A feasibility study on conversion of an ethanol plant to a butanol plant

KET050 easibility Studies on Industrial Plants Dept of Chemical Engineering, Lund Institute of Technology A feasibility study on conversion of an ethanol plant to a butanol plant Presented to StatoilHydro Oslo, Norway May 16, 2008 Principal investigators: Emil Larsson, Mark Max-Hansen, Anton Pålsson, Ragnar Studeny Tutors: Hans Eklund and Børre T. Børresen StatoilHydro Guido Zacchi and Hans T. Karlsson Department of Chemical Engineering

Summary The interest for alternative fuels is increasing in the world, mainly because of the increasing oil demand and the negative impact of fossil fuels on the environment. According to EU directives from 2003 5.75% of all transportation fuel must be represented by biofuels by the year of 2010. Today ethanol is the most common biofuel to replace gasoline and is produced from different types of biomass such as sugar, starch and cellulosic material. Cellulosic raw material is of big interest because it is widespread and is not included in the human food chain. Today the biggest producers of ethanol are Brazil and USA. An alternative to ethanol is butanol which can be produced from the same raw materials as ethanol. The main advantage with butanol is that it has higher energy density than ethanol. The energy content for butanol is 28.5 MJ/l, compared to 23.5 MJ/l of ethanol. Another advantage is that butanol does not have any corrosive properties which make it easier to distribute with existing piping infrastructure. A preliminary study has been done to investigate the possibilities to convert an ethanol plant to produce butanol. The ethanol plant uses 181 000 tons of dry spruce as raw material per year and the annual production of ethanol is 50 000 m 3. The butanol plant is based on the same amount of raw material, in this way no changes are needed in the expensive pretreatment. The butanol process is designed to use as much of the existing equipment available from the ethanol plant as possible. Basically the only change is different microorganisms in the fermentation setup. Research regarding other setups are not investigated but mentioned. The ethanol process uses bakers yeast to ferment the sugar to ethanol. In the ABE process Clostridium cultures are used instead. These bacteria yield not only butanol, but also acetone and ethanol and therefore the name ABE. The main problem with these bacteria is their intolerance towards the produced solvents, the total ABE concentration cannot exceed 20gL -1. This leads to heavily diluted broth in the fermentation, which results in more energy demanding recovery. The technical calculations were performed in Aspen Plus. Because of the great amount of water in the process both the existing distillation and evaporation steps need additional process equipment, such as distillation columns and a whole new parallel evaporation line. This is also true for the fermentation step where additional tanks are needed. A sensitivity analysis was performed in regard to the bacteria properties. This is achieved by stating seven different cases where the bacteria properties are altered in different ways. Case I is based on experimental data found in the literature, and the subsequent cases had improved selectivity towards butanol, higher sugar conversion and higher solvent tolerance. Case I: In this case the bacteria tolerate up to 20 gl -1 solvents and the conversion of the released sugars is 60 %. Page 1 of 81

The economical evaluation includes capital investment costs, payback time and operation costs for the different cases. The investment cost for the ethanol plant is assumed to be paid off. The most important parameter that affects the economical profit was identified as the tolerance towards ABE. The only cases that turned out to be profitable were cases V, VI and VII. The investment cost for case I was estimated to 41.51 million US $. The lowest investment cost was for case VI and was estimated to 29.73 million US $. The payback time for V, VI and VII, which are the only cases that are profitable, were 4.7, 3.3 and 3.5 years respectively. The payback time is based on an interest of 10 % and a deprecation time of 15 years. The butanol production cost for these three cases were estimated to 0.92, 0.87 and 0.92 $/l respectively. The largest part of the investment cost is the new evaporation line and it is also the most power demanding step in the process. A potential alternative to evaporating the stillage is using biogasfermentation, an alternative method using anaerobic microbes to ferment the compounds in the stillage into biogas, however this has not been researched, so experimental data and research needs to be made on the subject. Page 2 of 81

Table of Contents Summary... 1 1. Introduction... 5 1.1 Background... 5 1.2 Aim and Method... 6 1.3 Ethanol and butanol... 7 2. The Ethanol Process... 9 2.1 Raw material... 9 2.2 Pretreatment... 10 2.3 Hydrolysis... 11 2.4 Enzymatic hydrolysis... 11 2.5 ermentation... 12 2.6 Simultaneous hydrolysis and fermentation... 12 2.7 Distillation... 12 2.8 Dewatering... 12 2.9 Evaporation and Drying... 13 2.10 The existing ethanol plant... 14 3. The Butanol Process... 17 3.1 Cases... 17 3.2 Changes in the existing process... 18 3.2.1 ermentation... 18 3.2.2 Distillation... 18 3.2.3 Evaporation... 19 3.3 The Butanol Process Setup... 20 3.4 Energy demand... 24 3.5 Equipment dimensions... 26 4. Economy... 28 4.1 Equipment costs... 28 4.2 Operation costs... 30 4.3 Incomes... 30 4.4 Investment analysis... 31 4.4 Pay-back time... 31 Page 3 of 81

5. Alternative methods and Research.... 32 5.1 Bacteria... 32 5.2 Extraction by Adsorption... 33 5.3 Extractive fermentation... 36 6. Conclusions... 37 7. References... 39 Appendix A Hydrolysis and fermentation... 40 Appendix B Simulation in Aspen Plus... 44 Appendix C Process calculations... 46 Appendix D Investment costs... 55 Appendix E Operating cost and Income... 73 Appendix Investment costs Ethanol plant... 80 Page 4 of 81

1. Introduction 1.1 Background The interest for alternative fuels is increasing, mainly because of climate changes and increasing oil consumption. A lot of oil fields are located in unstable regions, and as a result of this a stable supply is not guaranteed. urthermore the oil is not a renewable energy source why it one day will run out. Environmentally friendly fuels produced from biomass are renewable and do not contribute to net discharge of greenhouse gases. Ethanol is one of the candidates of replacing oil as a fuel. According to EUs directives from 2003, 5.75% of all transportation fuel will be represented by biofuels in the year of 2010. This will partially be achieved by blending ethanol with gasoline [1]. Ethanol can be made from sugar or starch using bakery yeast to ferment sugar. The biggest producers of ethanol today are Brazil and USA and the most common raw materials are sugar cane and corn. Major investments are taking place around the world to produce ethanol from cellulose to increase the production. Cellulosic resources are in general very widespread and abundant and are not included in the human food chain. This makes cellulosic materials relatively inexpensive for ethanol production. No full scale factories are yet available but there are some pilot plants running, for example SEKAB in Ornskoldsvik Sweden. [2] The world production of ethanol fuel in 2005 was about 35 million m 3. The total production is predicted to increase to about 60 million m 3 until 2010 [3]. An alternative to ethanol is butanol which can be produced from the same raw materials as ethanol. Some advantages with butanol are that it has a higher energy density than ethanol and is easier to distribute because of its non corrosive properties. Butanol can also be blended with diesel up to 10%. One process for producing biobutanol is called the ABE process. This process was first used in the early 20 th century and yields not only butanol but also acetone and ethanol. During the irst World War the main product was acetone but later on butanol became the more important product, especially for the lacquers industry. The ABE process was more or less entirely replaced by butanol production from fossil fuel after the Second World War. The main problem with butanol production using the ABE process lies within the fermentation step. The microorganisms that are used in the butanol process are producing not only butanol, but also ethanol and acetone. Another problem with the microorganisms is that they are inhibited when the concentration of solvents is higher than 20g/l. Page 5 of 81

1.2 Aim and Method The aim of this project is to investigate the possibilities to convert an ethanol from biomass plant to production of butanol instead. As a starting point an ethanol plant based on calculations from LTH was used. The plant was designed to produce 50 000 m 3 ethanol per year and the raw material used was assumed to be soft wood. The re-design of the plant is based on the same amount of raw materials used in the process. This way of attacking the problem results in less modifications needed compared with redesigning to the same production capacity of fuel product. The process calculations have been done with Aspen Plus. or the economical calculations Ulrichs method was used [4]. A literature survey including a presentation of the theoretical ethanol plant and proposals for butanol processes along with microorganism data was made, and used as a basis for the following calculations. A sensitivity analysis on the bacterial properties was made, to evaluate what improvements would be significant in a production environment. The parameters studied were solvent tolerance, conversion rate and selectivity towards butanol, to see how the profitability and power demand were affected. Page 6 of 81

1.3 Ethanol and butanol Ethanol is usually what is being referred to when speaking of alcohols. Ethanol consists of two carbon, six hydrogen atoms and one oxygen atom. Applications with ethanol mainly include solvents and use in beverages. Nowadays ethanol is also being used as a fuel or at least blended in the fossil fuel. Since the oil production one day will end, a lot of research considering an alternative fuel is made. Ethanol is one of the candidates for replacing gasoline. Ethanol as a fuel has a lot of advantages, for an example it can be produced from renewable raw materials such as grains, wood or biomass. Ethanol produced in this way does not contribute to the net discharge of carbon dioxide. Another advantage is the octane number which is very high in ethanol, even higher than for gasoline. That means that the probability of auto ignition is lower which in turn leads to that the motor can be run under a higher compression ratio, which gives better efficiency. Today ethanol is blended with regular gasoline, in several countries all gasoline contains 5 % ethanol. The corresponding numbers for USA and Brazil are 10 % respectively 24 %. There are also flexi fuel vehicles (V) available on the market. These vehicles are able to run with mixtures of up to 85 % ethanol (E85) with gasoline. In the year 2007, 27 models with V technology were available on the market. Table 1 shows the octane numbers, and energy densities and other physical properties are listed for some fuels. [5] Table 1. Octane numbers and Energy densities for some selected fuels. uel Density Energy density Oxygen content Heat of vaporization Octane number (RON) Gasoline 0.74 kg/l 34.68 MJ/l 0 0.36 MJ/kg 91-99 Butanol 0.81 kg/l 28.48 MJ/l 21.6 wt% 0.43 MJ/kg 96 Ethanol 0.79 kg/l 23.58 MJ/l 34.8 wt% 0.92 MJ/kg 130 One of the disadvantages with ethanol is that its energy content is not as high as regular gasoline. Gasoline contains about 30 % more energy per liter than ethanol. To get the same amount of energy of 1 liter of gasoline, 1.4 liters of ethanol is required. Ethanol also has some corrosive properties which makes it a bit harder to distribute through existing pipelines, and may require changes to existing fuel systems to facilitate the use of ethanol in regular gasoline cars. Regarding diesel engines up to 15 % ethanol can be blended with the diesel. However minor modifications need to be done. The injection pump needs to be adjusted to give a 67 % bigger volumetric flow. Since ethanol does not ignite as easy, help with the ignition must be provided [6]. Butanol is a four-carbon alcohol that is widely used as an industrial solvent. It is produced from fossil fuels, starting with propylene which is run through a hydroformylation reaction, also known as oxo synthesis, to form butanal, which is then reduced with hydrogen to butanol [7]. Butanol can also be produced from sugars through fermentation in the so called ABE process and modifications of it. The ABE process not only yields butanol but also ethanol and acetone. The problem with the process is that the yield of butanol has been too low to make it profitable. But a lot of research is performed in order to Page 7 of 81

improve the process. or example British petrol (BP) and DuPont entered a partnership in 2003 with the goal to produce cheap bio butanol. The main goal is to improve the fermentation step to get higher concentrations of butanol. This is believed to be achieved by developing better microorganisms. The pilot plant is expected to be running in the beginning of 2009 [8]. Butanol as a fuel has a lot of attractive properties. Because it behaves almost like gasoline it is considered by many to be a better option as the next generation of biofuels compared to ethanol. The main reason why butanol is well suited as a biofuel is its high energy content. The energy content of butanol is 28.5 MJ/l, compared to the 23.5 MJ/l of ethanol. Butanol can be used in Otto engines without any modifications needed. Butanol can be blended with diesel up to 15 % butanol and used in diesel engines without modifications [1]. Butanol does not have any corrosive tendencies why it is easier to distribute than ethanol. The octane number for butanol is lower than for ethanol which means that it is a slightly more inefficient fuel compared to ethanol. Page 8 of 81

2. The Ethanol Process In this chapter the principle of producing ethanol is presented. A schematic figure over the ethanol plant is shown in figure 1. Spruce Steam Water Enzym & Nourishment Raw material Treatment Pretreatment SS Distillation Ethanol 94% Dewatering Ethanol 100% Condensate Evaporation ilter Drying Lignin igure 1. Ethanol production with enzymatic hydrolysis 2.1 Raw material To produce ethanol, sugar is needed for the fermentation. There are several raw materials that can be used as sugar sources, examples of such materials are corn (starch), sugar cane (sugar), wheat (starch) and wood (cellulose). Both cellulose and starch are built up by glucose chains and have the formula (C 6 H 10 O 5 ) n. The difference is the binding between the glucose molecules, starch has a α-binding and cellulose has a β-binding. Pretreatment is needed to break down starch and cellulose to single glucose molecules. Page 9 of 81

The reference ethanol production plant used in the present study is based on wood as a sugar source. The species of wood that is used in this process is spruce with 15% bark. Spruce can be 20-60 m tall when mature and can be recognized by their whorled branches and conical form. Wood consists of cellulose and hemicellulose fibers which are bound together with lignin. The ratio between these three is approximately 40-50 % of cellulose, 15-25 % of hemicellulose and 15-30 % of lignin. Cellulose has the formula (C 6 H 10 O 5 ) n and is a polysaccharide with a linear chain which is built up by several hundreds to tens of thousands glucose units. In contrast to cellulose, hemicellulose is built up by several different sugars, and not only glucose. It also includes xylose, mannose, galactose and arabinose. Hemicellulose consists of shorter chains than cellulose, around 200 sugar units, and has branched chains. Lignin works as the glue for the tree and keeps the fibers of cellulose and hemicelluloses together, and gives the tree its mechanical properties. Lignin is a large cross-linked macromolecule with molecular masses in excess of 10000u. The composition of spruce and its bark is seen in table 2. The fourth column shows the numbers that are used in the calculations later in this report. [3] Table 2 Raw material compositions. [3] Component Spruce Bark Model Glucan 44.0 31.3 42.1 Xylan 6.0 4.0 5.7 Galaktan 2.3 3.4 2.5 Arabinan 2.0 5.0 2.6 Mannan 13.0 4.2 11.7 Lignin 27.0 31.9 27.7 Ash - - 2.0 Other 3.5-5.8 2.2 Pretreatment The raw material is crushed into fine particles mechanically in a hammer mill, before it is hydrolyzed. If acid is used for the hydrolysis, no further preparation is needed. But if enzymes are used for the hydrolysis, further preparation is needed as the enzymes cannot hydrolyze untreated cellulose. The preparation needed for the enzymatic hydrolysis is usually called pretreatment. Several pretreatment methods are proposed. In this study the biomass is exposed to steam and acid at a high pressure and temperature, for a short time. The steam together with the acid hydrolyses the hemicelluloses and makes cellulose accessible to enzymatic attack. Page 10 of 81

2.3 Hydrolysis Cellulose and hemicelluloses must be hydrolyzed to monomeric sugars before they can be fermented. There are three ways of doing that: concentrated acid, dilute acid or with enzymes. The acid attacks the bindings randomly and are therefore not selective to the bindings between the sugar molecules. Because of this the formed sugars can be broken down to so called sugar degradation products, these products are mainly furans and acids, and are not wanted in the process, as they may inhibit the fermentation. Hydrolysis with concentrated acid and with diluted acid works the same way with the difference that the diluted acid method needs higher pressure and temperature. [3,9] 2.4 Enzymatic hydrolysis To break the cellulose and hemicelluloses to monomeric sugars, three kinds of enzymes are used, endo-glucanases (EG),cellobiohydrolases (CBH) and β-glucosidase, these enzymes are called cellulases. Simplified EG attacks the amorphous parts of the cellulose and cuts of long fragment from the chain, which creates a lot of chain ends. The CBH enzymes are then attached to these chain ends and break the chain down to cellobiose which is two glucose units. inally β-glucosidase breaks down the cellobiose into simple sugar molecules as shown in figure 2. The enzymes have maximum activity at a temperature between 50-60 0 C and ph 4,5 6,0. Compared to acid hydrolysis, this method has a better selectivity. A disadvantage with this method is that the cellulases stop working when the concentration of sugars is high. This problem is solved if the hydrolysis and fermentation step is run at the same time, using so called simultaneous scarification and fermentation (SS). The enzymatic method is also a very slow process compared to the acid method. The enzymatic method takes several days and the acid method needs only minutes. igure 2. EG attacks the cellulose, CBH then divide polysaccharides into shorter chains. inally b-glucosidase cuts it into monosacharides. Page 11 of 81

2.5 ermentation The fermentation can be run in separate stages or simultaneous with the hydrolysis. If the fermentation is separate from the hydrolysis, the solid materials mostly consisting of lignin is separated after the hydrolysis and the rest goes to the fermentation process. The fermentation is where sugars are transformed by the yeast Saccharomyces Cerevisiae into ethanol. C 6 H 12 O 6 2 C 2 H 5 OH + 2CO 2 2.6 Simultaneous hydrolysis and fermentation In SS the sugar is transformed to ethanol immediately after it is produced and therefore does not inhibit the enzymes. This method leads to a higher yield and productivity compared to the method with separate hydrolysis and fermentation steps. If the fermentation and hydrolysis are to be simultaneous, the hydrolysis must be enzymatic. A disadvantage with this method is that the enzyme cannot be reused, and that the process conditions must be chosen so that they fit both enzymes and the yeast. 2.7 Distillation After the fermentation the ethanol is separated from the byproducts using multiple stage distillation, consisting of two strippers and a rectifier column. The broth is fed into the top of the first column. The distillate contains concentrated ethanol. In the bottom of the column the byproducts, also known as stillage or syrup is obtained, and parts of this stream can be used to dilute the stream going in to the fermentation. In this way the use of freshwater can be minimized. The rest of the stillage goes to the evaporation stage. The ethanol and water vapor from the top of the first column is not free from byproducts, this stream also includes substances such as methanol, propanol and aldehydes. The separation from these substances take place in the second column called rectification column. The bottom fraction (liquid) goes with the stillage to the evaporation stage. The main goal in the second column is to obtain as pure ethanol as possible but because of an azeotrope between water and ethanol the maximum concentration of ethanol that can be obtained is 95,6 %w/w. [9] 2.8 Dewatering Because of the azeotrope in the distillation further concentration is needed. In this process a molecular sieve is used to remove water. The molecular sieve consists of synthetic zeolites, and under pressure these zeolites adsorb small molecules with dipoles. Water is such a kind of molecule and the ethanol passes through the sieve. The lower limit of water in the outgoing ethanol is 20 ppm. The sieve is saturated after 5-10 minutes and needs to be regenerated. To regenerate the sieve the pressure is lowered, hot ethanol vapor is passed through in opposite direction and the vapor brings along the water molecules. The ethanol and water is then recirculated into the distillation column. To make the process continuous more than one molecular sieve is needed. [3,9] Page 12 of 81

2.9 Evaporation and Drying There are two kinds of byproducts from the distillation, solids and dissolved byproducts. The solid part consists of mostly lignin and can be used to make pellets or be burned to produce energy for the process. The dissolved byproducts are burned to produce energy for the process. To do this the stillage needs to be concentrated. The stillage goes to a filter press where the liquid is separated from the solids. The filter cake contains non fermentable lignin residues which have a high heat of combustion and therefore is suitable to use as fuel. The liquid from the filter press is concentrated in a multiple stage evaporator to form syrup with approximately 50 % dry substance. The filter cake is dried in a steam dryer. The remaining solid material could either be burned as it is to produce energy in the process or used to make pellets which can be sold as a solid fuel. [3,9] Page 13 of 81

2.10 The existing ethanol plant This chapter gives a detailed description over the existing ethanol plant. A schematic figure of the existing ethanol plant is shown in figure 3. igure 3 Schematic figure of the existing ethanol process Page 14 of 81

The ethanol plant which is to be converted into producing butanol is described as follows. The process is dimensioned to produce 50 000 m 3 of pure ethanol per year. In the process lignin is taken out and can be sold as a fuel in form of pellets, the amount of lignin from the process is 61 000 ton per year. [3] irst there is a mill which crushes the trees into smaller parts. The mill is a high speed hammer mill and has a capacity of 22600 kg dry substance per hour. Next sulfuric acid (2 weight %) is added to start the cleaving. After that the pressure is increased to 20 bar using steam. The acid and the high pressure split the chips into smaller particles. After that the pressure is dropped in a flash chamber to atmosphere pressure. The fine particles are diluted with water before the fermentation. When diluted the temperature drops from approximately 95 degrees to 37 degrees Celsius. In the fermentation tanks yeast and enzymes are added to the mixture. The fermentation step consists of 9 stirred tanks. The tanks have a volume of 1000 m 3 each and the effective volume is 800m 3. The stream from the fermentation is heated from 37 degrees to approximate 118 degrees before entering the distillation process. In table 3 the heat exchanger areas are shown. Table 3 Heat exchanger areas. Heat exchanger HE 6 HE7 HE 8 HE9 Area (m 2 ) 55 55 140 109 The distillation process consists of two strippers and one rectifier. The trays are called donut trays are used to avoid the strippers to clog. Table 4 shows the dimensions for the strippers and the rectifier. Table 4 Dimensions for strippers and rectifier. Stripper 1 Stripper 2 Rectifier Height (m) 14.6 14.6 20.1 Diameter (m) 1.4 1.4 2.3 Number of trays 25 25 35 Rebolier area (m 2 ) 598 687 839 Condenser area (m 2 ) - - 278 Page 15 of 81

The stillage from the two strippers is sent to a filter press where the solid material is separated from the liquid. The liquid is the sent to the evaporation step. The filter cake is then sent to a drier and formed to pellets. The evaporation step consists of 5 effects. In the first effect 4 bar live steam is used as heating medium and all the following effects are driven by secondary steam from the previous effect. The sizes for the five effects are shown in table 5. Table 5 Dimensions for the evaporation Effect Area (m 2 ) 1 438 2 240 3 271 4 341 5 1288 In table 6 a summary of the important streams in the process are shown. Table 6 low rate of important streams. Mass frac (% of total flow) low Total flow (kg/h) Ethanol Temperature ( C) To distillation 131 700 3.7 37 To filter press 121 000 0.02 120 To evaporation 107 600 0.02 120 Stream 1 4938 100 35 rom evaporation 8 400 0 61 rom filter press 13 400 0 97 The energy demand for the ethanol process is presented in table 7. Table 7 Energy demand for the ethanol process Process Pretreatment Distillation Evaporators Dryer Total Energy demand (MW) 6.3 18 11 0.9 36.2 Page 16 of 81

3. The Butanol Process 3.1 Cases Seven different cases have been studied and simulated. The inhibition and bad yield of the bacteria restrict the process and therefore seven cases where the bacteria are assumed to have been improved in different ways were simulated in Aspen Plus. In the first four cases the bacteria are assumed to tolerate a concentration of 20 gl -1 produced solvent which corresponds to the maximum found in the literature for cellulose based processes. In case III and IV the sugar conversion is improved by 20 %. In case V, VI and VII the bacteria is assumed to tolerate a 20% higher concentration of solvents. Table 8 presents the important parameters in the different cases. Case I: This is the original case and based on information found [10] and referenced in appendix A. Case II: The same as case I except that the selectivity towards butanol is assumed to have been improved so that produced solvents are 98 % butanol, 1 % ethanol and 1 % acetone. Case III: The same as case I, except that the conversion of sugar to solvents is assumed to be improved by 20 %. Case IV: The same as case III except that the selectivity towards butanol is assumed to be 98 %. Ethanol and acetone are assumed to have selectivity of 1 % each. Case V: The same as case I except that the bacteria is assumed to tolerate a 20 % higher concentration before it gets inhibited and stops produce solvents. Case VI: The same as case V but assuming the same selectivity improvement as case II and IV. Case VII: The same as case IV except the tolerance is assumed to be the same as case V and VI. Table 8. Comparison between cases. The ethanol production in the existing plant was 6.25 m 3 /h I II III IV V VI VII Overall yield of solvents (%) 62 62 74 74 62 62 74 Inhibition concentration (g/l) 20 20 20 20 24 24 24 ABE ratio %wt/wt 15:80:5 1:98:1 15:80:5 1:98:1 15:80:5 1:98:1 1:98:1 Butanol production (m 3 /h) 4.2 5.0 5.0 6.1 4.2 5.0 6.1 Page 17 of 81

3.2 Changes in the existing process or process schematics, please refer to chapter 3.3. 3.2.1 ermentation The fermentation step is using the SS method, and is where the first modifications are required. The bacteria get inhibited of the produced solvents and therefore the slurry needs to be heavily diluted. The ethanol process had a ethanol concentration of 41 g/l, while the butanol process has 20-24 g/l. The plant is supposed to handle the same amount of raw material as the ethanol plant and the dilution lead to more fermentation tanks. rom the ethanol plant nine tanks with an effective volume of 800 m 3 each are available to use in this process as well. 3.2.2 Distillation The distillation setup was simulated in Aspen Plus. The design that was developed is shown in figure 4. The stream from the fermentation is split into four stripper columns. Two of them are from the existing ethanol plant and two of them have to be built. Two strippers have a pressure of 2.4 bar and are heated with live steam. The other two have a pressure of 0.9 bar so that the steam from the top of the high pressure columns can be used as heating medium in the strippers with lower pressure. In the strippers the solvents are separated from the broth. The feed contains solid material and therefore so called donut trays are used, which have bigger openings so that the solid material does not clog the stripper. rom the strippers the top product is fed to a decanter where butanol and water form two phases. The organic phase which mostly consists of butanol, acetone and ethanol is fed in a distillation column, rectifier 1, where all acetone and most of the ethanol are obtained in the distillate and water and butanol are obtained in the bottom stream. The distillate is sent to rectifier 2 where pure acetone is obtained as distillate. The butanol/water mixture is fed to a second decanter and once again two phases are formed. The organic phase is fed to one last column, rectifier 3, where the azeotrope between water and butanol are the top product and the excess of high temperature boiling butanol is taken out as the bottom product. The description above describes the distillation setup for process case I, III, V. In the other four process cases where the selectivity of the microorganism towards butanol is assumed to be higher the third rectifier and the second decanter are removed. The rectifier is removed because there are very small amounts of the other solvents and there is no need to purify these. Instead they are separated in the second rectifier and then burned. The second decanter is removed because the butanol concentration from the first rectifier is high enough to obtain pure butanol in rectifier two. To avoid product loss, streams need to be recycled. All the streams except the product and bottoms streams from the strippers are recycled to the first decanter. Page 18 of 81

igure 4 Distillation setup in the butanol process 3.2.3 Evaporation The bottom streams from the four stripper columns are sent to a filter press where solid material is separated. As the same amount of dry material is used, the filter press is assumed to be sufficient. After the filter press the liquid stream is sent to the evaporator step. The existing evaporator line cannot handle the big flow rate so one more line has to be built. The stream therefore needs to be split, the stream is split so that the live steam flow to the old evaporation plant is the same as before and the dry substance from the last effects is 60%. The old and the new evaporator lines consist of five effects. The first effect on each line has a working pressure of 3 bar and the fifth a pressure of 0.2 bar. The pressure of the other effects are 1.7, 0.9 and 0.45 bar respectively. In the first effect 4 bar live steam is used as heating medium and all the following effects are driven by secondary steam from the previous effect. The concentrated evaporation residue is burned to generate steam to the process. The filter cake is dried in a steam dryer and then formed to pellets. In the case of energy shortage, some or all of the filter cake will be burned to produce live steam. Page 19 of 81

3.3 The Butanol Process Setup On the following pages, process setup for cases I, III and V will be presented, together with a summary of the important streams in the process shown in table 9-11. The process setup for cases II, IV, VI and VII are seen in figure 6 and the important streams are shown in table 12-15. igure 5 Butanol process setup case I,III,V, grey symbols indicate existing equipment. Page 20 of 81

Case I Table 9. Resulting data for important streams, Case I Mass frac (% of total flow) low Total flow (kg/h) Butanol Ethanol Acetone Temperature ( C) To distillation 245 582 1.4 0.08 0.4 37.0 To filter press 232 682 0 0 0 113.9 To evaporation 225 310 0 0 0 113.9 Stream 1 935 0 0 100 28.0 Stream 2 265 6 68 1 54.8 Stream 3 3 406 100 0 0 90.5 rom evaporation 9 395 0 0 0 62.8 rom filter press 225 310 0 0 0 113.9 Case III Table 10. Resulting data for important streams, Case III Mass frac (% of total flow) low Total flow (kg/h) Butanol Ethanol Acetone Temperature ( C) To distillation 288 850 1.4 0.4 0.4 37.0 To filter press 283 363 0 0 0 113.9 To evaporation 267 632 0 0 0 113.9 Stream 1 1 117 0 0 100 28.0 Stream 2 283.2 2.6 70 8.5 49.7 Stream 3 4 087 100 0 0 90.4 rom evaporation 6 270 0 0 0 62.7 rom filter press 15 731 0 0 0 113.9 Case V Table 11. Resulting data for important streams, Case V Mass frac (% of total flow) low Total flow (kg/h) Butanol Ethanol Acetone Temperature ( C) To distillation 207 504 1.7 0.09 0.5 37.0 To filter press 202 896 0 0 0 113.9 To evaporation 187 163 0 0 0 113.9 Stream 1 935 0 0 100 28.0 Stream 2 265 6 68 0.9 54.8 Stream 3 3 407 100 0 0 90.4 rom evaporation 9 339 0 0 0 62.9 rom filter press 15 732 0 0 0 113.9 Page 21 of 81

igure 6 Butanol process setup case II, IV, VI and VII, grey symbols indicate existing equipment. Page 22 of 81

Case II Table 12. Resulting data for important streams, Case II Mass frac (% of total flow) low Total flow (kg/h) Butanol Ethanol Acetone Temperature ( C) To distillation 245 414 1.7 0.02 0.02 37.0 To filter press 241 177 0 0 0 113.5 To evaporation 225 505 0 0 0 113.5 Stream 1 150 8 33 42 50.9 Stream 2 4 087 100 0 0 90.5 rom evaporation 9 460 0 0 0 62.9 rom filter press 15 672 0 0 0 133.5 Case IV Table 13. Resulting data for important streams, Case IV Mass frac (% of total flow) low Total flow (kg/h) Butanol Ethanol Acetone Temperature ( C) To distillation 269 521 2 0.02 0.03 37.0 To filter press 264 450 0 0 0 113.3 To evaporation 248 755 0 0 0 113.3 Stream 1 155 2 39 49 45.6 Stream 2 4 916 100 0 0 90.4 rom evaporation 6 261 0 0 0 62.7 rom filter press 15 694 0 0 0 113.3 Case VI Table 14. Resulting data for important streams, Case VI Mass frac (% of total flow) low Total flow (kg/h) Butanol Ethanol Acetone Temperature ( C) To distillation 193 406 2.2 0.028 0.035 37.0 To filter press 189 169 0 0 0 113.7 To evaporation 173 456 0 0 0 113.7 Stream 1 150 8.2 33 42 50.8 Stream 2 4 087 100 0 0 90.4 rom evaporation 9 365 0 0 0 62.9 rom filter press 15 710 0 0 0 113.7 Page 23 of 81

Case VII Table 15 Resulting data for important streams, Case VII Mass frac (% of total flow) low Total flow (kg/h) Butanol Ethanol Acetone Temperature ( C) To distillation 227 140 2.2 0.028 0.035 37.0 To filter press 222 070 0 0 0 113.3 To evaporation 207 690 0 0 0 113.3 Stream 1 155 2 39 49 45.5 Stream 2 4 916 100 0 0 90.4 rom evaporation 6 260 0 0 0 62.7 rom filter press 15 710 0 0 0 113.3 The annual production of butanol, acetone and pellets for the different cases are shown in table 16. Table 16 Annual production of butanol, acetone and pellets Product Butanol (m 3 /year) Acetone (m 3 /year) Pellets (ton/year) Case I 33 700 9 500 0 Case II 40 400 0 0 Case III 40 400 11 300 0 Case IV 48 600 0 0 Case V 33 700 9 500 0 Case VI 40 400 0 5 100 Case VII 48 600 0 0 3.4 Energy demand The process steps that need steam are divided into four posts: pretreatment, distillation, evaporation and drying. The theoretical energy demands for the process were calculated with Aspen Plus, a description of how the simulations were performed is shown in appendix B. There are two kinds of live steam in the pretreatment, 4 bar steam to heat the incoming wood and 20 bar steam to use in the high pressure dilute acid hydrolysis pretreatment. In the distillation, 4 bar live steam is used to preheat the streams and to heat the boilers in the high pressure strippers. The rest of the columns use steam from the strippers so the energy used in these are not included here. Steam with the pressure of 4 bar is used to heat the first two evaporators. In the pretreatment after the acid step there is a flash that gives 4 bar steam that can be used to heat the evaporators. The steam from the pretreatment is not enough to heat the evaporators and live steam is used to cover the energy shortage. The total power demand in MW for cases I-VII is presented in table 17. Page 24 of 81

Table 17 Total theoretical power demand in MW Process Pretreatment Distillation Evaporators Dryer Total Case I 18.6 23.6 19.4-61.6 Case II 18.6 23.1 19.5-61.2 Case III 18.6 28.0 25.0-71.5 Case IV 18.6 25.2 29.7-73.5 Case V 18.6 19.9 14.7-53.2 Case VI 18.6 18.4 13.1 0.35 50.5 Case VII 18.6 18.2 17.9-54,7 The steam is generated in a boiler where the syrup from the evaporation is used as fuel. If the energy from the syrup is not enough the lignin from the filter press can also be used in the burner. The burner has been assumed to have an efficiency of 90 %. Because of the high energy demand all of the lignin and the syrup have to be used as fuel in cases I-V and VII. In case VI some of the lignin has to be burned, and this has to be optimized so that the most possible amount of lignin can be used to produce pellets. Table 18 presents the actual energy need and the energy produced in the boiler. This process uses substantially more energy in comparison with the ethanol process, why the existing boiler might be under dimensioned, which leads to additional investments. This is however not considered in the present study. Table 18 Realistic energy demand and production. Process Power from boiler (MW) Power demand for live steam generation (MW) Surplus (MW) Demand (MW) Case I 59.1 68.4-9.30 Case II 58.7 68.0-9.27 Case III 52.8 79.5-26.7 Case IV 52.6 81.6-29.0 Case V 59.4 59.1 0.23 - Case VI 56.1 56.1 0.05 * - Case VII 52.5 60.8-8.3 * Some of the filter cake is used to produce pellets, with a total effective combustion power of 2.82 MW. The energy demand per m 3 produced butanol is shown in table 19. Table 19 The energy demand per m 3 produced butanol Case I II III IV V VI VII (MJ/m 3 ) 58 600 49 000 57 200 48 200 50 700 40 400 36 100 Page 25 of 81

3.5 Equipment dimensions Tables 20 through 26 shows the equipment necessary to retrofit the existing ethanol plant. More specific data on each apparatus will be presented in appendix E. Table 20. Heat exchangers 1-5, preheating distillation Case I II III IV V VI VII HE 1 (m 2 ) 75 75 75 75 75 75 75 HE 2 (m 2 ) 80 80 80 80 80 80 80 HE 3 (m 2 ) 139 148 165 169 115 114 122 HE 4 (m 2 ) 21 26 25 31 21 26 31 HE 5 (m 2 ) 21 20 19 18 16 20 18 Table 21. Design data for Stripper 1 Stripper 1 Case I II III IV V VI VII Diameter (m) 1.2 1.3 1.6 1.4 1.3 0.9 1 Height (m) 10.4 10.4 10.4 10.4 10.4 10.4 10.4 Area boiler (m 2 ) 393 281 218 331 267 162 192 Number of trays 17 17 17 17 17 17 17 Table 22. Design data for Stripper 2 Stripper 2 Case I II III IV V VI VII Diameter (m) 1.3 1.2 1.8 1.5 1.2 1.1 1.4 Height (m) 10.4 10.4 10.4 10.4 10.4 10.4 10.4 Area boiler (m 2 ) 572 222 768 280 387 132 252 Number of trays 17 17 17 17 17 17 17 Table 23. Design data for Rectifier 1 Rectifier 1 Case I II III IV V VI VII Diameter (m) 1.2-1.2-1.2 - - Height (m) 10.4-10.4-10.4 - - Area boiler (m 2 ) 146-147 - 148 - - Area Condenser (m 2 ) 62-65 - 62 - - Number of trays 17-17 - 17 - - Page 26 of 81

Table 24. Design data for Rectifier 2 Rectifier 3 Case I II III IV V VI VII Diameter (m) 1.5 1.3 1.4 1.6 1.2 1.2 1.6 Height (m) 10.4 10.4 10.4 10.4 10.4 10.4 10.4 Area boiler (m 2 ) 26 16 26 12 13 10 12 Area Condenser (m 2 ) 21 23 23 45 16 20 24 Number of trays 16 16 16 16 16 16 16 Table 25. Design data for Evaporators Case I II III IV V VI VII Area effect 1 (m 2 ) 560 515 670 600 385 335 445 Area effect 2 (m 2 ) 520 525 680 615 390 340 460 Area effect 3 (m 2 ) 640 540 830 750 480 420 550 Area effect 4 (m 2 ) 730 735 945 855 550 480 604 Area effect 5 (m 2 ) 3 750 3 750 4 810 4 350 2 800 2 450 3 250 Table 26. Design data for Decanters Case I II III IV V VI VII Decanter 1 L (m) 4.3 4.1 4.6 3.8 4.1 3.8 3.8 D (m) 1.4 1.4 1.5 1.3 1.4 1.3 1.3 Decanter 2 L (m) 2.4-2.6-2.4 - - D (m) 0.8-0.9-0.8 - - Page 27 of 81

4. Economy 4.1 Equipment costs The calculations involving the process equipment cost only include the costs for the additional equipment. Ulrich s method [4] was used. Ulrich method consists of databases for purchased equipment costs (Cp). Adjustment factors such as for installation, P for pressure and M for material choice are then introduced to calculate the bare module cost C for each process unit (see equations below). This value contains the direct and indirect cost for every process unit. The reaction enthalpy during fermentation has not been considered and therefore no heat exchanger costs are calculated for the fermentation step. [3] C =C p C =C P P M The bare module cost (C ) is calculated in US $ from 1982. To update the costs Marshall and Swift equipment cost index was used, however the latest index available was from 2004 which has been used in this study. MS2004 C 2004 C where I MS1982 I I I MS2004 MS1982 1175 746 Compared to the ethanol plant changes in fermentation and distillation are needed. However because of a significant increase of water in the process, changes in the evaporation unit has to be done as well. All the economy calculations are shown in appendix D. Table 27 presents the bare module costs in 2004 US $. Table 27. Bare module costs for case I-VII in million US $ (2004) Process unit Case I Case II Case III Case IV Case V Case VI VII Hydrolysis/ ermentation 3.91 3.91 5.03 5.03 2.80 2.80 3.35 Pre heating 0.35 0.36 0.35 0.37 0.32 0.32 0.33 Distillation 3.73 2.25 4.45 1.56 4.45 1.17 1.89 Evaporation 33.45 33.27 39.69 36.62 28.11 25.37 31.0 Pumps 0.065 0.065 0.065 0.065 0.065 0.065 0.065 Total 41.51 39.86 49.59 43.65 35.75 29.73 36.6 Page 28 of 81

The largest investment costs appear in Case III and Case IV. In these cases the conversion of sugars to ABE is better. To avoid inhibition of the bacteria more water must be added to keep the concentration of ABE to the maximum of 20 g/l. The lowest investment costs are for Case V and VI and this is where the bacteria are assumed to be more resistant towards the solvents and therefore less water is needed in the process. A more fair comparison between the cases is to calculate the investment cost per m 3 produced butanol which is shown in table 28. Table 28 Investment cost/m 3 butanol Case I II III IV V VI VII Investment cost / butanol ($/m 3 *year) 1235 997 1240 895 1063 744 755 The result shows that case VI has the lowest investment cost per m 3 produced butanol. Page 29 of 81

4.2 Operation costs The operation costs include all the factors that are necessary to run the process. These factors are, with belonging costs, identified and presented in table 28. The fixed costs are the costs of keeping stock. The costs are presented in 2004 US $ per year. or more detailed calculations see appendix E. Table 29 Annual operating costs in million US $ ixed capital Case I Case II Case III Case IV Case V Case VI Case VII Wood 0.23 0.23 0.23 0.23 0.23 0.23 0.23 SO 2 0.0043 0.0043 0.0043 0.0043 0.0043 0.0043 0.0043 Pellets( to burner) 0.068 0.068 0.2 0.21 0 0 0.061 Enzyme 0.076 0.076 0.076 0.076 0.076 0.076 0.076 Butanol 0.13 0.16 0.16 0.19 0.13 0.16 0.19 Acetone 0.029 0 0.035 0 0.029 0 0 Pellets 0 0 0 0 0 0.0085 0 Repair parts 0.013 0.013 0.015 0.011 0.012 0.01 0.01 Direct variable costs Raw material 21.64 21.64 21.64 21.64 21.64 21.64 21.64 SO 2 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Enzymes 7.14 7.14 7.14 7.14 7.14 7.14 7.14 Pellets 6.4 6.36 18.3 20 0 0 5.72 Electric energy 0.02 0.02 0.02 0.02 0.02 0.02 0.02 Maintenance reparation 0.13 0.13 0.15 0.11 0.12 0.1 0.109 Process operators 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Shift management 0.18 0.18 0.18 0.18 0.18 0.18 0.18 Laboratory staff 0.18 0.18 0.18 0.18 0.18 0.18 0.18 Indirect variable costs Overhead personal 0.97 0.97 0.97 0.97 0.97 0.97 0.97 Administration 0.24 0.24 0.24 0.24 0.24 0.24 0.24 R&D 0.8 0.81 1.06 1.1 0.68 0.68 0.783 Total (U i ) 39.85 39.82 52.20 53.90 33.25 33.24 39.15 4.3 Incomes The income come from selling the produced butanol and in some cases the acetone and the pellets. The butanol is assumed to be sold at a price of 1.11 US $/liter and the acetone 0.87 $/liter. [3,11] The butanol price is based on the selling price of ethanol which is 0.92 US $/liter [3]. To be able to compete with ethanol, the price for each energy unit cannot be higher in butanol than ethanol. In table 30 a compilation of the annual income is presented see Appendix E Page 30 of 81

Table 30 Annual income from products in million US $ Case I Case II Case III Case IV Case V Case VI VII Butanol Sales 37.37 44.8 44.8 53.89 37.37 44.8 53.9 Acetone Sales 8.18-9.77-8.18 - - Pellets Sales - - - - - 0.87 - Total 45.6 44.8 54.6 53.9 45.6 45.7 53.9 4.4 Investment analysis The depreciation of capital cost is estimated using the annuity method. The depreciation of capital cost together with the operation costs will represent the total annual production costs. To calculate a production cost for the butanol the total annual production costs are divided with the annual volume produced butanol. The base investments were assumed to have a depreciation of 15 years with a real interest rate of 10%. The annuity factor f A =0.13 was used. See Appendix E. The production cost for butanol is presented in table 31. Table 31 Calculated butanol production cost in US$/L Case I Case II Case III Case IV Case V Case VI Case VII Butanol production cost 1.13 1.14 1.24 1.23 0.92 0.89 0.92 The price of butanol is set to be able to compete with ethanol, in cases I-IV the production costs per liter is higher than the competitive price. In case V and VI the production costs is lower than the market price and a profit can be obtained. 4.4 Pay-back time To calculate the number of years needed to pay back the investment the pay-back method is used. The results are presented in table 32. Detailed calculations are shown in appendix E. Table 32 Number of years needed to pay back the investment Case I Case II Case III Case IV Case V Case VI Case VII Pay-back year - - - - 4.7 3.3 3.5 Only three cases have an opportunity to pay back the investment. The three cases with a payback time within 15 years are V, VI and VII. In these cases the bacteria is assumed to be more resistant towards ABE. The most important parameter to make the process economically feasible is the resistance towards the produced ABE. The selectivity towards butanol does not affect the economy as much as expected. Page 31 of 81

5. Alternative methods and Research. To rectify some of the problems associated with butanol fermentation, such as low solvent tolerance, and low selectivity towards butanol, and low conversion rates, research is being done in ways to extract the solvents from the fermentation broth, to maintain a low concentration of solvents, and thereby increase conversion rates. urthermore a lot of research is being done on the microorganisms, and other bacteria, such as E. Coli are genetically modified to produce butanol. 5.1 Bacteria Acetone, butanol and ethanol are produced by solventogenic Clostridia. The most commonly used microorganism is Clostridium acetobutylicum. However the relatively new developed Clostridium beijerinckii BA 101 is more attractive because it produces higher concentrations butanol. C.acetobutylicum produces butanol concentrations in the range of 10-16 gl -1 whereas C.beijerinckii produces butanol in the range of 18-25 gl -1. [13] The concentration of ABE in the fermentation is limited due to the toxicity for the culture. The highest possible concentration of ABE is 20 gl -1. [14] In acid hydrolysis of agricultural biomass compounds such as furfural, hydroxyl methyl furfural (HM), ferulic-, acetic, glucuronic, r-coumaric acids are produced. These compounds are often associated with inhibitory effects on microorganisms. r-coumaric- and ferulic acids decreases the ABE production and bacteria growth significantly. urfural and HM are not inhibitory to C. Beijerinckii BA 101; rather they have stimulatory effect on the growth of the microorganisms and ABE production. Acetic acids are not considered to have any inhibitory effects [10]. The robustness of clostridium is considered stable enough for industrial fermentations. Compared to ethanol producing organisms, clostridiums are able to produce solvents from both hexoses and pentoses. In figure 7 the ABE production from different types of sugar is presented. [10] Page 32 of 81

igure 7 Production of ABE from individual sugars (55g/l) using C.beijerinckii Ba 101 [10]. Another type of bacteria that is reported to be able to produce butanol from biomass is E-coli. By leveraging the native metabolic networks in E-coli and alter its intracellular chemistry scientists at UCLA claims the bacteria produces butanol from glucose. The produced butanol includes: isobutanol, 1-butanol, 2-methyl-1-butanol and 3-methyl-1-butanol. In particular the research team achieved high yield, high-specificity production of isobutanol from glucose [15]. This may be an interesting application in the future. However it still remains on the research stage. No data regarding these bacteria is yet available and therefore no calculations performed in the subject. 5.2 Extraction by Adsorption The extraction by adsorption is based on the use of a solid phase adsorbent [16], to adsorb the desired product. Silicalite has been found to be very selective towards the adsorption of butanol [17]. This results in a stream of concentrated butanol, with up to 10% wt/wt of water and acetone and ethanol, which is good because it is above the binary water-butanol azeotrope. [7] There are a few different methods to achieve this, such as using two adsorption towers, see figure 9. By loading on one of them and regenerating the other at the same time, continuous operation can be achieved. The adsorbed species are desorbed by heat treatment, with a temperature ramp up to 200 C, which is far below the degradation temperature of the silicalite, which is 1000 C. This method produces a stream consisting of over 90% butanol, which needs to be distilled to reach 100%, but the energy amount that is saved, when compared to distilling it with a feedback to break the azeotrope is substantial. Page 33 of 81

This process however requires a substantial amount of silicalite, due to the adsorption capacity of silicalite being 97g / kg, with only ethanol and butanol, or 48g / kg when used in an ABE-system. This would lead to approximately two columns of 50 ton each, under the assumption that the loading and desorption times would be 2. 30 minutes. igure 9. Bioreactor and Adsorption columns for continuous adsorption/desorption. One problem with this method is that it is uncertain how the microorganisms will react to the silicalite, and that SS results in solids in the fermentation broth. A way to work around this is to use an ultrafiltration membrane, to make sure that the cells, and other solids, stay in the fermentation loop, see figure 10. igure 10. Bioreactor with U membrane and two adsorption columns. This method keeps the cells and solids in the bioreactor, and uses simultaneous adsorption/desorption Page 34 of 81