From: Energy Applications of Biomass, Michael Z. Lowenstein (Ed). (Elsevier Applied Science Publishers, 1985)

Scanned by F. Marc de Piolenc

3. Liquefaction

Liquefaction of biomass and wastes is accomplished by natural, direct and indirect thermal, and fermentation methods. Natural liquefaction systems were referred to in Sec. 2.2 of this paper in connection with certain arid-land plants and microalgae growth and the resultant formation of lipids and hydrocarbons. Other natural processes that produce liquids suitable as fuels are performed by certain tree species (e.g., the Brazilian Copaifera langsdorfii tree that yields sesquiterpenes that can be used as diesel fuels without modification, and plants that bear oil seeds; e.g., sunflowers). Research is continuing in all of these areas.

One of the most interesting approaches to the natural production of liquid fuels by biomass is under investigation by Nobel prize winner Melvin Calvin using a combination of natural photosynthesis and genetic manipulation. The overall process consists of three steps: hybridization of Euphorbia lathyris with E. esula,which produces fewer hydrocarbons than E. lathyris but grows as a perennial rather than an annual; modification of the photosynthetic pathway of the hybrid to cyclize C 15 intermediates so that sesquiterpenes are formed; and transfer of the gene that codes for sesquiterpene production from C. langsdorfii to the plant.

Conceptually, this sequence would optimize for sesquiterpene production by a herbaceous plant that can be grown in the United States at high annual yields without replanting each year. This process would provide a significant advance over present techniques of liquid hydrocarbon production from biomass.

Currently, more research is being done on direct and indirect thermal liquefaction methods for biomass and wastes than on the other methods. Direct liquefaction is either reaction of biomass components with smaller molecules such as H2 and CO (e.g., PERC and LBL processes) or short-term pyrolytic treatment, sometimes in the presence of gases such as H2. [Note: the PERC process is the Wood-to-Oil process reported in Considine's Energy Technology Handbook.] Indirect liquefaction involves successive production of an intermediate, such as synthesis gas or ethylene, and its chemical conversion to liquid fuels, In 1983, after several years of laboratory and pilot-plant work on the PERC and LBL processes,which involve reaction of product oil or water slurries of wood particles with H2 and CO at temperatures up to about 370 deg C and pressures up to 4000 psig in the presence of sodium carbonate catalyst, researchers concluded that neither process can be commercialized for liquid fuel production without substantial improvement. The most attractive approach to such improvement is believed to be a combination of solvolysis with a pyrolysis or reduction step. However, the oxygen content of the resulting complex liquid mixture is still high (-6 to 10 wt %), and considerable processing would appear to be necessary to upgrade this material.

A convenient classification of biomass pyrolytic processes is shown in Table 4. [Table not available.] Maximum liquids yields are usually obtained in the intermediate temperature range if the residence time is short. Among the short residence-time processes (0.5 to 5 s) under development are vacuum pyrolysis at about 300 to 400 deg C and 0.3 atm (U. of Sherbrooke, Canada), flash pyrolysis at about 500 to 650 deg C and 1 atm (U. of Waterloo, Canada), hydropyrolysis in an atmosphere of hydrogen at about 500 to 600 deg C and 5 to 6 atm (HYFLEX TM , IGT), and flash pyrolysis in atmospheres of hydrogen or methane at 600-1000 deg C and 1 to 70 atm (Brookhaven National Laboratory). An interesting report of a relatively long residence time (10 to 15 min heat-up, several hours at temperature) pyrolysis study at reduced pressures of 0.0004 to 0.004 atm and temperatures of 250 to 320 deg C of wild cherry wood seems to contrast with the results of several reports on flash pyrolysis. In this study, about 70 wt % of the sample was volatilized at 290 to 315 deg C over the pressure range studied; the major products were methanol, acetone, acetic acid, cresols, and substituted phenols. These results suggest that the combination of lower temperature, reduced pressure, and long residence time may provide a technique for minimizing char and heavy tar formation. In any case, the liquid products from all direct pyrolysis processes are highly oxygenated and acidic. Chemical rather than fuel applications would appear to be more feasible with these wood oils at this time.

Fundamental studies of the mechanisms of biomass pyrolysis continue to shed more light on the complex chemistry of direct thermal conversion. One of the most interesting techniques developed by the Solar Energy Research Institute (SERI) for this work uses direct mass spectrometric sampling of pyrolysis products from wood. The goal of these studies is to determine, in molecular detail, the chemistry and kinetics of the primary and secondary pyrolysis processes for biomass and its constituents. "Fingerprints" characteristic of the particular biomass used and identification of the broad range of compounds formed including specific polynuclear aromatics will undoubtedly make this technique very useful.

Copaifera langsdorfii Desf.
Diesel tree

Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.

That the oleoresin called copaiba could be obtained by incising the trunk was first reported in England in 1625, in a work published by Purchas, "...a single tree is said to yield about 40 litres." (Grieve, 1931, reprinted 1974). Quoting nobel-laureate Calvin, Maugh says (1979), "Natives ... drill a 5 centimeter hole into the 1-meter thick trunk and put a bung into it. Every 6 months or so, they remove the bung and collect 15 to 20 liters of the hydrocarbon. Since there are few Rabbit diesels in the jungle, the natives use the hydrocarbon as an emollient and for other nonenergy-related purposes. But tests have shown, he says, that the liquid can be placed directly in the fuel tank of a diesel-powered car." (Maugh, 1976). The copal is used in lacquers, massage preparations, medicines, and paints. Wood and resin can be used for fuel. The wood is used in carpentry (Burkart, 1943).

Other potential fuel trees:

Euphorbia lathyris
Petroleum plant

See also:

Pittosporum resiniferum
Petroleum nut

Simmondsia chinensis

See also:

Moringa oleifera
Horseradish-tree, Ben-oil tree, Drumstick-tree

See Wood-to-Oil Process

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