WO2014022218A1

WO2014022218A1 - Production of hydrocarbons from select coal and algal biomass mixtures

Info

Publication number: WO2014022218A1
Application number: PCT/US2013/052241
Authority: WO
Inventors: Patrick G. Hatcher
Original assignee: Old Dominion University Research Foundation
Priority date: 2012-07-31
Filing date: 2013-07-26
Publication date: 2014-02-06

Abstract

Hydrocarbons suitable for commercial use or further refining are produced by a process that mixes an aliphatic-rich biomass and coal to obtain a feedstock. The feedstock is then subjected to a conversion process to produce a product mixture. The bio-oil, or hydrocarbons, is separated from the resulting product mixture for use or further processing. Separating the bio-oil can be done, for example, using liquid-liquid extraction to obtain an organic phase comprising the bio-oil, an aqueous phase and a solid residue. Also provided is a feedstock comprising an aliphatic-rich biomass and coal.

Description

PRODUCTION OF HYDROCARBONS FROM

SELECT COAL AND ALGAL BIOMASS MIXTURES

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to Provisional Application Serial No. 61/677,807, filed July 31, 2012, which is hereby incorporated by reference in its entirety.

BACKGROUND

[0001] There is recent consensus that addition of modern biomass to coal in attempts to produce coal-derived liquid fuels reduces the life cycle analysis (LCA) carbon emissions sufficiently to warrant further development of the technology. Much of the studies to demonstrate this carbon LCA reduction have utilized conventional commercial coal reserves to which woody or terrestrial biomass is employed as a co-feed material to the conversion that includes numerous conversion technologies such as gasification/Fischer-Tropsch synthesis (FTS) and catalytic liquefaction.

SUMMARY

[0002] Very little attention has been given to selection of a coal or biomass feedstocks that have the potential to produce hydrocarbons that are prime candidates for refining operations. Perhaps in the case of the gasification/FTS technology this is not as important a criterion because the synthesis process leads to hydrocarbon products that match well with conventional refinery operations; but in the case of catalytic/noncatalytic conversion to liquid fuels, this factor is an important consideration.

[0003] Most coals are typically aromatic solids that yield aromatic liquid fuels upon conversion. However, there are some coals (as commercially large deposits) that are very aliphatic in nature, giving them the propensity to yield hydrocarbon-rich fuels upon conversion and are, thus, ideally suited for the coal-biomass-to-liquids (CBTL) technology. The Wyodak- Anderson coal bed contains in its upper horizons a unit that has been shown to be high oil- yielding in Fischer Assay tests. Based upon these findings and on preliminary pyrolytic data, these coal units may be ideal and high oil-yielding feedstocks for the hydrous pyrolysis process disclosed herein. When subjected to gasification, these aliphatic coals may yield substantial amounts of hydrogen that would promote a more efficient FTS to liquid fuels.

[0004] Likewise, micro-algae is an aliphatic-rich biomass. These algae can be grown and harvested on a large scale in open pond systems. Proper selection of algal strains can provide a feedstock to coal conversion processes that adds to the propensity for the production of liquid hydrocarbons. Thus, the novel CTBL technology disclosed herein for the production of hydrocarbon fuels from coal-biomass mixtures involves a feedstock selectivity concept. Blending algae in the range of 8-15 wt. % with coal is disclosed for liquid fuels production. Feedstock selection for the conversion processes of highly aliphatic coal and biomass are disclosed to ensure that hydrocarbon rich fuels are produced in abundance. The gasification/FTS and hydrous pyrolysis of a novel blend of algae and aliphatic coal produces oils that can be subjected to a patented catalytic upgrading to optimize fuel quality. Optimum processes are disclosed for conversion of this coal/biomass mixture to a drop-in fuel that is readily refined by conventional refineries. The hydrocarbons produced by hydrous pyrolysis can be readily upgraded

catalytically to hydrocarbon-rich fuels because they are primarily composed of hydrocarbons initially. Catalytic upgrading technology is ideally suited for taking the oils produced from hydrous pyrolysis and converting them to hydrocarbon-rich fractions suitable for commercial use or further refining.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The various features, advantages and other uses of the present invention will become more apparent by referring to the following detailed description and drawing in which:

[0006] Fig. 1 is a schematic of blue-green algae;

[0007] Fig. 2 is a schematic of product separation after microalgae liquefaction;

[0008] Fig. 3 is 13 C NMR spectra collected for whole algae before and after subcritical temperature treatment;

[0009] Fig. 4A shows analysis of the oil produced at 360°C for 72 hours by gas chromatography and gas chromatography/mass spectrometry of whole algae; [0010] Fig. 4B shows analysis of the oil produced at 360°C for 72 hours by gas chromatography and gas chromatography/mass spectrometry of the algaenan isolate from the algae;

[0011] Fig. 5 illustrates the vertical and lateral extent of the various facies in the

Wyodak- Anderson seam near Gillette, WY;

[0012] Fig. 6 shows the yield of tar from Fisher Assay for the various samples of the

Wyodak- Anderson seam plotted against the amounts of crypto-eugelinite in the samples;

[0013] Fig. 7 shows NMR data for samples of the Wyodak- Anderson coal that is rich in crypto-eugelinite;

[0014] Fig. 8 shows pyrolysis/gas chromatography/mass spectrometry trace of a sample of the Wyodak- Anderson seam that is rich in crypto-humotellinite;

[0015] Fig. 9 shows gas chromatography/mass spectrometry trace of the flash pyrolysis products from the crypto-eugelinite-rich sample;

[0016] Fig. 10A is GC/MS data of the total ion current for the oil produced obtained by hydrous pyrolysis of the crypto-eugelinite facies of the Wyodak- Anderson coal bed;

[0017] Fig. 10B is GC/MS data of the extracted ioin chromotagram for m/z 57 for the oil produced obtained by hydrous pyrolysis of the crypto-eugelinite facies of the Wyodak- Anderson coal bed; and

[0018] Fig. 11 is a flow diagram of a process of producing hydrocarbons as disclosed herein.

DETAILED DESCRIPTION

[0019] Liquid (hot compressed) water below the critical point is referred to as subcritical water. Ambient water is polar, has infinite networks of H-bonding and does not solubilize most organics. As water is heated, the H-bonds start weakening, allowing dissociation of water into acidic hydronium ions (H₃O⁺) and basic hydroxide ions (OFT). In the subcritical region, the ionization constant (K_w) of water increases with temperature and is about three orders of magnitude higher than that of ambient water. The dielectric constant (ε) of water drops from 80 to 20 in the subcritical region. A low dielectric constant ε allows subcritical water to dissolve organic compounds, while a high ionization constant K_w allows subcritical water to provide an acidic medium for the hydrolysis of biomass components. In addition, the physical properties of water, such as viscosity, density, dielectric constant and ionic product, can be tuned by changes in temperature and/or pressure in the subcritical region. For example, the dielectric behavior of 200°C water is similar to that of ambient methanol, 300°C water is similar to ambient acetone, and 370°C water is similar to methylene chloride.

[0020] Application to Biofuels: Subcritical water offers several advantages over other biofuels production methods. Some of the major benefits are (i) high energy and separation efficiency, (ii) versatility of chemistry (solid, liquid and gaseous fuels), (iii) reduced mass transfer resistance, (iv) ability to use mixed feedstock as well as wet biomass, and (iv) completely sterilized products with respect to any pathogens including biotoxins, bacteria or viruses. The technology can be applied to produce solid, liquid, and gaseous fuels depending on the processing conditions. The substantial changes in the physical and chemical properties of water in the vicinity of its critical point can be utilized advantageously for converting lignocellulosic biomass/algae to desired biofuels.

[0021] Energy Balance of Subcritical Water Processes: In subcritical water based processes, water is kept in the liquid phase by applying pressure. Thus, latent heat required for phase change of water from liquid to vapor phase (2.26 MJ/kg of water) is avoided, reducing the energy requirement compared to steam based processes. As an example, 2.869 MJ/kg of energy is required to convert ambient water to steam at 250°C and 0.1 MPa, whereas only 0.976 MJ/kg of energy is required to convert ambient water to subcritical water at 250°C and 5 MPa. The energy contained in the subcritical water is insufficient to vaporize the water on decompression. Further, much of the heat can be recovered from subcritical water. In the case of microalgae, energy required for the dewatering process may account for more than 75% of the total energy consumption. Typical thermal dryers use significantly more energy per kilogram of evaporated water (3.3-3.9 MJ/kg). The drying steps lead to large parasitic energy losses that can consume much of the energy content of the biomass. The fossil energy ratio, the ratio of higher heating value of biofuel products to fossil energy input, for dry and wet process was reported as 1.50 and 1.37, respectively. The dry route may be more interesting on a short term basis because of a slightly higher fossil energy ratio, but for the long term, the wet route has more potential because of the opportunity to produce advanced biofuels.

[0022] Aqueous Liquefaction of Microalgae in Subcritical Water: Microalgae are relatively small and protected, in many cases, by a thick cell wall as represented in Fig. 1, a schematic of blue- green algae. The schematic in Fig. 1 illustrates the cell wall 10, lipid granules 12, photo synthetic membranes 14, ribosomes 16 and nucleoid 18. Typically, very harsh conditions (e.g. mechanical, chemical extraction) are required to break the cell walls 10 for extracting the bioactive compounds. The main structural elements of all plant cell walls are polysaccharides. The resistance of the algal cell wall 10 to microbial attack is generally attributed to the discrete structural entities and resistance of cell walls to decompose.

[0023] Microalgae cell walls 10 mostly consists of carbohydrates (polymers of glucose, mannose, xylose, galactose, galacturonic acid, etc.) and little protein or lipids. Table 1 shows the chemical composition of the cell walls 10 of two species. Most algae have a variety of water- soluble polysaccharides. Cellulose, a part of the cell wall 10 in algae, is very widely distributed in the different species. The cell wall 10 also consists of alkali- soluble hemicelluloses and alkali- insoluble rigid walls. Cell walls, in general, are organized in a conventional framework. The basic framework is highly polymeric. Interspersed within are lower molecular weight polymers and oligomers (often gel like fibers) and inorganic and non-monomeric compounds.

[0024] The polymeric components of microalgae, namely carbohydrates, proteins, and lipids, have different depolymerization kinetics in the subcritical water medium. The hydrolysis rate increases with reaction temperature for these polymers. The hydrolysis of polysaccharides starts above 180°C in subcritical water within a residence time of seconds to a few minutes. The carbohydrates, such as hemicelluloses, starches, and amorphous cellulose, are known to start depolymerizing to water soluble products in subcritical water above 180°C. In fact, hydrothermal degradation of cellulose is a heterogeneous and pseudo-first-order reaction for which detailed chemistry and mechanisms have been proposed.

[0025] The depolymerization of protein is low or non-existent at temperatures below

200°C in subcritical water. Peptide bonds of proteins exhibit much higher stability compared to the β-1, 4- and β-1, 6- glycosidic linkages in cellulose and starch, respectively. Protein hydrolysis to amino acids was found to be fairly low even at 230°C in subcritical water after hours of exposure. Lipids are non-polar compounds. The reactions of lipids and water strongly depend on the phase behavior. The higher temperature causes increased solubility of fat and oils in subcritical water and ultimately they become completely soluble by the time water has reached its supercritical state. Earlier studies show that the hydrolysis of triacylglycerols (TAG) and fatty acids, along with their methyl esters, follows the first-order reaction kinetics. The hydrolysis of TAG in subcritical water starts above 280°C and conversion in excess of 95% were achieved at 340°C within a residence time of 12 minutes.

[0026] The subcritical water liquefaction (also termed hydrothermal liquefaction) process can utilize mixed biomass feedstock without any pretreatment or drying, at a comparatively low temperature. The process is used to convert biomass components to liquid products termed "biocrude." Biocrude, sometimes also referred as bio-oil, is an aqueous oxygenated solution derived from the direct liquefaction of biomass that can be converted to liquid fuel, hydrogen, or chemicals. Liquefaction of biomass in subcritical water proceeds through a series of structural and chemical transformations involving:

• Solvolysis of biomass resulting in micellar-like structure,

• Depolymerization of cellulose, hemicelluloses, and lignin, and

• Chemical and thermal decomposition of monomers to smaller molecules.

[0027] A study was performed using a hydrothermal upgrading process, where biomass was subjected to subcritical water at 330°C to produce biocrude. In some tests, biocrude yield was 23 wt% at 300°C in presence of 5 wt% Na₂CO₃. The higher heating value (HHV) of the biocrude was reported as 28-30 MJ/kg. The biocrude was a complex mixture of ketones, aldehydes, phenols, alkenes, fatty acids, esters, aromatics, and nitrogen containing heterocyclic compounds. Acetic acid was the main component of the water-soluble products. The bio-oil production is compared in Table 2 from three different microalgae strains and a cyanobacteria conducting hydrothermal liquefaction at 350°C and 20 MPa. Microalgae included Chlorella vulgaris, Nannochloropsis occulata and Porphyridium cruentum, and the cyanobacteria such as Spirulina with the biochemical properties given in Table 2.

[0028] The yields of biocrude were 5-25 wt% higher than the lipid content of the algae depending upon biochemical composition. The yields of bio-crude followed the trend lipids > proteins > carbohydrates. Table 3 shows the HHV of the bio-oil was in the range of 33-39 MJ/kg when microalgae and cyanobacteria were used as feedstock. The HHV of bio-oil from

Nannochloropsis oculata was highest among these strains which are probably due to its higher lipid contents. The nitrogen content in bio-oil is due to the presence of protein fractions in the feedstock. Biocrude with low nitrogen and high carbon content is desirable. Nitrogen in fuel directly forms NO_x compounds which are undesirable due to environmental pollution and legislative reasons. The energy recovery is calculated as the ratio of energy contained in biocrude to the energy contained in the feedstock. The study showed that each biochemical component (lipid, carbohydrate, and protein) of feedstock contributes to the bio-oil production which is a distinct advantage of hydrothermal liquefaction compared to conventional physical oil extraction methods.

[0030] The products from hydrothermal liquefactions mainly consist of bio-oil, an aqueous phase (dissolved organics), light gases, and insoluble residual solids. For the efficient liquefaction process, most of the carbon and hydrogen in the algal biomass should appear in bio- oil. The product separation is one of the most important aspects of hydrothermal liquefaction. In standard laboratory practice, an organic solvent such as dichloromethane, chloroform, hexane, and cyclohexane is used to separate bio-oil from the product mixture by liquid-liquid extraction step. Subsequently, organic solvent is evaporated to recover bio-oil.

[0031] Fig. 2 shows the general schematics of product separation after microalgae liquefaction. The microalgae slurry 50 undergoes hydrothermal liquefaction 52, resulting in a product mixture 54. Gases 56 are removed from the product mixture 54 and the liquids undergo liquid-liquid extraction 58. An organic phase 60, an aqueous phase 62 and a solid residue 64 result from the liquid- liquid extraction 58. The organic solvent is removed from the organic phase 60 by drying 66, and the bio-oil 68 is recovered.

[0033] A typical gas phase composition from hydrothermal liquefaction is CO₂ (66.2%),

CH₄ (1.9%), and H₂ (29.7%) along with nitrogen and traces of C₂ and C₃ gases. Generally CO₂ consist of more than 85% of gas phase when reaction is conducted at lower temperature (≤ 300°C), which decreases with temperature. Hydrogen becomes a significant component of the gas phase at higher temperature (≥ 350°C). Overall, hydrothermal liquefaction of microalgae provides two major advantages over the other liquefaction processes. First, it can utilize biomass with very high water content and thus saves a considerable amount of energy required for dewatering. Second, the method is not species (type of feedstock) dependent where only species of high lipid contents can be used. The other polymeric components of microalgae such as proteins and carbohydrates also convert to bio-oil during the process so that, generally, higher bio-oil yield is achieved.

[0034] Pyrolysis of algae containing algaenan: Some groups of green algae, such as eustigmatophytes and dinoflagellate, are known to metabolize single layers of the protective outer wall that is composed of an aliphatic polyethylene biopolymer called algaenan. This protective algaenan biopolymer is a recalcitrant material that is insoluble and non-hydrolyzable. It has been shown that the algaenan may be selectively preserved in sediments because of its recalcitrance and is thought to be converted into petroleum over geological time. Previous research has shown that one can simulate the process by which this algaenan converts to petroleum- like hydrocarbons using pyrolysis approaches. When pyrolyzed, they produce a suite of hydrocarbons with chain lengths from 6 to 32 carbons, not unlike many petroleum

hydrocarbons. These hydrocarbons are likely the precursors of kerogen in shales that yield paraffinic petroleums upon natural maturation. Moreover, when pyrolysis techniques are employed for studies of algaenan, a near- 100% conversion to paraffinic oils is observed, particularly in the presence of water or hydrogen.

[0035] Finding an economically viable alternative to fossil fuels, one that reverses or at least maintains neutrality in the global buildup of fossil-fuel derived CO₂, should be and is a target of much applied and fundamental research. It is believed that algae has not been specifically targeted for its production of algaenan, which is pyrolytically convertible to hydrocarbons.

[0036] The experimental cracking experiments performed on algaenan via closed system pyrolysis show a release of CO₂, CO and C₁₄₊ hydrocarbons which all suggest that the main thermal degradation involves cleavage of esters and aldehydes and cracking of the C-C backbone. The numerical molecular modeling simulations confirm the experimental observations and show that the weakest bonds in this algaenan structure correspond to the C-O and C-C bonds of the ester and the C-C bonds adjacent to the double bonds, whereas the aldehyde groups remain stable during the numerically simulated thermal decomposition. A different mechanism is expected for the lipid triglycerides, which are decomposed into free fatty acids. [0037] One mechanism is to treat the solid residue with sodium hydroxide, which involves a saponification of the ester functions and leads to the formation of sodium salts of fatty acids. The sodium salt acts like an anchor on the carboxylic acid groups of the fatty acid, the same way that the ester functions are immobilized in the algaenan structure leading to facile cleavage of the carboxylic group (acid or ester) under pyrolytic conditions. With thermal cracking using Curie-point pyrolysis of sodium salts of fatty acids that are representative of natural biomacromolecules in sedimentary organic matter, the distribution of the compound series produced during the pyrolysis essentially depends in the nature and the position of the functional groups in the alkyl structure. The homolytic cleavage adjacent to the carboxylic group is a dominant process in the cracking of functionalized alkyl structures.

[0038] Both algaenan and whole algae were subjected to hydrous pyrolysis at three different temperatures in Parr autoclaves to determine the kinetics of the process and the optimum conditions for the process. Four different products were collected: 1) gas, 2) hydocarbon oil floating on the surface of the water, 3) the water, and 4) the remaining solid residue. Each of these isolates was analyzed for their chemical composition.

[0039] ¹³C NMR spectra were collected for whole algae before and after subcritical temperature treatment, as shown in Fig. 3. At 260°C for 72 hours, there is a complete disappearance of peaks corresponding to proteins and carbohydrates (peaks at 50, 65, 72, 105, and 175 ppm). These results indicate that carbohydrates and proteins are rendered soluble as they are removed from the solid phase, which is consistent with expectations based on the flash hydrolysis treatment discussed above. The main peak remaining in the residue is that of aliphatic algaenan (33, 25, 15 ppm) along with a broad peak for aromatic carbons (100-160 ppm). At this temperature, the oil produced is small (8.5% of dry starting mass) and the reactivity is similar to the subcritical water extraction process discussed above. At 360°C for 72 hours, the percentage of oil increases significantly to 16.7%. The residue at this temperature shows an increasing amount of aromatic (100-160 ppm) character, and the aliphatic algaenan signals diminish in comparison. These results indicate the following: (a) that carbohydrate and protein separation from algaenan occurs at low temperature (< 260°C), (b) that cracking of the algaenan occurs and is greatest at about 360°C, and (c) that a significant amount of oil is produced at the higher temperature.

[0040] Analysis of the oil produced at 360°C for 72 hours by gas chromatography and gas chromatography/mass spectrometry is shown in Figs. 4A and 4B, showing that the major components are saturated normal hydrocarbons, similar to those observed in some crude oils. Fig. 4A is analysis of the whole algae and Fig. 4B is analysis of the algaenan isolate from the algae. The oil obtained from hydrous pyrolysis of the algaenan shown in Fig. 4B is similar in composition to the whole algae in Fig. 4A. The yield of the whole algae at this temperature is 58% of the algaenan organic matter. This indicates that the oil produced during hydrous pyrolysis of the whole algae is primarily sourced from the algaenan. The presence of some additional peaks in the oil from whole algae, compared with that from algaenan, is attributable to either lipid triglycerides or presently unknown components of the whole algae. Note that palmitic and oleic acid are present in the oils and these likely derive from the TAGs of algae.

[0041] Some of the peaks are alkylated aromatic hydrocarbons derived from hydrous pyrolysis of proteins, from condensation of aliphatic structures or from aromatization of alicyclic components of algae. Even though hydrocarbon-based fuels can be readily produced from the whole wet algae, the crude oil still contains protein and carbohydrate-derived compounds in the form of molecules that contain nitrogen and oxygen atoms. This means that this crude oil will need further treatment in order to refine the crude to fuels. Thus, there is a need for catalytic upgrading. The composition of the crude oil from the algaenan is composed mainly of hydrocarbons and will require less treatment to be refined.

[0042] Reaction of Coal in Subcritical Water: Coalification of plant materials requires millions of years to occur and leads to the formation of coal in place that is now mined commercially. This process consists of a slow removal of carbohydrates and proteins, initially components of the plant materials, and of a reorganization of the remaining fraction. This remaining fraction is a heterogeneous copolymer of units comprising aromatic rings and oxygenated aliphatic hydrocarbon structures, and the relative proportion of each component varies from one coal sample to another. Under subcritical water conditions, also called steam pyrolysis, depolymerization of coal commences above 300°C and under a pressure of IMPa. It is believed that below this temperature, water assists in the disruption of hydrogen bonds, important crosslinks in the coal structure that prevent them from re-forming. Disruption of the polymeric network is the start of hydrocarbon formation. With increasing severity of hydrous pyrolysis, the nature of produced hydrocarbons is modified.

[0043] At temperatures from 290 to 350°C, the dielectric constant of liquid water becomes as low as that of polar organic solvents, such as pyridine and tetrahydrofuran. These solvents are very efficient in swelling coal materials, allowing extraction of a significant portion. At this temperature, the ionic character of water is greater by 1 to 2 orders of magnitude than that at ambient temperature. Similar extraction efficiency can be obtained by subcritical water liquefaction. At IMPa between about 320 and 360 °C, plastic coals begin to soften or melt. As expected, yield of liquefaction products increase with temperature. A jump in yield from 40 to 85% occurs between 300 and 320 °C. This process seems to be related to the decrease in acidity of coal around this temperature and is explained by the breakdown of hydrogen bonds. Hydrogen bonds are important crosslinks in coal and their rupture marks the beginning of the

depolymerization of coal. Then volatiles (CO₂, CH₄) and alkylphenols are released from the coal starting at 320 °C, corresponding to the hydrolysis of aromatic ethers and esters. In the early stages of liquefaction, ether oxygen is released faster than phenolic hydroxyl groups. Also, the loss rate of oxygen and sulfur is similar during liquefaction. Thus, sub-critical water can act as an acid and/or base catalyst for reactions such as hydrolysis of ether and/or ester bonds, particularly abundant in coal, and also as a solvent for extraction of low molecular-mass products.

[0044] Most of the studies on the aqueous liquefaction of coal have been performed on humic coal and not on aliphatic hydrogen-rich coals. The processes discloses herein focus on aliphatic hydrogen-rich coal as it is contemplated that it yields more oil.

[0045] Pyrolysis of coal: Multiple pyrolysis techniques exist, such as open (Fischer assay, Rock Eval) and closed pyrolysis under hydrous or anhydrous conditions. The nature of products generated is always the same; however, the yield is usually more important under hydrous conditions. The water under sub- or super critical pyrolysis conditions becomes a good solvent that is able to extract tar. Under thermal stress, coal is decomposed into CO₂, hydrocarbon gas, extractable tar and residual char. The molecular transformation is driven by the formation of free radicals and their aptitude to capture hydrogen-atoms or recombine with other radicals or molecules. Carbon dioxide is essentially generated by decarboxylation of carboxylic acid or ester groups. Hydroxyl radicals are formed from defunctionalization of hydroxyl groups and from water under subcritical conditions. These radicals will ultimately form some water molecules or will recombine with other radicals to form hydrophilic molecules.

[0046] Depolymerization of the aliphatic side chains in coal yields methane and other low molecular weight hydrocarbons. Therefore the selection of hydrogen-rich coal that contains a significant polymethylene component is important for the production of oil and gas from coal. Another source of methane is from the defunctionalization of methoxy groups connected to aromatic rings. This reaction also yields hydroxylated alkylaromatic compounds such as phenol and alkylphenols by hydrogen abstraction. The nature of the residual char will vary depending on the type of pyrolysis performed. Under anhydrous closed pyrolysis, aromatic character of the char structure increases with temperature. Because of the confinement and of the limited amount of hydrogen donors, defunctionalization of the aliphatic chains leads to the formation of double bonds conjugated to the aromatic rings. In a hydrous environment, water derived hydrogen will combine with aliphatic side chains and aromatic ring radicals, avoiding extensive aromatization of the residue.

[0047] It is clear that long-chain paraffinic structures or polymethylenes which form part of the macromolecular structure of hydrogen-rich coals are of fundamental importance for the generation oil and gas from the aqueous pyrolysis process.

[0048] Gasification of Coal and Biomass: Gasification is a chemical process by which carbonaceous materials (coal, petroleum coke, biomass, etc.) are converted to a synthesis gas (syngas) by partial oxidation process with air, oxygen, and/or steam. As an important industrial raw material, syngas may be converted to a wide range of fuels and chemicals using several reaction pathways. Fischer-Tropsch synthesis (FTS) is a major part of gas-to-liquids (GTL) technology, which converts syngas into liquid fuels with a wide-range liquid hydrocarbon fuels and high-value added chemicals. [0049] Biomass gasification is attracting more attention due to the demand for renewable energy. However, biomass has a low energy density and high moisture content leading to high production and processing costs. Coal has been used in the commercial industry for syngas production for more than one century due to its abundance, relatively low cost and high energy density. Unfortunately, humic coal has a low hydrogen to carbon ratio and higher CO₂ emission for liquid fuel production by FTS. Moreover, there are more inorganic contents in coal which lead to higher impurities in the derived syngas.

[0050] Co-gasification of coal and biomass as disclosed herein has several advantages.

The addition of biomass to coal gasification reduces the cost of the feedstock. The addition of biomass to coal gasification reduces CO₂ emissions and also reduces problems caused by sulfur and ash contained in coal, because the biomass has almost no sulfur and low ash content.

Therefore, co-gasification can not only reduce the cost of the feedstock, but also reduce the problems that occur in plant operation due to the production of tar. The methods disclosed herein for co-gasification of coals and biomass address at least the following. How should the coal and biomass be mixed? How does the quality of the feedstock affect the quality of the product syngas? What are the optimum percentages of various blends of coal and biomass? What coals should be used for optimum hydrocarbon yields?

[0051] Feedstock selection:

[0052] Selection of Algae: An initial survey of 39 eutrophic ponds and lakes in southeastern Virginia was conducted to identify algae with high growth potential and lipid composition. Chlorophytes were among the most abundant taxa. In addition, their chemical composition was analyzed for carbon, nitrogen, and lipid content to determine which species would be ideal for growing and converting these products into biofuel. After laboratory growth experiments, algae belonging to the Scenedesmus/Desmodesmus complex were selected for mass harvesting and inoculation. Subsequent molecular genetic analysis identified the major species for the processes disclosed herein as Desmodesmus cf. asymmetricus . In addition, there are taxa among the chlorophytes that are known to synthesize single layers of a protective outer wall that are composed of an aliphatic polyethylene biopolymer called algaenan (~10 wt%). Both lipids and algaenan fractions in microalgae are the aliphatic energy-rich macromolecules having a higher H/C ratio compared to carbohydrates and are best suited for biofuels production. Growth and lipid studies have indicated that Scenedesmus spp. (Scenedesmus/Desmodesmus group) may be an ideal species for large scale conversion to biodiesel, including Desmodesmus cf.

asymmetricus which contains algaenan.

[0053] Selection of coal: A key element of the novel production of liquid hydrocarbons from coal is to determine coal that has the highest propensity to yield those liquid hydrocarbons during either of two conversion technologies-FTS or hydrous pyrolysis. Many coals of medium or low rank are mainly composed of a core aromatic structure. This is mainly because the source materials that formed the coals millions of years ago were mainly vascular plant materials rich in lignin. This lignin undergoes a molecular transformation during coalification to produce the aromatic core of coal. When subjected to liquefaction, the resultant liquids are very aromatic in character, in part due to the paucity of hydrogen-rich aliphatic structures. Before these highly aromatic liquids can be utilized for fuels, they need to be upgraded via hydrogenation chemistry. In the case of low-rank coals having substantial amounts of oxygenated aromatic structures, additional deoxygenation is required to yield liquids that are useful for internal combustion engines or refining.

[0054] Some coals are not overly aromatic because they derive from plant materials other than terrestrial plants. Cannel coals are known to be mostly composed of plant spores (pollen), while boghead coals are mainly derived from algal organic matter. In many cases, these types of coals are not laterally extensive and, consequently, are not mined extensively. There are other coals comprising major seams in which aliphatic-rich lithotypes are recognized. One of these is the Wyodak- Anderson coal bed in the Powder River Basin of Wyoming. In its upper section of approximately 4 meters of a lithofacies called by Stanton et al. crypto-eugelinite rich facies, which is laterally quite extensive as shown in Fig. 5. Fig. 5 illustrates the vertical and lateral extent of the various facies in the Wyodak- Anderson seam near Gillette, WY. When examined by Fisher Assay, this unit produces the highest oil yield for all facies examined by Stanton, R.W.,Warwick, P.D., and Swanson, S.M., Tar yields low-temperature carbonization of coal facies from the Powder River Basin, Wyoming, USA, Int. J. Coal Geol., 2005. 63: p.13-26 (Stanton et al.). There is a good correlation in the entire seam, of 30 meters or more, between the amount of crypto-eugelinite in the samples and their tar yields, as shown in Fig. 6. (Stanton et al.) Fig. 6 shows the yield of tar from Fisher Assay for the various samples of the Wyodak- Anderson seam plotted against the amounts of crypto-eugelinite in the samples.

[0055] Samples of the Wyodak-Anderson coal that is rich in crypto-eugelinite is subjected to both solid-state 13 C NMR and flash pyrolysis/gas chromatography/mass

spectrometry. The NMR data shown in Fig. 7 clearly indicates that this section of the coal seam is rich in aliphatic components with peaks in the 10-60 ppm range. In contrast, a more aromatic crypto-humotellinite-rich sample shows flash pyrolysis peaks dominated by phenolic and aromatic moieties in Fig. 8, typical of traditional vitrinitic coal that is not very aliphatic. The crypto-eugelinite-rich sample, however, shows an abundance of hydrocarbons in the pyrolyzates in Fig. 9, indicating that the coal in this upper part of the seam is capable of producing hydrocarbon-rich oils which is consistent with the findings of Stanton et al. Fig. 9 shows gas chromatography/mass spectrometry trace of the flash pyrolysis products from the crypto- eugelinite-rich sample. The trace is the total ion current with numbers that denote alkanes and alkenes in the products. P is prist- 1-ene and DBF is a dibenzofuran. Note the homologous distribution of hydrocarbons extending from C₉ to C₃₂. Some small quantities of phenols are present along with retene from resins.

[0056] The coal from the crypto-eugelinite facies is subjected to hydrous pyrolysis at 360

°C for 72 hours. After cooling the reactor to room temperature, a layer of oil is discovered floating on the water in the reactor. This oil was recovered and analyzed by GC/MS. The GC/MS data for the oil produced obtained by hydrous pyrolysis of the crypto-eugelinite facies of the Wyodak-Anderson coal bed is shown in Figs. 10A and 10B. Fig. 10A is the total ion current (TIC) while Fig. 10B is the extracted ion chromatogram for m/z 57 (EIC) that is indicative of alkane-like hydrocarbons. Figs. 10A and 10B show the dominance of n-alkanes extending from C₆ to C₃₃. Isoprenoid alkanes (I), benzenes and alkylbenzenes (B), naphthalenes and

alkylnaphthalenes (N), and alkylphenanthrenes (P) are also shown. The oil is dominated by the n-alkane hydrocarbons like those observed from petroleum and from the hydrous pyrolysis of algaenan. These n-alkanes extend from C₆ to C₃₃ in chain length and are characteristic of paraffinic oil that is often associated with coal-bearing strata in the geologic realm. [0057] It is clear that the crypto-eugelinite-rich facies in the upper sections of the

Wyodak- Anderson coal are ideally suited for fuel production. However, currently these units of the Wyodak- Anderson coal are removed from the main body of the mined coal units and discarded as this facies is not ideal for use in combustion, like most coal from the Wyodak- Anderson seam. This is consistent with its high tar yields, which tends to be problematic for optimum combustion.

[0058] Admixing the coal with a biomass such as algae or algaenan from algae, especially those algae that are enriched in the algaenan, provides an ideal blend of products that will yield valuable amounts of hydrocarbon-rich fuel-like products when subjected to hydrous pyrolysis or any other fuel conversion process that relies on the production of hydrogen-rich intermediate chemical species in the feedstocks (e.g., gasification, hydrothermal liquefaction, catalytic liquefaction, etc.).

[0059] Referring to Fig. 11 , hydrocarbons suitable for commercial use or further refining are produced by a process that mixes an aliphatic-rich biomass and coal to obtain a feedstock in step 100. The feedstock is then subjected to a conversion process to produce a product mixture in step 102. The bio-oil, or hydrocarbons, is separated from the resulting product mixture in step 104 for use or further processing. Separating the bio-oil can be done, for example, using liquid-liquid extraction to obtain an organic phase comprising the bio-oil, an aqueous phase and a solid residue. The process can further comprise refining the bio-oil in step 106 if desired or required depending on the intended use of the bio-oil.

[0060] The aliphatic-rich biomass can be, for example, an algal biomass. The algal biomass can be mixed and processed wet, saving energy, time and costs by eliminating the need to dewater the biomass. The algal biomass can be about 8-15 wt. % of the feedstock, but is not limited to this range. The range may be different depending on the type of algae selected. The algal biomass can be selected from the Scenedesmus/Desmodesmus group, as a non-limiting example. One such algal selection is Desmodesmus cf. asymmetricus. The coal can be an aliphatic -rich coal, such as the eugelinite-rich coal described herein above. The coal can be selected from a hydrogen-rich coal containing polymethylene.

[0061] The conversion process can be hydrothermal liquefaction. The hydrothermal liquefaction can occur at a temperature between about 320°C and 360°C. The conversion process can also be hydrous pyrolysis or a gasification process.

[0062] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.

Claims

What is claimed is:

1. A process for producing hydrocarbons comprising:

admixing an aliphatic -rich biomass and coal to obtain a feedstock;

subjecting the feedstock to a conversion process to produce a product mixture; and separating bio-oil from the product mixture.

2. The process of claim 1 , wherein the conversion process is hydrothermal liquefaction.

3. The process of claim 2, wherein the hydrothermal liquefaction is undergone at a temperature between about 320°C and 360°C.

4. The process of claim 1, wherein the conversion process is hydrous pyrolysis.

5. The process of claim 4, wherein separating bio-oil comprises using liquid-liquid extraction to obtain an organic phase comprising the bio-oil, an aqueous phase and a solid residue.

6. The process of claim 1, wherein the conversion process is gasification.

7. The process of claim 1 further comprising refining the bio-oil.

8. The process of any one of the preceding claims, wherein the aliphatic-rich biomass is an algal biomass.

9. The process of claim 7, wherein the algal biomass is provided wet.

10. The process of claim 7, wherein the algal biomass is 8-15 wt. % of the feedstock.

11. The process of claim 7, wherein the algal biomass is selected from the

Scenedesmus/Desmodesmus group.

12. The process of claim 10, wherein the algal biomass is Desmodesmus cf.

asymmetricus.

13. The process of any one of the preceding claims, wherein the coal is an aliphatic- rich coal.

14. The process of claim 13, wherein the aliphatic -rich coal is a eugelinite-rich coal.

15. The process of any one of claims 1 to 12, wherein the coal is selected from a hydrogen-rich coal containing polymethylene.

16. A feedstock for the production of hydrocarbons comprising:

an admixture of an aliphatic-rich biomass and an aliphatic-rich coal.

17. The feedstock of claim 16, wherein the aliphatic-rich biomass is an algal biomass.

18. The feedstock of claim 17, wherein the algal biomass is 8-15 wt. % of the

admixture.

19. The feedstock of claim 17, wherein the algal biomass is selected from the

Scenedesmus/Desmodesmus group.

20. The feedstock of claim 19, wherein the algal biomass is Desmodesmus cf.

asymmetricus.

21. The feedstock of any one of claims 16 to 20, wherein the aliphatic-rich coal is a eugelinite-rich coal.