FIELD OF THE INVENTION

[0001] The present invention provides an improved device for heating a feedstock. [0002] BACKGROUND OF THE INVENTION

[0003] There is increasing interest in producing fuel ethanol or other fermentation products from lignocellulosic feedstocks such as, for example, wheat straw, corn stover, and switch grass.

[0004] One process for producing a fermentation product, such as ethanol, from lignocellulosic feedstocks is to carry out a pretreatment, followed by enzymatic hydrolysis of the cellulose to glucose. The pretreatment generally disrupts the fiber structure of the lignocellulosic feedstock and increases the surface area of the feedstock to make it accessible to cellulase enzymes. The pretreatment can be performed so that a high degree of hydrolysis of the xylan and only a small amount of conversion of cellulose to glucose occurs. The cellulose is hydrolyzed to glucose in a subsequent step that uses cellulase enzymes. Other pretreatment processes, such as certain alkali pretreatments, do not hydrolyze or result in limited xylan hydrolysis. Moreover, it is possible to hydrolyze both xylan and cellulose using more severe chemical treatment, such as concentrated acid hydrolysis.

[0005] Regardless of the method for producing fermentable sugar, the addition of water to the incoming feedstock to form a slurry is often carried out to facilitate the transportation and mechanical handling of the cellulosic feedstock. The slurry consists of lignocellulosic feedstock pieces or particles in water. In many lignocellulosic conversion processes described in the prior art to produce fermentable sugar, the solids content, measured as undissolved solids (referred to herein as "UDS"), is between 5 and 12 wt%.

[0006] However, for lignocellulosic conversion processes to be more economical, it would be desirable for them to operate with lower water content. The processing of feedstock containing high solids content has numerous advantages in various stages of the process, one of which is reductions in equipment size, which, in turn, reduces capital cost. Further benefits of low water content include reduced energy consumption including reductions in costs for pumping, heating, cooling and evaporating. Moreover, water usage adds significant expense to the process, especially in arid climates.

[0007] A stage of the process that particularly benefits from utilizing low levels of water is pretreatment or other stages that require heat to treat the feedstock. During these treatments, the amount of energy required for heating up the feedstock slurry, upstream of the reactor, or within the reactor itself, is a direct function of the total mass of the feedstock slurry, including the water added for transportation of the feedstock. Operating a pretreatment or hydrolysis process with low levels of water can reduce the energy required for heating. Various methods are known for heating feedstock including indirect heating methods, such as heating jackets, the addition of heated water to a chamber such as disclosed in Canadian Patent Application No. 2,638,152, or the addition of steam to a reactor itself (U.S. Patent No. 5,338,366).

[0008] One method for reducing water content, and the consequent energy requirements for heating, is to dewater the incoming feedstock slurry and form a compacted plug of feedstock prior to carrying out pretreatment or hydrolysis in a downstream reactor (see co-owned and co-pending WO 2010/022511 , which is incorporated herein by reference). Plugs of feedstock can be produced by various devices, such as plug screw feeders and pressurized screw presses. Often the water content of the feedstock is reduced so that the solids content is high enough for plug formation to occur. Dewatering can take place within a plug formation device or dewatering and plug formation can be carried out in separate pieces of equipment. Alternatively, it is possible to eliminate dewatering upstream of plug formation if the feedstock solids content is already at a desired high consistency.

[0009] The plug that is formed can prove to be difficult to heat prior to its entry into the downstream reactor. Often the plug discharges into large segments, which can be 3-5 inches in diameter or even larger. Such large segments prevent rapid penetration of steam into the fibrous material and result in uneven temperature distributions. The inventors have recognized that uneven temperature distributions in the plug, or segments thereof, can result in overcooking or undercooking of the feedstock in the downstream reactor. Overcooking in the reactor can result in degradation of the feedstock, while undercooking can result in low xylose yield and difficult cellulose hydrolysis.

[0010] Thus, there is a need in the art for an improved device for heating a feedstock. [0011] SUMMARY OF THE INVENTION

[0012] It is an object of the invention to provide an improved device for heating a feedstock.

[0013] The present invention provides a device for heating a feedstock comprising an elongate chamber having at least a portion thereof that is cylindrical. The chamber comprises (a) an inlet for receiving the feedstock and an outlet for withdrawing heated feedstock; (b) a rotatable shaft mounted co-axially in the chamber; which shaft comprises (i) an inlet section comprising an auger for conveying and breaking up the feedstock in the inlet region of the chamber, wherein the auger comprises notches or grooves formed around its circumference for breaking up the feedstock; and (ii) a plurality of disintegrating elements mounted on at least a mid section of the shaft for disintegrating the feedstock, which disintegrating elements project outwardly from the shaft and are pitched at an angle that is off-set from a line drawn transverse to the shaft; and (c) means for heating the disintegrated feedstock particles as they are conveyed through the chamber.

[0014] According to one embodiment of the invention, the notches or grooves are v-shaped or substantially v-shaped.

[0015] According to a further embodiment, the disintegrating elements are pitched at an angle that is off-set from between about 5 to about 30° from a line drawn transverse to the shaft.

[0016] In yet a further embodiment of the invention, the means for heating the disintegrated feedstock particles comprises one or more inlets for introducing steam.

[0017] According to another embodiment of the invention, the disintegrating elements are arranged on the shaft so as to sweep the inner surface of at least a region of the chamber. [0018] According to a further embodiment of the invention, the disintegrating elements are configured such that the outer edges thereof describe one or more circles that are concentric or essentially concentric in relation to the inner surface of the chamber.

[0019] In a further embodiment of the invention, the disintegrating elements are blades, bars, paddles, pegs or arms.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the accompanying drawings,

[0021] FIG. 1 is a flow diagram of a method according to an embodiment of the invention; and

[0022] FIG. 2 is a cross-section of a sawtooth auger utilized in a heating chamber according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The following description is of a preferred embodiment by way of example only and without limitation to the combination of features necessary for carrying the invention into effect. The headings provided are not meant to be limiting of the various embodiments of the invention. Terms such as "comprises", "comprising", "comprise", "includes", "including" and "include" are not meant to be limiting. In addition, the use of the singular includes the plural, and "or" means "and/or" unless otherwise stated. Unless otherwise defined herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

Feedstock and feedstock size reduction

[0024] The feedstock for the process is a lignocellulosic material. By the term "lignocellulosic feedstock", it is meant any type of plant biomass such as, but not limited to, plant biomass, cultivated crops such as, but not limited to grasses, for example, but not limited to, C4 grasses, such as switch grass, cord grass, rye grass, miscanthus, reed canary grass, or a combination thereof, sugar processing residues, for example, but not limited to, bagasse, such as sugar cane bagasse, beet pulp, or a combination thereof, agricultural residues, for example, but not limited to, soybean stover, corn stover, rice straw, sugar cane straw, rice hulls, barley straw, corn cobs, wheat straw, canola straw, oat straw, oat hulls, corn fiber, or a combination thereof, forestry biomass for example, but not limited to, recycled wood pulp fiber, sawdust, hardwood, for example aspen wood, softwood, or a combination thereof. Furthermore, the lignocellulosic feedstock may comprise lignocellulosic waste material or forestry waste materials such as, but not limited to, newsprint, cardboard and the like. Lignocellulosic feedstock may comprise one species of fiber or, alternatively, lignocellulosic feedstock may comprise a mixture of fibers that originate from different lignocellulosic feedstocks. In addition, the lignocellulosic feedstock may comprise fresh lignocellulosic feedstock, partially dried lignocellulosic feedstock, fully dried lignocellulosic feedstock, or a combination thereof. Moreover, new lignocellulosic feedstock varieties may be produced from any of those listed above by plant breeding or by genetic engineering.

[0025] Lignocellulosic feedstocks comprise cellulose in an amount greater than about 20%, more preferably greater than about 30%, more preferably greater than about 40% (w/w). For example, the lignocellulosic material may comprise from about 20% to about 50% (w/w) cellulose, or any amount therebetween. Such feedstocks comprise hemicellulose, including xylan, arabinan, mannan and galactan. Furthermore, the lignocellulosic feedstock comprises lignin in an amount greater than about 10%, more typically in an amount greater than about 15% (w/w). The lignocellulosic feedstock may also comprise small amounts of sucrose, fructose and starch.

[0026] The lignocellulosic feedstock is typically subjected to size reduction by methods including, but not limited to, milling, grinding, agitation, shredding, compression/expansion, or other types of mechanical action. Size reduction by mechanical action can be performed by any type of equipment adapted for the purpose, for example, but not limited to size reduction devices selected from the group consisting of hammer mills, tub-grinders, roll presses, refiners and hydra- pulpers. Feedstock may be reduced to particles having a length of about 1/16 to about 8 in., or any amount therebetween. The length of the reduced particles may also be such that at least about 90% by weight of the particles have a length less than about 5 inches or even shorter; for example, at least about 90% by weight of the particles may have a length less than about 4, about 3, about 2, about 1 or about ½ inch. Washing may be carried out to remove sand, grit and other foreign particles as they can cause damage to the downstream equipment. It will be understood that the lignocellulosic feedstock need not be subjected to size reduction, for example if the particle size of the feedstock is already between ½ to 8 inches.

[0027] For the purposes of this specification, the size of the feedstock particles is determined by image analysis using techniques known to those of ordinary skill in the art. An example of a suitable image analysis technique is disclosed in Igathinathane (Sieveless particle size distribution analysis of particulate materials through computer vision, Computers and Electronics in Agriculture, 2009, 66: 147-158, the subject matter of which is hereby incorporated by reference), which reports particle size analyses of several different hammer milled feedstocks. The measurement may be a volume or a weight average length.

Feedstock Consistency

[0028] Prior to feeding the lignocellulosic feedstock to the plug formation device, the amount of undissolved solids in the lignocellulosic feedstock may be adjusted to a desired consistency. The lignocellulosic feedstock can have a solids consistency of between about 1 wt% and about 40 wt% or between 4 wt% and about 20 wt% (undissolved dry solids), upon entering the plug formation device and all ratios therebetween. The percent of undissolved dry lignocellulosic feedstock solids may be determined at the inlet of a plug formation device. The desired consistency is determined by factors such as pumpability, pipe-line requirements and other practical considerations.

[0029] The consistency (also referred to herein as undissolved solids or "UDS") of the lignocellulosic feedstock can be determined by methods known to those of skill in the art. One known method is to filter a sample to remove dissolved solids and then dry the sample at a temperature and for a period of time that is sufficient to remove water from the sample of slurry or wet material, but does not result in thermal degradation of the feedstock solids. After the water removal, or drying, the dry solids are weighed and the weight of water in the sample of slurry or wet material is the difference between the weight of the sample of slurry or wet solids and the weight of the dry solids. The amount of undissolved dry solids in an aqueous slurry may be referred to as the consistency of the slurry. Consistency may be expressed as the weight of dry solids in a weight of slurry, for example, grams per kilogram, or as a percent on a weight basis, for example, % (w/w). [0030] Prior to feeding the lignocellulosic feedstock to a plug formation device, the feedstock may be soaked in an aqueous solution including water, or a solution comprising chemical.

Dewatering

[0031] The feedstock may be dewatered to increase the undissolved solids consistency within a desired range prior to plug formation. However, it should be understood that dewatering may not be required if the consistency of the feedstock is already at a desired level when it is fed to the plug formation device. The dewatering may involve removing water under pressure from the feedstock, or at atmospheric pressure, as discussed below.

[0032] A plug formation device may be configured to dewater the feedstock, although separate respective devices for dewatering and plug formation can be employed. Without being limiting, a plug formation device incorporating a dewatering section suitable for use in the invention may be a pressurized screw press or a plug screw feeder, as described in co-pending and co-owned WO 2010/022511 , which is incorporated herein by reference. Water expressed from the lignocellulosic feedstock by the dewatering step may be reused in the process, such as for slurrying and/or soaking the incoming feedstock.

[0033] There are a variety of known devices that can be utilized to dewater the feedstock prior to plug formation. Examples include drainers, filtration devices, screens, screw presses, extruders or a combination thereof.

[0034] If the feedstock is subjected to dewatering under pressure, the pressure increase may be caused by one or more high pressure pumps. The pump or other feeding device increases the pressure of the feedstock prior to dewatering to e.g., about 45 psia to about 900 psia, or about 70 psia to about 800 psia or about 140 psia to about 800 psia. The pressure may be measured with a pressure sensor located at a feedstock inlet port on a dewatering device or a plug formation device that also dewaters the feedstock. Alternatively, the feedstock subjected to dewatering may be at atmospheric pressure or at a pressure below about 45 psia.

[0035] There may be an optional step of pre-draining the feedstock in order to drain out aqueous solution from the feedstock slurry at atmospheric pressure or higher. This pre-drained feedstock slurry can then be subjected to further dewatering. Plug formation devices

[0036] Plug formation can be considered an integration of lignocellulosic particles into a compacted mass referred to herein as a plug. Plug formation devices form a plug that acts as a seal between areas of different pressure. In embodiments of the invention, the plug seals against higher pressure in a device downstream of the plug. However, it should be understood that the pressure can be higher at the inlet of the plug formation device.

[0037] As mentioned previously, the plug formation device may dewater the feedstock, or this function may be carried out by an upstream dewatering device. Plug formation devices that dewater may comprise a housing or shell with openings through which water can pass. The plug formation device may be operated at atmospheric pressure or under pressure.

[0038] Without being limiting, the plug formation device may be a plug screw feeder, a pressurized screw press, a co-axial piston screw feeder or a modular screw device.

[0039] The plug of lignocellulosic feedstock may have a weight ratio of water to undissolved dry lignocellulosic feedstock solids of about 0.5:1 to about 5:1 , or about 1 :1 to about 4:1 , or about 1.5: 1 to about 4: 1 , or about 1.5:1 to about 3.5: 1 , and all ratios therebetween. The weight ratio of water to dry undissolved lignocellulosic feedstock solids in the plug of lignocellulosic feedstock may be determined by the method described previously. Alternatively, the weight ratio of water to dry undissolved lignocellulosic feedstock solids may be determined by mass balance calculations.

Disintegration and steam contact

[0040] The lignocellulosic feedstock is fed to a downstream elongate chamber, also referred to herein as a "high shear heating chamber" or a "heating chamber", in which the feedstock is disintegrated into particles by disintegrating elements as it is conveyed therethrough. Typically, the heating chamber is horizontally-oriented or essentially horizontally- oriented. The disintegrated particles are heated by direct steam contact, which allows for efficient heat transfer. [0041] At least a portion of the heating chamber is cylindrical. For example, at least a mid-region of the chamber may be cylindrical and the inlet and outlet regions of the chamber may be of a different shape, although chambers that are cylindrical along their entire axial length are preferred. It should be understood that the term "cylindrical" includes frusto -conical or other shapes that are substantially cylindrical.

[0042] The plug, or segments thereof, need not be fed directly into the heating chamber. Any of a variety of known devices may be positioned between the plug formation device and the heating chamber. Without being limiting, examples of such devices include mechanical restricting devices, restraining devices, scrapers and conveyors. It should be understood that the plug may break into segments as it is discharged from the plug formation device, or into other devices positioned downstream of the plug formation device, or as it is fed into the heating chamber.

[0043] The chamber comprises steam addition means for direct steam addition and a rotatable shaft mounted generally co-axially within the chamber comprising the one or more disintegrating elements that project outwardly from the shaft. Advantageously, it has been found that effective disintegration of a plug or plug segments can be achieved using disintegrating elements that impart energy into the plug or plug segments in a shearing action. As discussed below, operating parameters can be selected as required for optimal feedstock disintegration.

[0044] As used herein, the term "disintegrating element" refers to one or more members arranged on the shaft that convey the feedstock plug or segments thereof through the chamber and that impart sufficient shear to the feedstock, thereby producing disintegrated feedstock particles when the shaft rotates at a suitable speed. The disintegrating elements may comprise blades, bars, paddles, pegs, arms, or a combination thereof. It should be understood that the disintegrating elements can vary in length.

[0045] Disintegration involves transforming the plug or segments thereof into disintegrated particles. By disintegrated particles, it is meant that, in the heating chamber, clumps of fiber originating from the plug are broken down into their constituent particles, or that the clumps are substantially reduced in size in the high shear heating chamber. Without being limiting, if wheat straw is utilized, the clumps may be less than about 10 mm, or preferably less than about 5 mm in their least dimension.

[0046] The tip speed of the disintegrating elements is selected to cause feedstock disintegration and is generally higher than that utilized in mixing conveyors known in other industries. The tip speed of the disintegrating elements may be between about 200 m/min and about 1000 m/min, or between about 450 and about 800 m/min or any range therebetween. The shearing action is generally a function of the shape of the disintegrating elements, the number of disintegrating elements (if more than one disintegrating element is used) and tip speed. These parameters can be adjusted as required to achieve a desired rate of shear.

[0047] In some embodiments of the invention, the disintegrating elements are located on the shaft on at least a mid-region thereof. The inlet region of the shaft may comprise means for feeding and conveying the plug, or segments thereof, to the mid-region of the shaft where a more aggressive disintegration of the feedstock may occur. The outlet region of the shaft may comprise means for conveying the plug to the outlet of the chamber.

[0048] In further embodiments of the invention, the disintegrating elements are located on the inlet and/or outlet regions of the shaft. According to these embodiments, the elements on the inlet and/or outlet regions of the shaft not only convey the feedstock, but also disintegrate the feedstock. In some embodiments of the invention, the inlet region of the shaft comprises a ribbon feeder, a cut flight auger or a sawtooth auger. This configuration may improve the throughput capacity and minimize blockage upstream of the heating chamber.

[0049] Some or all of the disintegrating elements may be pitched in the direction of feedstock movement through the heating chamber so as to facilitate conveyance of the feedstock therethrough. That is, a disintegrating element may be mounted on the shaft at an angle off-set from a line drawn transverse to the heating chamber. Such a configuration may reduce the residence time distribution of the feedstock, which in turn minimizes overheating or underheating of the feedstock. For example, disintegrating elements may be mounted on the shaft at an angle that is off-set by between 0 and about 45° from a line drawn transverse to the shaft. For example, the disintegrating elements may be mounted on the shaft at an angle that is off-set by between 1 and about 45° from a line drawn transverse to the shaft, or at an angle that is off-set by between 5 and about 30° from a line drawn transverse to the shaft.

[0050] The steam addition means may comprise one or more inlets for direct steam injection. The introduction of steam along the length of the chamber at spaced-apart injection points allows for more even heating of the feedstock particles. The steam may be introduced through the feedstock inlet, inlets disposed along the length of the chamber, or a combination thereof. Additionally, chemical utilized for pretreatment or hydrolysis may be introduced into the heating chamber.

[0051] The operating pressure and temperature of the heating chamber will typically correspond to the pressure and temperature of the downstream reactor. The operating pressure of the chamber may be at least about 90 psia. Examples of suitable operating pressures include between about 90 and about 680 psia.

[0052] The temperature of the heating chamber will be greater than about 100°C. Examples of temperature ranges include between about 100°C and about 280°C, or between about 160°C and about 260°C.

[0053] In some embodiments of the invention, the disintegrating elements project outwardly from the shaft and are configured so that the outer edges thereof describe one or more circles that are concentric or essentially concentric in relation to the inner surface of the chamber. By the term "essentially concentric", it is meant that the eccentricity of the one or more circles described by the outer edges is less than about 10% of the diameter of the heating chamber.

[0054] According to one embodiment of the invention, the distance between the inner surface of the chamber and the outer edge of the disintegrating element that is closest to the inner surface (also referred to herein as "clearance") is less than about 10% of the inside diameter of the chamber. As mentioned previously, the lengths of the disintegrating elements can vary. Consequently, the clearance is measured at the outer edge of the disintegrating element that is closest to the inner surface of the chamber. In some embodiments of the invention, the clearance is between about 2% and about 8%, or between about 2.5% and about 6% of the inside diameter of the chamber. [0055] The disintegrating elements are arranged on the shaft so as to sweep the inner surface of at least a region of the chamber. By sweeping the inner surface of the chamber in at least a region thereof, the disintegrating elements can reduce or remove scale build-up, including lignin deposits that can reduce the transport and mixing capacity of the heating chamber.

[0056] By the term "sweep", it is meant that the distance between the inner surface of the chamber and the outer edge of the disintegrating element that is closest to the inner surface is less than 5% of the inside diameter of the chamber. By utilizing such a clearance, scale build-up can be removed from the inner surface of the chamber or the build-up can be reduced. Examples of suitable clearance ranges for sweeping include about 1.0% to about 5.0%, about 1.5% to about 4.5%, or about 2.0% to about 4.0%.

[0057] Furthermore, if discrete disintegrating elements are mounted on the shaft, e.g. blades, bars, paddles, pegs, arms, the spacing between adjacent elements, may be chosen so as to eliminate stagnant zones on the inner surface of the chamber between adjacent disintegrating elements where organic deposits accumulate on the inner surface of the chamber. For example, the disintegrating elements may overlap so as to provide continuous axial sweeping along at least a region of the chamber, thereby reducing or eliminating the stagnant zones.

[0058] The present invention also relates to a lignocellulosic feedstock composition comprising: (i) disintegrated lignocellulosic feedstock particles; (ii) about 15 to about 30 wt% undissolved solids, wherein the undissolved solids comprise between about 20 and about 60 wt% cellulose and between about 10 and about 30 wt% xylan; and (iii) a mineral acid, wherein the feedstock does not primarily contain wood chips or pulp, and wherein the pH of the feedstock composition is between about 0.5 and about 3.5.

[0059] According to some embodiments of the invention, the undissolved solids content is 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29 or 30 wt%. The range of undissolved solids in the feedstock composition may include numerical limits of any of these values. According to further embodiments of the invention, the undissolved solids content is between about 18 and about 28 wt%. [0060] According to further embodiments of the invention, the pH of the feedstock composition is 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 or 3.5. The pH range of the feedstock composition may include numerical limits of any of these values. According to further embodiments of the invention, the pH is between about 0.5 and about 3.0. The mineral acid may be sulfuric acid, sulfurous acid, hydrochloric acid, phosphoric acid or any combination thereof. Without being limiting, the acid may be sulfuric acid.

[0061] The undissolved solids may contain 20, 25, 30, 35, 40, 45, 50, 55 or 60 wt% cellulose. The range of cellulose content in the undissolved solids may include numerical limits of any of these values. According to further embodiments of the invention, the cellulose content in the undissolved solids may be between about 30 and about 60 wt%.

[0062] The undissolved solids may contain 10, 15, 20, 25 or 30 wt% xylan. The range of xylan content in the undissolved solids may include numerical limits of any of these values. According to further embodiments of the invention, the xylan content in the undissolved solids may be between about 15 and about 30 wt%.

[0063] The temperature of the composition may be between about 100°C, 120, 140, 160, 180, 190, 200, 220, 240, 260 or 280°C. The temperature range may include numerical limits of any of these values. According to further embodiments of the invention, the temperature range is between 160 and 280°C.

[0064] By the phrase "does not primarily contain", it is meant that the feedstock composition does not contain more than about 50 wt% wood chips or pulp. In some embodiments of the invention, the feedstock composition does not primarily contain forestry biomass.

Pretreatment and hydrolysis

[0065] After raising the temperature of the disintegrated feedstock particles in the heating chamber, they may be pretreated or hydrolyzed.

[0066] The term "pretreatment" or "pretreat" means a process in which the lignocellulosic feedstock is reacted under conditions that disrupt the fiber structure and that increase the susceptibility or accessibility of cellulose within the cellulosic fibers for subsequent enzymatic or chemical conversion steps. A portion of the xylan in the lignocellulosic feedstock may be hydrolyzed to xylose and other hydrolysis products in a pretreatment process, although pretreatment processes that do not hydro lyze xylan are also encompassed by the invention. In embodiments of the invention, the amount of xylan hydrolyzed to xylose is more than about 50, about 60, about 70, about 80 or about 90 wt%.

[0067] By the term "pretreated feedstock", it is meant a feedstock that has been subjected to pretreatment so that the cellulose contained in the cellulosic fibers has an increased susceptibility or accessibility to subsequent enzymatic or chemical conversion steps. The pretreated feedstock contains cellulose that was present in the feedstock prior to pretreatment. In some embodiments, at least a portion of the xylan contained in the lignocellulosic feedstock is hydrolyzed to produce at least xylose in a pretreatment.

[0068] According to embodiments of the invention, pretreatment or hydrolysis may or may not include the use of chemical (e.g., hydrothermal pretreatment) and the pretreatment or hydrolysis may be a multi-stage or a single stage process that produces fermentable sugar or prepares the feedstock for subsequent conversion to fermentable sugar. All or a portion of the polysaccharides contained in the feedstock may be converted to oligomeric or monomeric sugars, or a combination thereof during pretreatment or hydrolysis. In further embodiments of the invention, the pretreatment or hydrolysis includes the use of organic solvents, oxidizing agents, or inorganic acids or bases. Lignin may or may not be removed during the pretreatment or hydrolysis.

[0069] According to one embodiment of the invention, at least a portion of polysaccharides contained in the lignocellulosic feedstock is hydrolyzed to produce one or more monosaccharides.

[0070] Various types of reactors may be used to pretreat or hydrolyze the feedstock including two or more reactors, arranged in series or parallel.

[0071] According to one embodiment of the invention, the reactor is a vertical reactor, which may be either an upflow or a downflow vertical reactor. In another embodiment of the invention, the reactor is a horizontal or inclined reactor. The reactor may be equipped with an internal mechanism, such as a screw, conveyor, scraper or similar mechanism, for conveying the lignocellulosic feedstock therethrough and/or to aid in discharging the reactor.

[0072] The chemical for pretreating or hydrolyzing the feedstock may be added to the feedstock during a soaking process carried out prior to dewatering, prior to plug formation, into the heating chamber, into the plug formation device, into the reactor, or a combination thereof.

[0073] According to embodiments of the invention, the pressure in the reactor is between about 90 psia and about 680 psia and any pressure therebetween. The pressure in the reactor may be measured with one or more pressure sensors. If the one or more reactors are configured so that there are different pressure levels within each, the pressure at the location where the feedstock enters the first reactor is considered herein to be the pressure of the reactor.

[0074] In some embodiments of the invention, the lignocellulosic feedstock is treated in the reactor under acidic conditions. For acidic conditions, a suitable pH is from about 0 to about 3.5 or about 0.2 to about 3 or about 0.5 to about 3 and all pH values therebetween.

[0075] According to further embodiments of the invention, the acids added to set acidic conditions in the reactor are sulfuric acid, sulfurous acid, hydrochloric acid, phosphoric acid or any combination thereof. The addition of sulfurous acid includes the addition of sulfur dioxide, sulfur dioxide plus water or sulfurous acid. Organic acids may also be used, alone or in combination with a mineral acid.

[0076] According to another embodiment of the invention, the alkali added to set the alkaline conditions in the reaction zone is ammonia, ammonium hydroxide, potassium hydroxide, sodium hydroxide or any combination thereof.

[0077] A suitable temperature and time of reaction in the reactor will depend upon a number of variables, including the pH in the reactor and the degree, if any, to which hydrolysis of the polysaccharides is desired.

[0078] Without being limiting, pretreatment of the lignocellulosic feedstock may take place under acidic or alkaline conditions. In an acidic pretreatment process, according to exemplary embodiments of the invention, the time in the pretreatment reactor may be from about 10 seconds to about 20 minutes or about 10 seconds to about 600 seconds or about 10 seconds to about 180 seconds and any time therebetween. The temperature may be about 150°C to about 280°C and any temperature therebetween. The pH for the pretreatment may be between about 0.5 and about 3, or between about 1.0 and about 2.0.

[0079] In an alkaline pretreatment process, the time in the reactor is from about 1 minute to about 120 minutes or about 2 minutes to about 60 minutes and all times therebetween, and at a suitable temperature of about 20°C to about 220°C or about 120°C to about 220°C and all temperatures therebetween.

[0080] Ammonia fiber expansion (AFEX), which is an alkali pretreatment method, may produce little or no monosaccharides. Accordingly, if an AFEX treatment is employed in the reaction zone, the hydrolyzate produced from the reaction zone may not yield any monosaccharides.

[0081] According to the AFEX process, the cellulosic biomass is contacted with ammonia or ammonium hydroxide, which is typically concentrated, in a pressure vessel. The contact is maintained for a sufficient time to enable the ammonia or ammonium hydroxide to swell (i.e., decrystallize) the cellulose fibers. The pressure is then rapidly reduced which allows the ammonia to flash or boil and explode the cellulose fiber structure. The flashed ammonia may then be recovered according to known processes. The AFEX process may be run at about 20°C to about 150°C or at about 20°C to about 100°C and all temperatures therebetween. The duration of this pretreatment may be about 1 minute to about 20 minutes, or any time therebetween.

[0082] Dilute ammonia pretreatment utilizes more dilute solutions of ammonia or ammonium hydroxide than AFEX. Such a pretreatment process may or may not produce any monosaccharides. Dilute ammonia pretreatment may be conducted at a temperature of about 100 to about 150°C or any temperature therebetween. The duration for such a pretreatment may be about 1 minute to about 20 minutes, or any time therebetween.

[0083] When sodium hydroxide or potassium hydroxide are used in the pretreatment, the temperature may be about 100°C to about 140°C, or any temperature therebetween, the duration of the pretreatment may be about 15 minutes to about 120 minutes, or any time therebetween, and the pH may be about pH 11 to about 13, or any pH value therebetween.

[0084] Alternatively, an acidic or alkaline hydrolysis process may be operated under conditions sufficiently harsh to hydrolyze cellulose to glucose and other products.

[0085] Acidic hydrolysis that is harsh enough to hydrolyze xylan and cellulose may be conducted for about 10 seconds to about 20 minutes, or any time therebetween. The temperature may be between about 180°C and about 260°C, or any temperature therebetween. The pH may be between Oand about 1 or any pH therebetween.

[0086] Alkali hydrolysis that is harsh enough to hydrolyze xylan and cellulose may be conducted at about 125°C to about 260°C, or about 135°C to about 260°C, or about 125°C to about 180°C, or any temperature therebetween, for about 30 minutes to about 120 minutes, or any time therebetween and at about pH 13 to about 14, or any pH therebetween.

[0087] The pretreated or hydrolyzed feedstock may be discharged into a discharge device such as a screw discharger, a swept orifice discharger, a rotary discharger, a piston type discharger and the like. Two or more reactors, arranged in series or in parallel, may be used.

[0088] The hydrolyzed or pretreated feedstock exiting the reaction zone may be depressurized and flash cooled, for example to between about 30°C and about 100°C. In one embodiment of the invention, the pressure is reduced to about atmospheric. The cooling and depressurization may be carried out by one or more flash vessels.

Enzymatic hydrolysis and fermentation

[0089] If the hydrolyzed or pretreated feedstock exiting the reactor contains cellulose, it may be subjected to cellulose hydrolysis with cellulase enzymes. By the term "cellulase enzymes", "cellulase", or "enzymes", it is meant enzymes that catalyze the hydrolysis of cellulose to products such as glucose, cellobiose, and other cello-oligosaccharides. Cellulase is a generic term denoting a multienzyme mixture comprising exo-cellobiohydrolases (CBH), endoglucanases (EG) and β-glucosidases (βϋ) that can be produced by a number of plants and microorganisms. The process of the present invention can be carried out with any type of cellulase enzymes, regardless of their source.

[0090] Optionally, prior to the enzymatic hydrolysis, the sugars arising from pretreatment are separated from the unhydrolyzed feedstock components in the pretreated feedstock slurry. Expedients for carrying out the separation include, but are not limited to, filtration, centrifugation, washing or other known processes for removing fiber solids or suspended solids. The aqueous sugar stream may then be concentrated, for example, by evaporation, with membranes, or the like. Any trace solids are typically removed by microfiltration.

[0091] In one embodiment, the aqueous sugar stream separated from the fiber solids is fermented to produce a chemical of interest, including, but not limited to, a sugar alcohol. The sugar alcohol may be selected from xylitol, arbitol, erythritol, mannitol and galactitol. Preferably, the sugar alcohol is xylitol. Alternatively, the sugar is converted to an alcohol, such as ethanol or butanol, by fermentation with a naturally-occurring or recombinant bacterium or fungus.

[0092] Generally, a temperature in the range of about 45°C to about 55°C, or any temperature therebetween, is suitable for most cellulase enzymes, although the temperature may be higher for thermophilic cellulase enzymes. The cellulase enzyme dosage is chosen to achieve a sufficiently high level of cellulose conversion. For example, an appropriate cellulase dosage can be about 5.0 to about 100.0 Filter Paper Units (FPU or IU) per gram of cellulose, or any amount therebetween. The FPU is a standard measurement familiar to those skilled in the art and is defined and measured according to Ghose (1987, Pure and Appl. Chem. 59:257-268). The dosage level of β- glucosidase may be about 5 to about 400 β-glucosidase units per gram of cellulose, or any amount therebetween, or from about 35 to about 100 β-glucosidase units per gram of cellulose, or any amount therebetween. The β-glucosidase unit is also measured according to the method of Ghose (supra).

[0093] The enzymatic hydrolysis of the cellulose continues for about 24 hours to about 250 hours, or any amount of time therebetween, depending on the degree of conversion desired. The slurry thus produced is an aqueous solution comprising glucose, xylose, other sugars, lignin and other unconverted, suspended solids. Other sugars that may be produced in the reaction zone may also be present in the aqueous solution. The sugars are readily separated from the suspended solids and may be further processed as required, for example, but not limited to, fermentation to produce fermentation products, including, but not limited to ethanol or butanol by yeast or bacterium. If ethanol is produced, the fermentation may be carried out with a yeast, including, but not limited to

Saccharomyces cerevisiae.

[0094] The dissolved sugars that are subjected to the fermentation may include not only the glucose released during cellulose hydrolysis, but also sugars arising from a pretreatment, namely xylose, glucose, arabinose, mannose, galactose or a combination thereof. These sugars may be fermented together with the glucose produced by cellulose hydrolysis or they may be fed to a separate fermentation. In one embodiment of the invention, such sugars are converted to ethanol, along with the glucose from the cellulose hydrolysis, by a Saccharomyces cerevisiae yeast strain having the capability of converting both glucose and xylose to ethanol. The Saccharomyces cerevisiae strain may be genetically modified so that it is capable of producing this valuable byproduct (see, for example, U.S. Patent No. 5,789,210, which is incorporated herein by reference), although it has been reported that some Saccharomyces cerevisiae yeast strains are naturally capable of converting xylose to ethanol.

DETAILED DESCRIPTION OF THE FIGURES

[0095] As seen in Fig. 1 , a slurry of lignocellulosic feedstock having a consistency of about 1% to about 10% (w/w), preferably about 3% to about 5% (w/w) in slurry line 102 is pumped by means of pump 104 through in-feed line 106 into pressurized dewatering screw press indicated by general reference number 108. Pressurized dewatering screw press 108 comprises a solid shell 105 having a feedstock inlet port 1 12 and a pressate port 114. In-feed line 106 feeds lignocellulosic feedstock into the dewatering screw press 108 through the feedstock inlet port 1 12 at a pressure of, e.g., about 70 psia to about 900 psia. The pressure may be determined by measuring the pressure with a pressure sensor located at feedstock inlet port 112.

[0096] A screen 1 16 is disposed within shell 105 to provide an outer space 1 18 between the screen and the inner circumference of shell 105. A screw 120 is concentrically and rotatably mounted within the screen 116. The flights 122 of the screw 120 are of generally constant outside diameter and attached to a screw shaft with a core diameter that increases from the inlet end 124 to the outlet end 126 of the pressurized dewatering screw press 108.

[0097] Water and any other liquids, including dissolved solids, which have been expressed from the lignocellulosic feedstock slurry are withdrawn into the space 118, which serves as a collection chamber for the withdrawn water. The space 1 18 is connected through the pressate port 1 14 to a turbine 132 that draws withdrawn water through a pressate line 130. The withdrawn water, or pressate, may then be sent to a pressate return slurry make-up system (not shown) via line 134.

[0098] The partially dewatered lignocellulosic feedstock exits the dewatering and plug formation zone of the screw press 108 at the outlet end 126. The ratio of the weight of dry lignocellulosic feedstock solids in the partially dewatered lignocellulosic feedstock preferably is in the range of about 1 :5: 1 to about 4: 1. The weight ratio of water to dry lignocellulosic feedstock solids in the dewatered lignocellulosic feedstock may be determined by collecting a sample of the feedstock from, e.g., outlet end 126 of the screw press, and determining the weight ratio in the sample by the method described hereinabove. Alternatively, the weight ratio of water to dry lignocellulosic feedstock solids in the partially dewatered lignocellulosic feedstock may determined by mass balance calculations.

[0099] The outlet end 126 of the pressurized screw press 108 is operatively connected to a plug zone 136. A plug of the partially dewatered lignocellulosic feedstock is forced through the plug zone 136 and is discharged at plug outlet 137. There may also be a restraining device (not shown) at the plug outlet 137.

[00100] A steam inlet port 138 and/or ports 138A are supplied by a source of steam via steam inlet line 139. The plug of partially dewatered feedstock, which contains water in the range of about 0.5 to about 5 times the weight of the dry feedstock solids, is fed into a high shear heating chamber 140 via a feed chamber 141.

[00101] In the high shear heating chamber 140, the feedstock plug, or segments thereof, is disintegrated into particles, which are heated by direct steam contact via steam introduced through line 139 and/or ports 138 A. Steam may also be introduced into the body of the heating chamber 140. As mentioned previously, the plug may break into segments as it is discharged from the pressurized screw press 108, or as it is fed into other devices positioned downstream of the screw press 108.

[00102] The heating chamber 140 is a cylindrical, horizontally-oriented device having a concentric, rotatable shaft 142 mounted co-axially in the chamber. The concentric shaft 142 comprises a plurality of disintegrating elements 143 mounted on its mid-region and that project radially therefrom. Some disintegrating elements comprise a distal end 144 that is "T-shaped" for sweeping the inner surface of the chamber 140, as described below. The inlet region of the shaft 142 comprises an inlet auger 145 for conveying the plug, or segments thereof, into the mid- region of the chamber. In addition, an outlet auger 146, with opposite pitch, is provided in an outlet region of the shaft 142 for discharging heated, disintegrated feedstock produced in the heating chamber 140 into a pretreatment reactor 152.

[00103] Shearing action is imparted to the feedstock plug or segments thereof, in the heating chamber 140 by the plurality of disintegrating elements 143. The tip speed of the shaft is such that the feedstock segments are disintegrated and is typically within a range of between 450 m/min to about 800 m/min so as to achieve optimal disintegration. The extent of shearing action is largely a function of the number and shape of the disintegrating elements times the tip speed. During disintegration, the feedstock plug or segments thereof are broken down into small particles.

[00104] Each disintegrating element is configured so that the clearance between the inner surface of the chamber 140 and the outer edge of the distal "T-shaped" end 144 of each disintegrating element is less than 4 percent of the inside diameter of the chamber 140. Such a clearance allows the disintegrating elements 143 to sweep the inner surface of the chamber 140.

[00105] Moreover, the disintegrating elements 143 are arranged on the shaft 142 so that there is continuous axial sweeping of the inner surface of the chamber 140. According to this embodiment of the invention, the end portions of each "T-shaped" disintegrating element overlap corresponding end portions of an adjacent T-shaped element. This allows the area swept by each T-shaped element to overlap the area swept by an adjacent T-shaped element so that there are no stagnant zones for organic deposits to accumulate on the inner surface of the chamber.

[00106] According to another embodiment of the invention, the disintegrating elements are "Y- shaped". In addition, a combination of "Y-shaped" and "T-shaped" disintegrating elements may be arranged on the shaft.

[00107] The auger 145 for conveying the plug, or segments thereof, into the mid-region of the chamber 140 may be sawtooth auger. Cross-sections of various auger configurations suitable for use in the invention are shown in Figure 2. The provision of such an auger at the inlet region facilitates conveyance of the plug, or segments thereof, through the heating chamber 140. In addition, a sawtooth auger functions to disintegrate the feedstock plug or segments as it enters the heating chamber.

[00108] The heated, disintegrated feedstock is discharged from the heating chamber 140 into the pretreatment reactor 152, which comprises a cylindrical, horizontally-oriented vessel within which is mounted a screw conveyor 154 having flights 156. The pretreatment reactor 152 operates at a pressure of about 90 psia to about 680 psia, a pH of about 0.5 to about 3.0 and a temperature of about 160°C to about 260°C. The lignocellulosic feedstock is treated in the reactor for a time of about 10 to about 600 seconds. The desired pH in the reactor 152 may be obtained by adding acid to the lignocellulosic feedstock prior to the inlet of the pressurized screw press.

[00109] A discharge device 158 discharges the pretreated feedstock from the pretreatment reactor 152. Subsequently, the pretreated feedstock is flashed in a flash vessel or vessels (not shown) to cool it before enzymatic hydrolysis.