Ethanol-blended fuel is widely used in Brazil, the United States, and Europe. Furthermore, many cars today are flexible-fuel vehicles able to use 100% ethanol fuel. Ethanol is traditionally produced by a fermentation process. Bioethanol is a form of renewable energy that can be produced from forest and agricultural feedstocks. It can be made from very common crops such as wood, hemp, sugarcane, potato, cassava and corn. There has been considerable debate about how useful bioethanol is in replacing gasoline. Concerns about its production and use relate to increased food prices due to the large amount of arable land required for crops, as well as the energy and pollution balance of the whole cycle of ethanol production, especially from corn. Recent developments with cellulosic ethanol production and commercialization may allay some of these concerns.

Cellulosic ethanol offers promise because cellulose fibers, a major and universal component in plant cells walls, can be used to produce ethanol. Paper waste, recycled paper and recycled cotton and viscose textiles consist mainly of cellulose. According to the

International Energy Agency, cellulosic ethanol could allow ethanol fuels to play a much bigger role in the future.

Alcoholic fermentation in its simplest form converts one mole of glucose into two moles of ethanol and two moles of carbon dioxide, producing two moles of ATP in the process.

The overall chemical formula for alcoholic fermentation is:

C ₆ Hi2 0 ₆ ® 2C ₂ HS OH + 2C0 ₂

Hemicelluloses, the second most abundant polysaccharide in nature may also be suited for ethanol production. The major fraction in hemicelluloses is pentosans, however the conversion of pentosans to ethanol is not as straightforward as for glucose or other hexosans. In recent years, significant advances have been made towards the technology of pentosans to ethanol conversion. A significant amount of carbon dioxide is formed in the fermentation process representing about one third of the carbon in the glucose feedstock. Furthermore, ethanol fermentation is not 100% selective with other side products such as acetic acid, glycols and many other products produced. They are mostly removed during ethanol purification. Fermentation takes place in an aqueous solution. The resulting solution has an ethanol content of around 15%. Ethanol is subsequently isolated and purified by a combination of adsorption and distillation.

One of the main challenges when a biochemical conversion technique is employed to produce cellulosic ethanol is the low concentration of ethanol in the fermentation broth, which increases the energy demand for recovering and purifying ethanol to fuel grade.

Simple distillation cannot be used to distill ethanol above the azeotropic composition. The state of the art technique used in the corn-ethanol industry to produce fuel ethanol is distillation close to the azeotropic composition followed by dehydration in a molecular sieve based adsorption unit.

This approach can be used for recovering and purifying ethanol from the fermentation broth obtained from cellulosic feedstock. However, there is a drastic increase in the distillation energy demand as the ethanol concentration in the fermentation broth from cellulosic sources is relatively low. Heat integrated distillation operations such as multi-effect distillation and vapor recompression can reduce distillation energy demand. These energy saving techniques have been shown to significantly reduce the distillation energy demand for the water-ethanol system; for instance, distillation energy demand reduction on the order of 42% has been reported for double effect distillation with split feed compared to conventional distillation with a single column for distilling 93 wt% ethanol from a feed containing 7 wt% ethanol. Conversely, the VLE of the water-ethanol system can be improved towards ethanol separation by dissolving a salt in the liquid phase to raise the equilibrium vapor ethanol content. Isobutene (2-methylpropene) is one of those chemicals for which bio-based production might replace the petrochemical production in the future. Currently, more than 10 million metric tons of isobutene are produced on a yearly basis. Even though bio-based production might also be achieved through chemocata lytic or thermochemical methods, this review focuses on fermentative routes from sugars. Although biological isobutene formation is known since the 1970s, extensive metabolic engineering is required to achieve

economically viable yields and productivities. Two recent metabolic engineering

developments may enable anaerobic production close to the theoretical stoichiometry of lisobutene + 2C0 ₂ + 2H ₂ 0 per mol of glucose. One relies on the conversion of 3- hydroxyisovalerate to isobutene as a side activity of mevalonate diphosphate decarboxylase and the other on isobutanol dehydration as a side activity of engineered oleate hydratase. The latter resembles the fermentative production of isobutanol followed by isobutanol recovery and chemocatalytic dehydration. The advantage of a completely biological route is that not isobutanol, but instead gaseous isobutene is recovered from the fermenter together with C0 ₂ . The low aqueous solubility of isobutene might also minimize product toxicity to the microorganisms. Although developments are at their infancy, the potential of a large scale fermentative isobutene production process is assessed. The production costs estimate is 0.9€ kg ¹ , which is reasonably competitive. About 70% of the production costs will be due to the costs of lignocellulose hydrolysate, which seems to be a preferred feedstock.

To achieve an economically and ecologically sustainable process, future isobutene processes might be focused on using lignocellulosic hydrolysate as a substrate. This might be obtained by processes that are still in the development stage. Analogous to ethanol- producing microorganisms, isobutene-producing microorganisms could be engineered for conversion of all C5- and C6-sugars in lignocellulose hydrolysate into product and for tolerance towards potential inhibitors such as furanics, phenolics, and acetic acid. In ethanol manufacturing, the achievable mass concentrations of ethanol will be at most 50% of the feed concentration of lignocellulose hydrolysate. Therefore, efficient ethanol distillation relies on fermentation of relatively concentrated hydrolysates. Isobutene production might use more dilute hydrolysate because the isobutene concentration in the off-gas will not depend on it. Besides, the risk that contaminants from the hydrolysate complicate the product recovery is much smaller for isobutene than for other fermentation products.

In addition to about 2/3 carbon dioxide and 1/3 isobutene, the off-gas will be saturated by water (4,000 Pa vapor pressure at 30 °C, corresponding to 1.5% (w/w)). It will contain traces of other volatile components, such as acetic acid, at concentrations determined by the fermentation feedstock composition and the side reactions in the fermenter. The allowable concentrations of contaminants in purified isobutene will depend on its use. There are several possible ways to achieve C0 ₂ and H ₂ 0 separation from isobutene:

• Stage-wise condensation to liquid

• Pressure swing adsorption

• Membrane permeation

• Absorption

• Combinations of the aforementioned methods

Stage-wise condensation might seem straightforward because of the large difference in boiling points (-78 °C, -7 °C, and 100 °C for CO2, isobutene, and water, respectively). This would have to be driven by electricity, which is a relatively expensive energy source. A preliminary calculation, assuming pressurizing the off-gas at 20 °C showed that condensed water might contain a certain percentage of isobutene. This stream is small, so this might be acceptable as product loss. More importantly, isobutene that would condense subsequently might contain ~2% CO2. To obtain a purer product stream, a counter current condensation-vaporization operation (continuous cryogenic distillation) might be required.

See fig. 1 for a block scheme of an option for fermentative isobutene production and recovery. Pressure swing adsorption should be able to achieve the required purity because in an adsorption column, poorly adsorbed species will be pushed forward by stronger adsorbed species. Such an adsorption processes may use relatively expensive adsorbent material and will operate at high pressure, so the capital investment may be high. For membrane technology, this also holds: membranes are expensive and the process runs at moderate to high pressure. Separation of isobutene from C0 ₂ by either adsorption or permeation might be achieved using DD3R-zeolite, for example. Isobutane molecules do not penetrate in the zeolite while carbon dioxide molecules can. The molecular sizes of isobutane and isobutene are almost similar.

As done industrially for flue gases, C0 ₂ removal can be accomplished by absorption in aqueous amine solutions. The absorbed CO2 can be liberated by heating. The water would still need to be removed from the remaining isobutene gas by one of the aforementioned methods. The disadvantage of the adsorption, permeation, and absorption configurations is that CO2 rather than isobutene is captured, while isobutene is the minor component of the two. In that respect, condensation to liquid is more favourable.

Several other cellulosic feed fermentation processes produces a significant amount of C02 concomitantly with production of the desired products including production of higher alcohols such as isopropanol, butanol by the ABE process or other butanol processes including fermentation etc.

Prior to fermentation step, the biomass (which may be any type of biomass comprising carbon and oxygen) need to be pre-treated by one or more of the methods described in Table 1 (presented in the figures as Figure 2).

While it has been suggested that the carbon dioxide stream from fermentation processes could be utilized for various purposes it has been found that this stream advantageously can be valorised and used for production of automotive fuels such as diesel, gasoline or kerogene. Furthermore, by integration of the fermentation and fermentation product upgrade process with CO2 recovery and upgrade in accordance with the present invention, significant energy saving can be made through heat integration. The utilization of C0 ₂ as raw material for valuable products has attracted worldwide attention in both industrial and academic research using heterogeneous, homogeneous, photo or electro catalysts. One particularly desirable process is to convert the C0 ₂ stream from fermentation by reverse gas shift (RWGS) followed by Fischer Tropsch (FT), methanol or DME synthesis. The hydrogen can come from any source such as gasification of biomass and water gas shift to hydrogen followed by hydrogen purification, steam reforming of carbonaceous material, however hydrogen for RWGS is advantageously produced by electrolysis of water.

Reactors for RWGS and FT systems used in the current invention are preferably of the microchannel type. These devices are characterized by paralleled arrays of microchannels with typical dimensions in the 0, 1 - 5.0 mm range. Processes are accelerated 10 to 1,000 fold by reducing heat and mass transfer limitations, decreasing transfer resistance between process fluids and channel walls.

The FT synthesis is preferably performed in once through mode without recycling of tail gas. The CO conversion should be higher than about 80 %. The tail gas from FT synthesis is burned alone or together with residues from the fermentation process (bagasse residue, molass, lignin etc.) using an oxidant consisting of air, oxygen enriched air or oxygen. Such oxygen can advantageously be produced by electrolysis, simultaneously generating hydrogen for the RWGS process.

The catalyst use in the FT process is preferable a dual function catalyst enabling the product slate to be enriched in drop in diesel components or jet fuel range components with a minimum formation of waxy hydrocarbons and methane. Alternatively, the FT products may be distilled for fractionation into different automotive fuels. The FT product may also partly of fully be transported to petroleum refineries as green feedstocks for further refinement to premium quality biofuels.

There are numerous advantages in combining the fermentation process with upgrade of CO2 containing gases to hydrocarbons in accordance with the present invention. In particular, several heat integration schemes can be foreseen including heat integration between endothermal and exothermal unit operations. In particular, the exothermal FT process can be heat integrated with both RWGS and distillation and concentration of fermentation broth and fermentation products. Waste generated in the fermentation process such as lignin residues from upstream fermentation (biomass fractionation steps) can advantageously be combined with the tailgas from an FT synthesis to generate steam and heat for various unit operations in the combined fermentation C02 conversion process of the present invention.

Several advance options for heat exchange between hot cold and hot streams in the combined process will ensure high overall energy efficiency from biomass to biofuels.

Below, the present invention and embodiments thereof are summarized.

In its most general aspect, the present invention relates to a process for the production of biofuels or fine chemicals from biomass, characterized by the following steps

a) Providing a carbonaceous material originating from biomass in a form suitable for fermentation;

b) Fermentation of carbonaceous material from step a for the production of at least one main fermentation product and a carbon dioxide containing gas;

c) Recovering carbon dioxide containing gas from step b and after optional purification, combining carbon dioxide containing gas with a hydrogen containing gas to form a synthesis gas containing carbon monoxide and hydrogen;

d) Converting synthesis gas comprising carbon monoxide and hydrogen by a catalytic process to provide biofuels or biofuel components; and

e) Transferring heat by heat transfer at least between process steps d) and process b) and c).

According to one specific embodiment of the present invention, step a) comprises a step wherein the biomass is pre-treated by an acid or by a steam explosion process in order to concentrate a formation process feed with respect to sugars (glucose, fructose, pentoses). According to yet another specific embodiment, the fermentation process product is ethanol, butanol or isobutene.

Furthermore, according to one embodiment, wherein step c) comprises that carbon dioxide gas is reacted with carbon dioxide gas in a catalytic or non-catalytic reversed gas shift reactor operating at a temperature above about 500^C.

Moreover, step d) preferably is a Fischer Tropsch synthesis gas conversion step.

According to yet another embodiment, a product slate from the Fischer Tropsch reaction step is substantially composed of diesel and kerogen range chemicals.

Furthermore, according to one embodiment a fraction of waxy products from the Fischer Tropsch reaction step is lower than 10 % by weight, preferably lower than about 5 % by weight.

Moreover, tail gas from a Fischer Tropsch reaction step is suitably combusted to raise steam or heat at least partially used for purification or concentration of fermentation process product.

According to yet another specific embodiment, hydrogen gas combined with carbon dioxide gas is produced by electrolysis of water and formed oxygen optionally is at least partially used as oxidant for combustion of fermentation residues or Fischer Tropsch tail gas.