Abstract: A modular process for organosolv fractionation of lignocellulosic feedstocks into component parts and further processing of said component parts into at least fuel-grade ethanol and four classes of lignin derivatives. The modular process comprises a first processing module configured for physico-chemically digesting lignocellulosic feedstocks with an organic solvent thereby producing a cellulosic solids fraction and a liquid fraction, a second processing module configured for producing at least a fuel-grade ethanol and a first class of novel lignin derivatives from the cellulosic solids fraction, a third processing module configured for separating a second class and a third class of lignin derivatives from the liquid fraction and further processing the liquid fraction to produce a distillate and a stillage, a fourth processing module configured for separating a fourth class of lignin derivatives from the stillage and further processing the stillage to produce a sugar syrup.

Abstract: The invention relates to a method for separating hemicelluloses from a biomass containing hemicelluloses. The method includes the steps of: a) extracting the hemicelluloses from the biomass containing hemicelluloses by treating them with a complex compound in an aqueous solution, and forming a soluble hemicellulose complex, and b) separating the complexed hemicelluloses from the biomass. The method is especially suitable for producing high-quality chemical conversion pulp from raw cellulose. The products produced with the method of the invention have a high degree of purity, and the method is extremely economical and causes few emissions. Hemicelluloses in a pure form can be obtained as by-products of the method.

Abstract: This invention relates to a process of treating a lignocellulosic material to produce bio-ethanol. The process includes the steps of: (a) exposing the lignocellulosic material to conditions including a pH not less than about 8, and steam at a first pressure, to produce a step (a) product; (b) explosively discharging the step (a) product to a second pressure less than the first pressure to produce a step (b) product; and (c) further processing the step (b) product to produce bio-ethanol and other co-products. In another embodiment, the invention relates to a conical auger fractionation column. The fractionation column includes a column body having an input and an output. A conical filter is positioned inside the column body, the filter having a larger diameter end directed toward the input and a smaller diameter end directed toward the output.

Abstract: Systems and methods by which to subject cellulosic fibers to alkaline treatment are provided. The systems and methods of the invention include equipment, such as nanofiltration units and slurry concentrators, which result in a lowered overall consumption of alkaline solution during alkaline treatment. The systems and methods of the invention further allow the components of hemicaustic streams produced by such alkaline treatments to be utilized in higher value end uses.

Abstract: A pressure diffuser is disclosed having a pressurized vessel having an inlet adapted to receive a slurry of cellulosic fibrous material and cooking liquor; an outer chamber having an assembly of screens, wherein the slurry flows through the outer chamber and a portion of the cooking liquor is extracted through the screens; a center chamber to receive cooking liquor extracted through the screens; an inner head capping the center chamber, wherein the inner head is impervious to gases escaping from the cooking liquor and collecting underneath the inner head, and a gas exhaust conduit extending from the inner head to an outlet external of the pressure diffuser, wherein the conduit has an inlet below the inner head.

Abstract: A method of producing useful products, for example, gypsum and sugar products, from pulp and paper industry wastes.

Abstract: A multi-function process is described for the separation of cellulose fibers from the other constituents of lignocellulosic biomass such as found in trees, grasses, agricultural waste, and waste paper with application in the preparation of feedstocks for use in the manufacture of paper, plastics, ethanol, and other chemicals. This process minimizes waste disposal problems since it uses only steam, water, and oxygen at elevated temperature in the range of 180° C. to 240° C. for 1 to 10 minutes plus a small amount of chemical reagents to maintain pH in the range 8 to 13. An energy recuperation function is important to the economic viability of the process.

Abstract: A multi-function process is described for the separation of cellulose fibers from the other constituents of lignocellulosic biomass such as found in trees, grasses, agricultural waste, and waste paper with application in the preparation of feedstocks for use in the manufacture of paper, plastics, ethanol, and other chemicals. This process minimizes waste disposal problems since it uses only steam, water, and oxygen at elevated temperature in the range of 180° C. to 240° C. for 1 to 10 minutes plus a small amount of chemical reagents to maintain pH in the range 8 to 13. An energy recuperation function is important to the economic viability of the process.

Abstract: In a tall oil refining operating plant, a warm water loop is disclosed for cooling the tall oil heads fraction extracted from the crude tall oil, rather than the conventional use of cold water. This avoids condensation and the subsequent solidification of athraquinone pulping aid remaining in the crude tall oil; thus, avoiding fouling of the cooling towers. The temperature of the warm-water is controlled automatically by tempering the cold water entering the warm water “cooling” loop, while removing excessively warm water from said loop to the cooling tower system, as needed.

Abstract: By the utilization of a jet ejector (such as a thermocompresser) in a cellulose chemical pulp mill, it is possible to effectively increase the utilization of steam. The volume of steam from a flash tank which flashes black liquor from a pulp digester may be increased (e.g. at least about 10%), while the volume and temperature of the liquor discharged from the flash tank are decreased and its concentration increased, by operatively connecting the jet ejector to the steam discharge from a flash tank. The jet ejector is supplied with higher pressure steam from another source which can result in a low pressure or partial vacuum condition in the flash tank. The flash tank may be a single flash tank or one of a series of flash tanks, and an ejector can be associated with at least another flash tank in the series.

Abstract: The invention relates to a process system and a method for preliminary treatment of disintegrated cellulose-containing material, preferably wood chips, prior to pulp digestion. The process system and the method according to the invention make use of a process vessel intended to function both as a so-called chip bin and as a pre-impregnation vessel. The characteristics of the invention are that a sloping steaming vessel is arranged downstream of the process vessel for the purpose of separating an excess of pre-impregnation liquid from the pre-impregnated cellulose-containing material, that the sloping steaming vessel is arranged for supplying steaming vapor which preferably has been generated by flashing of extraction liquor from a pulp digester, and that the sloping steaming vessel is connected to a chip chute communicating with a condenser for connection to a system for managing foul-smelling process gases.

Abstract: A method of recovering chemicals from spent black liquor used in a kraft pulping process comprising organic materials having oxygen containing functional groups, the method comprising heating the black liquor in the presence of lime at an elevated temperature and at a corresponding pressure at which there is no or substantially no boiling of the black liquor, until all or a portion of the oxygen is converted into carbon dioxide to form a slurry comprising microparticulate char and a white liquor suspension. The heating can be accomplished with any suitable means. For example, black liquor is evaporated in an evaporator train, and the liquor pumped in a high pressure pump to a suitable pressure, as for example, a pressure of from about 1200 psig to about 2000 psig. Thereafter, the liquor is transferred to a heat exchanger and heated to the elevated temperature, as for example a temperature of at least about 475° F.

Abstract: A recycling process for garbage containing a high proportion of paper where printed paper is first separated from the garbage. The garbage is then into pieces and light and heavy components are separated out in a classification tank. The remaining organic mass suspended in water is hydrolyzed and subjected to anaerobic digestion followed by aerobic co-composting. The resulting solid is a high grade fertilizer while biogas produced by the process is converted to electrical energy in a combined cycle installation.

Abstract: The present invention reduces the sulfur and odor emissions from a paper-making Kraft process by recovering the sulfur in the non-combustible gases (NGCs) emitted by the Kraft process. In a first embodiment of the invention, the NGCs are flamelessly oxidized in a flameless thermal oxidizer to form a sulfur oxide-containing, gaseous products stream. The gaseous products stream is scrubbed with a scrubber solution stream to remove the sulfur components resulting in a scrubbed gas stream and spent scrubber solution stream having S.sub.2 O.sub.3 and SO.sub.4, and SO.sub.3 soluble salts. At least a portion of the spent scrubber solution from the scrubber is directed back into the Kraft process, thus recovering the sulfur. In a second general embodiment of the invention, the NGCs are flamelessly oxidized in a moving, packed bed calcinator. The calcinator receives a lime mud stream from the Kraft process, forms a packed bed therefrom, calcines the packed bed, and releases it as a quick lime stream.

Abstract: A method of recovering chemicals from spent black liquor used in a kraft pulping process comprising organic materials having oxygen containing functional groups, the method comprising heating the black liquor at an elevated temperature and at a corresponding pressure at which there is no or substantially no boiling of the black liquor, until all or a portion of the oxygen is converted into carbon dioxide to form a slurry comprising microparticulate char and a green liquor suspension. The heating can be accomplished with any suitable means. For example, black liquor is evaporated in an evaporator train, and the liquor pumped in a high pressure pump to a suitable pressure, as for example, a pressure of from about 1200 psig to about 2000 psig. Thereafter, the liquor is transferred to a heat exchanger and heated to the elevated temperature, as for example a temperature of at least about 475.degree. F.

Abstract: A method of creating a number of separate product streams from an agricultural waste material, comprising: providing a starting material consisting of an agricultural waste material; hydrolyzing the starting material with an acid solution at atmospheric pressure, and temperatures not exceeding about 100.degree. C., to create an absorbent, hydrolyzed solid residue and a xylose-containing liquor; reserving the xylose-containing liquor; and delignifying the hydrolyzed solid residue with a basic solution, to create a fiber solid residue suitable for use as an absorbent material, and a dissolved lignin-containing solution.

Abstract: Method of reducing corrosion in a power boiler of a pulp mill using biofuel and suspended matter obtained from the waste water treatment of the mill. In the method flue gases obtained from a waste heat boiler are fed into the power boiler, causing the sulfur dioxide contained in them to react with the alkali chlorides in the boiler and the chlorine to form hydrogen chloride.

Abstract: This invention relates generally to a method for extracting lignosulfonate for the manufacture of vanillin and other specialty chemicals. Specifically, the invention relates to a method for recovering lignosulfonates from newsprint comprising the steps of:a) converting newsprint to a crumb pulp comprising of from about 20% to about 50% crumb pulp fiber solids by weight on an oven dry basis and the remainder water;b) cooking the crumb pulp in a medium comprising crumb pulp and cooking acid solution selected from the group consisting of sodium bisulfite, magnesium bisulfite, ammonium bisulfite, calcium bisulfite or mixtures thereof wherein the weight ratio of cooking acid solution to the crumb pulp fiber is from about 3 to about 6 for sufficient time and sufficient temperature and pressure for lignosulfonate removal;c) separating the crumb pulp fiber from the spent sulfite liquor; andd) recovering the lignosulfonates from the spent sulfite liquor.

Abstract: Biomass, such as bagasse, is pre-hydrolyzed, to ultimately effect hydrolysis of hemicellulose to sugars. Biomass is mixed with a mineral acid solution to form a slurry having a consistency of about 8 to 12% so that the acid solution properly wets the biomass. Then the slurry is dewatered to about 35 to 50% consistency, and is heated to reaction temperature (e. g. about 320.degree. F.) by direct contact with steam in the vapor phase of a vertical pressurized reactor, having a pressure of about 40 psig. A fluffer is preferably provided in the top of the reaction vessel. After a reaction time of about 30 minutes, the biomass is diluted and cold blown out of the bottom of the reactor. Pressate from the dewatering has acid added to it and is heated by indirect heat exchange with a sugar solution obtained by washing of the biomass discharged from the reactor, and is then mixed with the biomass as the acid solution.

Abstract: Paper pulp (e.g. kraft pulp) is produced utilizing at least two different supplies of cooking liquor, one having low sulfide content, and the other high sulfide content. The high sulfide content supply is typically used to impregnate the pulp or otherwise treat it first, while the second supply is used in other cooking stages (e.g. a digester), whether co-current or countercurrent. The different sulfur content liquors are obtained by heat treating (under pressure) black liquor to drive off sulfur compounds, and absorbing them into white liquor to produce a high sulfide stream. The low sulfide stream is made by conventional treatment of the black liquor after heat treating and evaporation. Utilizing multiple sulfide content supplies results in an optimum viscosity/kappa ratio and/or pulp strength properties for the pulp produced.

Abstract: Off gases from black liquor heat treatment, evaporators, wood pulp digesters, etc. are treated to produce primarily hydrogen sulfide and sulfur free fuel gases such as methane, carbon monoxide, hydrogen, and ethylene. Then the hydrogen sulfide is used to produce sodium polysulfide in white liquor for cooking wood chips to produce pulp by the kraft process. Polysulfide may be formed in three different ways: by supplying air to a fuel cell into which white liquor and the hydrogen sulfide containing gas have been introduced; by bringing clarified white liquor and hydrogen sulfide containing gas into contact with a wet-proofed activated carbon catalyst and oxygen containing gas; or by bringing unclarified white liquor into contact with the gas and oxygen containing gas, with lime mud acting as a catalyst, and then clarifying the polysulfide-rich white liquor produced to remove the lime mud. The white liquor produced contains about 0.5-8% on wood sodium polysulfide.

Abstract: A plurality of reactors, which can all be interconnected selectively by way of pipes, are used for the hydrolytic separation of a cellulose-containing substrate so that a stepwise pressure reduction in one reactor is made possible and thus a stepwise pressure build-up in all the other reactors. The steam entering and leaving the reactors is used to produce a fluidized bed of the substrate. A high output with a low specific expenditure of energy is achieved by these measures.

Abstract: The chemical components of lignocellulosic material which have been dissociated by a steam explosion process can be extracted from the mixture of components using a solvent extraction process. The solvents are water, alcohol and a mild caustic in that order, or the alcohol step can be by-passed and only water and caustic are used. The caustic is a stronger solvent and it will extract the alcohol solubles along with the caustic only solubles. The eluant from the these extractions contains a range of lignin derived substances, which have different applications, such as thermoplastic and thermosetting characteristics. This invention describes a method for partitioning these lignin components into reproducible fractions having definable characteristics for particular applications. For instance, many copolymer applications require a thermosetting only fraction of the lignin. Other applications require a thermoplastic only lignin.

Abstract: A process is disclosed for separating low molecular weight components from complex aqueous organic mixtures. The process includes preparing a separation solution of supercritical carbon dioxide with an effective amount of an entrainer to modify the solvation power of the supercritical carbon dioxide and extract preselected low molecular weight components. The separation solution is maintained at a temperature of at least about 70.degree. C. and a pressure of at least about 1,500 psi. The separation solution is then contacted with the organic mixtures while maintaining the temperature and pressure as above until the mixtures and solution reach equilibrium to extract the preselected low molecular weight components from the organic mixtures. Finally, the entrainer/extracted components portion of the equilibrium mixture is isolated from the separation solution.

Abstract: There has been provided a system and apparatus for recovering turpentine from a thermomechanical pulping process for making paper, which thermomechanical pulping process utilizes a plug screw conveyor for squeezing and feeding pulp chips. The thermomechanical pulping process is conventional. The liquid effluent from said plug screw conveyor contains an appreciable amount of turpentine. The liquid effluent is collected under superatmospheric pressure and flashed into vapor/liquid separator by releasing the pressure on the liquid. This vapor is condensed in a suitable condenser and the condensate collected in a decanter where the turpentine collects as a separate phase and the water also as a separate phase. Condensate from various vents in the conventional thermomechanical pulping process may be collected for more nearly compelete removal of turpentine and other oleoresinous components.

Abstract: In a combined process for the thermal and chemical treatment of lignocellulose-containing biomass and for the production of furfural, biomass is supplied to a cooker in batches, is heated in the cooker under the addition of cooking liquor, and cellulose or pre-treated biomass is withdrawn from the cooker in batches. In order to guarantee a high yield of furfural, cooking liquor is withdrawn from the cooker during the heating phase and is fed to a furfural production plant, and the cooking liquor at least largely freed from pentoses and furfural is returned to the cooker.

Abstract: Lignin is removed from a crude tall oil in the production of tall oil fractions suitable for use as chemical ingredients and additives in other products by sparging the crude tall oil at a temperature of between about 350.degree. F. to 400.degree. F. with a carrier gas to depolymerize and remove from the tall oil lower molecular weight lignin materials.

Abstract: A method of rapidly and efficiently treating ligno-cellulosic material for removal of lignin and other non-carbohydrates as well as non-cellulosic carbohydrates from cellulosic matter. Such material is first impregnated with a liquor which is a reaction product obtained by mixing triethyleneglycol with an arylsulfonic or other organic acid. The impregnated material is then rapidly heated by microwaving or application of rf energy to a temperature between about 119 degrees Centigrade to 130 degrees Centigrade and maintained at that temperature for only two to five minutes to reduce the effects of hydrolysis. Thereafter, conventional filtration and washing techniques are applied to achieve a residue material suitable for further use as a wood pulp or for further hydrolysis for the production of organic chemicals.

Abstract: Described herein is a process for producing potassium salts from potassium-based liquors for pulping of lignocellulosic material. The process comprises the steps of(a) digesting lignocellulosic material with a potassium-base aqueous cooling liquor to obtain an aqueous slurry of partially delignified pulp of the lignocellulosic material;(b) separating the pulp from the spent potassium-base aqueous cooling liquor;(c) concentrating the spent pulping liquor; and(d) recovering potassium salts including potassium carbonate, potassium sulphate and potassium lignosulphonate from the concentrated spent pulping liquor. The recovered potassium salts find numerous uses, an example being use in fertilizers.

Abstract: A method for acid-catalyzed hydrolytic splitting of cellulose to give a high yield in sugar with a minimal expenditure in energy, in particular, with the smallest possible charge of live steam. Admission of steam is performed in a plurality of successive, discrete reaction stages having in each case defined temperature and pressure values in such a manner that the temperature rises from one stage to the next while the reaction time decreases and a rapid expansion takes place subsequently to the last reaction stage. A high pressure poured bed reactor is used for performing this method.

Abstract: Microcrystalline cellulose has many applications in the pharmaceutical, food, paper and structural composite industries. Level off DP (Degree of Polymerization) microcrystalline cellulose is made up of a chain of about 250 glucose molecules in the form of microcrystal. In nature, several microcrystals are hinged together and surrounded by amorphous cellulose to form a cellulose microfibril. If the amorphous cellulose is removed, the resultant product is called level off DP (Degree of Polymerization) microcrystalline cellulose. When lignocellulosic material is processed according to applicant's earlier processes (Canadian Pat. Nos. 1,096,374 and 1,141,376), the dissociated material is partitioned by removing the lignin and the xylan leaving a low DP (320) cellulose fraction.

Abstract: A method of treating biomass having fermentable material is provided utilizing acid hydrolysis in a countercurrent diffusion treatment structure. By practicing the invention acid usage is minimized, pentose concentration in the hydrolysate solution is maximized, and ethanol, butanol, butanediol, and the alcohols can be produced without the input of any external energy whatsoever into the production method. Biomass is particlized and slurried, and then is continuously subjected to acid hydrolysis at temperature, acid concentration, and residence time conditions sufficient to effect hydrolysis of the hemicellulose in the biomass to effect separation of pentose and hexose sugars into a hydrolysate having insufficient furfural to substantially inhibit fermentation microorganism growth, while not substantially hydrolyzing the cellulose in the biomass.

Abstract: The semi-continuous process according to the invention for hydrolyzing cellulose-containing material (substrate) with gaseous hydrogen fluoride comprises sorption and subsequent desorption of HF in a total of n steps. The substrate is divided into n batches in n reactors (1a, 1b, 1c, . . . ); each batch passes through the n process steps in one reactor (1a, . . . ). Initially, sorption is carried out in the first to the (n/2)th step by the action of HF-inert gas mixtures, having an HF concentration which increases from sorption step to sorption step, at a temperature above the boiling point of HF. Subsequently, desorption is brought about in the ((n/2)+1)th to nth step by treating with heated HF-inert gas mixtures having an HF concentration which decreases from desorption step to desorption step; n is an even number from 4 to 12 and the n steps each take place in the same time segments (periods). The sequence of steps is displaced by one period from each batch to the next batch.

Abstract: The continuous process for hydrolyzing cellulose-containing material (substrate) is carried out by sorption of gaseous HF in a sorption reaction (1) and subsequent desorption in n steps, which are carried out in n reactors which are separated from one another in a gas-tight manner. The substrate is introduced via a gas-tight valve into the sorption reactor (1), passes through this and then reaches consecutively, through gas-tight valves, a hold-up reactor (2) and the first (3c), second (3b), . . . nth desporption reactor, from which it is then removed. The desorption is carried out in each case by the action of one of the n inert gas streams on the substrate at different temperatures, the particular inert gas stream being enriched with the HF being liberated during desorption.

Abstract: A continuous process for hydrolyzing cellulose-containing material (substrate) with gaseous hydrogen fluoride, HF is sorbed by the substrate at a temperature above its boiling point in n sorption steps and thereafter the sorbed HF is removed from the substrate by heating in n desorption steps. The number n of sorption steps and of desorption steps is identical and the reaction steps mentioned each occur in reactors which are separated from one another in a gas-tight manner. After introduction into the first sorption reactor (1a), the substrate passes consecutively through gas-tight valves into the second (1a) . . . nth sorption reactor and from the latter, optionally via a hold-up reactor (2) into the first, second, . . . nth desorption reactor (3a) and is removed from the nth desorption reactor (3a). The streams of HF gas, which contain an inert carrier gas in addition to HF, are circulated between the first (1a) or second (1b) or . . . (n-1)th or nth sorption reactor and the nth (3a) or (n-1)th (3b) . . .

Abstract: A method and apparatus for continuously producing pulp from previously unusable agricultural fibers, such as plantain. The pulp is used in papermaking. The pulp effluent is recycled and concentrated during the process, thereby enabling economical recovery of chemical by-products for use as fertilizer or animal feed material.

Abstract: Comminuted cellulosic materials which may or may not contain lignin are partially or totally hydrolyzed or saccharified by an improved organosolv process using an aqueous acetone solvent mixture containing a small amount of an acidic compound and containing at least about 70 percent by volume of acetone and up to virtually anhydrous acetone. The process is performed at elevated reaction temperatures, preferably at 145.degree. C. to 230.degree. C., for a limited period of time and then with cooling such that the resultant dissolved sugars from the hydrolysis are not degraded into non-sugars. In particular the reaction is conducted such that the cellulosic material is dissolved and such that at least ninety percent or more of available sugars in the cellulosic material are recovered. Unexpectedly it has been found that acetone at high concentration forms stable complexes with the sugars which prevents their degradation and also facilitates separation of the sugars.

Abstract: Cellulose-containing material is rapidly saccharified to convert pentosans and hexosans to sugars by cooking under pressure at from 180.degree. C. to 220.degree. C. with acetone-water solvent mixture carrying from 0.05 to 0.25 weight percent of phosphoric, sulfuric or hydrochloric acids.A predominantly cellulosic material, e.g. a delignified pulp, is hydrolysed to yield relatively pure glucose recoverable from liquor which is flowed through the cellulose, then withdrawn and cooled and neutralized within an elapsed time of a minute or less.Whole wood is nearly totally dissolvable by the process, yielding mixed pentoses and hexoses. The dehydration and degradation products of sugars are formed by prolonging retention time of liquor from 20 to 45 minutes.

Abstract: A versatile process and apparatus is presented for producing, in high yields, many different grades of pulp from a single wood specie or for pulping any specie or type of woody material, and for storage and recycling of the by-product liquid and gaseous materials. The process of this invention is virtually pollution free, and the reactant chemicals are recoverable from the by-products. In the alternative, the by-products themselves have a commercial value which may forestall recovery of the reactants. The lignin constituent extracted from the pulp is usable as a resin binder, a wood rehardening agent, or a glue.

Abstract: Chemicals produced during pulping operations are recovered and separated by passing chemical-containing liquors from said operations through one or more units containing activated carbon. The chemicals are recovered from said units by introducing a solvent into said unit and separating the materials removed therefrom in a fractionating column.

Abstract: A method and means for purifying the waste water from paper and pulp mill wastes obtained from a mill using the Kraft process by first precipitating lignins and lignin derivatives from the waste stream with quaternary ammonium compounds, removing other impurities by activated carbon produced from the cellulosic components of the water, and thereafter separating water from the precipitate and solids. The activated carbon also acts as an aid to the separation of the water and solids. If recovery of lignins is also desired, then the precipitate containing the lignins and quaternary ammonium compound is dissolved in methanol. Upon acidification, the lignin is precipitated from the solution. The methanol and quaternary ammonium compound are recovered for reuse from the remainder.

Abstract: Cellulosic fibers are removed from seed hulls such as cottonseed hulls by a process including (a) in the absence of mechanical action sufficient to cause degradation of fiber properties, contacting the seed hulls which comprise both cellulosic fibers (linters and hull fibers) and non-fibrous hull components with an alkaline solution and an oxygen-containing gas until the cellulosic fibers are substantially free of the non-fibrous hull components, and (b) recovering the cellulosic fibers from the non-fibrous hull components so as to produce readily washable cellulosic fibers having substantially unimpaired mechanical properties. The cellulosic fibers may then be washed and separated according to known fiber fractionation procedures. The cellulosic fibers produced according to this improved process have substantially unimpaired mechanical properties and contain substantially no polyphenolic materials or extraneous color components.

Abstract: Method and apparatus for the continuous acid hydrolysis of pentosan-containing material at a temperature between 80.degree. and 120.degree. C and at a pH lower than 5. At least two portions of hydrolysate are re-cycled back into the hydrolysis vessel. One recycle portion having a lower acid concentration is supplemented with additional acid before being returned to the hydrolysis vessel.