Patent Application
20140069012
None.
This disclosure relates to pyrolysis of organic matter into useful chemical or fuel products. More specifically, this disclosure pertains to methods and systems for decreasing the entrainment of char and other particulate contaminants in pyrolysis vapors by utilizing a pelletized biomass feedstock in to a specific size range. A binder material in the pelletized feedstock facilitates maintaining the diameter of the feedstock pellets above a given threshold size both before and during pyrolysis. The binder material optionally possess catalytic activity.
The U.S. Renewable Fuel Standards (RFS) mandate will require higher volumes of advanced biofuels to be produced in the near future. One method being developed to meet this mandate is the fast pyrolysis of biomass. Conventional biomass fast pyrolysis requires rapid heating of biomass in the absence of oxygen. Products include a solid carbonaceous char that contains the vast quantities of metals (e.g. Na, K, Mg) present in the biomass feedstock. The products also include a highly-oxygenated pyrolysis oil (or pyoil) that is not practical for upgrading to a transportation fuel because of thermal stability issues associated with highly reactive oxygenated components. The remainder of the pyrolysis product is classified as non-condensable gas.
To generate a viable transportation fuel, catalysts may be employed during the fast pyrolysis process. Several known classes of catalysts can deoxygenate the primary products from pyrolysis to create chemical intermediates that can be further upgraded to a hydrocarbon-rich fuel using conventional refining methodology. Optionally, hydrogen may also be added to perform hydro-catalytic pyrolysis, which improves the quality of the products by significantly lowering the oxygen content, the acid content, etc. The use of hydrogen increases the yield of pyrolysis oil by hydrogenating the primary pyrolysis products, which removes oxygen as water instead of oxides of carbon. The relatively low oxygen content intermediate product is easily upgradable to bio-derived fuels.
Unfortunately, when employing this process, the catalysts tend to rapidly deactivate when contacted by char fines composed of carbon and metals. Additionally, the char fines are often carried out of the pyrolyzer by entrainment with the hot pyrolysis vapor, resulting in a condensed liquid product containing solids and metals that can negatively impact downstream processes.
There is a need to improve fast pyrolysis technology to allow for rapid catalytic upgrading of primary pyrolysis products into products that are fungible with current petroleum-derived liquid hydrocarbon fuels, while preventing char and associated metals from entrainment with these vapors to cause catalyst deactivation and equipment fouling.
Certain embodiments comprise a biomass pyrolysis process, including the steps of: a) providing a particulate biomass feedstock; b) mixing the particulate biomass feedstock with a binder material to produce a mixture, and compressing the mixture to form pellets; c) pyrolyzing the pellets in a reactor to form a product comprising pyrolysis vapors and char particles, where the presence of the binder material in the pellets decreases the rate of mechanical attrition, thermal attrition and dissociation of the pellets into particles smaller than 300 microns in diameter either prior to, or during the pyrolyzing; d) obtaining pyrolysis vapors from an outlet of the reactor that comprise less entrained char (by weight) due to the increased average diameter of the char particles of step c).
Optionally, during the pyrolyzing the binder material may catalytically transform at least a portion of the pyrolysis vapors to compounds fungible with a petroleum-derived transportation fuel, transportation fuel component, mixtures thereof, or a catalytically upgradeable intermediate that is further upgraded to compounds fungible with a petroleum-derived transportation fuel, transportation fuel component or mixtures thereof. Optionally, the binder material additionally functions to alter the variety and complexity of chemical compounds produced during the pyrolyzing of step (c).
In certain embodiments, the pyrolysis vapors of step (d) comprise less entrained metals (by weight) due to the decreased rate of mechanical attrition, thermal attrition and dissociation of the pellets into particles smaller than 300 microns, 500 microns, or 750 microns in diameter in step (c). In certain embodiments, the presence of the binder material in the pellets decreases mechanical attrition, thermal attrition and dissociation of the pellets into particles smaller than 300, 500 or 750 microns in diameter either prior to, or during the pyrolyzing.
In certain embodiments, the mixture is compressed to form pellets that are in a range from 300 microns to 1250 microns in diameter, or alternatively in a range of 750 microns to 1250 microns in diameter, and wherein the presence of the binder material in the pellets decreases mechanical attrition, thermal attrition and dissociation of the pellets into particles smaller than 750 microns in diameter while the pellets remain inside the reactor.
In certain embodiments, during the pyrolyzing, the binder material catalytically transforms at least a portion of the pyrolysis vapors to product compounds suitable for use as a hydrocarbon fuel, a hydrocarbon fuel component, a catalytically upgradeable intermediate or mixtures thereof, where the product compounds obtained from an outlet of the reactor comprise less entrained char (by weight) due to the presence of the binder material in the pellets.
A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings in which:
The FIGURE is a simplified diagram of one embodiment of the inventive process and system depicting a pyrolysis reactor with an upgrading reactor to receive and upgrade the vapors from the pyrolysis reactor.
The invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale. It should be understood that the drawings and their accompanying detailed descriptions are not intended to limit the scope of the invention to the particular form disclosed, but rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
Conventional pyrolysis methods and systems have suffered from either 1) char and/or metal entrainment in the pyrolysis vapors, leading to deactivation of any downstream upgrading catalyst, or 2) use of mechanical separation devices to remove entrained char from pyrolysis vapors, leading to an undesirable delay prior to catalytic upgrading and increased maintenance due to fouling/plugging of the separation device. Such a delay can allow secondary pyrolysis reactions to occur in the primary pyrolysis vapors that leads to products that may be difficult to upgrade into a bio-derived hydrocarbon transportation fuel.
In conventional fast-pyrolysis, an emphasis has been placed on converting the biomass feedstock to a particle size of less than 20 microns (preferably 1 to 3 microns for fluidized bed pyrolysis). This allows more rapid heat transfer to the feedstock particles during pyrolysis, and may minimize char formation. However, we have found that utilizing feedstock particles less than 300 microns in diameter in the pyrolysis process also correlates directly with entrainment of significant quantities of char and metals in the vapors produced during pyrolysis, as well as product pyrolysis oil. Such contamination is believed to contribute to the instability of pyrolysis oils by catalyzing numerous reactions that increase the viscosity of the oil and make further upgrading difficult.
In the inventive processes and systems described herein, a particulate biomass feedstock is fed to a pyrolysis reactor for conversion by pyrolysis and subsequent catalytic upgrading to produce a mixture comprising hydrocarbons that are fungible with petroleum fractions and petroleum-derived fuels. Such fuels may include, but are not limited to, gasoline, jet/kerosene, diesel and gasoil. The methods and systems described herein facilitate this conversion process by one or more of the following: 1) preventing catalytic transformation of the pyrolysis vapors via contact with entrained char, as well as via metals impregnated on the char, 2) preventing poisoning of catalysts utilized to upgrade the pyrolysis vapors, thereby extending the lifespan of catalysts, and 3) narrowing the product distribution by limiting the variety and complexity of chemical compounds produced in the primary pyrolysis vapors to facilitate catalytic upgrading. Other benefits of the present processes and systems are disclosed in greater detail below.
We show herein that during biomass pyrolysis, metals derived from the feedstock are largely retained in the solids fraction (see Example 1). Further, when we sized the feedstock to eliminate feedstock particles smaller than 300 microns, total metal content in the resulting pyrolysis oil fractions decreased by 94-97% relative to the content detected in the feedstock, while metal content was found to be 16-fold higher in the solids fraction (comprising mostly char) versus the feedstock. Similarly, when the feedstock was sized to eliminate feedstock particles having a diameter less than 750 microns, total metal content detected in the resulting pyrolysis oil fractions decreased even further (95-99 wt. %) relative to the content found in the feedstock, while detected metal content was 8-fold higher in the solids fraction versus the starting feedstock.
While not wishing to be bound by theory, we hypothesize that conventional pyrolysis processes utilize smaller feedstock particles, which results in the formation of smaller char particles during pyrolysis. These smaller char particles are then more easily entrained into the produced pyrolysis vapors and are difficult to separate from the pyrolysis vapors without implementing a mechanical separation step such as, for example, hot vapor filtration or cyclone separation. If not removed prior to cooling and condensation of the vapors, entrained char particles (and associated metals) may catalyze undesirable reactions within uncondensed pyrolysis vapors that prevent subsequent upgrading of the vapors to fuels. Alternatively, if the pyrolysis vapors are cooled and condensed to pyrolysis oil, the entrained char and associated metals contaminate the oil and are associated with a decrease in pyrolysis oil stability.
The inventive processes and systems disclosed herein may serve to decrease the quantity of char (by weight) entrained in the pyrolysis vapors passing out of the reactor. In certain embodiments, this is accomplished by utilizing a biomass feedstock that does not comprise particles smaller than a certain minimum threshold diameter. Alternatively, this may be accomplished by compressing a particulate biomass feedstock to form feedstock pellets larger than a certain threshold diameter.
By decreasing char entrainment, the inventive process and system also decreases entrainment of metals in the vapors, leading to decreased metal content in the produced pyrolysis oil, fuel precursor product or hydrocarbon fuel depending upon the desired product specification. This is achieved without the need for mechanical separation of char from the primary pyrolysis vapors. An additional potential benefit is that the flow of pyrolysis vapors leaving the pyrolysis reactor may be increased without dramatically increasing entrainment of char particles (due to their increased size and weight). This can facilitate decreased residence times of the pyrolysis vapors prior to contacting an upgrading catalyst, while allowing the upgrading catalyst (or catalysts) to be housed in a container/reactor that is separate from the pyrolysis reactor. In summary, the inventive process and system can 1) maximize production of pyrolysis vapors, and 2) minimize residence time of pyrolysis vapors prior to upgrading, thereby preventing detrimental secondary pyrolysis reactions, all while 3) effectively preventing poisoning of downstream pyrolysis vapor upgrading catalyst(s) resulting from contact with char particles and metals.
To achieve these benefits, certain embodiments utilize a particulate biomass feedstock comprising particles that are equal to or smaller than 300 microns in diameter, or equal to or smaller than 500 microns in diameter. In certain embodiments, this particulate biomass feedstock is combined with a binder material to form a mixture that is then mechanically compressed to form biomass feedstock pellets that are larger than certain threshold diameter. In certain embodiments, the threshold diameter may be, for example, larger than 300 microns, 500 microns or 750 microns. In certain embodiments, the pellets may be sized to a defined range of sizes, such as for example, from 300 to 500 microns, or 750 to 1250 microns. Preferably, the resulting compressed feedstock pellets are resistant to mechanical attrition, thermal attrition and dissociation following compression and also during pyrolysis. In certain embodiments, the presence of the binder material in the pellets decreases the rate of mechanical attrition, thermal attrition and dissociation of the pellets into particles smaller than 300 microns in diameter either prior to, or during the pyrolyzing. In certain embodiments, the presence of the binder material in the pellets prevents mechanical attrition, thermal attrition and dissociation of the pellets into particles smaller than 300 microns (optionally 400, 500, 600, or 750 microns) in diameter either prior to, or during the pyrolyzing.
In certain embodiments, the compressing of the feedstock is accomplished by conventional means, such as by a mechanical or hydraulic press. While not wishing to be bound by theory, increasing the average size of char particles formed during pyrolysis may decrease entrainment of such particles in the pyrolysis vapors produced during pyrolysis of the feedstock. Metals present in the feedstock are believed to be highly associated with the char particles.
The pyrolysis process may comprise adding a binder material to particulate biomass (e.g. by mixing or impregnation) followed by compressing the biomass to form pellets and using the pellets as feedstock for pyrolysis. In certain embodiments, the presence of a binder material during compressing or pelletization further increases resistance of the compressed pellets to mechanical attrition, thermal attrition and dissociation. Pelletization of the biomass feedstock also allows for a consistent, uniform feed, and higher transportation densities than uncompressed biomass feedstocks. The binder material optionally also functions as a catalyst either before, during, or after, pyrolysis of the feedstock. This will be discussed in greater detail later.
Optionally, the binder material may additionally comprise an additive that functions during pyrolysis of the biomass to alter via chemical interaction at least one of the variety, quantity and complexity of chemical compounds produced by the pyrolysis process. In certain embodiments, the additive may function to provide a chemical product distribution of reduced complexity that enables the selection and development of more task-specific catalysts for upgrading the pyrolysis vapors. The upgrading (e.g., reduction in the quantity of carboxylic acids and aldehydes, or hydrodeoxygenation of phenolics) may occur as a subsequent process step and/or concurrently with the pyrolysis of the feedstock. The end result of the process is a product that is partially (or fully) upgraded to a hydrocarbon transportation fuel, transportation fuel blend component, or mixtures thereof depending on the desired specifications.
When the binder material additionally comprises an additive, the feedstock may optionally be acted on by the additive during the pelletization step, thereby eliminating a separate additive pretreatment process step. For example, a pretreatment step with an additive solution that contacts the biomass may be used to passivate alkali metals, thereby improving sugar yields for upgrading. In the current process, such passivation could be performed concurrent with pelletization of the feedstock.
In addition to eliminating a process step, the use of the solution as a binder ensures more uniform coverage (better alkali passivation) through intimate contact of biomass and pretreatment solution. Furthermore, water is a typical binder for biomass pellets, meaning that the acid concentration can be controlled so that moisture content of the pellets (which is critical in pyrolysis) is unaffected. Preferably, the moisture content of the feedstock pellets is below 15 wt. %. The invention may be also combined with a torrefaction process so that torrefied biomass, which has low moisture, may pelletized and pretreated. Torrefied biomass may also be mixed with untreated biomass prior to pretreatment.
In certain embodiments, the additive may be a salt (e.g., magnesium chloride), an acid or base (e.g., boric acid, sodium bicarbonate), a hydrated salt (e.g. magnesium chloride hexahydrate). The additive may be combined with water (0.1-99.9 wt %, based on the wt of the biomass) thereby enabling steam-catalyzed dehydration reactions. The additive may optionally be chosen to be recyclable or disposable. If disposable, the additive may be chosen to enhance the composition of the char for soil amendment or other applications. While not wishing to be bound by theory, it is hypothesized that certain additives may act by retaining water in the biomass to higher temperatures, allowing for steam pyrolysis to take place rather than charring of the biomass. The resulting pyrolysis vapors are consequently higher in dehydrated products (such as, for example, furfural) than when conducting conventional pyrolysis in the absence of an additive, thereby allowing a more targeted selection of catalyst(s) for upgrading the pyrolysis vapors.
A product distribution of reduced complexity enables the selection, or potential development, of more task-specific catalyst(s) for upgrading the pyrolysis vapors (e.g., reduction of carboxylic acids and aldehydes, or hydrodeoxygenation of phenolics). Such upgrading may occur during pyrolysis, after pyrolysis, or combinations thereof. The end result would be a partially-upgraded or fully-upgraded pyrolysis oil, depending on the desired product specifications. One example of pyrolysis conducted in the presence of an additive is disclosed in Example 2.
In certain embodiments, the additive also functions as the binder material that acts to further increase resistance of the pellets to mechanical attrition, thermal attrition and dissociation (both before and during pyrolysis) to particles having a diameter equal to or less than a given minimum threshold. In certain embodiments, this minimum threshold may be less than or equal to 300 microns, less than or equal to 500 microns, or less than or equal to 750 microns. When the additive serves to pre-treat the feedstock material
In certain embodiments, the additive also serves as an upgrading catalyst (or catalysts) that catalytically transforms the pyrolysis vapors either inside the pyrolysis reactor, or downstream in an upgrading reactor. The binder material may optionally also have catalytic activity that upgrades the pyrolysis vapors either immediately following pyrolysis of the compressed feedstock pellets, or later in a separate step that is optionally carried out in a separate reactor. Such catalytic activity may comprise, for example, a depolymerization catalytic activity, such as may be provided by a metal oxide or acid to reduce the degree of polymerization in the pyrolysis vapors. The catalytic activity may optionally hydrodeoxygenate the pyrolysis vapors non-selectively, or selectively reduce certain compounds, such as phenolics or furfurals into saturated hydrocarbons. In certain other embodiments, the binder material and a physically distinct catalyst may both be mixed with the particulate biomass feedstock prior to compressing the feedstock into pellets. The catalytic activity of the binder material or the physically distinct catalyst may additionally comprise one or more of catalytic condensation, deoxygenation, denitrogenation, decarboxylation, dehydration, dimerization, oligomerization, alkylation, or combinations of two or more of these catalytic reactions.
The reactor utilized for conducting pyrolysis of the particulate biomass feedstock (or pelletized feedstock) can be of any variety, but preferably comprises at least one auger that assists in rapidly and evenly distributing heat throughout the feedstock, as well as helping to convey the feedstock through the pyrolysis reactor from an inlet end portion towards an outlet end portion.
Oxygenated hydrocarbon vapors are produced in the pyrolysis reactor, and these vapors are conveyed generally upward and out of the pyrolysis reactor while maintaining the vapors at a temperature that prevents their condensation. The char created by the process described herein is conveyed through the reactor along with heat carrier by the at least one auger, then optimally falls by force of gravity into a sealed char catch and is eliminated from the reactor. Removing char prior to contacting pyrolysis products with catalyst prevents catalyst fouling/poisoning.
The pyrolysis vapors are preferably contacted with at least one upgrading catalyst in at least one upgrading reactor to convert the vapors into a hydrocarbon mixture that is fungible with current petroleum-derived fuels or upgradeable intermediate compounds that may be more easily upgraded to a liquid hydrocarbon fuel. Residence time between production of pyrolysis vapors (i.e., the primary pyrolysis product) and contact with the at least one upgrading catalysts is preferably minimized to prevent secondary pyrolysis reactions that decrease upgradability of the compounds in the pyrolysis vapors to compounds suitable for use as a transportation fuel or transportation fuel component. The upgrading reactor may be operated as a fixed packed bed, fluidized bed, ebullating bed, or moving bed. The products from the final upgrading reactor are condensed to a liquid that if fungible with a hydrocarbon transportation fuel, transportation fuel, or mixtures thereof.
Examples of biomass feedstock used in the present invention include, but are not limited to, oil-containing biomass, such as jatropha plant, macroalgae or microalgae. Carbohydrate-based biomass may also be used as feedstock, where carbohydrate-based refers to biomass where at least a fraction of its composition is made of carbohydrates. Carbohydrate-based biomasses are available from a variety of sources including cellulosic biomass and algal biomass. Specific examples of feedstock useful in the current invention include, but are not limited to: sugars, carbohydrates, fatty acids, proteins, oils, eucalyptus oil, forest residues, dead trees, branches, leaves, tree stumps, yard clippings, wood chips, wood fiber, sugar beets, miscanthus, switchgrass, hemp, corn, corn fiber, poplar, willow, sorghum, sugarcane, palm oil, corn syrup, algal cultures, bacterial cultures, fermentation cultures, paper manufacturing waste, agricultural residues (e.g., corn stover, wheat straw and sugarcane bagasse), dedicated energy crops (e.g., poplar trees, switchgrass, and miscanthus giganteus sugarcane) sawmill and paper mill discards, food manufacturing waste, meat processing waste, animal waste, biological waste and/or municipal sewage.
The FIGURE depicts an exemplary embodiment for a process and system for conducting pyrolysis of organic material or biomass to useful chemical products or fuel products. A pyrolysis reactor 5 comprises an external housing 20, an inlet 17 for a heat carrier 15, an inlet 10 for a pelletized biomass feedstock 12 and one or more helical augers 22 that when driven by a motor 25 to rotate about a longitudinal axis convey the pelletized biomass feedstock 12 along the length of the reactor 5 from an inlet end 18 towards an outlet end 28. Near the outlet end 28, the large majority of char particles formed during pyrolysis of the pelletized biomass feedstock 12 fall into a char catch 31 by gravitational force. The pelletized biomass feedstock 12 is heated in the pyrolysis reactor 5 by at least one heating source that may include a heating jacket surrounding the housing 20, at least one heated auger 22, or via introduction of a heat carrier 15 via a heat carrier inlet 17 proximal the inlet end 18 of the reactor. The pyrolysis reactor depicted in the FIGURE is operated to exclude most oxygen or air by the introduction of a sweep gas. In the embodiment shown in the FIGURE, the sweep gas 19 enters through sweep gas inlet 23 near the outlet end 28 of the housing 20, although the sweep gas 19 may alternatively enter the system via other points of entry, such as the biomass feedstock inlet 10 or heat carrier inlet 17. As the particulate biomass feedstock 12 is rapidly heated, pyrolysis vapors 37 are produced and rise to the upper portion (or headspace) of the pyrolysis reactor housing 5 and is swept toward the outlet end portion 28, exiting through a first outlet 32.
Further referring to the FIGURE, arranged within close proximity of the pyrolysis reactor first outlet 32 is an upgrading reactor 40 containing at least one bed of one or more active upgrading catalyst(s) 42, wherein each bed of upgrading catalyst 42 may comprise any conventional configuration (e.g, fixed bed, fluidized bed, bubbling bed, moving bed etc.). In certain embodiments, the pyrolysis reactor 5 is in direct contact with the upgrading reactor 40 with minimal distance between the first outlet 32 and the at least one bed of upgrading catalyst 42 contained within upgrading reactor 40. In the embodiment depicted in the FIGURE, a distributor plate 52 is placed above the outlet 32. The distributor plate may optionally assist in retaining within the reactor 5 any residual particulates that may be entrained in the pyrolysis vapors 37 leaving the reactor 5 through outlet 32. Distributor plate 52 may optionally serve to evenly distribute the pyrolysis vapors within the upgrading reactor 40. In certain alternative embodiments, the inventive process minimizes the quantity of char particles that become entrained in the pyrolysis vapors to the point where there is no need to employ any mechanical device (e.g., a distributor plate or filter) to assist in retaining such particles within the pyrolysis reactor.
When the pyrolysis reactor described herein comprises at least one auger, the reactor is more efficient in char removal than a conventional fluidized bed pyrolysis reactor that produces char fines by attrition that elutriate into the pyrolysis vapors. Again referring to the FIGURE, in certain embodiments the majority of char formed during pyrolysis is conveyed by the at least one auger along with heat carrier toward the outlet end 28 of the pyrolysis reactor 5. There, the vast majority of char and heat carrier fall together by force of gravity into a char catch 31 and are removed from the reactor. Thus, the char is prevented from becoming entrained in the pyrolysis vapors, from entering the upgrading reactor 40, and from coming in contact with the upgrading catalyst bed 42. This dramatically enhances the longevity of the upgrading catalyst(s).
As noted above, it is common for the pelletized biomass feedstock 12 to include measurable amounts of metals that act as poisons to desirable upgrading catalysts, and we have found that this metal content becomes concentrated in the char produced during pyrolysis. Utilizing the processes and systems described herein, catalysts that are more susceptible to poisoning by metals may be used to upgrade the pyrolysis vapors, since the impact of metal poisoning and coke formation is dramatically reduced. In addition, the product leaving the upgrading bed is free of solids and metals, thereby removing the need for subsequent particle removal
The temperature within the pyrolysis reactor may be maintained via one or more of several mechanisms, such as heating of the reactor housing, heating of the at least one auger, microwave or inductive heating of the biomass, addition of a heated sweep gas, and addition a of a solid particulate heat carrier that has been pre-heated. Regardless of the heating mechanism utilized, preferably the pyrolysis reactor and its contents are maintained at a temperature of at least 600° F. (315° C.). The pyrolysis may be conducted in an inert environment such as nitrogen or helium, or in a reactive environment containing 0.1-100% reactive gas or gas mixtures (e.g. hydrogen, methane, alcohols, steam, oxygen, etc.).
Again referring to the embodiment depicted in the FIGURE, a disengagement zone 45 is located proximal to the outlet end 28 of the pyrolysis reactor 5, and near the first outlet 32. The disengagement zone is designed to provide a space where the upward local velocity of the pyrolysis vapors 37 prior to passing through the first outlet 32 is sufficient to entrain less than 0.5% (by wt.) of the char produced by the pyrolysis of the pelletized biomass feedstock. In certain embodiments, the upward local velocity of the pyrolysis vapors 37 prior to passing through the first outlet 32 entrains less than 0.1% (by wt.) of the char produced by the pyrolysis of the pelletized biomass feedstock 12. Achieving this low percentage of char carryover requires designing the height and diameter of the disengagement zone to allow the terminal falling velocity of the char and heat carrier particles to exceed the upward local velocity of the pyrolysis vapors in the disengagement zone, 45 such that nearly all char particles (greater than 99%, 99.5% or even 99.9% by weight) being retained in the pyrolysis reactor 5, thereby preventing these particles from being carried with the pyrolysis vapors 37 exiting via the first outlet 32 and preventing contact with upgrading catalyst bed 42.
In certain embodiments, a sweep gas is employed that may comprise one or more of many gases that are either inert or reactive. For example, the sweep gas may comprise gases such as nitrogen, helium, argon, hydrogen, methane and mixtures thereof. If the sweep gas comprises a reactive gas, the reactive gas may optionally react with the biomass during pyrolysis, may serve as a reactant when the pyrolysis products are upgraded by contacting the upgrading catalyst(s), or both. The sweep gas may be injected into the system at more than one point, or injected simultaneously at multiple points. One point may comprise combining the sweep gas with the feedstock prior to entering the pyrolysis reactor, while another may comprise injecting sweep gas directly into the pyrolysis reactor proximal to the biomass feedstock inlet. A third point may comprise injecting the sweep gas proximal to the first outlet of the pyrolysis reactor. This may be preferable if the sweep gas is to be used as a reactant during upgrading of the primary pyrolysis product.
In certain embodiments, a gas may be injected just upstream of the pyrolysis reactor first outlet in order to 1) assist in preventing entrained char and heat carrier particles from leaving the pyrolysis reactor, 2) quench the primary pyrolysis product to a lower temperature, 3) heat the primary pyrolysis product to a higher temperature, or combinations thereof. In embodiments where the sweep gas serves to quench the primary pyrolysis product, such quenching may prevent coking. Embodiments where the sweep gas serves to heat the primary pyrolysis product may prevent formation of char and secondary pyrolysis reactions that may reduce the subsequent upgradability of the primary pyrolysis product to a bio-derived fuel. However, quenching is limited such that the quenched primary pyrolysis product does not condense prior to contacting the upgrading catalyst(s). Typically, this requires that the quenched primary pyrolysis product still maintains a temperature of at least 250° C. to prevent condensation.
The volumetric flow rate, or “standard gas hourly space velocity” (SGHSV) of the sweep gas is adjusted to minimize the time between pyrolysis and catalytic upgrading, such that the upgrading catalyst (or optionally, catalysts) contacts primary products of pyrolysis and not secondary pyrolysis products that comprise 16 or more carbons and are more difficult to upgrade to a bio-derived fuel. Volumetric flow rate for a given embodiment depends upon factors including, but not limited to, the volume of the pyrolysis reactor, the temperature and pressure at which the pyrolysis reactor is maintained, the feed rate of the particulate biomass feedstock to the pyrolysis reactor, and the type of feedstock utilized. A paper by J. N. Brown, et al. provides one example of how these variables can be adjusted to determine an optimal volumetric flow rate for a desired pyrolysis outcome, including, for example, the pyrolysis liquid to pygas ratio, and the relative percentage of the feedstock converted to char.
The pressure maintained within the pyrolysis reactor is generally within a range of about 0 psig to 3000 psig. Preferably, the pyrolysis reactor is maintained at a pressure in the range of 100 psig to 500 psig to increase throughput of particulate biomass feedstock, and in certain embodiments, facilitate catalytic upgrading of the primary pyrolysis product.
The primary pyrolysis product is driven by the sweep gas (or optionally, a pressure differential) from the pyrolysis reactor via the first outlet and enters an upgrading reactor and contacts an upgrading catalyst. Minimizing residence time of the primary pyrolysis product in the pyrolysis reactor is important for maximizing the percentage of primary pyrolysis product that is successfully upgraded to a bio-derived fuel. Conditions of temperature and pressure, as well as reactor dimensions are chosen to assure a residence time of the primary pyrolysis product in the pyrolysis reactor that is less than 5 seconds, preferably less than 3 seconds, more preferably less than 1 second, even more preferably less than 0.3 second, and most preferably less than 0.1 second.
Minimizing residence time of the primary pyrolysis product in the pyrolysis reactor prevents the occurrence of secondary pyrolysis reactions that form larger oxygenated species comprising 16 or more carbon atoms. These larger oxygenated species are likely to form coke, which is extremely detrimental to the process by fouling process equipment and heat carrier. Additionally, diversion of the primary pyrolysis product into secondary pyrolysis reactions decreases the conversion efficiency of the feedstock into smaller species that are more easily upgraded into a bio-derived fuel.
The physical distance between the pyrolyzer and the upgrading catalyst(s) contained within the upgrading reactor may vary, but is preferably minimized, taking into consideration the space velocity of the primary pyrolysis product (optionally in a mixture with a sweep gas) out of the pyrolysis reactor. Minimizing this distance assists in decreasing the time between production of the primary pyrolysis product and subsequent contacting with one or more upgrading catalyst(s). Through optimizing the variables of distance and space velocity, the current invention assures that the upgrading catalyst sees primary products from pyrolysis and not secondary products created by reactions occurring after pyrolysis. Generally, the distance between the pyrolyzer and the upgrading catalyst(s) is less than 4 ft. More preferably, this distance is less than 1 ft., and most preferably, less than 6 inches.
Optionally, the disengagement zone between the pyrolyzer and the upgrading catalyst may include additional features to limit reactivity of the primary pyrolysis product prior to contact with the upgrading catalyst(s). These may include (but are not limited to) temperature control, introduction of a gas or fluid to quench the primary pyrolysis product (as mentioned previously), flow control through judicious choices in geometry (preferably, a geometry minimizing bends and small orifices to decrease the potential for vapor condensation), the presence of a pre-catalyst (such as zeolite monolith, or any of the above-mentioned upgrading catalysts) at the interface between reactors.
In some embodiments, a catalyst monolith may be utilized as a pre-catalyst bed, or guard bed, while in other embodiments, the pre-catalyst may comprise a fluidized bed of catalyst integrated with the distributor assembly to control reactivity in this region. The fluidized bed of catalyst may additionally function as a moving bed filter to remove residual particulates. Such methods may be as described in U.S. Pat. No. 8,268,271, which is hereby incorporated by reference.
The at least one upgrading bed may utilize any type of reactor configuration including, but not limited to, a fixed bed, a bubbling bed, a circulating bed, a moving bed, a counter current reactor or combinations of two or more of these configurations. Each catalyst may be periodically or continuously regenerated as needed. In certain embodiments, regeneration may comprise transporting the catalyst to a regenerator for de-coking, then returning to the pyrolysis reactor. Optionally, fresh catalyst may be added on a periodic or continuous basis to the pyrolysis reactor to account for catalyst attrition.
Examples of some upgrading catalysts and typical reaction conditions are disclosed in U.S. patent application Ser. No. 13/416,533, although any catalyst known to catalyze the conversion of primary pyrolysis products to a bio-derived fuel may be utilized. The catalyst may include, but is not limited to zeolites, metal modified zeolites, and other modified zeolites. Other catalysts may include forms of alumina, silica-alumina, and silica, unmodified or modified with various metals, not limited but including, Nickel, Cobalt, Molybdenum, Tungsten, Cerium, Praseodymium, Iron, Platinum, Palladium, Ruthenium and Copper or mixtures thereof. Still other catalysts may include unsupported metals, supported or unsupported metal oxides or metal phosphides, and mixtures thereof. Catalyst types include deoxygenation catalysts, hydrogenation catalysts, hydrotreating catalysts, hydrocracking catalysts, water-gas-shift catalysts, and condensation catalysts. Catalysts may be sulfided or un-sulfided. In certain embodiments, each catalyst bed may comprise mixtures of one or more catalysts of the types described above. Optionally, multiple catalyst beds may be placed within a single reactor, or multiple catalyst beds may be placed in different reactors to facilitate different reaction conditions. When multiple reactors are utilized, they may be arranged to either in parallel or series.
If multiple upgrading reactors are utilized, different conditions may be maintained in each reactor in order to facilitate a given catalytic reaction. To facilitate flow of the vapors through multiple reactors, a pressure differential may be maintained wherein the pressure in each successive reactor progressively decreases.
The residence time of the pyrolysis vapors in each upgrading reactor generally ranges from 0.01 sec to 1000 sec. Preferably, the residence time is in a range from 0.05 sec to 400 sec. More preferably, the residence time is in a range from 0.1 sec to 200 sec. Most preferably, the residence time is in a range from 0.1 sec to 100 sec.
The temperature maintained within each upgrading reactor is generally in the range from 72° F. to 1500° F. Preferably, the temperature is in the range from 100° F. to 1000° F., although if multiple upgrading reactors are used, each may be maintained at a different temperature within this range. The flow of one or more of gas, vapors and liquids within each upgrading reactor is preferably upward, although downward or lateral gas flow may also be utilized.
Certain upgrading reactions may be advantageously performed on the pyrolysis vapors, while other upgrading reactions may advantageously be performed following condensation of the vapors to a liquid. Condensation of the vapors may be achieved by any conventional means known in the art. In certain embodiments, vapors may be directed to a condensation system that functions to reduce the temperature of vapors to a temperature that is at or below the dew point for at least one component of the vapors. Typically, the conditions utilized do not result in the condensation of methane, but preferably will condense C4+ hydrocarbons.
Hydrogen may be separated from the non-condensed gas by a variety of conventional methods and recycled as the sweep gas. In certain embodiments, the recycled hydrogen may be added directly into, or just upstream from, an upgrading reactor to facilitate one or more upgrading reactions. Alternatively, the entirety, or some fraction, of the bulk non-condensable gas is used for the same purpose. In another embodiment, the entirety, or some fraction, of the bulk of the non-condensable gas is sent to a combustor or hydrogen generation unit (e.g., a reformer) to generate either heat or hydrogen, respectively. The resulting heat or hydrogen may then be partially or entirely recycled back to the process.
Certain upgrading reactions are advantageously conducted at a pressure that is greater than atmospheric pressure. The pressure that is maintained in the one or more upgrading reactors may range from 0-3000 psig, although a preferred pressure range is zero to 1000 psig. In certain embodiments, the pressure may range from 10 to 800 psig, from 20 to 650 psig, from 100 to 500 psig. An exemplary pressure might be 400 psig.
The following examples of certain embodiments of the invention are given. Each example is provided by way of explanation of the invention, one of many embodiments of the invention. The examples are intended to be illustrative of specific embodiments and should not be interpreted to limit, or define, the scope of the inventive processes and systems as disclosed herein.
Kiln-dried Red Oak was ground and the particles were subjected to pyrolysis (“Raw Biomass” in Table 1) or pre-sized into two fractions with a particle diameter ranging from of 300 to 500 microns or a particle size ranging from 750 to 1250 microns (see Table 1).
Biomass was added to a pyrolysis reactor with a heat carrier heated to a temperature greater than about 1200° F. to thermally decompose solid biomass to condensable pyrolysis vapors, char, and non-condensable gases. The pyrolysis vapors passed out of the pyrolysis reactor and were cooled and collected in a collection system comprised of electrostatic precipitators (ESPs). These ESP collected vapors that condensed at greater than about 180° F., while water-cooled condensers collected vapors that condense at a temperature of less than 180° F.
In the experiment, solids remained in the pyrolysis reactor (Table 1) and two fractions were collected (refer to Tables 2 and 3, respectively: 1). The vapor-gas stream was cooled from 850° F. to 320° F. The condensed liquid droplets and aerosols were then collected in an ESP. This fraction consisted primarily of anhydrosugars, oligosaccharides, and phenolic oligomers. 2). Sub-cooled nitrogen further cooled the vapor stream to 180° F. at the entry to a second ESP. The condensed liquid droplets were collected. This fraction contains mainly phenolic and furanic species. The chosen temperature minimized water condensation while still effectively condensing phenols and furans.
Following collection, pyrolysis oils and biochar were analyzed by inductively coupled plasma (ICP) for metal content. Solid weight fraction was estimated by comparing the amount of potassium and calcium in the pyrolysis oil to the amount of Ca and K per unit weight of biochar. Biochar was assumed to be the only solid found in the pyrolysis oils and the only source of Ca and K. This assumption was made because the Ca/K ratio for biomass, biochar, and the oils was substantially similar.
The data shows that upon the pyrolysis of red oak, metals derived from the feedstock are largely retained in the solids fraction (Table 1). When the feedstock was sized to a particle diameter ranging from 300-500 microns (second column), total metal content in the resulting pyrolysis oil fractions decreased by 94% in the first fraction (Table 2 second column) and by 97% in the second pyrolysis oil fraction (Table 2 second column) relative to the content detected in the feedstock (Table 1, column 1). Detected metal content was 16-fold higher in the solids fraction (Table 1, second column) versus the feedstock (Table 1, first column). Similarly, when the feedstock was sized to a particle diameter ranging from 750-1250 microns (Tables 1-3, third column), total metal content detected in the resulting pyrolysis oil fractions (Tables 2 and 3) decreased even further (95-99%, respectively) relative to the metal content found in the feedstock (Table 1, first column), while detected metal content was 8-fold higher in the solids fraction (Table 1, third column) versus the metal content detected in the feedstock (Table 1, first column).
One example of a compound that can be used as an additive in the inventive processes and systems described herein is magnesium chloride. We performed pyrolysis of red oak impregnated at 1:10 ratio of magnesium chloride to biomass and dried at 70° C. Pyrolysis was performed at 475° C. in a non-reactive helium atmosphere. Production of furfural (and other C5+ oxygenates) and anhydrosugar were enhanced as compared to conventional pyrolysis. Lower yields of phenolics and oxygenated aromatics were also observed. Catalytic pyrolysis of the same feedstock with ZSM-5 catalyst in a 5:1 ratio resulted in a decreased yield of oxygenates and higher yield of hydrocarbons compared to non-impregnated biomass (see Table 4; numbers represent percent of total carbon yield as determined by Gas Chromatography/Mass Spectrometry). The yield of char decreased marginally for pyrolysis of impregnated biomass, improving overall liquid yield.
As used herein, the term “entrainment” is defined as transport of a solid particle by a gas stream. Entrainment of a given solid particle typically occurs when the local velocity of a gas stream exceeds the terminal falling velocity of the particle.
As used herein, the term “standard gas hourly space velocity” or “SGHSV” refers to the gas hourly space velocity of a gas stream measured at standard conditions.
Feedstock particles are by their nature irregularly shaped. Thus, as used herein, the “diameter” of a particle refers to its diameter at the widest cross-section of the particle.
In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present disclosure, in particular, any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as an additional embodiment of the present invention.
Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.
All of the references cited herein are expressly incorporated by reference. The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication data after the priority date of this application. Incorporated references are listed again here for convenience:
This application is a non-provisional application which claims benefit under 35 USC §119(e) and priority to U.S. Provisional Application Ser. No. 61/699,036 filed Sep. 10, 2012, entitled “Processes For Decreasing Char Entrainment During Pyrolysis”, which is hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61699036 | Sep 2012 | US |
