Biorefinery process for extraction, separation and recovery of fermentable saccharides, other useful compounds, and yield of improved lignocellulosic material from plant biomass

Abstract

Non-food plant biomass is subjected hot-water extraction in a pressurized vessel at an elevated temperature up to about 250 C. without addition of reagents, to yield an aqueous extract containing hemicellulosic components and a lignocellulosic residue. The process leaves the lignocellulose substantially intact, but with the hemicellulosic content largely removed. The separated aqueous extract or liquor is concentrated and purified, and long-chain sugars are reduced into monomer saccharides. The lignocellulosic residue may be further processed, to yield a useful fibrous material that is highly resistant to sorption of water. This material may be used for composite materials that resist water degradation, or may be used to produce a higher thermal-yield, water-resistant fuel, or may be used as bioconversion feedstock for producing high-value, lignocellulosic derivatives.

Claims

1. Process of producing improved wood fiber for product uses from green non-food plant biomass, the process comprising: a) hot-water extraction carried out by contacting a charge of the green non-food plant biomass material with liquid water in the absence of any added reagents, in a pressurized vessel at an elevated temperature up to about 250 C., in which the hot-water extraction is adapted so as to yield an aqueous extract containing hemicellulosic components and an improved post-treatment lignocellulosic solid residue as residue material in which the hemicellulosic components thereof are substantially removed therefrom, but in which the cellulose and lignin components are substantially unchanged such that the post-treatment residue material retains its pre-treatment shape, size, and structural integrity; b) separating the aqueous extract from the lignocellulosic residue; c) further processing the separated aqueous extract; and d) processing the improved lignocellulosic residue while leaving the cellulose and lignin contents thereof substantially unchanged but in which a significant portion of the hemicellulosic components are absent to yield useful products with significantly reduced moisture reactivity.

2. The process of claim 1 wherein said step a) includes increasing the chemical reactivity of the lignocellulosic residue, reducing the content thereof of its hydrophilic components, reducing the ash content thereof, and increasing its BTU content per unit weight.

3. The process of claim 1, further comprising processing the residue of step d) to produce wood composite products suitable for use as structural materials said products belonging to a group that consists of chip board, flake-board, oriented-strand-board, fiber board, decking material, and cellulose-polymer mixtures.

4. The process of claim 1, further comprising processing the residue of step d) into lignocellulosic fuel pellets.

5. The process of claim 1 wherein the step a) of hot-water extraction is effective to unbind, separate, and remove between 10% to 35% of the mass of the charge of non-food plant biomass.

6. The process of claim 5 wherein the step a) is effective to remove substantially 23% of the mass of the charge of non-food plant biomass.

7. The process of claim 1 wherein said charge of green non-food plant biomass material consists of wood chips.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The sole FIGURE of Drawing is a flow chart for explaining the process of this invention.

DETAILED DESCRIPTION OF THE DRAWING

(2) The right-hand side of the sole Drawing FIGURE is a process flow chart for explaining the extraction process producing concentrates and permeates from which useful lignocellulosic-sugar feedstocks, and other lignocellulosic-derived compounds are separated and recovered.

(3) The left side of the Drawing depicts a process flow through which the solid component of the extracted, lignocellulosic material, with reduced hydrophilicity, is forwarded for use as fuel, or for further manufacture into wood products, wood derivatives, or other useful lignocellulosic materials.

(4) The generalized flow of the extraction process depicted in the Drawing can be described as follows.

(5) The first step, Step 1, is the receiving and pre-processing of available non-food lignocellulosic feedstock [10], which may include, e.g., wood chips, straw, or any other plant matter. There is a gross screening process in which oversized materials (large chunks of wood) and contaminates (stones, soil, etc.) are selected and removed. This may include organic debris, detritus, as well as some lignocellulosic material. This is followed by a fine screening, in which undersized particles, or fines, including contaminates, such as sand, soil or the like, are separated and removed. This may also include organic debris, detritus, and lignocellulosic material. The remaining lignocellulosic material may be triturated (e.g., by chipping, tub grinding, hammer milling, or other available comminuting procedure) to reduce the feedstock to preferred size (comparable to commercial woodchips for pulping or smaller) and condition for further handling and processing. Magnetic screening and separation is applied at this time to remove any tramp metals that may be present in the lignocellulosic stream.

(6) Then Step 2, a hot water extraction process [11] is applied to the prepared non-food lignocellulosic material, which is effective for a mass removal, most preferably between about ten percent and thirty-five percent. This may be done by batch processing, continuous processing, or semi-continuous processing. The hot water extraction process involves contacting the charge of prepared non-food lignocellulosic material with water (with or without small amounts of acetic acid, furfural, or other process enhancing compounds/materials), in a pressurized vessel, at an elevated temperature up to about 250 C. to yield an aqueous extract (or liquor) containing solubilized components of the lignocellulosic material. The residual non-food lignocellulosic material [12] (i.e., fibrous material) is separated from the liquor or extract [13], and each may be further processed as discussed below.

(7) The separated aqueous extract [13] is processed in a series of stages to isolate and recover valuable hemicellulosic, and other lignocellulosic derived, compounds; this is shown on the right-hand branch of the Drawing.

(8) A first-stageStep 3[14] involves filtration and separation, which may involve flocculation, and/or sedimentation, and/or centrifugation, and/or filtration, and/or hydro-cyclone separation. Larger aromatic and oligomeric molecules separated from the aqueous extract at this point are recovered and stored for sale or future processing [15].

(9) In the next stageStep 4[16], a concentrated, water-based solution of complex and simple saccharides [17] is created by further filtering the aqueous extract stream to remove non-sugar compounds, many of which are inhibitory to fermentation, into a permeate solution [18]. This partitioning/concentration [16] can be carried out via membrane separation, and/or evaporation, and/or solvent extraction, and/or by any combination of these processes.

(10) Thereafter, the sugar concentrate [17] is subjected to Step 5, hydrolysis [19] via a process that may involve an enzyme treatment, and/or acid treatment, and/or heat, and/or solid acid, and/or any combination of these.

(11) In the next stageStep 6[20], the acid hydrolyzed sugar solution may be pH-corrected (with an alkali or base) as necessary, before being further treated to isolate and recover commercially valuable chemicals [21 and 22]. This isolation and recovery step may collectively involve centrifugation, and/or membrane separation, and/or sedimentation, and/or filtration, which serve to remove aromatic products [21] from the hydrolyzed sugar solution. Step 7, comprised of further product separation [22] is necessary for final removal of inhibitory compounds, either by diafiltration using a single- or multi-stage membrane with counter-current or non-counter-current flow, and/or solvent separation using selective chemical separation involving water-immiscible solvents. As output streams from the Step 7 product separation [22], the inhibitory chemical solution is then conveyed [24] to a recovery phase [18], while the remaining aqueous concentrate now consists mainly of fermentable, monomeric sugars [23] of the types mentioned above. There can be successive stages of hydrolysis, concentration, and separation to increase the yield of useful sugars from the feedstock. The pH correction shown at [20] may be conducted after the product recovery stages [21] and/or [22].

(12) In the first Step 3 purification step [14], larger aromatic and oligomeric molecules are removed and recovered as products [15]. In subsequent purification steps [16, 19, 20, and 22], organic chemicals, such as acetic acid and other inhibitory compounds which have been solubilized in the aqueous extract, are separated so that the complex saccharides can be further hydrolyzed and purified to yield fermentable, short-chain sugars. The separated inhibitory materials [18 and 24] are combined, and processed as discussed next.

(13) As shown at the right hand sub-branch, the permeate solution of inhibitory products isolated in previous steps, Step 4 and Step 7, [16 and 22] is processed in Step 8 [25] to separate and recover component commercial chemicals, e.g., acetic acid, formic acid, methanol, furfural, and water. This separation and recovery may be achieved by solvent extraction, and/or distillation, and/or membrane separation, and/or pervaporation, and/or crystallization, and/or any combination of these. The isolated compounds are available for commercial sale as platform chemicals [15 and 26].

(14) Again referring to the Drawing, the initial steps [10] and [11], Steps 1 and 2, lead to two product streams: the previously discussed aqueous extract [13], as well as to the extracted lignocellulosic material [12]. The residual fibrous biomass material with the extracted materials removed [12], may be forwarded (Step 9) as raw material [30] for use as fuel, or for manufacture of wood products and/or wood derivatives. As previously described, the process begins with Step 1the autocatalytic, hot-water separation of hemicellulosic compounds from the lignocellulosic biomass. The process generally includes the receiving and pre-processing of lignocellulosic material as described above [10], followed by Step 2cooking the lignocellulosic material in hot water [11]. The liquor or aqueous extract [13] is removed from the cooked biomass solids [12]. The cooking process removes a significant portion (typically 23%) of the hydrophilic or water sorptive chemicals from the lignocellulosic material. The residual biomass solids are thus significantly less dense than the starting feedstock materials, and are also characterized by significantly reduced hydrophilicity (i.e., less attractive to water). Products made from this reduced hydrophilic material are less prone to water sorption from the environment, and thus will be less prone to softening from contact with water, and less prone to rot or deterioration. In addition, because this material equilibrates at very low water content and is relatively free from ash producing inorganic elements and hemicellulose compounds, it can serve as an increased BTU-content fuel in the form of chips or pellets [31]. These pellets burn hotter, with less ash residue and less propensity to form clinkers. In addition to fuel, other more valuable end-uses for the extracted lignocellulosic material are: pulp [32], wood composites [33], or as a bio-conversion feedstock [34].

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(15) In an embodiment of the process, the wood-yard supplies woodchip feedstock and handles oversized material, dust, and tramp metals. Screening and magnetic separation can be used for this preparatory phase. Favorably, storage for up to forty-five days worth of green wood will be available to maintain feedstock supply to the extraction operation. Self-dumping trucks deliver wood chips to the facility, and the wood is automatically handled by conveyor and/or mobile equipment (skid-steer, front loader, etc.).

(16) In another embodiment, the extraction of lignocellulosic materials via water-based autohydrolysis removes from 10 percent up to 35 percent (typically 23%) of the mass of the lignocellulosic materials in a continuous, semi-continuous, or batch process operation. The lignocellulosic materials are contacted with water at an elevated temperature up to 250 C. to yield an aqueous extract and extracted, but largely intact, lignocellulosic materials.

(17) A heated pressure vessel is used for extraction, and a two-stage washing system can be included to provide improved capture of extracted material. Chip feed and removal, in combination with liquid handling equipment are employed to fill and evacuate the pressure vessel. A heat exchanger is used to cool the extract or liquor, and to recover and recycle heat back to the hot water extraction pressure vessel. A holding tank stores the extract for downstream processing. A transfer pump and bag filter may be used to transfer and clean the extract in preparation for first-stage filtration.

(18) In another embodiment following hot water extraction and coarse materials removal, first-stage filtration operates as a lignin and high molecular weight removal system for improving the efficiency of further extract solution downstream processing. During first-stage filtration, high molecular weight and suspended materials are dissociated from the extract solution by one or more of: sedimentation, centrifugation, filtration, hydro-cyclone, and/or flocculation. The cleaned extract solution from this step is cooled as necessary for the next processing stage.

(19) In yet another embodiment following first-stage filtration, the next stage further refines the cleaned extract solution by separating monomeric and oligomeric sugars from inhibitory compounds such as acetic acid and furfural. This partitioning step can be accomplished by membrane separation, evaporation, and/or solvent extraction. The output products from this stage consist of a concentrated sugar solution (primarily oligomers with some monomers and dimers), and a solution containing inhibitory and other compounds. Both solutions will be further refined and/or transformed into commercial chemicals.

(20) In a further embodiment, acid hydrolysis is performed on the concentrated sugar solution to break apart long-chain sugar polymers to monomeric or dimeric form by one or more of enzyme, acid, solid acid, and/or heat treatments. The addition of acid causes precipitation of residual aromatic materials and certain suspended solids from the concentrated sugar solution; these solids are later recovered. Then, application of heat to the hydrolysis process releases further materials into solution and suspension. Following hydrolysis these newly-released materials are removed and recovered from solution by centrifugation, filtration, membrane separation, and/or hydro-cyclone. The solution may then be pH-corrected as needed for further processing.

(21) In still another embodiment following acid hydrolysis, additional fermentation inhibitors such as acetic acid and furfural released during hydrolysis must be removed from the sugar stream. This purification step may occur before or after pH correction, and is accomplished using single or multi-stage membrane separation, either with counter-current flow or non-countercurrent flow, and/or solvent separation (i.e., selective chemical separation with water immiscible solvents). In the case of the membrane separation, called diafiltration, two new streams are produced: a short-chain sugar solution containing xylose, mannose, arabinose, rhamnose, galactose, and glucose (5 and 6-carbon sugars), and a new permeate solution containing chemicals such as acetic acid, formic acid, furfural, and methanol. The sugar stream, now significantly reduced in content of inhibitory substances, may be converted by fermentation into such products as butanol, acetone, ethanol, et al. If pH correction has not been performed before separation of the inhibitory products, it will be performed before fermentation, and the target pH will be determined to satisfy desired conditions for the fermentation organism and corresponding end product.

(22) In a yet further embodiment, chemicals in the permeate solution (acetic acid, methanol, formic acid, furfural) may be separated for commercial sale by solvent extraction, distillation, crystallization, membrane separation, and/or pervaporation.

(23) In still another embodiment, water from both the sugar and permeate streams may be recovered by evaporation-condensation and/or membrane separation and/or steam stripping and/or air stripping.

(24) In a still further embodiment, following hot water extraction, the residual lignocellulosic fiber may be manufactured into fuel pellets by comminuting the residual fiber to a size appropriate for extrusion through a pelletizer.

(25) In another important embodiment, following hot water extraction, the improved residual lignocellulosic fiber may be manufactured into wood composites by comminuting the residual fiber to a size appropriate for mixing with adhesive additives to create structural or architectural members. The improved residual lignocellulosic fiber may be mixed with a plastic resin binder, e.g., recycled polyethylene or other material. These composite materials may then be used, for example, to manufacture into furniture products, or as structural members as building materials, as a plastic/wood composite decking, or for many other applications that may call for reconstituted wood products. Because of the significantly reduced hydrophilicity of the improved lignocellulosic fiber material, the structural material and products manufactured from it enjoy superior performance and longer useful life, especially in an outdoor environment.

(26) In another embodiment, following hot water extraction, the improved residual lignocellulosic fiber may be manufactured into crystalline cellulose by de-lignifying the fiber using Kraft, sulfite, or organosolve pulping procedures, and then subjecting the de-lignified cellulose to acid hydrolysis or enzymolysis and/or sonication to produce a mixture of crystalline cellulose and predominately fermentable glucose.

(27) While the invention has been described with reference to specific examples and embodiments, the invention is not to be limited to those embodiments, but the scope of the invention is to be ascertained from the appended claims.