The present invention pertains generally to processes for producing biofuel. More particularly, the present invention pertains to methods for processing cellulosic material to convert its constituents into biofuel in an optimal manner. The present invention is particularly, but not exclusively, useful as a system and method for producing biofuel from hydrocarbons derived from cellulose and lignins supplied from a biomass feedstock.
As worldwide petroleum deposits decrease, there is rising concern over shortages and the costs that are associated with the production of hydrocarbon products. As a result, alternatives to products that are currently processed from petroleum are being investigated. In this effort, biofuels have been identified as a possible alternative to petroleum-based transportation fuels. In general, biofuels are comprised of mono-alkyl esters of long chain fatty acids derived from plant oils or animal fats. In industrial practice, biofuel is created when plant oils or animal fats are reacted with an alcohol, such as methanol.
For plant-derived biofuel, solar energy is first transformed into chemical energy through photosynthesis. The chemical energy is then refined into a usable fuel. Currently, the process involved in creating biofuel from plant oils is expensive relative to the process of extracting and refining petroleum. It is possible, however, that the cost of processing a plant-derived biofuel could be reduced by minimizing the costs of the plant source and by maximizing the energy extracted from the plant source. For the former concern, the use of cellulosic materials such as agricultural wastes, paper and food wastes, and quick-growing energy crops can reduce feedstock costs. Specifically, the cellulosic raw material is plentiful as it is present in every plant and plant-derived product. It is estimated that between 500 million and 1 billion tons of cellulosic materials are discarded in the United States each year. This includes over 30 million dry tons of urban wood wastes, 90 million dry tons of primary mill residues, 45 million dry tons of forest residues, and 150 million dry tons of corn stover and wheat straw. Due to its ubiquity, the cost of cellulosic material for use as biofuel feedstock is estimated to be about $30 to $60 per ton. In addition to using inexpensive raw materials, biofuel production processes that utilize cellulosic waste may substantially reduce the rate of landfill use. For instance, paper, cardboard, and packaging comprise about 40% of the solid waste sent to landfills in the United States each day.
In order to make use of these cellulosic materials as feedstock in biofuel production, their processing into fuel must be optimized. Therefore, a biofuel production method should utilize each possible source of energy within the cellulosic feedstock in order to efficiently produce a biofuel.
In light of the above, it is an object of the present invention to provide a system and method for producing biofuel which maximizes the energy provided from a biomass feedstock. Another object of the present invention is to provide a system and method for producing a jet fuel surrogate biofuel produced from the enzymatic conversion of cellulosic material into sugars. Still another object of the present invention is to provide a system and method for producing biofuel from the microbial conversion of sugars to lipids. Still another object of the present invention is to provide a method and system for producing biofuel that converts lignin in a biomass feedstock into hydrocarbons for use in the biofuel. Another object of the present invention is to provide a method and system for producing biofuel that processes hydrocarbons derived from cellulosic materials along with hydrocarbons derived from lignin. Yet another object of the present invention is to provide a system and method for producing biofuel that is simple to implement, easy to use, and comparatively cost effective.
In accordance with the present invention, a method and system are provided for producing biofuel from cellulosic materials. During the method, sugars are converted into triglycerides, rather than to the shorter chain alcohols commonly created during the formation of cellulosic ethanol and butanol. Importantly, triglycerides are much closer to traditional petroleum based fuels in energy content. In addition, unlike typical systems for converting cellulose into fuel, the present method utilizes algae fermentation of sugars. As a result, unlike the typical systems, large sterile reactors are not necessary. Moreover, the present method utilizes the lignin present in cellulosic feedstock to supply cyclic compounds, thereby reducing the amount of refining needed for the cellulose-derived hydrocarbons. As a result, the cellulose is converted into primarily straight chain paraffins or esters in a less-energy intensive process. Also, the use of lignin greatly increases the fuel energy per pound of cellulosic feedstock.
In operation, cellulosic feedstock is pretreated to separate the cellulose, hemicellulose, lignin, extractables, and co-products. Thereafter, the cellulose and hemicellulose are transformed into straight-chain hydrocarbons while the lignin is transformed into ringed hydrocarbons. Specifically, the cellulose and hemicellulose are first converted into sugars through hydrolysis. Then, the sugars are microbially converted into lipids by heterotrophic microalgae. After the lipids are extracted from the microalgae, they are converted into straight chain paraffins and esters.
Parallel to the processing of the cellulose and hemicellulose, the lignin is converted into hydrocarbons. Specifically, the lignin is converted into ringed hydrocarbons such as aromatic hydrocarbons and cycloalkanes like cycloparaffins. During the formation of the biofuel, the hydrocarbons derived from cellulosic material and the ringed hydrocarbons derived from lignin are blended and processed. Also, aromatic extractables separated at the pretreatment stage are added to the other hydrocarbons. As a result, a biofuel having a high energy content is produced to perform as a surrogate for jet fuel.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
Referring initially to
As shown in
Still referring to
Depending on the biomass used in the feedstock 14 and upon other considerations, the initial treatment 16 of the feedstock 14 may involve strong acid hydrolysis, solvent extraction, screw extraction with a weak acid, steam explosion, microwave treatment, ammonia fiber expansion, alkaline wet oxidation and/or ozone pretreatment. Referring to
As shown in
While a strong acid hydrolysis method is illustrated in
In another embodiment, the initial treatment 16 involves screw extraction with a weak acid. In this step, the feedstock 14 is first ground into particles and then fed to a pressurized chamber designed for counter-current processing. Next, a biomass fractionation process separates the three primary constituents of the feedstock 14: cellulose 28, hemicellulose 30, and lignin 20. This continuous fractionation process employs a counter-current extraction technique that separates the cellulose 28 and hemicellulose 30 fractions from the lignin 20 fractions into two high-quality liquid streams. As a result, one stream contains a solid fraction with relatively pure cellulose fiber. Thereafter, the cellulose is converted to sugar as discussed above.
In still another embodiment, steam explosion is used in the initial treatment 16. In this embodiment, the feedstock 14 is first prepared by properly sizing fibers in the feedstock 14 and removing dirt and ash. During this process, the surface area of the fibers is increased for maximum exposure during bioprocessing. Thereafter, the biomass enters a high-pressure continuous feeder where heat and moisture are added before a rapid depressurization. This step is known as steam explosion. After the steam explosion step, the materials are separated in a cyclone. Afterwards, the cellulose and hemicellulose go through enzymatic hydrolysis into C6 and C5 sugars. Further, the lignin fraction is taken off for further processing. The steam explosion process avoids the use of costly acids or recovery systems, and can provide significant cost reductions.
In yet another embodiment, the initial treatment 16 involves the use of microwave energy. Specifically, for feedstock 14 including wood material, the wood or wood bark is pretreated with microwave energy to open it up to acid, basic, or alkaline peroxide solutions. Thereafter, the cellulosic content of the wood is hydrolyzed with commercial enzymes to sugars. Further, pulping liquors can be used to separate carbohydrates and lignin, which can be used in further processing.
Referring back to
As shown in
Further, some of the co-products 24 can be recycled and used during steps within the process to optimize efficiency. For instance, acetic acid can be used as feedstock (as shown by arrow 80). Also, oil elicitor can be used in action block 66 during microbial lipid 68 production. Further, furfural and certain components of the extractables 22 can be sold. In addition to co-products 24 from the initial treatment 16, secondary co-products, such as animal feed, can also be obtained from the remaining algae after extraction of the lipids 68.
Referring to
While the particular Method and System for Microbial Conversion of Cellulose to Fuel as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.