Patent Application
20110094505
The present invention relates to an acid hydrolysis process of cellulosic and lignocellulosic materials, digestion vessel and hydrolysis reactor. Sugars are obtained according to this invention through acid hydrolysis of cellulosic materials, such as paper and cardboard, and lignocellulosic materials, such sugarcane bagasse, vegetable straws and wood, using a suitable solvent to remove lignin before the hydrolysis reaction. The obtained sugars can be used as chemical intermediates or converted into ethanol that, in its turn, can be employed as fuel.
For effect of this invention, cellulosic and lignocellulosic materials are characterized as complex mixtures containing mainly cellulose, hemicellulose and lignin. In addition to the three mentioned compounds, lignocellulosic materials contain smaller proportions of proteins, oils, silica and calcium, sodium, potassium, and iron salts, among others. Cellulose, which is a glucose polimer, can be presented in proportions between 30 and 80% in weight, depending on the type of material. Hemicellulose, which is a polimer composed by units of xylose, arabinose and galactose, can be present on proportions between 20 and 40% in weight. Lignin is a complex phenolic polymer, present in natural lignocellulosic materials.
Many cellulosic and lignocellulosic materials constitute industrial and domestic residuals, which present problems of industrial or municipal waste because, although biodegradable, they can occupy big volumes in sanitary landfills. Incineration of these materials can be put in force, but its produced ashes or fumes can represent a serious restriction to this alternative. For other side, there is a growing concern with the burning of fossil fuels because of the generation of CO2 and other gasses that tend to make the global heating worse. It is very well established that the hydrolysis of cellulosic materials produces its respective sugars. These substances can be converted into several organic products through the processes of chemical or biological conversion. The most important of these products is ethanol, which can be obtained through glucose fermentation or from pentoses deriving from hemicellulose. Ethanol can be used as liquid fuel in internal combustion engines in place of gas and diesel oil, which are fuels from fossil origin. Optionally, hexoses can be hydrogenated to obtain manitol e sorbitol, which are important chemical intermediates. The pentoses can be hydrogenated to xylitol that has sweetener properties or can be fermentated in such a way to obtain mainly methane that can be used as industrial or domestic fuel in place of the liquid petrol gas (LPG). Lignin can be the source of phenolic compounds or can be used as fuel in industrial boilers or heaters. These possibilities justify the technological effort that has been employed, for some decades, to obtain technical and economically viable processes for the hydrolysis of cellulosic and lignocellulosic materials in such a way to obtain corresponding sugars.
The cellulose and hemicellulose hydrolysis can be made at room temperature using enzymes as catalysers. The enzymes are more selective. In the case of lignocellulosic materials, however, cellulose and hemicellulose fibers are encapsulated by structures composed by lignin, which are chemically more resistant and make difficult to access enzymes, rendering slower its action. Additionally, the formed sugars tend to inhibit the catalytic action of enzymes limiting this way the concentrations that can be obtained. An alternative has been conducted the sugar fermentation to form ethanol, but it restricts the process application exclusively for the production of ethanol. These limitations allied to the high cost of enzymes commercially available render processes of enzymatic hydrolysis not much attractive by an economic point of view.
The catalytic activity of strong acids for reactions of cellulose and hemicellulose hydrolysis is known for more than one century. The use of concentrated sulphuric acid to promote hydrolysis of cotton cellulose was documented for the first time in 1883. In 1918, it was proposed by researchers of the United State Department of Agriculture a process for the production of sugars and other products from corn seed fibers, in two stages, using diluted sulphuric acid in the first one and concentrated acid in the second one. In 1937, in Germany, it was operated the first industrial unit of catalyzed wood hydrolysis by hydrochloric acid. In 1948, it was developed in Japan a hydrolysis process using concentrated sulphuric acid. Sugars produced by the hydrolysis reaction were separated from the acid passing the mixture through membranes. More recently, the hydrolysis process based on the use of concentrated acids was enhanced, being proposed the use of ion exchange resins to separate the solution acid from sugars by means of chromatographic processes. HESTER and HESTER & FARINA related processes of this nature in the U.S. Pat. No. 5,407,580, published on Apr. 18, 1995, and number U.S. Pat. No. 5,538,637, published on Jul. 23, 1996, respectively.
Processes using concentrated sulphuric acid have the advantage of operating in relatively low temperatures (80 to 100° C.) as showed by FARONE in the U.S. Pat. No. 5,562,777, published on Oct. 8, 1996. The use of concentrated acid, however, suffers some inconveniences, such as low yield in sugars, and the necessity of relatively high investments in the chromatographic system of sugar separation and in the acid re-concentration unit. Moreover, the acid re-concentration process consumes big quantities of energy.
Processes using diluted acids do not require acid separation and re-concentration. Additionally, with diluted acids it is possible to use cheaper materials to build equipments. Processes of such type have been described since the end of XIX century. It is known that hemicellulose can suffer acid hydrolysis in relatively mild conditions for acid temperature and concentration. In counterpart, cellulose is sufficiently resistant to acid hydrolysis, requiring longer contact times and higher temperatures. When it is used sulphuric acid, the more frequently indicated concentrations are from 0.5% to 3% and the temperatures are between 130° C. and 260° C. That, however, can be a serious inconvenience because these conditions can favor parallel reactions, particularly sugar decomposition, reducing the process yield.
One example of the hydrolysis processes of cellulosic and lignocellulosic materials catalyzed by diluted acids is described by BRELSFORD in the U.S. Pat. No. 5,411,594, published on May 2, 1995. This process is conducted in two stages. In the first stage, the cellulosic material, along with recycled liquid of the second stage, is introduced, under pressure, in a cased reactor externally heated with steam where is kept a temperature between 135 to 195° C. and a residence time between 1 and 20 minutes. The liquid reactor effluent, containing pentoses and hexoses, constitutes the process product. The solid part is separated, receives a solution of sulphuric acid, and follows for the second stage what is also an externally heated cased reactor, operated between 165 and 260° C., with a residence time between 0.5 and 20 minutes. The second stage effluent is separated in two currents. The solid current is composed essentially of lignin and non-hydrolyzed cellulose. The liquid current, containing acid and cellulose hydrolizate is recycled for' the first stage. In the patent of BRELSFORD, it is also described depressurization schemes of reactor effluents, made with the objective of reducing the material temperature before perform the respective separations and utilization ways of the steam produced in the depressurization systems. In the typical example presented in the patent, it is indicated a yield of 86.6% related to pentoses and 79% related to hexoses. According to the publication of the United States Department of Energy that presents the process described in the patent of BRELSFORD in “The BEI Cellulose Hydrolysis Process and Reactor System (BEI CHP&RS)” of August 2002, the conversation is from 70 to 80% of hemicellulose in the first stage and from 60 to 70% of cellulose in the second one.
As previously noted, the use of diluted acid requires more elevated temperatures and longer reaction times, when compared to the processes using concentrated acid. This can be a serious inconvenience because the permanence of sugars by relatively long times, in high temperatures, can promote a significant decomposition of these sugars, leading to the formation of several by-products. The dehydratation of pentoses produces mainly furfural while the dehydratation of the hexoses produces 5-hydroxymethylfurfural. The lignin itself can partially decompose forming aromatic alcohols. Other by-products of sugars resulting from decomposition are observed, such as acetic acid and methanol, which reduce the process yield. Besides, when sugars are used for producing ethanol by fermentation, these sub-products can act as growth inhibitors and microorganism activity.
Other inconvenient of the processed using acids in concentrations over 1% is the relatively high quantity of alkali required to neutralize the sugar solution and the necessity of effluent discard that result in the neutralization. When sulphuric acid is used as catalyser of hydrolysis reactions and limewater as neutralizing agent, it is formed hydrated calcium sulfate, which is solid. Although this material founds application in civil construction, big quantities cannot find consumption and become a serious problem for disposal.
An alternative for the hydrolysis processes of cellulosic materials is to combine acid hydrolysis with the enzymatic hydrolysis. In this case, the first stage, also called pretreatment stage, is generally an acid hydrolysis. The conditions are such that all hemicellulose and part of cellulose are hydrolyzed. The hydrolizate is then separated from the residual solids, which contain mainly lignin and cellulose. This solid material undertakes enzyme action (cellulases), which hydrolyzes the cellulose molecules. A process presenting these characteristics is on development in the US Department of Energy's (DOE) Renewable Energy Laboratory (NREL), in the Biomass Program: “The DOE Bioethanol Pilot Plant A Tool for Commercialization” DOE/GO-10200-1114, September, 2000. The pretreatment equipment described in this publication is constituted by a horizontal and a vertical cylindrical body in the interior from which the mixture movement of the biomass and the acid solution is promoted by the action of threads assembled around the coaxial axis with the cylindrical bodies. The separation of the hydrolizate from the residual solids that leave the pretreatment reactor requires the use of filters built from materials resistant to acid used as catalyst. After washed, solids can then be subjected to enzymatic hydrolysis.
The process described above has the inconvenience of high energy necessary to feed the cellulosic material and the high investment required for building reactors, filters and ancillary equipments that contacts the acid solution. These factors, in addition to other ones such as high cost of enzymes used in the enzymatic hydrolysis stage, have hampered the commercial use of these processes for lacking of economic viability.
An additional serious difficulty observed in the hydrolysis processes of lignocellulosic materials is the presence of lignin. This substance has a rigid physical structure and is chemically very resistant. Lignin involves polysaccharide currents, making difficult to access enzymes and diluted acids that catalyze the hydrolysis. Many processes have been proposed for treating cellulosic materials before or during hydrolysis processes. The explosion with steam is one of the most cited. FUNK, for example, in the U.S. Pat. No. 4,070,232 of Jan. 24, 1978, describes a pre-hydrolysis process in presence of a chloridric, formic or acetic acid and water steam. Although efficient as a way to reduce the lignin inhibiting action, the process described by FUNK has the inconvenience of consuming great quantities of energy and generating considerable quantities with acid-contaminated steam, which presents a difficult reutilization. Other alternatives have been proposed. It is well known that certain organic compounds can dissolve lignin from lignocellulosic materials. KLEINERT et al, in the U.S. Pat. No. 1,856,567 published on May 3, 1932, have already proposed the use of acid solutions of alcohols, particularly ethanol, in high pressures and temperatures over 150° C. to remove lignin from wood. However, the contact time (two steps with 3 hours each) is excessively long for a practical application of the process such as originally described. PASZNER and CHANG, in the U.S. Pat. No. 4,470,851, published on Sep. 11, 1984, describe a process of “quick” hydrolysis of lignocellulosic materials with simultaneous lignin dissolution using a concentrated aqueous solution of acetone, containing small quantities of acid. The dissolution and hydrolysis are conducted to a temperature preferably between 160 and 210° C. with an acid concentration between 0.05 and 0.5% in weight. Similar process is described by HILST in the Brazilian patent PI 9600672-2 A, published on Dec. 30, 1997 (RPI 1410). The hydrolysis reactor described by HILST is a stainless steel vertical vessel. The feeding of lignocellulosic material is made at the top, keeping a descendant flow along the reactor. An aqueous solution, containing a solvent, typically ethanol, water and catalyst is fed through vertical concentric piping installed in the reactor center and distributed through sprinkler holes. The reactor also is provided from several systems of external liquid recirculation, which is removed through filtration screens and returned through piping concentric to feeding pipes of the solvent acid solution. The removal of liquids is made in the recirculation systems, containing lignin and soluble sugars, essentially pentoses and hexoses. These currents are subjected to a flash evaporation that rapidly reduces the temperature and separates part of the solvent. The rest of the solvent is separated by distillation. Lignin, insoluble in the remnant sugar solution, is then separated by decantation. It is indicated a recovery of up to 85% of the sugars after a contact time of 10 to 40 minutes and a temperature from 160 to 250° C. From the process analysis described by HILST, it is understood that practically all lignin and the cellulosic material are solubilized, remaining only mineral material, which is deposited at the bottom of the reactor. Processes described by PASZNER and CHANG and by HILST, taken here as reference, are typical from the processes described in the state-of-art, being characterized by lignin solubilization with reactions of cellulose and hemicellulose hydrolysis.
It was now discovered that the processes based on the use of lignin solvents can present bigger yields if the lignin dissolution step, hemicellulose acid hydrolysis and cellulose hydrolysis were conducted in distinct steps, in separated vessels, or in the single vessel with restricted for each step. The operation in separated steps was observed to optimize the conditions occurring in each step and, thus, optimize the process as a whole, obtaining sugar yields bigger than those described in the previous art.
The present invention relates to process for obtaining sugars by acid hydrolysis of cellulosic and lignocellulosic materials characterized by the fact that comprise the steps:
(a) lignin dissolution: step where it is performed the lignin dissolution;
(b) pre-hydrolysis: step where it is conducted mainly the hemicellulose hydrolysis;
(c) cellulose hydrolysis;
being that the steps above can happen separately or distinctly, in this order or in which step (b) comes first than step (a).
Although there are several arrangement options to conduct the several steps, the preferred arrangement, according to this invention, is a sequence in that first it is performed the lignin dissolution, then it is conducted mainly hemicellulose hydrolysis (pre-hydrolysis) and finally it is made cellulose hydrolysis. Preferably the solid material currents effluent from the first and second steps are washed out with water in such a way to minimize the contamination of the following steps with the compounds prevailing in the previous steps. The lignin solution and the sugar solution are obtained in distinct currents and optionally the sugar current rich in pentoses monomers and oligomers to be obtained separately from sugar current rich in hexose monomers and oligomers.
Characteristics bringing the main benefits of the process focused in this invention are:
a) conduct the first step (lignin dissolution) in conditions such as hemicellulose or cellulose hydrolysis rate is minimal and separate the major part of lignin solution before feeding the cellulosic material for the pre-hydrolysis step;
b) conduct the pre-hydrolysis step in relatively mild conditions for acid concentration and temperature and separate partial or totally the sugar solution (monomers and oligomers) before feeding the residual cellulosic material to the cellulose hydrolysis step;
c) conduct the cellulose hydrolysis step in more severe conditions for acid concentration and temperature and remove the sugar solution (monomers and oligomers) as an isolated current or a current mixed to the sugar current deriving from the pre-hydrolysis step.
1. The lignin dissolution step can be conducted using suitable solvents and conditions favoring the action of these solvents at the same time in which minimize the hemicellulose hydrolysis. The preferred solvents, according to the objective of this invention, include: ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, or its mixtures, in neutral or slightly acid media; aliphatic alcohols and glycols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-butanol, 1-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol or ethyl, propil and butyl glycols, and its mixtures, in neutral, alkaline or slightly acid media; ketone mixtures, aliphatic alcohols and/or glicols in neutral or slightly acid media and its mixtures in neutral, alkaline or slightly acid media; mixtures of ketones and aliphatic alcohols and/or glycols in neutral or slightly acid media. These solvents being either anidrous or, preferably, in aqueous solutions. The temperature range required for lignin dissolution is from around 70 to around 200° C. The preferably employed solvent is the ethanol in aqueous solution.
During the lignin dissolution step, the temperature is kept in the range from around 70 to around 200° C., being that the major part of the lignin solution is separated from the residual solids right after the formation of the referred solution.
The cellulosic material obtained after the lignin dissolution step is subjected to a water washing or, optionally, a diluted sugar solution, in countercurrent, in such a way to eliminate the major part of the solvent dragged by the cellulosic material. Particularly it can happen washing water injection in countercurrent of the residual material obtained after cellulose hydrolysis after removing the referred residual reactor material, in such a flowing that apart from the present sugar concentration in the solution that leaves the cellulose hydrolysis solution is between around 5 and around 35% in weight The dissolution step happens in the digestion vessel with the following characteristics:
vertical cylindrical shape preferably;
the feeding area of the lignocellulosic material and solvent is located in one of its tips;
the digestion vessel can be provided from a separation device and liquid removal, which constitutes the lignin solution;
The process according to the invention employs preferably reactor in which is conducted the pre-hydrolysis step and the hydrolysis step of cellulosic and lignocellulosic materials for obtaining sugars, being it is presented in the form of a vessel or a set of cylindrical, conical or partially cylindrical or partially conical vessels serially interlinked, being that the cellulosic or lignocellulosic material is fed in one of its tips and the residual material removed in the opposed tip, and where it can be identified: (a) a pre-hydrolysis area or vessel; (b) a hydrolysis area or vessel; (c) a washing area of the residual material after the hydrolysis area. It is employed preferably vertical vessels, being that the area of pre-hydrolysis is preferably cylindrical and the area of hydrolysis is preferably partially cylindrical and partially cylindrical and partially conical.
The steps of hemicellulose and cellulose steps are conducted in acid media. Inorganic acids such as sulphuric, nitric, phosphoric and hydrochloric are effective to obtain these conditions. Sulphuric acid and nitric acid are preferred. When these acids are used, it is required concentration ranges between 0.1 and 2.0 g/L with temperatures between 70 and 200° C., preferably between around 100 to around 160° C. and a residence time of 1 to 20 minutes in the pre-hydrolysis step and concentrations between 0.2 and 4.0 g/L, with temperatures between 130 and 250° C., preferably between around 130 to around 200° C., for a residence time of 2 to 40 minutes, in the hydrolysis step.
The pre-hydrolysis step is conducted in relatively mild conditions for acid concentration and temperature and of which the sugar solution, mainly pentose monomers and oligomers is separated before feeding the cellulosic material for the following steps, obtaining a yield in sugars superior to 85% from which theoretically could be obtained from the hydrolyzed cellulosic material, being possible to reach 95% if the conditions were optimized.
The step of cellulose hydrolysis is conducted in more severe conditions that the pre-hydrolysis step for acid concentration and temperature and by the fact that the sugar solutions, mainly hexose monomers and oligomers, is removed as an isolated current or, optionally, in mixture with the sugar current deriving from the pre-hydrolysis step, obtaining a yield in sugars superior to 85% from which theoretically could be obtained from the hydrolyzed cellulosic material.
The invention also relates to digestion vessel employed in the lignin dissolution step, of vertical cylindrical aspect, to which is fed with lignocellulosic material and solvent in one of its tips, being provided a liquid removal device separated from the solids through which is removed the lignin solution and of a feeding and water distribution device or, optionally, of diluted sugar solution, immediately before the exit tip of the cellulosic material.
The invention also relates to reactor in which is conducted the pre-hydrolysis step and the step of cellulosic and lignocellulosic material hydrolysis for obtaining sugars characterized by the fact that it is a vessel or a set of cylindrical, conical or partially cylindrical or partially conical vessels serially interlinked, being that the cellulosic or lignocellulosic material is fed in one of its tips and the residual material removed in the opposite tip, and where can be identified: (a) an pre-hydrolysis area or vessel; (b) a hydrolysis area or vessel; (c) a washing area of the residual material after the hydrolysis area. Preferably this cylindrical or partially cylindrical and partially conical vertical vessel receives feeding of cellulosic material in the upper tip and the residual material is removed in the lower tip, or also can receive the feeding of the cellulosic material in the lower tip and the residual material is removed in the upper tip.
Some complementary characteristics on the reactor according to the invention:
The following examples have only an elucidating nature and shall not been taken for limiting effects of the invention.
The process focused on this invention, in its preferred form, is described in this paragraph with the aid of
Other system construction options, not showed in
Annexed
The lignin solution leaving the reactor follows to a solvent recovery system, lignin separation and removal of the major part of water introduced in the process. Details for the system depend on the type of solvent used, relation between water and solvent present in the mixture and energy consumption needed for performing the separation. For suitable solvents to the process subjected of this invention, the mixture separation processes of these solvents with water and solid materials are known in the state of art and do not constitute part of the object of this invention. However, given the characteristics of the process and the Digestion Vessel that constitute the object of this invention, the solvent recuperation and the lignin and water separation are made without the presence of significant big quantities of acid or residual sugars, which simplifies the separation operations and allows the use of cheaper equipments, since they are required special materials. Even small sugar quantities deriving from hemicellulose hydrolysis in the lignin digestion area can be recovered if the solution is used as washing water of the residual cellulosic material after lignin digestion (Current (13) presented in
Sugar currents removed from the Reactor contain small quantities of acid, products of sugar decomposition and solvent traces. These current demand only an acid neutralization and solid material separation, as showed in
The residual solid current removed from the ReactOr contains small quantities of acids. This current demands only an acid neutralization and separation of solid materials, as showed in
| Number | Date | Country | Kind |
|---|---|---|---|
| PI0500534-5 | Feb 2005 | BR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/BR2006/000019 | 2/9/2006 | WO | 00 | 12/12/2007 |
