BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates generally to the upgrading of the liquid product obtained by pyrolysis of biomass material, and more particularly to the upgrading of the oily phase of the liquid pyrolysis product.

2. description of the Related Art

[0002] Biomass material, in particular solid ligno-cellulosic biomass, is being studied as a feedstock for producing liquid fuel products. At this time, the most promising route to preparing liquid products from ligno-cellulosic biomass is pyrolysis. The pyrolysis reaction may be carried out with or without a catalyst. If carried out without a catalyst, the pyrolysis process is referred to as thermal pyrolysis. If carried out in the presence of a catalyst, the pyrolysis process is referred to as catalytic pyrolysis.

[0003] In general, the pyrolysis reaction produces gaseous, liquid, and solid reaction products. For producing liquid fuels, it is possible to convert biomass to a syngas, which in rum can be converted to a liquid fuel using a Fischer-Tropsch synthesis. Although this route results in a high quality hydrocarbon fuel, the process is expensive.

[0004] It is economically more attractive to conduct the pyrolysis reaction in such a way as to maximize the yields of liquid product, while minimizing the yields of gaseous products and solid products. In general, catalytic pyrolysis has a higher liquid yield than thermal pyrolysis, and the quality of the liquid product tends to be better. Nevertheless, the liquid product needs to be upgraded before it can be processed in conventional refinery equipment

[0005] US Patent 6,086,751 to Biensiock et al. discloses a process for treating TAN containing oils, e.g., crudes. By flashing to remove substantially all of the water therefrom, thermally treating the recovered liquid to reduce the naphthenic acid content thereof, and recombining light gases recovered from the flashing step with the treated liquid. The '751 patent specifies that the thermal treatment is carried out in the absence of any catalyst for promoting the conversion of napfcthenic acids, in absence of any material added to react with or complex with uaphthenic acids, and in absence of absorbents for naphthenic acids. The process disclosed in the '751 patent is unsuitable for upgrading liquid biomass pyrotysis products, because it is impossible to remove water therefrom by flashing, due to the hydrophilic nature of biomass pyrolysis products.

[0006] US Patent 6,063,266 to Grande et al. discloses a process for removing naphthenic acids from a crude oil. The crude oil is hydrogenated at. 1 -SO bars and 100- 300 oC over a catalyst of the kind used for hydrogenation of atmospheric residue oils. Preferred catalysts are Ni-Mo and Ni-Co, deposited on alumina as a earner material.

[0007] The catalyst used in the *26δ patent was not pre-sulfided. Although sulfur was present in the feedstock, the reaction was preferably carried out in such a way as to avoid the formation of H2S. The TAN of the feedstock was reduced from 2.6 mg KOH/g to less than 0.5 mg KOH/g.

[0008] Mahfud, "Exploratory Studies on Fast Pyrolysis Oil Upgrading" (ISBN 978-90-367-3236-9) reports on a number of different approaches to the upgrading of biomass-derived pyrolysis oil. Chapter 2 of the thesis reports on catalytic hydrodeoxygenation experiments. Catalysts used were Ni-Mo and Co-Mo on alumina; 5% Pt on activated carbon; and 5% Ru on alumina. The pyrolysis oil had an oxygen content of 41.2 wt%, a pH of 2.5, and a water content of 30.10 wt%. The Ni- Mo and Co-Mo catalysts were used in the pre-sulfided form; no sulfur was added to the feedstock.

[0009] In a batch reaction, the pyrolysis oil was reacted with hydrogen at 300 oC for 15 minutes, and subsequently at 400 oC for 3 hours, Jn a representative nra with the Ni-Mo catalyst the oxygen content of the pyrolysis oil was reduced to 10.5 wt%.

[0010] Zhang et al., Bioresource Technology 96 (2005) 545-550, discloses experiments on a liquid product obtained in thermal pyrolysis of saw dust. Most of the water was removed from the liquid pyrolysis product by induced phase separation. Inducement of phase separation involved water addition to the liquid pyrolysis product to the point that phase separation occurred. The "oil" phase was soluble in methanol, insoluble in toluene, and had an oxygen content of 41.8 wt%.

[0011] The "oil" phase was subjected to a batch-wise hydrogenation reaction, using sulfide Co-Mo-P in gamma-alumina as catalyst The upgraded oil was insoluble in methanol, soluble in toluene, and had an oxygen content of 3 wl%.

[0012] The disclosed process is not suitable for commercial scale-up, because the induced phase separation introduces large volumes of water. Ia addition, the catalyst could not be used in a continuous process, as it would quickly lose its activity absent sulfur replenishment

[0013] As has been disclosed in European Patent Application 08 15 3229.3-2104 _» the quality of the liquid product can be improved further by forming an intimate mixture of the biomass material and a catalyst, prior to contacting the material with a hot catalyst for effecting the pyrolysis reaction.

[0014] This prior art process makes it possible to produce pyrolysis oil having a low enough Total Add Number to make it suitable for further processing in standard refinery processes and equipment However, the operator may prefer to operate the process under conditions that produce a higher Total Acid Number, for example in order to further increase the liquid yield. In addition, there is a need for upgrading the liquid products of less sophisticated pyrolysis processes.

[0015] Thus, there is a need for a viable commercial-scale process for upgrading the liquid product of a biomass pyrolysis reaction. There is a particular need for such a process that does not require the addition of significant quantities of water.

BRIEF SUMMARY OF THE INVENTION

[0016] The present invention addresses these problems by providing a process for upgrading a liquid product of a biomass pyrolysis reaction, said liquid product comprising water and oxygenated hydrocarbons, said liquid product having an oxygen content of less than 30 wt%, said process comprising the steps of (i) allowing the liquid product to settle into an aqueous phase and an oi! phase; (ii) separating the oil phase from the aqueous phase; (iii) subjecting the oil phase to a hydrogen treatment step to form a mixture comprising low oxygen bio-oil and water; and (iv) removing water from the low oxygen bio~oil.

[0017] Another aspect of the invention is the low oxygen bio oil produced by the process of this invention.

BRIEF DESCRIPTION OF THE DRAWING

[0018] Figure 1 shows a schematic diagram of a process for separating the oil phase and the aqueous phase of a bio-crude.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Although often referred to as bio-crude, the liquid product of a biomass pyrolysis reaction us very different from petroleum crude.

[0020] Firstly, bio-crude contains significant amounts of water. Taking ligiio- ceUulosic biomass as an example, as harvested it contains generally from about 1 S to close to 50% water. Although it is possible to dry biomass material prior to using it as a feedstock in a pyrolysis reaction, drying is energy intensive and therefore costly. Even "dry" biomass still contains between 5 and 15% moisture. Drying the biomass further would require an inordinate amount of energy, and is therefore economically unattractive. Tn addition, very dry biomass presents a fire hazard, and handling difficulties due to the formation of static electricity, In general, therefore, biomass material used as a feedstock in pyrolysis reactions contains between 15 and 30% moisture, which is carried into the liquid product of the pyrolysis reaction.

[0021] In addition, several of the pyrolysis reactions create water as a byproduct For example, oxygenated compounds are partially converted to char and coke by dehydration reactions.

[0022] The presence of significant amounts of water in the liquid pyrolysis product is virtually unavoidable.

[0023] A second difference between organics in crude and bio-crude is the high oxygen content of the organic components of bio-crude. Cellulose has an oxygen content of about 44%, and the oxygen content of most forms of ligno-eeliulosic biomass is near 40%. Standard pyrolysis processes produce a liquid product having high oxygen content, as reflected in a Total Acid Number in the range of from 50 to 70. With the process of European Patent Application 08 153229.3-21.04 a liquid pyrolysis product can be produced having a Total Acid Number of less than 10. Although this product is of sufficient quality to be processed m standard refinery equipment, its oxygen content is still much higher than that of petroleum crude.

[0024] This high oxygen content makes the liquid product chemically unstable. In addition, the liquid product is corrosive due to the presence of carboxylic acids. A significant portion of the organic component of the bio-crude is soluble in water. Even the water insoluble organic compounds have a significant degree of hydrophilicity. These water insoluble hydrophilic compounds act as emulsifiers, making it difficult to separate the aqueous phase from the oil phase.

[0025] Due to the high oxygen content of the bio-crude it is necessary to upgrade the biocrude before it can be used as a fuel for internal combustion engines. The present invention provides a process for upgrading bio-crude, said process comprising the steps of (i) allowing the liquid product to settle into an aqueous phase and an oil phase; (ii) separating the oil phase from the aqueous phase; (Hi) subjecting the oil phase to a hydrogen treatment step to form a mixture comprising low oxygen bio-oil and water, and (iv) removing the water from the low oxygen bio-oil.

[0026] As mentioned above, the liquid product of a biomass pyrolysis reaction comprises water and oxygenated organic compounds. It is desirable to remove a significant portion of the water prior to subjecting the organic liquids to the hydrogen treatment step. An important aspect of the present invention is the oxygen content of the liquid product, which is less than 30 wt%. This is considerably lower than the oxygen content of a typical flash pyrolysis oil, which is 40 wt% or more. As a result of this relatively low oxygen content the liquid product generally spontaneously separates into an aqueous phase and an oil phase, without requiring the inducement of phase separation. If water addition is needed to induce phase separation, the amount of water needed for inducement is far reduced, which facilitates the subsequent upgrading of the aqueous phase. [0027] Accordingly, the water removal step generally requires just allowing the liquid product to settle into an aqueous phase and an oil phase. Any phase separation technique may be used for this water removal step. It should be kept in mind, however, that bio oil has a higher density than water. Any technique for separating water from oil can be used for the present purpose, with the proviso that in the case of liquid pyrolysis products, the oil and water phases trade places because of the respective densities. The density of a typical bio-oil is about 1.2.

[0028] Figure 1 shows a skimming tank 10 that is suitable for use in the present invention. Bio-crude 11 enters the skimming tank 10 at or near the top of the tank. The tank is sized as a function of the flow rate of bio crude 11 to ensure a sufficient residence time in the tank. In general, the residence time should be at least about 10 minutes, and is preferably between about 30 minutes and about 60 minutes. Tank inlet 18 at the top may be provided with a deflector (not shown) to minimize turbulence caused by the incoming liquid.

[0029] The oil phase 12 settles in the lower part of tank 10; the aqueous phase 13 collects at the top. The two phases are separated by interface 14. The oil phase leaves tank 10 via control valve 16, The aqueous phase 13 leaves tank 10 via control valve 17. The respective flow rates of oil phase 12 and aqueous phase 13 are controlled so that the level of interface 14 remains more or less constant. The level of interface 14 may be allowed to vary during the operation of tank 10, provided that it does not rise to above the level of valve 17.

[0030] Due to the presence of organic compounds having emulsifying properties, the oil phase recovered from step (ii) may still contain significant amounts of water. As a general rule, if the liquid product has a low oxygen content, its emulsifying properties are less, and the water removal steps (i) and (ii) result in the removal of a larger portion of the water.

[0031] It may be desirable to reduce the emulsifying properties of the oil phase by adding a de~emuisifier. De-emulsifiers are well known in the art. These materials generally act by reducing the surfactant properties of compounds having a hydrophilic portion and a lipophilic portion. For example, the surfactant properties of long chain carboxylic acids can be broken by the addition of a divalent metal ion, such as Ca or Mg. The water-solubility of divalent metal salts of long chain carboxylic acids is generally poor. Effectively, the addition of a divalent metal reduces the hydrophilic properties of the carboxylic acid.

[0032] The oil phase is subjected to a hydrogen treatment step. This step comprises reacting the liquid with hydrogen. Preferably, mis reaction is carried out under a partial hydrogen pressure of at least about 34 bar.

[0033] Desirably, the hydrogen treatment step is carried out in the presence of a catalyst. Examples of suitable hydrogen treatment processes include hydrocracking and catalytic distillation. Catalytic hydrocracking may be carried out in a fixed bed reactor. Preferably the catalyst used in catalytic hydrocracking comprises a zeolite.

[0034] The hydrogen treatment reaction may also include the use of a hydrogenation catalyst. Suitably, the hydrogenation catalyst may be a conventional hydrotreatment catalyst. Depending on its origin, the biomass feedstock may contain little or no nitrogen or sulfur compounds. Accordingly, there is little or no need for the hydrogen treatment to provide hydro- desulfurization activity and hydro- denitrogenation activity. Therefore, hydrogenation catalysts that have little or no desulfurization properties are suitable for use in the process of the present invention, although catalysts with desulfurization and/or denitrogenation activity would also be suitable tor use in the present invention. Suitable examples include catalysts comprising platinum and other metals from the platinum group of the periodic table, such as Ru. Nickel is another well known hydrogenation catalyst, and is preferred to platinum and similar metals because of its lower cost. Preferred hydrogenation catalysts are those that contain nickel.

[0035] Reduced-metal hydrogenation catalysts tend to be susceptible to catalyst poisoning. The more resilient traditional hydrotreatment catalysts are also suitable for use in the hydrogen treatment reaction of the process of the present invention. Preferred examples include Co-Mo, Ni-Mo, and Ni-Co-Mo catalysts, for example on an alumina carrier. Although no desulfurization needs to be achieved, the hydrotreatment catalyst preferably is introduced in its pre-sulfided form. [0036] As generally no sulfur is present in the feedstock, it is preferred to add a small amount of a sulfur compound to the reaction mixture in order to maintain optimum catalyst activity. Suitable sulfur compounds are well known in. the hydrotreatment art. Specific examples include hydrogen sulfide (H2S), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS). The sulfur compound can be selected from the group consisting of H2S, DMS, DMDS, and combinations thereof. Small amounts, in general in the range of from about 10 to about 50 ppm by weight of the feedstock, are sufficient to keep the catalyst sulfided.

[0037] Water is an important byproduct of the hydrogen treatment step, because most of the hydrogen is consumed by converting oxygen present in the organic compounds. As mentioned before, the oil phase from step (ϋ) already contains significant amounts of water because of the incomplete removal during steps (i) and (n). As a result of the hydrogen treatment, the emulsifying properties of the bio-oil are much reduced. Therefore, virtually all of the water now present in the bio oil can be removed by a skimming step as described herein above. If necessary, de~emulsifiers may be added to further improve the efficacy of this water removal step. The low oxygen bio-oil produced by hydrogen treatment of the oil phase is suitable for blending in a diesel fuel, as oxygenated additives for gasoline, for heating oil, or for blending in kerosene, and the iike.

[0038] An important advantage of the process of the present invention is that the relatively expensive hydrogen treatment step is only used for the oil phase of the bio- crude. The organic compounds in the oil phase have a lower oxygen content than the organic compounds dissolved in the aqueous phase. By removing the aqueous phase prior to the hydrogen treatment step, consumption of hydrogen by the high oxygen compounds present in the aqueous phase is avoided.

[0039] The aqueous phase itself may be subjected to a de-oxygenation step. The organic compounds present in the aqueous phase can be converted to noncorrosive oxygenated compounds that can be used in polymer chemistry and as oxygenated additives of gasoline. [0040] As mentioned earlier, if. is advantageous to use a liquid pyrolysis product of good quality. Therefore, in a preferred embodiment, the liquid pyrolysis product that is used as the feedstock for the present process is one having pH of about 4.S or higher. Feedstocks of this quality can be stored and processed in equipment made of stainless steel, or even soft steel, which represents a significant cost savings compared to the sophisticated alloys required for processing and storage of pyrolysis liquids having a lower pH.

[0041] Another advantage of using a feedstock having a pH of about 4,5 or higher is that the hydrogen consumed in the hydrogen treatment step is less, and that the hydrogen consumption results in an upgrading of the bio-oil in terms of heat content and hydrocarbon compatibility, rather than being required for stabilizing the bio-oil.

[0042] While the technology has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the technology as defined by the appended claims.