PRETREATMENT ARRANGEMENT COMPRISING A SLUICE VESSEL

The present disclosure generally relates to a pretreatment arrangement (100) for pretreatment of lignocellulosic biomass. The pretreatment arrangement (100) comprises a reactor vessel (101) having an upstream inlet (102) for receiving biomass and a downstream outlet for discharging biomass (103). The pretreatment arrangement (104) further comprises a sluice vessel (104). The present disclosure also relates to a method (200) for pretreating lig- nocellulosic biomass.

TECHNICAL FIELD

The present disclosure generally relates to a pretreatment arrangement for pretreatment of lignocellulosic biomass and to a system comprising the pretreatment arrangement. The pretreatment arrangement comprises a reactor vessel having an upstream inlet for receiving biomass and a downstream outlet for discharging biomass. The pretreatment arrangement further comprises a sluice vessel. The present disclosure also relates to a method for pretreating lignocellulosic biomass.

BACKGROUND

Production of renewable chemicals and fuels has attained increasing interest during the last years due to environmental concerns as well as the importance of energy security. The production typically takes place in a biorefinery, and the use of lignocellulosic biomass as feedstock is an attractive route due to its abundancy and low cost.

Lignocellulosic materials are composed of cellulose, hemicellulose and lignin. Cellulose and hemicellulose can be hydrolyzed to fermentable sugars. From these sugars, various fermentation products, such as ethanol, can be produced by fermentation with microorganisms, e.g.Saccharomyces cerevisiae.

To facilitate the hydrolysis and subsequent fermentation to increase the yield of ethanol, a pretreatment process is typically conducted, wherein the hemicellulose is degraded, and cellulose is made more accessible as well as, to some extent, converted into fermentable sugars.

Pretreatment is an important step in the process of converting biomass into fermentation products since it has a direct effect on downstream processes and ultimate sugar yield. A typical process for pretreatment involves breaking the recalcitrant structure of the lignocellulosic biomass to increase the accessible surface of the lignocellulosic material for subsequent enzymatic hydrolysis.

For example, the recalcitrant structure may be broken in a process involving steam explosion. In such a process, the lignocellulosic biomass is steam-heated at an increased pressure during a certain time followed by a rapid discharge into atmospheric pressure, causing the biomass to explode due to the pressure drop. The release of pressure causes the biomass to disintegrate into smaller particles. Smaller particles are beneficial to increase the enzyme accessibility for subsequent hydrolysis.

The pretreatment process is typically carried out in a pretreatment arrangement, such as a pretreatment reactor. The pretreatment reactor generally comprises an inlet for receiving the biomass to be pretreated and an outlet for discharging the pretreated biomass, and a closed vessel wherein the pretreatment process is carried out.

If the pretreatment involves steam explosion, such a process poses demands on the equipment utilized. The high temperatures and pressures used within the reactor may result in the formation of deposits within the reactor, and such deposits may build up on the reactor walls. The formation of deposits may be a result of charring of the biomass and degradation of sugar and lignin. Furthermore, when the biomass is discharged from the reactor outlet, the significant pressure drop may cause undesirable fluctuations in temperature and pressure within the reactor. This may further enhance the formation of deposits within the reactor.

There is therefore a need for improvements with respect to preventing the formation of deposits during pretreatment and for overcoming problems with temperature and pressure fluctuations within the pretreatment reactor. Particularly, there is a need to provide a pretreatment system, wherein the discharge of biomass is improved and controlled without yielding significant pressure or temperature drops in the reactor.

SUMMARY

In view of the above, it is an object of the present disclosure to provide improvements with respect to systems for pretreatment of lignocellulosic biomass, particularly with respect to reducing the formation of deposits within the reactor during operation, and to improve and control the discharge of biomass from the reactor.

According to a first aspect of the present disclosure, there is provided a pretreatment arrangement for pretreatment of lignocellulosic biomass comprising

a) a reactor vessel having an upstream inlet for receiving biomass and a downstream outlet for discharging biomass,

b) at least one sluice vessel arranged downstream of and in fluid communication with the outlet, wherein the sluice vessel comprises a first discharge valve, a second discharge valve arranged downstream of the first discharge valve and a compartment arranged between the first and the second discharge valve; the first and the second discharge valves being configured to be operable between an open and a closed position, and

c) means for increasing the pressure in the compartment of the sluice vessel when the first and the second discharge valves are in a closed position.

The present inventive concept is based on the realization that the biomass can be treated in the reaction vessel under optimum conditions for pretreatment (i.e. suitable time, pressure and temperature), and the discharge of biomass is performed separate from the reactor vessel, yielding a more controlled and improved discharge of biomass. Increasing the pressure in the compartment of the sluice vessel, and subsequently releasing the biomass into atmospheric pressure upon discharge of the biomass causes the biomass to be disintegrated into smaller particles. Increasing pressure difference between discharge pressure and atmospheric pressure results in decreased particle size due to stronger disintegration of the biomass into particles. Increasing pressure requires increasing temperature, and high temperatures may cause burning or charring of sugars and biomass within the reactor vessel. As a result, deposits may build up within the reactor. Increasing the pressure in a sluice vessel arranged downstream of the pretreatment reactor allows for pretreatment processes involving steam explosion to achieve process conditions that prevent charring of biomass, degradation of sugars, and deposits to build up in the pretreatment reactor. The arrangement of the sluice vessel downstream of the pretreatment reactor allows for an increase in pressure to be achieved in the sluice vessel, thereby yielding a higher pressure difference than if the material had been released directly from the pretreatment reactor. The higher pressure difference results in smaller particle size of biomass which is beneficial for subsequent hydrolysis and release of sugars from the biomass during hydrolysis, while not risking destroying sugars and biomass due to overly high temperatures and pressures under extended residence times in the pretreatment reactor.

The sluice vessel may be attached to the reactor vessel or it may be connected to the reactor vessel by means of a pipe.

In embodiments, the compartment may comprise a tank and/or a pipe

A tank may be advantageous as it allows more material to be treated or pressurized at the same time. A pipe may be advantageous as it facilitates achieving an increased pressure in a shorter time (due to the smaller size of the pipe).

In embodiments, the means for increasing the pressure is a means for supplying gas, such as steam, to the compartment. A rapid increase in pressure can thereby be achieved.

In embodiments, the sluice vessel comprises means for measuring the pressure in the sluice vessel. This is to secure that the pressure within the compartment and the sluice vessel is sufficient to enable disintegration into smaller particles and to avoid increasing the pressure to an unnecessarily extent.

In embodiments, the second discharge valve is configured to be opened in one step or in multiple steps.

In other words, the pressure drop from the increased pressure within the compartment to a lower pressure, e.g. atmospheric pressure may be performed simultaneously with discharge of the biomass. Alternatively, if the second discharge valve is configured to be opened in multiple steps, the biomass may be gradually discharged from the sluice vessel.

In embodiments, the second discharge valve is configured to be opened in multiple steps, such as two steps, wherein the first step is conducted at a lower speed than the following step(s).

This allows for a gentler, yet controlled, discharge of biomass since the time period for decreasing the pressure from the increased compartment pressure to a lower pressure (typically atmospheric pressure) is longer.

In embodiments, the reactor vessel is a vertical reactor vessel. In a vertical reactor vessel, the biomass flows from the inlet to the outlet by means of gravity and no additional means to increase the flow of biomass within the reactor vessel is required.

Preferably, the sluice vessel is adapted for steam explosion.

As mentioned hereinbefore, if steam explosion is performed upon a direct discharge of biomass from the outlet of the reactor vessel, this may cause imbalanced and impaired reaction conditions within the reactor rendering the pretreatment unstable and increasing the risk of deposit formations. A sluice vessel adapted for steam explosion reduces such risks and renders the pretreatment arrangement, particularly the discharge means, stable and controlled.

In embodiments, the sluice vessel is a first sluice vessel and wherein the pretreatment arrangement further comprises a second sluice vessel; the second sluice vessel being arranged in parallel with the first sluice vessel or downstream of the first sluice vessel.

Under certain circumstances, it may be beneficial to include at least one more sluice vessel in the pretreatment arrangement. For example, if the second sluice vessel is arranged downstream of the first sluice vessel, the pressure may increase and decrease in various steps. Steam explosion may be performed at least twice in such a set-up, wherein the first steam explosion step may result in the disintegration into particles of a larger size than the second steam explosion step, where the particles are typically smaller. If the sluice vessels are arranged in parallel, more material may be pretreated simultaneously.

In embodiments, the reactor vessel further comprises a scraping device configured to scrape deposits formed on the interior walls of said reactor vessel.

A scraping device may be arranged in the reactor vessel to prevent the formation of deposits on the interior reactor walls and to scrape off deposits potentially formed.

To further secure optimal and stable reaction conditions and to prevent undesirable temperature and pressure fluctuations within the reactor vessel, the pretreatment arrangement may comprise a gas valve configured to remove gas from the reactor vessel.

During pretreatment; i.e. during degradation or partial degradation of the biomass, gases and volatile compounds may be liberated from the biomass, resulting in the accumulation of gases in the reactor. The accumulation of gases may result in undesirable temperature and pressure fluctuations within the reactor, and eventually lead to problems with deposits in the reactor. Thus, the removal of gases from the reactor vessel during the pretreatment reaction provides for improvements with respect to maintaining balanced temperature and pressure conditions in the reactor during the pretreatment, and thereby also reducing the formation of deposits on the interior walls of the reactor.

According to a second aspect of the present disclosure, there is provided a method for pretreatment of lignocellulosic biomass comprising:

a) pretreating the lignocellulosic biomass in a pretreatment arrangement at a first pressure (p1), wherein the pretreatment arrangement comprises a reactor vessel having an upstream inlet for receiving biomass and a downstream outlet for discharging biomass; the pretreatment arrangement further comprising a sluice vessel comprising a first discharge valve, a second discharge valve arranged downstream of the first discharge valve, and a compartment arranged between the first and the second discharge valves,

b) discharging the biomass into the compartment by opening the first discharge valve,

c) closing the first discharge valve,

d) increasing the pressure in the compartment to a second pressure (p2),

e) discharging the biomass by opening the second discharge valve.

By increasing the pressure inside the sluice vessel to pressure (p2), a higher pressure drop when discharging the biomass from the second valve can be obtained. Consequently, the treated biomass will be divided into smaller pieces compared to if a direct discharge from the reactor would have been performed. Furthermore, the time that the biomass is kept at the increased pressure (p2), (and consequently increased temperature), compared with the time that it is exposed to the reactor pressure (p1) may be shorter.

As mentioned hereinbefore, it is advantageous to avoid significant pressure increases within the reactor vessel since this may result in burning and charring of sugars, and biomass yielding deposits. The pressure may be increased by supplying gas, such as steam to the compartment

In embodiments, the second pressure, p2, is 1-40 bar, such as 2-30 bar, such as 4-20 bar higher than the first pressure, p1.

According to another aspect, there is provided a system for treatment of lignocellulosic biomass comprising a pretreatment arrangement as described hereinbefore and a hydrolysis unit arranged in fluid communication with and downstream of the pretreatment arrangement, and optionally, a fermentation unit arranged in fluid communication with and downstream of the hydrolysis unit.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the present invention to the skilled person.

FIG.1illustrates a pretreatment arrangement100for pretreatment of lignocellulosic biomass comprisinga) a reactor vessel101having an upstream inlet102for receiving biomass and a downstream outlet103for discharging biomass,b) a sluice vessel104arranged downstream of and in fluid communication with the outlet103, wherein the sluice vessel104comprises a first discharge valve105, a second discharge valve106arranged downstream of the first discharge valve105and a compartment107arranged between the first105and the second106discharge valve; the first105and the second106discharge valves being configured to be operable between an open and a closed position, andc) means108for increasing the pressure in the compartment107of the sluice vessel104.

Both discharge valves are in a closed position when the pressure is increased within the compartment107.

Lignocellulosic biomass119enters the reactor vessel101by means of the inlet102. InFIG.1, the biomass is fed into the reactor vessel101by means of a plug screw feeder124. The plug screw feeder124secures an even flow of biomass into the reactor vessel101without disrupting the pressure inside the reactor vessel. The pretreatment arrangement is not limited to a specific type of inlet or means for feeding biomass, but any inlet or feeding means known to those skilled in the art may be used. The inlet and/or outlet may e.g. be a blow line or a blow valve.

The lignocellulosic biomass may be, but is not limited to hardwoods, softwoods, sugarcane bagasse, energy cane, corn stover, corn cobs, corn fibers, straw from rice, wheat, rye and other crops residues.

When the biomass slurry has been pretreated within the reactor vessel101, the biomass is discharged from the reactor vessel101through the outlet103and enters the sluice vessel104. The biomass is discharged by first opening the first discharge valve105, allowing an amount of pretreated biomass to enter the compartment107. The second discharge valve106is kept closed during discharge from the first discharge valve105into the compartment107. The first discharge valve105is thereafter closed. Both discharge valves are in a closed position when the pressure is increased within the compartment107. When the second discharge valve106is opened, the biomass is discharged from the compartment107of the sluice vessel104. Upon discharge, the pressure drop (from the pressurized atmosphere in the compartment to the lower pressure, e.g. atmospheric pressure) causes the biomass to become disintegrated into smaller particles. Typically, this is achieved by means of steam explosion. In other words, the pretreatment arrangement100of the present disclosure provides for an improved and more controlled discharge of biomass. Particularly, it allows for an improved steam explosion to be carried out.

The sluice vessel104is arranged downstream of the reactor vessel101. The sluice vessel104may be a separate component from the reactor vessel101or it may be an integrated component of the pretreatment arrangement100.

In other words, the sluice vessel104may be attached to the reactor vessel101or it may be connected to the reactor vessel101by means of a passage, such as a pipe, a tube or a screw. InFIG.1, the sluice vessel104is connected to the reactor vessel101by means of a pipe109.

In embodiments, the compartment107comprises a pipe. A compartment in the form of a pipe facilitates an increase of pressure in the sluice vessel104.

In alternative embodiments, the compartment107comprises a tank107b, as illustrated in figure lb. In figure lb, the tank107bis connected to the first105and second106discharge valves by means of a pipe110. Alternatively, the first105and the second106discharge valves are directly attached to the tank107b. For example, the discharge valves105and106may form the inlet, and the outlet, respectively of the tank.

The means108for increasing the pressure in the sluice vessel104may be connected to the tank107bor to the pipe110. It may be advantageous that the compartment comprises a tank since more material can be treated at the same time at an increased pressure.

As used herein, the term “tank” means a receptacle or a chamber for holding, storing and transporting biomass from the first discharge valve105to the second discharge valve106. The volume of a tank is considerably larger than that of a pipe.

As indicated by the arrow108inFIG.1, the means108for increasing the pressure is a means for supplying gas, such as steam, to the compartment107.

The means to supply gas may e.g. comprise a pipe connected to the compartment107of the sluice vessel104, and which pipe is connected to a suitable gas source. The means108is adapted to supply gas, such as steam, e.g. pressurized steam, to the compartment107. The supply of gas into the compartment107causes the pressure to increase within the compartment107.

The pressure of the gas or the steam supplied into the compartment107may be in the range of from 25-55 bar, such as 35-45 bar.

The means108for increasing pressure may further comprise a valve111to control the supply of gas into the compartment107.

The sluice vessel104may comprise means for measuring the pressure of the sluice vessel.

The means for measuring the pressure may e.g. comprise a pressure meter, a pressure sensor or a pressure gauge. The means for controlling the pressure may be arranged in the first discharge valve105, in the second discharge valve106or in the compartment107. Preferably, it is arranged in the gas supplying means108. In embodiments, both the means for increasing the pressure108, e.g. the tube, and the sluice vessel104are equipped with means for measuring the pressure.

The supply of gas (or pressure of the supplied gas) into the compartment107may be controlled and adjusted in response to the measured pressure, for example by means of the valve111.

In embodiments, the second discharge valve106is configured to be opened in one step or in multiple steps.

In cases where the second discharge valve106is configured to be opened in one step, the discharge of biomass from the compartment107is performed simultaneously with the drop in pressure from the compartment to lower pressure, typically atmospheric pressure. In cases where the second discharge valve107is opened in multiple steps, the biomass is gradually and more gently discharged from the sluice vessel.

The second discharge valve106may be configured to be opened in multiple steps, such as two steps, wherein the first step is conducted at a lower speed than the following step(s).

This way, the time taken for the pressure to decrease from a higher compartment pressure to a lower pressure, e.g. atmospheric pressure is prolonged. The discharge is thereby performed in a more controlled manner.

The reactor vessel101inFIG.1is a vertical reactor vessel. However, the pretreatment arrangement of the present disclosure is not limited to the use of a vertical reactor vessel. Horizontal reactor vessels are also conceivable for the purpose of the present disclosure. However, a vertical reactor vessel is preferred due to a more simple construction and the fact that the flow of biomass does not require the aid of additional means to facilitate the transport of biomass through the reactor vessel.

As illustrated inFIG.1, the reactor vessel101is a vertical reactor vessel extending along a longitudinal center line118. The biomass119fed into the reactor vessel101flows from the inlet102to the outlet103by means of gravity, and does not require additional feeding or mixing means to support the flow in the reactor vessel101.

Typically, the reactor vessel101is cylindrical and has a circular or oval cross-section, which cross-section area may be constant or vary along the longitudinal center line.

In embodiments, the reactor vessel101has a rotational symmetry with respect to the longitudinal center line118.

Preferably, the sluice vessel104is adapted for steam explosion. In other words, the reactor vessel101is a unit in which the biomass is pretreated, and the sluice vessel104is a unit in which steam explosion of the pretreated biomass is carried out. The reactor vessel101may be adapted to operate under process conditions optimal for the pretreatment, whereas the more harsh or severe pretreatment conditions (large pressure increases and pressure releases) are performed in the sluice vessel104. This way, the risk of deposit formation and formation of inhibitory agents are prevented within the reactor vessel. A more controlled steam explosion is thereby achieved.

In embodiments, the sluice vessel104is adapted to withstand pressures up to 100 bar, e.g. up to 75 bar, e.g. up to 50 bar.

The pretreatment arrangement100may comprise more than one sluice vessel. In embodiments, the sluice vessel104is a first sluice vessel and the pretreatment arrangement further comprises at least a second sluice vessel; the second sluice vessel being arranged in parallel with the first sluice vessel104or downstream of the first sluice vessel104(not shown).

In case the second sluice vessel is arranged in parallel with the first sluice vessel104, both the first and the second sluice vessel are arranged in fluid communication with the reactor vessel101. If the second sluice vessel is arranged in series with the first sluice vessel104, the second sluice vessel is arranged downstream of and in fluid communication with the first sluice vessel104. In such embodiments, the biomass may be subjected to a step-wise pressure increase and decrease. For example, the pressure of the first compartment107of the first sluice vessel104may be lower than the pressure of the compartment of the second sluice vessel, and vice versa. A first steam explosion step may occur upon discharge from the first sluice vessel104and a second steam explosion step may occur upon discharge from the second sluice vessel.

As illustrated inFIG.1, the arrangement100for pretreatment of lignocellulosic biomass may further comprise a scraping device111. The scraping device111secures a continuous flow of biomass in the reactor vessel, while scraping deposits formed on the interior walls112of the reactor vessel101. The scraping device111prevents build-up of deposit inside the reactor vessel101, and the full interior volume of the reactor vessel101can therefore be utilized for the pretreatment of lignocellulosic biomass.

The scraping device111may comprise a shaft113and at least two scraping blades114extending from the shaft113. The scraping blades114are preferably configured to follow the contour of, without contacting the interior walls112of at least a portion of the lower portion115of the reactor vessel101. The shaft113may be arranged outside of the reactor vessel101or may be configured to extend into the upper portion117of the reactor vessel101. Preferably, the shaft113does not extend into the lower portion115of the reactor vessel101. In other words, the shaft113does not extend into a portion of the vessel where slurry is present. The reason is that a shaft113extending into the slurry may form an additional surface onto which deposit may form and develop.

The scraping blades114are arranged to rotate about the longitudinal center line118and are preferably arranged to provide an efficient scraping of the interior reactor walls112without risking that these become damaged by the blades. Therefore, a small gap should preferably be provided between scraping blades114and the interior walls112.

In embodiments, the scraping blades114are arranged at a distance, dl, from the interior walls112of the reactor vessel101, wherein the distance, dl, corresponds to from 0.5 to 20%, preferably from 2 to 15% of the inner diameter of the reactor vessel101.

InFIG.1, the exterior walls of the reactor vessel101are denoted116. The exterior walls116may be configured to taper towards the outlet103in the lower portion115of the reactor vessel. This way, an improved discharge of biomass from the outlet103towards the sluice vessel104is achieved.

The arrangement100for pretreatment of lignocellulosic biomass may further comprise a gas valve120configured to remove gas from the reactor vessel101.

The gas valve120preferably has an adjustable opening configuration. The gas valve120may be attached to the reactor vessel101or connected to the reactor vessel101by means of a tube (the latter of which is illustrated inFIG.1).

The reactor vessel101may further comprise measuring means121for measuring a number of process parameters of the pretreatment in the reactor vessel101. Such process parameters include at least a temperature parameter and a pressure parameter.

The pretreatment arrangement100may further comprise gas flow control means122configured to adjust the outflow of gas from the gas valve120in response to the measured process parameters. This way, a controlled outflow of gas from the reactor vessel101is achieved. Accordingly, a more controlled pretreatment is achieved. The temperature and pressure have been identified as key parameters, together sufficient for achieving stable pretreatment conditions, which implies an efficient pretreatment and reduced formation of deposits on the interior walls of the reactor.

The relationship between the pressure and the temperature is preferably monitored throughout the pretreatment reaction, and when the temperature (or the pressure) deviates from a desired, preferably substantially constant, pressure-to-temperature relationship, this is typically an indication that gases, e.g. inert gases, have started to accumulate within the reactor vessel101. Such gases may then be removed from the reactor vessel101by means of the gas valve120. The outflow of gas from the gas valve120may be adjusted and regulated in response to deviations in temperature or pressure.

In embodiments, the gas flow control means122is configured to adjust the outflow of gas from the gas valve120in response to the relationship between the temperature and pressure, e.g. expressed as a ratio between temperature and pressure, so as to achieve a controlled flow of gas out from the reactor vessel.

Furthermore, the gas flow control means122may be configured to determine a ratio between the temperature parameter and the pressure parameter and to adjust the outflow of gas from the gas valve120in response to the determined ratio. The gas flow control means122may be configured to adjust the outflow of gas from the gas valve120if the determined ratio deviates from a predetermined reference ratio interval for the pretreatment.

By adjusting the outflow of gas from the gas valve120in response to the relationship between the temperature and pressure, the temperature and pressure, or the ratio between temperature and pressure, can be held within a predetermined interval of deviation (basically constant, if the interval is comparatively narrow) for the specific pretreatment to be carried out.

Such pretreatment arrangements will counteract or compensate for imbalance between the temperature and pressure within the reactor caused by the liberation of gases from the biomass during degradation or partial degradation, and which is particularly problematic if the pretreatment is carried out by applying steam or additional catalysts, particularly gaseous catalysts, leading to an excess amount of accumulated gases in the reactor.

In embodiments, the pretreatment arrangement100comprises a flow meter123configured to measure the outflow of gas from the reactor vessel101. The flow meter123may indicate that the flow of gas is too high or too low, and the gas flow control means122may be configured to adjust the opening of the gas valve120in response to the measured outflow of gas.

According to another aspect, the present disclosure further provides a method for pretreatment of lignocellulosic biomass. The steps of the method are schematically outlined inFIG.2. The references related to the pretreatment arrangement ofFIG.1are kept throughout the description of the method.

The method200for pretreatment of lignocellulosic biomass comprises

a) pretreating the lignocellulosic biomass in a pretreatment arrangement100at a first pressure (p1), wherein the pretreatment arrangement100comprises a reactor vessel101having an upstream inlet102for receiving biomass and a downstream outlet103for discharging biomass; the pretreatment arrangement further comprising a sluice vessel104comprising a first discharge valve105, a second discharge valve106arranged downstream of the first discharge valve105, and a compartment107arranged between the first105and the second106discharge valve (this step is illustrated by201inFIG.2),

b) discharging the biomass into the compartment107by opening the first discharge valve105(illustrated by202inFIG.2),

c) closing the first discharge valve105(illustrated by203inFIG.2),

d) increasing the pressure in the compartment107to a second pressure (p2) (illustrated by204inFIG.2),

e) discharging the biomass by opening the second discharge valve106(illustrated by205inFIG.2).

The pressure of step d) may be increased by supplying gas, such as steam, to the compartment107. The gas may be supplied by means of a tube.

The second pressure (p2) may be 1-40 bar, such as 2-30 bar, such as 4-20 bar higher than the first pressure (p1). The pressure (p1) may be 15-30 bar, such as 10-20 bar. The gas for increasing the pressure inside the sluice vessel may be steam, such as pressurized steam. The higher the pressure of the saturated steam, the higher is also the temperature. The pressure of the saturated steam may be30-55bar, such as35-45bar. A second pressure (p2) that is higher than pl allows for an efficient division of the lignocellulosic biomass into small particles upon release of pressure to lower pressure, typically atmospheric pressure.

The residence time, t2, of the lignocellulosic biomass in the compartment107in step d) may be from 1 second to 10 minutes, e.g. from 5 seconds to 5 minutes, e.g. from 5 to 60 seconds.

The residence time, t1, in the reactor vessel101is preferably 2-500 times longer, such as 50-500 times longer, such as 100-400 times longer, such as 200-400 times longer, such as 300-400 times longer than the residence time, t2, in the sluice vessel104(step d). The residence time in the reactor vessel is suitably 3-60 minutes, such as 5-50 minutes, such as 10-40 minutes. The residence time, t2, in the sluice vessel is preferably limited so that burning of sugars and decomposition of sugars and lignin into undesired compounds is avoided.

Pressures above 20-22.5 bar, i.e. temperatures above 215-220° C., in combination with standard residence times e.g. 30 minutes, inside the reactor vessel may be harmful for the lignocellulosic biomass and may cause burning of sugars and decomposition of sugars and lignin into undesired compounds.

The pressure may be monitored to ensure that the desired pressure is obtained in the sluice vessel. This may be achieved by the provision of means of measuring pressure in the sluice vessel104.

As illustrated by the step206inFIG.2, the second discharge vessel105may be opened in one step, allowing the pressure to drop to a lower pressure (usually atmospheric pressure) than the pressure, p2, of the sluice vessel104at the same time as the lignocellulosic biomass is discharged.

Alternatively, the second discharge vessel106is opened in multiple steps (see207inFIG.2) so that the pressure is dropped to lower pressure, typically atmospheric pressure while the lignocellulosic biomass is gradually discharged. For example, the first step may be conducted at a lower speed than the following steps, allowing for a milder pretreatment as the decrease in pressure is allowed to take more time.

By increasing the pressure inside the sluice vessel104and thereafter decreasing the pressure upon opening of the second discharge vessel106, a steam explosion is conducted when the lignocellulosic biomass exits the sluice vessel104.

In the context of the present disclosure steam explosion refers to an increase of pressure in one or several step(s) followed by a rapid decrease of pressure that causes the lignocellulosic biomass to explode into smaller pieces.

As an illustrative example, lignocellulosic biomass may be steam heated at a certain temperature and pressure for a given time, e.g. 205° C., at a pressure of 18 bar for 10 minutes, followed by a rapid pressure increase, e.g. to twice the amount of pressure for a short period of time, e.g. during less than 60 seconds, followed by discharge to a lower pressure, e.g. atmospheric pressure, causing the lignocellulosic biomass to explode. InFIG.1a,the addition of steam into the reactor vessel101is denoted125.

With reference toFIG.3, the present disclosure further provides a system300for treatment of lignocellulosic biomass comprising a pretreatment arrangement301for pretreatment of lignocellulosic biomass according to the first aspect of the present disclosure, a hydrolysis unit302arranged downstream of and in fluid communication with the pretreatment arrangement301, and optionally, a fermentation unit303, such as a fermentation vessel, arranged downstream of and in fluid communication with the hydrolysis unit302. The system300may comprise additional units and components known to those skilled in the art. For example, a separation unit may be arranged after pretreatment, such as between the pretreatment arrangement301and the hydrolysis unit302, and/or between the hydrolysis unit302and the fermentation unit303.

In the hydrolysis unit, the pretreated biomass is subject to enzymatic hydrolysis by means of saccharification enzymes. Fermentation of the hydrolysate into a target chemical is typically performed by means of fermenting organism, such as bacteria and/or yeast. The system300may also comprise a product recovery unit, such as distillation or ion exchange chromatography, arranged downstream of and in fluid communication with the fermentation unit303.

Terms, definitions and embodiments of all aspects of the present disclosure apply mutatis mutandis to the other aspects of the present disclosure.

Even though the present disclosure has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.