A hybrid hydrogen-carbon (H2CAR) process for the production of liquid hydrocarbon fuels is proposed wherein biomass is the carbon source and hydrogen is supplied from carbon-free energy. To implement this concept, a process has been designed to co-feed a biomass gasifier with H 2 and CO2 recycled from the H2-CO to liquid conversion reactor. Modeling of this biomass to liquids process has identified several major advantages of the H 2CAR process. (i) The land area needed to grow the biomass is <40% of that needed by other routes that solely use biomass to support the entire transportation sector. (ii) Whereas the literature estimates known processes to be able to produce Ϸ30% of the United States transportation fuel from the annual biomass of 1.366 billion tons, the H 2CAR process shows the potential to supply the entire United States transportation sector from that quantity of biomass. (iii) The synthesized liquid provides H 2 storage in an open loop system. (iv) Reduction to practice of the H 2CAR route has the potential to provide the transportation sector for the foreseeable future, using the existing infrastructure. The rationale of using H 2 in the H2CAR process is explained by the significantly higher annualized average solar energy conversion efficiency for hydrogen generation versus that for biomass growth. For coal to liquids, the advantage of H 2CAR is that there is no additional CO2 release to the atmosphere due to the replacement of petroleum with coal, thus eliminating the need to sequester CO 2. biofuels ͉ coal ͉ hydrogen ͉ oil

We have estimated sun-to-fuel yields for the cases when dedicated fuel crops are grown and harvested to produce liquid fuel. The stand-alone biomass to liquid fuel processes, that use biomass as the main source of energy, are estimated to produce one-and-one-half to three times less sun-to-fuel yield than the augmented processes. In an augmented process, solar energy from a fraction of the available land area is used to produce other forms of energy such as H(2), heat etc., which are then used to increase biomass carbon recovery in the conversion process. However, even at the highest biomass growth rate of 6.25 kg/m(2).y considered in this study, the much improved augmented processes are estimated to have sun-to-fuel yield of about 2%. We also propose a novel stand-alone H(2)Bioil-B process, where a portion of the biomass is gasified to provide H(2) for the fast-hydropyrolysis/hydrodeoxygenation of the remaining biomass. This process is estimated to be able to produce 125-146 ethanol gallon equivalents (ege)/ton of biomass of high energy density oil but needs experimental development. The augmented version of fast-hydropyrolysis/hydrodeoxygenation, where H(2) is generated from a nonbiomass energy source, is estimated to provide liquid fuel yields as high as 215 ege/ton of biomass. These estimated yields provide reasonable targets for the development of efficient biomass conversion processes to provide liquid fuel for a sustainable transport sector.

When compared with biomass gasification/Fischer‐Tropsch synthesis, hydropyrolysis/hydrodeoxygenation (HDO)‐based processes have a potential to achieve high biomass carbon conversion to liquid fuel with much lower amounts of supplementary H2. On the basis of this observation, we suggest a Hydrogen Bio‐oil (H2Bioil) process using fast hydropyrolysis/HDO that has a potential to produce nearly double the amount of liquid fuel when compared with the existing biofuel processes while requiring only modest quantities of supplementary H2. The optimal operating mode for the H2Bioil process is suggested to be in an entrained bed mode in presence of H2 with gas phase HDO of hydropyrolyzed vapors. A remarkable result due to reduced need for the supplementary H2 is that it provides synergistic integration of the H2Bioil process with a coal gasification power plant or a small scale steam natural gas (NG) reformer leading to a dramatic increase in the liquid fuel production from biomass and coal or NG. Here, hot synthesis gas (T>500°C) from a coal gasifier or methane reformer supplies H2/CO for hydropyrolysis and deoxygenation as well as heat for the process. This result is exciting, because it presents us with an option to build integrated H2Bioil processes sooner rather than later when the cost effective H2 becomes available from a carbon‐free energy source such as solar or nuclear. The H2Bioil process and its integrated version with a small scale NG reformer have strong potential to be attractive on a small scale while being more efficient than any current biomass to liquid fuel process in operation. © 2009 American Institute of Chemical Engineers AIChE J, 2009

In a solar economy, sustainably available biomass holds the potential to be an excellent nonfossil source of high energy density transportation fuel. However, if sustainably available biomass cannot supply the liquid fuel need for the entire transport sector, alternatives must be sought. This article reviews biomass to liquid fuel conversion processes that treat biomass primarily as a carbon source and boost liquid fuel production substantially by using supplementary energy that is recovered from solar energy at much higher efficiencies than the biomass itself. The need to develop technologies for an energy-efficient future sustainable transport sector infrastructure that will use different forms of energy, such as electricity, H(2), and heat, in a synergistic interaction with each other is emphasized. An enabling template for such a future transport infrastructure is presented. An advantage of the use of such a template is that it reduces the land area needed to propel an entire transport sector. Also, some solutions for the transition period that synergistically combine biomass with fossil fuels are briefly discussed.

This study presents a systems approach for comparing alternative routes for converting CO 2 to liquid fuel using solar energy based on a novel metric of sun-to-fuel (STF) efficiency. The metric refers to the fraction of incident solar energy that is recovered in the liquid fuel. The STF efficiency analysis identifies energy and land use efficient routes that require immediate research and development effort to speed up their progress toward long-term cost-effectiveness. The analysis' unique insights are particularly relevant for densely populated regions, having scarce per capita land availability relative to the per capita energy demands. With atmospheric CO 2 as the renewable carbon source, we present a detailed case study comparing the currently known photosynthetic routes with a theoretical route based on direct extraction of CO 2 from air and its subsequent thermochemical conversion to liquid fuel. The findings indicate that the latter route could be potentially more energy and thereby land use efficient than any of the currently known photosynthetic routes, therefore, warranting its inclusion in any transportation fuels research portfolio. An interesting finding of our study is that for the interim period while CO 2 extraction is still uneconomical and CO 2 sourced from power plants is instead used, the relative energy efficiency of different routes remains unchanged. This suggests that the results in general are independent of the concentration of the CO 2 source.