WO2000014120A1 - Procede de solubilisation d'hemicellulose presente dans une matiere lignocellulosique - Google Patents

Procede de solubilisation d'hemicellulose presente dans une matiere lignocellulosique Download PDF

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Publication number
WO2000014120A1
WO2000014120A1 PCT/DK1999/000471 DK9900471W WO0014120A1 WO 2000014120 A1 WO2000014120 A1 WO 2000014120A1 DK 9900471 W DK9900471 W DK 9900471W WO 0014120 A1 WO0014120 A1 WO 0014120A1
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process according
oxygen
lignocellulosic material
hulls
hemicellulose
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PCT/DK1999/000471
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English (en)
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Anne Belinda Thomsen
Jens ØSTERGAARD JENSEN
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Forskningscenter Risø
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Priority to AU55039/99A priority Critical patent/AU5503999A/en
Publication of WO2000014120A1 publication Critical patent/WO2000014120A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
    • C08H8/00—Macromolecular compounds derived from lignocellulosic materials
    • C—CHEMISTRY; METALLURGY
    • C13—SUGAR INDUSTRY
    • C13K—SACCHARIDES OBTAINED FROM NATURAL SOURCES OR BY HYDROLYSIS OF NATURALLY OCCURRING DISACCHARIDES, OLIGOSACCHARIDES OR POLYSACCHARIDES
    • C13K13/00—Sugars not otherwise provided for in this class
    • C13K13/002—Xylose

Definitions

  • the present invention relates to a process, more specifically a wet-oxidative process, whereby a high degree of solubilization of the hemicellulose present in a lignocellulosic material of plant origin, i.e. biomass of plant origin, is achievable.
  • US 3,565,687 discloses a method for manufacturing xylose from cottonseed hulls, wherein a mixture of the hulls and dilute alkali (typically aqueous ammonia solution) is initially boiled under a pressure between ambient pressure and 1 kg/cm 2 to remove "obstructive materials" (such as tannic acid). After separating the thus boiled, solid hull material from the solution phase and - preferably - washing it with water, it is then saccharified (hydrolyzed) by heating with sulfuric acid (typically dilute, aqueous sulfuric acid).
  • alkali typically aqueous ammonia solution
  • sulfuric acid typically dilute, aqueous sulfuric acid
  • xylose is crystallized from the solution, preferably after a purification step employing active carbon and/or ion- exchange resin.
  • US 5,411 ,594 discloses a two-stage, dilute-acid hydrolysis process and apparatus for the continuous saccharification of lignocellulosic biomass, or other cellulosic material feedstocks.
  • the apparatus employed comprises two double-tube heat-exchanger and plug-flow-reactor systems in series, and the process involves reverse interstage transfer- flow, opposite to biomass, of second-stage surplus of: 1. process heat, 2. dilute acid and ⁇ 3. ingredient and solution water, all in an alpha-cellulose hydrolysate, dilute-acid solution; the disclosed process also comprises recycling a fraction of unhydrolyzed alpha-cellulose hydrolysis residue, thereby increasing the hydrolytic conversion of alpha-cellulose to glucose.
  • the process leads to a primary final liquid product containing the combined hydrolysate sugars, including "pentose, hexose and glucose sugars", and a secondary final solid product in the form of lignin residue solids.
  • feedstock materials which are mentioned as being relevant for use in the described process are: lignocellulosic biomass, soft wood, hard wood, wood wastes, logging slash, crop residues. Pine soft wood, sugar cane bagasse and rice hulls are mentioned specifically.
  • EP 0 161 766 A1 relates to a process for converting a lignocellulosic material into a reconstituted composite product.
  • the process in question initially involves treating the lignocellulosic material in divided form with steam (under pressure) to heat the material to a temperature high enough to release hemicellulose, but not exceeding the temperature of carbonization, for a time sufficient to decompose and hydrolyze hemicellulose into free sugars, sugar polymers, dehydrated carbohydrates, furfural products and other decomposition products.
  • these decomposition/hydrolysis products are used to bind the solid, treated lignocellulosic material (i.e.
  • the solid residue remaining after the initial hemicellulose decomposition/hydrolysis treatment into a composite product by means of a thermal treatment.
  • the steam pressure may either be released suddenly (so-called "steam explosion), whereby the treated, residual solid material expands and becomes fibrous and lumpy, or more gradually, whereby the treated, residual solid material more or less retains its original form and bulk.
  • Types of lignocellulosic materials which are mentioned as being relevant for use in the described process are materials derived from forest vegetation and agricultural plants of woody or non-woody nature in the form of stem, stalk, shrub, foliage, bark, root, shell, pod, nut, husk, fibre, straw, vine, grass, bamboo and reed, singularly or in a mixture, and the divided lignocellulosic material may be in the form of particles, fibres, strands, wafers or flakes.
  • materials include rice husks, wheat straw, peanut shells, spruce (shavings), aspen (wafers) and sugar cane bagasse.
  • US 4,181 ,796 discloses a process for obtaining xylan and fibrinous material from xylan- containing vegetable raw material which can be disintegrated by steam pressure treatment and defibration, which process comprises: treating the raw material with saturated steam at a temperature of from 160°C to 230°C for a period of 2 minutes to 4 hours; lixiviating the treated vegetable raw material with an aqueous solution, whereby xylan and xylan fragments are extracted from the disintegrated raw material producing an aqueous xylan extract solution and a fibrinous residue.
  • the lixiviation is preferably carried out successively with water, optionally repeated several times, and with an aqueous alkali solution, likewise optionally repeated several times.
  • the xylan and xylan fragments in the extract solution may further be hydrolyzed, by treatment with "hydroiyzing agents” (e.g. acids), to give xylose.
  • hydroiyzing agents e.g. acids
  • Types of lignocellulosic materials which are mentioned as being relevant for use in the described process are hardwoods, straw, bagasse, grain husks and corn-cob residues. Specifically mentioned materials include maize straw, wheat straw, oat straw, barley straw, red beech (chips or sawdust), poplar (sawdust), birch (sawdust), oak (sawdust) and eucalyptus (sawdust).
  • US 5,352,264 relates to a method for preparing a mixture of polyhydroxycarboxylic acids, carbohydrates and alcohols with plant growth regulating and fruit development properties.
  • "vegetable residues” primarily rice and/or oat hulls, which are rich in hemicellulose of the glucoxylan type
  • dilute aqueous nitric acid in a liquid:solid ratio of 3:1 to 5:1 to extract pentoses (e.g. xylose).
  • the pentoses are subsequently oxidized in situ (i.e. without any isolation thereof from the mixture of treated vegetable material and extract solution) by adding further nitric acid and heating at a temperature of 75-85°C by injection of steam at a pressure of 7-9 kg/cm 2 for a period of 8-20 hours.
  • wet oxidation as employed in the study in question (reaction involving oxygen and water at an elevated temperature and pressure, performed in a recirculatory "loop reactor") is efficient for breaking down lignin to carboxylic acids and for bringing cellulose and hemicellulose into a form in which a high degree of conversion of, in particular, cellulose to glucose is achievable by subsequent treatment with a cellulolytic enzyme (i.e. a cellulase).
  • a cellulolytic enzyme i.e. a cellulase
  • reaction vessel for both steaming and wet oxidation achieved up to about 55% solubilization/recovery of hemicellulose with steaming of birch wood (treatment time 10 minutes; temperatures from 170°C to 210°C), whereas less than 35% solubilization/recovery was achieved with wet oxidation (60 g/L material; 6.5 g/L sodium carbonate; 12 bar oxygen pressure; treatment time 15 minutes; temperatures from 185°C to 210°C).
  • One aspect of the invention thus relates to a process for solubiiizing hemicellulose present in such a lignocellulosic material, wherein the lignocellulosic material in question is heated in a liquid, aqueous medium in a reactor in the presence of an appropriate oxidizing agent
  • the amount of oxidizing agent employed will in general be an amount which is effective to substantially prevent or minimize formation of undesirable reduction products, e g furfural and/or furfural derivatives (vide infra), and at the same time lead to improved yield of monosaccha ⁇ de(s) obtainable by hydrolysis of species present in the solution produced in the solubilization of hemicellulose
  • a well suited oxidizing agent is oxygen per se, and preferred processes of the invention are performed in the presence of oxygen introduced into the reactor at an initial partial pressure of oxygen equal to or exceeding ambient partial pressure of oxygen.
  • preferred embodiments of the process of the invention are those wherein at least 80% or more, preferably at least 90%, more preferably at least 95%, of the hemicellulose present in the lignocellulosic material employed is solubilized.
  • cellulose and any remaining hemicellulose present in the unsolubilized solid residue is rendered more susceptible (relative to cellulose and hemicellulose in lignocellulosic material which has not been treated in the manner of the invention) to chemical or enzymatic hydrolysis to give the constituent monosaccharides (D-glucose in the case of cellulose, and primarily D-xylose and/or other pentoses in the case of most hemicelluloses), thereby facilitating, inter alia, the application of further, subsequent procedures (such as fermentation to convert glucose to ethanol or to convert xylose to xylitol or lactose.
  • the resulting product or products may be isolated and purified by known methods.
  • microorganism- and/or enzyme-inhibitory substances which may subsequently inhibit microorganisms [e.g. microorganisms employed to ferment sugars (such as glucose derived from, in particular, cellulose) to ethanol] and/or inhibit the catalytic action of enzymes added for the purpose of facilitating, for example, hydrolysis of cellulose to glucose or hydrolysis of components of solubilized hemicellulose (such as xylans, mannans or arabinans) to the corresponding monosaccharides.
  • microorganisms e.g. microorganisms employed to ferment sugars (such as glucose derived from, in particular, cellulose) to ethanol] and/or inhibit the catalytic action of enzymes added for the purpose of facilitating, for example, hydrolysis of cellulose to glucose or hydrolysis of components of solubilized hemicellulose (such as xylans, mannans or arabinans) to the corresponding monosaccharides.
  • the unsolubilized solid residue remaining after performing the process of the invention appears to be well suited for use as animal feed, or as a supplement to animal feed, for animals - notably ruminants, such as cattle, sheep, goats or deer - of importance in farming or agriculture.
  • the solid residue which is rich in cellulose fibres, also appears to have applications in the areas of plant-growth media (e.g. in potting soils/composts and in organic media of the peat moss type and the like), soil-improvement agents (materials added to soil to improve, e.g., water retention, soil aeration, root penetration, etc.) and composite materials [structural materials which are produced by combining the solid residue with one or more other materials (e.g.
  • wet oxidation and “wet-oxidative” as employed in relation to processes according to the invention disclosed in the present specification and claims are intended to denote a process which takes place in a liquid, aqueous medium, i.e. liquid water or a liquid medium containing at least a substantial proportion of liquid water, in the presence of an oxidizing agent which reacts oxidatively in some manner and to some extent with one or more components or species present (as a solid or solids, and/or in dissolved form) in the liquid medium.
  • the process normally takes place at an elevated temperature, i.e.
  • hemicellulose is intended to indicate conversion of hemicellulose from a substantially insoluble material (in the lignocellulosic material to be treated) to species (including soluble poly- or oligosaccharide species) which may be found in the liquid phase (solution phase) remaining after the process; any relatively volatile species (e.g. carbon dioxide or lower carboxylic acids) which may be formed to some extent from hemicellulose during the process, but which partly or completely escape from the liquid phase are regarded in this context as being solubilization products of hemicellulose.
  • a substantially insoluble material in the lignocellulosic material to be treated
  • species including soluble poly- or oligosaccharide species
  • any relatively volatile species e.g. carbon dioxide or lower carboxylic acids
  • the degree of hemicellulose solubilization may be calculated from a determination of the hemicellulose content of (i) the lignocellulosic starting material (calculated as dried material) and (ii) the quantitatively isolated solid residue (calculated as dried material) remaining after treatment of a known quantity of the lignocellulosic material in question by the process according to the invention.
  • a suitable method for determining the hemicellulose content of a lignocellulosic starting material and the solid residue remaining after treatment thereof is that described by H.K. Goering and P.J. van Soest in: Forage fiber analyses (apparatus, reagents and some applications), Agricultural Handbook No. 379, Agricultural Research Service, United States Department of Agriculture, Washington DC, pp. 1 -20.
  • Lignocellulosic materials As already indicated, hemicellulose solubilization processes according to the invention employ hemicellulose-containing lignocellulosic material of plant origin, the lignocellulose which is the principal component of such materials being built up predominantly of cellulose, hemicellulose and lignin.
  • Cellulose which is a ⁇ -glucan built up of anhydro D-glucose units, is the main structural component of plant cell walls and normally constitutes about 35-60% by weight (% w/w) of lignocellulosic materials.
  • Hemicellulose is the term used to denote non-cellulosic polysaccharides associated with cellulose in plant tissues. Hemicellulose frequently constitutes about 20-35 % w/w of lignocellulosic materials, and the majority of hemicelluloses consist predominantly of polymers based on pentose (five-carbon) sugar units, such as D-xylose and D-arabinose units, although more minor proportions of hexose (six- carbon) sugar units, such as D-glucose and D-mannose units, are generally also present.
  • pentose (five-carbon) sugar units such as D-xylose and D-arabinose units
  • hexose (six- carbon) sugar units such as D-glucose and D-mannose units
  • Lignin which is a complex, cross-linked polymer based on variously substituted p-hydroxyphenylpropane units, generally constitutes about 10-30% w/w of lignocellulosic materials. It is believed that lignin functions, inter alia, as a physical barrier to the direct bioconversion (e.g. by fermenting microorganisms) of cellulose and hemicellulose in lignocellulosic materials which have not been subjected to some kind of pretreatment process (which may very suitably be a process according to the present invention) to disrupt the structure of lignocellulose.
  • lignocellulosic materials in the context of the invention are so-called hulls.
  • hull generally denotes the outer covering, rind, shell, pod or husk of any fruit or seed, but the term as employed herein also embraces, for example, the outer covering of an ear of maize.
  • Relevant hulls include hulls selected among the following:
  • oat Avena spp., such as A. sativa
  • barley ⁇ Hordeum spp. such as H. vulgare
  • wheat Triticum spp., including T. durum
  • rye Secal cereale
  • rice Oryza spp.
  • millet e.g. species of Digitaria, Panicum, Paspalum, Pennisetum or Setaria
  • sorghum Sorghum spp., including S. bicolor var. durra (known, inter alia, as "durra") and milo]
  • buckwheat F.gopyrum spp.
  • esculentum , maize [also known as corn (Zea mays), including sweetcorn], corn cob, rape-seed (from Brassica spp., such as B. napus, B. napus subsp. rapifera or B. napus subsp. oleifera), cotton-seed (from Gossypium spp., such as G. heraceum), almond [Prunus dulcis, including both sweet and bitter almond) and sunflower seed (Helianthus spp., such as H. annuus).
  • Brassica spp. such as B. napus, B. napus subsp. rapifera or B. napus subsp. oleifera
  • cotton-seed from Gossypium spp., such as G. heraceum
  • almond Panus dulcis, including both sweet and bitter almond
  • sunflower seed Helianthus spp., such as H. annuus
  • Hulls of cereals i.e. hulls of gramineous plants which yield edible grain or seed, including not only those mentioned among the above, but also hulls of cereals other than those mentioned among the above, are generally of interest in the context of the invention, and preferred hulls, such as oat hulls and barley hulls, belong to this category.
  • hemicellulose which when fully hydrolyzed yields monosaccharides with a high proportion of D-xylose), it is possible to remove at least 95 % or more [at least 97 % in one of the experiments reported herein (vide infra)] of the hemicellulose from the hulls - in contrast to a maximum of about 80% removal from wheat straw (which contains about 30-35% w/w hemicellulose) and about 75% removal from loblolly pine (which contains about 24% w/w hemicellulose). It is further apparent that high yields of monosaccharides (e.g. D-xylose) are obtainable from the solubilized products present in the solution phase produced in a process according to the invention employing oat hulls.
  • monosaccharides e.g. D-xylose
  • hulls of relevance in relation to processes of the invention include, for example, palm shells, peanut shells, coconut shells, other types of nut shells, and coconut husk.
  • Peanut shells are interesting in this respect.
  • cereal grain or seed hulls in general including oat hulls as employed in the working examples reported herein, have in their native form sufficiently small dimensions and a sufficiently high surface area to mass ratio to enable them to be used directly, without prior comminution, as lignocellulosic materials in a process according to the present invention.
  • the initial ratio of solid, lignocellulosic material to liquid, aqueous medium (e.g. water) in the reactor will generally be in the range of 0.02-1 kg/liter, often 0.05-0.35 kg/liter, such as 0.05-0.2 kg/liter, depending on the form, bulk and/or dimensions of the lignocellulosic material as treated.
  • aqueous medium e.g. water
  • lignocellulosic materials e.g. shells of certain nuts
  • a comminution procedure e.g. by milling, abrading, grinding, crushing, chopping, chipping or the like
  • enhancing e.g., the physical mobility, mixability, ratio of surface area to mass and the like of the material.
  • an organic solvent e.g. an alcohol, hydrocarbon, chlorinated hydrocarbon or the like
  • solvent-extractable, water-insoluble substances such as fats, oils or aroma substances
  • Oxidizing agents As already indicated, (vide supra), a preferred oxidizing agent in the context of processes according to the invention is oxygen perse.
  • oxidizing agents which may - at suitable concentrations and under suitable conditions of temperature and reaction time - be appropriate for use in a process according to the invention include, in particular, hydrogen peroxide.
  • Hydrogen peroxide is very soluble in water, is readily available commercially as aqueous solutions of concentration ranging from relatively dilute (e.g. hydrogen peroxide concentrations of around 3% w/w ) to relatively concentrated (e.g. hydrogen peroxide concentrations of about 30-35% w/w) and is - like oxygen - a very acceptable oxidizing agent from an environmental point of view.
  • Hydrogen peroxide is thus generally well suited for inclusion - either alone or in combination with one or more other oxidizing agents, e.g. oxygen - as an oxidizing agent in the liquid, aqueous medium employed in processes according to the invention, and in such cases the initial concentration of hydrogen peroxide in the liquid, aqueous medium will normally suitably be in the range of 0.5-10% w/w.
  • oxidizing agents e.g. oxygen - as an oxidizing agent in the liquid, aqueous medium employed in processes according to the invention, and in such cases the initial concentration of hydrogen peroxide in the liquid, aqueous medium will normally suitably be in the range of 0.5-10% w/w.
  • Oxidizing substances which are not well-suited as oxidizing agents in the context of the process of the invention include oxidizing acids, such as concentrated or dilute nitric acid.
  • oxygen is employed as oxidizing agent
  • initial oxygen partial pressures of at least 0.5 bar, normally in the range of 0.5-35 bar.
  • Typical initial partial pressures of oxygen will be in the range of 1-15 bar, such as 3-12 bar, e.g. 5-12 bar.
  • the solubility of oxygen in water at temperatures of relevance for the process of the invention increases with oxygen partial pressure, and the use of such elevated partial pressures of oxygen can thus be advantageous in ensuring the availability of sufficient oxygen in dissolved form.
  • the oxygen employed may be added in the form of substantially pure oxygen or in the form of an oxygen-containing gas mixture (such as atmospheric air) which in addition to oxygen is constituted by one or more other gases (e g nitrogen and/or an inert gas, such as argon) that are not detrimental to the performance of the process of the invention; it will, however, often be advantageous to employ substantially pure oxygen (such as oxygen of >99% purity, which is readily commercially available in conventional gas cylinders under pressure).
  • an oxygen-containing gas mixture such as atmospheric air
  • other gases e g nitrogen and/or an inert gas, such as argon
  • an appropriate, effective quantity of oxygen may - particularly in the case of batch processes in which a chosen quantity (batch) of appropriate lignocellulosic material is treated according to the invention in a reactor which may be closed and, optionally, pressurized - be introduced into the reactor in question as a single charge at an appropriate initial pressure.
  • Reactors of this type employed in batch processes according to the invention will, in addition to containing a certain volume of aqueous liquid phase in which the solid lignocellulosic material in question is contained, generally enclose a free volume or headspace above the liquid phase, and disregarding other considerations it will then be apparent that the greater the ratio of the headspace volume to the liquid phase volume, the lower the initial pressure (partial pressure) of oxygen that will be required to ensure the presence of an effective amount of oxygen gas within the reactor; the partial pressure of oxygen in the reactor - measured at the initial temperature in the reactor or reaction vessel - will decrease during the course of the process of the invention owing to consumption of oxygen in the oxidation reactions which occur.
  • a batch reactor which can be closed and pressurized e.g. a loop-reactor of the type described and employed in connection with the working examples provided herein
  • an aqueous liquid phase containing about 60 grams of lignocellulosic material per liter of liquid phase
  • an appropriate effective amount of oxygen will typically be ensured by employing a ratio of headspace volume to liquid phase volume of about 1 :1 and an initial oxygen pressure (partial pressure) in the range of 0.2-12 bar.
  • solubility of oxygen (and a number of other gases, including nitrogen) in water at partial oxygen pressures of interest in the present context increases with temperature above about 100°C, and increases rapidly with temperature above about 140°C [see Pray et al., Solubility of Hydrogen, Oxygen, Nitrogen and Helium in Water, Ind. Eng. Chem. 44 (1952) pp.
  • oxygen or an oxygen-containing gas mixture may be introduced essentially continuously (or at least at suitably frequent intervals) into the reactor at a suitable pressure so as to ensure the continued availability of sufficient oxidizing agent.
  • Reactors i.e. vessels, containers and the like in which the process of the invention is performed
  • Reactors suitable for use in a process of the invention are generally closed (not open to the surrounding atmosphere) and, optionally, pressurizable reactors; some types of closed, pressurizable reactors suitable for, in particular, batch-type processes according to the invention have already been mentioned above.
  • reactors for performing batch or essentially continuous processes include substantially vertically disposed reactors in which the liquid, aqueous medium and the lignocellulosic material in question may be contained and into which oxygen or an oxygen-containing gas mixture (suitably air) may be introduced - continuously or at intervals - under pressure via one or more inlets, ports, valves or the like situated at or near the bottom of, and/or at other locations along the length of, the reactor containing the liquid, aqueous medium with the lignocellulosic material; such reactors, which may suitably, but optionally, have an upper headspace or free volume, may be essentially cylindrical, tubular or of any other appropriate form.
  • Vertical tower reactors suitable for use in the context of the invention are described, for example, in GB 706,686 and GB 812,832.
  • Reactors for performing continuous or essentially continuous processes in accordance with the invention may, for example, also be tubular or substantially tubular reactors - very suitably essentially horizontally disposed - through which the liquid phase is pumped or otherwise driven, and which in principle have little or no headspace (free volume) available for, e.g., oxygen in gaseous form.
  • Such reactors will normally comprise one or more appropriately positioned injection inlets, ports, valves or the like for admitting oxygen gas (or, less preferably, an oxygen-containing gas mixture) under pressure more or less directly into the liquid phase - e.g.
  • temperatures in the vicinity of, or in excess of, 100°C In general, temperatures in the range of 120-240°C, such as 130-220°C, more typically in the range of 150-220°C, will be be appropriate for the vast majority of embodiments of the process according to the invention, and when using lignocellulosic materials of preferred types (vide supra) it will be usual to employ temperatures in the range of 160-210°C, such as 180-210°C. Good results appear to be obtainable with temperatures around 185- 195°C. As already indicated, the temperature employed should be a temperature at which boiling of the liquid, aqueous medium does not occur under the pressure conditions in question.
  • Heat may be supplied to the reaction mixture (notably the liquid phase/lignocellulosic material) by any suitable method, such as by immersing the reactor or reaction vessel in an appropriate heating bath (comprising, e.g., an oil, a molten salt or molten salt mixture, superheated steam, etc.), by means of thermally conductive (typically metal) tubing which is wound around the outside of the reactor or reaction vessel, and/or is immersed in the reaction medium itself, and through which suitably hot oil, superheated steam or the like is passed, or - similarly - by means of one or more electrical resistance heating elements wound around the outside of the reactor or reaction vessel and/or immersed in the reaction medium.
  • suitable methods of heating include induction heating (e.g. of a metal reactor casing) and microwave heating.
  • Heating of the lignocellulosic material(s) in the liquid, aqueous medium in the manner according to the invention will normally be carried out for a period of time ranging from about 1 minute to about 1 hour (i.e. about 1-60 minutes), depending not only on the other reaction conditions (e.g. the reaction temperature, and the type and concentration of oxidizing agent) employed, but also on the reactivity (rate of reaction) of the lignocellulosic material.
  • Practicable embodiments of the process of the invention will normally employ reaction times in the range of 5-30 minutes, often 5-15 minutes, and when other reaction conditions are in preferred ranges [such as an oxygen (partial) pressure in the range of about 3-12 bar, e.g. 3-10 bar, and a temperature in the range of about 160-210°C] suitable reaction times will often lie in the range of about 10 to about 15 minutes.
  • a wet-oxidation process according to the invention may be carried out with satisfactory results without any adjustment of the pH of the liquid reaction mixture before, or during, the performance of the process; thus, for example, as illustrated by the working examples herein (vide infra), excellent results with respect to (i) hemicellulose removal/solubilization and (ii) subsequent formation/yield of monosaccharide(s) are achievable without the need for addition of a pH-adjusting agent (e.g. an alkali or base) to the liquid medium.
  • a pH-adjusting agent e.g. an alkali or base
  • an appropriate alkali or base e.g. an alkali metal hydroxide such as sodium or potassium hydroxide, an alkaline earth metal hydroxide such as calcium hydroxide, an alkali metal carbonate such as sodium or potassium carbonate or another base such as ammonia
  • an appropriate alkali or base e.g. an alkali metal hydroxide such as sodium or potassium hydroxide, an alkaline earth metal hydroxide such as calcium hydroxide, an alkali metal carbonate such as sodium or potassium carbonate or another base such as ammonia
  • a buffer system e.g. an alkali metal hydroxide such as sodium or potassium hydroxide, an alkaline earth metal hydroxide such as calcium hydroxide, an alkali metal carbonate such as sodium or potassium carbonate or another base such as ammonia
  • the immediate products of the process of the invention are (a) a liquid phase (solution) comprising, inter alia, soluble poly- and/or oligosaccharide hydrolysis products of hemicellulose, and (b) a solid, unsolubilized residue normally comprising a substantial proportion of cellulose together with some hemicellulose and some lignin. It will thus normally be appropriate to separate the liquid phase from the solid residue (e.g. by simple filtration) before subjecting the solid phase or the liquid phase to any further treatment.
  • Chemical hydrolysis may normally very suitably be achieved in a known manner by treatment with an acid, such as treatment with dilute (e.g. 2-10% w/w, typically 4-7% w/w) aqueous sulfuric acid, at a temperature in the range of about 100-150°C, e.g. around 120°C, for a period of 5-15 minutes, such as 5-10 minutes. Treatment with ca. 4% w/w sulfuric acid for 5-10 minutes at ca. 120°C is often very suitable.
  • an acid such as treatment with dilute (e.g. 2-10% w/w, typically 4-7% w/w) aqueous sulfuric acid
  • Enzymatic hydrolysis may likewise be achieved in a known manner by treatment with an appropriate carbohydrase (a glycosidase, EC 3.2), e.g. a xylanase (such as an endo-1 ,4- ⁇ -xylanase, EC 3.2.1.8) in the case of hydrolysis of xylans to xylose, or a ⁇ -glucanase [such as an endo-1 ,3(4)- ⁇ -glucanase, EC 3.2.1.6] in the case of hydrolysis of soluble fragments of cellulose to glucose.
  • carbohydrase a glycosidase, EC 3.2
  • a xylanase such as an endo-1 ,4- ⁇ -xylanase, EC 3.2.1.8
  • a ⁇ -glucanase such as an endo-1 ,3(4)- ⁇ -glucanase, EC 3.2.1.6
  • the monosaccharide product(s) obtained by hydrolysis may be purified and isolated by well-known procedures, and they may, where appropriate, be subjected to further transformation to give other desired products.
  • D-xylose - obtained by hydrolysis of solubilized, xylan-containing hemicellulose - may, for example, be transformed to xylitol by established methods (e.g by catalytic hydrogenation or by fermentation, both of which are mentioned in the foregoing)
  • the present invention also embraces products obtained by, or obtainable by, a process according to the invention as disclosed herein.
  • the invention encompasses solid products obtainable as a solid residue by a process according to the invention, as well as liquid products obtainable as a liquid phase (solution phase) by a process according to the invention.
  • the invention embraces, for example, the use of a solid product of the invention as, or in the manufacture of, an animal feed an animal feed additive, a plant-growth medium, a soil-improvement agent or a composite material.
  • the invention also embraces the use of a liquid product of the invention in the production of a monosaccharide or a derivative thereof, such as a substantially pure, isolated monosaccharide or derivative thereof;
  • a monosaccharide or a derivative thereof such as a substantially pure, isolated monosaccharide or derivative thereof;
  • the hemicellulose in the lignocellulosic material employed in the process according to the invention is a hemicellulose containing polysaccharides built up wholly or largely of D-xylose units
  • the monosaccharide in question may suitably be D-xyiose
  • the derivative thereof may suitably be xylitol (xylo- pentane-1 ,2,3,4, 5-pentol).
  • Oat Hulls were obtained from a Danish plant which produces oatmeal products, such as rolled oats ("porridge oats”), from oat grain, and were used as supplied.
  • the loop reactor in question which has previously been described by Bjerre et al. (loc. cit.) is made of Sandvik Sanicro 28 acid- and alkali-resistant steel (27% Chromium, 31% Nickel, 3.5% Molybdenum, 1% Copper), and comprises a steel container in the form of a cylinder having an inner diameter of about 11 cm and a height of 18 cm, and an externally placed steel tube with a length of 160 cm and an inner diameter of 22 mm.
  • One end of the tube is welded to the outside of the bottom of the container, and the other end is welded to the outside of the lower part of the side of the container.
  • a centrifugal impeller wheel which provides the recirculatory flow of the suspension/solution to be treated.
  • the impeller wheel is driven by an electric motor via a magnetic coupling, the electric motor being placed outside the container.
  • the top of the container is equipped with a steel lid which may be tightly bolted down against a flange assembly.
  • the lid is equipped with an inlet valve for admitting air, oxygen or any other appropriate oxygen-containing gas (typically from a high-pressure gas cylinder) or other gas/vapour to the air-space (free volume) above the liquid phase in the loop reactor.
  • An inlet valve for admitting air, oxygen or any other appropriate oxygen-containing gas (typically from a high-pressure gas cylinder) or other gas/vapour to the air-space (free volume) above the liquid phase in the loop reactor.
  • Fig. 1 A sectional view of the loop reactor is shown in Fig. 1.
  • the loop reactor was heated by immersing it in a thermostatted bath of molten salt consisting of a 1 :1 (w/w) mixture of anhydrous sodium nitrate and anhydrous sodium nitrite, and it was subsequently cooled by immersion in cold water.
  • molten salt consisting of a 1 :1 (w/w) mixture of anhydrous sodium nitrate and anhydrous sodium nitrite
  • the desired temperature was typically attained within about 3 minutes; with respect to cooling, about 1 minute was required to attain thermal equilibrium.
  • the loop reactor thus constitutes a closed-loop system in which a reaction mixture - in the present examples in the form of a suspension of lignocellulosic biomass in an aqueous medium under some pressure of oxygen- containing gas - introduced into the container may be recirculated for a chosen length of time at a chosen temperature.
  • the loop reactor has a capacity of 1 liter of liquid suspension, and the remaining free volume of 1 liter can, where appropriate, be pressurized with air, oxygen or the like from a gas cylinder.
  • each suspension was filtered through filter paper on a B ⁇ chner funnel, and the solid residue (filter cake) on the filter was washed with 200 mL deionized water, and dried at 20°C and a relative humidity of 65% .
  • each filtrate containing solubilized hemicellulose (vide infra), was measured using a pH meter.
  • the various filtrates were subjected to acid hydrolysis (4% w/v aqueous H 2 S0 4 ) at 1 21 °C for 10 minutes, and the hydrolysates were purified as described by Bjerre et al. in Quantification of solubilized hemicellulose from pretreated lignocellulose by acid hydrolysis and high performance liquid chromatography, in publication Ris ⁇ -R-855 (EN), Ris ⁇ National Laboratory (1 996).
  • Monosaccharides xylose, arabinose and glucose were quantified (vide infra) by means of High Performance Liquid Chromatography (HPLC) using an AminexTM HPX- 87H column (BioRadTM) with 0.004 M aqueous sulfuric acid as eluent.
  • HPLC High Performance Liquid Chromatography
  • Table 2 summarizes the analytical results for the filter cakes from the various treatments as listed in Table 1 , above; for comparison purposes, data are also given for a sample of dried, but otherwise untreated oat hulls as employed in 01 -05.
  • Table 3 gives the calculated percentage removal of hemicellulose from oat hulls following each of the treatments 01 -05; the data given take account of a water content in the filter cakes and the untreated hulls (dried at 20°C and relative humidity 65 %) of ca. 1 0% w/w (determined by weighing the material before and after drying in a drying cabinet at 105 °C for 2 hours.
  • Table 4 summarizes the analytical results for the various filtrates from 01 -05. TABLE 2. Analysis of filter cake material
  • Table 2 It can be seen from Table 2 that the starting material (oat hulls) employed has a high content of hemicellulose, and rather less cellulose. As is apparent from Table 3, temperature and treatment time are important parameters with regard to removal of hemicellulose. However, in relation to the value of the invention described herein in the production of sugars from hemicellulose solubilization products, Table 4 demonstrates (see the results for 04 and 05) that raising the initial oxygen partial pressure in the reaction vessel from ambient partial pressure to 9 bar leads not only to a significant increase in the degree of removal (solubilization) of hemicellulose, but also to a marked increase in the yields of the three monosaccharides in question.
  • oxidizing conditions in the process of the invention thus appears to have a beneficial effect with regard, inter alia, to hindering degradation of hydrolyzable sugar precursors (such as soluble poly- and/or oligosaccharide fragments of hemicellulose) formed in the solubilization process.
  • hydrolyzable sugar precursors such as soluble poly- and/or oligosaccharide fragments of hemicellulose

Abstract

L'invention se rapporte à un procédé de solubilisation d'hémicellulose présente dans une matière lignocellulosique telle que des coques de fruits ou des enveloppes de graines. Selon ce procédé, on chauffe la matière lignocellulosique en question dans un milieu aqueux, liquide, à l'intérieur d'un réacteur, en présence d'un agent d'oxydation, par exemple de l'oxygène. Les produits solides qu'il est possible d'obtenir sous forme de résidu solide restant après la mise en oeuvre du procédé en question s'avèrent utiles, notamment dans la fabrication d'aliments pour animaux, d'agents d'amélioration du sol ou de matières composites, et les produits liquides qui sont récupérables sous forme de phase liquide après mise en oeuvre dudit procédé peuvent être utilisés pour produire des monosaccharides et/ou des dérivés de monosaccharides (du type xylose et/ou xylitol).
PCT/DK1999/000471 1998-09-09 1999-09-07 Procede de solubilisation d'hemicellulose presente dans une matiere lignocellulosique WO2000014120A1 (fr)

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AU55039/99A AU5503999A (en) 1998-09-09 1999-09-07 A process for solubilizing hemicellulose present in a lignocellulosic material

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6555350B2 (en) 2000-02-17 2003-04-29 Forskningscenter Riso Method for processing lignocellulosic material
WO2006017786A2 (fr) * 2004-08-06 2006-02-16 Grain Processing Corporation Procede aqueux en continu permettant d'isoler l'hemicellulose des enveloppes de mais et d'autres enveloppes de vegetaux
WO2006032282A1 (fr) 2004-09-24 2006-03-30 Cambi Bioethanol Aps Procede de traitement de biomasse et de dechets organiques pour la generation de produits a base biologique desires
CN103937005A (zh) * 2014-04-29 2014-07-23 天津博生源肥料科技发展有限公司 一种农业用可溶性腐植酸节能环保生产方法
US9034620B2 (en) 2010-03-19 2015-05-19 Poet Research, Inc. System for the treatment of biomass to facilitate the production of ethanol
WO2016066752A1 (fr) 2014-10-29 2016-05-06 Cambi Technology As Procédé et dispositif pour le traitement de biomasse et de déchets organiques
US9611158B2 (en) 2009-04-01 2017-04-04 Earth Renewal Group, Llc Waste treatment process
US9663807B2 (en) 2011-01-18 2017-05-30 Poet Research, Inc. Systems and methods for hydrolysis of biomass
US9982317B2 (en) 2011-07-07 2018-05-29 Poet Research, Inc. Systems and methods for acid recycle
US10533203B2 (en) 2010-03-19 2020-01-14 Poet Research, Inc. System for the treatment of biomass

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GB1598513A (en) * 1978-02-03 1981-09-23 Cotton Inc Process for obtaining seed hull commodities including cellulosic fibers and xylitol

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Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6555350B2 (en) 2000-02-17 2003-04-29 Forskningscenter Riso Method for processing lignocellulosic material
WO2006017786A2 (fr) * 2004-08-06 2006-02-16 Grain Processing Corporation Procede aqueux en continu permettant d'isoler l'hemicellulose des enveloppes de mais et d'autres enveloppes de vegetaux
WO2006017786A3 (fr) * 2004-08-06 2006-06-15 Grain Processing Corp Procede aqueux en continu permettant d'isoler l'hemicellulose des enveloppes de mais et d'autres enveloppes de vegetaux
WO2006032282A1 (fr) 2004-09-24 2006-03-30 Cambi Bioethanol Aps Procede de traitement de biomasse et de dechets organiques pour la generation de produits a base biologique desires
US9902632B2 (en) 2009-04-01 2018-02-27 Earth Renewal Group, Llc Waste treatment method
US9611158B2 (en) 2009-04-01 2017-04-04 Earth Renewal Group, Llc Waste treatment process
US9034620B2 (en) 2010-03-19 2015-05-19 Poet Research, Inc. System for the treatment of biomass to facilitate the production of ethanol
US10533203B2 (en) 2010-03-19 2020-01-14 Poet Research, Inc. System for the treatment of biomass
US9663807B2 (en) 2011-01-18 2017-05-30 Poet Research, Inc. Systems and methods for hydrolysis of biomass
US9982317B2 (en) 2011-07-07 2018-05-29 Poet Research, Inc. Systems and methods for acid recycle
US10731229B2 (en) 2011-07-07 2020-08-04 Poet Research, Inc. Systems and methods for acid recycle
CN103937005A (zh) * 2014-04-29 2014-07-23 天津博生源肥料科技发展有限公司 一种农业用可溶性腐植酸节能环保生产方法
WO2016066752A1 (fr) 2014-10-29 2016-05-06 Cambi Technology As Procédé et dispositif pour le traitement de biomasse et de déchets organiques
US10214751B2 (en) 2014-10-29 2019-02-26 Cambi Technology As Method and device for treating biomass and organic waste

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