Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F11/00—Compounds of calcium, strontium, or barium
  • C01F11/18—Carbonates
• • A—HUMAN NECESSITIES
  • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
  • A23K—FODDER
  • A23K10/00—Animal feeding-stuffs
  • A23K10/30—Animal feeding-stuffs from material of plant origin, e.g. roots, seeds or hay; from material of fungal origin, e.g. mushrooms
  • A23K10/32—Animal feeding-stuffs from material of plant origin, e.g. roots, seeds or hay; from material of fungal origin, e.g. mushrooms from hydrolysates of wood or straw
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
  • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
  • C12P7/06—Ethanol, i.e. non-beverage
  • C12P7/08—Ethanol, i.e. non-beverage produced as by-product or from waste or cellulosic material substrate
  • C12P7/10—Ethanol, i.e. non-beverage produced as by-product or from waste or cellulosic material substrate substrate containing cellulosic material
• • C—CHEMISTRY; METALLURGY
  • C13—SUGAR INDUSTRY
  • C13K—SACCHARIDES OBTAINED FROM NATURAL SOURCES OR BY HYDROLYSIS OF NATURALLY OCCURRING DISACCHARIDES, OLIGOSACCHARIDES OR POLYSACCHARIDES
  • C13K1/00—Glucose; Glucose-containing syrups
  • C13K1/02—Glucose; Glucose-containing syrups obtained by saccharification of cellulosic materials
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P2201/00—Pretreatment of cellulosic or lignocellulosic material for subsequent enzymatic treatment or hydrolysis
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E50/00—Technologies for the production of fuel of non-fossil origin
  • Y02E50/10—Biofuels, e.g. bio-diesel

Definitions

• the invention relates to methods for the pretreatment of a lignin containing biomass to render the biomass amenable to digestion.
• Pretreatment comprises the addition of calcium hydroxide and water to the biomass to form a mixture, and maintaining the mixture at a relatively high temperature.
• an oxidizing agent selected from the group consisting of oxygen and oxygen-containing gasses, may be added under pressure to the mixture.
• the invention also relates to the digested products of the pretreated biomass which includes useful feedstocks, fuels, and chemicals such as sugars, ketones, fatty acids and alcohols, and to a method for the recovery of calcium from the pretreated biomass.
• Biomass can be classified in three main categories: sugar-, starchand cellulose-containing plants.
• Sugar-containing plants e.g. sweet sorghum, sugarcane
• starch-containing plants e.g. corn, rice, wheat, sweet potatoes
• Cellulose-containing plants and waste products e.g. grasses, wood, bagasse, straws
• a well engineered process to convert them to feedstock may potentially be economical since the costs of feedstock are much less than those of sugar- and starchcontaining biomass.
• Cellulose-containing materials are generally referred to as lignocellulosics because they contain cellulose (40% - 60%), hemicellulose (20% - 40%) and lignin (10% -25%).
• Non-woody biomass generally contains less than about 15-20% lignin.
• Cellulose, a glucose polymer can be hydrolyzed to glucose using acid, enzymes or microbes. Glucose can serve as a feedstock for fuel alcohol and single-cell protein production.
• Microbial hydrolysis produces cellular biomass (single-cell protein) and metabolic waste products such as organic acids. Acid hydrolysis, although simple, produces many undesirable degradation products. Enzymatic hydrolysis is the cleanest and most preferred approach.
• lignocellulose can be used as inexpensive cattle feed. Since raw lignocellulose cannot be easily digested by cattle, it must be processed to improve its digestibility before it can be fed to ruminants. Also, anaerobic fermentation using rumen microorganisms can produce low molecular weight volatile fatty acids.
• Cellulose is the world's most abundant biological material. Approximately 40% to 45% of the dry weight of wood species is cellulose. The degree of polymerization ranges from 500 to 20,000. Cellulose molecules are completely linear, unbranched and have a strong tendency to form inter- and intra-molecular hydrogen bonds. Bundles of cellulose molecules are thus aggregated together to form microfibrils in which highly ordered (crystalline) regions alternate with less ordered (amorphous) regions. Microfibrils make fibrils and finally cellulose fibers. As a consequence of its fibrous structure and strong hydrogen bonds, cellulose has a very high tensile strength and is insoluble in most solvents.
• Hemicellulose is the world's second most abundant carbohydrate and comprises about 20% to 30% of wood dry weight. Hemicelluloses, although originally believed to be intermediates in cellulose biosynthesis, are formed through biosynthetic routes different from cellulose. Hemicellulose are heteropolysaccharides and are formed by a variety of monomers. The most common monomers are glucose, galactose and mannose (the hexoses) and xylose and arabinose (the pentoses). Most hemicelluloses have a degree of polymerization of only 200. Hemicelluloses can be classified in three families, xylans, mannans and galactans, named for the backbone polymer.
• Lignin is the world's most abundant non-carbohydrate biomaterial. It is a three dimensional macromolecule of enormously high molecular weight. Since its units are extensively cross-linked, it is difficult to define an individual molecule. Lignin provides strength by binding cellulose fibrils together. Being hydrophobic in nature, it prevents water loss from the vascular system and, being highly resistant to enzymatic degradation, it protects plants from insects and microbial attack.
• Phenylpropane an aromatic compound, is the basic structural unit of lignin.
• the monomers not only cross-link with each other, but also covalently bond to hemicellulose.
• a great constraint to cellulose and hemicellulose accessibility is the presence of lignin. It has been shown that decreased lignin content causes increased digestibility. Lignin can be removed by physical, chemical, or enzymatic treatments. It must be decomposed to smaller units that can be dissolved out of the cellulose matrix.
• pulping methods that disintegrate and remove lignin, leaving the cellulose fairly intact. Conventional pulping processes, such as Kraft and sulfite pulping, are too costly as bioconversion pretreatments. Also, economical use of the removed lignin is difficult because its chemical structure and size distribution are highly heterogeneous.
• enzymatic cellulosic hydrolysis Another major deterrent to enzymatic cellulosic hydrolysis is the highly ordered molecular packing of its crystalline regions. Cellulolytic enzymes readily degrade the more accessible amorphous portions of cellulose, but are unable to attack the less accessible crystalline material. Thus, enzymatic hydrolysis rates increase with decreasing crystallinity index measured by X-ray diffraction methods.
• the moisture content of cellulose fibers influences enzymatic degradation.
• Cellulosic materials are effectively protected from deterioration by enzymes or microbes provided the moisture content is maintained below a critical level characteristic of the material and the organism involved. In general, this critical level is slightly above the fiber saturation point, approximately 40% of dry weight.
• Moisture plays three major roles: (1) it swells the fibers by hydrating cellulose molecules, thus opening up the fine structure and increasing enzyme access, (2) it provides a diffusion medium for enzymes and for partial degradation products, and (3) it is added to cellulose during hydrolytic cleavage of the glycosidic links of each molecule.
• the surface area of lignocellulose is another important factor that determines susceptibility to enzymatic degradation. It is important because contact between enzyme molecules and the cellulose surface is a prerequisite for hydrolysis to proceed. A few other factors that also influence susceptibility include size and diffusibility of enzyme molecules in relation to size and surface properties of capillaries, unit cell dimensions of cellulose molecules, and conformation and steric rigidity of hydro-glucose units.
• lignocellulose pretreatment is an essential requirement.
• the heterogeneous enzymatic degradation of lignocellulosics is primarily governed by its structural features because (1) cellulose possesses a highly resistant crystalline structure, (2) the lignin surrounding the cellulose forms a physical barrier and (3) the sites available for enzymatic attack are limited.
• An ideal pretreatment therefore, would reduce lignin content, with a concomitant reduction in crystallinity and increase in surface area.
• Pretreatment methods can be classified into physical, chemical, physicochemical, and biological, depending on the mode of action. The literature available on this subject is voluminous. The various pretreatment methods that have been used to increase cellulose digestibility are summarized in Table 1.
• Biological pretreatments employ fungi for microbial delignification to make cellulose more accessible.
• Major biological lignin degraders are the higher fungi, Ascomycetes and Basidiomycetes. Fungal degradation is a slow process and most fungi attack not only lignin, but cellulose also, thus resulting in a mixture of lignin fragments and sugars. Improvements may require developing more specific and efficient microbes.
• Physical pretreatments can be classified in two general categories: mechanical (involving all types of milling) and nonmechanical (involving high-pressure steaming, high energy radiation and pyrolysis).
• mechanical pretreatments e.g. shearing, compressive forces
• lignocellulose e.g., lignocellulose
• These physical forces reduce crystallinity, particle size and degree of polymerization and increase bulk density.
• These structural changes result in a material more susceptible to acid and enzymatic hydrolysis.
• Nonmechanical physical pretreatment methods also increase digestibility, but have similar disadvantages and thus are not economical for real processes.
• the AFEX pretreatment process soaks lignocellulose in liquid ammonia at high pressure and then explosively releases the pressure.
• Pretreatment conditions (30°C - 100°C) are less severe than steam explosion.
• U.S. Patent No.4,644,060 to Chou is directed to the use of super-critical ammonia to increase lignocellulose digestibility.
• U.S. Patents Nos. 4,353,713 and 4,448,588 to Cheng are directed to the gasification of biomass or coal which is an endothermic process. These patents also relate to a method for adding the required thermal energy by reacting lime with carbon dioxide which is an exothermic reaction.
• U.S. Patent No.4,391,671 to Azarniouch is directed to a method for calcining calcium carbonate in a rotary kiln.
• the reference relates to the paper/pulp industry where the calcium carbonate would be contaminated with waste biomass. The waste biomass is burned to provide the needed heat of reaction.
• U.S. Patent No. 4,356,196 to Hulquist is directed to treating biomass with ammonia.
• U.S. Patent No. 4,227,964 to Kerr is directed to the use of ammonia to promote the kinking of pulp fiber to increase paper strength, not to break down the fibers.
• U.S. Patent No. 4,087,317 to Roberts is directed to the use of lime and mechanical beating to convert pulp into a hydrated gel. There is no mention of lime recovery or enzymatically hydrolyzing the hydrated gel.
• U.S. Patent No. 4,064,276 to Conradsen directed to a process where biomass is covered with a tarp and then ammoniated with ammonia, which is allowed to dissipate into the atmosphere.
• U.S. Patent No. 3,939,286 to Jelks is directed to oxidizing biomass with high-pressure oxygen under elevated temperature and pressure in the presence of an acid catalyst, and a metal catalyst, ferric chloride, to break lignin bonds and to increase digestibility.
• the catalysts are described as essential to the process and calcium hydroxide is utilized as a neutralizing agent to adjust the resulting pH of the hydrolyzed biomass.
• U.S. Patent No. 3,878,304 to Moore is directed to production of slow-release nonprotein nitrogen in ruminant feeds.
• An amide, urea is reacted with waste carbohydrates in the presence of an acid catalyst.
• the resulting material is pelleted and used as animal feed. Since the nitrogen is released slowly in the rumen, it is nontoxic to the animal.
• U.S. Patent No. 3,944,463 to Samuelson et al. is directed to a process for producing cellulose pulp of high brightness.
• the cellulose is pretreated with an alkaline compound at a temperature of between about 60°C to about 200°C so as to dissolve between 1 and 30% of the dry weight of the material in the pretreatment liquor.
• the pretreatment liquor preferably contains sodium carbonate, sodium bicarbonate or mixtures thereof, or possible sodium hydroxide.
• U.S. Patent No. 3,639,206 to Spruill is directed to the treatment of waste water effluent derived from a pulping process with calcium oxide or hydroxide to reduce the fiber and color content of the effluent.
• U.S. Patent No. 4,048,341 to Lagerstrom et al. is directed to a process for increasing the feed value of lignocellulosic material by contacting the material with an alkaline liquid, specifically, sodium hydroxide.
• the alkaline liquid supplied in excess, is allowed to run off the material before any essential alkalization effect has been reached. After the liquid absorbed in the material has provided its effect, an acid solution is added to the material to neutralize the excess alkali.
• the reference does not disclose the interrelationship of temperature and time of alkali treatment, nor does it disclose the optimal amounts of the sodium hydroxide and water.
• U.S. Patent No. 4,182,780 to Lagerstrom et al. is directed to a process for increasing the feed value of lignocellulosic materials by alkali treatment and subsequent neutralization of the materials with an acid in a closed system under circulation of the treating agents.
• U.S. Patent No. 4,515,816 to Anthony is directed to a process in which lignocellulose is treated with dilute acid in an amount of about 1.5 to 2.5% of the dry weight of lignocellulose. The mixture is then stored at ambient conditions for 5 to 21 days in an air-free environment.
• U.S. Patent No. 4,842,877 to Tyson is directed to a process for the delignification of non-woody biomass ( ⁇ 20% lignin).
• non-woody biomass is treated with a chelating agent, to prevent unnecessary oxidation, and maintained at high pH and high temperatures (150oF to 315°F) in the presence of hydrogen peroxide and pressurized oxygen.
• Hydrogen peroxide is stated to cause a reaction on the cell walls to allow the hemicellulose and lignin to solubilize and be removed through a subsequent hydrolysis process.
• Oxygen is added to initiate and accelerate the activation of hydrogen peroxide.
• Waller and Riopfenstein (1975) used various combinations of NaOH, Ca(OH) 2 and NH 4 OH for treating feed for lambs and heifers and reported that the highest daily gain and lowest feed/gain was obtained for the 3% NaOH + 1% Ca(OH) 2 rations.
• Darwish and Galal (1975) used maize cobs treated with 1.5% Ca(OH) 2 in a milk production ration and found no significant change in milk output.
• Felix et al. (1990) evaluated the effects of ensiling and treating soya-bean straw with NAOH, Ca(OH) 2 and NH 4 OH on ruminant digestibility. Results indicate that there was no significant improvement due to alkali treatment of dry and unensiled straw, although alkali treatment improved digestibility of ensiled straw.
• One embodiment of the invention is directed to an economical process for pretreating a lignocellulose-containing biomass to render the biomass amenable to digestion.
• Pretreatment comprises adding calcium hydroxide and water to the biomass, and subjecting the biomass to relatively high temperatures for a period of time.
• the pretreated biomass is digested to produce a useful product.
• Another embodiment of the invention is directed to an economical pretreatment method comprising adding calcium hydroxide and water to the biomass to form a mixture, adding an oxidizing agent, selected from the group consisting of oxygen and oxygen-containing gasses, to the mixture under pressure, and subjecting the biomass to relatively high temperatures for a period of time.
• the pretreated biomass is digested to produce a useful product.
• Another embodiment of the invention is directed to a process for recovering calcium from a biomass. After pretreatment, the biomass is carbonated with a carbonating agent to form calcium carbonate. Calcium carbonate is recovered from the pretreated mixture or recovered after digestion and can be reconverted into calcium hydroxide.
• Figure 1 is a schematic diagram of Reactor System 3.
• Figure 2 is a glucose calibration curve for the filter paper assay.
• Figure 3 is an enzyme calibration curve for the filter paper assay.
• Figure 4 is a calibration curve for the DNS assay.
• Figure 5 is a flow diagram for continuous calcium hydroxide recovery.
• Figure 6 is a techematic diagram of one embodiment of using a hydroclone to separate lime solids from lime solution.
• Figure 7 is a schematic diagram of another embodiment of using a hydroclone to separate lime solids from lime solution.
• Figure 8 is a schematic diagram showing different possible permutations of pretreating biomass with lime.
• Figure 9 shows the lime treatment process for ruminant animal feed production.
• Figure 10 is a graph of oxygen pressure verses yield to show the effect of oxygen on the hydrolysis of newspaper.
• Figure 11 is a graph of pretreatment time verses yield to show the effect of treatment time on the hydrolysis of newspaper. Description of the Invention
• the present invention comprises economical methods for the pretreatment of a biomass.
• Pretreatment comprises the addition of calcium hydroxide and water to a biomass to render the biomass susceptible to degradation.
• Calcium hydroxide is inexpensive and much cheaper than other alkalis. It is safe to handle and, unlike the sodium residue, the calcium residue is little or no problem for animal feed. In an artificial rumen, calcium hydroxide produces calcium acetate which is also safe and nontoxic. Calcium hydroxide (Ca(OH) 2 ) as the lignocellulose pretreatment agent is therefore very economical. Further, there was also no significant difference in digestibility between Ca(OH) 2 pretreated material and NH 3 or NaOH pretreated material in animals.
• the operating conditions of the pretreatment methods of the invention are a significant improvement over the existing literature. Previous researchers restricted their operating temperature to ambient and below in order to create a very simple process without heaters. These simple processes required extremely long treatment times typically ranging from 8 to 150 days. Raising the treatment temperature could decrease the treatment time, but runs the risk of degrading the lignocellulose. High-temperature treatment conditions have been identified that did not degrade the lignocellulose and resulted in treatment times that were orders of magnitude shorter. The economic impact is significant since the reactor can be orders of magnitude smaller.
• the invention is directed to a method for pretreating a lignocellulose-containing biomass to render the biomass amenable to digestion and comprises providing a lignocellulose-containing biomass, adding calcium hydroxide and water to the biomass to form a mixture, and maintaining the mixture at an elevated temperature and for a period of time sufficient to render the biomass of the mixture amenable to digestion.
• Types of useful biomass include grass, wood, bagasse, straw, paper, plant material, and combinations thereof.
• Lignocellulose-containing biomass to which the process of the invention is directed is preferably biomass containing greater than 15% lignin and more preferable biomass containing greater than 20% lignin.
• biomass to be pretreated is fed into a chipper, grinder, chopper, shredder or the like, to be reduced in size.
• Resulting biomass chips or particles are preferable about one-half inch or smaller.
• the biomass particles are then combined with calcium hydroxide and water to form an alkaline biomass mixture.
• the mixture contains between about 6 to about 19 grams of water per gram of dry biomass and preferably about 16 grams of water per gram of dry biomass.
• the mixture also contains between about 2 to about 50 grams of calcium hydroxide per 100 grams of dry biomass and preferably contains about 30 grams of calcium hydroxide per 100 grams of dry biomass.
• the preferable amount may be more or less.
• Calcium hydroxide may be added before or after the water or as an aqueous solution or dispersion.
• the aqueous calcium hydroxide/biomass mixture is maintained in reaction chambers, which are preferably stainless steel, at between about 40°C to about 150°C, preferably between about 100°C to about 140°C, and more preferably at about 120°C.
• reaction chambers which are preferably stainless steel
• the temperature range may be between about 70°C to about 110°C, between about 110°C to about 150°C, or between about 50°C to about 65°C.
• the temperature is maintained for between about 1 to about 36, preferably between about 1 to about 20 hours, more preferably about 3 hours. Again, depending on the type of biomass, the time period may be longer or shorter such as between about 15 to about 25 hours.
• Another embodiment of the invention is directed to a method for converting a lignocellulose-containing biomass into a useful product and comprises providing a lignocellulose-containing biomass, adding calcium hydroxide and water to the biomass to form a mixture, oxygenating the mixture with pressurized oxygen, maintaining the mixture at an elevated temperature and for a period of time sufficient to render the biomass of the mixture amenable to digestion, and digesting the biomass of the mixture to convert the biomass into the useful product.
• Oxygen is relatively inexpensive and readily available as pressurized oxygen gas, pressurized air, and other pressurized oxygen-containing gasses. Oxygen is also non-toxin and non-polluting to the environment.
• Calcium hydroxide is added to a biomass as described above to form a mixture.
• an oxidizing agent under pressure selected from the group consisting of oxygen and oxygen-rich gasses.
• the added oxygen-containing gas has a pressure of between about 20 to about 500 psig (pounds per square inch gauge), preferably greater than about 50 psig, and more preferably greater than about 100 psig.
• the pretreated biomass is digested by hydrolysis such as acid hydrolysis, enzymatic action, fermentation, or a combination of digestion methods.
• the digested biomass comprises material which are useful products such as alcohols, acids such as organic acids, sugars, ketones, starches, fatty acids, or combinations thereof. These products can be made into feedstocks such as chemical feedstocks, fuels, and other useful products. Due to the relatively gentle pretreatment conditions, the useful products are obtained in higher quantities and are of a higher quality than products obtained after other pretreatment methods. The maximum amount of material is converted into useful product with as little waste as possible. Further, no toxins or harmful chemicals are introduced into the biomass therefore none need to be removed or even tested for in the final product.
• Another embodiment of the invention is directed to a method for recovering calcium from a biomass pretreatment process comprising pretreating the biomass with calcium hydroxide and water to form a mixture, optionally adding an oxidizing agent selected from the group consisting of oxygen and oxygen-containing gasses to the mixture under pressure, and maintaining the mixture at an elevated temperature and for a period of time sufficient to render the biomass of the mixture amenable to digestion, carbonating the mixture or the liquid portion thereof to precipitate calcium carbonate, and recovering the precipitated calcium carbonate.
• the pH of the carbonated mixture is between about 8.5 and about 10.5, and preferably between about 9.0 and about 10.
• the calcium carbonate is precipitated in the mixture and can be recovered by filtration, hydroclone separation, sedimentation, centrifugation, or by combinations of these methods.
• the calcium carbonate may also be heated and converted into carbon dioxide and calcium oxide, and the calcium recovered as calcium oxide.
• the pretreated mixture is treated with a carbonating agent, which is preferably carbon dioxide gas which is bubbled into the mixture, forming calcium carbonate.
• a carbonating agent which is preferably carbon dioxide gas which is bubbled into the mixture, forming calcium carbonate.
• the pretreated and carbonated biomass is digested and the useful product separated from the remaining mixture or residual mixture.
• the residual mixture comprising lignin and calcium carbonate, is heated, for example in a kiln, preferably a lime kiln, to convert the calcium carbonate into calcium hydroxide.
• the heat supplied to the kiln may be derived from the burning of the lignin, making for a highly economical overall process.
• Raw bagasse was collected from the Animal Science Department of Texas A&M University. For three years, it was lying in the open, covered only by a plastic sheet. Thus, it was first thoroughly washed with water and then dried in an oven (at 80°C) for about 8 hours. Also, because bagasse deteriorates with storage time, the bagasse used in the present study was more recalcitrant than that used by Holtzapple et al., Appl. Biochem. Biotech.28/29, 59 (1991). The wheat straw was already clean and did not require washing. Softwood newspaper was the Bryan/College Station, Texas, Eagle newspaper. It was first shredded in a paper shredder.
• Calcium hydroxide pretreatment involves reacting biomass with calcium hydroxide in the presence of water at a relatively high temperature.
• the effectiveness of the pretreatment process was studied for several different reaction conditions. Process variables studied were lime loading (2 to 30 g Ca(OH) 2 /100 g dry biomass), water loading (6 to 19 g water/g dry biomass), treatment temperature (50°C to 145°C) and treatment time (1 hour to 36 hours). The following three types of reactor systems were employed.
• Reactor System 1 For initial pretreatment experiments, 500-mL glass Erlenmeyer flasks were used as reactors. The flasks were sealed with rubber stoppers and placed in a 100-rpm shaking water-bath. This method was limited to 65°C, the highest temperature attainable by the water bath.
• Reactor System 2 Erlenmeyer flasks were placed in an oven, with periodic manual shaking. Only one experiment, at 65°C, was performed by this method. This method resulted in lower yields, thus demonstrating that continuous shaking was required for effective mass transfer.
• Reactor System 3 Steel reactors were used for experiments in the 65°C and 145°C temperature range. To resist the corrosive nature of calcium hydroxide solutions, the reactors were constructed of 304 stainless steel. The reactors were, 1.5 "I.D. ⁇ 5" long, cylindrical nipples, with end caps on both ends. To provide mixing inside the reactors, a rotating device was fabricated in the Texas A & M Chemical Engineering Department's machine shop. A schematic diagram of this reactor system is shown in Figure 1. This device holds the reactors (R) inside the oven (0) and, by rotating them continuously, provides tumble mixing of the contents. It has a steel rod (R1) supported from both ends on two ball bearings (B).
• the bearings are bolted on a steel frame (SF) that can be placed inside the oven. Six holes are drilled through this rod to hold the clamps (C) that hold the reactors. Set screws hold the clamps in place during rotation. Through the back side of the oven, a 1" hole is drilled. A small rod (R2) supported by a ball bearing (bolted on the oven wall) passes through this hole. A pulley (P) is mounted on the end that is outside the oven. A variable speed AC/DC motor (M) mounted on the top of the oven rotates R2.
• the steel rc>d that holds the reactors (R1) has a splined end (a small nut (N)) that couples with the pulley (via a socket (S)). This coupling arrangement allow the reactors to be placed in, and removed from, the oven with ease.
• the reactors were prepared by winding at least four layers of Teflon tape on both ends. One end was closed by placing the nipple in a vice and tightening the end cap by a pipe wrench.
• the reaction mixture was prepared by placing the measured quantities of biomass (7.5 g dry weight) and Ca(OH) 2 (according the lime loading) inside the reactors. The material was thoroughly mixed inside the reactors using a spatula. Measured amounts of water were then added to this dry mixed sample. The end cap was placed on the other end of the nipple and tightened. The reactors were then placed in boiling water for 5 to 15 minutes (depending on the pretreatment temperature) to pre-warm them. Prewarming the reactors is necessary to rapidly bring them to higher temperatures.
• oxygen-containing gas is introduced into the reactor from a high-pressure gas container or tank attached to the system.
• the gas may be pure pressurized oxygen, compressed air (which is very economical) or any oxygen-containing gas under pressure.
• the pressure of the oxygen-containing gas can be determined from a pressure gauge ounted on the gas supply container or on the reactor.
• Example 3 Calcium Hydroxide Pretreatment - Reactor System 3 1. Remove the old Teflon tape and clean the threads at both ends.
• the filter paper assay is commonly used to quantitatively study cellulose hydrolysis and measure cellulose activity.
• Filter paper is used since it is a readily available and reproducible substrate and is neither too susceptible nor too resistant to cellulase enzymes.
• the filter paper is incubated with various amounts of cellulose enzyme for 1 hour at 50°C and pH of 4.8.
• the amount of reducing sugars released in 1 hour is measured by the Dinitrosalicylic Acid (DNS) assay. (Also see below).
• DNS Dinitrosalicylic Acid
• ACF (Abs A - Abs B)
• the pretreated material (7.5 g dry weight) was transferred from the reactors to 500-mL Erlenmeyer glass flasks.
• the operating pH and temperature for the enzyme system were kept at 4.8 and 50°C respectively.
• the pH was reduced from about 11.5 to 4.8 by adding acetic acid.
• the total liquid volume was increased to 150 mL by adding distilled water to obtain a
• This measured sugar in the enzyme amounts to a correction of 45 mg eq. glucose/g dry biomass that was subtracted from the 3-day reducing sugar yields from the pretreated biomass.
• the hydrolysis samples were diluted from 13 to 33 times to bring the concentration within the assay range (0.1 - 1.0 mg/mL).
• Cytolase 300 P filter paper activity, 215 IU/g powder
• cellobiose Novozyme
• the DNS assay is the most commonly used technique for measuring reducing sugars released by cellulose hydrolysis.
• a glucose standard is used for the calibration, thus the reducing sugars are measured as "equivalent glucose.”
• the method for recovering Ca(OH) 2 is to wash the pretreated material with water, and to contact or react this wash water containing lime with carbon dioxide. This converts soluble Ca(OH) 2 to insoluble CaCO 3 that can be removed by precipitation. The CaCO 3 can then be heated to produce CaO and CO 2 . The CaO is hydrated to Ca(OH) 2 which can be reused as the lignocellulose treatment agent. Carbon dioxide can, in turn, be reused for lime recovery. Thus, ideally, it is a system capable of total recycling.
• the carbonate concentration is quite low when the pH is below 9.5. Thus, to form and precipitate more CaCO 3 , the pH was maintained above 9.5.
• FIG. 5 A systematic flow diagram of the continuous recovery experimental apparatus is shown in Figure 5.
• the pretreated bagasse was packed in a 1" I.D. ⁇ 8.5" high glass column. Rubber stoppers at both ends had connections for the inlet (bottom) and the outlet (top). Filters (nylon cloth) were glued on both stoppers.
• a peristaltic pump (Watson-Marlow, 502S) pumped water through the column. The average volumetric flow rate was 20 ml/min.
• the outlet from the column went to a 300-mL flask. Carbon dioxide was bubbled thought the lime-saturated liquid in this flask to produce CaCO 3 .
• a pH probe was placed in this flask to continuously monitor the pH.
• a glass fiber filter (G6, Fisher Scientific, Inc.) was placed between the fritted glass filter and glass jar. A clamp was used to hold it and provide a good seal. The pump suction was the driving force for filtration. The filters were replaced periodically when they clogged with the CaCO 3 paste. The filtered water was then pumped back to the column for washing, thus completing the cycle.
• the washing was stopped after about one hour.
• the wash water left in the glass jar clamped to the filter, was transferred to the flask and left for 24 hour to let CaCO 3 settle.
• Clear liquid (1 mL) was taken from the top of the flask.
• the clear liquid was decanted slowly and collected in another beaker.
• the bottom portion containing much higher amounts of CaCO 3 was discarded after measuring its volume.
• the same volume of fresh water was added to the system so that the liquid volume before and after precipitation and decantation remained the same. Further recovery of the lime remaining in the biomass was performed with this batch of decanted water for about 45 minutes.
• the CaCO 3 -saturated water was again left for precipitation and a sample of clear liquid was taken after this second precipitation.
• the 3-day reducing sugar yields were used as the measure of enzymatic susceptibility of lime-treated bagasse.
• the reducing sugar yields were calculated as mg equivalent glucose/g dry bagasse.
• 50% and 85% of the 3-day sugars were released in 6 hours and 24 hours, respectively.
• Table 7 summarizes the conditions and the reactor systems used in the various bagasse experiments.
• This pretreated material was hydrolyzed in enzyme solutions containing various calcium acetate concentrations.
• the calcium acetate solutions were prepared by adding various amounts of Ca(OH) 2 (according to the lime loadings used for the pretreatment) to 150 mL water, and then adding acetic acid to reduce the pH to 4.8.
• the enzymes were added to solutions only after the pH was brought to 4.8, thus there was no loss of enzyme acidity due to high pH.
• the 3-day sugar yield obtained from this ammonia-treated material clearly shows that increased calcium hydroxide loadings decrease sugar yields due to calcium acetate inhibition of the enzyme.
• the sugar yield was 390 mg eq. glucose/g dry bagasse. This yield is 1.16, 1.14, 1.16, 1.15, 1.25 and 1.22 of that obtained rom samples hydrolyzed in the solutions with 2, 5, 10, 15, 20 and 30 g Ca()H) 2 /100 g dry bagasse, respectively.
• these factors were used to correct the sugar yields. Since this approach is simplified and only approximately corrects for calcium acetate inhibition, the original data (without the correction factor) are reported in addition to the corrected data.
• the 3-day reducing sugar yield for untreated bagasse sample (used as a control) was 40 mg eq. glucose/g dry bagasse which is only about 6% of the theoretical yield.
• Many different conditions as listed in Table 7 produced high sugar yields.
• Six high yielding conditions are tabulated in Table 8. The choice of conditions to be used industrially will depend not only on the sugar yields, but also on the expense associated with conditions.
• Softwood newspaper is the largest fraction of most residential municipal solid waste. Profitable utilization of softwood newspaper could help solve the ever-growing trash disposal problem.
• the composition of softwood newspaper is about 70% polysaccharides and 30% lignin, thus, the theoretical yield is bout 750 mg eq. glucose/g dry newspaper.
• the purpose of this study was to check the feasibility of using Ca(OH) 2 to pretreat newspaper.
• the conditions used for pretreating softwood newspaper are summarized in Table 9.
• Wheat straw is one of the most abundant agricultural cop residues. In the United States, about 20% of cropland produces wheat, thus large quantities of wheat straw are generated. Typically, based on dry weight, wheat straw is 39% cellulose, 36% hemicellulose, and 10% lignin. According to his composition, the maximum theoretical yield is about 800 mg eq. glucose/g dry wheat straw.
• Ca(OH) 2 was leached or washed out of the pretreated biomass.
• the lime-saturated wash water was carbonated to convert Ca(OH) 2 to insoluble CaCO 3 that was subsequently settled.
• the recovered CaCO 3 can be calcinated to form CaO, which can be hydrated to Ca(OH) 2 , and thus reused.
• the washing, carbonation and precipitating steps were performed.
• the experiments were conducted by two different approaches, namely, continuous and batch recovery processes.
• the calcium content in the raw bagasse sample was 0.4 g Ca/100 g dry bagasse.
• the residual calcium content in the bagasse sample was brought down to about 2 g Ca/100 g dry bagasse from 5.4 g Ca/100 g dry bagasse
• the first three samples (D, E, and F) used six washings whereas the other samples used ten washings.
• the calcium concentration was reduced to about 1.7 g Ca/100 g dry bagasse
• the calcium concentration was reduced to about 2.2 g Ca/100 g dry bagasse.
• Sample F and G received the same lime treatment. Whereas sample F was washed six times Sample G received four additional washings. These additional washings reduced the residual calcium content from 2.2 to 1.5 g Ca/100 g dry bagasse. Thus ten washings were able to remove 86% of the added calcium.
• KH 4 OH was a 30% (w/w) solution of ammonia in water.
• Trichoderma reesei cellulase operates at pH 4.8.
• the pH of pretreated biomass is about 11.5, so an acid must be added to lower the pH.
• CO 2 is generated, so it will be the cheapest acid for pH adjustment.
• a simple experiment was performed in which a few lime-saturated wash water samples were bubbled with 1 atmosphere CO 2 for about 15 min. The minimum pH that was reached was about 6.5. Thus a stronger acid than CO 2 will be required to lover the pH to 4.8. It would be more desirable to use a cellulase system that operates at pH 7 such as those in bacteria (e.g. Clostridium thermocellum).
• calcium hydroxide is an excellent pretreatment agent. Many different conditions produced high sugar yields. There was no significant effect of water loading on sugar yields, although 10 g water/g dry material produced slightly higher yields. lime loadings of 10 and 15 g Ca(OH) 2 /100 g dry material worked well. It was generally found that the lover temperatures (50°C, 65°C) required longer times (24 hours), whereas higher temperatures (135°C) needed shorter times (1 hour) to produce high yields.
• the recovery process was able to reduce the calcium content in biomass from 8.1 to about 1.5 g Ca/100 g dry material, thus recovering 86% of the added calcium.
• the biomass may be contacted with a solution of hot lime water. This may be accomplished in a number of ways:
• Method 1 A solution of hot (temperature range of from about 40°C to about 150°C) saturated lime water is circulated through a packed bed of biomass for a time period of from about 1 hour to about 36 hours. As the solution exits the bed, it is heated to replace heat loss in the packed bed.
• the solution of saturated lime water can be prepared by mixing excess lime with water and separating the excess solid lime from the water phase by filtration, hydroclone separation ( Figure 6), settlement, or centrifugation.
• Method 2 A solution of hot (temperature range of from about 40°C to about 150°C), saturated lime water is circulated through a stirred slurry of biomass for a time period of from about 1 hour to about 36 hours.
• the biomass is separated from the solution by a filter, hydroclone ( Figure 7), settler, or centrifuge. As the solution exits the hydroclone, it is heated to replace heat loss in the stirred slurry of biomass.
• the solution of saturated lime water can be prepared by mixing excess lime with water and separating the excess solid lime from the water phase by filtration, hydroclone separation ( Figure 7), settlement, or centrifugation.
• Method 1 the lime solids must always be kept in contact with hot water at the highest temperature in the loop, such as between 40°C and 150°C. This is required because lime is relatively more soluble in cold water than in hot water, if the water contacting the lime solids were cold, it would dissolve too much lime. Then, if the lime solution were heated later, lime would either precipitate out and foul the heat exchanger or deposit on the biomass. This explains why the water is heated before it contacts lime solids rather than after.
• the materials needed for this invention include: Biomass, lime, or calcium hydroxide, and water.
• the manipulative procedures for this invention include: Mixing, heating, and simultaneous mixing and heating. Thus, these materials and procedures are capable of a number of permutations, as diagrammatically shown in Figure 8.
• the notations used in Figure 8 are: L - lime; W - water; B - biomass; M - mixing; H - heating; and M & H -simultaneous mixing and heating.
• An arrow in Figure 8 signifies adding, introducing, or a step to be performed.
• FIG 9 shows the lime treatment process for ruminant animal feed production.
• the lime may be added directly to the biomass, as shown.
• the biomass may be contacted with a circulating solution of saturated lime water to avoid excess lime addition.
• the raw biomass is soaked in hot (ca. 65°C) lime water for about 24 hours.
• the lime water is circulated through an adsorption column where it is contacted with carbon dioxide.
• the carbon dioxide reacts with the lime to form insoluble calcium carbonate which is filtered out and sent to a lime kiln.
• the calcium carbonate is heated to about 1200°C in the lime kiln which drives off the carbon dioxide.
• the hot exit gases (primarily carbon dioxide with some nitrogen from the combustion air) are cooled in a countercurrent beat exchanger recovering high-pressure steam that may be used for electricity production and/or process heat.
• the cooled carbon dioxide is recycled to the absorption column where the carbon dioxide again reacts with lime water. Inert, such as nitrogen, will exit the absorption column. Make-up carbon dioxide must be added to replace any losses.
• the circulating lime water will contain free sugars and protein extracted from the biomass. In addition, there will be some calcium acetate produced from the acetyl groups on the hemicellulose. A bleed stream will be taken off from the circulating loop that will be acidified with sulfuric acid so the calcium ions are precipitated as gypsum.
• the free sugars, protein, and acetic acid (HAc) will be concentrated by an appropriate technology (e.g reverse osmosis or multi-effect evaporation). It may be sold as monogastric (e.g. chickens, pigs) animal feed.
• the treated biomass will emerge from the process in a wet state. If the ruminant animals are located close to the processing plant, they may eat it directly in the wet state. If it must be stored for awhile before it is consumed, it may be dried in the steam driers we have previously described in past disclosures.
• Oxygen is believed to partially oxidizes the lignin which opens the biomass structure making it more enzymatically digestible.
• Oxygen from high-pressure oxygen tanks was added to samples of newspaper under increasing pressure (Figure 10). Treatment conditions were consistent with those previously described. Temperature of the biomass was 120°C for 24 hours with 30 g calcium hydroxide/100 g dry newspaper, and water at 16 g/g dry newspaper. Increasing amounts of oxygen-containing gas was introduced to samples of newspaper from high-pressure tanks. After pretreatment, samples were digested enzymatically and the yield of glucose determined after three days. Newspaper treated with only lime resulted in a yield of 418 mg eq. glucose/g dry newspaper. For comparison purposes, untreated raw newspaper yields 240 mg eq. glucose/g dry newspaper. With 20 pounds/square inch gauge (psig), glucose yield increased over 10%. With increasing oxygen pressure up to 100 psig, glucose yield increased to over 500 mg eq.
• Useful oxygen pressures are between about 20 psig to about 500 psig and preferable are between about 100 to about 400 psig.
• Oxygen is supplied to the biomass from high-pressure sources such as pure oxygen gas, oxygen-containing gas, or compressed air.

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• 1993
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