An alternative method for the production of second-generation biofuels

Abstract

Biogenic energy cycle: Manifold types of biological wastes can be converted into a valuable coal by hydrothermal carbonization (HTC). Hereafter green biofuels can be obtained by direct coal liquefaction (DCL) more efficiently than directly from biomass. After combustion of biofuels, carbon dioxide and water can be used for plant growth to close the energy cycle in an environmentally sustainable way.

Direct liquefaction of lower-rank coals and biocoals with magnetically separable catalysts as a sustainable route to fuels

“…A sample of the ''Biocoal'' was obtained from SunCoal and produced out of plant remains. The pretreatment and storage methods of the coals are described elsewhere [19,32]. The results for the higher heating values, the proximate and the ultimate analysis for the three coals are shown in Table 1.…”

“…The values for a biopetroleum comprise an H/C molar ratio >1.5, a higher heating value (HHV Oil ) > 40 MJ kg À1 and an oxygen content w O < 6.0 wt.% [33]. Our biocoal DCL yielded up to 32 wt.% biooils which could fulfill the last two criteria using a Ni/TiO 2 catalyst at pressures of 21 MPa and temperatures of 673 K [32].…”

“…The DCL of biocoals which are produced by the hydrothermal carbonization (HTC) of biomass was proposed by Bergius at the beginning of the last century and has not been considered for several decades [31]. In our previous publication, we could show that the DCL of biocoals, from a wide range of biomass raw materials, is under modern liquefaction conditions superior to other biomass liquefaction techniques in literature [32]. The combustion gases of the thus produced biofuels could be recycled for plant growth, and the plants could be again energetically densified by HTC and the following DCL to biofuels [32].…”

“…The combustion gases of the thus produced biofuels could be recycled for plant growth, and the plants could be again energetically densified by HTC and the following DCL to biofuels [32]. This alternative route could be economically and ecologically beneficial, since no new CO 2 emissions are generated [32]. However, this technique is still in its infancy and has to be further investigated.…”

“…In our previous publication, we could show that the DCL of biocoals, from a wide range of biomass raw materials, is under modern liquefaction conditions superior to other biomass liquefaction techniques in literature [32]. The combustion gases of the thus produced biofuels could be recycled for plant growth, and the plants could be again energetically densified by HTC and the following DCL to biofuels [32]. This alternative route could be economically and ecologically beneficial, since no new CO 2 emissions are generated [32].…”