Method and system for pretreating lignocellulosic biomass material

Abstract

A method for pretreating lignocellulosic biomass material is provided The method comprises treating (2) the biomass material in at least one reactor at a first pressure by means of adding steam thereto such as to subject the biomass material to auto hydrolysis, steam explosion discharging (3) of the biomass material from said at least one reactor, and after said steam explosion discharging, adding at least one treatment additive such as a catalyst to the biomass material, and after or simultaneously with said adding, subjecting the biomass material to pre-hydrolysis (4) in a pressure vessel at a second pressure by means of adding steam thereto, wherein said second pressure is lower than said first pressure. A corresponding system is also provided.

Description

[0001] METHOD AND SfSTEM FOR PRETREATING LIGNOCELLULOSIC BIOMASS MATERIAL

[0002] TECHNICAL FIELD

[0003] The invention relates to the field of pretreatment of lignocellulosicbiomass mat erial precedi ng for example enzymatic or acid hydrolysisto hydrolyze cellulose into sugars.

[0004] BACKGROUND

[0005] Processes for pretreatment or more specifically pre-hydrolysis of lignocellulosicbiomass material are known in the art. Pre-hydrolysis, which may also be referred to as hydrothermal treatment, is carried out at milder conditions compared to a hydrolysis process and is used for hydrolyzing the hemicellulose content of the biomass. The pre-hydrolysis process can be used for example as a pretreatment stage in the pre-hydrolysis Kraft process (PHK) for producing cellulose pulp, or in processes for producing ethanol as a pretreatment stage preceding a hydrolysis stage for hydrolyzing celluloseto sugar for subsequent fermentation to ethanol.

[0006] The pre-hydrolysis / hydrothermal treatment is performed at elevated pressure and temperature by feeding the biomass to apressurized reactor into which steam is added for heating the biomass. The reactor may be horizontally or vertically arranged. The pre-hydrolysis process may be performed with an added catalyst (such as an acid catalyst) or without added catalyst (so-called autohydrolysis).

[0007] Recent work has shown that pre-hydrolysiswith acid catalyst provides a higher ethanol yield from downstream hydrolysis and fermentation stages. Acid pre-hydrolysis of the biomass material requires additional equipment for feeding and impregnation, however. This adds additional cost to the projects. Furthermore, the addition of an acid catalyst has proven to result in formation of sticky lumps and scaling in the reactors which leads to operational issues with the reactor system (reactors, discharger screws) . Operational issues include frequent plugging of discharger screws with hard lumps formed over time and scaling on reactor & discharger screws. These issues may lead to maintenance st ops for cleaning which reduces the available operational time of the plant.

[0008] SUMMARY

[0009] An object of the invention is to provide a method and asystem for pretreatment of lignocellulosic biomass material which solves or at least improves on the problems identified in the background section. These and other objects are achieved by the present invention by means of a method and asystem according to the independent claims.

[0010] According to a first aspect of the invention, a method for pretreating lignocellulosic biomass material is provided. The method comprises treating the biomass material in at least one reactor at a first pressure by means of adding steam thereto such as to subject the biomass material to auto hydrolysis, steam explosion discharging of the biomass material from said at least one reactor, and after said steam explosion discharging, adding at least one treatment additive such as a catalyst to the biomass material, and after or simultaneously with said adding, subjecti ng the biomass material to pre-hydrolysis in a pressure vessel at asecond pressure by means of adding steam thereto, wherein said second pressure is lower than said first pressure. A second temperature in the at least one pressure vessel may, but does not necessarily need to, be lower than a first temperature in said at least one reactor.

[0011] In other words, the method comprises subjecting the biomass material to autohydrolysis treatment in at least one reactor at a first pressure and discharging the hydrothermally treated biomass material from the at least one reactor while undergoing pressure decrease which may be described as rapid or instantaneous (steam explosion discharge). The treated and steam exploded biomass material isthereafter subjected to pre-hydrolysisin thepresenceof at least onetreatment additive such as a catalyst in a pressure vessel at a second pressure which is lower than the first pressure. If the at least one treatment additive comprises or is a catalyst, the treated and steam exploded biomass material is subjected to catalyzed pre-hydrolysis. It is understood that at least one reactor may refer to asingle reactor, two or more parallel reactors, or two or more consecutive reactors. Steam explosion discharge is well known in the art and refers to a process step where the material undergoes a rapid / instantaneous pressure decrease. Hot and softened biomass is released / blown from the pressurized reactor through a blow valve or orifice, while the pressure drops to an environment with substantially lower pressure. The structure of the biomass breaks, partly due to the expanding steam, and partly by the shear forces and impact during the blow through the orifice or valve. It is understood that the treatment additive may be provided to the biomass material prior to beingfed tothepressurevessel or may be added directly to the pressure vessel. The treatment additive may also be referred to as atreatment chemical. Implicit from the term “pressure vessel” is that it is pressurized, i.e. the second pressure in the pressure vessel is above atmospheric pressure.

[0012] The invention is based on the insight that the cause of the for mat ion of the compounds leading to problems such as sticky lumps and scaling is the combination of the treatment additive and high temperature / pressure. The problematic compounds may, in the case of an acid catalyst, for examplebe humins and / or furans. High temperature and pressure are, however, necessary in the pretreatment for delignification and making the biomass cell wall structure accessible for downstream processing. The invention is furthermore based on the insight to separate the pretreatment into two stages, a first pre-hydrolysis / autohydrolysis pretreatment st age carried out at relatively high temperature / pressure such as to also delignify and make the biomass material more accessible for downstream processing, and a second pre-hydrolysis pretreatment stage carried out at lower temperature / pressure to avoid formation of compounds leading to sticky I umps and scali ng. The lower temperature / pressure i n the second stage meanst hat t he equi pment (pressure vessel, reactor etc.) can be made simpler and cheaper compared to the reactor used for the first (autohydrolysis) pretreatment stage. Furthermore, since the treatment additive / catalyst is added after steam explosion, the cell structure has been opened which makesthecell structure more accessible for the treatment additive / catalyst. This may result in improved hydrolysis. Furthermore, the treatment additive can be added in a simplified manner, for example directly into the pressure vessel. Consequently, t he impregnator which usually precedes the (single) catalyzed pre-hydrolysis st ep can be omitted.

[0013] In embodiments, the at least onetreatment additivecomprises (or consists of) at least onecatalyst such as an acid catalyst. The acid catalyst may for example be sulphuric acid. Alternatively, the at least one treatment additive may comprise an alkali such as sodium hydroxide and / or sodium sulfite. The al kali may also be referred to as a pulping chemical.

[0014] The first temperature may be within a range from 175 to 240 degrees G The second temperature may be within a range from 1 10 to 210 degrees C. The second temperature may be within a range from 1 10 to 175 degrees Csuch as 165 to 175 degrees G

[0015] The first pressure may be within a range from 8 to 25 bar (g), i.e. from 8 to 25 bar overpressure. Thesecond pressure may be within a range from 1 to 16 bar (g) such as 6 to 8 bar (g), i.e. from 1 to 16 bar, such as from 6 to 8 bar, overpressure.

[0016] The residence time in the at least one reactor (autohydrolysis reactions) may, depending on the biomass material, be within a range from 5 to 45 minutes. The residence time in the at least one pressure vessel (pre-hydrolysis reactionswith treatment additive) may, depending on the biomass material and thetreatment additive, be within a rangefrom 3 to 45 minutes. In thecase of an acid catalyst, the residence time is typically within the lower part of this range, such as from 3 to 15 minutes. It is understood that the pressures, temperatures, residence ti mes (and dosing of treatment additive for the pre-hydrolysis step) are selected to achieve a severity such that the biomass material is subjected to pre-hydrolysis (hydrolyzing hemicellulose for example), i.e. not (full) hydrolysisfor example in thesensethat thecellulose is hydrolyzed into sugars.

[0017] Thestep of treating thebiomass material in at least one reactor may be carried out without added catalyst, i.e. the treating step solely comprises autohydrolysis treatment of the biomass material. In other embodiments within the scope of the invention, catalyst isadded not only to the pressure vessel, but also to the at least one reactor, although i n such small quantitiesthat scaling and other problems are negligible.

[0018] The step of steam explosion discharging may comprise discharging the biomass material at pressure decrease to the second pressure. This allows the biomass material to be fed directly to the pressure vessel. The pressure decrease to the second pressure may be described as rapid or instantaneous (which is an inherent property of steam explosion discharging).

[0019] In embodiments, the method further comprises steam explosion discharging of the biomass material from the at least one pressure vessel. The steam explosion discharging may be carried out to reduce the pressure to substantially atmospheric pressure.

[0020] In embodiments, the method further comprises discharging the biomass material from said at least one pressure vessel by means of cold blow discharge. Cbld blow discharge is well known in the art and comprises cooling the biomass material at a discharge end (such as the bottom or lower portion) of the pressure vessel by means of adding dilution liquid thereto prior to discharge from the pressure vessel. A cold blow discharger may beprovided with an agitator and thedilution liquid isadded to maintain slurry consistency and level to maintain a discharge flow. Consequently, level head and pressure above level head drives the transportation of slurry from the cold blow discharger to ablow line / blow tank.

[0021] The lignocellulosic biomass material may be any type of annual fiber or wood biomass material. Examples of annual fiber biomass material include straw (all types of straw, rice straw, wheat straw etc.) , bagasse and EFB (Empty Fruit Brunch). The wood biomass material may comprise softwood, hardwood or a combination thereof. Examples of softwood are spruce and pine. Examples of hardwood are oak and eucalyptus. The lignocellulosic biomass material may be provided to reactor as “dry biomass” at a moisture content within a range of 35-95% dry matter content (DM), or as “wet biomass” at a moisture content of 15-35 % DM.

[0022] According to a second aspect of the invention, there is provided a method for treating biomass material comprising pretreating the biomass material using the method according to the first aspect of the invention or embodiments thereof, and after the pretreating, subjecting the pretreated biomass material to at least one further treatment step.

[0023] In embodiments, the at least one further treatment step comprises enzymatic or acid hydrolysis to hydrolyze cellulose into sugars and optionally also fermenting the biomass material having been subjected to enzymatic or acid hydrolysis.

[0024] In embodiments, the at least one further treatment step comprises subjecting the pretreated biomass material to apulping process such as the Kraft process.

[0025] In embodiments, the at least onefurther treatment step comprises separating hemicellulose from thepretreated biomass material and convertingthehemicelluloseto abio-product such as polyols (which can be used for manufacturing polyethylene for example). Methods for separating hemicellulose are known in the art. Methods for conversion of hemicellulose are also known in the art. This embodiment may be combined with the above-described embodiment comprising subjecting the pretreated biomass material to a pulping process (wherein the hemicellulose is separated from the pulp formed from the pulping process) .

[0026] In embodiments, the at least one further treatment step comprises extracting lignin from the pretreated biomass material and converting the lignin to a bio-product such as polymers or fuel additives. This embodiment may be combined with the above-described embodiment comprising subjecting the biomass material to a pulping process (wherein the lignin is separated from the black liquor formed in the pulping process).

[0027] According to a third aspect of the invention, there is provided a system for pretreating I i gn ocel I u I osi c bi om ass m at er i al . Th e syst em co m pr i ses: at least one reactor arranged to receivesaid biomass material, the at least one reactor being provided with steam addition means to thermally treat the biomass material in the at least one reactor; at least one steam explosion discharge device arranged to discharge the biomass material from the at least one reactor while undergoing (rapid) pressure decrease from a first pressure in the at least one reactor to a second pressure; at least one pressure vessel connected to the at least one steam explosion discharge device at pressure seal to receive biomass material therefrom at the second pressure, the at least one pressure vessel being provided with steam addition means to thermally treat the biomass material at the second pressure, and

[0028] - treatment additive addition means arranged to add at least one treatment additive to the at least one pressure vessel and / or to biomass material upstream of the at least one pressure vessel (such as between the steam explosion discharge device and the at least one pressure vessel).

[0029] The at least one reactor may comprise a single reactor, two or more parallel reactors, or two or more consecutive reactors. The reactor(s) may be substantially horizontally or substantially vertically arranged. The system may be configured to subject the biomass material to autohydrolysis in the at least one reactor in the sense that the at least one reactor does not comprise any catalyst injection means and is not preceded by any impregnator. The at least one steam explosion discharge device may comprise a discharge / blow valve and a discharge screw feeding the material towards the discharge / blow valve for discharge therethrough. The at least one pressure vessel is connected to the steam explosion discharge device at pressure seal, for example via a plug screw feeder. It is understood that the second pressure in the at least one pressure vessel is the same as the decreased pressure after steam explosion discharge device, which consequently is lower than the first pressure in the at least one reactor (the pressure prior to steam explosion) . The treatment additive addition means may be provided in the form of one or more nozzles for injecting the treatment additive into the at least one pressure vessel and / or into afeeding screw or the I ike between thesteam explosion dischargedevice and theat least one pressure vessel. Snce the at least one pressure vessel operates at a lower pressure than the at least one reactor, the pressure vessel(s) can be of a less complicated construction than the react or (s). The pressure vessel (s) mayfor examplebeformed of a“T-pipe” with adischargedevice at its bottom portion. The system may be configured to subject the biomass to pre-hydrolysis (in the presence of the at least one treatment additive such as acatalyst) in the at least one pressure vessel. If the at least one treatment additive comprises or is a catalyst, the biomass material is subjected to catalyzed pre-hydrolysis in the pressurevessel. In embodiments, the system further comprises an at least one additional steam explosion discharging device arranged to discharge the biomass material from the at least one pressure vessel.

[0030] In other embodiments, the system further comprises a cold blow discharge device arranged to discharge the biomass material from the at least one pressure vessel. The cold blow discharge device may comprise an agitator, adilution liquid inlet at abottom or lower portion of thepressure vessel(s) and adischarge opening connected or connectableto ablow line / blow tank.

[0031] Accordingtoafourth aspect of the invention, there is provided asystem for treating lignocellulosic biomass mat erial. The system comprises asystem for pretreating lignocellulosicbiomass material according to the third aspect of the invention or embodiments thereof and at least one further treatment device for further treatment of pretreated biomass material. The at least one further treatment device may comprise at least one reactor configured for enzymatic or acid hydrolysis to hydrolyze cellulose into sugars and optionally also at least one fermenting device arranged to receivebiomass material having been subjected to enzymatic or acid hydrolysis. Alternatively, the at least one further treatment device may comprise a pulping process line such as the Kraft process.

[0032] Thefeaturesof theembodimentsdescribed above arecombinable in any practically realizableway to form embodiments having combinations of these features. Furthermore, all features and advantages of embodiments described above with reference to the first and second aspects of the invention may be applied in corresponding embodiments of the systems according to the third and fourth aspects of the invention and vice versa.

[0033] BRI EF DESCRI PTI ON OF TH E DRAWI NGS

[0034] Above discussed and other aspects of the present invention will now be described in more detai I using the appended drawings, which show presently preferred embodiments of the invention, wherein: fig. 1 shows a flowchart of illustrating an embodiment of the method according to the second aspect of the invention; fig. 2 shows a schematic illustration of an embodiment of the system according to the third aspect of the invention, and fig. 3 shows a schematic illustration of another embodiment of the system according to the third aspect of the invention. DETAILED DESCRI PTION

[0035] Fig. 1 shows a flowchart of illustrating an embodiment of the method according to the second aspect of the invent ion (steps 1 -7). Fig. 1 also illustrates an embodiment of the method according to the first aspect of the invention (steps 2-5) . The method comprises supplying 1 lignocellulosic biomass material such as woody biomass or stray, feeding the biomass material to a pressurized reactor in which the biomass material is thermally treated 2 at elevated (first) pressure P1 and elevated (first) temperature T1 by means of adding steam to the reactor. No catalyst is added to the reactor, or upstream thereof, which means that the thermal treatment 2 solely comprises autohydrolysistreatment of the biomass material. The biomass material is thereafter discharged 3 from the reactor by means of steam explosion discharge, i.e. rapid pressuredecreasethrough a blow valve from pressure PI in the reactor to a lower second pressure P2. After the steam explosion discharging, the biomass material is fed to a pressurized pressure vessel in which the biomass material issubjected to acid catalyzed hydrolysis 4 in at said second pressure P2 and at a second temper atureT2 by means of adding steam and acid catalyst (sulpuricacid for example) to the pressure vessel .

[0036] The operating conditionscan be as fol lows:

[0037] P1 = 15 bar (g)

[0038] P2 = 6-8 bar (g)

[0039] T1 = 180-200 degrees C T2=165-175 degrees C

[0040] It is noted that these are only exemplary values. In other embodiments, the pressures and temperaturescan vary (for example within the intervals provided in theclaims) as long as P2<P1. T2 is typically also lower than T1 , but this is not necessarily the case. For example, T2 can be equal to or higher than T1 when using superheated steam.

[0041] The biomass material is discharged from the pressure vessel by means of steam explosion discharge 5, for example to substantially atmospheric pressure. Thereafter, the pretreated biomass material is subjected to enzymatic hydrolysis 6 to hydrolyze cellulose into sugars and fermenting 7 to produce ethanol.

[0042] Fig. 2 shows aschematic illustration of an embodiment of the system according to the third aspect of the invention. The system comprises a screw feeder 101 which feeds lignocellulosic biomass material (such as straw) to a horizontally arranged pressurized reactor 102. The reactor is provided with steam nozzles 103 adding steam into the reactor to thermally treat the biomass material . It is noted that, unlike prior art systems, the system does not comprise any means for adding acatalyst (such as a PREXimpregnator) along with associated feeding screws prior to the reactor 103. Thus, the biomass material in reactor 130 is subject solely to autohydrolysis (not catalyzed hydrolysis). A transport screw is arranged in the reactor 102 to feed towards a steam explosion discharge device 104 comprising afeed screw 104afeedi ng the biomass mat erial to be discharged through a blow valve 104b. The steam explosion discharge device is arranged to discharge the biomass material from the reactor 102 while undergoing rapid pressure decrease from a first pressure PI in the reactor to asecond pressure P2. The blow valve connects via a blow line to a pressure vessel 105 being a T-shaped vessel (also referred to as a “T-pipe”) at pressure seal (i .e. the pressure is maintained) such that the pressure is the vessel 105 is P2. The pressure vessel 105 is provided with at least one steam nozzle 106 for adding steam to thermally treat the biomass material, and at least one acid catalyst addition nozzle 107 arranged to add acid catalyst intothepressurevessel such that thebiomass material issubjected to acid pre-hydrolysis. A steam explosion discharge device 108 is connected to a bottom portion of the pressure vessel 105 to discharge the biomass material from while undergoing rapid pressure decrease. The above description of the steam explosion discharge device 104 applies to device 108 too. The operating conditions can correspond to those described above with reference to the embodiment in fig. 1.

[0043] Fig. 3 shows a schematic illustration of another embodiment of the system according to the third aspect of the invention. The system comprises a screw feeder 201 which feeds lignocellulosic biomass material (such as woody biomass) to a vertically arranged pressurized reactor 202. The reactor is provided with at least onesteam nozzle 203 adding steam into the reactor to thermally treat the biomass material. Just like in the embodiment in fig. 2, no catalyst is added to / prior to the reactor, and the biomass material is thus subjected to autohydrolysis only. A steam explosion discharge device 204 at a bottom of the reactor 202 comprises a feed screw 204a feeding the biomass material to be discharged through a blow valve 204b. The steam explosion discharge device is arranged to discharge the biomass material from the reactor 202 while under goi ng rapid pressure decrease from a first pressure PI in the reactor to a second pressure P2.

[0044] The blow valve connects via a blow line to a pressure vessel 205 being a T-shaped vessel (also referred to as a “T-pipe”) at pressure seal (i.e. the pressure is maintained) such that the pressure is the vessel 205 is P2. The pressure vessel 205 is provided with at least onesteam nozzle 106 for addingsteam to thermally treat thebiomass material, and at least one acid catalyst addition nozzle 207 arranged to add acid catalyst into the pressure vessel such that the biomass material is subjected to acid pre-hydrolysis. A cold blow discharge device 208 is connected to a bottom portion of the pressure vessel 205 to discharge the biomass material from while undergoing rapid pressure decrease. The cold blow discharge device comprises an agitator 208a and dilution liquid nozzle 208b to add dilution liquid for cooling and maintaining slurry consistency and level to maintain adischarge flow. The operating conditionscan correspond to those described above with reference to the embodiment in fig. 1.

[0045] The descript ion above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be madewithin the scope of the invention.

Claims

CLAIMS1. Method for pretreating lignocellulosic biomass material, said method comprising: treating (2) the biomass material in at least one reactor at a first pressure by means of addi ng steam thereto such as to subject the biomass material to auto hydrolysis;- steam explosion discharging (3) of the biomass material from said at least one reactor, and after said steam explosion discharging, adding at least one treatment additive to the biomass material, and after or simultaneously with said adding, subjecting the biomass material to prehydrolysis (4) in a pressure vessel at a second pressure by means of adding steam thereto, wherein said second pressure is lower than said first pressure, and wherein said steam explosion discharging (3) comprisesdischargi ng thebiomass mat erial at pressure decrease to said second pressure.

2. Method according to claim 1 , wherein said at least one treatment additive comprises an acid catalyst.

3. Method according to claim 1 , wherein said at least one treatment additive comprises an alkali.

4. Method according to any of the preceding claims, wherein asecond temperature in said at least one pressure vessel is lower than a first temperature in said at least one reactor.

5. Method according to cl aim 4, wherein said first temperature is within a range from 175 to 240 degrees Cand said second temperature is within a range from 1 10 to 210 degrees G6. Method according to claim 5, wherein said second temperature iswithin arangefrom 1 10 to 175 degrees C.

7. Method according to any of the preceding claims, wherein said first pressure is within a rangefrom 8 to 25 bar (g) and said second pressure iswithin arangefrom 1 to 16 bar (g) .

8. Method according to any of the preceding claims, wherein said treating (2) the biomass material in at least one reactor iscarried out without added catalyst.

9. Method according to any of the preceding claims, further comprising steam explosion discharging (5) of the biomass material from said at least one pressure vessel.

10. Method according to any claims 1 -8, further comprising discharging the biomass material from said at least one pressure vessel by means of cold blow discharge, said cold blow discharge comprising adding dilution liquid to the biomass material prior to discharging.11 . Method for treating biomass material comprising: pretreating the biomass material using the method according to any of the preceding claims, andafter said pretreating, subjecting thebiomass material to at least onefurther treatment step.

12. Method according to cl aim 1 1 , wherein said at least onefurther treatment step comprises enzymatic or acid hydrolysis (6) to hydrolyze cellulose into sugars, and optionally fermenting (7) the biomass material having been subjected to enzymatic or acid hydrolysis.

13. Method according to claim 1 1 , wherein the at least one further treatment step comprises subjecting the pretreated biomass material to a pulping process.

14. 9 / stem for pretreating lignocellulosicbiomass mat erial, the system comprising: at least one reactor (102; 202) arranged to receive said biomass material, said at least one reactor being provided with steam addition means (103; 203) to thermally treat the biomass material in the at least one reactor; at least one steam explosion discharge device (104; 204) arranged to discharge the biomass material from said at least one reactor whi le undergoing pressure decrease from a first pressure in the at least one reactor to a second pressure; at least one pressure vessel (105; 205) connected to the at least one steam explosion dischargedevice (104; 204) at pressureseal to receive biomass material therefrom at said second pressure, said at least one pressure vessel being provided with steam addition means (106; 206) to subject thebiomass material to pre-hydrolysis, and- treatment additive addition means (207) arranged to add at least one treatment additiveto the at least one pressure vessel (105; 205) and / or to the biomass material between the at least one steam explosion discharge device and the at least one pressure vessel.

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