MEMORANDUM

Subject: Assessment of Advanced Biofuel Technologies
From: Lester Wy borny Chemical Engineer
To: EPA Air Docket Number EPA

- HQ

- OAR

- 2010

- 01 33
1. Background Information of Cellulosic Biofuel Production The biochemical conversion of cellul osic biomass to fuels requires a detailed understanding of the chemistry of the cellulosic biomass. Unlike grain feedstocks where the major carboh ydrate is starch, lignocellulosic biomass is composed mainly of cellulose (40

- 60 % ) and hemicellulose (20

- 40 % ). The remainder consists of lignin, a complex poly mer which serves as a stiffening and hy drophobic (water

- repelling ) agent in cell walls. 1 Cellulose and hemicellulose are made up of sugars linked together in long chains called pol ys accharides . Once hy drol yz ed, they can be fermented into ethanol. Currently , lignin cannot be fermented into ethanol , but could be burned as a b y - product to generate electricit y or converted by the other technologies discussed in this document into biofuels

. Both starch ( e.g. corn grain) and cellulosic feedstocks must be hydrolyzed prior to fermentation. Structural differences at the molecular level make it far more difficult, and therefore more costly , to hydrol yz e cellulosic biomass than it is to hydrolyze starch. Gl ucose, C 6 H 12 O 6 , the repeating monomer in both starch and cellulose, is a six

- sided ring, similar in conformation to the classic ‘chair’ conformation of cyclohexane or benzene, except one carbon atom in the ring is replaced b y an ox ygen atom. For uniformity (and ease) of discussion, it is generall y assumed that the first carbon atom next to the ox ygen, is carbon #1; the numbering, 2

- 5, continues around the ring with oxygen in the 6 th position; one of the four bonds of the fifth carbon atom is attached to th e ox ygen atom to complete the ring, one is attached to hydrogen atom and the fourth to a - CH 2 OH group. Thus, a glucose molecule/monomer is a six

- sided molecule, but not a six

- carbon ring (although there are six

- carbon molecules present, one of which is in the

– methylhydrox y group). The main difference between starch and cellulosic plant matter is that starch poly saccharides are made up of  - glucose monomers, uniformly strung together by  - linked 1,4

- glucosidic bonds whereas cellulosic poly saccharides ar e made up of β

- glucose monomers, strung together through β

- linked 1,4

- glucosidic bonds. In starch with the  - conformation, the h ydroxyl group on carbon #1 is in the axial or  - position, which causes the

- OH’s on each successive glucose monomer to end up o n the same side of the poly mer. There are also 1,6

- linked glucose branches that occur irregularly on approximately

one in twenty

- five glucose units. 2 The

- OH groups on the same side of the poly mer, along with the randoml y attached 1,6

- glucose branches, leaves starchpoly

mers relativel y weak, flexible, and able to easily wrap and twist together to form tiny granules ( e.g., common, everyday corn starch ). Cellulosic poly saccharides are in the β

- conformation with the hydrox yl group on carbon #1 is positioned away from the ring, in the equatorial or β

- position, which causes the

- OH’s on each successive glucose monomer, added to the chain, to end up on opposi te sides of the polymer. The h ydrox yl groups lined up evenly and uniformly

along opposite sides of each poly mer strand allow intra

- molecular h ydrogen bonds to develop within each monomer. They also allow inter

- molecular hydrogen bonds to develop between adjacent poly

mers to form tight, rigid, strong, mostly straight pol ymer bundles called microfibrils that act as the core constituent in the formation of plant cell walls that are also ins oluble in water and resistant to chemical attack. The β

- conformation and the resulting h ydrogen bonds stabilize the glucose chair structure to help minimize the poly mer’s flexibility

(which hinders h ydrol ys is) and to add to its strength. The second cel lulosic component is called hemicellulose. It consists mainly of a random mixture of highly branched and heavily substituted five

- and six

- carbon rings. The five

- carbon residues are usuall y D

- xylose and L

- arabinose; the six

- carbon residues are usuall y D

- galactose, D

- glucose, and D

- mannose, and uronic and acetic acid. Hemicellulose is not as rigid or strong as cellulose, but does contribute additional strength and helps protect the plant cell wall against attack by microbes or water. Hemicellulose is rel atively easy to hydrol yz e, due to its highly branched, somewhat random or non

- uniform structure.
Li gnin, the third principle component, is a complex, cross

- linked poly meric, high molecular weight substance derived principall y from coniferyl alcohol b y ex tensive condensation poly

merization. Covalently

bonded to the hemicellulose, it is essentially a glue

- like pol ym er that covers the cellulose and hemicellulose poly mer cell walls and helps hold them together, provides additional strength, helps resist micr obial decay , and perhaps most importantly, for this discussion, inhibits hydrol ys is. Its molecular weight is around 10,000. 3 While both cellulose and hemicellulose contribute to the amount of fermentable sugars for ethanol production, lignin does not, but can be combusted to provide process energy

in a biochemical plant or used as feedstock to a thermochemical process. 4
A significant part of the reason it is more difficult and more costl y to produce ethanol from cellulosic feedstocks , has to do with th e differences in the molecular structures of simple starch es and oils and those of cellulosic plant matter . That is, as a plant grows, glucose monomers are added to the poly saccharide chains of the plant cell walls through condensation reactions. In gene ral, condensation is a chemical process by which two molecules are joined together to make a larger, more complex molecule, and a molecule of water is a b yproduct of the reaction. In the formation of pol ys accharides, and enzy me catal yz es the reaction wher ein the

- OH group on carbon #1 of one monomer, or glucose residue, reacts with the

- OH on carbon #4 or #6 of another residue. An H

- OH (H 2 O or water) molecule is removed leaving an

- O

- that links the monomers together toform the poly saccharide chain. Ag ain, depending on the direction of the

– OH group at

carbon 1, it may

be called an alpha (as in starch) or a beta (as in cellulose) linkage. 5 Hy droly sis is the reverse reaction. The

- H from an H

- OH (water) molecule is added to one monomer and the remai ning

- OH is added to its pair, e.g., to the next monomer on the chain, to regenerate separate glucose monomers. During starch hydrol ys is, water and water borne hydrolyzing enzy mes can easil y penetrate the randomly formed pol ym ers (the tiny granular partic les or bundles) in order to break the bonds to release glucose monomers. However, the cellulosic or glucan poly mers formed in tightly packed, dense, rigid microfibrils are especiall y resistant to water and hydrol yz ing enzy

mes. Xylan, the main constituent of hemicellulose, is more easil y hydrol yz ed than cellulose , but not easily fermented. C ellulose is not easily hydrol yz ed, but readily

ferments into alcohol . These are two of the major problems that must be satisfactoril y resolved for biochemical convers ion of cellulosic feedstocks

. While the b iochemical process primaril y uses enzymes or acids to disassemble the cellulose and hemicellulose followed b y fermentation, the thermochemical process operates substantiall y differentl y. In the thermochemical proc ess, b iomass is gasified at temperatures that are above 850°C. The gasification process partially oxidizes all biomass carbonaceous feed stock into gas, which is high in energy and consists of CO, CO 2 , CH 4 , H 2 and H 2 O, along with other minor constituents

. The CO and hydrogen are the main building block components for making liquid fuels via conversion through downstream s ynthesis reactions. Because of the thermal oxidation that occurs , all of the cellulosic biomass feedstock, including the lignin compo nent, can be used to make renewable fuels. T he thermochemical process may be more feedstock flexible than the biochemical process. In general, the lignin fraction content in woody feedstock s is higher than fractions found in herbaceous biomass (e.g., gra sses, straw, corn stalks ). Therefore, thermochemical technologies may

be more compatible than other cellulosic biofuel technologies for processing wood

- based feedstocks. W ood products generall y have higher heating values than other biomass stocks, such a s stover, grasses etc which mak es them better feedstock s for a thermochemical unit. Higher energy cellulosic feeds yi eld more CO and hy drogen sy nthesis gas, resulting in higher liquid yields per ton of feedstock

. 2. Emer ging Technologies When evaluati ng the array of biofuel technologies which could produce one or more fuels that could qualify under RFS2, we found that it is helpful to organize them into fuel technology

categories. Organizing them into categories eases the task of understanding the cos ts and life cy cle impacts of these technologies because like technologies likely

have similar cost and life cy cle impacts. The simplest organization is by the fuel produced. However, we frequentl y found that additional subdivisions were also helpful. Ta

ble 2.1 provides a list of technologies, the cellulosic fuels produced and a list of many

of the companies which we learned are pursuing the technology (or something very

similar to the technology listed in the category).Table 2.1

List of Biofuel Categories, the Fuels Produced and the Companies Pursuing Cellulosic Biofuel Technologies Technology Category Technology Fuels Produced Companies
Biochemical Enzymatic Hydrolysis Ethanol Abengoa, AE Fuels, DuPont/Danisco, Florida Crystals, Gevo, Poet, ICM, Ioge n, BPI, Energy, Fiberight, KL Energy. Acid Hydrolysis Ethanol Agresti, Arkenol, Blue Fire, Pencor, Pangen, Raven Biofuels Dilute Acid, Steam Explosion of Cellulose Ethanol Verenium, BP, Central Minnesota Ethanol Coop. Consolidated Bioprocessing (one step hydrolysis and fermentation) of Cellulose Ethanol Mascoma, Qteros

Conversion of

Cellulose via carboxylic acid Ethanol, Gasoline, Jet Fuel, Diesel Fuel Terrabon, Swift Fuels

One step C onversion of Cellulose to distillate Diesel, Jet Fuel or Naphth a Bell Bioenergy, LS9

Thermochemical Thermochemical/Fischer Tropsch Diesel Fuel and Naphtha Choren, Flambeau River

Biofuels, Baard, Clearfuels, Gulf Coast Energy, Rentech, TRI. Thermochemical/Fischer Tropsch DME Chemrec, New Page. Thermochemical/Cata ly

tic conversion of syngas to alcohols Ethanol Range Fuels, Pearson Technologies, Fulcrum Bioenergy, Enerkem, and Gulf Coast Energy. Hy brid Thermochemical w/ Biochemical

catalyst Ethanol Coskata, INEOS Bio Acid Hydrolysis of cellulose to intermediate; hydrogenation using Thermochemical syngas from non

- cellulose fraction Ethanol, Other alcohols Zeachem

Depolymerization Catalytic Depolymerization of

Cellulose Diesel, Jet Fuel or Naphtha Cello Energy , Covanta, Kior,

University of Massachusetts Py rolysis of Cellulose Diesel, Jet

Fuel, or Gasoline Envergent (UOP/Ensyn),

Dynamotive, Petrobra s Other Catalytic Reforming of Sugars

f rom Cellulose Gasoline VirentOf the technologies listed above, man y of them are considered to be “second

generation” biofuels or new biofuel technologies capable of meeting either the advanced biofuel or cellulosic biofuel RFS standard. The following sections describe specific companies and the new biofuel technologies which the companies have developed or are developing. This summary is not meant to be an unabridged list of new biofuel technologies, but rather a description of some of the more prominent or interesting of the new biofuel technologies that serve to provide a sense of the technology categories listed above . The process technology summaries are based on information provided by the respective companies. EPA has not been able to confirm all of the information, statements, process conditions , and the process flow steps necessary for any of these processes and compan ies.
3. Biochemical Process for the Production of Cellulosic Biofuels Biochemical conversion refers to a broad grouping of processes that use biological organisms to convert cellulosic feedstocks into biofuels. While no two processes are identical, many of these processes follow a similar basic pathway to convert cellulosic materials to biofuel. The general process of most biochemical cellulosic biofuel processes consists of five main steps, feedstock handling, pretreatment, hydrol ys is, fermentation/fuel conversion, and distillation/separation. The feedstock handling step reduces the particle size of the incoming feedstock and removes any contaminants that may

negativel y impact the rest of the process. In the pretreatment step the structure of the lignin and hemicellulose is disrupted, usually using some combination of heat, pressure, acid, or base, to allow for a more effective h ydrol ys is of the cellulosic material to simple sugars. In the h ydrol ys is stage the cellulose and an y remaining hemicellu lose is converted into simple sugars, usually using an enz ym e or strong acid. In the fermentation or fuel conversion step, the simple sugars are converted to the desired fuel by a biological organism. In the final step the fuel that is produced is separated from the water and other b yproducts by distillation or some other means. A basic diagram of the biochemical conversion process can be found in Figure 3.1 below. Figure 3.1 1

1 Image From: http://www.afdc.energy.gov/afdc/ethanol/production_cellulosic.htmlWhile this diagram shows the production of ethanol from cellulosic bioma ss, it is

possible to use the same process to produce other fuels or specialty chemicals using different biological organisms. The following sections will discuss each of these steps in greater detail, discuss some of the variations to this general proces s, and discuss some of the advantages and disadvantages of the biochemical process of producing biofuel from cellulosic materials as compared to other fuel production processes. Seven of the eight companies that EPA believes may produce cellulosic biofue l in 2011 plan to use a biochemical process to produce biofuels. Five of these companies, AE Biofuels, Dupont Danisco Cellulosic Ethanol, Fiberight, Io gen, and KL energy , all plan to use an enzy

matic h ydroly sis, while Agresti biofuels are Bell Bio

- Energy are pursuing gravity pressure vessel and single step process technologies respectivel y. The main reason for the dominance of biochemical technologies in 2011 is the relatively low capital costs of these projects compared to other cellulosic biofuel facili ties. Biochemical projects also benefit less from economies of scale, making smaller and less capital intensive commercial facilities more feasible. The following sections provide more information on the biochemical processes being pursued by majority of the companies we expect to produce cellulosic biofuels and make them commerciall y available in 2011, as well as man y other companies planning to begin production in later ye ars. 3.1 Feedstock Handling The first step of the biochemical conversion proce ss is to insure that the biomass stream can be utilized by the rest of the conversion process. This most often takes the form of size reduction, either by grinding or chipping as appropriate for the ty pe of biomass. While this is a relativel y simple proc ess it is essential to allow the following steps of the process to function as designed. It is also a potentially energy intensive process. It may

be possible for biofuel producers to purchase cellulosic material that is alread y of the appropriate size, however we believe that in the near term this is unlikely and most biofuel producers will have to invest in equipment to reduce the size of the material they

receive as needed for their process. In coming y ears, as the market for cellulosic materials expands, purchasing feedstock that has alread y been ground or chipped may

be possible and cost effective, as these processes increase the density of this material and may

reduce transportation costs. In addition to size reduction, steps must also be taken to remove an y m aterial from the feedstock that might be detrimental to the fuel production process. Contaminants in the feedstock would at best travel through the fuel production process unchanged, resulting in reduced fuel production capacit y. Depending o n the ty pe of contaminant they

may also be converted to undesired b yproducts that must be separated from the fuel. They

could also be toxic to the biological organisms being used to convert the sugars to fuel, necessitating a shut down and restart of the plant. Either of these scenarios would result in a significant cost to the fuel producer. Feedstocks such as agricultural residues, wood chips, or herbaceous or wood y energy crops are likely tocontain far fewer contaminants than more heterogeneous feeds tocks such as municipal

solid waste (MSW).
3.2 Biomass Pretreatment The purpose of the biomass pretreatment stage is to disrupt the structure of the cellulosic biomass to allow for the h ydrol ys is of the cellulose and hemicellulose into simple sugars. The ideal pretreatment stage would allow for a high conversion of the cellulose and hemicellulose to simple sugars, minimize the degradation of these sugars to undesired forms that reduce fuel yi elds and inhibit fermentation, not require especially large o r expensive reaction vessels, and be a relatively robust and simple process. No single biomass pretreatment method has y et been discovered that meets all of these goals, but rather a variet y of options are being used b y various cellulosic fuel producers, each with their own strengths and weaknesses. Dilute acid pretreatment and alkaline pretreatment are two methods currentl y being used that attack the hemicellulose and lignin portions of the cellulosic biomass respectively . Other methods, such as steam e xplosion and ammonia fiber expansion, seek to use high temperature and pressure, followed b y rapid decompression to disrupt the structure of the cellulosic biomass and allow for a more efficient hydrol ys is of the cellulose and hemicellulose to simple sugar s. The cost and characteristics of the cellulosic feedstock being processed is likely to have a significant impact on the pretreatment process that is used.
3.2.1 Dilute Acid Pretreatment The dilute acid pretreatment uses a dilute acid solution, gen erall y ~1%, sulfuric, hydrochloric, or nitric acid, at a high temperature, usually greater than 160° C to hydrol yz e the hemicellulose to simple sugars. The dilute acid pretreatment produces very high yi elds of x yl ose, the most important sugar in the hemic ellulose, and requires very short reaction times, often as low as several minutes. It also allows for high converstion rates of the cellulose to glucose in the later stages of the process. Using a dilute acid pretreatment, however, is a relativel y expens ive method. Corrosive resistant materials must be used for the reaction vessels due to the presence of the acid. The acid must also be neutralized prior to the cellulose h ydrol ys is stage if enzy mes are to be used, and before the fuel production stage as it is harmful to the biological organisms used for the fuel production. L ime can be used to neutralize the acid, however this produces gy psum that must be removed from the process. Other compounds, such as ammonia, can be used that do not produce solids, but the higher costs for these compounds generall y negates an y savings from the lack of equipment required to separate the gypsum.
3.2.2 Alkaline Pretreatment The alkaline pretreatment process is designed to dissolve and disrupt the structure of the l ignin portion of the lingocellulosic materials rather than the hemicellulose. This method exposes the feedstock to an alkaline solution, usually a solution of 1

- 2% sodium hydroxide, calcium hydroxide, or ammonia. The reaction time is approximately one ho ur, however this can vary depending on the feedstock being used. High temperaturesare not required for this process, however they are sometimes used to decrease the reaction time or increase the sugar conversion of the cellulose and hemicellulose in late r stages of the process. If an alkaline pretreatment is used a different combination of enzy mes are required for the subsequent hydrol ys is step, as now the hemicellulose must be hydroly

zed in addition to the cellulose. Alkaline pretreatment has lower cap ital costs than dilute acid pretreatment as cheaper materials are able to be used for the reaction vessels. The alkaline solution can also be recovered and recycled rather than neutralized which decreases the cost of chemical usage and waste water treatme nt. The main disadvantage of the alkaline pretreatment process is that yields of the sugars from the cellulose and hemicellulose tend to be lower than those for other processes. This must be weighed against the potential cost savings when considering usi ng an alkaline pretreatment process. DuPont Danisco Cellulosic Ethanol is one compan y planning on using an alkaline pretreatment in the production of cellulosic biofuels.
3.2.3 Steam Explosion In the steam explosion pretreatment process the lingocellu losic feedstock is treated with high temperature and pressure saturated steam. The feedstock is held at high temperature and pressure, up to 50 bar and 290° C for a period of time ranging from several seconds to ten minutes, and then undergoes a sudden de compression to atmospheric pressure. This degradation causes a disruption of the lignin and hemicellulose structure allowing for h ydroly sis of the remaining hemicellulose and cellulose in later steps. This process is advantageous in that it uses no acids or bases for the pretreatment resulting in decreased costs and environmental impacts. In the rapid decompression, however, compounds can be formed that can inhibit the later h ydrol ys is and fuel production processes. The pretreated biomass will likely have to be washed to remove these compounds. This washing can also result in the loss of soluble hemicellulose and ultimately simple sugars and fuel produced. Some steam explosion processes add small amounts of acid with the saturated steam to increase the hydroly sis of hemicellulose and cellulose in later steps and to decrease the production of undesired compounds that inhibit simple sugar and fuel production. The addition of acid, however, increases the capital costs and adds acid neutralization costs as discussed in section 3.2.1 above. Companies using steam explosion to produce cellulosic biofuels include IOGEN and Verinium.
3.2.4 Ammonia Fiber Explosion Ammonia Fiber Explosion (AFEX) operates much like steam explosion. Li gn ocellulosic feedstock i s treated with liquid ammonia at a high temperature (~90° C) and pressure. These conditions are held for much longer than with steam explosion, approximately

30 minutes, before being rapidl y decompressed to atmospheric pressure. As with the steam explosi on process where acid has been added no compounds that would interfere with later hy drol ys is and fuel production steps are not produced, so a wash step to remove these compounds is not necessary . In order for the AFEX pretreatment process to be economical ly feasible the ammonia must be recovered and reused. This process produces a treated feedstock with high rates of simple sugarproduction in the hy drolysis step as long as the li gn ocellulosic feedstocks have relatively

low lignin content. It is effectiv e at treating herbaceous energy crops and agricultural residues such as corn stover and wheat and barley straw. AFEX is not an effective pretreatment process for feedstocks with high lignin content such as wood chips or newspaper. If the AFEX pretreatment is used for feedstocks with high lignin content the result will be low sugar production in the hy droly sis stage.
3.3 Hy droly sis In the h ydrol ys is step the cellulose and an y remaining hemicellulose are converted to simple sugars. There are two main m ethods of hy droly sis, acid hy drol ys is and enzy matic h ydroly sis. Acid hy droly sis is the oldest technology for the conversion of cellulosic feedstock to ethanol and can onl y be used following an acid pretreatment process. An alternative method is to use a combination of enzy mes to perform the hydrol ys is after the biomass has been pretreated. This process is potentially more effective at h ydrol yz ing pretreated biomass but in the past has not been economically feasible due to the prohibitively high cost of the enzy

mes. The falling cost of these enzy mes in recent ye ars has made the production of cellulosic biofuels using enz ym atic hydrol ys is possible. The lignin is largel y unaffected by the h ydrol ys is and fuel production steps but is carried through these pr ocesses until it is separated out in the fuel separation step and burned for process energy or sold as a co

- product.
3.3.1 Acid Hy drol ys is Acid hydroly sis is a technique that has been used for over 100 y ears to convert cellulosic feedstocks into fuels. In the acid hydrolysis process the lignin and cellulose portions of the feedstock that remain after the hemicellulose has been dissolved, hydrol yz ed, and separated during the dilute acid pretreatment process is treated with a second acid stream. This se cond acid treatment uses a less concentrated acid than the pretreatment stage but at a higher temperature, as high as 215° C. This treatment hydrol yz es the cellulose into glucose and other 6 carbon sugars that are then fed to biological organisms to produ ce the desired fuel. It is necessary to hydrol yz e the hemicellulose and cellulose in two separate steps to prevent the conversion of the pentose sugars that result from the hydroly sis of the hemicellulose from being further converted into furfural and oth er chemicals. This would not only reduce the total production of sugars from the cellulosic feedstock, but also inhibit the production of fuel from the sugars in later stages of the process. The acidic solution containing the sugars produced as a resu lt of the h ydrolysis reaction must also be treated so that this stream can be fed to the biological organisms that will convert these sugars into fuel. In order to operate an acid h ydrolysis process cost effectivel y the acid must be recovered, not simply neutralized. Methods currentl y being used to recover this acid include membrane separation and continuous ion exchange. The advantages of using an acid hydroly sis are that this process is well understood and capable of producing high sugar yi elds from a wide variet y of feedstocks. Capital costs are high however, as materials compatible with the acidic streams must beextensively utilized. The high temperatures necessary for acid h ydrol ys is also result in considerable energy

costs, and profitability

is h ighly dependent on the ability

to effectivel y recover and reuse the acid.
3.3.2 Enzy

matic Hydrol ys is The enzy matic h ydrol ys is process uses enz ym es, rather than acids, to hy droly ze the cellulose and an y remaining hemicellulose from the pretreatment proc ess. This process is much more versatile than the acid h ydrolysis and can be used in combination with any of the pretreatment processes described above, provided that the structure of the lignocellulosic feedstock has been disrupted enough to allow the en zy mes to easily

access the hemicellulose and cellulose. After the feedstock has gone through pretreatment a cocktail of cellulose enzymes is added. These enzymes can be produced b y the cellulosic biofuel producer or purchased from enz ym e producers such a s Novozy mes, Genencor, and others. The exact mixture of enzy mes used in the enzy

matic h ydrol ys is stage can vary greatly depending on which of the pretreatment stages is used as well as the composition of the feedstock. The main advantages of the enzy mat ic h ydroly sis process are a result of the mild operating conditions. Because no acid is used special materials are not required for the reaction vessels. Enzy

matic hydroly sis is carried out at relativel y low temperatures, usually around 50° C, and atmosp heric pressure and therefore has low energy requirements. These conditions also result in less undesired reactions that would reduce the production of sugars and potentially inhibit fuel production. Enzy matic hydroly sis works best with a uniform feedstoc k, such as agricultural residues or energy crops, where the concentration and combination of enzy mes can be optimized for maximum sugar production. If the composition of the feedstock varies daily, as can be the case with fuel producers utilizing MSW or o ther waste streams, or even seasonall y, it would make it more difficult to ensure that the correct enz ym e cocktail is being used to carry out the hydrol ys is as efficientl y as possible. The main hurdle to using an enzy matic hydroly sis has been and continue s to be the costs of the enz ymes. Recent advances by companies that produce enz ym es for the hydroly sis of cellulosic materials have resulted in a drastic cost reduction of these enzy mes. If, as many

researchers and cellulosic biofuel producers expect, th e cost of these enzy mes continues to fall it is likely that enz ym atic hydroly sis will be a lower cost option than acid h ydrol ys is, especiall y for cellulosic biofuel producers utilizing uniform feedstocks.
3.4 Fuel Production After the cellulosic biomas s has been h ydrolyzed to simple sugars this sugar solution is converted to fuel by biological organisms. In some biochemical fuel production processes the sugars produced from the fermentation of the hemicellulose, which are mainly

five carbon sugars, are converted to fuel in a separate reactor and with a different set of organisms than the sugars produced from the cellulose h ydrolysis, which are mainl y six carbon sugars. Others processes, however, produce fuel from the five and six carbon sugars in the s ame reaction vessel.A wide range of biological organisms can be used to convert the simple sugars

into fuel. These include yeasts, bacteria, and other microbes, some of which are naturall y occurring and others that have been genetically modified. The ideal biological organism converts both five and six carbon sugars to fuel with a high efficiency , is able to tolerate a range of conditions, and is adaptable to process sugar streams of varying compositions that may result from variations in feedstock. M any cellulosic biofuel producers have their own proprietary

organism or organisms optimized to produce the desired fuel from their unique combination of feedstock, pretreatment and hydroly sis processes, and fuel conversion conditions. Other cellulosic fue l producers license these organisms from biotechnology

companies who specialize in their discovery and production. The man y different biological organisms being considered for cellulosic biofuel production are capable of producing man y different types of fuels. Many cellulosic biofuel producers are working with organisms that produce ethanol. In many way s this is the most simple fuel to produce from lignocellulosic biomass as the production of ethanol from simple sugars is a well understood process. Others intend to produce butanol or other alcohols that have higher energy content. Butanol may

be able to be blended into gasoline in greater proportion to ethanol and therefore has a potentially greater market as well as value due to its higher energy c ontent. Yields for butanol, however, are currentl y significantl y lower per ton of feedstock than ethanol. Some of the fuel producers who plan to produce alcohols are considering purchasing and modifying already existing grain ethanol plants. This would potentially have significant capital cost savings as many of the units used in a grain ethanol process are very similar to those required by the biochemical fuel production process and could be used with minimal modification. Other cellulosic biofuel pro ducers intend to produce h ydrocarbon fuels very similar to gasoline, diesel, and jet fuel. These fuels command a higher price than alcohols, have a greater energy densit y, and are potentially drop in fuels that could be used in an y conventional vehicles w ithout strict blending limits. They could also be transported b y existing pipelines and utilize the same infrastructure as the petroleum industry . Some of the processes being researched by fuel producers produce a single compound, such as iso

- octane, that would need to be blended into petroleum gasoline in order to be used while others produce a range of hydrocarbons very similar to those found in gasoline or diesel fuel refined from petroleum and could potentially be used in conventional vehicles without blending. While the prospect of producing hydrocarbon fuels from cellulosic feedstock is promising, the current yi elds of fuel produced by these organisms are significantly lower than those that are producing ethanol and other alcohols. Improvement in the yields of these organisms will have to be realized in order for cellulosic h ydrocarbon fuels produced via a biochemical process to compete with cellulosic ethanol, and ultimately petroleum based fuels.
3.5 Fuel Separation In the fuel separation stag e the fuel produced is separated from the water, lignin, any un - reacted hemicellulose and cellulose, and any other compounds remaining after thefuel production stage. The complexity of this stage is highl y dependent on the ty pe of fuel produced. For pro cesses producing hy drocarbon fuels this stage can be as simple as a settling tank, where the hydrocarbons are allowed to float to the top and removed. Recovering the ethanol is a much more difficult task. To recover the ethanol a distillation process, ne arl y identical to that used in the grain ethanol industry, is used. The ethanol solution is first separated from the solids before being sent to a distillation column called a beer column. The overheads of the beer column are fed to a second distillation column, called a rectifier for further separation. The rectifier produces a stream with an ethanol of approximately

96%. A molecular sieve unit is then used to deh ydrate this stream to produce fuel grade ethanol with purity greater than 99.5%. Gasoline is added to the fuel ethanol as a denaturant before the fuel is stored. The distillation of ethanol is a very energy intensive process and new technologies, such as membrane separation, are being developed that could potentially reduce the energy

intensi ty , and thus the cost, of the ethanol deh ydration process. After the fuel has been recovered the remaining lignin and solids are dried and either burned on site to provide process heat and electricity or sold as a by product of the fuel production process. The waste water is either recy cled or sent to a water treatment facility

. 3.6 Process Variations While the process described above outlines the general biochemical process used by man y cellulosic biofuel producers, there are several prominent variati ons being pursued b y prospective biofuel producers. These variations usually seek to simplify the biochemical fuel production process b y combining several steps into a single step or using other means to reduce the capital or operating costs of the proces s. Simultaneous Saccharification and Fermentation (SSF), Simultaneous Saccharification and Co

Fermentation (SSCF), Consolidated Bio

- Processing (CBP), and Single Step Fuel Production are all production methods being developed by various biofuel production companies to combine two or more of the steps outlined above. These modifications are usually enabled by

a proprietary

technology

or biological organism that makes these changes possible.
3.6.1 Simultaneous Saccharification and Fermentation (SSF)
In s imultaneous saccharification and fermentation (SSF), the cellulose hydroly sis and fuel conversion steps are combined. After the lingocellulosic biomass has been pretreated cellulose enzymes and fuel conversion organisms, usually y east, are added simultane ously . As the cellulase enzy mes convert the cellulose to simple sugars the y east immediately

convert the sugars to ethanol. There are several benefits of SSF. The first is the potential lowering of capital costs as now onl y a singe reaction vessel is re quired for both the hydrol ys is of the cellulose and the fuel production from the resulting sugars. In addition, the products or the cellulose h ydrol ys is, the glucose and other simple sugars, are inhibitors to the enzy

mes performing the h ydrol ys is. By converting them to ethanol as they are produced the sugar concentration is kept low and the conversion rate of the cellulose into simple sugars is maximized. There are several drawbacks to this process. The rate of ethanol production is now limited by the enzy me activity . The idealconditions for cellulose hydroly sis and the fermentation of the resulting sugars are not the

same. This can result in slower overall reaction rates, and the fuel yi elds using this technology

are not currently

as high as when th ese two steps are performed separately

. 3.6.2 Simultaneous Saccharification and Co

- Fermentation (SSCF) Simultaneous saccharification and co

- fermentation (SSCF) is very similar to SSF. This process, however, combines the hy drol ys is of the cellulose and the fermentation of the resulting six carbon sugars with the fermentation of the five carbon sugars produced form the h ydrol ys is of the hemicellulose. The advantages and disadvantages of this process are also very

similar to SSF, with further reductions in capital cost possible. Conditions also move further away from the optimal conditions for each of the three reactions and slower reaction rates and lower yi elds can result.
3.6.3 Consolidated Bio

- Processing (CBP) Consolidated Bio

- Processing (CBP) further increases the simplicity of the process from SSCF. CBP uses geneticall y engineered organisms that are capable of producing cellulase enz ym es and fermenting the simple sugars to ethanol. By combining all these steps into one process the fuel product ion process is greatl y simplified and the cost of fuel production is potentially reduced. The simple process and mild conditions could result in both capital cost reductions as well as operating cost reductions. While CBP is a promising technology , there are currently no organisms that can efficiently produce cellulase enz ym es and ferment sugars to ethanol. Organisms have been found in nature that possesses one or the other of these qualities, but not both together. Significant research is being done to produce such an organism, usually by starting with an organism that naturally

expresses one of the desired traits and inserting genetic material to allow for the expression of the other desired trait. The commercial viability of CBP is dependent on the d iscovery of an organism that can perform both these tasks efficientl y. 3.6.4 Sing l e Step Fuel Production Further simplification of the biochemical cellulosic biofuel process would include the elimination of the pretreatment stage. Bell Bio

- Energy , a c ellulosic biofuel company who aims to start up a commercial scale facility in mid 2010, claims to have developed such a process. In this process the lingocellulosic feedstock is first ground to reduce the size and then immersing the ground with geneticall y engineered bacteria and water. The bacteria begin to digest the cellulose after onl y several hours, but require 30 to 60 days to fully digest the cellulose. The produced fuel is constantly removed from the reaction vessel, and a significant amount of o rganic material is also produced which will be marketed as potting soil. The process is expected to produce 30 to 40 gallons of renewable fuel per ton of feedstock and the simplicity of the process results in low capital costs per volume produced. While this process may

appear very

similar to those discussed above (SSF, SSCF, and CBP) it differs in several important way s. The fuel produced by the process is adiesel like fuel that would need to be upgraded before being used as a transportation fuel,

rather than ethanol. Bell Bio

- Energy is currently

working with the University of North Dakota to develop a process for upgrading the fuel they produce. The amount of time required for the organisms to produce fuel from the lingocellulosic feedstock is also much longer, 30

– 60 days rather than hours. The yields of fuel per ton of biomass are much lower in this process, 30

– 40 gallons per ton versus 80

– 100 gallons per ton with most biochemical processes. Finall y, the b yproduct of this process is a pottin g soil, which Bell Bio

- Energy

has found avenues to sell, rather than lignin. Despite the disadvantages listed above, the extremely low capital and operating costs of this process and high value b yproduct may allow for commercial success. As this technolo gy has not been studied as extensively as man y of the alternative methods at a small scale, there is greater technical uncertainty associated with this process.
3.6.5 Gravity

Pressure Vessel Another variation of the general biochemical cellulosic fuel production process is the use of a gravity

pressure vessel for the pretreatment and hy droly sis of the lingocellulosic biomass. Using this process the feedstock material is pumped deep underground, to a depth of approximately 2000 feet. At this depth the pressure is near 60 bar and the solution is heated to approximately 250 ° C. Under these conditions the lignin is dissolved and oxygen is added to combust the lignin to provide heat to maintain this high temperature. Next a weak acid is added to h ydroly z e the remaining hemicellulose and cellulose into simple sugars. Once the h ydrolysis is complete the acid is neutralized, the solution is returned to the surface, and the sugars are fed to the fuel producing organisms. The gravit y pressure vessel allow s the extreme conditions necessary for the break down and h ydrol ys is of the lingocellulosic material to be achieved with relatively little energy inputs, taking advantage of the naturall y high pressure deep underground and the combustion of the lignin to p rovide the required heat. The two main downsides of using the gravity

pressure vessel are high capital costs and no by product recovery . The gravit y pressure vessel is an expensive piece of equipment, and because the lignin is combusted to provide process heat for the hydroly sis it cannot be recovered and used to provide process heat for fuel separation or sold as a potentially valuable by

product. Agresti Biofuels is planning to use a gravit y pressure vessel to produce ethanol from MSW at a facility in Pi ke County , Kentucky . Agresti plans to begin production on this facility in the summer of 2010.
3.7 Current Status of Biochemical Conversion Technology The biochemical cellulosic fuel production industry is currentl y transitioning from an industry

cons isting mostly

of small scale research and optimization focused facilities to one capable of producing fuel at a commercial scale. Companies such as I ogen, DuPont Danisco Cellulosic Ethanol, and KL Energy are just beginning to market the fuel they are prod ucing at their first small scale commercial fuel production facilities. By 2011 we expect several other cellulosic fuel production facilities using biochemicalprocesses to come online, including the first commercial scale facilities of AE Advanced

Fuels, Agresti Biofuels, Bell Bio

- Energy , and Fiberight. Many other facilities, including some large scale facilities capable of producing tens of millions of gallons of fuel are planned to come online starting in 2012 and in the following ye ars. There are many

factors that are likel y to continue to drive the expansion of the cellulosic biofuel industry. The high price of petroleum fuels and the mandates put into place b y the RFS2 program have created a large demand for cellulosic biofuels. The biochemical p roduction process also has several advantages over other methods of producing fuel from cellulosic feedstocks including relativel y low capital costs, highl y selective fuel production, flexibility in the t yp e of fuel produced, and the promise of future prod

uction cost reductions. While the poor worldwide econom y and tight credit markets has had a negative impact on the biofuel industry as a whole the cellulosic biofuel producers utilizing biochemical processes have not been as hard hit as many others in th e industry . This is partially due to the relatively

low capital costs of biochemical production plants as a result of the relative simplicity and mild operating conditions of these plants. Several companies have been able to purchase distressed grain eth anol plants and are in the process of modifying them to produce cellulosic ethanol, further reducing the capital costs of their initial facilities. Once biochemical fuel production facilities have been constructed another advantage they have over other fu el production processes is that their high selectivity

in the fuels they

produce. Unlike chemical catal ys ts, which often produce a range of products and b yproducts, biological organisms often produce a single ty pe of fuel, which leads to very high fuel pr oduction rates per unit sugar. Finally , there is a large potential to further decrease the production costs of cellulosic biofuels using the biochemical processes. Unlike other production methods such as gasification which are relativel y mature technolog ies, biochemical production of fuels is a y oung technology

. One of the major costs of the biochemical fuel production processes currently are the enzy mes. Great strides have been made recently in reducing the cost of these enzy mes, and as the price of en zymes continues to fall so will the operating costs of biochemical fuel production processes.
3.8 Path to Commercialization While there are man y promising qualities of the biochemical fuel production process we have identified several different aspects of the process which can be further improved

. T he pretreatment processes can be improved to speed the conversion of cellulose and hemicellulose to simple sugars and to minimize the production of other undesired compounds, especiall y those that may inhibi t the fuel production process. The ability of the biological fuel production organisms to process a wide range of both five and six carbon sugars can also be improved. Both these improvements will increase the fuel yield per ton of cellulosic feedstock, reducing the operating costs of the process. Finally , the enzy

me production processes can be further optimized which would lower the price for enzy

mes and improve the economics of hy drolyzing cellulose to sugars.Another opportunity for improvement would be the profitable utilization of the lignin portion of the cellulosic feedstock. Unlike some of the other cellulosic biofuel production processes, the biochemical process does not convert the lignin to fuel. Cellulosic feedstock can contain up to 40% li gnin, depending on the t ype of feedstock used, so the effective utilization of this lignin is an important piece of the profitability of the biochemical process. One option for the use of the lignin is to burn it to provide process heat and electricity , a s well as excess electricity to the grid. While this would provide good value for the lignin, it would require fairl y expensive boilers and turbines that increases the capital cost of the facility . If the lignin cannot be used as part of the fuel product ion process it may be able to be marketed as a solid fuel with high energy density and low carbon intensity

. These various improvements to the cellulosic biofuel plants would make biochemical processes more cost

- competitive with petroleum and other cellul osic biofuels. While decreases in production costs are not a given there is a wide consensus within the cellulosic biofuels industry that future technological developments and econom y of scale benefits from commercial scale production will result in sign ificant production cost reductions. An anal ys is conducted by the National Renewable Energy Laboratory

in 2008 projected the cost of cellulosic ethanol production via the biochemical pathway

decreasing from $2.43 per gallon in 2010 to $1.21 per gallon in 2 022 6

. A table from this report, found below, shows how the operating costs of different parts of the cellulosic ethanol production process are expected to change over time. Table 3.1 7 Changes in Operating Cost of Cellulosic Ethanol via the Biochemical Pr ocess Over Time

In considering NREL’s analy sis of changes in the cost of production of cellulosic biofuels via the biochemical pathway over time, as well as studies conducted by other parties, there are three main areas from which the majority of the c ost improvements are expected; feedstock cost, the cost of enzy mes, and yields per ton of feedstock. The cost of feedstock is a large contributor to the cost of ethanol, responsible for approximately 40% of the cost of a gallon of ethanol in all three cas es above. An y reductions in the cost of cellulosic feedstocks to the biofuel producers will have a direct and potentially significant impact on the overall cost of cellulosic biofuel production. Efforts to decrease the cost of cellulosic feedstocks are t aking place on a wide variety of fronts. Work in the area of plant breeding and genetics is underway to increase the efficiency with which plants utilize water and nutrients in order to decrease the cost of growing plants used bycellulosic ethanol facili ties. Another area of much interest is increasing the annual

growth rate of crops that can potentiall y be use for biofuel production. This would decrease the number of acres needed to suppl y a cellulosic biofuel production facility as well as decrease th e transportation cost for the feedstock by decreasing the area from which a production facility would have to import feedstock. New harvesters are being developed to increase the efficiency of harvesting cellulosic biomass. These are just some of the man y different ways in which the cost of feedstocks for cellulosic biofuel producers is likel y to decrease in the future. A second area of significant potential cost savings for cellulosic biofuel producers is the cost of enzy

mes. Enzy

me cost has long been a major hurdle to the economic production of cellulosic biofuel via the biochemical process, and it continues to be a major factor in the overall production cost. The recent trends in the cost of enzy mes necessary to produce cellulosic biofuel, however, are promising. In February 2010 Novozy mes announced that it had reduced the cost of enzy mes require for cellulosic ethanol production to less than $0.50 per gallon of ethanol produced, an cost reduction of 80% in the past two y ears alone 8 . It is likely that the costs of the enz ym es required for cellulosic biofuel production, and thus the overall cost of cellulosic biofuel production via the biochemical process, will continue to decrease. A third way

in which the cost of cellulosic biofuel production is expected to decrease is b y increasing the yield of fuel per dry ton of biomass. As with the feedstock costs, there are man y different way s in which cellulosic biofuel yields may be increased. Feedstocks are being developed with lower lignin content and h igher cellulose and hemicellulose content to enable a larger portion of the biomass to be converted into biofuels. More effective pretreatment methods and enzy mes will likely

convert more of the cellulose and hemicellulose into simple sugars. More versat ile biological organisms may be able to convert more of the simple sugars into fuel. The cost impacts of increasing the yi eld of biofuel per ton of feedstock are similarl y diverse. Greater yi elds mean a lower feedstock cost on a per gallon of fuel basis. They also mean lower capital costs due to relativel y smaller production facilities to produce the same amount of biofuel. Relatively

smaller biofuel production facilities mean lower costs for other raw materials and energy

inputs. The combination of th ese man y effects would have a significant impact on the cost of cellulosic biofuel production. While it is impossible to precisel y determine the extent of the progress in each of these areas over time, it highly likely that progress in some or all of thes e areas will contribute to decrease in production costs of cellulosic biofuels via the biochemical process into the future.
4

. Thermochemical Process for the Production of Cellulosic Biofuels Thermochemical conversion involves b iomass being broken down into intermediates using heat and upgraded to fuels using a combination of heat and pressure in the presence of catal ys ts. 9 For the sake of th e discussion here , we are defining Thermochemical to mean gasification processes (partial oxidation in the presen ce of a gasifying agent, usuall y air, ox yge n, and/or steam ) that convert the biomass to a sy n - gas, but not including other processes such as py rol ys is (discussed below) which occurs in theabsence of ox ygen and at lower temperatures

. The thermochemical pr ocess is also

applicable to other feedstocks (e.g., coal or natural gas); the main difference is that a renewable feedstock is used (i.e. biomass) to produce cellulosic biofuel. A thermochemical unit can also complement a biochemical processing plant to e nhance the economics of an integrated biorefinery by converting lignin

- rich, non

- fermentable material left over from high

- starch or cellulosic feedstocks conversion. 10 Thermochemical conversion processes using gasification can be designed to either prod

uce primaril y ethanol (alcohols) or other petroleum like fuels such as diesel and naphtha, which is commonly referred to as a Biomass to liquids (BTL) thermochemical process. The processing steps, however, used to produce either ethanol or BTL fuels in a thermochemical unit are similar until the fuel sy nthesis and product separation stages, as discussed below. Compared to corn ethanol or biochemical cellulosic ethanol plants, the use of biomass gasification may allow for greater flexibility to utilize d ifferent biomass feedstocks at a specific plant. Mixed biomass feedstocks may be used, based on availability

of long

- term suppliers, seasonal availability , harvest cy cle, and costs. Agricultural residue, energy crops, wood residue s , and municipal solid w aste are all being considered as potential feedstocks. Geographic location, availability of biomass, the existence of biomass suppliers, and costs would all likely influence the mix of biomass feedstocks utilized. The general steps of the gasification th ermochemical process include: feedstock handling, gasification, gas cleanup and conditioning, fuel sy nthesis, and separation. Refer to Figure 4 .1 for a schematic of the thermochemical cellulosic ethanol production process through gasification

. For greate r detail on the thermochemical mixed

- alcohols route refer to NREL technical documentation. 11 Refer to F igure 4.2 for a schematic of a block diagram of a BTL Thermochemical process.Figure 4.1 Cellulosic Ethanol Thermochemical Gasification Process

Figure 4.2 Biomass to Liquids (BTL) Thermochemical Gasification Process4.1 Feedstock Handling The particle size requirement for a thermochemical process is around 10

- mm to 100

- mm in diameter. 12 Once the feed is ground to the proper size, flue ga ses from the char combustor and tar reformer catal ys t regenerator dry the feed from the as received moisture level of around 30% to 5 0% moisture to the level required b y the gasifier.
4.2 Gasification Id eall y the gasification process would completel y convert biomass to CO and H 2 , although the process is not completely efficient as some CO 2 , water, methane and coke/ tars are also produced. The gasification of biomass feedstock is carried out in the presence of a low concentration of oxygen, with oxygen levels that are only about 30% of that required for complete combustion. Tars and coke are also formed as biomass is gasified, which is primarily influenced by

the gasifier operating conditions, gasifier residence time, gasifier design and operating temp erature, with less influence based on the cellulosic feedstock type. The tar yi eld can vary by a wide range based on these parameters. There are many t yp es of gasifiers, many

designs resulting in different performance and conversion of biomass. For most gasifiers, the overall efficiency for converting biomass into sy nthesis gas of CO and hy drogen, is only about 70 to 80% efficient, as some of the biomass energy is converted into CO 2 , H 2 O and tars. Additionally , there is heat loss and other energy losses in the gasifier, that also lower efficiency . Downstream of the gasifier, additional energy is also lost when converting the sy nthesis gas of CO and H 2 into ethanol and liquids, which lowers the overall process efficiency to about 42

- 57% (amount of biomas s energy converted to liquid fuels) for currentl y explored thermochemical designs 13

. The amount of carbon, hydrogen and oxygen present within the cellulosic biomass feedstock can vary from feedstock to feedstock or even within a feedstock. As the relative amount of carbon and hydrogen in the feedstock varies, the amount of CO and hy drogen produced during gasification would vary as well which ultimately affects the amount of fuel which can be produced. If the ox ygen content of the feedstock varies, the amo unt of air or ox yg en which are added to the gasifier , to help oxidize the biomass and combust an y char being formed , can also be varied to balance the overall quantity oxygen needed for gasification. For a thermochemical unit, an elemental chemical anal ys is of the feedstock, to identify the amounts of carbon, ox ygen, h ydrogen, sulfur, nitrogen and other organic elements will indicate the potential volume of liquid fuels that can be produced. However, not all of the available energy in biomass feedstock is converted to fuels, due to inefficiencies in the thermochemical process.The presence of moisture in feed stocks, though, has a detrimental impact on the

process yi elds and process efficiency of a gasification unit. This is because any moisture in the feedstocks must be vaporized in the gasifier, which diverts energy away from the production of liquid fuels. So, feedstocks with higher moisture content have lower overall process efficiencies than feedstocks with lower moisture content. Wood has higher moisture content, with values around 50%, than other cellulosic stocks that have dried in the field (around 15%) vi . Wood’s high heating value, though, outweighs the negative effects of its higher moisture content versus other cellulosic feedstocks. There are two general classes of gasifiers. First, partial oxidation (POx) gasifiers (directl y - heated gasifiers) use the exothermic reaction between oxygen and organics to provide the heat necessary to devolatilize biomass and to convert residual carbon

- rich c hars. In POx gasifiers, the heat to drive the process is generated internally within the gasifier. A disadvantage of POx gasifiers is that oxygen production is expensive and ty picall y requires large plant sizes to improve economics. The second general c lass, called indirect gasification, uses steam gasifiers to accomplish gasification through heat transfer from a hot solid or through a heat transfer surface. Either the b yp roduct char and/or a portion of the product gas can be combusted with air (externa l to the gasifier itself) to provide the energy required for gasification. M ost steam gasifiers operate at low pressure and therefore require product gas compression for downstream purification and sy nthesis unit operations. 14 , 15
In either the direct or indirect ty pe, c urrent designs, find it advantageous to use pure ox ygen instead of air to the gasifier, as pure ox ygen does not add nitrogen into the sy nthesis gas, which results in cost savings from smaller equipment sizes for downstream equipment. There are different subcategories of gasifiers which are either directly or indirectly heated. One subcategory is termed a bubbling fluidized bed gasifier and it employ es a bubbling fluidized bed of inert material and the reactant (biomass) is also bubbled thr ough the fluidized bed. A second variant is the circulating fluidized bed gasifier which is similar to the bubbling fluidized bed reactor except that a high feedstock and air flow rate circulates the fluidized bed out of and back into the reactor. For th e fluidized bed, the bed material may either be inert alumina or sand which helps the heat transfer. There are also fixed bed reactors which either feed the reacting gas (oxy gen or air) upward or downward through a fixed bed of the reactant (biomass). Be cause of the tar formed when using biomass as a feedstock, a second reactor is sometimes added which solely

targets converting the tar to s yn - gas. If the biomas feedstock is ground to a sufficiently

small particle size, or liquefied, the biomass is consid ered to be “entrained” in the reactor, and the reactor is defined as an entrained flow reactor. The indirect gasification process begins as the biomass is fed to the reactor containing a heat transfer media, such as sand, and is partially reacted with a ir (or oxygen) which is introduced to the bottom of the reactor. The air serves as the carrier

-gas and as the oxidant for partiall y oxidizing the biomass to sy n - gas, carbon monoxide and hy drogen. In addition to the sy ngas produced, char and coke are also formed

. The h eat for the endothermic gasification reactions is supplied by circulating heat transfer media (e.g. s ythetic sand) between the gasifier and the char combustor. The heat generated b y the combustion of the char and coke heats the heat transfe r media to over 1800°F. The s yn gas is separated from the sand and ash and sent to gas cleanup.
4.3 Gas Cleanup & Conditioning Once the biomass is gasified and converted to s yn gas, the s yn gas must be cleaned and conditioned. Inorganic materials and mi nerals, such as sulfur, sodium, silica and potassium are found within the cellulosic material and are also accumulated from dirt and the environment upon biomass collection and transport. The minor components, tars, sulfur, nitrogen oxides, alkali metals, and particulates have the potential to negativel y affect the s yn gas conversion steps. Most of this material is deposited in the gasifier as a molten slag and is removed as a waste b yproduct. Additionally, ash content in agriculture residues (from fertil zers, dirt) and woods place a burden on the process, as ash must be scrubbed out of flue gas that exits the process, though woods feedstocks have less ash than agriculture resides. Scrubbing the ash from the s yn - gas consumes power and requires expensive c apital for flue gas scrubber s ys tem. Sulfur in biomass is converted into gaseous H 2 S in the gasifier which is poisonous to the Fischer Tropsch process as it deactivates the downstream reformer and Fischer Tropsch sy nthesis catal ys t. H 2 S is therefore remo ved from the gasifier s ynthesis gas via an acid gas scrubbing section prior to entry

into the reformer catal ys t. Wood has low sulfur levels with a ty pical values estimated around 10 ppm, while energy crops, such as corn stover and switch grass have much h igher values with estimates around 500 ppm 16 . The gasifier also converts some of the nitrogen in biomass to NH 3 and HCN, which is also removed in the downstream acid gas scrubbing section, as these are poisonous to cataly st. If scrubbers are being used an yw ay s, thermochemical technologies may be better suited to process municipal solid waste which can contain a significant amount of contaminants. The gasification reactors and the downstream scrubbers ty picall y used in thermochemical processes reduces the chance that contaminants contained in the feedstock make it into the final fuel. Gas conditioning steps include sulfur polishing to remove trace levels of H 2 S and water

- gas shift to adjust the final H 2 /CO ratio for optimized fuel sy nthesis.
4.4 Fuel Sy

nthesis and Product Separation After cleanup and conditioning, the “clean” s yn gas is comprised of essentially CO and H 2 . The sy

ngas is then converted into a liquid fuel by either a catal yt ic process or through the use of a microorganism. T he fuel produc er has the choice of producing diesel fuel or alcohols from sy ngas by optimizing the ty

pe of catal ys t used and the H 2 /CO ratio. Diesel fuel has historically been the primary focus of such processes, as it produces a high quality

distillate product, howeve r, with the 45 cent tax subsidy currently available for ethanol production, it may be economically

advantageous for fuel producers to convert s yn gas to ethanol instead of to diesel fuel. Below, we discuss the processing steps for a plant configured to mak e either ethanol or BTL fuels.4.5 Heat & Power For either an ethanol or BTL plant configuration, a carefull y integrated conventional steam cycle produces process heat and electricit y (excess electricity is exported). Pre

- heaters, steam generators, and super - heaters generate steam that drives turbines on compressors and electrical generators. The heat balance around a thermochemical unit or thermochemical/biochemical combined unit must be carefull y designed and tuned in order to avoid unnecessary heat l osses. 17 Any unreacted carbon monoxide and hydrogen and any gaseous hy drocarbon material from the process are burned to produce electricity in a turbine. The waste heat from the gas turbine along with the steam created to cool the sy n - gas, may

be sent to s team turbines to produce additional electricit y. Most of the electricity would be used within the thermochemical plant, however, some could be sold to raise additional revenues.
4. 6a Ethanol Production Conceptual designs and techno

- economic models have b een developed for ethanol production via mixed alcohol sy nthesis using catal yt ic processes. The proposed mixed alcohol process produces a mixture of ethanol along with higher normal alcohols (e.g., n

- propanol, n

- butanol, and n

- pentanol). The by

- product h igher normal alcohols have value as commodity chemicals and fuel additives. Ty pically the mixed alcohol products are high in methanol, but contain a wide distribution of several different alcohols. One concept proposed in literature is to completely recy cle this methanol in order to increase the production of ethanol and higher alcohols which are generall y more valuable. This concept was modeled b y NREL for the thermochemical production of ethanol for the ye ar 2012 , using a Mol ydenum Sulfide type catalys t

. Total mixed alcohol yi eld was 94.1 gallons per dry ton, in which 85 % of the total alcohol product was ethanol. This was made possible through the addition of an almost complete recy cle of methanol within the process. 18 For the final rule, we worked with NRELto develop the thermochemical mixed

- alcohols model for the 2015 and 2022 timeframe 19

. The liquid rundown from the low

- pressure separator is dehy drated in vapor

- phase molecular sieves, producing the deh ydrated mixed alcohol feed into a methanol/eth anol overhead stream and a mixed, higher molecular weight alcohol bottom stream. The overhead stream is further separated into a methanol stream and an ethanol stream. Range Fuels produces cellulosic biofuel via a two step thermochemical process. Their technology

converts biomass to sy

ngas followed by

cataly tic conversion of the sy ngas to alcohols. Range claims that their technology is capable of produc ing more ethanol than other cellulosic technologies based on yields per energy input. Th ey

utilize a two step process which can use man y forms of non food biomass, such as agriculture waste, wood, and corn stocks. Additionally , the technology can process feed stocks with variable water content. Range has operated a pilot plant for over 7 ye ars using ove r 20 different nonfood feedstocks. Range broke ground building its first commercial plant late in late 200 8 andis expected to be operational in 2010 . This plant will be located in Soperton, Georgia and

is partially

funded from proceeds of a DOE grant. The plant will use wood, grasses, and corn stover as feedstocks. Inits initial phase, the Range plant is expected to produce 4 million gallons per year of methanol. After the company is confident in its operations, Range will begin efforts to expand the plant and add additional reaction capacity to convert the methanol to ethanol. Enerkem is another company like Range Fuels pursuing cellulosic ethanol production via the thermochemical route. The Canadian

- based compan y was recently announced as a reci pient of a $50 million grant from DOE to build a 10 MGY woody biomass

- to

- ethanol plant in Pontotoc, MS. The U.S. plant is not scheduled to come online until 2012, but Enerkem is currentl y building a 1.3 MGY demonstration plant in Westbury , Quebec. Accord ing to the compan y, plant construction in Westbury started in October 2007 and the facility is currentl y scheduled to come online around the middle of 2010. While this fuel would likely be eligible to generate RINs under the RFS program if imported, Enerk em has indicated that they plan to use all the fuel locally and do not plan to export any

fuel to the United States.
4. 6b BTL Production In this configuration, the sy ngas is fed to a Fischer

- Tropsch (FT) reactor to primarily produce diesel fuel and some naphtha

. 20 The cleaned and water

- shifted sy ngas is sent to the FT reactor where the carbon monoxide and h ydrogen are react ed over a FT catal ys t. The FT cataly st is either iron

- based or cobalt

- based. The cobalt cataly st is more expensive, although it doe s not require a recy cle, while the less expensive iron catal ys t does require a recy cle. The FT reactor creates a sy ncrude, which is a variety of hydrocarbons that boil over a wide distillation range (a mix of heavy and light hydrocarbons). The s yncrude f rom the FT reactor is sent to a distillation column where it is separated into various components based on their vapor pressure, mainl y liquid petroleum gas (LPG), naphtha, distillate and wax fractions. The heavier compounds are hydrocracked to maximize the production of diesel fuel. The distillate boiling compounds have high cetane and thus are of high quality for blending into diesel fuel. Conversel y, the naphtha material is very low in octane thus, it would either have to be upgraded, or blended down with high octane blendstocks (i.e., ethanol), or be upgraded to a higher octane blendstock to have much value for use in gasoline. The naphtha could also be sold as feedstock for the petrochemical market for manufacturing chemical products such as eth yl en e and benzene. Choren has a technology

called Carbo

- V, which is a Fischer

- Tropsch process that can be used to make diesel fuel. The process can process a wide variety biomass and recy cled material materials as feedstocks. The process converts agricult ure biomass, forestry biomass, biogenic waste and recy cling substances into a s ynthesis gas which can be further converted to a diesel fuel using a Fischer

- Tropsch reactor. The Carbo

- V process can also be configured without the Fischer

- Tropsch h ydrocracki ng technology , so as to produce electricit y, heat and power, methanol, and other chemical feedstocks.The principal aspect of the Carbo

- V Process is a three

- stage gasification process

consisting of low temperature gasification, high temperature gasificat ion and endothermic entrained bed gasification. In the first stage, biomass is partially oxidized with air or oxygen at temperatures between 400 and 500 °C. This breaks down the feedstock into a gas containing tar and solid carbon. In the second stage, the tar is oxidized at temperature s higher than the ash’s melting point, converting the tar into a sy nthesis gas. In the third stage, solid carbon is mechanicall y pulverized and blown into the hot gasification stream. The fluidized carbon endothermicly r eacts with the gasification stream and is converted into a sy nthesis gas. In the next Fischer

- Tropsch stage of the process, the s ynthesis gas (CO and H2) reacts with the aid of a catal ys t to form hydrocarbons. The resulting hy drocarbons produced from the three stages can then be sent to a hydrocracking process to produce primarily diesel fuel. Choren will be building a commercial Plant in Freiberg/ Saxony German y that is expected to be operational in 2011 or 2012 . Initially , the plant will use biomass from nearb y forests, the wood

- processing industry and straw from farmland.
4.7 Pathway s to Commercialization Although there are examples of thermochemical gasification processes which process coal and natural gas, a thermochemical plant which must gather, pretreat and gasify cellulosic biomass has not y et been demonstrated on a commercial scale

. The capital costs for thermochemical plants are much higher per volume of fuel produced than other cellulosic biofuel technologies , due to the complexity of their design which requires man y process stages, expensive equipment pieces and high catal yst costs. The first investors in these thernochemical plants that process cellulosic biofuels are expected to be those which are willing to tolerate the somewhat hi gher risk of investing in a new application of an existing technology

. Once th e first several thermochemical plants which process cellulosic biofuels are built, it will provide confidence to mo re investors that these plants will have long term reliable pe rformance and that the product yields will be satisfactory

for economic pay off

. Ad ditionall y, optimization and improvements to the gasification stage, catal yst sy nthesis stages and overall configuration of the plant will help to lower the capital an d oper ating costs to further improve the competitiveness of this technology

. 5

. Hy

brid Thermochemical/Biochemical Processes Hy brid technologies include process elements involving both the gasification stage of a t ypical thermochemical process, as well as th e fermentation stage of a ty pical biochemical process and therefore cannot be placed easily into either category

. For more specific information regarding either biochemical processes or thermochemical, please see Sections 3 and 4 of this technical memo re spectively

. Currentl y, there are several strategies for the production of ethanol through h ybrid processes; these strategies are differentiated b y the order in which the thermochemical and biochemical steps take place within the process, as well as how th e intermediate products from each step are used. The following subsections describe these different processes; specificall y how they differfrom processes that may use only one technology

ty pe (either thermochemical or biochemical).
5 .1 “Thermochemical First” Process The ‘thermochemical first’ strategy involves the gasification of all feedstock material to sy

ngas before being processed into ethanol using a fermenter. Hence, the first steps in this process most closely resemble a ty

pical thermochemical process, while the following steps most closely resemble that of a t yp ical biochemical process. Stage 1

– 3: Feedstock Handling, Gasification and Cleanup The first stages do not differ in an y significant way from the respective stages found in a tradi tional thermochemical process. Gasification converts carbonaceous material under high heat and pressure to a mixture of mainly carbon monoxide and hydrogen gasses. This mixture is commonly referred to as s yn gas. This gas may also contain other compounds such as metallics or sulfur; these compounds can be detrimental or poisonous to steps farther downstream in the process and therefore must be removed before further treatment of the sy ngas. More information regardi ng these steps can be found in S ection 4 of this technical memo. Stage 4 : Fuel Synthesis After gasification, the s yngas stream is cooled and bubbled into a fermenter containing geneticall y m odified microorganisms. Unlike traditional fermentation, where C5 and C6 sugars are digested to ethan ol, these microorganisms are engineered to convert the carbon monoxide and hy drogen contained in the sy ngas stream directl y into ethanol. Using a fermenter in this hy brid process replaces the catal ys t needed in a thermochemical process. Traditional therm ochemical cataly sts require a very specific ratio of carbon monoxide to hydrogen in the sy ngas stream in order to reach efficient conversions. This requirement necessitates the inclusion of an additional water

- shift step for thermochemical fuel production

. A water

- shift reaction is used to balance the ratio of carbon dioxide and hydrogen gas to that required by the traditional thermochemical catal ys t. The microorganisms used in a hy brid process allow for more variation of the incoming s yn gas stream ratio , therefore avoiding the water

- shift reaction preceding ty pical thermochemical conversion. Thermochemical catal ys ts also are required to operate under high pressure and heat. The microorganisms and are able to operate at significantl y lower temperatures and pressures than those required for a traditional catal yt ic conversion to ethanol. Microorganisms, unlike a catal ys t, are also self

sustaining and do not require periodic replacement. They are; however, susceptible to bacterial and viral infections whi ch requires periodic cleaning of the fermentation reactors. Stage 5: Product SeparationAfter fermentation, the effluent water/ethanol stream from the fermenter is

separated similarly

to a biochemical process; usually using a combination of distillatio n and molecular sieves. The separated water can then be recy cled back into the fermentation stage of the process. Ty pical yields of ethanol are predicted in the 100

- 130 gallon per ton range, similar to that of a traditional thermochemical process. For m ore information regarding product separation, refer to S ection 3.5 biochemical product separation. Coskata has a gasification

- based technology which produces ethanol from biomass and other forms of carbon through a biofermentation route. A wide variet y of feedstocks can be used including municipal solid waste, agriculture waste and other carbonaceous containing material. Since this process uses combustion and biofermentation, we classifi ed it as a hy brid technology

. This process requires th at the bioma ss or carbon ac eous material be processed to a small particle size and then it is injected into a gasifier. The gasifier combusts any dry carboneous feed stocks into sy ngas
. The syngas produced is fermented in a reactor b y micro

- organisms, which conver t the carbon monoxide and hydrogen directly into ethanol. The micro

- organisms are low cost and can process a wide range of carbon monoxide and hydrogen molar ratios in the sy ngas, providing feedstock processing flexibility . No other enzy mes are required by

this process for producing ethanol, providing significant cost savings over current cellulosic and corn based fermentation production methods. The Coskata micro

- organism reactor is operated at low temperatures and pressures, which offers savings on cap ital and energy costs. Additional energy

savings can be re a lized by employing membrane technology to separate ethanol from the reactor decant liquid. This technology uses gravity

and filtration to recover ethanol, resulting in significant savings on dist illation capital and energy costs used in other cellulosic and corn based ethanol production methods. In itial ethanol production cost estimates are lower than the biochemical and thermochemical cellulosic technologies

. F or wood y biomass, Coskata estimates that each ton of this feedstock would generate about 100 gallons of ethanol and small amounts of ash which would be burned to supply energy needs for the process. Corn stover is expected to provide similar ethanol yields as woody

biomass feed stocks, though details about yields from the various feed suppl y stocks are not y et public. Coskata has a bench scale pilot plant in Warrenville, IL, and its larger 40,000 gallon per year pilot plant became operational in 2009 in Madison, Pennsylvania. Cos kata is targeting to design and build a 5 5 million gallon per y ear commercial demonstration plant that it expects to be operational in 201 2

. IN EOS Bio also has been developing a thermochemical first technology . INEOS Bio (along with partner New Planet En ergy) has recentl y been selected for a $50MM DOE grant for the construction of an 8 MGPY plant in River County , Florida; predicted to finish construction in late 2011.5 .2 “Biochemical First” Process A ‘biochemical first’ process involves the gasificat ion of the ty picall y unfermentable feedstock fraction (lignin) concurrently with a fermentation step; and subsequent reaction of the produced s yn gas with the product of the fermented stream. Stage 1

– 2: Feedstock pretreatment and hydrolysis Feedstock s are prepared for this process in the same fashion as a tr aditional biochemical plant. In coming feedstock is pretreated and hy drol yz ed to separate fermentable sugars from non

- fermentable compounds such as lignin. More information on these steps can be f

ound in S ection s 3. 2 and 3.3 of th e biochemical technology Section of this technical memo. Stage 3a: Fermentation Stage 3a and 3b in this process take place concurrently ; before fermentation, the unfermentable portion of feedstock (lignin, ash and othe r residue) is fractioned and sent to a gasifier, see stage 3b. The remaining fraction of feedstock is fermented using an acetogen microorganism, in a manner similar to that of a traditional biochemical process. The acetogen converts the sugars and mixed c arbohy drates of the feedstock to acetic acid. This reaction creates no carbon dioxide, unlike a ty pical fermentation using y east, preserving a higher amount of carbon in the finished fuel. Acetogens are also naturally occurring and therefore more robust against infection or contamination versus microorganisms that would be geneticall y engineered. The acetic acid stream is then stabilized to ethyl acetate. Ethyl acetate is both easier to store, as well as forming a precursor to man y other chemical compounds that can be created at a later stage in the process. Stage 3b: Gasification of unfermentable feedstock Meanwhile, the unfermentable fraction separated in stage 3a is fed to a gasification reactor similar to that found in a traditional thermochemica l process. Due to the reduced volume of feedstock going to this reactor, the size of the gasifier can be greatl y reduced compared to that of a thermochemical

- only process. The sy

ngas stream produced from the gasification of lignin and other residue is th en separated into its carbon monoxide and hydrogen components. The h ydrogen is fed to the next stage of the process, while excess carbon monoxide is combusted, producing enough energy to meet the needs of the other process stages. Stage 4: Product Produ ction The hydrogen stream from stage 3b is reacted with the ethyl acetate stream from stage 3a to form ethanol. Itis also possible, by changing reaction parameters, to form other chemical compounds from the eth yl acetate in order to meet the needs of c hangingmarket conditions; acetic acid and eth yl acetate form the precursors to many other chemical compounds and therefore may also be sold in addition to ethanol. Itis predicted that this process can achieve conversions of 130

- 150 gallons of ethanol per ton of fee d stock. A compan y currentl y pursing a biochemical first process technology is Zeachem In c. Zeachem is currentl y constructing a 250 thousand gallon per ye ar demonstration plant in Boardman, Oregon. They have received a $25MM DOE grant and ex pect to have a full commercial production facilit y operational in 2013.
5 .3 Path to Commercialization Since these h ybrid process technologies include steps from both biochemical and thermochemical processes, they also have some of the same commercia lization issues as both of these technology

ty pes. ‘Thermochemical first’ processes carry the same high capital costs as traditional thermochemical operations, as well as the complexity of heat transfer between stages required for these processes. Howeve r, because of the use of a biochemical stage instead of a cataly st, initial cataly st cost and tuning can be eliminated. This is offset by

initial microorganism cost and first batch startup of the microorganisms. The addition of a biological step also incre ases the need for sterile procedures in that part of the plant, adding costs that would not be present in a ty pical thermochemical operation. ‘Biochemical first’ processes also share man y of the commercialization issues of a ty pical biochemical process. F eedstock pretreatment and h ydrol ys is steps need to be improved on a large scale to achieve efficient production. The addition of a thermochemical processing step for lignin and unfermentable residue solves the problem of wasted feedstock; however, it adds both complexity and capital cost with the addition of a thermochemical step. Both h ybrid process pathways are able to achieve higher conversion rates than either of the sole technology processes, with the tradeoff of added complexity

. This added complex ity adds to startup time and capital costs, which may lengthen construction times

.

6

. Py

rol ys is and Catal yt ic Depoly merization Py rol ys is and cataly

tic depoly merization encompass a group of technologies which are capable of creating biofuels from cellulo se by either onl y rel yi ng on heat, or by relying on a combination of heat with cataly s is

. Py roly sis technologies are usually thought of being solel y or primarily thermal technologies , however, p yr olysis technologies are being developed which are attemptin g to integrate some cataly sts into the technology . These are all unique processes, ty pically with single companies developing the technologies, so they are discussed separately

.

6 .1 Py

rol ys isPy rol ys is oils, or bio

- oils, are produced b y decomposing cellulosic biomass at lower temperatures (400 to 800 degree Cels ius) than the gasification proce ss, thus producing a liquid bio

- oil instead of a s ynthesis gas

. 21 22 23 24 The reaction can occur either with or without the use of cataly sts, but it occurs witho ut an y additional ox ygen being present. The bio

- o il produced varies in ox ygen content or viscosit y according to the feedstock used and the reactor conditions

. Ty pically , to maximize the production of liquid fuels, the reactor temperature is controlled at 400 to 500 degrees Cels ius and the residence time is only

2 seconds

– hence the name “Fast p yrol ys is .” The fast py rol ys is uses sand (not cataly st) in a fluidized bed to transform bio

- fuels into a product named bio

- oil. The sand is used to enable the qu ick heat transfer needed to keep the reaction time to 2 seconds. Three products are produced by the fast py

rol ys is process, bio oil (60

- 75% by weight), char (15

- 20% wt.) and non

- condensable gases (10

- 20% wt.). The char produced is similar to coke and can be used as fuel by other industries while the gases yi elded from the process can be used to suppl y about 75% of the energy requirements of the py rol ys is process. Once the reaction is complete, the oil must have particulates and ash removed in filtration to create a homogenous product

. This separation is sometimes performed through the use of a cy clone. The bio

- oil is ty

picall y high in ox ygen content (i.e., 20%

– 30%) which makes this product immisible with petroleum, but enables it to be miscible with water. 25 Bio

- oil is also very

low in cetane and has about half the energy content per gallon of petroleum

based diesel fuel. Because of the high ox ygen content and the immersed water, the bio

oil has a density

more like that of water. Also the acid comp ounds in the bio

- oil cause the bio

- oil to be acidic which requires the metals in contact with the bio

- oil to be acid resistant stainless steels. This makes bio

- oil very challenging to use in internal combustion engines. If a use can be found for the bio

- oil, the production cost is very low due to the very

low capital and operating costs for these plants. 26 If p yrol ys is is to be widely used to generate as transportation fuels or for other uses, the bio

- oil will have t o be upgraded to hydrocarbon fuels

. 27 28 The upgrading process would likel y involve one or more reactor vessel s which likely w ould contain a catal ys t that reduces the acidity , reduces the viscosity and reduces the density of the bio

oil. One likely

technology

for this upgrading step would be h ydrotreating. 29 30 31 32 The Pacific Northwest National Laboratory (PNNL) has modeled hy drotreating as an upgrading strategy

for bio

- oils sourced from p yr oly sis. 33 PNNLprojected that two hydrotreating reactors would be needed. The first hydrotreater is proj ected to operate at a higher space velocit y and lower temperature than conventional hydrotreaters

- the lower temperature is used to avoid coke formation . The purpose of the first reactor would be to deox ygenate the more reactive acid and aldeh yd e oxygen - containing h ydrocarbon species, and saturate the more reactive olefins. After the first reactor, the bio

- oil would likely no longer be miscible with water and be blendable with hydrocarbons, which would allow an y entrained water to be separated from the bio

- oil. The second hydrotreater would operate at a temperature and space velocit y more like a conventional refinery hydrotreater and its primary purpose would be to drasticall y remove the ox ygen contained within the hydrocarbon molecules. The resultin g fuelwould still contain a small fraction of the ox ygen originall y contained within the

cellulose, but it would be much more like h ydrocarbon compounds sourced from crude oil. The downside for the hy drotreating route is that the hydrogen consumption fro m the two upgrading h ydrotreating reactors would be a very high

– on the order of 4600 standard cubic feet per barrel of feed . This level of hydrogen consumption is an order of magnitude higher than that ty pically experienced with distillate hydrotreating

. Instead of solel y relying on hydrotreating as the upgrading technology , the first reactor after the p yrol ys is reactor could contain a catal ys t which upgrades the bio

- oil without the use of hy drogen. The somewhat upgraded bio

- oil would still contain a significant amount of oxygen, but it may be sufficiently stable to store for a second upgrading step that could involve hydrotreating . Because the bio

- oil is stable, it perhaps could be transport ed to a refinery with extra hy drotreating capacit y to hydro treat the bio

oil. An important advantage of emplo yi ng a nonhydrotreating catal ys t as a first step would be to significantly

re duce the amount of h ydrogen required. The second advantage of this approach is the two upgrading duties can be optimized separatel y depending on the cellulosic biomass location and best location for fuels upgrading. For example, the py rol ys is reactors and upgrading reactor (first step) could be located close to where the cellulosic biomass is located avoiding the long distance shipments of the biomass (biomass is a solid which is more costly to handle, and it contains about 50% oxygen, which is deadweight because ox ygen does not add any energy value). Once the biomass has been “liquefied” and perhaps at least partiall y deox ygen ated, transportation is made easier, perhaps b y barges, ships and pipelines. The second upgrading step can be located further away

from the biomass harvesting locations where fewer but larger, more cost

efficient upgrading equipment could be utilized. Th e upgrading step can even occur using the existing capital at today ’s refineries. 34
There is another means other than using catal ys ts to stabilize bio

- oil. The National Renewable Energy L aboratory

(NREL ) has a proprietary technology named “hot filtration ” that apparently was able to stabilize bio

- oil samples for a very long period of time (y ears). NREL ’s py rol ys is reactor uses sand, but the resulting bio

- oil after their hot filtration will contain a much lower amount of contaminant metals and is stable. So, it will be easier to solve the second problem, the bio

- oil upgrading. Dy namotive Energy

S ys tems Corporation employs a fast p yrol ys is technology that uses medium temperatures and ox ygen free reactions to convert dry waste biomass and energy

crops into specialty

products. 35 The process is flexible on the ty pes of biomass feedstock’s that can be processed. T he bio

- oil produced b y their process contains significant amounts of water, it is not directly useable as fuel in conventional vehicles and would have to be converted via another cataly tic conversion processing step. The additional catal yt ic step Dy namotive envisions for upgrading their bio

- oil for this would combust the material into a sy nthesis gas which would then be converted into diesel fuel ( the BTL process)

. If upgraded, the diesel fuel produced is expected to be compatible with existing petroleum diesel fuels.Dy namotive has two small demonstration plants

. One demonstration plant is located in Guelph, Ontario, Canada and its capacity i s 66,000 dry

tons of biomass a y ear with an energy

output equivalent to 130,000 barrels of oil

. The West L orne plant has a capacity to convert 130 tonnes of biomass into bio

- oil per day which, if proportional to the Guelph plant, translates to an energy

- e quivalent of 84,500 barrels of oil per y ear. The other of its demonstration plant s is located in West L orne Ontario, Canada. This plant started operation in earl y 2005 using waste sawdust as a feedstock. Dy namotive does not have an y contracts in place t o supply U.S. based clients in y ear 2010 or 2011

. Additionally , Dy

namotive has not announced plans for building a bio

- oil upgrading facility

. Envergent is a compan y formed through a joint venture between Honeywell’s UOP and the Ens yn Corporation. Altho ugh Ens ynhas been using fast py roly sis for more than a decade to produce specialty chemicals, UOP is relying on its decades of experience developing refining technologies to convert the py rol ys is oils into transportation fuels. 36 Envergent is also working with Federal laboratories to further their technology . Based on their current technology and depending on the feedstock processed, about 70 % of the feedstock is converted into liquid products. The gasoline range products produced are high in octane, wh ile the diesel fuel products are low in cetane. Envergent is licensing this technology as well as working with a U.S. oil compan y to test out this technology in a commercial setting here in the U.S. Petrobras is working on developing a p yrol ys is technol ogy
. 37 A United States and Brazil Memorandum of Understanding to advance the cooperation on biofuels was signed by United States ’ Secretary

of State and Brazil’s External Relations Minister on March 9, 2007. A second Memorandum of Understanding was signed by P etrobras and the National Renewable Energy L aboratory

(NREL ) on September 2008 aiming at collaborating to maximize the benefit of their respective institutional interests in second generation biofuels. P etrobras is working with NRELto develop a py ro ly sis technology to produce biofuels from agricultural wastes such as sugar cane bagasse, wood chips or corn stove r
. NREL and P etrobras intend to use their combined expertise to develop a two

- step py

roly sis route to biofuels production. Petrobras is a lso working to develop a one

- step pyroly sis technology , although the compan y is somewhat skeptical that even if an effective one

- step py rol ys is catal ys t can be developed, it may

not be economically

viable for use in rural areas. The Cooperation Agreement with NREL covers the Life C ycl e Assessment and Technoeconomic Analy sis of both the two

- step and one

- step routes. 6 .2 One Step Cataly

tic Py roly sis and Catal yt ic Depoly merization It is possible to use a sophisticated catal ys t (instead of sand) to heat and depoly merize cellulose and at the same time produce a stable bio

- oil or even produce transportation quality

fuels. 38 Some papers in literature address these problems by using ZSM

- 5 zeolite. 39 The resulting bio

- oil is very aromatic, but theoreticall y it cou ld be used directly as transportation fuel and the posterior upgrading would be no longer necessary ,since fuel properties can be improved b y decreasing the amount of ox ygen in the bio

- oil

through deox ygenation and cracking to form H 2 O, CO and CO 2 . The ch allenge of this route is that many

of the available catal ys t s which are candidates are relatively expensive and they degrade quickl y due to the metals and water which are present. 40 There are at least two ways to address the cost impacts of using expensiv e catal ys ts which degrade over time from the contaminants. One solution would be to find a catal ys t formulation which is less expensive , but also robust enough to handle the high level of water and metal contaminants present in biomass, namely sodium, pot assium, magnesium, iron. Otherwise, the process will not be economically viable. Z eol yt ic catal ys t s are likel y not candidates because they deactivate from being exposed to most of these metals. A second approach would be to develop a new catal ys t which may still be expensive, but which is resistant to the contaminants. Alternatively, one could use a susceptible catal ys t, but somehow protect the cataly st from the contaminants, such as a guard bed. A guard bed would be placed above the rest of the catal y st and its role would be to adsorb the contaminants preventing the more expensive one

- step p yr oly sis catal ys ts located lower down in the reactor from being exposed to the contaminants. There seem to be several companies which have found catal ys ts which can function in the environments present when converting cellulosic biomass to biofuels. Since their processes are proprietary , some of the companies will not share what catal ys ts they are using, nor do we know the cy cle length of the catal ys ts they are u sing. Cello Energy has a catal ytic depolymerization process which reportedl y produces ASTM quality

fuels in two simple steps . At moderate pres sure and temperature, the Cello Energy

process cataly

tically removes the oxygen and minerals from the feedsto ck, primarily from the cellulose, hemicellulose, and lignin . This results in a mixture of short chain (3, 6 and 9 carbon) hydrocarbon compounds. The se short chain hydrocarbon compounds are pol ym erized to form compounds that boil in the naphtha, jet fuel or diesel boiling range. In December 2008, Cello completed construction on a 20 million gallon per y ear commercial demonstration plant in Bay Minette, Alabama

. As of mid

- 2010 , Cello is still working to make the ir commercial demonstration plant operati onal

. According to the compan y, they are currently working to resolve materials handling and processing issues that surfaced when they

attempted to scale up production to 20 MGY from a previousl y operated demonstration plant. They continue to work on the se issues and they hope to resolve these issues in 2010

. Two catal yt ic depol ym erization technologies which are very similar in nature are technologies offered b y AlphaKat and Green Power. These technologies react organic material or carbon

- containing was te material over a catal ys t and the process produces a hydrocarbon biofuel similar to naphtha, jet fuel and diesel fuel. The AlphaKat process is being demonstrated by

a 1 million gallon per y ear plant in New Jersey by a waste

- to

electricit y compan y named Covanta which purchased the rights to use the technology

. Covanta started up its demonstration plant mid

- 2010 and it is planning on using the fuel itproduces in oil

- fired heaters within its plant , and also in nonroad diesel engines within its

plant

. Gre enPower completed construction on a 100 tons per day demonstration plant in the State of Washington about March of 2008, although as of earl y 2010 the plant was still not operating. These processes catal yt ically depol ym erize cellulosic feedstocks at mo derate temperatures into liquid hydrocarbon s . The proposed feedstock is ground to a moderatel y smaller size , dried and then fed into the reactor along with a cataly st and some lime and some heavy oil, which provides a liquid medium for the reactions to take place

. The combination is heated to around 350 degrees Celsius and the feedstock is converted to fuels. The liquid fuels are separated from some solids which are present and are distilled into ty

pical fuel streams including naphtha, diesel fuel, kerose ne and fuel oil. The process es reportedl y produce about 1 00 gallons of fuel per ton of feedstock inputted into the process. A light hydrocarbon gas, which is mostly methane, is also produced, but this gas is expected to be burned to generate electricity and the waste heat is used for heating the process. Apparentl y, some carbon dioxide is also formed and is released from the process.
6 .3 Pathway s to Commercialization Py rol ys is technologies produce very low quality

products which cannot be used in to day ’s vehicles and engines. Therefore, the bio

- oil must be upgraded to improve the stability and the usability of the fuel and continued effort will likely be invested in improving the efficiency

and reducing the overall cost of upgrading the bio

- oil . Fo r those working with catal ys ts for combining with a p yr oly sis process, or for a cataly tic depoly merization process, the companies will likely continue to improve the effectiveness and lower the costs of their catal ys t.
7

. Cataly

tic Reforming of Sugars to Gasoline Virent is pursuing a process called “Bioforming” which functions similarly as the gasoline reforming process used in the refining industry . While refinery

- based reforming raises natural gasoline’s octane value and produces organic chemicals, be nzene, xylene and toluene as a b yp roduct, Bioforming reforms biomass

- derived sugars into hydrocarbons for blending into gasoline and diesel fuel. The process operates at moderate temperatures and pressures. The Bioforming process which initially was conc eived at the University of Wisconsin, is being developed through a partnership between Virent, Shell, Cargill and Honda. Virent currentl y has 16 benchscale pilot plants in operation , each of which is capable of producing about one gallon of product per da y
. In March of 2010, Virent announced that they had begun operating a larger pilot plant capable of about 30 gallons per day

. Commercialization of the Virent process will happen sometime after 2011. Biomass feedstocks for the Bioforming process are s ugar feeds, such a corn sy rup, sucrose, gl ycerol, sorbitol, x yl ose, glucose, cellulose and hemi cellulose. These are primarily converted into gasoline and diesel fuel, though other hydrocarbons such as jetfuel, LPG, benzene, toluene, xylene, hy drogen and natural gas can also be produced.

Water is also produced, as the reforming process removes oxygen from the sugar feeds. The resulting properties and energy content of gasoline and diesel produced , though , are phy sicall y comparable to those yielded from refining industry

. The v ariable operating co s ts of the Virent process are low because no distillation equipment is needed to separate the produced gasoline, diesel and other hydrocarbons, as these separate naturall y from the aqueous solutions generated in the reforming process. It appears that Bioforming is a promising technology , as production cost estimates are low in comparison to man y other renewable and biomass production processes while the products are compatible with traditional petroleum stocks s o they don’t need special handling

. For this technology

to become a cellulosic biofuel technology , it will be necessary to link this reforming technology with a technology

which breaks cellulose down into starch or sugars. In parallel with its Bioref orming work, Virent is working on a technology

to break down cellulose into sugars upstream of its technology which reforms sugars to gasoline.

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of Biomass Terms, National Renewable Energy L aboratory , Golden, CO. http://www.nrel.g ov/biomass/glossary .html 5 Condensation and Hy droly sis; http://www.biotopics .co.uk/as/disaccharideformation.html 6 Aden, And y and Ling Tao. “ Technoeconomic Modeling to Support the EPA Notice of Proposed Rulemaking (NOPR) ” . November 3, 2008. 7 Ib id 8 Novozy mes Press Release. “New Enzy mes Turn Waste into Fuel.” February 16, 2010. Accessed at: http://www.novozy

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.http://www1.eere.energy .gov/biomass/thermochemical_conversion.html

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L aboratory

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