with butanol through distillation using four columns. The gas purification process and its cost, and storage have not been considered in this analysis. Similarly, cost of the storage for product and byproducts have not been calculated. For baseline calculation, the cost of byproducts like acetone, ethanol, hydrogen and carbon dioxide, and residual biomass were considered $810, $890, $13, and $180 per tonne respectively according to current market value. The yield of 0.39 g/g of butanol was assumed for all raw materials,

Table 6 Fixed capital cost ($) based on 10,000 tonnes per annum biobutanol production. Cost of fermentors and distillation columns and other equipments were calculated based on the production. Items

Glucose

Equipment Raw material pretreatment and processing Storage tanks 135,850 Grinding mill – Steeping/hydrolysis/ – pretreatment tanks Sieving – Centrifuge – Treated raw material tank – Pumps(3) 40,756 Fermentation Inoculum preparation tank Media preparation tank Fermentors Centrifuge Pumps(5) Recovery Distillation columns(4) Boilers(4) Heat exchangers Storage tanks Pumps(12)

Corn, sugarcane, sago, bagasse, barley straw, wheat straw, corn fiber, corn stover, and switchgrass (Panicumvirgatum)

135,850 135,850 203,780 54,341 652,100 135,850 40,756

203,780

203,780

258,120 1,358,500 923,800 67,927

258,120 1,358,500 923,800 67,927

151,660 65,214 113,750 12,133 3033.2

151,660 65,214 113,750 12,133 3033.2

Installation Piping Instruments Electrical Land Fabrication Civil Buildings

395,260 494,070 494,070 263,500 263,500 1,482,200 395,260 395,260

541,980 677,470 677,470 361,320 361,320 2,032,400 541,980 541,980

Total fixed capital cost

7,476,900

10,252,000

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3.8748

5 4

0.6294

0.6856

0.7476

0.59

1

0.59

2

1.2953

3

0.6247

Unitary production cost of biobutanol ($/kg)

5.3298

which were selected for analysis (Table 4). The yield value was taken on the basis of studies conducted for investigating the productivity of butanol [14,15,37]. For this capacity, the requirement of 11 fermentors was evaluated assuming the capacity of 500 m3 for each fermentor. Total fermentation time has been considered 80 h including turnaround time for all selected raw materials. Necessary assumptions have been made in the designing of distillative recovery according to McCabe Thiele Method. Four distillation columns were designed for the separation of ethanol (BP 78.4 °C), butanol (BP 117.7 °C), acetone (BP 56.53 °C), and water (BP 100 °C) from fermentation broth (see Appendices Fig. A.2 for details). In first distillation column, ethanol and acetone were considered as key components because of their intermediate boiling

points. Hence, in this column acetone will evaporate with ethanol as distillate and butanol will come with water as residue. The second column was designed to separate ethanol–acetone mixture obtained from first column. The residue from first column (butanol/water) also makes an azeotrope. This azeotrope can be broken through the usage of two columns in series with a decanter. The distillation columns were designed based on 10,000 tonnes of butanol production and final recovery of the products from distillation columns was expected to be 99%. The implemented methods for calculating fixed capital cost and production cost were adopted from methodologies proposed in the studies of Qureshi and Blaschek [8] and Marlatt and Datta [43] (see Appendices Table A.1 for details). The in house model for designing fermentation and recovery parts of the plant incorporating several input information like prices of materials for equipment fabrication (mainly different type of steel), prices of raw materials, capacity of the plant, capacity of each fermentor, fermentation time, product yield and desired recovery of the end product, and flow rate for recovery section. It was considered that fixed capital cost has been borrowed at an interest of 12% and taxes will be paid at 10% of total capital cost. Insurance and depreciation of plant was assumed 10% of total capital cost separately (see Appendices Table A.1). Process design calculations and simulations for cost estimation have performed using MATLAB software (Mathworks, Natick, MA, USA).

3. Results and discussion

Switchgrass

Wheat straw

Barley straw

Corn stover

Bagasse

Sago

Corn

Sugarcane

Glucose

0

Feedstocks Fig. 2. Unitary production cost ($/kg) of biobutanol from various feedstocks (cellulosic and non-cellulosic) on the basis of plant capacity of 10,000 tonnes per annum.

In the current economic analysis, we have evaluated the production cost of biobutanol from various raw materials like glucose, sugarcane, starchy materials (corn and sago), and lignocellulosic materials. Total production cost of biobutanol is contributed by cost coming from initial capital investment and cost coming from running ABE plant. Further, to study the future trends of economic

Indirect production cost

Total production cost

Glucose, $69.0226 Switchgrass, $24.7927 Corn stover, $24.39874 Wheat straw, $25.3555 Barley Straw, $25.9746 Bagasse, $24.39874 Sago, $49.25102 Corn, $31.453 Sugarcane, $24.7458 Glucose, $7.6517 Switchgrass, $10.455 Corn stover, $10.455 Wheat straw, $10.455 Barley Straw, $10.455 Bagasse, $10.455 Sago, $10.455 Corn, $10.455 Sugarcane, $10.455

Fixed capital cost

Direct production

Glucose, $53.894

$0.00

Switchgrass, $4.0857 Corn stover, $3.69174 Wheat straw, $4.6485 Barley Straw, $5.2676 Bagasse, $3.69174 Sago, $36.541 Corn, $10.746 Sugarcane, $4.0388 Glucose, $7.4769 Switchgrass, $10.252 Corn stover, $10.252 Wheat straw, $10.252 Barley Straw, $10.252 Bagasse, $10.252 Sago, $10.252 Corn, $10.252 Sugarcane, $10.252

$10.00

$20.00

$30.00

$40.00

$50.00

$60.00

Millions Fig. 3. Distribution of fixed and annual production costs (direct, and indirect costs; in millions of US$) of biobutanol production from various feedstocks; direct production costs includes raw material costs, enzymes for hydrolysis, operating labor, executive employee, waste water treatment, maintenance, operating supply, laboratory, and other process costs and indirect cost includes taxes, insurance, Interest, and plant depreciation cost (for detail see Appendices Table A.2).

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cellulosic and non-cellulosic materials. Production costs of biobutanol from glucose and sago were around $5 and $4 per kg of butanol (Fig. 2), which were much higher than rest of the feedstocks. Production costs from the other lignocellulosic materials were in the range of $0.59–$0.75 kg 1 as these materials are cheaper. In an analysis, it was observed that cost of raw material itself contributed 65% of annual production cost. Although in the case of glucose, fixed capital cost is lesser but high cost of raw material plays dominant role in increasing the butanol production cost. Concisely, Fig. 3 shows different fixed and production costs and specifically direct production cost (includes cost of feedstock) is indicating the high contribution of feedstock cost. The direct production costs fluctuated with very sharp extent over the fixed and indirect costs. Here, it should be noted that utilization of cellulosic materials adds cost of 6% of total annual production cost as enzymes (cellulases) cost for desaccharification of cellulosic materials over the utilization of other raw materials. From the analysis, it is evident that all lignocellulosic feedstocks are compatible for biobutanol production. However, food competitive raw materials (glucose and sago) are uneconomical for biobutanol production.

feasibility, sensitivity analysis of butanol prices has been evaluated with respect to process parameters (product yield and plant capacity), design parameters (fermentation size), and feedstock prices. 3.1. Estimation of capital cost The baseline plant has been designed for 10,000 tonnes/year of butanol. The capital cost has been estimated as the percentage value of equipment costs. The economics of biobutanol production based on glucose, corn, sugarcane, and sago have been evaluated to compare with lignocellulosic materials (bagasse, barley straw, wheat straw, corn stover, and switchgrass). Distillation process has been selected for recovery of end product and byproducts. The cost of equipments contributed significantly towards the capital cost of the plant. Precisely the cost of fermentors and distillation columns were estimated based on process calculation as $1,358,500 and $151,660 respectively (Table 6). In the comparison based on raw materials, the capital cost of plant for glucose as raw material was estimated approximately 37% lower than the capital cost for other raw materials. This is because glucose does not require grinding, pretreatment and hydrolysis before fermentation. Therefore, costs of these processes affect significantly to total capital cost of biobutanol production.

3.2.1. Variation in production cost with capacity of fermentors/number of fermentors Unitary production costs also vary due to the influence of various process design parameters. Fig. 4a and b shows the variation in unitary production cost of biobutanol due to the capacity of each fermentor utilizing non-cellulosic and cellulosic feedstocks. With

3.2. Estimation of production cost

400

Glucose Sugarcane Corn Sago Capacity of each fermentor

4 3 2

300 200

20

30

40

50

60

500 400 Bagasse Barley Straw Wheat straw Corn stover Switchgrass Capacity of each fermentor

300 200 100

3

10

3

100

1

(b) Cellulosic feedstocks 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5

Capacity of each fermentor (m )

500 5

Unitary production cost of biobtanol ($/kg)

(a) Non-cellulosic feedstocks 6

Capacity of each fermentor (m )

Unitary production cost of biobutanol ($/kg)

The annual production costs of butanol production (based on 10,000 tonnes butanol production/year) were estimated with

10

20

Number of fermentors

30

40

50

60

Number of fermentors

Reduction in unitary production cost of biobutanol

(c) 50 40 30 20 10

Switchgrass

Corn stover

Wheat straw

Barley straw

Bagasse

Sago

Corn

Sugarcane

Glucose

0

Feedstocks Fig. 4. Sensitivity of unitary production cost (in US$/kg) of biobutanol from variation of fermentor capacity (a) non-cellulosic feedstocks (glucose, sugarcane, corn, and sago) (b) cellulosic feedstocks (bagasse, barley straw, wheat straw, corn stover, and switchgrass) (c) percent reduction in the unitary production costs of biobutanol for cellulosic and non-cellulosic feedstocks due to decreasing the number of fermentors from 57 to 11 (or increasing the capacity of each fermentor from 100 to 500 m3; see the secondary Y-axis of (a) and (b)) for same capacity of the plant (i.e., 10,000 tonnes per annum).

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an increase in fermentor size from 100 to 500 m3 or decreasing the number from 57 to 11 for same plant capacity (10,000 tonnes butanol per year), production cost is decreased in the case of both noncellulosic (Fig. 4a) and cellulosic feedstocks (Fig. 4b). Analysis also indicates that decrement in unitary production cost is around 50% for cellulosic materials with sugarcane for variation in the number of fermentors (Fig. 4c). However, the reduction in production cost for glucose and sago is approximately fivefold lesser than for cellulosic materials and sugarcane. This is mainly due to decrement of 40% in the total feedstock cost for utilizing all selected feedstocks. Also, the high cost of glucose and sago trigger less reduction of butanol cost, during variation of designing parameters. Therefore, this process design parameter can play important role in achieving the economical production of biobutanol from cheaper feedstocks (lignocellulosic materials). However, variation in fermentor size is insensitive for economics of biobutanol from high cost feedstocks (sago and glucose). 3.2.2. Effect of capacity of plant on production cost Scale of plant capacity can be one significant design parameter for butanol production cost. Therefore, variation of production cost was estimated by varying plant capacity. Fig. 5a and b shows the decrease in unitary production cost of biobutanol utilizing noncellulosic and cellulosic material respectively due to an increase in capacity of the plant. Analysis indicates that plant capacity

enhancement from 5000 to 25,000 tonnes/annum enforces the 9% and 3% decrease in unitary production cost of biobutanol from corn and sago (Fig. 5c). Fortunately, that reduction of butanol production is elevated to 15–18% in the case of cellulosic materials and sugarcane. These differences in the reduction are encouraged by differences of feedstocks costs. On the basis of results, production cost with cheaper feedstocks (cellulosic material and sugarcane) illustrates higher sensitivity to scale of plant capacity than costly feedstocks (sago and corn) with the exception of glucose. Contribution of fixed capital cost (37% lesser than other feedstocks) was less using costly glucose as raw materials. Interestingly, analysis also disclosed that production cost is rapidly decreased with increase in plant capacity from 5000 to 10,000 tonnes/annum in the case of non-cellulosic materials (Fig. 5a). However, reduction in the production cost for cellulosic materials is decreased continuous with approximate same proportion (Fig. 5b). Therefore, for non-cellulosic materials production cost is not much sensitive to plant capacity after the optimum increase of 10,000 tonnes/annum. Also, results indicate that scaling up the capacity of the plant is one of key parameter in economics while cheaper raw materials (cellulosic materials) are used. 3.2.3. Effect of yield The effect of the yield on production cost of biobutanol was analyzed by increasing yield of ABE from 20% to 40% (theoretical

(b) Cellulosic feedstocks

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Feedstocks Fig. 5. Effect of variation in plant capacity on unitary production cost of biobutanol (a) non-cellulosic materials (b) cellulosic materials (c) percent reduction in unitary production cost of biobutanol due to increasing plant capacity from 5000 to 25,000 tonnes per year for each fermentor capacity of 500 m3.

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3.2.4. Contribution of byproducts credits Acetone, ethanol, gases (hydrogen and carbon dioxide), and biomass were the byproducts of ABE fermentation and market values of these byproducts has been shown in Table 4. Effect of above mentioned byproducts on production cost may be one crucial parameter in economics of biobutanol and therefore, analysis has been performed accounting contribution of byproduct credit. Interestingly, results demonstrated that their selling can deduce 13% of total annual production cost. The effect of selling of byproducts on unitary production cost for individual feedstocks can be seen in Fig. 7a and b. Fig. 7a shows the comparative status of unitary production cost of butanol with and without selling of byproducts of fermentation. Due to less raw material cost, selling of byproducts contributes reduction of more than onefold in unitary cost of the butanol production on the consumption of cellulosic materials. However, for costly materials (glucose, corn, and sago) this reduction was negligible in comparison to cellulosic materials. It should be noted that contribution is accountable with decrease of 45–50% in unitary production cost using cellulosic materials even it is assumed that biomass and gases have zero market value. Therefore, the contribution of credits from byproducts is very predominant factor in economics of butanol production from cellulosic materials than costly non-cellulosic materials.

maximum [22]). This variation in the yield of ABE fermentation, using cellulosic and non-cellulosic materials, generates decrement in the production cost with different proportions (Fig. 6a and b). During analysis, major decrement of approximately half-fold in unitary production cost with increasing yield was detected for glucose and starchy materials (sago and corn) (Fig. 6c). However, on the consumption of cellulosic materials, the reduction in unitary cost was varied comparatively halffold than the non-cellulosic materials. This difference is occurred owing to the fact that product yield mainly affects the running cost of biobutanol production and running cost significantly depend on feedstock cost. Therefore, the effect of increasing the yield in the case of costly feedstocks (glucose, sago, and corn) is higher than the cheaper feedstocks (sugarcane and cellulosic materials) (Fig. 6a and b). Additionally, none of feedstocks showed any irregular behavior in production costs with the variation of yield. Experimentally, maximum theoretical yield have been achieved in various laboratory scale studies [13,15], while for pilot scale and industrial scale work is still being tried. Subsequently, accountable effects of yield on production cost is suggesting the tremendous scope of genetic and metabolic engineers in improving theoretical yield through genetic modification in genome of butanol producing microorganism or transfer the butanol producing genes in tractable microorganism.

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3.2.5. Sensitivity analysis for cost of raw materials It is important to analyze the influence of variation in the costs of raw materials on production cost of butanol as it contributes a

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significant amount in total production cost. Therefore, sensitivity analysis has been performed with variation of ±50% of raw material cost. The changes in unitary production cost of biobutanol with increment and decrement of the cost of raw materials have been shown in Fig. 8a and b. The 0% variation in plots indicates the baseline cost of raw materials. Results demonstrate that unitary production cost of butanol is highly sensitive to the cost of raw materials as if the prices of costly feedstocks like glucose increases 50%, an increase of 49% was detected in unitary production cost of butanol. Fortunately, the same increment in the costs of cheaper or cellulosic feedstock enforces the merely 15–22% of increase in unitary production cost. However, in the case of glucose the increasing proportion of cost is also higher than the other feedstocks (Fig. 8a) because of its high cost or more contribution of feedstock cost in production cost. Therefore, analysis indicates that the cost of feedstock is one of the vital and sensitive economic indicators at industrial scale production and it favors towards economic feasibility of butanol from cellulosic materials. Low cost and huge availability are the major advantages of the cellulosic materials. However, the availability of these materials is seasonal. Therefore, the flexibility of processes incorporating different cellulosic materials can favor running of the plant throughout the year. Because of the high sensitivity of production cost of butanol to raw material cost, the plant location should be selected near the available feedstocks. Analysis also shows that sugarcane can be economical along with the cellulosic materials. Therefore, biobutanol production can become economical in the sugarcane-rich countries like Brazil. Although economical evaluation has been performed based on countries, where food based materials are non-sustainable for biofuel production. However, this analysis will be applicable on agricultural based countries producing huge non-cellulosic materials as wastes. 3.3. Economic trends for future

Feedstocks Fig. 7. Effect of byproduct credits on unitary production cost of biobutanol (a) comparison between unitary production cost for various feedstocks with and without selling the byproducts (b) percentage of reduction in the unitary production cost of butanol from different feedstocks. Acetone, ethanol, hydrogen, gases (carbon dioxide, and biomass) were consider as byproduct of ABE fermentation with market cost of $890/tonne, $810/tonne, $13/tonne, and $180/tonne respectively.

In present scenario, market price of butanol mainly depends on petroleum crude price. Therefore, we were interested to evaluate the butanol price based on projected crude oil price over two decades. The dependency of the modern economy on oil prices is quite unique in nature. Any fluctuation in it has potentially far reaching effect on inflation and growth prospects of an economy. However, economic decision makers mostly have to react to this price fluctuation instantaneously, and have limited ability to control it. With

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Fig. 8. Sensitivity analysis of unitary production cost of biobutanol for the variation in cost of raw materials (a) for non-cellulosic feedstocks (b) for cellulosic feedstocks. At Xaxis, the 0% shows the baseline cost of feedstocks.

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the arrival of China and India as major growth centers, and also the recent geo-political tensions, there has been sustained pressure and significant fluctuations in world oil prices in the recent past. Considering the potential adverse effects of hardening of oil prices, it is imperative on all to prepare the economies for such an eventuality, and also invest in technology development to gradually reduce this dependency over time. If a very long term view of world oil prices covering the period 1869–2009 is taken, average US and World crude oil prices in 2008 US$ were $22.52 and $23.42 per barrel respectively, and half the time the prices were below the median price of $16.71 per barrel. The average prices, however, turns out to be higher by more than $10 if the analysis is limited to the post-1970 period. The US and World average oil price for this more recent and relevant period works out to be $32.36 and $35.50 per barrel, with median oil price at $30.04 per barrel (http://www.wtrg.com/prices.htm). The recent trend in average world oil prices for the period 1996–2010 has been shown in Fig. 9a. The data is obtained from Annual Energy Outlook 2010 (Release date: July 27, 2010) published by US Energy Information Administration (http://www.eia.gov/oiaf/archive/ aeo10/index.html) and are in 2008 US$. US Energy Information Administration reports the price of imported low-sulfur, light crude oil, which is similar to the West Texas Intermediate (WTI) prices, and widely used as a proxy for world oil prices in the trade press. Based on this historical data, expected world oil prices till 2030 are projected using the Autoregressive Moving Average tech-

(a)

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nique (Fig. 9a). The projected price per barrel for 2030 at $134 (in constant 2008 US$) turns out to be almost twice the near price projection. The price per barrel in current US$ for the same year is expected to be $203 assuming a secular 2% US inflation rate. The projections are comparable to the US Energy Information Administration forecasts for the same period. Fig. 9b shows the projected prices ($ per metric tonne of butanol) over the next two decades. The projection is based on a comparison between the 1-butanol weekend production prices reported for PetroChina Daqing Petrochemical (source: http:// www.price.alibaba.com) and the weekly average of world oil prices (source: http://www.eia.gov) over the period April 2010 and March 2011. Per metric tonne prices (in Current US$) of 1-butanol ranged from $1584 to $2138, and the average world oil prices for the same period moved in the $485 to $792 per metric tonne range. The average 1-butanol production price to world oil price ratio for the period concerned works out to be 3.31. The projected butanol price over the next two decades then is obtained using the projected oil prices over the next two decades and assuming that the butanol to oil price ratio remains at the same level as over the April 2010 to March 2011 period. Result demonstrates that butanol price becomes threefold higher than current price over two decades. The expected surge in oil prices over the next two decades necessitates development of an alternative energy policy. Major investments need to be made in research and development, and also successful commercialization of these technologies. Biofuels is one such alternative source of renewable energy which can reduce our dependence on non-renewable fossil fuel. Ethanol and biodiesel are currently the two widely used biofuels, but other alternatives such as butanol are also being aggressively explored. The main challenge in popularizing such green alternatives is developing cost effective production technology. However, investment in technology development in such fields can only be expected if the future price–cost scenario allows for a possibility of economic sustainability.

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In the present work, an economic feasibility analysis of the biobutanol production was performed on the basis of available feedstocks. Further, sensitivity analysis has been evaluated on varying various process and design parameters, which shows the future economic viability of ABE fermentation from cellulosic materials as substrate. Sensitivity analysis is also vital step to acquire a rationale idea about the effect of uncertainty of feedstacks related information on the product cost. According to analysis, for a plant having capacity of 10,000 tonnes of butanol per year, total capital investment of the process based on glucose as substrate is 37% lesser than the other cellulosic and non-cellulosic materials. However, unitary production cost based on glucose is fourfold higher than sugarcane and cellulosic materials due to its higher cost ($1.11 per kg). Process based on other costly feedstock, namely sago also indicates threefold higher unitary production cost of biobutanol than cellulosic materials. Therefore, glucose and sago were enforced to be economically unfeasible for ABE fermentation due higher raw materials cost. Further, sensitivity analysis also shows the enhancement of glucose cost by 50% enforced an increase of 49% in the unitary cost of the biobutanol. Sugarcane and cellulosic materials have shown significant capability for economical production of biobutanol owing to their low costs. Unitary production costs based on these feedstocks lie between 0.59 and 0.75 per kg, which are compatible with current market price. Moreover, the elevation in the design and process

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parameters based on sugarcane and cellulosic materials, namely fermentor size, plant capacity, product yield triggered significant reduction in unitary cost of butanol up to 53%, 19%, and 31% respectively. Apparently, this remarkable sensitivity of biobutanol cost from above parameters can aid to attractive designing of plant at the economic point of view. Results also demonstrate that the selling of byproducts also can contribute beneficially in the economical production of biobutanol for low cost raw materials. Furthermore, on the basis of future economic trends, elevation in cost of butanol production from petrochemicals illustrates the huge demand of renewable sources for butanol synthesis. Acknowledgments Kalyan Gayen acknowledges financial support for the research from Institute funding, IIT Gandhinagar and funding from Department of Science and Technology, India. Authors are also thankful to J.B. Joshi and Supreet Saini for their valuable inputs.

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