Patent Application
20080299628
This invention relates to fractionation of lignocellulosic feedstocks into component parts. More particularly, this invention relates to processes, systems and equipment configurations for recyclable organosolv fractionation of lignocellulosic material for continuous controllable and manipulable production and further processing of lignins, monosaccharides, oligosaccharides, polysaccharides and other products derived therefrom.
Industrial processes for production of cellulose-rich pulps from harvested wood are well-known and typically involve the steps of physical disruption of wood into smaller pieces and particles followed by chemical digestion under elevated temperatures and pressures to release and separate the cellulosic fibres from the constituent lignocellulosic fibrous matrices. The chemical digestion processes are commonly referred to as “kraft” and “sulfite” processes, and typically produce a solids fraction, referred to as pulp, comprising the cellulosic fibers and a liquids fraction commonly referred to as “black liquors” comprising the chemical solvents and solubilized materials released from the lignocellulosic fibrous matrices. The cellulosic fibrous pulps are typically used for paper manufacturing while the black liquors are usually processed to recover and recycle the chemical solvents, and the residues are typically combusted for in-house energy and/or heat production.
During the past two decades, those skilled in these arts have recognized that lignocellulosic materials including gymnosperm and angiosperm substrates (i.e., wood) as well as field crop and other herbaceous fibrous biomass, waste paper and wood containing products and the like, can be potentially fractionated using organic solvents for digestion, into multiple useful component parts that can be separated and further processed into high-value products such as fuel ethanol, lignins, furfural, acetic acid, purified monosaccharide sugars among others. Such systems have become known as “organosolv” and/or bio-refining systems (Pan et al., 2005, Biotechnol. Bioeng. 90: 473-481; Pan et al., 2006, Biotechnol Bioeng. 94: 851-861). Organosolv pulping processes and systems for lignocellulosic feedstocks are well-known and are exemplified by the disclosures in U.S. Pat. Nos. 4,941,944; 5,730,837; 6,179,958; and 6,228,177. After digestion has been completed in organosolv processes, the solids comprising the cellulosic fibrous pulps are separated from the spent digestion liquids i.e., black liquors and typically comprise organic solvents, solubilized lignins, soluble monosaccharides, oligosaccharides, polysaccharides, other organic compounds and minerals released from the wood during the chemical digestion. The black liquors are then usually processed to remove the soluble lignins after which, the organic solvents are recovered, purified and recycled. The lignins and remaining stillage from the black liquors are typically handled and disposed of as waste streams. Although it appears that biorefining using organosolv systems has considerable potential for large-scale fuel ethanol production, the currently available biorefining processes and systems are not yet economically attractive except at very large scale because they require expensive pretreatment steps and currently produce only low-value co-products (Pan et al., 2006, J. Agric. Food Chem. 54: 5806-5813).
The exemplary embodiments of the present invention relate to systems, processes and equipment configurations for receiving and controllably commingling lignocellulosic feedstocks with counter-flowing organic solvents while providing suitable temperature and pressure conditions for fractionating the lignocellulosic feedstocks into component parts which are then subsequently separated. The separated component parts are further selectively, controllably and manipulably processed.
According to one exemplary embodiment of the present invention, there is provided a modular processing system for receiving therein and fractionating a lignocellulosic feedstock into component parts, separating the component parts into at least a solids fraction and a liquids fraction, and then separately processing the solids and liquids fractions to further produce useful products therefrom. Suitable modular processing systems of the present invention comprise at least:
According to one aspect, the plurality of equipment in the first module is configured to continuously receive and convey therethrough in one direction a lignocellulosic feedstock ending with the discharge of a cellulosic solids fraction, while concurrently counter-flowing a selected suitable solvent through the equipment in an opposite direction to the conveyance of the lignocellulosic feedstock ending in a discharge of a spent solvents liquid fraction.
According to another aspect, the plurality of equipment in the first module is configured to receive a batch of a lignocellulosic feedstock and to continuously cycle therethrough a selected suitable solvent therethrough until a suitable solids fraction is produced from the batch of lignocellulosic feedstock.
According to yet another aspect, the plurality of equipment in the second module is configured to sequentially: (a) receive and reduce the viscosity of the cellulosic solids fraction discharged from the first module, then (b) progressively hydrolyze and saccharify the cellulosic solids into suspended solids, dissolved solids, hemicelluloses, polysaccharides, oligosaccharides thereby producing a liquid stream primarily comprising monosaccharides, (c) ferment the liquid stream, (d) distill and refine the fermentation beer to separate the beer into at least a fuel-grade ethanol and a stillage stream, (e) de-lignify the stillage stream, and (f) recycle the de-lignified stillage stream for reducing the viscosity of fresh incoming cellulosic solids fraction discharged from the first module.
According to a further aspect, the plurality of equipment in the second module may be optionally configured to sequentially: (a) receive and reduce the viscosity of the cellulosic solids fraction discharged from the first module, then (b) concurrently hydrolyze and saccharify the cellulosic solids into monosaccharides while fermenting the monosaccharides in the same vessel, (c) distill and refine the fermentation beer to separate the beer into at least a fuel-grade ethanol and a stillage stream, (d) de-lignify the stillage stream, and (f) recycle the de-lignified stillage stream for reducing the viscosity of fresh incoming cellulosic solids fraction discharged from the first module.
According to another aspect, the modular processing system of the present system may be additionally provided with a fifth module comprising an anaerobic digestion system provided with a plurality of equipment configured for receiving the semi-solid/solid waste material from the fourth module, then liquifying and gasifying the waste material for the bio-production of methane, carbon dioxide and water.
According to another exemplary embodiment of the present invention, there is provided processes for fractionating a lignocellulosic feedstock into component parts. First, foreign materials exemplified by gravel and metal objects are separated using suitable means, from the incoming lignocellulosic material. An exemplary separating means is screening. If so desired, the screened lignocellulosic feedstock may be further screened to remove fines and over-size materials. Second, the screened lignocellulosic feedstock is controllably heated for example by steaming after which, the heated lignocellulosic feedstock is de-watered and then pressurized. Third, the heated and de-watered lignocellulosic feedstock is commingled and then impregnated with a suitable aqueous solvent. Fourth, the commingled lignocellulosic feedstock and organic solvent are controllably cooked within a controllably pressurized and temperature-controlled system for a selected period of time. During the cooking process, lignins and lignin-related compounds contained within the commingled and impregnated lignocellulosic feedstock will be dissolved into the organic solvent resulting in the cellulosic fibrous materials adhered thereto and therewith to disassociate and to separate from each other. The cooking process will also release monosaccharides, oligosaccharides and polysaccharides and other organic compounds for example acetic acid, in solute and particulate forms, from the lignocellulosic materials into the organic solvents. Those skilled in these arts refer to such organic solvents containing therein lignins, lignin-related compounds, monosaccharides, oligosaccharides and polysaccarides and other organic compounds, as “black liquors” or “spent liquors”.
According to one aspect, controllably counter-flowing the organic solvent against the incoming lignocellulosic feedstock during the cooking causes turbulence that facilitates and speeds the dissolution and disassociation of the lignins and lignin-related components from the lignocellulosic feedstock. However, it is within the scope of this invention to alternatively provide turbulence during the cooking process with a controllable flow of organic solvent directed in the same direction as the flow of lignocellulosic feedstock, i.e., a concurrent flow, thereby controllably intermixing the solvent and lignocellulosic feedstock together. It is also within the scope of this invention to controllably partially remove the organic solvent during the cooking process and to replace it with fresh organic solvent.
According to another aspect, the lignocellulosic feedstock may comprise at least one of physically disrupted angiosperm, gymnosperm, and field crop fibrous biomass segments exemplified by chips, saw dust, chunks, shreds and the like. It is within the scope of this invention to provide mixtures of physically disrupted angiosperm, gymnosperm, and field crop fibrous biomass segments.
According to yet another aspect, the lignocellulosic feed stock may comprise at least one of waste paper, wood scraps, comminuted wood materials, wood composites and the like. It is within the scope of this invention to intermix lignocellulosic fibrous biomass materials with one or more of waste paper, wood scraps, comminuted wood materials, wood composites and the like.
According to a further aspect, the liquor to wood ratio, operating temperature, solvent concentration and reaction time may be controllably and selectively adjusted to produce pulps and/or lignins having selectable target physico-chemical properties and characteristics.
According to another exemplary embodiment of the present invention, there are provided processes and systems for separating the disassociated cellulosic fibers i.e. pulp, from the black liquors, and for further and separately processing the pulp and the black liquors. The separation of pulp and black liquors may be done while the materials are still pressurized from the cooking process or alternatively, pressure may be reduced to about ambient pressure after which the pulp and black liquors are separated.
According to one aspect, the cellulosic fibrous pulp is recoverable for use in paper-making and other such processes.
According to another aspect, there are provided processes and systems for further selectively and controllably processing the cellulosic pulps produced as disclosed herein. The pH and/or the consistency of the recovered pulp may be adjusted as suitable to facilitate the hydrolysis of celluloses to monosaccharides, i.e., glucose moieties in hydrolysate solutions. Exemplary suitable hydrolysis means include enzymatic, microbial, chemical hydrolysis and combinations thereof.
According to yet another aspect, there are provided processes and systems for producing ethanol from the monosaccarides hydrolyzed from the cellulosic fibrous pulp, by fermentation of the hydrolysate solutions. It is within the scope of this invention to controllably provide inocula comprising one or more selected suitable strains from yeast species, fungal species and bacterial species, to facilitate and enhance the rates of fermentation and/or fermentation efficiencies and/or fermentation yields. Suitable yeasts are exemplified by Saccharomyces spp. and Pichia spp. Suitable Saccharomyces spp are exemplified by S. cerevisiae such as strains Sc Y1528, Tembec-1 and the like. Suitable fungal species are exemplified by Aspergillus spp. and Trichoderma spp. Suitable bacteria are exemplified by Escherichia coli, Zymomonas spp., Clostridium spp. and Corynebacterium spp. among others, naturally occurring and genetically modified.
According to a further aspect, there are provided processes and systems for concurrently saccharifying and fermenting the cellulosic pulps produced as disclosed herein. It is within the scope of the present invention to controllably hydrolyze the cellulosic fibrous pulps into monosaccharides by providing suitable hydrolysis means exemplified by enzymatic, microbial, chemical hydrolysis and combinations thereof, while concurrently and controllably fermenting the monosaccharide moieties produced therein. It is within the scope of this invention to controllably provide inocula comprising one or more selected strains of Saccharomyces spp. to facilitate and enhance the rates of concurrent fermentation and/or fermentation efficiencies and/or fermentation yields.
According to a further aspect, there are provided processes and systems for further processing the ethanol produced from the fermentation of the hydrolysate solutions. Exemplary processes include concentrating and purifying the ethanol by distillation, and de-watering or dehydration by passing the ethanol through at least one molecular sieve or alternatively, through a suitable membrane filtration system.
According to a further exemplary embodiment of the present invention, there are provided processes and systems for recovering lignins and lignin-related compounds from the black liquors. An exemplary process comprises cooling the black liquor immediately after separation from the cellulosic fibrous pulp, in a plurality of stages wherein each stage, heat is recovered with suitable heat-exchange devices and organic solvent is recovered using suitable solvent recovery apparatus as exemplified by evaporation and cooling devices. The stillage, i.e., the cooled black liquors from which at least some organic solvent has been recovered, are then further cooled, pH adjusted (e.g., increasing acidity) and then rapidly diluted with water to precipitate lignins and lignin-related compounds from the stillage. The precipitated lignins and lignin-related compounds are subsequently washed at least once and then dried.
According to one aspect, the de-lignified stillage is processed through a distillation tower to evaporate remaining organic solvent, and to concurrently separate and concentrate furfural. The remaining stillage is removed from the bottom of the distillation tower. It is within the scope of the present invention to optionally divert at least a portion of the de-lignified stillage from the distillation tower input stream into the ethanol production stream for producing ethanol therefrom. Alternatively or optionally, at least a portion of the remaining stillage removed from the bottom of the distillation tower may be diverted into the ethanol production stream for producing ethanol therefrom.
According another aspect, the stillage recovered from the bottom of the solvent recovery column, is further processed by: (a) decanting to recover complex organic extractives as exemplified by phytosterols, oils and the like, and then (b) evaporating the decanted stillage to produce (c) a stillage evaporate/condensate comprising acetic acid, and (d) a stillage syrup containing therein dissolved monosaccharides. The stillage syrup may be decanted to recover (e) novel previously unknown low molecular weight lignins. The decanted stillage syrup may be optionally evaporated to recover dissolved sugars.
It is within the scope of this invention to further process the recovered organic solvent by purification and concentration steps to make the recovered organic solvent useful for recycling back into continuous incoming lignocellulosic feedstock.
According to one aspect, an organic solvent is intermixed and commingled with the lignocellulosic feedstock for a selected period of time to pre-treat the lignocellulosic feedstock prior to commingling and impregnation with the counter-flowing (or alternatively, concurrently flowing) organic solvent.
The present invention will be described in conjunction with reference to the following drawings, in which:
Exemplary embodiments of the present invention relate to systems, processes and equipment configurations for receiving and controllably commingling lignocellulosic feedstocks with counter-flowing aqueous organic solvents, thereby fractionating the lignocellulosic feedstocks into component parts which are then subsequently separated. The separated component parts are further selectively, controllably and manipulably processed. The exemplary embodiments of the present invention are particularly suitable for separating out from lignocellulosic feedstocks at least four structurally distinct classes of lignin component parts with each class comprising multiple derivative lignin compounds, while concurrently providing processes for converting other component parts into at least fuel-grade ethanol, furfurals, and monosaccharide sugar streams.
An exemplary modular processing system of the present invention is shown in
The first module A as exemplified in
The second module B is provided with a mixing vessel 60 wherein the viscosity of solids fraction, i.e., pulp discharged from the first module A is controllably reduced to a selected target viscosity, by commingling with a recovered recycled solvent stream delivered by a pipeline 130 from a down-stream component of module B. The reduced viscosity pulp is then transferred to a digestion vessel 70 where a suitable enzymatic preparation is intermixed and commingled with the pulp for progressively breaking down the cellulosic fibers, suspended solids and dissolved solids into hemicelluloses, polysaccharides, oligosaccharides and monosaccharides. A liquid stream comprising these digestion products is transferred from the digestion vessel 70 to a fermentation vessel 80 and is commingled with a suitable microbial inocula selected for fermentation of hexose and pentose monosaccharides in the liquid stream thereby producing a fermentation beer comprising at least a short-chain alcohol exemplified by ethanol and residual sediments. The fermentation beer is transferred to a first distillation tower 85 for refining by volatilizing then distilling and separately collecting from the top of the distillation tower 85 at least a fuel-grade ethanol which is transferred to a holding tank 90 and stored in a suitable holding container 100. We have discovered that the cellulosic solids fraction produced and separated in the first module A and delivered to the second module B for saccharification and fermentation, contains a unique class of lignin derivatives characterized by very high molecular weights (i.e., VHMW) in comparison to the classes of lignins commonly known to those skilled in these arts. The VHMW lignins are recoverable from the stillage produced in the second module B by removing stillage from the bottom of distillation tower 85 to separation equipment 110 configured to separate out the VHMW lignins which are then collected and stored in a suitable vessel 120 for further processing and/or shipment. It is within the scope of the present invention to heat the stillage to facilitate precipitation of the VHMW lignins prior to flowing the stillage through separation equipment 110. The de-lignified stillage may then be controllably recycled from equipment 110 via pipeline 130 to the mixing vessel 60 for reducing the viscosity of fresh incoming pulp from the first module A. Those skilled in these arts will understand that fusel oils comprising heavier alcohols exemplified amyl alcohols and furfurals are commonly produced in most fermentation processes and become concentrated in the “tails” and stillage at the ends of distillation runs. If allowed to accumulate in recycled stillage, the increasing concentrations of fusel oils will interfere with the fermentation efficiencies and rates. Therefore, as shown in
Suitable enzyme preparations for addition to digestion vessel 70 for progressively breaking down cellulosic fibers into hemicelluloses, polysaccharides, oligosaccharides and monosaccharides may comprise one or more of enzymes exemplified by cellulases, hemicellulases, β-glucosidases, β-xylosidases xylanases, α-amylases, β-amylases, pullulases and the like. Suitable microbial inocula for fermenting pentose and/or hexose monosaccharides in fermentation vessel 80 may comprise one or more suitable strains selected from yeast species, fungal species and bacterial species. Suitable yeasts are exemplified by Saccharomyces spp. and Pichia spp. Suitable Saccharomyces spp are exemplified by S. cerevisiae such as strains Sc Y1528, Tembec-1 and the like. Suitable fungal species are exemplified by Aspergillus spp. and Trichoderma spp. Suitable bacteria are exemplified by Escherichia coli, Zymomonas spp., Clostridium spp. and Corynebacterium spp. among others, naturally occurring and genetically modified. It is within the scope of the present invention to provide an inoculum comprising a single strain, or alternatively a plurality of strains from a single type of organism, or further alternatively, mixtures of strains comprising strains from multiple species and microbial types (i.e. yeasts, fungi and bacteria).
The black liquors discharged as a liquid fraction from the digestion/extraction vessel 40 of first module A, are processed in third module C to recover at least a portion of the digestion/extraction solvent comprising the black liquors, and to separate useful components extracted from the lignocellulosic feedstocks as will be described in more detail below. The black liquors are transferred by pipeline 47 into a flashing tower 140 wherein the pressure is reduced and the temperature subsequently reduced (i.e., “flashed”). We have discovered a second new class of lignin derivatives that precipitate from the liquids fraction during the flashing process that is characterized by high molecular weights (i.e., HMW) in comparison to the classes of lignins commonly known to those skilled in these arts. The HMW lignins 155 can be removed by a suitable separation device exemplified by a filter 150 thereby producing a first filtrate. The first filtrate is transferred to a mixing tank 160 where it is commingled with a supply of cold water thereby precipitating a third class of lignin derivatives characterized by medium molecular weights (MMW) from the first filtrate. Alternatively, a chilled stillage feed from a second distillation tower 180 may be used for commingling and intermixing with the first filtrate in the mixing tank 160 for precipitation of MMW lignins. MMW lignins are well-known and characterized. The precipitated MMW lignins are separated from the first filtrate by a suitable solids-liquids separation equipment 165 as exemplified by filtering apparatus, hydrocyclone separators, centrifuges and other such equipment, thereby producing a second filtrate. The separated MMW lignins are transferred to a lignin drier (not shown) for controlled removal of excess moisture, after which the dried MMW lignins are transferred to a storage bin 170 for packaging and shipping.
The second filtrate fraction is transferred from the separation equipment 165 to a second distillation tower 180 for vaporizing, distilling and recovering therefrom a short-chain alcohol exemplified by ethanol. The recovered short-chain alcohol is transferred to a digestion/extraction solvent holding tank 250 where it may, if so desired, be commingled with a portion of fuel-grade ethanol produced in module B and drawn from pipeline 95, to controllably adjust the concentration and composition of the digestion/extraction solvent prior to supplying the digestion/extraction solvent via pipeline 41 to the digestion/extraction vessel 40 of module A. It is within the scope of the present invention to recover furfurals from the de-lignified filtrate fraction concurrent with the vaporization and distillation processes within the second distillation tower, and transfer the recovered furfural rich side draw to a storage tank 190. An exemplary suitable process for recovering furfurals is to commingle the side drawl 81 with a water supply 182 and controllably cool or alternatively heat the commingled side draw to a suitable temperature thereby causing the side draw to separate into two phases; a lower oily furfural-rich phase and an upper aqueous ethanol phase. These two phases can be separated in a decanter 185, with the upper layer being returned to the distillation tower 180 via filtrate line 181 while the furfural-rich phase is transferred to a holding tank 190.
The stillage from the second distillation tower 180 is transferred to the fourth module D for further processing and separation of useful products therefrom. The hot stillage is transferred into a cooling tower or alternatively an evaporator 200 configured to collect a condensate comprising acetic acid that is then transferred to a suitable holding vessel 210. The stillage is then transferred to a stillage processing vessel 220 configured for heating the stillage thereby condensing and concentrating an oily layer at the bottom of the stillage. The oily layer comprises a fourth class of lignin derivatives well-known to those skilled in these arts, characterized by low molecular weights (LMW) which are then separated from a sugar syrup stream, and a semi-solid/solid waste material discharged into a waste disposal bin 226. The LMW lignins are transferred to a suitable holding container 230 for further processing and/or shipment. The sugar syrup stream, typically comprising at least glucose, mannose and galactose, is transferred to a suitable holding tank 247 prior to further processing and/or shipping. Those skilled in these arts will understand that the sugar syrup stream may be optionally diverted into a sixth optional module (not shown) comprising at least a fermentation vessel communicating with a distillation tower and stillage recovery equipment (not shown) for production of “sugar platform” chemicals exemplified by 1,3 propanediol, lactic acid and the like.
One exemplary embodiment includes provision of a pre-treatment vessel 25 for receiving therein processed lignocellulosic feedstock from the separating device 20 for pre-treatment prior to digestion and extraction by commingling and saturation with a heated digestion/extraction solvent for a suitable period of time. A suitable supply of digestion/extraction solvent may be diverted from pipeline 41 by a valve 42 and delivered to the pre-treatment vessel 25 by pipeline 43. Excess digestion/extraction solvent is squeezed from the processed and pre-treated lignocellulosic feedstock by the mechanical pressures applied by the first auger feeder 30 during transfer of the feedstock into the digestion/extraction vessel 40. The extracted digestion/extraction solvent is recyclable via pipeline 32 back to the pre-treatment vessel 25 for commingling with incoming processed lignocellulosic feedstock and fresh incoming digestion/extraction solvent delivered by pipeline 43. Such pre-treatment of the processed lignocellulosic feedstock prior to its delivery to the digestion/extraction vessel 40 will facilitate the rapid absorption of digestion/extraction solvent during the commingling and cooking process and expedite the digestion of the lignocellulosic feedstock and extraction of components therefrom.
Another exemplary embodiment illustrated in
Another exemplary embodiment illustrated in
However, a problem with anaerobic digestion of semi-solid/solid waste materials is that the first step in the process, i.e., the hydrolysis of complex organic molecules comprising the semi-solid/solid waste materials into a liquid stream containing soluble monomers such as monosaccharides, amino acids and fatty acids, is typically lengthy and variable, while the subsequent steps, i.e., acidification, acetification, and biogas production proceed relatively quickly in comparison to the first step. Consequently, such lengthy and variable hydrolysis in the first step of anaerobic may result in insufficient amounts of biogas production relative to the facility's requirements for power production and/or steam and/or hot water. Accordingly, another embodiment of the present invention, as illustrated in
Another exemplary embodiment of the present invention is illustrated in
Another exemplary embodiment of the present invention is illustrated in
A suitable exemplary modification of the batch digestion/extraction module component of the present invention is illustrated in
While this invention has been described with respect to the exemplary embodiments, those skilled in these arts will understand how to modify and adapt the systems, processes and equipment configurations disclosed herein for continuously receiving and controllably commingling lignocellulosic feedstocks with counter-flowing organic solvents. Certain novel elements disclosed herein for processing a continuous incoming stream of lignocellulosic feedstocks with countercurrent flowing or alternatively, concurrent flowing organic solvents for separating the lignocellulosic materials into component parts and further processing thereof, can be modified for integration into batch systems configured for processing lignocellulosic materials. For example, the black liquors produced in batch systems may be de-lignified and then a portion of the de-lignified black liquor used to pretreat a new, fresh batch of lignocellulosic materials prior to batch organosolv cooking, while the remainder of the de-lignified black liquor is further processed into component parts as disclosed herein. Specifically, the fresh batch of lignocellulosic materials maybe controllably commingled with portions of the de-lignified black liquor for selected periods of time prior to contacting, commingling and impregnating the batch of lignocellulosic materials with suitable organic solvents. Also, it is within the scope of the present invention, to provide turbulence within a batch digestion system wherein a batch of lignocellulosic materials is cooked with organic solvents by providing pressurized flows of the organic solvents within and about the digestion vessel. It is optional to controllably remove portions of the organic solvent/black liquors from the digestion vessel during the cooking period and concurrently introduced fresh organic solvent and/or de-lignified black liquors thereby facilitating and expediting delignification of the lignocellulosic materials. It is also within the scope of the present invention to further process the de-lignified black liquors from the batch lignocellulosic digestion systems to separate and further process components parts exemplified by lignins, furfural, acetic acid, monosaccharides, oligosaccharides, and ethanol among others.
Therefore, in view of numerous changes and variations that will be apparent to persons skilled in these arts, the scope of the present invention is to be considered limited solely by the appended claims.
This application claims priority from our prior provisional application Ser. No. 60/941,220 filed May 31, 2007.
| Number | Date | Country | |
|---|---|---|---|
| 60941220 | May 2007 | US |
