NL1035651C2 - Producing butanol and hydrogen from biomass by fermenting biomass to obtain butanol in a first reaction mixture, removing butanol to obtain effluent, and using the effluent as a substrate in a second reaction mixture - Google Patents

Abstract

Combined production of butanol and hydrogen from biomass comprises: (a) fermenting biomass to obtain butanol in a first reaction mixture; (b) removing the butanol from the first reaction mixture to obtain effluent; and (c) using the effluent as a substrate in a second reaction mixture in a process using low substrate concentrations, in particular a hydrogen production process.

Description

METHOD FOR THE COMBINED PRODUCTION OF BUTANOL AND HYDROGEN

The present invention relates to a method for the combined production of butanol, in particular acetone-5 butanol-ethanol (ABE), and hydrogen from biomass.

Biofuels are renewable fuels made from plant matter rather than fossil fuels. Today's primary liquid biofuels are ethanol and biodiesel. Other potential biofuels are butanol and hydrogen.

10 Butanol is a biofuel which has superior properties with respect to bioethanol. Firstly, butanol producing, or solventogenic, bacteria ensure the conversion of hexoses as well as pentoses in contrast to the ethanol producing yeasts which only utilise hexoses. This way the full utilisation of 15 second generation biomass comes within reach. Secondly, butanol can be applied as a fuel extender in the growing market of diesel engines, in contrast to ethanol which can be used in gasoline engines only. Furthermore, butanol cam be used to prevent evaporation of ethanol in ethanol-20 gasoline mixtures. Finally, butanol is an interesting building block in the chemical industry.

Hydrogen is the fuel of the future where fuel cells will replace combustion engines due to inter alia the superior energy conversion efficiency. As with butanol, 25 hydrogen is an important commodity in the chemical industry. Hydrogen is produced by many facultative and obligate anaerobic bacteria at various temperatures.

For butanol and hydrogen, applications are found in the biofuels market for automotive as well as stationary 30 applications and in the commodity market for industrial purposes .

The quest for methods for the production of biofuel from biomass is presently based on a few 1035651 2 thermochemical and biological processes. The intrinsic composition of the biomass governs the suitability of the process. Thermochemical processes are adequate for biomass with low water content (< 20%) and high lignin content and 5 biological (anaerobic!) processes are best suited for wet biomass and biomass with high carbohydrate content.

Within the biological processes a distinction can be made between the products, namely biogas (methane), ethanol, acetone-butanol-ethanol (ABE) and hydrogen.

10 ABE fermentation is a process that utilizes bacterial fermentation to produce acetone, butanol, ethanol and, to a lesser extent, iso-propanol and hydrogen from a carbohydrate containing substrate. The name ABE fermentation used in the following, stems from the past, where the 15 emphasis was on ABE production. The process is anaerobic. It usually uses saccharolytic solventogenic Clostridia.

Many Clostridia produce acetone, butanol and ethanol from carbohydrates, i.e. starch, glucose, xylose and other (oligo)saccharides. Other products are hydrogen, CO2, 20 iso-propanol and butyric acid. Butanol is the product with the highest value and much of the current research is devoted to optimise the ABE fermentation towards butanol production. Presently, butanol is mainly regarded as a biofuel to be added, after derivatisation, to diesel.

25 Additionally, butanol can be added to gasoline-ethanol mixtures to prevent evaporation of ethanol.

In a typical batch acetone-butanol-ethanol (ABE) fermentation, the process is characterized by two phases. In the first, known as the acidogenic phase, saccharides are 30 converted to acetic and butyric acids and hydrogen accompanied by a decrease in culture pH value. In the second, known as the solventogenic phase, sugars and some of the acids are converted to acetone, butanol and ethanol, 3 accompanied by a pH increase. Typical concentrations after batch fermentation are 15-19 g/L butanol, 4-6 g/L acetone and <1 g/L ethanol. Butanol is however toxic and bacteria are killed at concentrations above 20-25 g/L butanol.

5 A typical problem that may occur in a batch process is known as the "acid crash". When an acid crash occurs, excess acid production takes place without a significant switch to the solventogenic phase. To prevent acid crash of the bacteria, the substrate concentration is 10 usually around 6-8% (w/v) carbohydrate. This relatively high substrate concentration is also necessary to force Clostridia to ABE production during continuous fermentation.

For industrial ABE production, the main interest is in continuous fermentation. An important drawback 15 encountered with continuous fermentation is the waste of substrate due to the requirement for high substrate concentrations to prevent the acid crash. As a result, there is a residual substrate concentration of about 2-5 g/L carbohydrate which needs to be discarded. A common option is 20 to send this waste to a biogas fermentation unit where methane is produced.

To date the recovery of the ABE products is by distillation but there is great effort in finding alternative ways for downstream processing (membrane 25 separation, gas stripping, etc.). The amount of H2 is typically around 100 and 200 Nm3 per 1000 kg carbohydrate.

The production of H2 is in competition with the production of butanol, i.e. more hydrogen means less butanol.

In contrast to the ABE fermentation, fermentative 30 hydrogen production is much less studied. Interest in hydrogen production mainly stems from the expected introduction of fuel cells which need hydrogen as feedstock. Fuel cells show great promise with respect to very high 4 efficiency in conversion of chemical energy to electrical energy (>60% as compared to 30-40% with combustion engines). As a result a switch to a hydrogen-based economy is foreseen, where part of the hydrogen needs to be derived 5 from renewable resources to support its sustainability.

There are two distinctly different biological processes for hydrogen production, namely hydrogen production from sunlight and fermentative hydrogen production from biomass. This invention is concerned with 10 hydrogen production from biomass.

Many micro-organisms are able to produce hydrogen from mono- and oligosaccharides, starch and (hemi)cellulose under anaerobic conditions. The anaerobic production of hydrogen is a common phenomenon, occurring during the 15 process of anaerobic digestion. Here, hydrogen producing micro-organisms are in syntrophy with methanogenic bacteria which consume the hydrogen as soon as it is produced. In this way, hydrogen does not accumulate and methane is the end-product. By uncoupling hydrogen production from methane 20 production, hydrogen becomes available for recovery and exploitation.

The applicant previously described the use of extreme thermophilic (temperature > 70eC) bacteria for hydrogen production and the combination of a fermentative 25 step with a photo-heterotrophic fermentation to increase the overall yield. Mesophilic bacteria show fairly low yields of hydrogen due to the fact that these bacteria may have metabolic pathways with other, competing reduced end products (e.g. butanol or ethanol). Thermophilic bacteria 30 show yields which can be almost twice as high (e.g. >300 Nm3 per 1000 kg carbohydrate) , especially when acetic acid is the only other end product.

For hydrogen producing bacteria, the optimal 5 substrate concentration in batch fermentation for high hydrogen yield and productivity is relatively low.

According to the invention it was found that the drawbacks of the butanol production as for example in ABE 5 fermentation, i.e. waste of substrate in the effluent, and of the hydrogen fermentation, i.e. decreased performance at high substrate concentrations, are solved by the combination of ABE and hydrogen fermentation, yielding increased efficiency in terms of high product yield from biomass at 10 decreased cost.

The invention thus relates to a process for the combined production of butanol and hydrogen from biomass, comprising the steps of: a) fermenting biomass to obtain butanol in a first 15 reaction mixture; b) removing the butanol and hydrogen from the first reaction mixture to obtain effluent; and c) using the effluent as a substrate in a second reaction mixture in a process using low substrate 20 concentrations, in particular a hydrogen production process.

The butanol may be obtained in an ABE process, wherein it is produced in combination with acetone and ethanol. Alternatively, however, the butanol may be the main or only product of the fermentation process of step a when 25 process parameters are used that force the production in the direction of butanol or when bacteria are used that produce only or mainly butanol.

The second process can be any fermentation process that uses low concentrations of sugars. This process uses 30 the residual sugars from the first fermentation. It is however preferred according to the invention that the process is a hydrogen fermentation in which hydrogen is produced from the sugars in the effluent of the first 6 process. Other products that can be produced from the residual sugars are acetate, lactate, pyruvate, butyrate, succinate, formate and/or ethanol. These products may be a by-product of the hydrogen production process or can be the 5 main product of the second process.

In a preferred embodiment the end products from the second process are removed from the second reaction mixture to obtain an effluent that is returned to the first reaction mixture. For example, the metabolites, e.g. acetic 10 acid or butyric acid, in the effluent from the hydrogen fermentation are very useful in the ABE fermentation to increase the yield of butanol. Alternatively, the metabolites in the effluent can be recovered, e.g. in the case of ethanol.

15 In a particular embodiment of the invention, the process of the invention thus starts with butanol production, for example by ABE fermentation of carbohydrates in the biomass. The products thus obtained are removed from the effluent and the effluent is subsequently inoculated 20 with different bacteria for hydrogen production. The effluent leaving the hydrogen fermentor is preferably recycled to the ABE fermentor.

The Clostridia that are used in the ABE process are saccharolytic solventogenic Clostridium species, for 25 example selected from but not limited to the group consisting of Clostridium acetobutylicum, Clostridium beijerinckii, Clostridium saccharobutylicum and Clostridium butylicum. Many strains are commercially available (for example from DSM or from the ATCC) , or are selected from own 30 culture collections or can be produced by enrichments or genetic modification.

The bacteria that are used in the second process, in particular for hydrogen production are preferably 7 mesophilic, thermophilic, extreme thermophilic or hyperthermophilic anaerobic hydrogen producing species. Such bacteria may be selected from but are not limited to Caldicellulosiruptor saccharolyticus, Caldicellulosiruptor 5 owensensis, Caldicellulosiruptor Kristjanssohnii, Thermotoga elfii, Thermotoga neapolitana. Thermotoga maritima and Clostridium thermocellum.

The advantages of the combined process are many. The residual carbohydrate of the ABE fermentation is 10 converted to useful products such as hydrogen, acetate, lactate, pyruvate, butyrate, succinate, formate and ethanol in the hydrogen fermentation thus resulting in useful products instead of being discarded as waste.

The acid end products of the hydrogen 15 fermentation, e.g. acetate, are re-assimilated in the ABE fermentation to increase the butanol yield and the end product ethanol adds directly to an increased product yield.

The costs for hydrogen recovery and purification are shared between the ABE fermentation and the hydrogen 20 fermentation which leads to a cost reduction as compared to the two processes separately.

The costs for energy and/or heat demand are shared by downstream processing of the products after the ABE fermentation and energy and/or heat demand for product 25 recovery after the hydrogen production process.

A specific advantage when employing thermophilic hydrogen bacteria at circa 70SC is that the vegetative cells of the Clostridia will lyse in the hydrogen fermentation and thus add to the supply of nitrogenous nutrients. Clostridia 30 spores, however, remain intact or may germinate. Complete and controlled germination may be done by a temperature shock to circa 80aC which is close to the temperature of thermophilic fermentation, enabling energy saving. The 8 recirculation of heat-treated effluent to the ABE fermentation which runs at a lower temperature leads to a revitalization of the clostridial population, thus preventing degeneration of the ABE culture.

5 In the combined process of the invention, two high value, diverse products are produced, namely a liquid product with acetone, ethanol, iso-propanol and mainly butanol and a gaseous product with mainly hydrogen. The butanol is a C4 building block for the chemical industry or 10 biofuel for application in combustion engines and gaseous H2 as chemical commodity or biofuel for application in fuel cells. Finally, the process of the invention is a zero waste process.

In the present application the words "ABE 15 fermentation" are used to indicate the classic acetone- butanol -ethanol fermentation or butanol fermentation or the fermentation to produce any one of acetone, butanol and ethanol or combinations thereof.

The present invention will be further illustrated 20 in the Example that follows. The Example is not intended to limit the invention in any way. The process of the invention is schematically illustrated in the Figures which show:

Figure 1: a schematic overview of the process of the invention without ethanol recovery unit.

25 Figure 2: a schematic overview of the process of the invention with ethanol recovery unit.

EXAMPLE

Combined process of the invention 30 In a specific embodiment the process of the invention as shown in Figure 1 is performed with the following process parameters.

A concentrated sugar solution 1, containing 6-8% 9 carbohydrates is loaded into a mixing unit 2. The first reaction mixture 4 that is thus obtained contains about 330 mM sugar, Κ,Ρ,Ν salts as well as organic nitrogen and trace elements. For first inoculation, clostridial cells are added 5 to the fermentor 5. The pH at this point is about 6-7.

This mixture 4 is fed to the ABE fermentor 5. When the process has been running for a while the sugar solution 1 can be combined with a mixture 3 that comes from the hydrogen fermentor and contains about 56 mM acetate (about 10 pH 5-6) and germinating clostridial cells in addition to organic nitrogen and Κ,Ρ,Ν salts (about pH 5-6).

In the ABE fermentor 5 butanol, acetone and ethanol are mainly produced. Hydrogen (about 11 L) and CO2 (about 15 L) are gasses. Butanol (about 160 mM) and acetone 15 (about 86 mM) are volatile. These compounds are removed from the reactor 5 by means of gas stripping or any other useful process and in a first product stream 6 fed to a separator or condenser 7 to separate acetone and butanol (11) from the gasses H2 and CO2 (12).

20 The second product stream 8 still contains about 33 mM sugars, Κ,Ρ,Ν salts, as well as lysed clostridial cells and clostridial spores. The pH has dropped to about 5-6. This stream 8 is fed to a hydrogen fermentor 9. The fermentor produces about 3 L H2 and about 1 L C02 (13) which 25 are sent to the gas upgrading unit 14. The effluent is optionally heat treated in the heat treatment unit 10 to revitalize the Clostridia spores contained therein and recycled to the first process as stream 3. Stream 3 still contains about 22 mM ethanol.

30 In the gas upgrading unit about 14 L H2 (15) is recovered as well as about 16 L CO2 (16) . The CO2 can be recycled to the hydrogen fermentor 9.

Figure 2 shows another embodiment that comprises a 10 additional ethanol recovery unit 17. The about 22 mM ethanol that is fed to this unit from stream 8 is recovered here. Ethanol (about 56 mM) produced in the hydrogen fermentor 9 can also be recycled to this unit to be combined with the 5 ethanol from stream 8 resulting in stream 19 that comprises about 22 + 56 mM ethanol.

1035651

Claims (11)

A method for the combined production of butanol and hydrogen from biomass, comprising the steps of: a) fermenting biomass to obtain butanol in a first reaction mixture; b) separating the butanol and hydrogen from the first reaction mixture to obtain effluent; and c) applying the effluent as a substrate in a second reaction mixture in a method which uses low substrate concentrations, in particular in a hydrogen production process. 2. A method according to claim 1, characterized in that the butanol is produced in an acetone-butanol-ethanol (ABE) production process. 3. A method according to claim 1 or 2, characterized in that the method using low substrate concentrations is a hydrogen production process and at least a part of the end products of the hydrogen production process is removed from the second reaction mixture to obtain an organic acid containing effluent that is recycled to the first reaction mixture. The method according to claim 3, characterized in that the organic acid is acetate or butyrate. 5 Caldicellulosiruptor saccharolyCicus, Caldicellulosiruptor owensensis, Caldicellulosiruptor Kristjanssohnii, Thermotoga elfii, Thermotoga neapolitana, Thermotoga maritima and Clostridium thermocellum. 5. Method according to claim 2, 3 or 4, characterized in that the acetone-butanol-ethanol (ABE) production process uses solventogenic clostridia species, preferably selected from the group consisting of Clostridium acetobutylicum, Clostridium beijerinckii, Clostridium saccharobutylicum and Clostridium butyl icum. Method according to one or more of claims 1-5, characterized in that hydrogen production process uses 1035651 of mesophilic, thermophilic, extremely thermophilic or hyperthermophilic bacteria. The method according to claim 6, characterized in that the bacteria are selected from the group consisting of Process according to one or more of Claims 1-7, characterized in that the residual concentration of carbohydrates in the waste water from step b) is 2-10 g / L. Method according to one or more of claims 1-8, characterized in that step c comprises a thermophilic fermentation which is used for revitalization of the 15 Clostridium population in ABE production. Method according to one or more of claims 1-9, characterized in that the method further comprises the recovery of ethanol from the waste water from the process from step a. Method according to one or more of claims 1-10, characterized in that the method further comprises the recovery of ethanol from waste water from the process from step c. 25 1035651