While the focus of this chapter has been on biolipids it is important to note that any biomass can be converted to "bio-oil" via a high-temperature process known as pyrol­ysis. This "bio-oil" also known as Synfuel or Sunfuel is currently only produced on a small scale and it very much belongs to the second-generation biofuels, as it is a way of generating fuel from a range of biomass including straw, wood or other materials high in lignin, which are difficult to convert to bioethanol. The potential for mass production remains enormous. The production of this biomass to liquid or BtL fuel can vary in complexity and can vary depending on the individual needs, but it essentially comprises the following steps.

Gasification

Gasification is a form of incomplete combustion in which a fuel is burnt in an oxygen-deficient atmosphere. An energy-rich gas, consisting principally of methane, CO and hydrogen, is formed but heat release is mini­mized. Thus an energy-rich fuel (biomass) is converted into an energy-rich gas. There are differing processes for gasification. For example, a description of the

Carbo-V process first developed by Chloren Industries but now owned by Linde Engineering GmbH was out­lined in the Biofuel Technology Handbook (Rutz and Janssen, 2007). This involves low-temperature gasifica­tion, where low-temperature pyrolysis with air or oxy­gen at 400—500 °C allows the continuous production of a gas containing both tars (volatile component) and char (carbon solids). This is followed by a high — temperature gasification, where the gas is further oxidized (again hypostoichiometrically) in a combustion chamber. The third part involves blowing the pulverized char into the hot gasification medium. Pulverized char and gasification medium react endothermically in the gasification reactor and are converted into a raw synthe­sis gas. Other gasification processes can be found, such as the recently developed Bioliq®, which was formed by Lurgi AG (Frankfurt Germany) with Karlsruhe Insti­tute of Technology (Karlsruhe Germeny).

Cleaning Process

After gasification, it is usual to have many impurities and thus cleaning remains one of the most important and most technical challenges. Remaining tars tend to be refractory and difficult to remove by thermal or phys­ical processes. Generally, the impurities in biosyngas pro­duced from the gasifier can be grouped into three types: (1) organic impurities, such as tars, benzene, toluene, and xylenes; (2) inorganic impurities, such as O2, NH3, HCN, H2S, Carbonyl sulfide (COS), and HCl; and (3) other im­purities, such as soot and dust. Both thermal cracking, which involves the addition of steam and oxygen at 200—1000 ° C, and catalytic cracking at lower tempera­tures is possible, as is low-temperature scrubbing with an oil-based medium may all encompass the process. A multicontaminant syngas treatment process created by Southern Research Institute, Birmingham, Alabama, USA, uses a candle filter, which can be catalytic, closely coupled with the gasifier. A variety of sorbents is injected into the gasifier or between the gasifier and filter to remove various contaminants (e. g. alkali metals, sulfur species, and halides) both by reaction in the gas phase and on the filter cake. Catalysts may be incorporated into the candle filter or the filter may be coated with a catalyst to crack tar and ammonia depending on the oper­ating temperature of the candle filter. An outline of the process can be seen in Figure 12.1.

Synthesis

Two methods are available for this production step, but the Fischer-Tropsch (FT) synthesis is the most widely known. It was developed at the Kaiser-Wilhelm Institute for Research on Coal (Muhlheim/Ruhr) in 1925. In Germany, coal to liquid fuels have been

produced with the help of FT synthesis since 1938. During the process, CO and H2, with the aid of a catalyst, will form hydrocarbons. A variety of catalysts exist, but the most common are usually transition metals such as cobalt. In the case of biomass, however, an iron catalyst is often favored (Hu et al., 2012).

The other process is the methanol-to-gasoline® method, in which the syngas is first transformed into methanol as an intermediate state. In a following step, fuels can be obtained from this compound. Finally, after separating the produced liquid hydrocarbons into heavy, medium and light fractions, these hydrocarbons are refined and blended to achieve the desired fuel properties.

CONCLUSION

The search for a sustainable supply of fuel that does not contribute to global warming has consumed envi­ronmental scientists for decades. While it is unlikely there is a "silver bullet" solution to the pending energy crisis the use of biolipids has enormous potential to meet a large proportion of the global transport fuel requirements. Similarly, no Single lipid source is pro­duced in sufficient quantities to impact on the world’s fuel supplies; therefore, a combination of all biolipids outlined above will be required if biolipids are to be a realistic alternative to petroleum-based fuels. While plant-derived biolipids currently dominate the liquid bioenergy markets, microalgae remain the most prom­ising source of biolipids in the future. The limited land
usage requirement and efficient carbon fixing capabil­ities of microalgae make them the ideal choice as a source of biolipids; however, there are a number of stumbling blocks to be overcome before algal biofuels are a commercial reality. These include the challenge of growing algae at industrial scale to meet the increasing demand for liquid transport fuel, the energy input involved in harvesting and dewatering algae and finally the cost and environmental impact of efficiently extract­ing biolipids from algae. These challenges are far from insurmountable, however, and each challenge is being tackled by numerous academic institutions and increas­ingly, by large, multinational energy, food and industrial chemical companies. This concerted effort with regard to algae biofuels, coupled with the more established plant — and animal-based biofuel industries can supply a significant portion of the world’s energy needs in the future.