Hydrotreatment and fermentation of biomass represent two of the three main types of pathways under development: chemical, biochemical, and thermochemical.

• Chemical technologies include the hydrotreatment of oils; catalytic decarboxylation; and methanol production.

  Hydrotreatment—the chemical reaction of vegetable oils, animal-based waste fats, and by-products of vegetable oil refining with hydrogen—produces hydrocarbons with properties superior to conventional biodiesel and fossil diesel. The product is sulfur-, oxygen-, nitrogen- and aromatics-free diesel which can be used without modification in diesel engines.

  These diesel-type hydrocarbons, also referred to as hydrotreated vegetable oil (HVO) or a renewable diesel, can also be tailored to meet aviation fuel requirements. Hydrotreatment is the most successful chemical pathway so far, the report notes; companies applying this type of technology include Neste Oil and Dynamic Fuels.

• Biochemical technologies include the different processes for the extraction of sugars from biomass and their subsequent fermentation—e.g., cellulosic ethanol.

  Currently, the report notes,there are two basic R&D strategies in the field of fermentation: (a) using ethanologens like yeasts which are enhanced with the ability to use C₅ sugars, or (b) organisms capable of using mixed sugars (such as E. coli) are modified in their fermentation pathway in order to produce bioethanol. Further research activities focus on the increase of robustness towards inhibition as well as fermentation temperature.

  Other biochemical pathways under development include microbial fermentation via acetic acid (e.g., ZeaChem); microbial fermentation via farnesene (e.g., Amyris); yeast fermentation to butanol; and microbial fermentation of gases (e.g., Coskata, INEOS and Lanza Tech).

• Thermochemical processes include gasification, pyrolysis and torrefaction; the report focuses on the gasification pathway as the best currently developed.

  The resulting syngas can be processed into synthetic fuels via the Fischer-Tropsch process; upgraded to synthetic natural gas; or used to synthesize mixed alcohols.

  Development is recently focusing on the production of mixed alcohols rather than BtL-Diesel, the report finds.

The authors of the report, which is based on a database on advanced biofuels projects, excluded novel technologies that are mainly in the R&D and pilot stage, such as algae-based biofuels and the conversion of sugar into diesel-type biofuels using biological or chemical catalysts.

Economic reasons are driving this development, and concepts like the integration into existing industries and the production of several products instead of biofuel only (biorefinery concept) receive more attention lately. But, as expected, some of the projects for advanced biofuel production have failed.

As a result, companies are now more careful in making announcements of advanced biofuels projects, and several large-scale projects have been postponed recently, some even though public funding would have been granted.

—“Status of Advanced Biofuels Demonstration Facilities in 2012”

Cumulative capacities of projects in the overview report. Source: “Status of Advanced Biofuels Demonstration Facilities in 2012”. Click to enlarge.

The report gathered data from 71 actively pursued advanced biofuels projects. Of the 71 projects for which data was provided, 43 were classified to use a biochemical pathway; 20 use a thermochemical pathway; and 7 use a chemical pathway. One pilot plant is flexible and allows for both biochemical or thermochemical pathway; this project is counted half towards each of these technologies. Output capacities are in the range of <50 t/y through <800,000 t/y.

Chemical. 7 projects apply chemical pathways to produce advanced biofuels. Neste Oil (in 4 facilities worldwide) and Dynamic Fuels apply hydrotreatment of oils. Alipha Jet applies catalytic decarboxylation of crude fats. Both technologies produce biofuels of superior quality that can be tailored to meet aviation fuel requirements. BioMCN produces methanol from glycerine residue from biodiesel plants. Methanol can subsequently be converted into various fuels and chemicals.

While the resulting fuels are of high quality, the report notes, the drawback of these technologies is that they utilize potentially food feedstock such as oils and fats.

Biochemical. A variety of lignocellulosic feedstocks are being used in the 43 projects, including agricultural residues, wood and wood residues from forestry and forest products, dedicated energy crops, and municipal solid waste. The most frequently cited feedstocks are corn cobs, corn stover, wheat straw and wood waste.

Some technologies utilize gases as feedstock; these gases may be derived from biomass gasification or from other industrial processes.

The report found that most technologies include steam explosion or acids for pretreatment of lignocellulosic biomass, followed by enzymatic hydrolysis and fermentation. Enzymes are often provided by dedicated enzyme producers, but some companies such as Iogen and Mascoma produce their own enzymes. Mascoma combines enzyme production, hydrolysis and fermentation in a single step (consolidated bioprocessing).

Thermochemical. While biochemical projects are targeting agricultural residues and herbaceous feedstocks, thermochemical technologies focus on woody feedstock. Products from the 20 projects using the thermochemical pathway range from Fisher Tropsch (FT)-liquids; synthetic natural gas (SNG); and Di-Methyl-Ether (DME) to ethanol, methanol and mixed alcohols. The type of biofuel produced does not depend on the feedstock in use but on the demand for replacement of either gasoline or diesel fuel in the respective region.

Feedstocks used include wood chips and pellets from forestry and forestry residues, sorted municipal solid waste (SMSW), and sulphite spent liquor (SSL).

By end of 2012 the status of 48 projects is operational, 9 projects are under construction or under commissioning, and 14 projects are planned. Operational facilities are comparatively small except for the chemical facilities.

The largest chemical facilities are Neste Oil’s facilities in Rotterdam and Singapore; the largest biochemical facility is that of Borregaard Industries; and the largest thermochemical facility is that of Tembec Chemical Group, both of which produce app. 15,000 t/y of ethanol from spent sulphite liquor.

Resources

• Bacovsky, Dina; Ludwiczek, Nikolaus; Ognissanto, Monica; Wörgetter, Manfred (2013) Status of Advanced Biofuels Demonstration Facilities in 2012; A Report To IEA Bioenergy Task 39. Report T39-P1b