CA1322366C - Continuous leaching of lignin or hemicellulose and lignin from steam pretreated lignocellosic particulate material - Google Patents
Continuous leaching of lignin or hemicellulose and lignin from steam pretreated lignocellosic particulate materialInfo
- Publication number
- CA1322366C CA1322366C CA000614464A CA614464A CA1322366C CA 1322366 C CA1322366 C CA 1322366C CA 000614464 A CA000614464 A CA 000614464A CA 614464 A CA614464 A CA 614464A CA 1322366 C CA1322366 C CA 1322366C
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- CA
- Canada
- Prior art keywords
- lignin
- solvent
- hemicellulose
- counter
- leaching
- 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 - Fee Related
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Classifications
-
- 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
-
- 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
- D21C11/00—Regeneration of pulp liquors or effluent waste waters
- D21C11/0007—Recovery of by-products, i.e. compounds other than those necessary for pulping, for multiple uses or not otherwise provided for
-
- 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
- D21C3/00—Pulping cellulose-containing materials
- D21C3/20—Pulping cellulose-containing materials with organic solvents or in solvent environment
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- Polysaccharides And Polysaccharide Derivatives (AREA)
Abstract
ABSTRACT
This invention relates to a novel method of continuously leaching ligin or hemicellulose and lignin from steam pretreated lignocellulosic material as the starting substrate. In the continuous leach of lignin, the starting substrate has first had the hemicellulose removed therefrom and is then mixed with a concentrated alkali solution, such as sodium hydroxide, to adjust its pH within a range from 10.0 to 13Ø The pH adjusted substrate is then continuously leached of its lignin by an alkali solvent, such as sodium hydroxide, moving in counter-flow so that the lignin extract and the now hemicellulose and lignin depleted material can be separately recovered. The preconditioning of the substrate undergoing lignin leaching avoids the precipitation of lignin out of the lignin extract at its forward counter-flow interface with the substrate. The continuous extraction of hemicellulose advantageously takes place upstream of the lignin leaching operation and again involves the movement of hemicellulose leaching solvent, such as water, moving in counter-flow direction to that of the starting substrate.
Using a counter-current screw extractor in each leaching operation, high concentrations of hemicellulose and lignin in the extracts can be obtained and are superior in yield when compared to single batch leaching techniques.
This invention relates to a novel method of continuously leaching ligin or hemicellulose and lignin from steam pretreated lignocellulosic material as the starting substrate. In the continuous leach of lignin, the starting substrate has first had the hemicellulose removed therefrom and is then mixed with a concentrated alkali solution, such as sodium hydroxide, to adjust its pH within a range from 10.0 to 13Ø The pH adjusted substrate is then continuously leached of its lignin by an alkali solvent, such as sodium hydroxide, moving in counter-flow so that the lignin extract and the now hemicellulose and lignin depleted material can be separately recovered. The preconditioning of the substrate undergoing lignin leaching avoids the precipitation of lignin out of the lignin extract at its forward counter-flow interface with the substrate. The continuous extraction of hemicellulose advantageously takes place upstream of the lignin leaching operation and again involves the movement of hemicellulose leaching solvent, such as water, moving in counter-flow direction to that of the starting substrate.
Using a counter-current screw extractor in each leaching operation, high concentrations of hemicellulose and lignin in the extracts can be obtained and are superior in yield when compared to single batch leaching techniques.
Description
CONTINUOUS LEACHING OF I,IGNIN OR H~MICELLULOSE
AND LIGNIN FROM ST~AM PRETRE~TED LIGNOCELI.ULOSIC
PARTICULATE MATERIAL
FIEL _OF_INVENTION-This invention relates to a methocl of continuously leaching lignin or hemicellulose and lignin from steam pretreatecl lignocellulosic material. The continuous leaching technique is capable o~ providing high concentrations in the extracts, and cleanly separated fractions of hemicellulose, lignin and oellulose.
PRIOR ART
Steam pretreatment of lignocellulosic material i5 recognized as an ef~icient method of rendering such material accessible to fractionation and conversion. Various methods of stea~ pretre~tment are known in the art, such as the steam explosion process disclosed by DeLong in Canadian patent 1,096,3~4 is~ued February 24, 1981, and othPr steam pretreatment methods as disclosed, for example, in Canadian patent 1,163,058 - Foody issued March 6, 1984, Canadian patent 1,106,305 Dietr.ichs et al issued August 4, 19~1 and United 5tates patent 4,136,207.
Dietrichs et al, in Canadian patent 1,106,305 discloses a two stage leaching process for extracting hemicellulose (particularly xylan) and lignin utilizing a steam pretreated substrate as the starting meterial. The ex~raction steps are carried out in batch mode, using ,~
:'.' `'. ~.""' '' ' ` ' : , ', ~ 32~3~6 conventional filtration equipment. This batch extraction method involves high solvent consumption a~d produces relatively low concentrations of extracted product in the solvent. Conisequently, the downstream purification or conversion costs o~ the extracted material can be more c05tly than when starting with an extract containing relati~ely high concentrations of hemicellulose or lignin.
A~ opposed to batch leaching, continuous leaching normally entails subjecting a substrate to be leached a leaching solvent moving in a counter-flow direction to the movement of the substrate. Typically, continuousi solvent leaching can take place on a conveyor which moves the material to be leached (substrate) in one direction whilst the leachlng solvent i5 permitted to percolate therethrou~h in counter-flow direction. As is alsio known in the art, counter-current screw extractors can be used in con~inuous leaching operations and are typified, for example, in the Chemical En~ineer's Handbook, 5th Edition, page 19-43 entitled "Screw-Conveyor Extractors". Variations on this t~pe of screw-extractor are also disclosed in, inter alia, Vnited States patents 4,214,947 lssued July 29, 1980-Berger, U.S.P. 2,547,577 issued April 3, 1951 - Hamacher et al, U.S.P. ~,242,662 isisiued February 3, 1981 - Wallick, and 2S U.S.P. 3,652,384 issued March 28, 1972 - Sloman.
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None of the foregoin~ counter-current extractor~ are regarded as particularly suitable for continuously leaching l.ignin from lignocellulosic particulate material, as either high concentrations or large volumes of the solvent are re~uired for pr~per solvent leaching. Concentrated solvent, of course, contrihutes to higher costs of lignin extraction whilst lower concentration solvent produces a high solvent to dissolved solid extract ratio, which as above indicated contributes to downstream recovery or conver~ion costs.
Moreover, and unless the substrate undergoing lignin leaching i5 preconditioned as cliscussed in greater detail below, there i8 a high risk, during continuous leaching, that the dissolved lignin will precipitate out at the solvent-15 substrate interface, resulting in blockage of the counter-flow movement~ no matter what type of counter-flow extractor is u3ed.
SUMMARY OF INVF.NTION.
~ mploying steam pretreated llgnocellulosic particulate material as the starting material or substrate, and by extractin~ therefrom the hemicellulose with a solvent, such as water, the hemicellulose extract and the hemicellulose depleted material can be separately recovered as it is known in the art. The hemicellulose-depleted material as a starting substrate, however, unless pretreated .; . :., :
. , : , ; , . :. . ~ - ~
- ;, ;: i: : :
13223~
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50 a5 ~0 adjust its pH as discussed in greater detail below, cannot under~o continuous leaching of ~ nin therefrom, employing a suitable solvent for leaching the li~nin, such as an alkali. The alkali solution, which moves in a counter-current direction to the substrate, at its leading interface with the solvent is susceptible to havin~ the previously leached lignin in solution precipitate out, and hence effec~ively blocks or obstructs the continued passage of leachin~ ~olvent through the substrate.
In accordance with my invention, I have found that if the hemicellulose-depleted material which i5 u~ed as the substrate to undergo continuous lignin extraction is first preconditioned by mixing the substrate with an alkali solution 50 as to ad~ust its p~l within a range from 10.0 to 13.Q, continuous lignin leaching can be performed without the lignin precipitatin~ out of the leaching solution so as to block or plug the action of substrate and solvent moving in counter-current flow. The solvent used when continuously leachiny lignin is itself an akali; for example sodium hydroxide or potassium hydroxide and is preferably sodium hydroxide. Sîmilarly, the concentrated alkali solution used to adjust the pH of the hemicellulose-depleted is preferably sodium hydroxide, having a concentration of at least 10% by weight to minimize the amount of water added to the material.
. , . ,, , .., :
.:. ..
, - '' , ,: .~, , ~22~6 The solvent used for continuously leaching llgnin may have a concentration from 0.4% to 1.5% by weight, and has a preferred concentration range from n. 6~ to 0.~% by weight which has b~en found to produce high y:ields of dissolved lignill in the extract.
Having recognizecl that the pH adjustment of the hemicellulose-depleted material is essential to the successful leaching of lignin on a continuous basis, I have also found that the continuous leaching of the lignin can be adventageously carried out in a counter-current screw extractor. When using a counter~current screw extractor ~or the purpose of leaching the ligni~, employing a solvent within the concentration perimeters as above described, I
have succeeded in obtaining optimum yields when the ratio of addition o~ the solvent, measured in liters/minute, to the rate of supply of the pH adjusted hemicellulose-depleted material, measured in oven dry kilograms/minute i5 from 2.0 to 3.5, with a preferred ratio of from 2.0 to 2.5.
In accordance with yet another aspect of my invention, having been able to devise a method for continuously leaching lignin ~rom hemicellulose-depleted material preferably usin~ a counter-current screw~extractor, it is also now possible, in two separate stages, but in one overal operation, to first continuously extract the hemicellulose from steam pretreated lignocellulosic ~322~
particulate material as the starting material or substrate for hemicellulose extraction, and secondlyl to con~inuously extract lignin from the hemicellulose-clepleted material, using ~t as the starting material for the second stage or phase. This staging process also permit~ the same type of extraction aquipment to be employed at each stage, such as one counter-current screw extractor for the extraction of hemicellulose, and another counter-current screw extractor for lignin extraction.
During the continuous extraction of hemicellulose, the hemicellulose extract and the lignin-depleted material are separately recovered. Since the hemicellulose-depleted material carries with it a certain amount of residual solvent such as water, it too can be recovered, such as by pressing, and the expressed residual solvent is recycled back to the extractor. Similarly, in the second continuous stage, the lignin-depleted material and the lignin extract are separately recovered. As before, the lignin-depleted material will carry with it residual s~lvent leach or extract produced as a result of the lignin leaching step, and this residual also can be recovered for recycling, such as by pressing.
, ' ' ' '' ''''` :
.. . .
~3~23~'6 BRIEF_DESCRIPTION OF Tl~ DRAWINGS.
The invention will be more fully understood from the accompanying drawings and description as it applies to one method of continuously extracting hemicellulose and lignin using two stages usin~ steam treated lignoc~llulosic material as the starting material and wherein:
Figure 1 is a schematic diagram of an operating system for the continuous extraction of hemicellulose and lignin utilizing two inclined counter-current screw-conveyors for extracting the hemicellulose and lignin;
Figure 2 i5 a side view of an inclined counter-current screw-extractor i~cluding a substrate feed hopper and solvent recovery;
Figure 3 i~ a ~ectional view taken along the length of part of an inclined counter-current screw-extractor; and Figure ~ i5 a graph illustrating the solubility of l:lgnin in sodium hydroxide solution over different temperature ranges.
Referring firstly to the Figure 1 schematic, area A
represents -the processing apparatus used in continuousl~
separating hemicellulose from steam pretreated lignocellulosic particulate material such as steam exploded wood (SEW3. This material is introduced via supply 10 into the bottom end of inclined counter-flow screw-ex~ractor ll, and i5 transported upwardly therealong by a rotating screw, . .~: ; : : :
., i ~ .:: . ~ ::: : :
132~3~
not shown, but described hereinafter with reference to Figure 3. Hemicellulose leaching solvent, such as water, i~
introduced via supply 4 into extractor 11 at its upper end, and percola-tes throu~h the SE~ moving upwardly in extractor 11 in counter-flow direction, 50 that the ~olut:ion of solvent and leached hemicellulose can exit from the lower end of the extractor 11 through discharge pipe 12 for collection in hemicellulose extract tank 13.
The hemicellulose-depleted material, having been leached of its hemicellulose during its upward passage in extractor 11 i5 then fed by supply lin0 14 -to press 15 where residual solvent in the hernicellulose-depleted material is separated, and reintroduced into upper end of the extractor via return line 16.
The de-watered and hemicellulose-depleted material is then advanced to mixer 17 by line 18. Concentrated alkali, such as sodium hydroxide or potassium hydroxide is also introduced into the mixer at 19 in order to upwardly adJu~t the pH of the hemicellulose depleted material with which it i8 mixed to about 10.0 to 13.0, in order to effectively precondition the matexial for the continuous lignin extraction phase as exemplified by the processing apparatus ~ound in area B of Figure 1.
As illustrated, the equipment for continuously leachin~ the lignin i5 similar to that used when leaching ~322~;6~
g hemicellulose and :inclucle~ an inclined counter-current screw extractor 31, lignin extraction tank 33 and press 3~ for extracting residual lignin solvent.
The preconditioned hemicellulose-depleted lignocellulosic particulate material from mixer 11 is introduced at 32 located at the bottom end oP extractor 31 for upward passage therealong. Solvent for leaching by counterflow the material movin~ upwardly within extractor 31 is introduced at 34, with the lignin extract being recovered from the bottom end of the extractor at 32 and delivered to li~nin extract tank 33. Further, and in a manner similar to the hemicellulose extraction phase, the lignin depleted material at the top of extractor 31 is fed to press 35 via line 34 for the purpo~e of separating residual lignin so.lvent in the lignin depleted material.
As illustrated, the recovered solvent is reintroduced at the top of extractor 31 via line 36; the remaining ~aterial being delivered to washer ~0 by supply line 38.
This delivered material is ef~ectively cellulose and undergoes washing with water being introduced at 41, with the cellulose being separately recovered through drawoff line ~2 and the wash water recycled by line 47 into lignin solvent line 34. As also illustrated, concentrated lignin solvent is also introduced lnto supply line 34 at 45; the purpose of whieh is to maintain the concentra-tion of the alkali solvent ~, .... .
::.; , , .. ~ : , , :;. , ;
,. : ~ .: : : ,:: . ,:
: , :.: , 3~3~
used in leaching the lignin in a range from 0.4~ to 1~5% by weight.
Optionally, and as illustrated, hemicellulose extract tank 13 and lignin extract tank 33 can each be connected to a vacuum source (not shown) by vacuum lines 20 and 21 in order to promote the draw of the extracts into the tanks.
Referring now to Figures 2 and 3, and as above indicated, the extractor as illustrated can be used in either phase of the continuous hemlcellulose and lignin leaching operation, or used simply for leaching hemicellulose, or lignin, as the case may be. Using lignin leaching a~ the example, steam pretreated lignocellulo~ic particulate material such as steam exploded wood which has further undergone the pH conditioning as above described, is introduced at 50 into feeder 51 located at the lower end of inclined counter~current screw-extractor 52. Employing drive motor 53, material in feeder 51 is fed into the extractor 52 in a known manner and is then caused to be moved upwardly therealong by helical screw 53 consisting o~ rotatable shaft 54 an~ helix or- flight 55. As illustrated in Figure 3, flight 55 alony its length includes holes or appertures 56 to better promote the counter-current flow of leaching solvent in the direction of arrows 57 toward the bottom end of the extractor. Fresh solven t is introduced at the upper end of -:~ .
- , :....... ' . ~ .
~ 3~
the extractor at 58, and the extract is withdrawn at the bottom end 67 as illustrated.
Depending upon its application, either th~
hemicellulose-depleted material of lignin-depleted material which has under~one solvent leach, is drawn off from the inclined extractor 52 at 59 and delivered to press 60 which is driven by motor 61, and which separates residual solvent from the remaining solids which are discharged at 62.
Using pump 63, recovered residual extract is recyclecl by supply line 64 and reintroduced at the upper end of the extractor, as shown.
With particular reference to Figure 3, screw 53 rotates in a direction so as to move the material to undergo leaching upwardly in the direction of arrow 65. Solvent introduced at the upper end of the extractor, and as previously indicated, moves in a counter-current direction illustrated by arrows 5~. Thu.~ the solvent can percolate through the material along the conveyor flight path and due to openings or appertures 56 in the flight, also in a direction parallel to shaft 54. This crossiny of flow directions insures a thorough we-tting of the substrate with the solvent and assists in establishing a high concentration of leached material of the forward-flow interface of the ~olvent with the material moving in counter-direction, a5 illustrated in shaded area 66.
., . , ~, ;. . . ; : :
:, -- ~322366 Avert.ing to the first phase or ~tage of continuous separation, namely the separation of hemicellulose, using steam exploded wood having a moisture content o~ about 65~ by 5 weight as the starting material and water as the leaching solvent in an inclined counter-current extractor as above described, it has bean determined that the S~W conveyed inside the inclined extractor ha~ a moisture content ln the range of 89 - 92% by weight. It has also been found that employing fresh water a~ the solvent, the rate o~ fresh water input measured in liters~minute to the rate of steam exploded wood supply measured in oven-dry kilograms/minute varies between 1.0 and ~.5 and depends, in part, on the upon the amount of recovered residual extract which is recovered and recycled in the extractor. Thls ratio can be favourably compared with current batch hemicellulose extraction processes, where the average ra~io value is about 13. As a result, and again on a comparative basis, by usin~ a screw extractor, hemicellulose extracts having a dissolved solids content of up to 15~ by weight can be obtained. On a single batch leaching basis, this Eigure i5 much lower and typically in the order of 1.0 to 1.5 weight percent.
Although a slight improvement in hemicellulose extraction appears when operating at elevated temperatures (such as 60 C) over room temperature, it has been observed that at elevated temperatures, the more acidic compounds are , . . ..:
:
~3223~
removed, and downst~eam, has the favourable ef~ect of reducing the amount of concentrated alkali required for pH
adjustment in advance of the cont.inuous lignin extraction stage. By way of illustration, at an extraction temperature of 20 C, 1.~ grams of sodium hydroxide is required per 100 grams of de-watered steam exploded aspen wnod to raise its pH
to 11, ~ut this figure drops to 0.5 gram~ if the hemicellulose extraction is carried out at 60 C.
Upstream of the continuous lignin extraction phase, and assuming steam exploded wood has been employed as the starting material and undergone hemicellulose leaching as herein described, the de-watered steam exploded wood from press 35 of Figure 1 or press 60 of Figure 2 is sprayed evenly with a concentrated alkali, such as sodium hydroxide of 10 weight percent or more to achieve a pH o~ at least 10 and preferably 11 or higher, 50 that the lignin does not precipitate out when it comes in contact with the more dilute ~orm o~ lignin leach solvent, which preferably is also sodium hydroxide and which is introduced into the cou~ter-current extractor 31 seen in Figure 1. As the alkali solution percolates counter-currently through the sub~trate, the dissolved lignin concentration in the solvent increases, and an inter~ace establishes flow regime between the descending lignin ~olution and the moisture in the incoming material a~
illustrated in shaded area 66. If the incoming material is .. , ~. - - .;, ;.~ . . . ~ . : .
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,:
~3223~
not impregnated with concentrated alkali, such as sodium hydroxide, the low alkali concentration at the downstream side of this interface wlll cau~e the lignin to precipitate out of ~olution and result in blockage.
As evident from Figure 4, the sa,lubility of lignin (isolated from a substrate material ~uch as steam exploded a~pen wood) i5 a function of alkali concentration and temperature, and as a result, increase in alkali concentration or temperature, or both, will raise the lignin ~olubility. However, high alkali concentration and temperature levels can swell the material undergoing lignin leach, again re~ulting in extractor blockage. For this reason, a concentration of the lignin leach solvent from 0.4%
to 1.5% by weight is regarded as ~atisfactory and from 0.6 to 0.~% by weight, preferred.
While the temperature during lignin extraction can range from 20 C to 80 C, the preferred range is from 40 C
to 60 C. Employing a counter-current extractor of the screw type a~ disclosed hereinj and using sodium hydroxide as the lignin leaching solvent hav.ing a concentration ~rom 0.4 to 1.5~ by weight, the ratio of input of the solvent measured in liters/minute to the rate of supply of said material measured in oven dry lcilograms/minute in the counter-current extractor is from 2.0 to 3.5. The moisture content of the lignin-depleted material exiting the top of extractor 31, following ~ : ~
., ~322~
a period of continuous operation, was found to average about 88% and was reduced to approximately ~0-75% a~ter extracting residual solvent in press 35.
The lignin content at the bottom of the extractor 31 had an established average between 5-6 weight percent, which can favourably be compared with a 1.0 -l.5 weiyht percent recovery which i5 typically obtained when extracting lignin on a single batch basis.
It will be recognized that the continuous hemicellulose extraction and continuous lignin extraction technique as disclo~ed hereln, and the resultant extract yield is dependent upon several variables, all o~ which can be accommodated for depending upon the type of continuous extraction apparatus employed. For example, during hemicellulose extraction, the water to steam pretreated lignocellulosic particulate starting material ratio may vary, a lower ratio producing higher dissolved hemicellulose content. However, too little water may not effectively Z0 remove all of the water solubles. Additionally, the type of steam pretreatment material will also have a b~aring on the result obtained as will the type of wood being treated. The temperature, as above indicated, is also a factor as is, obviously, the length o~ the extractor and the rotational spped o~ the screw, and hence the exposure time of the solvent moving in counterflow during extraction.
~322:3~
The same general considerations apply during the continuous leaching of lignin.
. .
,. , ,.. - ., . , - ~ .
AND LIGNIN FROM ST~AM PRETRE~TED LIGNOCELI.ULOSIC
PARTICULATE MATERIAL
FIEL _OF_INVENTION-This invention relates to a methocl of continuously leaching lignin or hemicellulose and lignin from steam pretreatecl lignocellulosic material. The continuous leaching technique is capable o~ providing high concentrations in the extracts, and cleanly separated fractions of hemicellulose, lignin and oellulose.
PRIOR ART
Steam pretreatment of lignocellulosic material i5 recognized as an ef~icient method of rendering such material accessible to fractionation and conversion. Various methods of stea~ pretre~tment are known in the art, such as the steam explosion process disclosed by DeLong in Canadian patent 1,096,3~4 is~ued February 24, 1981, and othPr steam pretreatment methods as disclosed, for example, in Canadian patent 1,163,058 - Foody issued March 6, 1984, Canadian patent 1,106,305 Dietr.ichs et al issued August 4, 19~1 and United 5tates patent 4,136,207.
Dietrichs et al, in Canadian patent 1,106,305 discloses a two stage leaching process for extracting hemicellulose (particularly xylan) and lignin utilizing a steam pretreated substrate as the starting meterial. The ex~raction steps are carried out in batch mode, using ,~
:'.' `'. ~.""' '' ' ` ' : , ', ~ 32~3~6 conventional filtration equipment. This batch extraction method involves high solvent consumption a~d produces relatively low concentrations of extracted product in the solvent. Conisequently, the downstream purification or conversion costs o~ the extracted material can be more c05tly than when starting with an extract containing relati~ely high concentrations of hemicellulose or lignin.
A~ opposed to batch leaching, continuous leaching normally entails subjecting a substrate to be leached a leaching solvent moving in a counter-flow direction to the movement of the substrate. Typically, continuousi solvent leaching can take place on a conveyor which moves the material to be leached (substrate) in one direction whilst the leachlng solvent i5 permitted to percolate therethrou~h in counter-flow direction. As is alsio known in the art, counter-current screw extractors can be used in con~inuous leaching operations and are typified, for example, in the Chemical En~ineer's Handbook, 5th Edition, page 19-43 entitled "Screw-Conveyor Extractors". Variations on this t~pe of screw-extractor are also disclosed in, inter alia, Vnited States patents 4,214,947 lssued July 29, 1980-Berger, U.S.P. 2,547,577 issued April 3, 1951 - Hamacher et al, U.S.P. ~,242,662 isisiued February 3, 1981 - Wallick, and 2S U.S.P. 3,652,384 issued March 28, 1972 - Sloman.
:~
~; :
.: . ~
. .
132231~
None of the foregoin~ counter-current extractor~ are regarded as particularly suitable for continuously leaching l.ignin from lignocellulosic particulate material, as either high concentrations or large volumes of the solvent are re~uired for pr~per solvent leaching. Concentrated solvent, of course, contrihutes to higher costs of lignin extraction whilst lower concentration solvent produces a high solvent to dissolved solid extract ratio, which as above indicated contributes to downstream recovery or conver~ion costs.
Moreover, and unless the substrate undergoing lignin leaching i5 preconditioned as cliscussed in greater detail below, there i8 a high risk, during continuous leaching, that the dissolved lignin will precipitate out at the solvent-15 substrate interface, resulting in blockage of the counter-flow movement~ no matter what type of counter-flow extractor is u3ed.
SUMMARY OF INVF.NTION.
~ mploying steam pretreated llgnocellulosic particulate material as the starting material or substrate, and by extractin~ therefrom the hemicellulose with a solvent, such as water, the hemicellulose extract and the hemicellulose depleted material can be separately recovered as it is known in the art. The hemicellulose-depleted material as a starting substrate, however, unless pretreated .; . :., :
. , : , ; , . :. . ~ - ~
- ;, ;: i: : :
13223~
`
50 a5 ~0 adjust its pH as discussed in greater detail below, cannot under~o continuous leaching of ~ nin therefrom, employing a suitable solvent for leaching the li~nin, such as an alkali. The alkali solution, which moves in a counter-current direction to the substrate, at its leading interface with the solvent is susceptible to havin~ the previously leached lignin in solution precipitate out, and hence effec~ively blocks or obstructs the continued passage of leachin~ ~olvent through the substrate.
In accordance with my invention, I have found that if the hemicellulose-depleted material which i5 u~ed as the substrate to undergo continuous lignin extraction is first preconditioned by mixing the substrate with an alkali solution 50 as to ad~ust its p~l within a range from 10.0 to 13.Q, continuous lignin leaching can be performed without the lignin precipitatin~ out of the leaching solution so as to block or plug the action of substrate and solvent moving in counter-current flow. The solvent used when continuously leachiny lignin is itself an akali; for example sodium hydroxide or potassium hydroxide and is preferably sodium hydroxide. Sîmilarly, the concentrated alkali solution used to adjust the pH of the hemicellulose-depleted is preferably sodium hydroxide, having a concentration of at least 10% by weight to minimize the amount of water added to the material.
. , . ,, , .., :
.:. ..
, - '' , ,: .~, , ~22~6 The solvent used for continuously leaching llgnin may have a concentration from 0.4% to 1.5% by weight, and has a preferred concentration range from n. 6~ to 0.~% by weight which has b~en found to produce high y:ields of dissolved lignill in the extract.
Having recognizecl that the pH adjustment of the hemicellulose-depleted material is essential to the successful leaching of lignin on a continuous basis, I have also found that the continuous leaching of the lignin can be adventageously carried out in a counter-current screw extractor. When using a counter~current screw extractor ~or the purpose of leaching the ligni~, employing a solvent within the concentration perimeters as above described, I
have succeeded in obtaining optimum yields when the ratio of addition o~ the solvent, measured in liters/minute, to the rate of supply of the pH adjusted hemicellulose-depleted material, measured in oven dry kilograms/minute i5 from 2.0 to 3.5, with a preferred ratio of from 2.0 to 2.5.
In accordance with yet another aspect of my invention, having been able to devise a method for continuously leaching lignin ~rom hemicellulose-depleted material preferably usin~ a counter-current screw~extractor, it is also now possible, in two separate stages, but in one overal operation, to first continuously extract the hemicellulose from steam pretreated lignocellulosic ~322~
particulate material as the starting material or substrate for hemicellulose extraction, and secondlyl to con~inuously extract lignin from the hemicellulose-clepleted material, using ~t as the starting material for the second stage or phase. This staging process also permit~ the same type of extraction aquipment to be employed at each stage, such as one counter-current screw extractor for the extraction of hemicellulose, and another counter-current screw extractor for lignin extraction.
During the continuous extraction of hemicellulose, the hemicellulose extract and the lignin-depleted material are separately recovered. Since the hemicellulose-depleted material carries with it a certain amount of residual solvent such as water, it too can be recovered, such as by pressing, and the expressed residual solvent is recycled back to the extractor. Similarly, in the second continuous stage, the lignin-depleted material and the lignin extract are separately recovered. As before, the lignin-depleted material will carry with it residual s~lvent leach or extract produced as a result of the lignin leaching step, and this residual also can be recovered for recycling, such as by pressing.
, ' ' ' '' ''''` :
.. . .
~3~23~'6 BRIEF_DESCRIPTION OF Tl~ DRAWINGS.
The invention will be more fully understood from the accompanying drawings and description as it applies to one method of continuously extracting hemicellulose and lignin using two stages usin~ steam treated lignoc~llulosic material as the starting material and wherein:
Figure 1 is a schematic diagram of an operating system for the continuous extraction of hemicellulose and lignin utilizing two inclined counter-current screw-conveyors for extracting the hemicellulose and lignin;
Figure 2 i5 a side view of an inclined counter-current screw-extractor i~cluding a substrate feed hopper and solvent recovery;
Figure 3 i~ a ~ectional view taken along the length of part of an inclined counter-current screw-extractor; and Figure ~ i5 a graph illustrating the solubility of l:lgnin in sodium hydroxide solution over different temperature ranges.
Referring firstly to the Figure 1 schematic, area A
represents -the processing apparatus used in continuousl~
separating hemicellulose from steam pretreated lignocellulosic particulate material such as steam exploded wood (SEW3. This material is introduced via supply 10 into the bottom end of inclined counter-flow screw-ex~ractor ll, and i5 transported upwardly therealong by a rotating screw, . .~: ; : : :
., i ~ .:: . ~ ::: : :
132~3~
not shown, but described hereinafter with reference to Figure 3. Hemicellulose leaching solvent, such as water, i~
introduced via supply 4 into extractor 11 at its upper end, and percola-tes throu~h the SE~ moving upwardly in extractor 11 in counter-flow direction, 50 that the ~olut:ion of solvent and leached hemicellulose can exit from the lower end of the extractor 11 through discharge pipe 12 for collection in hemicellulose extract tank 13.
The hemicellulose-depleted material, having been leached of its hemicellulose during its upward passage in extractor 11 i5 then fed by supply lin0 14 -to press 15 where residual solvent in the hernicellulose-depleted material is separated, and reintroduced into upper end of the extractor via return line 16.
The de-watered and hemicellulose-depleted material is then advanced to mixer 17 by line 18. Concentrated alkali, such as sodium hydroxide or potassium hydroxide is also introduced into the mixer at 19 in order to upwardly adJu~t the pH of the hemicellulose depleted material with which it i8 mixed to about 10.0 to 13.0, in order to effectively precondition the matexial for the continuous lignin extraction phase as exemplified by the processing apparatus ~ound in area B of Figure 1.
As illustrated, the equipment for continuously leachin~ the lignin i5 similar to that used when leaching ~322~;6~
g hemicellulose and :inclucle~ an inclined counter-current screw extractor 31, lignin extraction tank 33 and press 3~ for extracting residual lignin solvent.
The preconditioned hemicellulose-depleted lignocellulosic particulate material from mixer 11 is introduced at 32 located at the bottom end oP extractor 31 for upward passage therealong. Solvent for leaching by counterflow the material movin~ upwardly within extractor 31 is introduced at 34, with the lignin extract being recovered from the bottom end of the extractor at 32 and delivered to li~nin extract tank 33. Further, and in a manner similar to the hemicellulose extraction phase, the lignin depleted material at the top of extractor 31 is fed to press 35 via line 34 for the purpo~e of separating residual lignin so.lvent in the lignin depleted material.
As illustrated, the recovered solvent is reintroduced at the top of extractor 31 via line 36; the remaining ~aterial being delivered to washer ~0 by supply line 38.
This delivered material is ef~ectively cellulose and undergoes washing with water being introduced at 41, with the cellulose being separately recovered through drawoff line ~2 and the wash water recycled by line 47 into lignin solvent line 34. As also illustrated, concentrated lignin solvent is also introduced lnto supply line 34 at 45; the purpose of whieh is to maintain the concentra-tion of the alkali solvent ~, .... .
::.; , , .. ~ : , , :;. , ;
,. : ~ .: : : ,:: . ,:
: , :.: , 3~3~
used in leaching the lignin in a range from 0.4~ to 1~5% by weight.
Optionally, and as illustrated, hemicellulose extract tank 13 and lignin extract tank 33 can each be connected to a vacuum source (not shown) by vacuum lines 20 and 21 in order to promote the draw of the extracts into the tanks.
Referring now to Figures 2 and 3, and as above indicated, the extractor as illustrated can be used in either phase of the continuous hemlcellulose and lignin leaching operation, or used simply for leaching hemicellulose, or lignin, as the case may be. Using lignin leaching a~ the example, steam pretreated lignocellulo~ic particulate material such as steam exploded wood which has further undergone the pH conditioning as above described, is introduced at 50 into feeder 51 located at the lower end of inclined counter~current screw-extractor 52. Employing drive motor 53, material in feeder 51 is fed into the extractor 52 in a known manner and is then caused to be moved upwardly therealong by helical screw 53 consisting o~ rotatable shaft 54 an~ helix or- flight 55. As illustrated in Figure 3, flight 55 alony its length includes holes or appertures 56 to better promote the counter-current flow of leaching solvent in the direction of arrows 57 toward the bottom end of the extractor. Fresh solven t is introduced at the upper end of -:~ .
- , :....... ' . ~ .
~ 3~
the extractor at 58, and the extract is withdrawn at the bottom end 67 as illustrated.
Depending upon its application, either th~
hemicellulose-depleted material of lignin-depleted material which has under~one solvent leach, is drawn off from the inclined extractor 52 at 59 and delivered to press 60 which is driven by motor 61, and which separates residual solvent from the remaining solids which are discharged at 62.
Using pump 63, recovered residual extract is recyclecl by supply line 64 and reintroduced at the upper end of the extractor, as shown.
With particular reference to Figure 3, screw 53 rotates in a direction so as to move the material to undergo leaching upwardly in the direction of arrow 65. Solvent introduced at the upper end of the extractor, and as previously indicated, moves in a counter-current direction illustrated by arrows 5~. Thu.~ the solvent can percolate through the material along the conveyor flight path and due to openings or appertures 56 in the flight, also in a direction parallel to shaft 54. This crossiny of flow directions insures a thorough we-tting of the substrate with the solvent and assists in establishing a high concentration of leached material of the forward-flow interface of the ~olvent with the material moving in counter-direction, a5 illustrated in shaded area 66.
., . , ~, ;. . . ; : :
:, -- ~322366 Avert.ing to the first phase or ~tage of continuous separation, namely the separation of hemicellulose, using steam exploded wood having a moisture content o~ about 65~ by 5 weight as the starting material and water as the leaching solvent in an inclined counter-current extractor as above described, it has bean determined that the S~W conveyed inside the inclined extractor ha~ a moisture content ln the range of 89 - 92% by weight. It has also been found that employing fresh water a~ the solvent, the rate o~ fresh water input measured in liters~minute to the rate of steam exploded wood supply measured in oven-dry kilograms/minute varies between 1.0 and ~.5 and depends, in part, on the upon the amount of recovered residual extract which is recovered and recycled in the extractor. Thls ratio can be favourably compared with current batch hemicellulose extraction processes, where the average ra~io value is about 13. As a result, and again on a comparative basis, by usin~ a screw extractor, hemicellulose extracts having a dissolved solids content of up to 15~ by weight can be obtained. On a single batch leaching basis, this Eigure i5 much lower and typically in the order of 1.0 to 1.5 weight percent.
Although a slight improvement in hemicellulose extraction appears when operating at elevated temperatures (such as 60 C) over room temperature, it has been observed that at elevated temperatures, the more acidic compounds are , . . ..:
:
~3223~
removed, and downst~eam, has the favourable ef~ect of reducing the amount of concentrated alkali required for pH
adjustment in advance of the cont.inuous lignin extraction stage. By way of illustration, at an extraction temperature of 20 C, 1.~ grams of sodium hydroxide is required per 100 grams of de-watered steam exploded aspen wnod to raise its pH
to 11, ~ut this figure drops to 0.5 gram~ if the hemicellulose extraction is carried out at 60 C.
Upstream of the continuous lignin extraction phase, and assuming steam exploded wood has been employed as the starting material and undergone hemicellulose leaching as herein described, the de-watered steam exploded wood from press 35 of Figure 1 or press 60 of Figure 2 is sprayed evenly with a concentrated alkali, such as sodium hydroxide of 10 weight percent or more to achieve a pH o~ at least 10 and preferably 11 or higher, 50 that the lignin does not precipitate out when it comes in contact with the more dilute ~orm o~ lignin leach solvent, which preferably is also sodium hydroxide and which is introduced into the cou~ter-current extractor 31 seen in Figure 1. As the alkali solution percolates counter-currently through the sub~trate, the dissolved lignin concentration in the solvent increases, and an inter~ace establishes flow regime between the descending lignin ~olution and the moisture in the incoming material a~
illustrated in shaded area 66. If the incoming material is .. , ~. - - .;, ;.~ . . . ~ . : .
`. .. : , ~ . ', . :
,:
~3223~
not impregnated with concentrated alkali, such as sodium hydroxide, the low alkali concentration at the downstream side of this interface wlll cau~e the lignin to precipitate out of ~olution and result in blockage.
As evident from Figure 4, the sa,lubility of lignin (isolated from a substrate material ~uch as steam exploded a~pen wood) i5 a function of alkali concentration and temperature, and as a result, increase in alkali concentration or temperature, or both, will raise the lignin ~olubility. However, high alkali concentration and temperature levels can swell the material undergoing lignin leach, again re~ulting in extractor blockage. For this reason, a concentration of the lignin leach solvent from 0.4%
to 1.5% by weight is regarded as ~atisfactory and from 0.6 to 0.~% by weight, preferred.
While the temperature during lignin extraction can range from 20 C to 80 C, the preferred range is from 40 C
to 60 C. Employing a counter-current extractor of the screw type a~ disclosed hereinj and using sodium hydroxide as the lignin leaching solvent hav.ing a concentration ~rom 0.4 to 1.5~ by weight, the ratio of input of the solvent measured in liters/minute to the rate of supply of said material measured in oven dry lcilograms/minute in the counter-current extractor is from 2.0 to 3.5. The moisture content of the lignin-depleted material exiting the top of extractor 31, following ~ : ~
., ~322~
a period of continuous operation, was found to average about 88% and was reduced to approximately ~0-75% a~ter extracting residual solvent in press 35.
The lignin content at the bottom of the extractor 31 had an established average between 5-6 weight percent, which can favourably be compared with a 1.0 -l.5 weiyht percent recovery which i5 typically obtained when extracting lignin on a single batch basis.
It will be recognized that the continuous hemicellulose extraction and continuous lignin extraction technique as disclo~ed hereln, and the resultant extract yield is dependent upon several variables, all o~ which can be accommodated for depending upon the type of continuous extraction apparatus employed. For example, during hemicellulose extraction, the water to steam pretreated lignocellulosic particulate starting material ratio may vary, a lower ratio producing higher dissolved hemicellulose content. However, too little water may not effectively Z0 remove all of the water solubles. Additionally, the type of steam pretreatment material will also have a b~aring on the result obtained as will the type of wood being treated. The temperature, as above indicated, is also a factor as is, obviously, the length o~ the extractor and the rotational spped o~ the screw, and hence the exposure time of the solvent moving in counterflow during extraction.
~322:3~
The same general considerations apply during the continuous leaching of lignin.
. .
,. , ,.. - ., . , - ~ .
Claims (30)
1. A method of extracting hemicellulose and lignin from steam pretreated lignocellulosic particulate material comprising the steps of:
(a) leaching hemicellulose from a supply of said particulate material with a first solvent, and separately recovering the hemicellulose extract and the hemicellulose-depleted material;
(b) mixing said hemicellulose depleted material with a concentrated alkali solution to adjust its pH within a range from 10.0 to 13.0; and (c) continuously leaching lignin from a supply of said pH adjusted, hemicellulose-depleted material with a second solvent, and separately recovering the lignin extract and the lignin depleted material.
(a) leaching hemicellulose from a supply of said particulate material with a first solvent, and separately recovering the hemicellulose extract and the hemicellulose-depleted material;
(b) mixing said hemicellulose depleted material with a concentrated alkali solution to adjust its pH within a range from 10.0 to 13.0; and (c) continuously leaching lignin from a supply of said pH adjusted, hemicellulose-depleted material with a second solvent, and separately recovering the lignin extract and the lignin depleted material.
2. The method as claimed in Claim 1, wherein said particulate material has been steam exploded, said first solvent is water, and said second solvent and said concentrated alkali solution is at least one of sodium hydroxide and potassium hydroxide.
3. The method as claimed in Claim 2, wherein residual first solvent is extracted from said hemicellulose-depleted material prior to step (b).
4. The method as claimed in Claim 3, wherein the lignin is continuously leached in a counter-current screw-extractor.
5. The method as claimed in Claim 3, wherein the hemicellulose and lignin are continuously leached in separate counter-current screw-extractors.
6. The method as claimed in Claim 3, wherein residual second solvent is extracted from said lignin-depleted material.
7. The method as claimed in Claims 1, 2 or 3, wherein the concentrated alkali solution is sodium hydroxide and has a concentration of at least 10% by weight.
8. The method as claimed in Claims 4, 5 or 6, wherein the concentrated alkali solution is sodium hydroxide and has a concentration of at least 10% by weight.
9. The method as claimed in Claims 1, 2 or 3, wherein said second solvent is sodium hydroxide and has a concentration from 0.4% to 1.5% by weight.
10. The method as claimed in Claims 4, 5 or 6, wherein said second solvent is sodium hydroxide and has a concentration of from 0.4% to 1.5% by weight.
11. The method as claimed in Claims 1, 2 or 3, wherein said second solvent is sodium hydroxide and has a concentration of from 0.6% to 0.8% by weight.
12. The method as claimed in Claims 4, 5 or 6, wherein said second solvent is sodium hydroxide and has a concentration of from 0.6% to 0.8% by weight.
13. The method as claimed in Claim 5, wherein the ratio of addition of said first solvent measured in liters/minute to the rate of supply of said particulate material measured in oven dry kilograms/minute in said counter-current extractor is from 1.0 to 2.5.
14. The method as claimed in Claim 5, wherein the ratio of addition of said first solvent measured in liters/minute to the rate of supply of said particulate material measured in oven dry kilograms/minute in said counter-current extractor is from 1.0 to 1.5.
15. The method as claimed in Claims 4 or 5, wherein the ratio of addition of said second solvent measured in liters/minute to the rate of supply of said pH adjusted hemicellulose-depleted material measured in oven dry kilograms/minute in said counter-current extractor is from 2.0 to 3.5.
16. The method as claimed in Claims 4 or 5, wherein the ratio of addition of said second solvent measured in liters/minute to the rate of supply of said pH adjusted hemicellulose-depleted material measured in oven dry kilograms/minute in said counter-current extractor is from 2.0 to 2.5.
17. The method as claimed in Claims 3, 4 or 5, wherein the residual first solvent extracted from said hemicellulose-depleted material is added to said first solvent.
18. The method as claimed in Claims 6, wherein the second solvent is sodium hydroxide and said residual second solvent extracted from said lignin depleted material is added to said second solvent.
19. The method as claimed in Claims 1, 2 or 3, wherein the hemicellulose is continuously leached at a temperature from 20°C to 80°C.
20. The method as claimed in Claims 4, 5 or 6, wherein the hemicellulose is continuously leached at a temperature from 40°C to 60°C.
21. The method as claimed in Claim 1, 2 or 3, wherein the lignin is continuously leached at a temperature between 20°C
and 80°C.
and 80°C.
22. The method as claimed in Claim 4, 5 or 6, wherein the lignin is continuously leached at a temperature between 40°C
and 60°C.
and 60°C.
23. A method of extracting lignin from hemicellulose depleted lignocellulosic particulate material comprising mixing said material with concentrated alkali solution to adjust the pH of the material to between 10.0 and 13.0, and thereafter continuously leaching the lignin therefrom with solvent comprising at least one of sodium hydroxide and potassium hyrdoxide having a concentration from 0.4% to 1.5 by weight, in a counter-current extractor.
24. The method as claimed in Claim 23, wherein said concentrated alkali solution is sodium hydroxide, said solvent is sodium hydroxide and the ratio of input of solvent measured in liters/minute to the rate of supply of said material measured in oven dry kilograms/minute in said counterflow extractor is from 2.0 to 3.5.
25. The method as claimed in Claim 24, wherein said ratio is from 2.0 to 2.5.
26. The method as claimed in Claim 23, wherein the lignin is leached in said counterflow extractor at a temperature from 20°C to 80°C.
27. The method as claimed in Claim 26, wherein said temperature is from 40°C to 60°C.
28. The method as claimed in Claims 23, 24 or 25, wherein the solvent has a concentration from 0.6% to 0.8% by weight.
29. The method as claimed in Claims 23, 24 or 25, wherein the concentrated alkali solution has a concentration of at least 10% by weight.
30. The method as claimed in Claim 23, 24 or 25, wherein the concentration of concentrated alkali solution is at least 10% by weight and the concentration of solvent is from 0.6 to 0.8% by weight.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000614464A CA1322366C (en) | 1989-09-29 | 1989-09-29 | Continuous leaching of lignin or hemicellulose and lignin from steam pretreated lignocellosic particulate material |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000614464A CA1322366C (en) | 1989-09-29 | 1989-09-29 | Continuous leaching of lignin or hemicellulose and lignin from steam pretreated lignocellosic particulate material |
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| Publication Number | Publication Date |
|---|---|
| CA1322366C true CA1322366C (en) | 1993-09-21 |
Family
ID=4140792
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000614464A Expired - Fee Related CA1322366C (en) | 1989-09-29 | 1989-09-29 | Continuous leaching of lignin or hemicellulose and lignin from steam pretreated lignocellosic particulate material |
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| WO2008017145A1 (en) * | 2006-08-07 | 2008-02-14 | Emicellex Energy Corporation | Process for recovery of holocellulose and near-native lignin from biomass |
| CZ298831B6 (en) * | 1999-04-12 | 2008-02-20 | Rhodia Acetow Gmbh | Method for separating lignocellulose-containing biomass |
| CN101143881B (en) * | 2007-10-11 | 2011-03-16 | 孔延华 | Method for synchronously extracting hemicellulose, cellulose and lignin and reclaiming phenolic acid compounds |
| ES2405298A1 (en) * | 2011-11-23 | 2013-05-30 | Universidad De Huelva | Process of fractionation of lignocellulosis biomass. (Machine-translation by Google Translate, not legally binding) |
| US8545633B2 (en) | 2009-08-24 | 2013-10-01 | Abengoa Bioenergy New Technologies, Inc. | Method for producing ethanol and co-products from cellulosic biomass |
| US8778084B2 (en) | 2008-07-24 | 2014-07-15 | Abengoa Bioenergy New Technologies, Llc. | Method and apparatus for treating a cellulosic feedstock |
| WO2014160262A1 (en) | 2013-03-14 | 2014-10-02 | Abengoa Bioenergy New Technologies, Llc | Methods for converting cellulosic waste to bioproducts |
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