Patent Application
20080029233
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings wherein like reference numerals are used throughout the several drawings to refer to similar components. In some instances, a sublabel is associated with a reference numeral and follows a hyphen to denote one of multiple similar components. When reference is made to a reference numeral without specification to an existing sublabel, it is intended to refer to all such multiple similar components.
Systems and methods for processing lignocellulosic feedstocks are described. The feedstocks may be processed to separate cellulose fibers from other constituents of a lignocellulosic biomass, such as found in trees, grasses, shrubs, agricultural waste, and waste paper. The separated cellulose fibers may be used as a component in the manufacture of paper, plastics, ethanol, and a variety of other materials and chemicals.
Counter-flow operation provides for the efficient use of processing reagents. Processed solids encounter fresh reagents just before discharge, while the fresh and reactive feedstock first meets with nearly exhausted liquid reagent about to be discharged. Advantageously, countercurrent flow can establish a non-equilibrium steady state in which the reacting liquids and solids experience different histories. In combination with temperature gradients, this permits manipulation of reaction rates for competing chemical interactions to improve yields by minimizing degradation reactions. Elevated temperatures reduce processing times for fractionation. As a rough rule, every ten degrees Celsius rise in temperature reduces processing time by a factor of two and can thus increase materials throughput by this same factor for similarly sized apparatus. In many cases, however, with increased temperature comes increased pressure to prevent liquid boiling. Further, increased temperature can result in undesirable degradation of biomass. Both of these considerations may have an effect in the temperature range from 210 to 230° C., depending on details of the fractionation chemistry.
In a countercurrent system, it is possible to incorporate a rinsing feature that provides in-situ recovery and full use of reagents that might otherwise be discharged with the processed solids. This additional processing can occur at the elevated temperature and pressure where reaction rates are high and mobilized components remain in solution. A rinse liquid can even be used to cool the solid product with in-situ recuperation of the heat energy in the solid product. Reagents and energy needed for biomass fractionation can be costly and efficient utilization may be required if the fractionation process is to be economically viable. Advantageously, embodiments of the present invention provide efficient utilization as a process feature. In-situ separation of liquid and solid flows in a countercurrent system provide opportunities for significant savings in downstream processing. Processed solids can thus be discharged in a clean, cooled condition as a fully prepared intermediate product. Depending on the particulars of the biomass and the intermediate products desired from the fractionation, one or more processing steps may be involved. For example, a simple extraction of oils or other extractables might involve only a single stage, while a more complete fractionation might involve multiple stages for sequential recovery of extractives, hemicellulose, lignin, and cellulose with intermediate rinsing. Embodiments of the present invention provide the ability to carry out such multiple processing steps while maintaining operating temperatures and flows.
Embodiments provided herein include various implementing devices, however, knowledgeable readers will readily see the applicability of the techniques described herein in a broad range of related situations depending on such factors as the particular biomass feedstock, the marketable fractionation products to be recovered, the scale of the operation, and the availability of certain manufactured components. Embodiments of the present invention involve the fractionation of biomass, and in some cases it is assumed that certain feedstock preparation steps such as cleaning, sizing, and wetting have already been accomplished, as needed. Fractionation chemistry can be carried out in a sequence of steps in a reactor configured to provide a plurality of countercurrent zones. Although applicable for a single or multi-stage fractionation process, the following steps would characterize one embodiment of a two-stage, countercurrent fractionation process: (1) Feed prepared (cleaned and/or size-reduced) biomass into the pressurized reactor. (2) Discharge a first liquid with dissolved extractives, hemicellulose, etc. (3) Provide a zone for chemical reaction at elevated temperature. (4) Inject a first reagent, liquid or solvent to mix with rinse liquid. (5) Provide a zone for countercurrent rinsing of the solids. (6) Input a rinse liquid (e.g. water). (7) Provide an interstage separation zone with negligible liquid flow. (8) Discharge a second liquid with dissolved hemicellulose, lignin, etc. (9) Provide a zone for chemical reaction at elevated temperature. (10) Inject a second reagent, liquid or solvent to mix with rinse liquid. (11) Provide a zone for countercurrent rinsing of the solids. (12) Input a rinse liquid (e.g. water). (13) Discharge the solid product. In some embodiments, hemicellulose and extractives can be removed in the first stage, and thus an ethanol extraction in the second stage can be more efficient.
Further details of the fractionation chemistry are provided herein. For aqueous based biomass processing, the first reagent will often be either water itself or a dilute mineral acid. The second reagent will often be a solution of water and an alkali such as sodium or ammonium hydroxide. Some of the water may be replaced by ethanol. Many process variations are contemplated by embodiments of the present invention. For example, fractionation can begin with an additional stage optimized for the recovery of extractives before proceeding to hemi-cellulose extraction. Another example might involve an alternative to discharging the solid product in which an additional stage is optimized for rapid acid hydrolysis of the cellulose and discharge of the resulting sugars for further processing. Embodiments described herein can provide precise control of the movement of liquids and solids in the reactor, and maintenance of desired pressures and temperatures throughout, to enhance the performance of the implementing apparatus.
The present systems integrate a plurality of processing steps, which may include chemical reactions, mixing steps at elevated temperatures and/or pressures, liquid/solid separation steps at elevated temperatures and/or pressures, and controlled discharge of liquid and solid products, among other steps. A description of other apparatuses and methods for processing lignocellulosic feedstocks are described in co-assigned, U.S. Pat. No. 6,419,788, issued Jul. 16, 2002; U.S. Pat. No. 6,620,292, issued Sep. 16, 2003, and U.S. patent application Ser. No. 11/158,831, filed Jun. 21, 2005, the entire contents of which are all herein incorporated by reference for all purposes.
An exemplary implementing apparatus includes a twin-screw conveyor with housing designed for operating pressures of 400 psi or more and with metallurgy compatible with the reagents expected to be used. This conveyor is the reaction vessel and is sized for the desired throughput and reaction time. A crammer-feeder with a safety shutoff can be used to take biomass from a feed hopper and inject it continuously into the reaction vessel. The screw conveyor creates a moving bed of solids while liquid is forced countercurrently. Pressure pumps with flow sensors and pressure gauges are required for each of the liquid inputs. Positive displacement pumps (e.g. Moyno type pumps) run in reverse are used for each of the liquid discharges and for the solid product discharge. In some applications, a double valve system can be used instead of a pump to discharge product while maintaining pressure. Liquid/solid separators are used on each of the liquid discharge ports to extract liquid while keeping solids in the reactor. A heating system with temperature sensors is used to achieve necessary reaction temperatures (up to 230° C.). Heat exchangers are used between liquid feed and discharge lines for energy conservation and to prevent flashing of liquid discharges. A control system is used to use temperature, flow, and pressure information to maintain desired operating conditions throughout the reactor.
In some embodiments, the present invention provides continuous, countercurrent processes of one or more stages for the fractionation of lignocellulosic biomass feedstock. Processes may include, for example, feeding biomass into the first stage of a pressurized reaction vessel, injecting a first wash liquid into said first stage countercurrently to said biomass, discharging said first wash liquid from said first stage, optionally conveying said biomass into a second stage of said reaction vessel, injecting a second wash liquid into said second stage countercurrently to said biomass, discharging said second wash liquid from said second stage, optionally conveying said biomass into additional stages of said reaction vessel with provision for injecting and discharge wash liquids, and finally discharging a solid biomass product in slurry form. In some cases, one or more wash liquids are injected into the reaction vessel as two streams; a water rinse and a concentrated chemical reagent that mix to form the working wash liquid. The wash liquid for the first stage may be selected for optimal recovery of oils, proteins, and other extractives. Embodiments encompass multi-stage processing in which the wash liquid in one stage is water or a solution of water and a mineral acid to emphasize hydrolysis of hemicellulose, and the wash liquid in the following stage is a solution of water and a strong base such as sodium or ammonium hydroxide and may include 40 to 60% ethanol by weight to emphasize hydrolysis of lignin. The temperature in one or more stages may be maintained in the range 190° C. to 240° C.
In related embodiments, continuous, countercurrent systems of one or more stages for the fractionation of lignocellulosic biomass may include means for feeding said biomass into an elongated, pressurized reaction vessel, means for conveying said biomass through the length of said reaction vessel, means for discharging processed biomass from said reaction vessel, means for injecting a countercurrent flow of pressurized wash liquid into each stage of said reaction vessel, means for discharging wash liquid from each stage of said reaction vessel, means for separating liquids from solids prior to discharging wash liquids, means for maintaining desired temperatures in each stage of said reaction vessel, means for transferring heat from liquid being discharged to liquid being injected, means for controlling pressures throughout said reaction vessel such that boiling nowhere occurs, separate countercurrent flows are established in each stage where desired, and mixing of liquids between stages is minimized. A pressurized reaction vessel may include an elongated barrel accommodating twin screws for conveying the biomass, the screws being driven by a gearbox and motor. The length of the barrel and screws, the rotation rate of the screws, and the diameter of the screws may be determined by the number of stages, the time necessary for processing, and the biomass throughput desired. Systems may be configured to discharge liquid and solid slurry products by means of progressive cavity pumps operated in reverse to reduce pressure while avoiding clogging from liquid-solid separation. Liquids may be separated from solids prior to liquid discharge by means of small, twin-screw extruders operated so as to force solids back into the reaction vessel.
For various reasons (e.g. feedstock characteristics or economics) moving bed fractionation systems may not always provide an optimal or preferred solution. In such cases, a simulated moving bed (SMB) system may be used to implement the fractionation chemistry. An SMB system can be thought of as an actual moving bed system, such as previously described herein, that is physically divided into a series of segments (from one or two to up to more than a dozen for each stage of the process) within which the solids remain fixed. Liquid feed and discharge flows and liquid flows between segments are then switched by valves from one segment to the next such that both the solids and liquids experience a time history similar to what would be experienced in an actual moving bed system. The larger the number of segments in each process stage, the more closely an SMB operation can match an actual moving bed system, but at an increasing capital investment cost. Reactor segments are loaded and unloaded sequentially to accompany the switching of liquid flows. One advantage of the SMB system is that reactor segments can be loaded and unloaded at atmospheric pressure and temperature thereby avoiding the shear forces and physical degradation encountered when solids must be injected, transported, and discharged under pressure in screw based, continuous flow apparatus. SMB fractionation systems are also advantageous because they have great versatility and flexibility in adapting to different feedstocks through computer-based reconfiguration. They also can make use of previously developed product discharge technology, and allow countercurrent operation in multiple stages with all the benefits such operation provides in terms of process control and product purity. What is more, SMB systems allow operation at lower temperatures and longer residence times such as may be needed to get sufficient chemical diffusion when processing large feedstock chips such as are customary in wood pulping. SMB system designs can be easily modified by addition of more reactor sections to provide for additional processing stages (e.g. more than two) as desired.
Turning now to the drawings,
Embodiments of the present invention provide for the maintenance of independent countercurrent flows of liquid in each of the stages or processing zones. This can involve variable speed pumps with speed controllers that respond to signals from pressure or flow sensors. A multi-stage countercurrent system can have pressure differentials in each stage to drive the liquid flows, in addition to zones of constant pressure between stages to separate flows.
Liquid feed rate can be controlled by pumps as described above. In some cases, the first stage is a simple, countercurrent water wash 16 with auto-catalyzed hemicellulose hydrolysis. The second stage ends with a countercurrent water rinse 13 before discharge of solids 10. The countercurrently flowing rinse water is then augmented with countercurrently flowing ethanol and alkali 14 to mobilize lignin. The flow of liquid input 13, 14, and 16 is controlled by variable speed pressure pumps that are, in turn, controlled by flow sensors on these input lines with manual set points determined by the details of the chemistry desired. Solids discharge 10 from the second stage 9 may be controlled by a variable speed, positive displacement pump of the Moyno type whose speed is set manually to accommodate the solids feed (after processing) plus sufficient water to provide a manageable slurry. Liquid discharge from the second stage 15 is controlled by a second Moyno type pump with variable speed drive controlled by a pressure sensor 11 having an electrical output proportional to pressure. The pressure signal is compared to a manually set reference voltage. If the pressure is too high, the continuous Moyno speed is increased; if the pressure is too low, the Moyno speed is decreased. A small “dead zone” minimizes hunting. The reference pressure (voltage) is set manually to prevent boiling of the ethanol-water mixture at the highest temperature in the second stage. Liquid discharge 17 from the first stage is controlled by a third Moyno type pump with variable speed drive controlled by a differential pressure sensor 12 having a bi-polar electrical output proportional to the deviation from zero of the pressure differential across the compression zone 8 This signal is then used to speed up or slow down the Moyno type pump. In some embodiments, the goal is to have no pressure differential across the compression zone, to prevent or inhibit liquid flow and mixing of liquids between the two stages. For applications involving additional chemical processing stages, the first stage configuration (including compression zone, pumps, and controls) can be replicated for each additional stage.
The twin-screw embodiment creates a moving bed of solids that is then subjected to countercurrent flows of liquid. The continuous solids feeder, the action of the screws, and the continuous pump discharge all act mechanically to degrade the physical structure of the feedstock. In some applications, this can be an advantage by promoting mixing and degradation action and increasing the rate of chemical reaction. In other applications, however, the breakdown of the fibrous biomass structure may be undesirable. In such cases, the advantages of multi-stage, countercurrent flow can be achieved by use of apparatus in which the moving bed of solids is simulated rather than actual. A simulated moving bed (SMB) system for biomass fractionation is similar to conventional SMB systems for separation of components of a liquid in the sense that there are multiple reactor sections (e.g. columns or barrels) and a complex array of valves to direct liquid flows. It differs however in that full fractionation occurs in a single pass and the “stationary phase” (biomass) is replaced at an appropriate place in the processing cycle rather than being regenerated.
In the embodiment illustrated in
In some embodiments, the present invention provides a simulated moving bed system of one or more stages for the countercurrent fractionation of lignocellulosic biomass. The system may include a plurality of elongated pressurized reactors interconnected with plumbing for controlling and directing fluid flows, means for sequential loading of the reactors with biomass feedstock and for sequential unloading of processed biomass, means for injecting countercurrently pressurized wash liquid into each stage of the simulated moving bed system, means for discharging wash liquid from each stage of the simulated moving bed system, means for separating liquids from solids prior to discharging wash liquids and transferring wash liquids between reactors, means for maintaining desired temperatures in each reactor of said simulated moving bed system, means for transferring heat from liquid being discharged to liquid being injected, means for controlling pressures to prevent boiling and to maintain desired liquid flows throughout the SMB system, and means for sequential switching of valves to create the desired countercurrent, moving bed simulation. Biomass feedstock can be loaded into reactors by means of one or more augers and processed biomass can be unloaded by slurrying and washing with water. In some instances, biomass feedstock may be loaded into and unloaded from reactors while contained in full-length baskets. Liquid products can be discharged by means of progressive cavity pumps operated in reverse to reduce pressure while avoiding clogging from liquid-solid separation. Liquids can be separated from solids prior to liquid discharge by means of small, twin-screw extruders operated so as to force solids back into the reactors. In some cases, an electronic computer can be used to configure an SMB for a particular application and to automate the sequential switching of valves.
In the
Table 5 describes the action occurring in each reaction section and the settings of the valves in each reaction section at each step. The valves can be described as open (O) or closed (C). The valve settings for each step can be maintained for any desired period of time. For example, Step 1 may involve maintaining valve settings for a period of three minutes. Similar time periods may be maintained for Step 2, Step 3, and so on. This progression may be continued continuously, or for any desired length of time or number of steps. With reference to
Step 1: Reaction Section 401—Load Feedstock: When loading feedstock from the common feedstock hopper into reactor 220, an adjustable closure such as a ball valve 225 (valve 11′), which typically has an inner diameter that matches an inner diameter of the reactor, is opened to create a passage between the feedstock hopper and reactor 220. All other valves are closed, so that no other materials are introduced into reactor 220. Screw drive 216 is turned on to enable screw penetration, and screw positioning system 218 pushes at least a portion of a screw or threaded shaft (not shown) into the feedstock hopper. The screw continues to turn and draws feedstock from the hopper into reactor 220. After an appropriate time, the screw rotation is stopped and screw positioning system 218 withdraws the screw from the hopper back into reactor 220. Ball valve 225 is then closed.
In an alternative vertical configuration, feedstock can be loaded into baskets (e.g. in a loading operation external to the simulated moving bed) to be inserted into the reactors by opening and then closing covers on the reactors. At the end of processing, the cover can be opened, the basked of finished product removed, and a new basket of feedstock inserted, in an endless cycle. In some embodiments, ball valves, screws, motors, or positioning units may not be included or involved.
Step 1: Reaction Section 402—Soak Feedstock: Warm water valve 208 (valve 2′) and air vent 236 (valve 13′) are opened and reactor 220 of reaction section is filled with warm or heated water which mixes with the feedstock. In some embodiments, air vent 236 may include a liquid sensor that can trigger closure of valve 208 and vent 236. Optionally, warm water can be obtained via a heat exchange process involving liquid discharge originating from reaction section 403.
Step 1: Reaction Section 403—Stage 1 Liquid Discharge: Stage 1 liquid discharge valve 230 (valve 8′) is opened to allow stage 1 liquid discharge (e.g. with mobilized biomass constituents including extractives and hemicellulose) to exit reactor 220. Heat exchange inlet valve 204 (valve 4′) is opened so as to heat material that is being transferred from reaction section 404 as it passes through thermal unit 202. In some embodiments, heat exchange inlet valve 204 may be coupled with a steam source. Optionally, operation of heat exchange inlet valve 204 may be modulated with a thermocouple control. In one example, the temperature of contents passing through thermal unit 202 are heated to a temperature of about 2300C. It may be desirable to avoid high pressure regulatory requirements. For example, in some embodiments pressure is maintained below 600 psi. Relatedly, the temperature of reactors containing ethanol may be limited to 220° C. or lower. Other reactors may operate at 230° C. or more to meet chemical processing requirements, limited primarily by destructive degradation of the material being processed. Prior to solid product discharge, a reactor is often cooled below 100° C. to avoid flashing. This cooling can be accomplished with full recovery of heat values by countercurrent rinsing with cold water in the step just prior to discharge. The screw motor can be started in an oscillating mode, to provide a turning of the screw. In some embodiments, this may involve, for example, a turn or two of the screw in one direction and a turn or two in the other direction, for perhaps a duration of two seconds in each direction. This action can generate some stirring and can prevent channeling or uneven fluid flow at certain points within reactor 220. A steam jacket or other thermal device may be coupled with reactor 220 or any other appropriate element of the fractionation system to achieve a desired temperature control.
Step 1: Reaction Section 404—Countercurrent Fractionation: Heat exchange inlet valve 204 (valve 4′) is opened so as to heat material that is being transferred from reaction section 405. Passage valve 244 (valve 7′) is opened to provide countercurrent fractionate from reactor 220 to the adjacent reaction section 403. In some embodiments, this countercurrent fractionate comprises hemicellulose. The term countercurrent or counter-flow can be used to describe the flow of fractionate from a reactor containing more processed solids into a reactor containing less processed solids. Specifically, feedstock is passed from the common feedstock hopper into reactor 220 in a radially outward direction, via feedstock inlet port 226, passing from proximal end 220b toward distal end 220a of reactor 220. In contrast, fractionate from section 404 passes into reactor 220 in a radially inward direction, via fluid inlet port 212, passing from distal end 220a toward proximal end 220b of reactor 220.
Step 1: Reaction Sections 405 and 406—Countercurrent Fractionation: All valves retain their settings. Heat exchange inlet valve 204 (valve 4′) of reaction section 405 is opened so as to heat material that is being transferred from reaction section 406. Passage valve 244 (valve 7′) of reaction section 405 is opened to provide countercurrent fractionate from reaction section 405 to reaction section 404. In some embodiments, the fractionate may contain hemicellulose. Heat exchange inlet valve 204 (valve 4′) of reaction section 406 is opened so as to heat material that is being transferred from reaction section 407. Passage valve 244 (valve 7′) of reaction section 406 is opened to provide countercurrent fractionate from reaction section 406 to reaction section 405. In some embodiments, the fractionate may contain hemicellulose. More reaction sections can be added here with the same valve settings if desired for additional processing.
Step 1: Reaction Section 407—Reagent Feed: Acid reagent valve 240 (valve 5′) may be opened to provide acid or another reagent to enhance hydrolysis in countercurrent fractionation reaction sections 406, 405, and 404. Heat exchange inlet valve 204 (valve 4′) is opened so as to heat material that is being transferred from reaction section 408. Passage valve 244 (valve 7′) is opened to provide transfer of material to adjacent reaction section 406. The contents of this material, in some cases, is similar to that as described above except that it contains less hemicellulose and more acid. In some embodiments, the acid reagent has a pH within the range from about 2 to about 4. In some embodiments, the acid reagent has a temperature within the range from about 210° C. to about 230° C.
Step 1: Reaction Section 408—Countercurrent Rinse: Acid reagent valve 240 (valve 5′) is closed. Heat exchange inlet valve 204 (valve 4′) is opened so as to heat material that is being transferred from reaction section 409. Passage valve 244 (valve 7′) is opened to provide transfer of material to adjacent reaction section 407. In some cases, this involves a water rinse that contains residues from what was section 408 in the previous step. All other valves retain their settings for a countercurrent rinse.
Step 1: Reaction Section 409—Countercurrent Rinse: Passage valve 244 (valve 7′) is opened to provide transfer of material to adjacent reaction section 408. In some cases, this involves a water rinse that contains residues from what was section 409 in the previous step. All valves retain their settings as the countercurrent rinse continues. Heat exchange inlet valve 204 (valve 4′) may be opened, and water coming from valve 3 of section 410 can be heated. Although valve 3′ is for “hot” water, in some cases this water may not be hot enough for the desired process.
Step 1: Reaction Section 410—Stage 2 Liquid Discharge: Heat exchange inlet valve 204 (valve 4′) is opened so as to heat material that is being transferred from reaction section 411. Passage valve 244 (valve 7′) is closed, thus preventing passage of material to reaction section 409. Hot water valve 242 (valve 3′) is opened to provide Stage 1 rinse flow (replacing valve 7′ flow). With valve 7′ closed, water can pass to the previous section 409. Stage 2 liquid discharge valve 232 (valve 9′) is opened to allow stage 2 liquid discharge, which may contain for example primarily lignin in addition to stage 2 wash chemicals, to exit reactor 220.
Step 1: Reaction Section 411—Countercurrent Fractionation: Heat exchange inlet valve 204 (valve 4′) is opened so as to heat material that is being transferred from reaction section 412. Hot water valve 242 (valve 3′) and Stage 2 liquid discharge valve 232 (valve 9′) are closed. Passage valve 244 (valve 7′) is opened to provide transfer of countercurrent fractionate to adjacent reaction section 410. This fractionate may contain, for example, primarily lignin along with stage 2 wash chemicals. Progressing from section 410 through section 413, the lignin concentration may become lower and the chemical concentration may become higher.
Step 1: Reaction Sections 412 and 413—Countercurrent Fractionation: All valves retain their settings as fractionation continues. Heat exchange inlet valve 204 (valve 4′) of reaction section 412 is opened so as to heat material that is being transferred from reaction section 413. Passage valve 244 (valve 7′) of reaction section 412 is opened to provide countercurrent fractionate from reaction section 412 to reaction section 411. Heat exchange inlet valve 204 (valve 4′) of reaction section 413 is opened so as to heat material that is being transferred from reaction section 414. Passage valve 244 (valve 7′) of reaction section 413 is opened to provide countercurrent fractionate from reaction section 413 to reaction section 412. More reaction sections can be added here with the same valve settings if desired for additional processing.
Step 1: Reaction Section 414—Stage 2 Reagent Feed: Heat exchange inlet valve 204 (valve 4′) is opened so as to heat material that is being transferred from reaction section 415. Passage valve 244 (valve 7′) is opened to provide transfer of material to adjacent reaction section 413. Base reagent valve 238 (valve 6′) is opened to provide alkali or another reagent for Stage 2 processing in the countercurrent fractionation reaction sections 413, 412, and 411. In some embodiments, the alkali or base reagent has a pH within the range from about 8 to about 13. In some embodiments, the base reagent has a temperature within the range from about 180° C. to about 240° C. In some cases, the maximum may be about 220° C. when 50% ethanol is used.
Step 1: Reaction Section 415—Countercurrent Rinse: Heat exchange inlet valve 204 (valve 4′) is opened so as to heat material that is being transferred from reaction section 416. Passage valve 244 (valve 7′) is opened to provide transfer of material to adjacent reaction section 414. This may involve a water rinse that contains residues from section 414 in the previous step. Base reagent valve 238 (valve 6′) is closed. All other valves retain their settings for a countercurrent rinse.
Step 1: Reaction Section 416—Countercurrent Rinse: Heat exchange inlet valve 204 (valve 4′) is opened so as to heat material that is being transferred from reaction section 417. Passage valve 244 (valve 7′) is opened to provide transfer of material to adjacent reaction section 415. This may involve the continued washing out of residual chemicals. All other valves retain their settings as the countercurrent rinse continues.
Step 1: Reaction Section 417—Stage 2 Cold Water Rinse In: Passage valve 244 (valve 7′) is opened to provide transfer of material to adjacent reaction section 416. Heat exchange inlet valve 204 (valve 4′) is closed so as to reduce the temperature in reactor 220. Cold water valve 210 (valve 1′) is opened allowing cool water to enter and cool reactor 220, in preparation for the cellulose discharge. At the same time, this water is heated for energy recuperation and further use in the Stage 2 counter-flow rinse. In some cases, as the cold water flows into the section, the hot water in the section is forced out the other end as rinse for section 416. At the same time, the cold water is cooling the solids and being warmed. This process may continue, for example, until the temperature at the top or inner section of section 417 falls below 100° C.
Step 1: Reaction Section 418—Cellulose Discharge: Passage valve 244 (valve 7′) to reaction section 417 is closed to retain pressure downstream. Discharge port 222 (valve 10′) is opened to discharge cellulose product from reactor 220. Cold water valve 234 (valve 12′) is opened to flush the cellulose with cold water. The screw drive is activated to move cellulose toward discharge port 222. In some embodiments, cold water valve 210 (valve 1′) is opened for additional washing action. At the end of the cellulose discharge period, reactor 220 can be emptied and made available for filling with feedstock in Step 2.
In some embodiments, a vacuum stuffer operates at all times except when a section is being emptied and filled. The vacuum stuffer can retain solids within a section while allowing liquid to discharge. In a vertical configuration using a basket system for filling, a vacuum stuffer may be replaced by a large, washable filter.
In one embodiment, a simulated moving bed fractionation system includes reactors having an inside diameter of 4 inches and a length of 80 inches (L/D=20). The empty volume of an individual reactor of the system is about 1000 cubic inches, less the screw volume or about 0.5 cubic feet or about 14 liters. The bulk density of corn stover, a source of cellulose, is about 76 grams per liter. Thus, a single reaction section will contain about one kilogram of corn stover feedstock. If the SMB is on a two minute cycle, this would result in a processing throughput of about 720 kilograms of corn stover per day, or about 0.8 English tons per day. With the reactor utilization shown in Table 5, a two minute cycle time would give about 8 minutes of maximum severity processing (for example sections 404-407 and 411-414) in each of the two stages. In contrast, a 100 ton/day commercial system with an L/D of 20 and the same two minute cycle time would require reactor sections of about 20 inches in diameter and 400 inches (33.3 feet) long. This illustrates the feasibility of a simulated moving bed system for scale-up to a small commercial configuration having similar proportions and reaction times. Although an L/D of 20 may be arbitrary, a slender reaction vessel may have advantages in handling expected pressures and minimizing undesirable mixing and channeling of the countercurrent liquid flow.
Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.
As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the electrode” includes reference to one or more electrodes and equivalents thereof known to those skilled in the art, and so forth.
Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups.
