SE1150059A1 - Procedure for iterative dissolution of biomass slurry - Google Patents

Abstract

16 AbstractThe present invention describes a process involving iterative Iique- 5 faction of a biomass slurry by treatment in hot compressed water (HCW) at sub- or super-critical temperature. Elected for publication: fig. 1

Description

PROCESS FOR THE ITERATIVE LIQUEFACTION OF BIOMASS SLURRY Field of the invention The present invention relates to a process for the Iiquefaction of abiomass slurry. More particular, the present invention relates to a process forthe separation or fractionation of a biomass slurry.

Technical Background Continuous flow processes for Iiquefaction of biomass feedstocks existtoday. lnter a|ia US 2010/0184176 A1 discloses a method for biomass hydro-thermal decomposition, which method includes feeding biomass materialunder normal pressure to under increased pressure, allowing the fed biomassmaterial to be gradually moved inside a device main body from either endthereof in a consolidated condition and allowing hot compressed water (HCW)to be fed from another end of a feed section for the biomass material into themain body, so as to cause the biomass material and the hot compressedwater to counter-currently contact with each other and undergo hydrothermaldecomposition, eluting a lignin component and a hemicellulose componentinto the hot compressed water, so as to separate the lignin component andthe hemicellulose component from the biomass material, and discharging,from the side where the hot compressed water is fed into the device mainbody, a biomass solid residue under increased pressure to under normalpressure.

Moreover, methods for separation of cellulose are known. For examplein US 2010/0170504 A1 there is disclosed a process for fractionatinglignocellulosic biomass, the process comprising providing lignocellulosicbiomass, providing a first solvent and combining with the lignocellulosicbiomass, wherein the first solvent dissolves at least some of the cellulosepresent in the lignocellulosic biomass; and providing a second solvent andcombining with the material from step (ii), wherein at least some of thecellulose that is dissolved by the first solvent in step (ii) precipitates out of theliquid phase. According to this method the first solvent is e.g. an acid and the second solvent e.g. an alcohol. 2 Furthermore, separation of cellulose in HCW is also performed today.For instance, it is known from US 2010/0175690 A1 to hydrolyze celluloseand/or hemicelluloses contained in a biomass into monosaccharides andoligosaccharides by using high-temperature and high-pressure water in asubcritical condition. The application provides a method comprising hydrolyticsaccharification of a cellulosic biomass with use of plural pressure vessels,the method comprising a charging step, a heating-up step, a hydrolyzing step,a temperature lowering step, and a discharging step, which are performedsequentially by each of said pressure vessels. According to the method, saidhydrolyzing step may be performed at a temperature of not lower than 140°Cand not higher than 180°C to hydrolyze hemicellulose into saccharides.Moreover according to the method, said hydrolyzing step may be performedat a temperature of not lower than 240°C and not higher than 280°C tohydrolyze cellulose into saccharides. The two different temperature rangesmay be used in one process sequence. The system shown in US2010/0175690 A1 is a sequencing batch system. As mentioned in US2010/0175690, the time needed for different steps, such as for loading, andthe actual reaction time is long, e.g. above 5 minutes for each step.

Many biomass feedstocks contain valuable components, and oneproblem with existing techniques is that the refining of the biomass feedstockto valuable products is not optimized. One aim of the present invention is toprovide a method which is optimized in terms of fractionation, separation andcollecting of valuable components from a biomass feedstock, especially alignocellulosic feedstock. Moreover, another purpose of the present inventionis to provide a method giving high yields of valuable product components,which method is fast in comparison to known methods and which methoddoes not impose severe stresses on the equipment used in the process.Summary of the invention The purposes above are achieved by a process (method) involvingiterative liquefaction of a biomass slurry by treatment in hot compressedwater (HCW) at sub- or super-critical temperature, said process comprising: 3 - feeding a biomass slurry into a continuous flow reactor no 1 in which part ofthe biomass is Iiquefied; - separating a liquid phase solution no 1, and hence water and water solublecomponents, from the biomass slurry being discharged from said flow reactorno 1; - feeding the biomass slurry containing the solid material into a continuousflow reactor no 2 in which part of the remaining biomass is Iiquefied; and - separating a liquid phase solution no 2, and hence water and water solublecomponents, from the biomass slurry being discharged from said flow reactorno 2.

Besides the optimization benefits of the iterative approach according tothe method of the present invention, the method disclosed is also mainlyintended for a continuous flow operation, which in itself provides advantages,such as faster production, more stable and precise process parameters,easier energy recovery and easier up and down scaling when compared to abatch or semi-batch operation. This is e.g. not contemplated in the methoddisclosed in US 2010/0175690 A1 which is provided for a batch system. lnthis sense, it should be noted that the present invention provides a methodwhich is suitable for a continuous flow system comprising e.g. several tubereactors. This is explained more in detail below and one specific embodimentof such a process system is shown in fig. 1. Moreover, the flow methoddisclosed is more lenient towards the used process equipment in comparisonwith a batch system operation as such operation implies the use of severalfast temperature and pressure peaks and drops during normal operation.Short description of the drawinq Fig. 1 shows a schematic view of a flow chart of a process according tothe present invention.

Fig. 2 shows examples of different possible temperature profiles insideof a reactor according to the present invention.

Detailed description of the invention Below, specific embodiments of the present invention are disclosed. As seen from the drawing, the system according to the present invention may 4 involve several reactor steps. Therefore, according to one specificembodiment of the present invention, additional and subsequent reactor(s)and hence feeding and separating steps are involved in the process so thatliquid phase solutions no 3 to N are separated after respective reactor no 3 toN. The number of reactors may vary according to the present invention,depending on the biomass feedstock and desired composition on separatedproducts.

According to one specific embodiment, the separation step accordingto the present invention implies that the water level is reduced in the biomassslurry phase going to the next reactor after separation. Therefore, accordingto one embodiment of the present invention, HCW is added to the residualbiomass slurry that is obtained after the separation steps, i.e. in the processflow part before the subsequent reactor. ln this context it is important torealize that HCW is also admixed with the biomass slurry feedstock from thebeginning before being added to the first reactor in the system according tothe present invention. lt should, however, be noted that it is possibleaccording to the present invention to aim for only pure lignin as the finalproduct obtained after the final reactor in the process, and according to suchspecific embodiment the water level does not have to be reduced betweensome of the final reactor steps _ By use of several reactors according to the present invention, it ispossible to optimise the refining of a biomass slurry feedstock and hence theseparation of components from the feedstock. By use of several reactorsteps, it is possible to involve different heating and cooling steps andtemperature ranges during the process according to the present invention.This is done in order to optimize the entire fractionating of the feedstock andto minimize the level of undesired decomposition products. Moreover, thepressure also changes during the process, either naturally during thetemperature increase and decrease or actively in or between different reactors as a process driving parameter.

According to one specific embodiment of the present invention, thetemperature of the biomass slurry during the process may be definedaccording to: - To1 before the reactor no 1; - TR1 for the temperature inside of the reactor no 1, where TR1_ max is themaximum temperature inside the reactor no 1; - Tog before the reactor no 2; - TRg for the temperature inside of the reactor no 2, where TRg max is themaximum temperature inside the reactor no 2; and so forth until - ToN before the last reactor no N; and - TRN for the temperature inside of the reactor no N, where TRN_ max is themaximum temperature inside the reactor no N; and wherein To1 < TR1_ max, Tog < TRg max and so forth so that ToN < TRN_ max, which imply thatthere is a temperature increase of the biomass slurry inside each reactor no 1to N.

As is shown in fig. 1 and mentioned above, Tox is the temperaturebefore reactor no X. The temperature may be seen as the temperature afterthe feed has been quenched when fed out from the preceding reactor, or thetemperature inside of the actual separating unit, or in fact the temperaturewhen HCW possibly has been added to the flow before going into thesubsequent reactor. However, Tox should not been seen as the temperatureinside of the reactor no X.

Different Tox, such as To1 and Tog, may vary in comparison to eachother. Tox may for instance be held around 200°C or lower. As is describedmore below in relation to the separating steps, 200°C or somewhat highermay be seen as the maximum temperature for the feed when being in theseparation units. Furthermore, Tox should be held below the temperature limitwhere a chemical decomposition occurs on the time scale of the residencetime for the flow between reactor no (X-1) and reactor no X. 6 The initial temperature of the slurry when it enters the process is atambient temperature, and thus a pre-heating step is required to reach the firsttemperature To1_ The time duration of this initial heating of the slurry is notcritical from a chemical point-of-view, because of the relatively lowtemperature, but it should nevertheless not exceed several minutes.

According to one specific embodiment of the present invention the timeof the temperature increase inside of the reactor from To>< to TR><_ max should beshort, at least shorter than the reaction time and preferably within e.g. 2.0seconds. The temperature increase time as well as the reaction time may ofcourse vary. The reaction time may for instance be around 10 seconds, butmay be longer or shorter depending on the desired product composition andthe starting material, etc. Typically, the reaction time is in the range of 2-15seconds, depending on the reaction temperature.

According to one specific embodiment of the present invention, thebiomass being discharged from the reactors are cooled so that Tog < TR1, Too < TRQ and so forth so that Toooi) < TRN. This cooling of the biomass slurrybeing discharged may be seen as a quenching of the reaction before going toseparation. This quick iterative quenching and separation method accordingto the present invention provides an important advantage. When liquefyingbiomass feedstocks, one existing problem today is to optimize the separationand not drive the reaction too short or too long in only one step. Whenliquefaction of a biomass feedstock is performed in only one reactor, eitherthe reaction is not driven enough so that only part of the solids are liquefied,or valuable components are further decomposed, which is undesirable, whenthe reaction is driven too far. Therefore, it is of interest to perform theliquefaction in iterative steps and separating the valuable fractions after eachreactor before going to next loop when liquefying the remaining solids. Bydoing so, it is according to the present invention possible to optimize eachreaction step differently and more economically beneficial in comparison to trying to liquefy in only one or possibly two steps. 7 The temperature profiles within each reactor and in comparisonbetween different reactors may vary according to the present invention.According to one specific embodiment of the present invention, TR1_ max s TR2_ max and so forth so that TR(N_1)_ maxs TRN_ max. This implies thatthere is a general maximum temperature increase during the process whenlooking at different reactors in comparison to each other. According to onespecific embodiment the temperature increase time should be held short. Forthis specific embodiment, TR1, TR2 and so forth until TRN is a temperatureincrease from T01, Tog, and TON, respectively, to TR1_ max, TR2_ max and TRN_ max,respectively, performed within 2.0 seconds. This implies that Tmax is reachedwithin 2.0 seconds in each reactor. According to one other possibleembodiment of the present invention, for instance TR1_ max ~ TR2_ max, however,the temperature integral with respect to time increases from one reactor to thenext one. This implies that although the maximum temperature is almost thesame, the decrease of the temperature after having reached the maximum isslower in a subsequent reactor than in a preceding reactor.

After that Tmax has been reached, the temperature is either heldconstant or is allowed to decrease inside of the reactor. Therefore, accordingto one specific embodiment, at least one of TR1, TRg and so forth until TRN isheld substantially constant in the reactors no 1, 2 to N after having reachedTR1_ max, TR2_ max and so forth until TRN_ max _ This also implies that thetemperature TX for at least one reactor has a profile of first involving anincrease to T><_ max and then being held constant at T><_ max. As may beunderstood from above, this temperature profile may be applied in severalreactors or all of them in a system according to the present invention.

According to another specific embodiment of the present invention, atleast one of the reactors no 1, 2 to N have a temperature profile whichrenders a temperature decrease inside of the reactor no 1, 2 to N after havingreached TR1_ max, TR2_ max and TRN_ max, respectively. As said, this implies thatthe temperature TX for at least one reactor has a profile of first involving anincrease to T><_ max and then involving a decrease from T><_ max to a specific setvalue. Also in this case several or all of the reactors may be set for such 8 temperature profiles, but also the profile above and this profile may be appliedin different reactors so that a mix is used in the entire system according to theinvention. The choice depends on several parameters, such as the feedstockbeing used, desired product compositions and reactor design. Moreover, inrelation to this it should be noted that a temperature involving a, incomparison, slower increase of the temperature TX to the maximum tempera-ture T><_ max inside of the reactor no X is also possible according to the presentinvention. This temperature profile may also imply a comparative highmaximum temperature T><_ max , which only is held during a very short time andthereafter TX is decreased. As such the total reaction time may be the sameor substantially the same as for a temperature profile involving a quickerincrease of the temperature. To summarize, the optimal temperature profileaccording to the present invention depends on the feed used and also theintended product composition in each reactor step.

The separation of the process according to the present invention maybe performed in different ways. According to one specific embodiment, thesteps of separating the solids from the liquid phase solutions involve applyingcentrifugal force to the process flow, i.e. forced sedimentation of the solids inthe process flow. Possible devices are e.g. centrifuges and hydrocyclones.According to another specific embodiment, the steps of separating the solidsfrom the liquid phase solutions involve filtration, either continuous self-cleaning filters or batch filters. Several batch filters could be used in parallel ateach separation step in order to yield pseudo continuous flow. ln yet anotherspecific embodiment, the steps of separating the solids from the liquid phasesolutions involve a combination of forced sedimentation and filtration. As maybe understood from above, according to one embodiment of the invention, thesteps of separating liquid phase solutions involve separation by use ofhydrocyclones, filters, centrifuges or a combination thereof, operating in batchor continuous mode.

As described shortly above, a maximum temperature level for theseparation is about 200°C, which is dependent on that further decompositionduring the separation should be suppressed. Moreover, a temperature around 9 200°C is a level which can be handled today by existing separation equip-ment, without too much stress on the equipment. lt should, however, be noted that for process economical reasons it isof interest to only quench the feed to a temperature/pressure which is lowenough. Then the needed temperature increase in the subsequent step iskept low, and heating energy is saved. Generally, the temperature for theseparation should be held between 90 and 200°C and the pressure may varybut should be sufficiently high in order to keep the process flow in the liquidphase. The temperature and pressure depends on the feed material used, thesize of the particles processed and produced and the equipment used, e.g.the hydrocyclones, filters, etc.

Furthermore, the line-up of the separation units may vary. For instancefilters may be used in connection with hydrocyclones, e.g. several batch filtersoperating together as one separation unit, e.g. three filters in each separatingstep, one in operation, one discharging/regenerating and one in queue. Thesetup used depends on the capacity of interest, the feed processed, thetemperature and pressure profiles used, etc. Nevertheless, the expression“separation unit” should not be seen as only implying one centrifuge or onehydrocyclone or one filter. As may be understood from above, the separationunit may for instance comprise one or several filters together with one orseveral centrifuges or hydrocyclones.

As mentioned above, the present invention provides a method whichallows for an optimized separation of valuable fractions from a biomass slurry.According to one specific embodiment of the present invention, a largerfraction of G5 and G6 sugars originating from hemicelluloses, if present in thebiomass slurry, is obtained in the separating of a liquid phase solution no 1and/or separating of a liquid phase solution no 2, when compared to sub-sequent steps involving separating of a liquid phase solution. The expression“a larger fraction” should be interpreted as a comparative measure implying acontent exceeding the average fraction content in the feedstock. This is interalia possible if Tmax is held within a range of about 230-280°C for this firstseparation step and/or second separation step.

According to another specific embodiment of the present invention, alarger fraction of glucose and glucose oligomers originating from cellulose isobtained in the separating of a liquid phase solution no 2 and/or in the sepa-rating of a liquid phase solution in subsequent steps, when compared to theseparating of a liquid phase solution no 1. This is inter alia possible if Tmax isheld within a range of around 280-350°C for this second separation stepand/or subsequent separation steps.

According to yet another embodiment, the biomass slurry feedstockcontains lignin and at least one of the final liquid phase solutions correspon-ding to final separating steps contain a high fraction of lignin and/or derivatesthereof, such as e.g. lignin polymers. Such feedstock could originate from e.g.softwood, hardwood, wheat straw and bagasse. lf a substantially or totallypure fraction of lignin is desired in one of the last steps or in fact in the lastseparation step, the maximum temperature Tmax in such step(s) should beheld below 380°C. However, it may be of interest according to the presentinvention also to decompose parts of a lignin fraction, and hence one orseveral of the last reactor steps may involve temperatures above 380°C, suchas around 400°C.

The design of the system and its components, such as heaters,reactors and separation units, may vary according to the present invention.The system according to the present invention is intended for a continuousflow setup, which implies that several possible hinders must be contemplated.First of all, there is the need for heating capacity when the biomass slurry flowenters the (tube) heating units, both the pre-heater and the primary heater.This could imply the need for an increase in existing heat transfer surface,which may imply going from one tubing outside of the heaters and intoseveral tubes inside of the heaters or different designs for the tubing inside ofthe heaters. lnter alia, flat designs for the tubing inside of the heater mayallow for an increase in heat transfer surface. Another very important aspectis mixing of the flow inside the tubing when heating is performed. A laminarflow profile will result in that that part of the flow which flows closest to thetubing surface will become excessively heated while the central part will be 11 heated to a lesser extent. lt is therefore important to ensure that the flowprofile is turbulent which thus will result in a more homogeneous heating. Thiscan be achieved by either increasing the flow velocity or by e.g. introducingobstacles in the flow space, zig-zaging or coiling the tubing which will facilitatemixing of the flow. Secondly, the cooling must be possible to perform asintended before the solubilized material, which should be separated in theseparation units, starts to decompose.

As may be noted from the discussion above the expression “heater” isused. The heater could in this context be interpreted as comprising the initialstage of the reactor where the temperature is increased from TOX to T><_ max,i.e. a heating part before the actual reaction part of the reactor. The distinctionbetween the heater and the reactor is however arbitrary since the thermo-chemical reaction starts already in the heater part, especially if the timeperiod of heating is non-negligible compared with the total reaction time. Theheater can also be seen as a separate unit placed just before the reactor. lnother words a preheater part and a reactor part may be arranged separatelyorjoined parts in one heater, e.g. in one tube heater. This should be notedwhen viewing fig. 1 in the drawings.

Detailed description of the drawinqs ln fig. 1 there is shown a flow chart of a system for performing a pro-cess according to the present invention. As shown, the system comprises aplurality of flow reactors no 1, 2 to N, operating in series. Moreover, betweenthe reactors there is provided a separation unit for separation of the liquidphase from the output product from each reactor. HCW is normally added tothe flow input to the next reactor after the separation has been performed.This may be performed before the inlet of some reactors (heaters), whichhowever is optional, so for some other reactors (heaters) this addition may beexcluded. ln fig. 1, the temperature and flow are shown schematically. The slurrytemperature before reactor no 1 is denoted as T01. Moreover, the temperatureof the slurry, where the expression “slurry” defines the feed material goinginto each reactor, before each reactor is denoted as Tog, Tog and so on to TON. 12 Furthermore, the temperature of the flow inside of the reactors is denoted asTR1, TRZ to TRN.

The composition of the different product streams from each reactorstep depends on the feed material as well as the operating parameters, suchas the temperature profiles within the different reactors. As described above,according to one embodiment, a larger fraction of G5 and G6 sugars origina-ting from hemice||u|oses may be separated in separation unit no 1, a glucoseor glucose oligomers rich fraction may be separated in a subsequent separa-tion unit and the final product contains a comparative high fraction of lignin,that is concentrated (purified) lignin. ln fig. 2 there is disclosed examples of different possible temperatureprofiles of the process according to the present invention inside of one reactor(heater). As can be noted, the temperature profiles may be very different. lntemperature profile 1, the time for the temperature to increase from its basetemperature Tox to TR><_ max is infinitesimal short. When the temperature hasreached its maximum (TR><_ max) it is held constant. Finally the temperature isdecreased, which also is performed in infinitesimal short time. Such infini-tesimal short temperature increase and decrease is not practically feasiblebut short increase and decrease times may be preferred, however, as notedfrom fig. 2 , many other types of temperature profiles are also possible accor-ding to the present invention, such as those involving only an infinitesimalshort temperature increase time and then having a temperature profile wherethe temperature decreases instead of being held constant, or like temperatureprofile 4 where the profile has a maximum in the interior of the reaction timeinterval involving a temperature increase to the TR><_ max, which temperaturedirectly thereafter is decreased. lt is important to understand that the shown temperature profiles in fig.2 are only examples of idealized profiles. Hence, many other variants arepossible according to the present invention.

Claims (13)

13 Claims

1. Process involving iterative Iiquefaction of a biomass slurry by treatment inhot compressed water (HCW) at sub- or super-critical temperature, saidprocess comprising: - feeding a biomass slurry into a continuous flow reactor no 1 in which part ofthe biomass is Iiquefied; - separating a liquid phase solution no 1, and hence water and water solublecomponents, from the biomass slurry being discharged from said flow reactorno 1; - feeding the biomass slurry containing the solid material into a continuousflow reactor no 2 in which part of the remaining biomass is Iiquefied; and - separating a liquid phase solution no 2, and hence water and water solublecomponents, from the biomass slurry being discharged from said flow reactorno 2.

2. Process according to claim 1, wherein additional and subsequent reactor(s)and hence feeding and separating steps are involved in the process so thatliquid phase solutions no 3 to N are separated after respective reactor no 3 toN.

3. Process according to claim 1 or 2, wherein HCW is added to the biomass slurry containing the solid material after the separation steps.

4. Process according to anyone of the preceding claims, wherein thetemperature of the biomass slurry during the process may be definedaccording to: - T01 before the reactor no 1; - TR1 for the temperature inside of the reactor no 1, where TR1_ max is themaximum temperature inside the reactor no 1; - Tog before the reactor no 2; 14 - TRg for the temperature inside of the reactor no 2, where TRg max is themaximum temperature inside the reactor no 2; and so forth until - ToN before the last reactor no N; and - TRN for the temperature inside of the reactor no N, where TRN_ max is themaximum temperature inside the reactor no N; and wherein To1 < TR1_ max, Tog < TRg max and so forth so that ToN < TRN_ max, which imply thatthere is a temperature increase of the biomass slurry inside each reactor no 1to N.

5. Process according to anyone of the preceding claims, wherein the biomassbeing discharged from the reactors are cooled so that Tog < TR1, Too < TRg andS0 TOFÉh S0 that T0(N+1) < TRN.

6. Process according to anyone of the preceding claims, wherein max S max max S max.

7. Process according to anyone of the preceding claims, wherein TR1, TRg andso forth until TRN is a temperature increase from To1, Tog, and ToN,respectively, to TR1_ max, TRg max and TRN_ max, respectively, performed within2.0 seconds.

8. Process according to claim 7, wherein at least one of TR1, TRg and so forthuntil TRN is held substantially constant in the reactors no 1, 2 to N after having reached TR1_ max, TRg max and so forth until TRN_ max _

9. Process according to claim 7, wherein at least one of the reactors no 1, 2to N have a temperature profile which renders a temperature decrease insideof the reactor no 1, 2 to N after having reached TR1_ max, TRg max and TRN_ max, respectively.

10. Process according to anyone of the preceding claims, wherein the stepsof separating liquid phase solutions involve separation by use ofhydrocyclones, filters, centrifuges or a combination thereof.

11. Process according to anyone of the preceding claims, wherein a largerfraction of G5 and G6 sugars originating from hemicelluloses, if present in thebiomass slurry, is obtained in the separating of a liquid phase solution no 1and/or separating of a liquid phase solution no 2, when compared to subsequent steps involving separating of a liquid phase solution.

12. Process according to anyone of the preceding claims, wherein a largerfraction of glucose and glucose oligomers originating from cellulose isobtained in the separating of a liquid phase solution no 2 and/or in theseparating of a liquid phase solution in subsequent steps, when compared to the separating of a liquid phase solution no 1.

13. Process according to anyone of the preceding claims, wherein thebiomass slurry contains lignin and at least one of the final liquid phasesolutions corresponding to final separating steps contain a high fraction of lignin and/or derivates thereof.