CA1267407B - Method of rendering lignin separable from cellulose and hemicellulose and the product so produced - Google Patents
Method of rendering lignin separable from cellulose and hemicellulose and the product so producedInfo
- Publication number
- CA1267407B CA1267407B CA529,627A CA529627A CA1267407B CA 1267407 B CA1267407 B CA 1267407B CA 529627 A CA529627 A CA 529627A CA 1267407 B CA1267407 B CA 1267407B
- Authority
- CA
- Canada
- Prior art keywords
- order
- lignocellulosic material
- pressure vessel
- lignin
- steam
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07G—COMPOUNDS OF UNKNOWN CONSTITUTION
- C07G1/00—Lignin; Lignin derivatives
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
- C08H8/00—Macromolecular compounds derived from lignocellulosic materials
-
- C—CHEMISTRY; METALLURGY
- 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
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C1/00—Pretreatment of the finely-divided materials before digesting
- D21C1/02—Pretreatment of the finely-divided materials before digesting with water or steam
-
- 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
Abstract
A METHOD OF RENDERING LIGNIN SEPARABLE FROM CELLULOSE AND
HEMICELLULOSE AND THE PRODUCT SO PRODUCED
ABSTRACT OF THE DISCLOSURE
In the process of rendering lignin in lignocellulosic material separable from the cellulose and hemicellulose wherein the lignocellulosic material is packed in a divided form in a pressure vessel which is rapidly filled with steam at a pressure of at least 500 psi to heat the lignocellulosic material to an extrudable condition at a temperature in the range 185 to 240°C in less than 60 seconds, followed by immediately extruding the lignocellulosic material to atmosphere, it has been found that the production of toxic components can be minimized by gently venting the pressure vessel to atmosphere to reduce the steam pressure to between of the order of 200 psi and of the order of 450 psi as soon as the extrudable condition is reached. The lignocellulosic material is then extruded instantly to atmosphere immediately after the venting step.
HEMICELLULOSE AND THE PRODUCT SO PRODUCED
ABSTRACT OF THE DISCLOSURE
In the process of rendering lignin in lignocellulosic material separable from the cellulose and hemicellulose wherein the lignocellulosic material is packed in a divided form in a pressure vessel which is rapidly filled with steam at a pressure of at least 500 psi to heat the lignocellulosic material to an extrudable condition at a temperature in the range 185 to 240°C in less than 60 seconds, followed by immediately extruding the lignocellulosic material to atmosphere, it has been found that the production of toxic components can be minimized by gently venting the pressure vessel to atmosphere to reduce the steam pressure to between of the order of 200 psi and of the order of 450 psi as soon as the extrudable condition is reached. The lignocellulosic material is then extruded instantly to atmosphere immediately after the venting step.
Description
~J2~ 7~
This invention relates to a method of renderin~
lignin separable from cellulose and hertlicellulose and the product so procluced.
It has already been proposed in Canadian Patent No. 1,096,37~ dated February 24, 1981 "Method of Rendering lignin separable from cellulose and hemicellulose in lignocellulosic material and the p.roduct so produced", E.A.
DeLong, to pack a pressure vessel, having a closed valved outlet, with lignocellulosic material in a divided, exposed, moist form, then to rapidly fill the pressure vessel with steam at a pressure of at least 500 psi (3450 kilo Pascals) to raise the temperature of the lignocellulosic material in less than 60 seconds to a temperature in the range 185C to 240C and thermally soften the lignocellulosic material into a plastic condition, and then, as soon as the plastic condition has been attained, opening the valved outlet and instantly expelling the lignocellulosic material to atmosphere. The lignocellulosic :material issues from the outlet in a particulate form with the lignin therein rendered into particles substantially in the range 1 to 10 microns and substantially without thermal degradation occuring to produce cross-links between the lignin, cellulose and hemicellulose, so that a substantial portion of the lignin is separable from the cellulose and hemicellulose by solvent extraction with, for example, ethanol or methanol at room temperature.
This invention relates to a method of renderin~
lignin separable from cellulose and hertlicellulose and the product so procluced.
It has already been proposed in Canadian Patent No. 1,096,37~ dated February 24, 1981 "Method of Rendering lignin separable from cellulose and hemicellulose in lignocellulosic material and the p.roduct so produced", E.A.
DeLong, to pack a pressure vessel, having a closed valved outlet, with lignocellulosic material in a divided, exposed, moist form, then to rapidly fill the pressure vessel with steam at a pressure of at least 500 psi (3450 kilo Pascals) to raise the temperature of the lignocellulosic material in less than 60 seconds to a temperature in the range 185C to 240C and thermally soften the lignocellulosic material into a plastic condition, and then, as soon as the plastic condition has been attained, opening the valved outlet and instantly expelling the lignocellulosic material to atmosphere. The lignocellulosic :material issues from the outlet in a particulate form with the lignin therein rendered into particles substantially in the range 1 to 10 microns and substantially without thermal degradation occuring to produce cross-links between the lignin, cellulose and hemicellulose, so that a substantial portion of the lignin is separable from the cellulose and hemicellulose by solvent extraction with, for example, ethanol or methanol at room temperature.
The Derlon~ process not only has the unique feature c~E
renderin~ a surprisin~ly high proportion of thermally undegraded lignin separable from the cellulose and hemicellulose, but has the additional unique Eeature that this -thermally undegraded lignin can be solven-t extracted without thermal degradation occuring of the lignin, cellulose and hemicallulose during khe solvent extraction step.
While the DeLong process has proved to be useful, it has been observed that when the starting material is nearly air dry as is often the case with straw and bagasse, and may be the case with a percentage of wood chips depending on how they have been stored, depolymerization of both lignin and xylan occurs producing toxic monomers of lignin and degrada~.ion components of xylan which, in some instances render the particulate material as it has issued from the outlet unacceptable for use in any form of fermentation process. These toxic components can be extracted by water or by the normal lignin solvents such as ethanol, methanol and sodium hydroxide. However, it may be desirable to use the particulate material as a ~ermentation feed stock, or as an animal feed, directly from the outlet, in which case it i5 desirable to minimize the depolymerization of both lignin and xylan so that the production of toxic components of lignin in the particulate material that issued rom the outlet is minimal and the depolymerization of the xylan is also minimized.
, , According to the present inven-tion there is provided a method o~ renclering :lignirl separab:Le from cellulose and hemicellulose in lignocellulosic material, comprising:
a) packing the lignocellulosic material in a divided, exposed, moist form in a pressure vessel having a valved outlet, b) with the outlet closed, rapidly filling the pressure vessel with steam to a pressure of at least 500 psi to bring, by means of the pressurized steam, substantially all of the lignocellulosic material to a temperature in the range of 185 to 240C in less than 60 seconds and thermally soften the lignocellulosic material into an plastic condition, c) as soon as the said plastic condition has been attained, gently venting the pressure vessel above the level of the lignocellulosic material to atmosphere to reduce the steam pressure in the pressure vessel to between 200 psi and 450 psi, and then immediately opening the valved outlet and e~plosively expelling the lignocellulosic material, in the said plastic condition, from the pressure vessel through the outlet to atmosphere so that the said material issues from the outlet in particulate form with lignin therein rendered into particles substantially in the range of 1 to 10 microns and separable from the cellulose and hemicellulose, the particulate lignin and cellulose being together in dissociated form havinq the appearance of potting soil with negligible cross linking oE the lignin ancl xylan having reoccurred so that the particulate material is directly useful in fermentation processes, a major portion oE the lignin being soluble in methanol or ethanol at room temperature and being thermoplastic, the cellulose being in the form o~ crystalline alpha cellulose microfibrils and suitable for diges-tion by microorganisms and enzymes.
The present invention also includes the product in particulate form when produced by the above method.
The pressure vessel is preferably vented to atmosphere over a period in the range of the order of 5 seconds to of the order of 30 seconds. The pressure vessel is preferahly rapidly filled with the said steam to bring the lS lignocellulosic material to a temperature in the range of the order of 200C to of the order of 238C, more specifically to a temperature of the order of 234Co The lignocellulosic màterial is preferably brought to the said temperature in less than of the order o-f 45 seconds. Preferably the expulsion o~
the lignocellulosic material to atmosphere is accomplis~ed in less than of the order of 500 milli-seconds.
In some embodiments of the present invention, the lignin in native form, having a purity of the order of 93 weight %, is solvent extracted from the particulate material, at a temperature of less than of the order of 45C, preferably room temperature, by a solvent selected from the group consisting of ethanol and methanol, the lignin so extracted ~eing readily reactive chemically, thermoplastic, having an in~rared spectrum approaching that of so called native lignin and a number average molecular weight of the order of 600 to o~
the order of 1000.
When the lignocellulosic material is freshly harvested moist wood, then the pressure vessel is preferably rapidly filled with the said steam to a pressure in the range of the order of 500 to of the order of 700 psi.
In other embodiments o-f the present invention the lignocellulosic material is a substance selected from the group consisting of wood and bagasse dried below the fibre saturation to a moisture content of less than of the order of 20 weight %
and the pressure vessel is rapidly filled with the said steam at a pressure in the range of the order of 400 to of the order of 600 psi.
In some embodiments of the present invention the lignocellulosic material is hardwood.
In other embodiments of the present invention the lignocellulosic material is annual plant material and the pressure vessel is rapidly filled with the said steam to a pressure in the range of the order oE 500 to of the order of 600 psi.
When the lignocellulosic material is annual plant materialt the pressure vessel is preferably rapidly filled with the said steam to a pressure of the order of 550 psi.
Preferably, condensate is removed from a bottom portion of the pressure vessel as it is formed.
Prefe~ably, the pressure vessel is gent:Ly ~ented to atmosphere -to a pressure of the order of 300 psi be~Eore the valved outlet is opened.
In the accompanying drawings which are provided to give an understa~ding of the present invention and, by way of example, to describe embodiments o-f the present invention;
Figure 1 is a sectional side view oE a pressure vessel having outlet, Figure 2 is a graph of the time t in seconds to heat lignocellulosic material plotted against the temperature T in C, with viscosity/temperature curves added for various constituents of the lignocellulosic material, and Figure 3 is a schematic representation of the cell wall structure o~ a ~ibre of lignocellulosic material.
In figure 1 there is shown a pressure vessel 2, having a valved outlet which in the embodiment illustrated is an extrusion die outlet 6, an extrusion die closure plug 30, a loading end closure flap ~ and steam inlet orifices 10 to 12.
The pressure vessel 2 has a bottle neck portion 14 leading to the die 4 and entry ports 16 and 18 ~or temperature probes (not shown).
The front end of the pressure vessel 2 containing the die outlet 4 has a flange 20 to which is sealed a curved impinging tube 22 which gradually reduces in cross-section in a downsteam direction. The curved impinging tube 22 has a spindle inlet sleeve 24 provided with a flange 26. A pneumatic xam 28 is attached to the flange 26 and has a die closure plug .
1 Z Ei ~ t3 7 30 mountecl on the spindle 32 oE the ram 28. A condensate drainage tank 31 is provided having an outlet valve 33.
The rear end 34 of the pressure vessel 2 is sealed to the remainder by flanges 36 and 38 and has the loading end closure flap 8 hinged thereto by a hinge 30 and sealable therewith by a clamp 42. The rear end 34 has a venting valve 44.
In operation the loading end closure flap 8 is opened and the pressure vessel 2 is loaded with lignocellulosic material in a divided form with the die closure plug 30 closing the outlet 4 and the valve 33 closed. A rod (not shown) is used to pack the lignocellulosic material in the pressure vessel 2.
With the pressure vessel 2 completely filled with lignocellulosic material the die closure plug 30 is sealed by the pneumatic ram 28 and the closure plug 8 is sealed to the rear end 34 by the clamp 42 and then the pressure vessel is filled with steam at a pressure of at least 500 psi, preferably in the range 500 to 700 psi, and at a sufficient temperature to raise the temperature of the lignocellulosic material to a temperature in the range 185 to 240C, preferably 200 to 238C
and in particular 234C, in less than 60 seconds (preferably less than 45 seconds) to plasticize the hemicellulose and the lignin in the lignocellulosic material so that the lignocellulosic material is thermally softened into a plastic condition, by injecting steam into the steam inlet oriEices lO to 12 to form a source (not shown).
:~Z~7'.~
The temperat-lre pro~es (rlot shown) in the ports 1~ and L8 are used to monitor the temperature oE the lignocellulo.sic material in the pressure vessel 2 to determine when the lignocellulosic material has reached the chosen temperature.
As soon as the lignocellulosic material in the pressure vessel 2 has reached the desired temperature the top of the pressure vessel 2 is gently vented to a-tmosphere by opening the valve 44 to reduce the steam pressure to between of the order of 200 psi to of the ordex of 450 psi, preEerably 300 psi and then the pneumatic ram 28 is immediately actuated to withdraw the closure plug 30 and immediately open the die outlet 4 to atmosphere so that the lignocellulosic material is explosively expelled through the die outlet 4 in the plastic condition along the curved impinging tube 22. The sudden release to atmosphere explosively expels the lignoceIlulosic material in a plasticized condition and produces a particulate material having .he appearance of potting soil which stains the fingers brown and has a high enough specific gravity to sink like a stone in water.
While the curved impinging tube is not essential it has the advantage of utilizing some of the ex,pulsion force to further comminute the lignocellulosic material in addition to the comminution obtained by extrusion.
During the heating cycle, condensate from the steam wiIl drain into tank 31 which is at the same temperature as the pressure vessel 2, and the condensate can be released Erom the tank 31. by the valve 33 after the lignocellulosic material has been expelled through the die outlet ~.
In Figure 2, a) Is a curve showing the relationship between time (t) seconds taken in the DeLong process, using an input steam temperature of 255C and pressure of 630 psi to reach a temperature (TC) of the lignocellulosic material.
b) Is a curve showing the relationship between lignin viscosity (N), which is higher in the direction of arrow H and lower in the direction of arrow L, plotted against the temperature (TC) of the lignin, c) Is a similar curve to (b) but of the hemicellulose (xylan) viscosity (N) plotted against the temperature (TC) of the hemicellulose, and l~ d) Is a similar curve to (b) but of the cellulose viscosity (N) plotted against the temperature (TC) of the cellulose .
For all of the curves (b) to (d), the point D' represents the degradation temperature for each component of the lignocellulosic material while point P on curve (a) represents the optimum time (t) in seconds and temperature (T) in C.
Referring to Figure 2, for a better understanding of the present invention, it is useful to review the chemical and physical effects which occur during the DeLong process:
At ~J125C, depending Oll moisture content, curve (b~
shows that the llgnin passes through its softening temperature.
.
.
,' : , It wants to become a 1iquid oE about the consisterlcy o~ table syrup.
At ~V165C, depending on moisture content, curve (c) shows that the xylan component of the hemicellulose passes through its softening temperature. It wants to become a liquid of about the consistency of tooth paste.
At r~234C, and affected very little by moisture, the crystalline alpha cellulose passes through its softening temperature.
It wants to yield like a soft willow. This is point P on curve (a).
Tests have shown that if too high a steam temperature is used, the material, depending on moisture content, will begin to pyrolize. This effect becomes progressively more pronounced above input steam pressures of 700 psi (262C). The material being treated is difficult for the steam to access, and it is an insulator. Thus, it requires about 45 seconds to raise the materi~l homogeneously to 234C. If the pressure is too high the outside material will burn before the inside of a wood chip achieves the required 234C~ If the steam temperature is too low then the time taken to raise the material to a homogenous 234C will be longer than 45 seconds.
After 30 seconds above 180C the lignin begins to condense, with the hemicellulose probably forming crosslinks which reduces the yield of pure lignin. Also, the xylan component of the hemicellulose is degraded above 220C. The degradation reactions become serious when these materials are ~ 11 --' . . ' - - :
. . ' ' ' , ' ' ' ' ' ' above their clegradation temperature for times beyoncl 30 seconds. Figure 2 shows that both softeniny temperatures (measured by viscosity) and degradation temperatures of lignin and hemicellulose (xylan) are achieved with tha DeLong process in 30 seconds or less.
At 180C the lignin begins to repolymerize. At 220C
the hemicellulose begins to degrade. Thus it is e~sential to spend as little time as possible above 180C, and no time above 240C (preferably no time above 234C), plus a small allowance for measurement error. It is the above physical factors which determine bringing the lignocellulosic material to a ~ temperature in the range 185C to 240C in less than 60 seconds ; and the preferred temperature range 200C - 238C tbetter still 234C) in less than 45 seconds.
In Flgure 3 the cell wall structure of a fibre of lignocellulosic material is depicted comprising a middle lamella 46, a primary wall 48 a secondary wall composed of layers 50 to 52, and a central lumen 54.
The effect of the ejection through the die outlet 3 and the instantaneous decompression of the lignocellulosic material is to produce a profound morphological and topochemical change, to quench the wood components in their transformed state and stop all further reaction. Some lignin, coalesced into droplets, i5 propelled along the fibre until it exits from the cell wall along with some hemicellulose.
Movement of coalesced lignin and hemicellulose along and out of the S2 layer 51 of the Eiber opens up the internal structure by ~;'7~
spreaclin~ the structuralIy weakened (softened) microEibrils in the fibre bundles~ Wherl the coalesced liynin reaches a weak spot in the ceLl wall it is ejected leaving a number of voids in a generally loosened cellulose structure. These voids, as well as the lack of the lignin protective coating accounts for the radically increased accessihility of the carbohydrate fraction to enzymes, microflora and acids. The exiting steam drops the temperature instantly to 100C which prevents further chemical change or re-combinations and stabilizes the cell structure in an open and easily accessible state.
The role of prehydrolysis is difficult to judge. It is clear that it is a Eactor. When the steam enters the deep cell structure the material is heated, and in the case of poplar, both acetic and uronic acid are produced (9.9~ of the dry weight of the starting material). Hydrolysis occurs at an acceleratir.g rate and the degree of polymerization of both the lignin and the xylan is reduced. The totally unexpected phenomenon which occurs during the process and subsequent ; decompression is that the hemicellulose and the lignin are 20 cleanly separated. This clean separation renders the lignin soluble in a mild organic solvent. The molecular weight of the lignin is reduced to the order of 800 (number average) and the DP of the xylan is reduced from ~v220 to rJ7.
In summary, the explosion process involves control of competing chemical and physical reactions:
a) hydrolysis and m~chanical severing of lignin/hemicellulose links;
~ .
.
7~7 b) repolymerization of lignln, c) degradation of organic matter;
d) uni~orm di~fusional penetration of heat and steam.
Because of the specific (temperature and pressure) and short reaction time, reaction (a) and process (d~ are favoured over the other two so that the desirable product is obtained.
It has been observed that two effects of the explosion are more pronounced when the starting material is below fibre saturation (20~ moisture). The first is the desirable effect of breaking of the cross links between the three major components of the lignocellulosic material. The second i~ the less desirable but often times useful effect o depolymerization of the three main polymers contained in lignocellulosic material (lignin, xylan and cellulose). Taken to e~treme and most pronounced with dry material, water soluble low molecular weight components of the lignin, such as phenol and benzene are produced. Phenol and benzene are toxic to microflora. In the case of the xylan some furfural may be produced.
Thus, for some applications it is desirable to achieve the dissociation of the lignin, xylan and cellulose by severing their cross links but reduce the amount of depolymerization of the lignin, xylan, and cellulose. This effect is achieved by processing the material in the reactor in the normal way until the optimum temperature (234) is achieved (usualLy in about 40 seconds) then gently reducing the pressure ~7~
in the reactor by venting the steam through the valve ~ to a pressure in the range of the order of 200 psi to of the order of ~50 psi (preferably o~ the order of 300 psi) preferably over a period of the order of 5 to of the order of 30 seconds (better still of the order of 15 seconds). Then release the material instantly to atmosphere in the normal way.
This procedure produces the following three effects:
a) the reduction in pressure while retaining the material in the vessel causes the steam in the microstructure of the cell to escape gradually. The temperature reduction in the material is also gradual because the steam temperature does not fall below the optimum temperature of the material until a pressure of 450 psi is reached. Thus, if the venting takes place at a substantially uniEorm rate, the microstructure of the material is subjected to the mechanical action of the escaping steam for a period of at least 10 seconds before the cellulose passes below its softening temperature. Thus while the mechanical effect on the layer 51 is milder, its duration is much longer and the net effect is the same.
b) At approximately 300 psi the steam temperature is 214C and the temperature of the material is below 220C. At these material temperatures, the depolymerizing effect oE the explosion is reduced and the explosive force because of the reduced pressure is also less. The primary e~fect, however, is undoubtely the reduced temperature of the material. The reduced temperature is sufficiently high ~o ;~26~
break the cross links but will reduce the depolymerization effect Oe the explosion.
c) The gradual venting of the reactor will vent off a major percentage of any toxic vapors such as furfural, which may have been produced. The boiling point of furfural is 161.7C. Thus it will vent quite readily and can be recovered as a valuable byproduct.
As a general rule, the total time taken for heating the lignocellulosic material to the desired temperature plus the valve down time should not be allowed to exceed about one minute. Beyond that time, the lignin will begin to degrade and the process will be less effective. By controlling the valve c~own time and the valve down pressure, some control over the degree of polymerization of the end products can be achieved.
If it is suspected that a significant percentage of the material may be dried below fibre saturation in the case of wood or bagasse, the input steam pressure should preferably be reduced from 650 psi to 550 psi as is preferably done for straw.
During the first few seconds after the steam is introduced into the reactor, contact with the relatively cool lignocellulosic material produces a condensate. This condensate covers between 10 and 20 percent of the ; lignocellulosic material depending on the moisture content and temperature of the starting lignocellulosic material, preventing proper processing of the submerged lignocellulosic ~6 ~7 material. Thu~, the tank 31 for removing khat condensate as it occurs substantially improves the performance of the process.
; 15 .
~20 ' :
:` :
,- .
. . . ' ' , ., -' ' ' ' ' ~' ' ' . ' '
renderin~ a surprisin~ly high proportion of thermally undegraded lignin separable from the cellulose and hemicellulose, but has the additional unique Eeature that this -thermally undegraded lignin can be solven-t extracted without thermal degradation occuring of the lignin, cellulose and hemicallulose during khe solvent extraction step.
While the DeLong process has proved to be useful, it has been observed that when the starting material is nearly air dry as is often the case with straw and bagasse, and may be the case with a percentage of wood chips depending on how they have been stored, depolymerization of both lignin and xylan occurs producing toxic monomers of lignin and degrada~.ion components of xylan which, in some instances render the particulate material as it has issued from the outlet unacceptable for use in any form of fermentation process. These toxic components can be extracted by water or by the normal lignin solvents such as ethanol, methanol and sodium hydroxide. However, it may be desirable to use the particulate material as a ~ermentation feed stock, or as an animal feed, directly from the outlet, in which case it i5 desirable to minimize the depolymerization of both lignin and xylan so that the production of toxic components of lignin in the particulate material that issued rom the outlet is minimal and the depolymerization of the xylan is also minimized.
, , According to the present inven-tion there is provided a method o~ renclering :lignirl separab:Le from cellulose and hemicellulose in lignocellulosic material, comprising:
a) packing the lignocellulosic material in a divided, exposed, moist form in a pressure vessel having a valved outlet, b) with the outlet closed, rapidly filling the pressure vessel with steam to a pressure of at least 500 psi to bring, by means of the pressurized steam, substantially all of the lignocellulosic material to a temperature in the range of 185 to 240C in less than 60 seconds and thermally soften the lignocellulosic material into an plastic condition, c) as soon as the said plastic condition has been attained, gently venting the pressure vessel above the level of the lignocellulosic material to atmosphere to reduce the steam pressure in the pressure vessel to between 200 psi and 450 psi, and then immediately opening the valved outlet and e~plosively expelling the lignocellulosic material, in the said plastic condition, from the pressure vessel through the outlet to atmosphere so that the said material issues from the outlet in particulate form with lignin therein rendered into particles substantially in the range of 1 to 10 microns and separable from the cellulose and hemicellulose, the particulate lignin and cellulose being together in dissociated form havinq the appearance of potting soil with negligible cross linking oE the lignin ancl xylan having reoccurred so that the particulate material is directly useful in fermentation processes, a major portion oE the lignin being soluble in methanol or ethanol at room temperature and being thermoplastic, the cellulose being in the form o~ crystalline alpha cellulose microfibrils and suitable for diges-tion by microorganisms and enzymes.
The present invention also includes the product in particulate form when produced by the above method.
The pressure vessel is preferably vented to atmosphere over a period in the range of the order of 5 seconds to of the order of 30 seconds. The pressure vessel is preferahly rapidly filled with the said steam to bring the lS lignocellulosic material to a temperature in the range of the order of 200C to of the order of 238C, more specifically to a temperature of the order of 234Co The lignocellulosic màterial is preferably brought to the said temperature in less than of the order o-f 45 seconds. Preferably the expulsion o~
the lignocellulosic material to atmosphere is accomplis~ed in less than of the order of 500 milli-seconds.
In some embodiments of the present invention, the lignin in native form, having a purity of the order of 93 weight %, is solvent extracted from the particulate material, at a temperature of less than of the order of 45C, preferably room temperature, by a solvent selected from the group consisting of ethanol and methanol, the lignin so extracted ~eing readily reactive chemically, thermoplastic, having an in~rared spectrum approaching that of so called native lignin and a number average molecular weight of the order of 600 to o~
the order of 1000.
When the lignocellulosic material is freshly harvested moist wood, then the pressure vessel is preferably rapidly filled with the said steam to a pressure in the range of the order of 500 to of the order of 700 psi.
In other embodiments o-f the present invention the lignocellulosic material is a substance selected from the group consisting of wood and bagasse dried below the fibre saturation to a moisture content of less than of the order of 20 weight %
and the pressure vessel is rapidly filled with the said steam at a pressure in the range of the order of 400 to of the order of 600 psi.
In some embodiments of the present invention the lignocellulosic material is hardwood.
In other embodiments of the present invention the lignocellulosic material is annual plant material and the pressure vessel is rapidly filled with the said steam to a pressure in the range of the order oE 500 to of the order of 600 psi.
When the lignocellulosic material is annual plant materialt the pressure vessel is preferably rapidly filled with the said steam to a pressure of the order of 550 psi.
Preferably, condensate is removed from a bottom portion of the pressure vessel as it is formed.
Prefe~ably, the pressure vessel is gent:Ly ~ented to atmosphere -to a pressure of the order of 300 psi be~Eore the valved outlet is opened.
In the accompanying drawings which are provided to give an understa~ding of the present invention and, by way of example, to describe embodiments o-f the present invention;
Figure 1 is a sectional side view oE a pressure vessel having outlet, Figure 2 is a graph of the time t in seconds to heat lignocellulosic material plotted against the temperature T in C, with viscosity/temperature curves added for various constituents of the lignocellulosic material, and Figure 3 is a schematic representation of the cell wall structure o~ a ~ibre of lignocellulosic material.
In figure 1 there is shown a pressure vessel 2, having a valved outlet which in the embodiment illustrated is an extrusion die outlet 6, an extrusion die closure plug 30, a loading end closure flap ~ and steam inlet orifices 10 to 12.
The pressure vessel 2 has a bottle neck portion 14 leading to the die 4 and entry ports 16 and 18 ~or temperature probes (not shown).
The front end of the pressure vessel 2 containing the die outlet 4 has a flange 20 to which is sealed a curved impinging tube 22 which gradually reduces in cross-section in a downsteam direction. The curved impinging tube 22 has a spindle inlet sleeve 24 provided with a flange 26. A pneumatic xam 28 is attached to the flange 26 and has a die closure plug .
1 Z Ei ~ t3 7 30 mountecl on the spindle 32 oE the ram 28. A condensate drainage tank 31 is provided having an outlet valve 33.
The rear end 34 of the pressure vessel 2 is sealed to the remainder by flanges 36 and 38 and has the loading end closure flap 8 hinged thereto by a hinge 30 and sealable therewith by a clamp 42. The rear end 34 has a venting valve 44.
In operation the loading end closure flap 8 is opened and the pressure vessel 2 is loaded with lignocellulosic material in a divided form with the die closure plug 30 closing the outlet 4 and the valve 33 closed. A rod (not shown) is used to pack the lignocellulosic material in the pressure vessel 2.
With the pressure vessel 2 completely filled with lignocellulosic material the die closure plug 30 is sealed by the pneumatic ram 28 and the closure plug 8 is sealed to the rear end 34 by the clamp 42 and then the pressure vessel is filled with steam at a pressure of at least 500 psi, preferably in the range 500 to 700 psi, and at a sufficient temperature to raise the temperature of the lignocellulosic material to a temperature in the range 185 to 240C, preferably 200 to 238C
and in particular 234C, in less than 60 seconds (preferably less than 45 seconds) to plasticize the hemicellulose and the lignin in the lignocellulosic material so that the lignocellulosic material is thermally softened into a plastic condition, by injecting steam into the steam inlet oriEices lO to 12 to form a source (not shown).
:~Z~7'.~
The temperat-lre pro~es (rlot shown) in the ports 1~ and L8 are used to monitor the temperature oE the lignocellulo.sic material in the pressure vessel 2 to determine when the lignocellulosic material has reached the chosen temperature.
As soon as the lignocellulosic material in the pressure vessel 2 has reached the desired temperature the top of the pressure vessel 2 is gently vented to a-tmosphere by opening the valve 44 to reduce the steam pressure to between of the order of 200 psi to of the ordex of 450 psi, preEerably 300 psi and then the pneumatic ram 28 is immediately actuated to withdraw the closure plug 30 and immediately open the die outlet 4 to atmosphere so that the lignocellulosic material is explosively expelled through the die outlet 4 in the plastic condition along the curved impinging tube 22. The sudden release to atmosphere explosively expels the lignoceIlulosic material in a plasticized condition and produces a particulate material having .he appearance of potting soil which stains the fingers brown and has a high enough specific gravity to sink like a stone in water.
While the curved impinging tube is not essential it has the advantage of utilizing some of the ex,pulsion force to further comminute the lignocellulosic material in addition to the comminution obtained by extrusion.
During the heating cycle, condensate from the steam wiIl drain into tank 31 which is at the same temperature as the pressure vessel 2, and the condensate can be released Erom the tank 31. by the valve 33 after the lignocellulosic material has been expelled through the die outlet ~.
In Figure 2, a) Is a curve showing the relationship between time (t) seconds taken in the DeLong process, using an input steam temperature of 255C and pressure of 630 psi to reach a temperature (TC) of the lignocellulosic material.
b) Is a curve showing the relationship between lignin viscosity (N), which is higher in the direction of arrow H and lower in the direction of arrow L, plotted against the temperature (TC) of the lignin, c) Is a similar curve to (b) but of the hemicellulose (xylan) viscosity (N) plotted against the temperature (TC) of the hemicellulose, and l~ d) Is a similar curve to (b) but of the cellulose viscosity (N) plotted against the temperature (TC) of the cellulose .
For all of the curves (b) to (d), the point D' represents the degradation temperature for each component of the lignocellulosic material while point P on curve (a) represents the optimum time (t) in seconds and temperature (T) in C.
Referring to Figure 2, for a better understanding of the present invention, it is useful to review the chemical and physical effects which occur during the DeLong process:
At ~J125C, depending Oll moisture content, curve (b~
shows that the llgnin passes through its softening temperature.
.
.
,' : , It wants to become a 1iquid oE about the consisterlcy o~ table syrup.
At ~V165C, depending on moisture content, curve (c) shows that the xylan component of the hemicellulose passes through its softening temperature. It wants to become a liquid of about the consistency of tooth paste.
At r~234C, and affected very little by moisture, the crystalline alpha cellulose passes through its softening temperature.
It wants to yield like a soft willow. This is point P on curve (a).
Tests have shown that if too high a steam temperature is used, the material, depending on moisture content, will begin to pyrolize. This effect becomes progressively more pronounced above input steam pressures of 700 psi (262C). The material being treated is difficult for the steam to access, and it is an insulator. Thus, it requires about 45 seconds to raise the materi~l homogeneously to 234C. If the pressure is too high the outside material will burn before the inside of a wood chip achieves the required 234C~ If the steam temperature is too low then the time taken to raise the material to a homogenous 234C will be longer than 45 seconds.
After 30 seconds above 180C the lignin begins to condense, with the hemicellulose probably forming crosslinks which reduces the yield of pure lignin. Also, the xylan component of the hemicellulose is degraded above 220C. The degradation reactions become serious when these materials are ~ 11 --' . . ' - - :
. . ' ' ' , ' ' ' ' ' ' above their clegradation temperature for times beyoncl 30 seconds. Figure 2 shows that both softeniny temperatures (measured by viscosity) and degradation temperatures of lignin and hemicellulose (xylan) are achieved with tha DeLong process in 30 seconds or less.
At 180C the lignin begins to repolymerize. At 220C
the hemicellulose begins to degrade. Thus it is e~sential to spend as little time as possible above 180C, and no time above 240C (preferably no time above 234C), plus a small allowance for measurement error. It is the above physical factors which determine bringing the lignocellulosic material to a ~ temperature in the range 185C to 240C in less than 60 seconds ; and the preferred temperature range 200C - 238C tbetter still 234C) in less than 45 seconds.
In Flgure 3 the cell wall structure of a fibre of lignocellulosic material is depicted comprising a middle lamella 46, a primary wall 48 a secondary wall composed of layers 50 to 52, and a central lumen 54.
The effect of the ejection through the die outlet 3 and the instantaneous decompression of the lignocellulosic material is to produce a profound morphological and topochemical change, to quench the wood components in their transformed state and stop all further reaction. Some lignin, coalesced into droplets, i5 propelled along the fibre until it exits from the cell wall along with some hemicellulose.
Movement of coalesced lignin and hemicellulose along and out of the S2 layer 51 of the Eiber opens up the internal structure by ~;'7~
spreaclin~ the structuralIy weakened (softened) microEibrils in the fibre bundles~ Wherl the coalesced liynin reaches a weak spot in the ceLl wall it is ejected leaving a number of voids in a generally loosened cellulose structure. These voids, as well as the lack of the lignin protective coating accounts for the radically increased accessihility of the carbohydrate fraction to enzymes, microflora and acids. The exiting steam drops the temperature instantly to 100C which prevents further chemical change or re-combinations and stabilizes the cell structure in an open and easily accessible state.
The role of prehydrolysis is difficult to judge. It is clear that it is a Eactor. When the steam enters the deep cell structure the material is heated, and in the case of poplar, both acetic and uronic acid are produced (9.9~ of the dry weight of the starting material). Hydrolysis occurs at an acceleratir.g rate and the degree of polymerization of both the lignin and the xylan is reduced. The totally unexpected phenomenon which occurs during the process and subsequent ; decompression is that the hemicellulose and the lignin are 20 cleanly separated. This clean separation renders the lignin soluble in a mild organic solvent. The molecular weight of the lignin is reduced to the order of 800 (number average) and the DP of the xylan is reduced from ~v220 to rJ7.
In summary, the explosion process involves control of competing chemical and physical reactions:
a) hydrolysis and m~chanical severing of lignin/hemicellulose links;
~ .
.
7~7 b) repolymerization of lignln, c) degradation of organic matter;
d) uni~orm di~fusional penetration of heat and steam.
Because of the specific (temperature and pressure) and short reaction time, reaction (a) and process (d~ are favoured over the other two so that the desirable product is obtained.
It has been observed that two effects of the explosion are more pronounced when the starting material is below fibre saturation (20~ moisture). The first is the desirable effect of breaking of the cross links between the three major components of the lignocellulosic material. The second i~ the less desirable but often times useful effect o depolymerization of the three main polymers contained in lignocellulosic material (lignin, xylan and cellulose). Taken to e~treme and most pronounced with dry material, water soluble low molecular weight components of the lignin, such as phenol and benzene are produced. Phenol and benzene are toxic to microflora. In the case of the xylan some furfural may be produced.
Thus, for some applications it is desirable to achieve the dissociation of the lignin, xylan and cellulose by severing their cross links but reduce the amount of depolymerization of the lignin, xylan, and cellulose. This effect is achieved by processing the material in the reactor in the normal way until the optimum temperature (234) is achieved (usualLy in about 40 seconds) then gently reducing the pressure ~7~
in the reactor by venting the steam through the valve ~ to a pressure in the range of the order of 200 psi to of the order of ~50 psi (preferably o~ the order of 300 psi) preferably over a period of the order of 5 to of the order of 30 seconds (better still of the order of 15 seconds). Then release the material instantly to atmosphere in the normal way.
This procedure produces the following three effects:
a) the reduction in pressure while retaining the material in the vessel causes the steam in the microstructure of the cell to escape gradually. The temperature reduction in the material is also gradual because the steam temperature does not fall below the optimum temperature of the material until a pressure of 450 psi is reached. Thus, if the venting takes place at a substantially uniEorm rate, the microstructure of the material is subjected to the mechanical action of the escaping steam for a period of at least 10 seconds before the cellulose passes below its softening temperature. Thus while the mechanical effect on the layer 51 is milder, its duration is much longer and the net effect is the same.
b) At approximately 300 psi the steam temperature is 214C and the temperature of the material is below 220C. At these material temperatures, the depolymerizing effect oE the explosion is reduced and the explosive force because of the reduced pressure is also less. The primary e~fect, however, is undoubtely the reduced temperature of the material. The reduced temperature is sufficiently high ~o ;~26~
break the cross links but will reduce the depolymerization effect Oe the explosion.
c) The gradual venting of the reactor will vent off a major percentage of any toxic vapors such as furfural, which may have been produced. The boiling point of furfural is 161.7C. Thus it will vent quite readily and can be recovered as a valuable byproduct.
As a general rule, the total time taken for heating the lignocellulosic material to the desired temperature plus the valve down time should not be allowed to exceed about one minute. Beyond that time, the lignin will begin to degrade and the process will be less effective. By controlling the valve c~own time and the valve down pressure, some control over the degree of polymerization of the end products can be achieved.
If it is suspected that a significant percentage of the material may be dried below fibre saturation in the case of wood or bagasse, the input steam pressure should preferably be reduced from 650 psi to 550 psi as is preferably done for straw.
During the first few seconds after the steam is introduced into the reactor, contact with the relatively cool lignocellulosic material produces a condensate. This condensate covers between 10 and 20 percent of the ; lignocellulosic material depending on the moisture content and temperature of the starting lignocellulosic material, preventing proper processing of the submerged lignocellulosic ~6 ~7 material. Thu~, the tank 31 for removing khat condensate as it occurs substantially improves the performance of the process.
; 15 .
~20 ' :
:` :
,- .
. . . ' ' , ., -' ' ' ' ' ~' ' ' . ' '
Claims (16)
1. A method of rendering lignin separable from cellulose and hemicellulose in lignocellulosic material, comprising:
a) packing the lignocellulosic material in a divided, exposed moist form in a pressure vessel having a valved outlet, b) with the valve closed, rapidly filling the pressure vessel with steam to a pressure of at least 500 psi to bring, by means of the pressurized steam substantially all of the lignocellulosic material to a temperature in the range 195 to 240°C in less than 60 seconds and thermally soften the lignocellulosic material into a plastic condition, c) as soon as the said plastic condition has been attained, gently venting the pressure vessel above the level of the lignocellulosic material to atmosphere to reduce the steam pressure in the pressure vessel to between of the order of 200 psi and of the order of 450 psi, and then d) immediately opening the valved outlet and explosively expelling the lignocellulosic material, in the said plastic condition, from the pressure vessel through the outlet to atmosphere so that the said material issues from the outlet in particulate form with lignin therein rendered into particles substantially in the range - Page 1 of Claims -1 to 10 microns and separable from the cellulose and hemicellulose, the particulate lignin and cellulose being together in dissociated form having the appearance of potting soil with negligible cross linking of the lignin and xylan having reoccurred so that the particulate material is directly useful in fermentation processes, a major portion of the lignin being soluble in methanol or ethanol at room temperature and being thermoplastic, the cellulose being in the form of crystalline alpha cellulose suitable for digestion by micro-organisms and enzymes.
a) packing the lignocellulosic material in a divided, exposed moist form in a pressure vessel having a valved outlet, b) with the valve closed, rapidly filling the pressure vessel with steam to a pressure of at least 500 psi to bring, by means of the pressurized steam substantially all of the lignocellulosic material to a temperature in the range 195 to 240°C in less than 60 seconds and thermally soften the lignocellulosic material into a plastic condition, c) as soon as the said plastic condition has been attained, gently venting the pressure vessel above the level of the lignocellulosic material to atmosphere to reduce the steam pressure in the pressure vessel to between of the order of 200 psi and of the order of 450 psi, and then d) immediately opening the valved outlet and explosively expelling the lignocellulosic material, in the said plastic condition, from the pressure vessel through the outlet to atmosphere so that the said material issues from the outlet in particulate form with lignin therein rendered into particles substantially in the range - Page 1 of Claims -1 to 10 microns and separable from the cellulose and hemicellulose, the particulate lignin and cellulose being together in dissociated form having the appearance of potting soil with negligible cross linking of the lignin and xylan having reoccurred so that the particulate material is directly useful in fermentation processes, a major portion of the lignin being soluble in methanol or ethanol at room temperature and being thermoplastic, the cellulose being in the form of crystalline alpha cellulose suitable for digestion by micro-organisms and enzymes.
2. A method according to claim 1, wherein the outlet is configured and dimensioned to afford substantial mechanical working of the material as it is explosively discharged through the outlet.
3. A method according to claim 1 or 2, wherein the pressure vessel is vented to atmosphere over a period in the range of the order of 5 seconds to of the order of 30 seconds.
4. A method according to claim 1, wherein the pressure vessel is rapidly filled with the said steam to bring the lignocellulosic material to a temperature in the order of 200°C
to of the order of 238°C.
to of the order of 238°C.
5. A method according to claim 1 or 2, wherein the pressure vessel is rapidly filled with the said steam to bring - Page 2 of Claims -the lignocellulosic material to a temperature of the order of 234°C.
6. A method according to claim 1, 2, or 4 wherein the lignocellulosic material is brought to the said temperature in less than of the order of 45 seconds.
7. A method according to claim 1 or 2, wherein the expulsion of the lignocellulosic material to atmosphere after venting is accomplished in less than of the order of 500 milli-seconds.
8. A method according to claim 1 or 2, wherein the lignin in native form, having a purity of the order of 93 weight %, is solvent extracted from the particulate material, at a temperature of less than of the order of 45°C, by a solvent selected from the group consisting of ethanol and methanol, the lignin so extracted being readily reactive chemically, thermoplastic, having an infrared spectrum approaching that of so called native lignin and a number average molecular weight between the order of 600 and the order of 1000.
9. A method according to claim 1 or 2, wherein the lignocellulosic material is freshly harvested, moist wood and the pressure vessel is rapidly filled with the said steam to a - Page 3 of Claims -pressure in the range of the order of 500 to of the order of 700 psi.
10. A method according to claim 1 or 2, wherein the lignocellulosic material is a substance selected from the group consisting of wood and bagasse dried below fibre saturation to a moisture content of less than of the order of 20 weight % and the pressure vessel is rapidly filled with the said steam at a pressure in the range of the order of 500 to of the order of 600 psi.
11. A method according to claim 1 or 2, wherein the lignocellulosic material is hardwood.
12. A method according to claim 1 or 2, wherein the lignocellulosic material is annual plant material and the pressure vessel is rapidly filled with the said steam to a pressure in the range of the order of 500 to of the order of 600 psi.
13. A method according to claim 1 or 2, wherein the lignocellulosic material is annual plant material and the pressure vessel is rapidly filled with the said steam to a pressure of the order of 550 psi.
- Page 4 of Claims -
- Page 4 of Claims -
14. A method according to claim 1 or 2, wherein condensate is removed from a bottom portion of the pressure vessel as it is formed.
15. A method according to claim 1 or 2, wherein the pressure vessel is gently vented to atmosphere to a pressure of the order of 300 psi before the outlet is instantly opened.
16. The product in particulate form when produced by the method claimed in claim 1 or 2.
- Page 5 of Claims -
- Page 5 of Claims -
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA529,627A CA1267407B (en) | 1981-11-12 | 1987-02-12 | Method of rendering lignin separable from cellulose and hemicellulose and the product so produced |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000389902A CA1141376A (en) | 1981-11-12 | 1981-11-12 | Method of rendering lignin separable from cellulose and hemicellulose and the product so produced |
| CA529,627A CA1267407B (en) | 1981-11-12 | 1987-02-12 | Method of rendering lignin separable from cellulose and hemicellulose and the product so produced |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1267407B true CA1267407B (en) | 1990-04-03 |
Family
ID=25669487
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA529,627A Expired CA1267407B (en) | 1981-11-12 | 1987-02-12 | Method of rendering lignin separable from cellulose and hemicellulose and the product so produced |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1267407B (en) |
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