CA1141376A - 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
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- CA1141376A CA1141376A CA000389902A CA389902A CA1141376A CA 1141376 A CA1141376 A CA 1141376A CA 000389902 A CA000389902 A CA 000389902A CA 389902 A CA389902 A CA 389902A CA 1141376 A CA1141376 A CA 1141376A
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
- C08H6/00—Macromolecular compounds derived from lignin, e.g. tannins, humic acids
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Abstract
T I T L E
A METHOD OF RENDERING LIGNIN SEPARABLE FROM CELLULOSE AND
HEMICELLULOSE AND THE PRODUCT SO PRODUCED
I N V E N T O R
Edward A. De Long ABSTRACT OF DISCLOSURE
In the process for 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 tempera-ture in the range 185 to 240°C in less than 60 seconds, followed by imme-diately 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.
A METHOD OF RENDERING LIGNIN SEPARABLE FROM CELLULOSE AND
HEMICELLULOSE AND THE PRODUCT SO PRODUCED
I N V E N T O R
Edward A. De Long ABSTRACT OF DISCLOSURE
In the process for 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 tempera-ture in the range 185 to 240°C in less than 60 seconds, followed by imme-diately 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
11~1376 This invention relates to a method of rendering lignin separable fro~ cellulose and hemicellulose and the product so produced.
It has already been proposed in Canadian Patent No. 1,096,374 dated February 24, 1981 "Method of Rendering lignin separable from cellulose and hemicellulose in lignocellulosic material and the product so produced", E.A. DeLong, to pack a pressure vessel, having a closed extrusion d~e as the 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 240 C and thermally soften the lignocellulosic material into an extrudable condition, and then, as soon as the extrudable condition has been attained, opening the extrusion die outlet and instantly extruding the lignocellulosic material to atmosphere. The lignocellulosic material issues from the extrusion die 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 De Long process not only has the unique feature of rendering a surprisingly high proportion of thermally undegraded lignin separable from the cellulose and hemicellulose, but has the additional unique feature that this thermally undegraded lignin can be solvent extracted without thermal degradation occuring of the lignin, cellulose and hemicellulose during the solvent extraction step.
While the De~ong 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, depoly-merization of both lignin and xylan occurs producing toxic monomers of , ~
3~7~
lignin and degradation components of xylan which, in some instances render the particulate material as it has issued from the extrusion die outlet unacceptable for use in any form of fermentation process. These toxic components can be extracted by water or by the normal lignin sol-vents such as ethanol, methanol and sodium hydroxide. However, it may be desirable to use the particulate material as a fermentation feed stock, or as an animal feed, directly from the extrusion die outlet, in which case it is 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 from the extrusion die is minimal and the depolymeri-ation of the xylan is also minimized.
According to the present invention there is provided a method of rendering lignin separable from cellulose and hemicellulose in lignocellu-losic material, comprising:
a) packing the lignocellulosic material in a divided, exposed, moist form in a pressure vessel having a closed extrusion die outlet.
b) 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 240 C in less than 60 seconds and thermally soften the lignocellulosic material into an extrudable condition, c) as soon as the said extrudable 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 extrusion die outlet and extruding the lignocellulosic material, in the said extrudable condition, from the pressure vessel through the extrusion die outlet to atmosphere so that the said material issues from the extrusion die 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 . ,, having the appearance of potting soil with negligi~le 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 microfibrils and suitable for digestion 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 preferably rapidly filled with the said steam to bring the 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 234C. The lignocellulosic material is preferably brought to the said temperature in less than of the order of 45 seconds. Preferably the extrusion of the lignocellulosic material to atmosphere is accomplished 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 45 C, preferably room temperature, 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 of the order of 600 to of the order of 1000.
~hen 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.
11'~1376 In other embodiments of the present invention the lignocellu-losic material is a substance selècted 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 4C0 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 lQ 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.
When the lignocellulosic material is annual plant material, 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.
Preferably, the pressure vessel is gently vented to atmosphere to a pressure of the order of 300 psi before the extrusion die outlet is opened.
In the accompanying drawings which are provided to give an understanding of the present invention and, by way of example, to describe embodiments of the present invention;
Figure 1 is a sectional side view of a pressure vessel having an extrusion die outlet, Figure 2 is a graph of the time t in seconds to heat }ignocellu-losic material plotted against the temperature T in C, with viscosity~
temperature curves added for various constituents of the lignocel~ulosic material, and Figure 3 is a schematic representation of the cell wall structure of a fibre of lignocellulosic material.
In figure 1 there is shown a pressure vessel 2, an extrusion 11~137~
die outlet 6, an extrusion die closure plug 30, a loading end closure flap 8 and steam inlet orifices 10 to 12.
The pressure vessel 2 has a bottle neck portion 14 ~ading to the die 4 and entry ports 16 and 18 for 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 downstream direction. The curved impinging tube 22 has a spindle inlet sleeve 24 provided with a flange 26. A pneumatic ram 28 is attached to the flange 26 and has a die closure plug 30 mounted on the spindle 32 of 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 ~ 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 ~ith 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 tempera-ture to raise the temperature of the lignocellulosic material to a temperature in the range 185 to 240 C, preferably 200 to 238 & and in particular 234 C, in less than 60 seconds (preferably less than 45 seconds) to plast~e the hemicellulose and the lignin in the lignocellulo-sic material so that the lignocellulosic material is thermally softened into an extrudable condition, by injecting steam into the steam inlet orifices 10 to 12 to form a source (not shown). The temperature probes (not shown) in the ports 16 and 18 are used to monitor the temperature , -5-11~137~;
of the lignocellulosic 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
It has already been proposed in Canadian Patent No. 1,096,374 dated February 24, 1981 "Method of Rendering lignin separable from cellulose and hemicellulose in lignocellulosic material and the product so produced", E.A. DeLong, to pack a pressure vessel, having a closed extrusion d~e as the 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 240 C and thermally soften the lignocellulosic material into an extrudable condition, and then, as soon as the extrudable condition has been attained, opening the extrusion die outlet and instantly extruding the lignocellulosic material to atmosphere. The lignocellulosic material issues from the extrusion die 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 De Long process not only has the unique feature of rendering a surprisingly high proportion of thermally undegraded lignin separable from the cellulose and hemicellulose, but has the additional unique feature that this thermally undegraded lignin can be solvent extracted without thermal degradation occuring of the lignin, cellulose and hemicellulose during the solvent extraction step.
While the De~ong 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, depoly-merization of both lignin and xylan occurs producing toxic monomers of , ~
3~7~
lignin and degradation components of xylan which, in some instances render the particulate material as it has issued from the extrusion die outlet unacceptable for use in any form of fermentation process. These toxic components can be extracted by water or by the normal lignin sol-vents such as ethanol, methanol and sodium hydroxide. However, it may be desirable to use the particulate material as a fermentation feed stock, or as an animal feed, directly from the extrusion die outlet, in which case it is 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 from the extrusion die is minimal and the depolymeri-ation of the xylan is also minimized.
According to the present invention there is provided a method of rendering lignin separable from cellulose and hemicellulose in lignocellu-losic material, comprising:
a) packing the lignocellulosic material in a divided, exposed, moist form in a pressure vessel having a closed extrusion die outlet.
b) 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 240 C in less than 60 seconds and thermally soften the lignocellulosic material into an extrudable condition, c) as soon as the said extrudable 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 extrusion die outlet and extruding the lignocellulosic material, in the said extrudable condition, from the pressure vessel through the extrusion die outlet to atmosphere so that the said material issues from the extrusion die 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 . ,, having the appearance of potting soil with negligi~le 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 microfibrils and suitable for digestion 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 preferably rapidly filled with the said steam to bring the 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 234C. The lignocellulosic material is preferably brought to the said temperature in less than of the order of 45 seconds. Preferably the extrusion of the lignocellulosic material to atmosphere is accomplished 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 45 C, preferably room temperature, 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 of the order of 600 to of the order of 1000.
~hen 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.
11'~1376 In other embodiments of the present invention the lignocellu-losic material is a substance selècted 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 4C0 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 lQ 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.
When the lignocellulosic material is annual plant material, 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.
Preferably, the pressure vessel is gently vented to atmosphere to a pressure of the order of 300 psi before the extrusion die outlet is opened.
In the accompanying drawings which are provided to give an understanding of the present invention and, by way of example, to describe embodiments of the present invention;
Figure 1 is a sectional side view of a pressure vessel having an extrusion die outlet, Figure 2 is a graph of the time t in seconds to heat }ignocellu-losic material plotted against the temperature T in C, with viscosity~
temperature curves added for various constituents of the lignocel~ulosic material, and Figure 3 is a schematic representation of the cell wall structure of a fibre of lignocellulosic material.
In figure 1 there is shown a pressure vessel 2, an extrusion 11~137~
die outlet 6, an extrusion die closure plug 30, a loading end closure flap 8 and steam inlet orifices 10 to 12.
The pressure vessel 2 has a bottle neck portion 14 ~ading to the die 4 and entry ports 16 and 18 for 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 downstream direction. The curved impinging tube 22 has a spindle inlet sleeve 24 provided with a flange 26. A pneumatic ram 28 is attached to the flange 26 and has a die closure plug 30 mounted on the spindle 32 of 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 ~ 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 ~ith 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 tempera-ture to raise the temperature of the lignocellulosic material to a temperature in the range 185 to 240 C, preferably 200 to 238 & and in particular 234 C, in less than 60 seconds (preferably less than 45 seconds) to plast~e the hemicellulose and the lignin in the lignocellulo-sic material so that the lignocellulosic material is thermally softened into an extrudable condition, by injecting steam into the steam inlet orifices 10 to 12 to form a source (not shown). The temperature probes (not shown) in the ports 16 and 18 are used to monitor the temperature , -5-11~137~;
of the lignocellulosic 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 atmosphere by opening the valve 44 to reduce the steam pressure to between of the order of 200 psi to of the order of 450 psi, preferably 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 extruded through the lQ die outlet 4 in the extrudable condition along the curved impinging tube 22. The sudden release to atmosphere extrudes the lignocellulosic material in a plasticized condition and produces a particulate material having the 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 extrusion force to further comminute the lignocellulosic material in addition to the comminution obtained by extrusion.
During the heating cycle, condensate from the steam will drain into tank.31 which is at the same temperature as the pressure vessel 2, and the condensate can be released from the tan~ 31 by the valve 33 after the lignocellulosic material has been extruded through the die outlet 4.
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 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~ 125C, depending on moisture content, curve (b) shows that the lignin passes through its softening temperature. It wants to become a liquid of about the consistency of table syrup.
Atrvl65C, 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.
Atrv234 C, 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 diffic~lt for the steam to access, and it is an insulator. Thus, it requires about 45 seconds to raise the material homogeneously to 234 C. 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.
~.., 11~1376 After 3Q seconds above 180 C the lignin begins to condense, with the hemicellulose probably forming crosslînks which reduces the yield of pure lignin. Also, the xylan component of the hemicellulose is degraded above 220C. The degradation reactions become serious when t'nese materials are above their degradation temperature for times beyond 30 seconds. Figure 2 shows that both softening temperatures (measured by viscosity~ and degradation temperatures of lignin and hemicellulose (xylan) are achieved with the DeLong process in 30 seconds or less.
At 180C the lignin begins to repolymerize. At 220C the hemicellulose begins to degrade. Thus it is essential 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 errDr. It is the above physical factors which determine bringing the lignocellulosic material to a temperature in the range 185C to 240 C in less than 60 seconds and the preferred temperature range 200C - 238C (better still 234C? in less than 45 seconds.
In Figure 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.
2Q 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, is 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 fiber opens up the internal structure by spreading the structurally weakened (softened) microfibrils in the fibre bundles. When the coalesced lignin 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 accessibility of the carbohydrate fraction to enzymes, ~141376 microflora and acids. The exiting steam drops the temperature instantly to lQ0~ which prevents further`chemicai 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 factor. ~hen the steam enters the deep cell structure the material is heated, and in the case of poplar, both acetic and uronic acid are produced (9.9Z of the dry weight of the starting material).
Hydrolysis occurs at an accelerating rate and the degree of polymerization of both the lignin and the ~ylan is reduced. The totally unexpected phenomenon which occurs during the process and subsequent decompression is that the hemicellulose and the lignin are 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 fromnJ 220 to~v 7.
In summary, the explosion process involves control of competing chemical and physical reactions:
a) hydrolysis and mechanical severing of ligninlhemicellulose links;
b~ repolymerization of lignin;
c) degradation of organic matter;
d) uniform diffusional penetration of heat and steam.
~ ecause 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 h~s been observed that two effects of the explosion are more pronounced when the starting material is below fibre saturation ( 2Q~ moisture). The first is the desirable effect of breaking of the cross links between the three major components of the lignocellulosic material. The second is the less desirable but often times useful effect of depolymerization of the three main polymers contained in lignocellulosic material (lignin, xylan and cellulose). Taken to extreme and most pronounced with dry material, water soluble low molecular weight components of the lignin, such as phenol and benzene 11~1376 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 in the reactor by venting the steam through the valve 44 to a pressure in the range of the order of 200 psi to of the order of 450 psi (preferably of the order of 300 psi) preferably over a period of the order of 5 to of the order of 30 seconds (better still of tne 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 escspe 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 uniform 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 220 C. At these material temperatures, the depolymerizing effect of the explosion is reduced and the explosive force because of the reduced pressure is also less. The primary effect, however, is undoubtely the reduced temperature of the material. The reduced temperature is sufficiently ~ 1376 high to break the cross lin~s but will reduce the depolymerlzation effect of the explosion.
c) The gradual ven~ing 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 161.7 C. 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. ~y controlling the valve down time and the valve down pressure, some control over the degree of polymerization of the end products can ~e achieved.
. .
If it is suspected that-a significant per~entage of thë
material may ~e dried below fibre saturation in the case of wood or bagasse, the input steam pressure should preferably be reduced from 65Q psi to 550 psi as i8 preferably done for straw.
During the first few seconds after the steam is introduced into the reactor, contact wlth 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, pre~enting proper processing of the submerged lignocellulosic material.
Thu9, the tanh 31 for removing that condensate as it occurs su~stantial~y improves the performance of the process.
,
While the curved impinging tube is not essential it has the advantage of utilizing some of the extrusion force to further comminute the lignocellulosic material in addition to the comminution obtained by extrusion.
During the heating cycle, condensate from the steam will drain into tank.31 which is at the same temperature as the pressure vessel 2, and the condensate can be released from the tan~ 31 by the valve 33 after the lignocellulosic material has been extruded through the die outlet 4.
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 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~ 125C, depending on moisture content, curve (b) shows that the lignin passes through its softening temperature. It wants to become a liquid of about the consistency of table syrup.
Atrvl65C, 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.
Atrv234 C, 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 diffic~lt for the steam to access, and it is an insulator. Thus, it requires about 45 seconds to raise the material homogeneously to 234 C. 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.
~.., 11~1376 After 3Q seconds above 180 C the lignin begins to condense, with the hemicellulose probably forming crosslînks which reduces the yield of pure lignin. Also, the xylan component of the hemicellulose is degraded above 220C. The degradation reactions become serious when t'nese materials are above their degradation temperature for times beyond 30 seconds. Figure 2 shows that both softening temperatures (measured by viscosity~ and degradation temperatures of lignin and hemicellulose (xylan) are achieved with the DeLong process in 30 seconds or less.
At 180C the lignin begins to repolymerize. At 220C the hemicellulose begins to degrade. Thus it is essential 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 errDr. It is the above physical factors which determine bringing the lignocellulosic material to a temperature in the range 185C to 240 C in less than 60 seconds and the preferred temperature range 200C - 238C (better still 234C? in less than 45 seconds.
In Figure 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.
2Q 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, is 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 fiber opens up the internal structure by spreading the structurally weakened (softened) microfibrils in the fibre bundles. When the coalesced lignin 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 accessibility of the carbohydrate fraction to enzymes, ~141376 microflora and acids. The exiting steam drops the temperature instantly to lQ0~ which prevents further`chemicai 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 factor. ~hen the steam enters the deep cell structure the material is heated, and in the case of poplar, both acetic and uronic acid are produced (9.9Z of the dry weight of the starting material).
Hydrolysis occurs at an accelerating rate and the degree of polymerization of both the lignin and the ~ylan is reduced. The totally unexpected phenomenon which occurs during the process and subsequent decompression is that the hemicellulose and the lignin are 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 fromnJ 220 to~v 7.
In summary, the explosion process involves control of competing chemical and physical reactions:
a) hydrolysis and mechanical severing of ligninlhemicellulose links;
b~ repolymerization of lignin;
c) degradation of organic matter;
d) uniform diffusional penetration of heat and steam.
~ ecause 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 h~s been observed that two effects of the explosion are more pronounced when the starting material is below fibre saturation ( 2Q~ moisture). The first is the desirable effect of breaking of the cross links between the three major components of the lignocellulosic material. The second is the less desirable but often times useful effect of depolymerization of the three main polymers contained in lignocellulosic material (lignin, xylan and cellulose). Taken to extreme and most pronounced with dry material, water soluble low molecular weight components of the lignin, such as phenol and benzene 11~1376 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 in the reactor by venting the steam through the valve 44 to a pressure in the range of the order of 200 psi to of the order of 450 psi (preferably of the order of 300 psi) preferably over a period of the order of 5 to of the order of 30 seconds (better still of tne 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 escspe 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 uniform 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 220 C. At these material temperatures, the depolymerizing effect of the explosion is reduced and the explosive force because of the reduced pressure is also less. The primary effect, however, is undoubtely the reduced temperature of the material. The reduced temperature is sufficiently ~ 1376 high to break the cross lin~s but will reduce the depolymerlzation effect of the explosion.
c) The gradual ven~ing 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 161.7 C. 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. ~y controlling the valve down time and the valve down pressure, some control over the degree of polymerization of the end products can ~e achieved.
. .
If it is suspected that-a significant per~entage of thë
material may ~e dried below fibre saturation in the case of wood or bagasse, the input steam pressure should preferably be reduced from 65Q psi to 550 psi as i8 preferably done for straw.
During the first few seconds after the steam is introduced into the reactor, contact wlth 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, pre~enting proper processing of the submerged lignocellulosic material.
Thu9, the tanh 31 for removing that condensate as it occurs su~stantial~y improves the performance of the process.
,
Claims (15)
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 closed extrusion die outlet.
b) 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 an extrudable condition, C) as soon as the said extrudable 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 extrusion die outlet and extruding the lignocellulosic material, in the said extrudable condition, from the pressure vessel through the extrusion die outlet to atmosphere so that the said material issues from the extrusion die in particulate form with lignin therein rendered into particles substantially in the range 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 closed extrusion die outlet.
b) 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 an extrudable condition, C) as soon as the said extrudable 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 extrusion die outlet and extruding the lignocellulosic material, in the said extrudable condition, from the pressure vessel through the extrusion die outlet to atmosphere so that the said material issues from the extrusion die in particulate form with lignin therein rendered into particles substantially in the range 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 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.
3. 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.
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 of the order of 234°C.
5. A method according to claim 1, 3, or 4 wherein the lignocel-lulosic material is brought to the said temperature in less than of the order of 45 seconds.
6. A method according to claim 1, wherein the extrusion of the lignocellulosic material to atmosphere after venting is accomplished in less than of the order of 500 milli-seconds.
7. A method according to claim 1, wherein 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.
8. A method according to claim 1, wherein the lignocellulosic material is freshly harvested, moist wood 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 700 psi.
9. A method according to claim 1, 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.
10. A method according to claim 1, wherein the lignocellulosic material is hardwood.
13 17. A method according to claim 1, 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.
12. A method according to claim 1, 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.
13. A method according to claim 1, wherein condensate is removed from a bottom portion of the pressure vessel as it is formed.
14. A method according to claim 1, wherein the pressure vessel is gently vented to atmosphere to a pressure of the order of 300 psi before the extrusion die outlet is instantly opened.
15. The product in particulate form when produced by the method claimed in claim 1.
Priority Applications (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 |
Applications Claiming Priority (1)
| 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 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1141376A true CA1141376A (en) | 1983-02-15 |
Family
ID=4121388
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000389902A Expired CA1141376A (en) | 1981-11-12 | 1981-11-12 | Method of rendering lignin separable from cellulose and hemicellulose and the product so produced |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1141376A (en) |
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