Biomass Derived Fuel Products

Biomass derived fuel products, which we generally refer to simply as biofuels, include a handful of specialized products such biodiesel, pyrolysis oil or biocrude, as well as practically the full range of gaseous and liquid fuels derived from petroleum including diesel oil, gasoline, kerosene, methane, syngas, and DME. There’s even a type of biomass derived coal substitute called E-Fuel which is indistinguishable in appearance from fossil bituminous coal and has very similar combustion properties. Most ethanol is in fact produced from biomass as well, though it can also be made from petroleum, natural gas, or coal, and, because of the predominance of biomass, we are including ethanol in this section.

In this section we’re focusing on the specialized products, that is, those unique to the biomass sector, and also on products such as ethanol that are primarily produced from biomass. Bio-based synfuels resembling refined petroleum products are treated elsewhere.

Biodiesel

Biodiesel, its name notwithstanding, possesses an entirely different chemical composition from that of petroleum derived diesel oil or synfuel diesel made from coal or natural gas. Most plant based biodiesel is what as known as methyl ester, a compound formed when plant oils such as cottonseed oil or soy oil are combined with methyl alcohol (also known as methanol) in the presence of a strong acid or base (caustic lye is often used in the manufacturing process). Biodiesel can also be manufactured with other, heavier forms of alcohol such as ethanol. Biodiesel made with ethanol is called ethyl ester.

Straight vegetable and seed oils can be and have been burned in compression ignition engines, but the practice is inadvisable. Such oils contain glycerine, a viscous fluid that tends to clog engines and can cause significant damage with protracted use. Fortunately, alcohol provides a solution. The alcohol used in biodiesel production bonds with the oil and is completely consumed in the manufacturing process, while, at the same time, causing the glycerine to separate from the oil and to sink to the bottom of the vat. This glycerine must be completely removed by the manufacturer before the biodiesel is made ready for sale.

Biodiesel has a slightly higher cetane than does petroleum diesel, which is advantageous, but has a somewhat lower energy content (cetane is a meaure of how readily a fuel ignites from the heat of compression). Biodiesel is mildly corrosive—perhaps it would be more accurate to call it a detergent—and it tends to remove carbon deposits built up on engines using conventional petroleum diesel. The residue dissolves into the biodiesel, and, in some cases, that can lead to engine problems. A straight diet of biodiesel or heavy biodiesel blends will eliminate such problems, however.

Biodiesel also has superior lubricity to petroleum diesel and exerts a lubricating effect that complements that of the motor oil in the crank case and lessens engine wear.

Most current generation compression ignition engines can utilize biodiesel with no problems, but relatively few operators use biodiesel in neat form. The more common practice is to blend biodiesel with ordinary petroleum diesel in proportions of eight parts petroleum diesel to two parts biodiesel.

Feedstocks

In the U.S. well over 90% of all biodiesel is made from soy oil, a high value crop whose price is reflected in the high purchase price of biodiesel itself. Biodiesel has been made from many other plant oils, incuding oils from pumpkinseed, cottonseed, peanuts, and palm. Of the food crops used to make biodiesel, palm offers the best economics, but its cultivation is of course restricted to tropical and subtropical areas.

Biodiesel can also be made from discarded cooking oil and tallow, what is known as trap oil in the case of the former, and yellow grease in the case of the latter, but such feedstock requires extensive cleanup and is scorned by most commercial manufacturers. It is commonly used by home brewers, however, who appreciate the fact that they can frequently obtain it free of charge.

As is stands, the high cost of feedstocks for mass producing biodiesel constitutes a major impediment to the growth of industry. Biodiesel today is not remotely competitive with conventional diesel fuel at an industrial scale except in instances where the user can produce it himself from surplus crop yields, as in large farms in the American Middle West. For this reason biodiesel producers are looking at a number of unconventional feedstocks that can be raised inexpensively with little cultivation and are not used for food or in cosmetics, lubricants, or other markets where they can command high prices.

The most frequently mentioned alternative crop is the jatropha bean tree, which is native to tropical regions and is vigorous and low maintenance. Commercial cultivation of jatropha for biodiesel has begun in Southeast Asia, and since the Government of India has launched a strong initiative to encourage the use of that fuel, a healthy market is almost assured. Unfortunately, jatropha requires five years to mature, a lengthy period in which to wait for payoff.

Another candidate is the Chinese tallow tree which we discuss at length in another section. The Chinese tallow tree is a hardy, fast growing, but invasive species capable of yielding up to fifteen times the amount of usable oil per acre as soy beans, and adaptable to both tropical and temperate zone climates, which is not the case with jatropha. The economics of this crop are probably better than for any rival feedstock, and it also produces useful lumber. Currently, however, no one is raising it commercially for fuel. Why not? Agriculture is a capital intensive business replete with uncertainties arising from weather patterns, the cost of irrigation, the price of labor, and the price of petroleum since most farm equipment will continue to utilize diesel oil for the foreseeable future. Add to this the larger uncertainty of the biodiesel market and one faces a real quandary. The tallow tree is not well established within other markets for vegetable oils, and so one is essentially betting on the biodiesel business. The likely much lower cost of a tallow tree feedstock vis a vis its competitors could be just what it takes to push biodiesel beyond the niche and regional markets it currently occupies and into the mainstream, but then again biodiesel’s competitors, considered in a following section, could achieve a decisive competitive advantage over it. Start a tallow tree plantation at your own risk.

We believe that the biodiesel industry, which has been subject to truly exponential growth over the course of the last five years, will continue to grow strongly into the next decade. Biodiesel’s further future is questionable though. Biodiesel does not utilize the entire plant or even most of it in the production process, and so the farmer ends up cultivating what turns out to be mostly agricultural waste, though in the case of some feedstocks like the coco palm, oil is merely one product among many derived from the crop. And, unlike bio-ethanol or bio-synfuel, or bio-DME, biodiesel may be only be produced from certain types of plants having very high oil contents.

Also to its detriment, biodiesel has an emissions profile that is inferior to that of DME, one of its principal rivals—which, as it happens, may also be produced from biomass and can thus be carbon neutral as well. Finally, biodiesel is not a suitable fuel for the new generation of two stroke diesel power plants for general aviation due to the relatively high vaporization temperature of methyl ester.

The Markets for Biodiesel

Biodiesel has been around for several decades but only began to garner attention in the decade of the nineteen nineties when the issue of global warming assumed prominence. Major sales momentum is much more recent and only dates from the beginning of this decade.

The biggest market by far for biodiesel is in Western Europe, but India promises to be a burgeoning market as well. Elsewhere in the world biodiesel is not particularly well established though interest throughout Southeast Asia is fairly strong.

In the U.S. the biodiesel industry is establishing itself and growing rapidly but has already been somewhat marginalized in our opinion by the phenomenon of home brewing. “Veggie vans”, old Volkswagen microbuses with diesel engines running on converted trap oil, may make for good editorial copy but do little to establish the seriousness of the industry. Worse yet, the home brew product is highly variable in purity and composition which won’t bode well for industry in the long term. Furthermore, the process of manufacturing home brew is fraught with danger due to the extreme toxicity of the methanol and caustic lye normally used by home brewers. On other hand, home brew has created an enthusiastic and highly energized grass roots constituency for biodiesel and a potent viral marketing movement behind it.

Still, home brew ultimately works against the interests of the larger biodiesel producers who have already succeeded in getting ASTM and SAE certification for their products. and who are attempting promote the same kind of rigorous standards that obtain in the petroleum industry. And it is upon these larger producers that the industry ultimately depends for pervasive distribution and mainstream acceptance.

Gaining such acceptance won’t be easy in the U.S. Compression ignition engines are used in less than one percent of passenger vehicles, and the American auto industry has given no indication that it will make any attempt to promote diesel automobiles once again as it did in the late seventies and early eighties. True, in Europe diesels will likely become the strong majority by the end of the decade, but nowhere else.

Biodiesel will continue make inroads where green fuel subsidies are offered for commercial vehicles, but unless the cost of manufacturing can be radically reduced, biodiesel will not account for a significant portion of the distillate fuel marketplace in the midterm.

But if biodiesel can succeed in Europe, why not the U.S.?

The answer to that question lies in the very different energy policies being pursued by most Western European nations. European governments, most of whom command no oil resources of their own, have chosen to tax petroleum fuels very heavily while taxing biodiesel at a much lower rate. On the one hand, this limits consumption of petroleum and makes those nations somewhat less vulnerable to oil price shocks than is the U.S., and, on the other hand, it allows governments to adjust petroleum fuel prices when price shocks do occur simply by lowering taxes.

Such high prices have encouraged Europeans to adopt the much more fuel efficient compression emission engine, and have spurred European auto makers to concentrate on ameliorating the traditional shortcomings of diesel engines. And to a large extent they have succeeded.

All this has been very good for biodiesel producers in Europe, but biodiesel still accounts for only a few percent of distillate fuel sales. We see that percentage increasing, but unless Europe can find substitutes for the expensive rapeseed feedstocks which predominate today, biodiesel’s penetration in the marketplace will necessarily be limited.

In any case, we see little likelihood of the European experience with biodiesel being replicated in the U.S. American politicians are not going to raise taxes on petroleum fuels nor are American auto makers going to reintroduce diesels any time soon.

The last point needs emphasis. The experience of the American consumer with passenger diesels in the past has not been favorable, and overturning the negative preconceptions and prejudices of American motorists in regard to diesel engines would not be easy. Not surprisingly, no American manufacturer, or a Japanese manufacturer, for that matter, has chosen to take that risk.

The Biodiesel Competition

Synfuel distillates resembling petroleum diesel can be produced from a number of feedstocks and by means of a number of conversion processes, though not all processes can be applied to all feedstocks.

The feedstocks include natural gas, coal, oil shale, biomass, and industrial wastes such as old tires and plastics which are made from petrochemicals. The processes include direct liquefaction, hydrothermal upgrading, and the well known Fischer Tropsch conversion which is used far more than any of the others. Except in the case of natural gas feedstocks, the Fischer Tropsch process is virtually always preceded by gasification, that is, heating the fuel to a gaseous state without initiating complete combustion.

Production of synthetic diesel from natural gas via the Fischer Tropsch process is already well proven both technically and economically. Whether the same can be said of gasification and Fischer Tropsch conversion of coal is less certain. Sasol of South Africa currently operates coal-to-liquids facilities without government subsidies, but the plants were built long ago with heavy support from the State. It remains to be seen if capital costs today would be low enough to ensure a reasonable return on investment for new facilities. Producing diesel from oil shale through pyrolysis and subsequent cracking is even more uncertain, while direct liquefaction of coal is more uncertain still. Hydrothermal upgrading of biomass and industrial waste is still largely experimental.

All of these processes result in distillate fuels that are very close in chemical composition to petroleum diesel; in other words, the synfuels are not fundamentally different chemicals like methyl ester. Thus any of these synfuels could be easily and completely integrated into the existing distribution, storage, and transport infrastructures for petroleum diesel.

We have previously made mention of DME as a competitor to biodiesel. DME is not yet a factor in the market but could well become one. The economics of producing DME from coal are fairly favorable by some accounts. Producing it from stranded natural gas resources appears to be even more cost effective. Deriving DME from biomass is more questionable in terms of cost competitiveness, but there are some emerging technologies that appear promising.

Here mention should be made of another rival which essentially forms a class of one, namely SunFuel, a trademarked product produced by Volkswagen and CHOREN Industries and sold on the European market on a pilot basis today. The feedstock may consist of forest or agricultural waste or short rotation fuel crops such as miscanthus, and some moisture is tolerable. The feedstock is subjected to pyrolysis, gasification, and then further processing involving pulverized char produced in the pyrolysis stage. The resulting syngas is then sent through a Fischer Tropsch processor that is not proprietary to Volkswage or CHOREN. The ultimate product contains the same kind of paraffin molecules that characterize Fischer Tropsch distillate synfuel.

Whether SunFuel can expand beyond the small niche market it currently occupies remains to be determined. We know of no independent analysis of the cost of production that would enable us to assess the competitiveness of the product.

Pyrolysis Oil

Pyrolysis oil, also known as biocrude, is produced by the process known as pyrolysis whereby biomass is raised to a temperature sufficient to permit vaporization but insufficient to ignite it. The process takes place in the absence of oxygen. Various types of pyrolyzers are described elsewhere on this Website.

Pyrolysis results in the transformation of a solid or moist feedstock into a liquid, with conversion efficiency normally exceeding fifty percent. Considerable quantities of char and other waste products are also produced and must be disposed of. The chemical composition of pyrolysis oil is highly dependent upon the feedstock utilized, but the process itself inevitably results in a complex mixture of chemicals, primarily consisting of hydrocarbons, and sometimes totaling more than a hundred. Pyrolysis oil is characteristically fairly viscous, brown in color, unstable, and quite corrosive. Energy content varies, but is roughly on a par with that of the heavy residual petroleum oil used for heating and for fueling large ships.

Pyrolysis oil as a commercial product scarcely exists today. Rather, the substance is normally produced on the spot for industrial use in heating and in operating stationary machinery.

Attempts have been made to crack and hydrotreat biocrude to produce more familiar refined products such as diesel oil, kerosene, and gasoline, but the conversion efficiency and energy efficiency of such cracking is poor, and near or mid term commercialization seems unlikely. An alternative processing strategy is to gasify the pyrolysis oil to produce syngas and then proceed with Fischer Tropsch catalytic processing to produce a range of refined synfuels—this on the theory that most gasifiers are better able to cope with liquids than solids. We have seen no rigorous cost accounting for this process and so must reserve judgment on the likelihood of it being commercialized. As indicated previously, the CHOREN Carbo-V process used to make SunFuel is an example of a combined pyrolysis-gasification production technology for converting biomass into liquid fuels.

Bio-alcohols

Here our concentration is mainly on ethanol, and, to a much lesser extent, upon butanol and mixed alcohols. Methanol has been produced from biomass in the past, but not very cost effectively, and although some promising new production processes have emerged, the general rejection of methanol as a primary liquid fuel by the industrialized world means that methanol is marginalized as an energy source unless direct methanol fuel cells or methanol to hydrogen reformers establish real markets for themselves, or unless the Mobil process for producing gasoline from methanol becomes widely adopted.

Ethanol, as explained elsewhere on this Website, is primarily produced from grains and sugar cane today. Grains are heavily predominant in the U.S., while sugar cane is the feedstock of choice in Brazil, the largest ethanol producer at present.

Production of ethanol from sugar is a very simple and relatively inexpensive process involving a single fermentation and subsequent distillation. Grain production requires two fermentations, one to transform starch into sugars and a second to produce ethanol from the sugars. Two types of grain ethanol production are currently extant in the U.S., dry milling and wet milling, with the latter predominating among large scale producers. Both types of mills are described elsewhere on this Website, as is the manufacturing process for sugar cane ethanol.

Ethanol can also be produced from other forms of biomass that do not fall under the nomenclature of food crops. One set of production processes is broadly applicable to what is known as cellulosic biomass, including fast growing fuel crops, agricultural waste such as bagasse and corn stover, and forest and wood processing waste, while a second set of techniques can make use of practically any form of inexpensive biomass including the cellulosic sort as well as the “black liquor” liquid produced by paper mills, animal wastes, and some types of landfill wastes.

Cellulosic Ethanol

The first category of ethanol production technologies falls under the rubric of cellulosic ethanol. The specifics of these processes are discussed elsewhere, but here we will state that all entail the fractionation of woody biomass, which is to say its division into its constituent chemicals.

Wood is made up, for the most part, of only three chemicals, cellulose, hemicellulose, and lignin. Cellulose, and to a lesser degree, hemicellulose provide the structural strength of wood. They are long chain molecules consisting of smaller linked sugar molecules. Cellulose, particularly, has extremely high tensile strength and gives to wood its largely unmatched structural properties.

Lignin serves as binder and holds the chains of cellulose and hemicellulose together. It is a very tough and chemically resistant material, which explains how wooden objects can survive for hundreds and even thousands of years.

Both cellulose and hemicellulose may be converted into sugars, though not the same sugars. Cellulose produces six carbon sugars such as glucose. Hemicellulose splits into five carbon sugars such as xylose.

Lignin, which is not sugar based, generally constitutes a waste product in cellulosic alcohol production, though it may be burned to provide processing heat or to generate electricity.

Cellulose and hemicellulose can be separated from lignin by exposure to solvents, generally acids, or by the action of enzymes, of which cellulase is the most frequently used. The enzymatic processes fall into the category of enzymatic hydrolysis, while those using acids are known collectively as acid hydrolysis. Acid hydrolysis technologies are further divided into two subcategories, concentrated acid hydrolysis and dilute acid hydrolysis. Both are discussed at length in another section.

Of the cellulosic ethanol manufacturing techniques, only the concentrated acid method can be said to have been commercialized, and only a single concentrated acid plant is currently in operation though several more are in the planning stage. Thus despite all the attention these methods have gotten in the press and the considerable amount of investment that has gone into companies developing them, cellulosic production techniques have not successfully challenged traditional grain alcohol wet mill processing in the U.S.

Capital costs for almost all innovative ethanol production techniques, including those for cellulosic ethanol, are much higher than is the case for traditional plants. Because of the theoretically superior conversion efficiency of cellulosic facilities, operational costs should be much lower, but proof from the field is generally lacking because production, such as it, is now takes place in small pilot plants where economies of scale are lacking and where the plants themselves are not obliged to turn a profit.

Moreover, most cellulosic ethanol manufacturing techniques are limited in the feedstocks they can accept. Most have difficulties in processing softwoods, which tend to be very high in lignin content, and, unfortunately, most wood waste comes from softwood sources. Agricultural wastes such as rice straw and corn stover are preferred, though many authorities believe dedicated energy crops such as switch grass, laurel, miscanthus, etc. will predominate as production ramps up.

Gasification Techniques

Ethanol can also be produced from syngas, variously derived from natural gas, coal, or biomass. In the case of biomass, any sort of feedstock may be gasified to produce syngas, but the gasifier in most cases should be optimized for one particular feedstock. Feedstocks that have not been milled or granulated, or contain much moisture, or are contaminated with noncombustible materials tend to pose problems for most designs of gasifiers extant today.

Gasifiers themselves are rather similar in basic design to pyrolysis reactors except that the feedstock is heated to a higher temperature and incompletely combusted rather than simply vaporized. The carbon monoxide in the resultant hydrogen/carbon monoxide mix represents the incomplete combustion of the carbon in the feedstock.

While gasifier manufacturers number in the hundreds, and scores of different designs exist, the cost effectiveness and long term reliability of many if not most of these designs is questionable under conditions of full scale industrial production. True, gasification of coal to meet the needs of the chemical industry already takes place on fairly large scale, but gasification of biomass is still somewhat experimental because a well proven business case does not exist for it, especially for the production of liquid fuels. Commercial electrical generation and cogeneration units using bio-syngas are on the market, but they’ve only been widely adopted in a few places such as the Scandinavian countries and India where local conditions favor them. Most biomass used in energy applications is simply combusted rather than gasified, and that isn’t apt to change quickly.

Two methods exist for transforming bio-syngas into ethanol or higher alcohols, use of catalysts or microbial conversion. BRI is the sole manufacturer of ethanol from syngas to utilize the microbial approach. No independent study has yet been made as to the market readiness or competitive advantages of either technology.

The advantage of gasification in general is that it can utilize many more types of feedstock than can cellulosic hydrolysis production techniques, let alone grain or sugar based ethanol plants. The drawback is that field experience with industrial scale biomass gasifiers is critically lacking. Consequently, it is very difficult to project capital or operational costs for the plants.

In spite of the many unanswered question as to the ultimate viability of the gasification approach to ethanol production, gasification technologies appear to be the focus of more startup activity today than are those involving cellulosic ethanol, although research bearing upon the latter technology is still heavily funded by the Department of Energy which has expressed great faith in the process in its publications. But as with so many other areas of alternate fuel production, the ultimate viability of the gasification approach cannot be determined with any certainty on the basis of public knowledge.

A further question arises as to whether production of ethanol or the production of synfuels represents the better strategy for gasification plants. Ethanol is considerably easier to produce than gasoline or distillate fuel but it is also has a considerably lower energy content and only addresses a single market, that of personal transportation. We would assume on the basis of plant complexity and the requirement of hydrogen in the refining and cracking of synfuels that ethanol is probably appreciably cheaper to produce from syngas than are synfuels, but gasification itself is the most expensive part of the production process in terms of capital and operational costs and so the cost discrepancy between the two fuels may not be overwhelming.