Process for treating lignocellulosic biomass

Abstract

There is provided a process (10; 20) for treating lignocellulosic biomass to produce organic chemicals. Biomass having one or more alkaline components is subjected to a pre-treatment step of introducing an acidic additive to the biomass, such that the biomass has a pH of less than or equal to 3 S120; S220. The biomass is then subjected to a single hydrolysis step before condensation so as to hydrolyse cellulose and vaporise the resulting products of cellulose hydrolysis S160; S260. The resulting vapours are then condensed to form an aqueous solution containing the products of cellulose hydrolysis S170; S270.

Description

[0001] Process for Treating Lignocellulosic Biomass

[0002] The present invention relates to a process for treating lignocellulosic biomass to produce organic chemicals.

[0003] As explained in EP 2 483 331 B (Nova Pangaea), there are environmental problems that arise from the use of fossil fuels, so that use of biomass as a source for fuel and organic chemicals would be advantageous. Fossil fuels are both limited in long term availability and cause a net increase of global carbon dioxide emissions which are implicated in global warming.

[0004] Woody or lignocellulosic biomass is largely composed of hemicellulose, cellulose and lignin. Cellulose is principally comprised of C6 sugars while hemicellulose comprises both C5 and C6 sugars. The sugars can be further processed to ethanol, a commercial fuel, and other fuels or fine chemicals.

[0005] Lignin is a complex polymer which gives physical strength to the biomass but which is tightly bound to the other components. Consequently, it is not straightforward to remove the sugars from the remainder of the biomass. Lignin may be further processed to fine chemicals, such as phenols and fuel additives, carbonized to a high carbon solid referred to as biochar, or burnt directly for heat and power.

[0006] Biochar has uses in sequestrating carbon and in agriculture to improve soil conditions by trapping of water, nutrients and providing a high surface area for increased growth of microorganisms that can absorb further carbon dioxide or fix nitrogen for improved plant growth.

[0007] EP 2 483 331 B teaches a method of fractionating lignocellulosic biomass by a sequence of steps. Biomass may be fed into a hemicellulose hydrolysis reactor to hydrolyse hemicellulose. A liquid component includes the products of hemicellulose hydrolysis, for example, in water, and the remaining solid component includes cellulose and lignin. The hemicellulose hydrolysis reactor may treat the material using steam at a temperature for example between 170°C and 250°C and at an elevated pressure for example between 10 bar(a) and 35 bar(a).

[0008] The remaining solid component is then fed to a cellulose hydrolysis reactor which may apply steam at a temperature of between about 400°C and 550°C, so as to hydrolyse cellulose and vaporise the resulting sugars. The resulting vapours are condensed. The solid material may instead be subjected to treatment such as drying and a further sizereduction, before being subjected to a process to bring about cellulose hydrolysis. This may be achieved using flash thermolysis using superheated steam, which may for example be at a temperature between 350°C and 550°C, and for example at a pressure between 1 bar(a) and 2 bar(a), such that the bond between lignin and cellulose is broken and the cellulose is hydrolysed into C6 sugars. The vaporised sugars and any other volatile compounds may then be separated from solid matter. The remaining solids may be in the form of a lignin char.

[0009] EP 3 830 099 A1 introduces a washing step using an aqueous solution after the first hydrolysis. The washing step removes water-soluble inorganic and organic acid and alkali material from the solid component, and also removes the products of hemicellulose hydrolysis that are in solution. It therefore produces washed solid components which can then be subjected to the second hydrolysis to form C6 sugars. The liquid mixture formed as a result of the washing step contains the soluble products of hemicellulose hydrolysis, which are predominantly C5 sugars, such as xylose, with some C6 sugars, such as glucose and mannose, along with the products of the second hydrolysis, which are predominantly C6 sugars. Consequently, the liquid mixture has a significantly higher total sugar content than would be achieved if the washing step had just used clean water.

[0010] Both processes as disclosed in EP 2 483 331 B and EP 3 830 099 A1 include two hydrolysis steps prior to the condensation of the products. Hydrolysis reactions require high energy inputs in the form of heat and pressure.

[0011] It is an object of the present invention to reduce or substantially obviate the aforementioned problems.

[0012] According to the present invention there is provided a process for treating lignocellulosic biomass to produce organic chemicals, the process comprising: a) subjecting biomass having one or more alkaline components to a pre-treatment step of introducing an acidic additive to the biomass, such that the biomass has a pH of less than or equal to 3; b) subjecting the biomass to a single hydrolysis step before step c) so as to hydrolyse cellulose and vaporise the resulting products of cellulose hydrolysis; and c) condensing the resulting vapours to form an aqueous solution containing the products of cellulose hydrolysis.

[0013] Hydrolysis causes the bond between lignin and cellulose to break forming monomeric C6 sugars, for example glucose. The cellulosic sugars, including glucose,levoglucosan, and levulinic acid, for example, and the other products collected may then be used for various commercial purposes or for further processing, such as fermentation to produce alcohols. Other downstream technologies which can utilize the primary products of this process include Virent's Aqueous Phase Reforming process for synthetic gasoline, jet fuel and diesel; Segetis Binary Monomer technologies; and other catalytic conversion processes and chemical or biochemical reaction processes.

[0014] The addition of the acidic additive removes the alkali components of the biomass before it is subjected to hydrolysis. If significant quantities of alkali are present then the cellulose hydrolysis tends to produce smaller molecules such as C1 to C3 aldehydes and ketones, and gases such as carbon monoxide and carbon dioxide which have fewer commercial uses.

[0015] A single hydrolysis step is performed before condensation which reduces the overall energy used by the process in comparison to known hydrolysis reactions while still obtaining the same end products, as heat and a pressurised environment are only used in one step before condensation.

[0016] The conditions of the one hydrolysis step allows both hemicellulose and cellulose to be hydrolysed before condensation without the need of another separate step to hydrolyse the remaining hemicellulose or cellulose. There is also no need to separate major components of biomass before the hydrolysis step.

[0017] Preferably, during step a) the pH of the biomass is between 1.9 and 2.1. A higher proportion of alkali is removed from the biomass when this pH is achieved.

[0018] Preferably, the process further comprises a washing step between step a) and b) of washing the biomass, such that the biomass has a pH of between 5 and 7. This is to remove residual additive or active ash components prior to thermal drying or pyrolysis, which could hydrolyse the products when heated. The cellulose hydrolysis step will produce a good yield of sugars or related compounds in the absence of significant quantities of alkali or acid. Sugars are more desirable, for example cellulose is principally comprised of C6 sugars, such as glucose, which can be further processed to ethanol, a commercial fuel, and other fuels or fine chemicals. If significant quantities of alkali or inorganic acid are present then the cellulose hydrolysis tends to produce smaller molecules such as C1 to C3 aldehydes and ketones, and gases such as carbon monoxide and carbon dioxide which have fewer commercial uses.Beneficially, demineralised water is used in the washing step. This ensures that no additives or contaminants are added to the biomass before hydrolysis.

[0019] Optionally, the process further comprises a de-watering step between step a) and b) of de-watering the biomass. Excess water is therefore removed before the hydrolysis step.

[0020] Beneficially, the process may further comprise a drying step between step a) and b) of drying the biomass. Preferably, the biomass is dried to have less than 10% water by weight of the biomass after the drying step. This removes excess moisture before the hydrolysis step and so improves the efficiency of the hydrolysis reaction.

[0021] Optionally, the drying step is carried out at less than 1 bar(a). Minimal thermal energy is therefore used to dry the biomass.

[0022] Preferably, step b) occurs in a reactor in which the vapour residence time is less than 5 seconds. More preferably, step b) occurs in the reactor in which the vapour residence time is less than 1 second. The gaseous products are carried out of the reactor quickly to be condensed into the aqueous solution containing the products of cellulose hydrolysis. This short residence time ensures that the vaporised sugars are removed from the reactor quickly before further decomposition occurs.

[0023] Preferably, step b) occurs in a reactor in which the solid residence time is greater than 30 seconds. More preferably, step b) occurs in the reactor in which the solid residence time is greater than 5 minutes. This increases the time in which the biomass solids are subjected to the conditions of the hydrolysis reaction and so can be efficiently degraded to hydrolyse cellulose.

[0024] Beneficially, step b) may occur in the reactor at a pressure of less than 1 bar(a). This low pressure accelerates the evaporation of the products before they decompose when present as a liquid. Performing the hydrolysis reaction at a low pressure also reduces the energy consumed by the process.

[0025] Optionally, during step b), steam at a temperature of at least 350°C is utilised. This temperature promotes the bond between lignin and cellulose to break and so promotes the hydrolysis of cellulose.

[0026] Preferably, there is a step prior to step a) of providing the biomass having a maximum particle size of less than a predetermined value, Optionally, the predetermined value is a maximum particle size of less than 10mm, and more preferably of less than 6mm.Smaller particle size increases the surface area to volume ratio of the cellulose and so increases the rate of hydrolysis.

[0027] Advantageously, the predetermined value may be predetermined by a particle selection means. This ensures that only the desired particle size is used in the hydrolysis reaction.

[0028] Preferably, the process further comprises a step prior to step a) of grinding the biomass. Larger particles of biomass are ground to achieve the desired particle size to pass through the particle selection means for hydrolysis.

[0029] Advantageously, there may be a step prior to step a) of adding the biomass to water to make a slurry. The biomass is in suspension and so a larger volume of the alkaline components of the biomass is more likely to come into contact with the acidic additive.

[0030] Preferably, the process further comprises a step d) following step c) of a further hydrolysis step to hydrolyse any unreacted biomass from the hydrolysis step b). Hydrolysis of cellulose and hemicellulose produces anhydro-sugars. The main product is levoglucosan (1,6 anhydro-p-D-glucopyranose). An acid hydrolysis step is required to produce the hydrated forms of the levoglucosan, such as glucose. This further hydrolysis also finishes the hydrolysis of any oligomers that are still present in the solution.

[0031] Optionally, there is a step of extracting excess acid from step a) and adding the excess acid to the further hydrolysis reaction of step d). This has the advantage that the minerals that have been washed out of the biomass in the pre-treatment are returned to the sugar solution. These minerals are required for a future fermentation step. Furthermore, the excess acid is recycled and used again rather than being disposed and removes the need to source a further volume of acid for the reaction.

[0032] Beneficially, the condensation step may be a single step process where water is introduced to the resulting vapours such that the resulting vapours dissolve directly into water. The vapours are thus condensed quickly as they come into direct contact with water after they exit the reactor. It is also advantageous to directly collect the sugars in an aqueous solution via condensation; many arrangements in the art collect bio-oil, from which sugars must be separately extracted in a further step.Preferably, the process further comprises a step e) of purifying the products of cellulose hydrolysis. This step produces a purified product and removes decomposition products such as furfural or organic acids which are not desirable.

[0033] Beneficially, after step b) and prior to step c) lignin char is removed from the reactor, the lignin char being further processed to produce biochar. Biochar has multiple advantages for example uses in sequestrating carbon and in agriculture to improve soil conditions by trapping of water.

[0034] For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which:

[0035] Figure 1 shows a flow diagram of a first embodiment of a process for treating lignocellulosic biomass according to a first aspect of the invention; and

[0036] Figure 2 shows a flow diagram of a second embodiment of a process for treating lignocellulosic biomass according to a first aspect of the invention comprising the recycling of excess acid.

[0037] Referring firstly to Figure 1 there is shown a flow diagram representing a first embodiment of a process for treating lignocellulosic biomass so as to obtain shorter chain sugars by breaking down the hemicellulose and cellulose polymers within the biomass. The short chain sugars, referred to as C5 and C6 sugars, may be for example xylose, glucose and mannose which can be used for various commercial purposes or for further processing. The terms C5 and C6 refer to the number of carbon atoms present in a molecule, for example glucose is a C6 sugar as it has six carbon atoms. The process is referenced throughout as 10.

[0038] Biomass that is high in lignocellulosic biomass is received in step S100. Sources of lignocellulosic biomass includes but are not limited to wood and wood residues, agricultural waste such as corn stover, wheat straw, sugar cane straw, rice straw, cassava stems, woody grasses and agricultural processing waste such as bagasse, corn cobs, wet grains, rice husks and whiskey draff. The biomass, containing alkali components, is preferably passed through magnetic and stone traps to remove debris prior to processing. This ensures that the biomass used in the hydrolysis process is not contaminated by debris.The biomass is then preferably passed through a particle selection means such as a sieve in step S110. The particle selection means predetermines a predetermined value of the biomass particles. Biomass particles with a maximum particle size of less than the predetermined value, preferably less than 6mm, pass through the sieve for further processing. A size of less than 6mm is defined as a maximum length or diameter of each of the biomass particles. It may be that a slightly larger particle size, or predetermined value, could work, such as less than 10mm. This size is desired for the efficient hydrolysis of the biomass. The small size of the particles provides a large surface area to volume ratio and so increases the rate of reaction of hydrolysis.

[0039] Biomass particles with a particle size of more than 6mm may be passed through a particle size reduction process. The particle size reduction process may include the use of a hammer mill, shredder or roll mill to crush, shred or grind the biomass into smaller particles. The processed biomass is then preferably passed back through the sieve to separate the biomass particles again. The particle size reduction process may be repeated multiple times until all of the biomass has as size of less than 6mm for pre-treatment.

[0040] In an alternative embodiment, the biomass particles may be required to have a size of less than 3mm, for example. It is also possible that the biomass particles may be required to have a size of less than 10mm. The particle selection means may be altered accordingly to accommodate smaller or larger particles.

[0041] It is also feasible that the biomass particles are provided to the user having a size of less than 6mm. The particle size selection process may therefore not be performed.

[0042] The biomass which has a particle size of less than 6mm may be heated to evaporate vapours, for example of naturally-occurring oils such as turpentine or eucalyptus oil if these are present in significant concentration.

[0043] The biomass is preferably added to water to form a slurry in step S111. The water is preferably demineralised water, although any water source could feasibly be used. The slurry is preferably held within a tank or container. This suspends the biomass particles, and the slurry may be mixed to prevent the biomass from settling in the tank.

[0044] In a pre-treatment step S120, an acidic additive is added to the slurry. Due to the particles being in suspension the acid additive is able to react with the alkali components in the biomass more efficiently. The slurry may be mixed to ensure that at least a majority of the alkali components, if not all, have reacted with the acidicadditive. The acidic additive may be any one of phosphoric acid, nitric acid, hydrochloric acid, sulphuric acid, formic acid, acetic acid or oxalic acid. It is feasible that the water is added at the same time as the acidic additive in step S122.

[0045] The addition of the acidic additive results in the biomass having a pH of less than or equal to 3. It is preferable that the pH of the biomass is between 1.9 and 2.1 depending on the concentration and type of acid added.

[0046] The acidic additive is preferably added to the slurry in the correct volume, for example the correct volume required to react with at least the majority of the alkali components in the biomass, to achieve a pH of between 1.9 and 2.1. It is however possible that a volume is added which results in a lower pH and / or an excess volume of acid.

[0047] The liquid is preferably drained from the slurry. A washing step S130 is then preferable to remove any residual acidic additive and obtain biomass with pH of between 5 and 7 before hydrolysis. Demineralised water may be used for this washing step, or other source of water if demineralised water is unable to be sourced.

[0048] Additional pre-treatment steps can be included to reduce protein or starch levels in the biomass if these are high in the feedstock.

[0049] The biomass is then de-watered in de-watering step S140 to remove as much water as possible. A mechanical press may be used for this step. The mechanical press may be a screw press, decanter centrifuge, filter press, vacuum press or similar.

[0050] To remove further water from the biomass, the biomass is dried using heat in drying step S150 so that less than 10% water by weight of the biomass remains. This ideally is carried out at reduced pressure, preferably less than 1 bar(a), to minimise thermal exposure.

[0051] The treated biomass is introduced, for example, with a screw conveyor into a reactor in which hydrolysis takes place in step S160. It will be appreciated that the chemical processes that take place when performing the operation referred to as "cellulose hydrolysis" may be more accurately referred to as thermolysis, pyrolysis, depolymerisation or degradation. The overall result is that cellulose is separated from lignin and is broken down into smaller organic compounds known as C5 and C6 molecules such as glucose. In this document the process of treating the material with high temperature steam to create smaller compounds from the cellulose is referred to as cellulose hydrolysis.In the cellulose hydrolysis reaction, the biomass is subjected to superheated steam at a high temperature in step S161, at least 350°C and preferably 550°C, substantially in the absence of air. The biomass particles are heated to a range of 380 to 410°C.

[0052] The solids are preferably transported within the reactor either by an auger screw or rotating tube rather than being entrained in the gas flow. The residence time of the solids may be more than 30 seconds, and is preferably 1 minute, or more preferably more than 5 minutes. The residence time is the amount of time the reactants and products stay within the hydrolysis reaction. Therefore, the longer the biomass particles remain in the reactor, the more time there is for hydrolysis to take place.

[0053] Under these conditions, the cellulose and any hemicellulose undergo degradation or hydrolysis, mainly producing monomeric sugars including levoglucosan and some oligomeric sugars and anhydro-sugars, which vaporise under the reaction conditions.

[0054] The gaseous products are carried out of the reactor by the gas flow, specifically by the steam as it exits the reactor. In other words, the steam is known as a gas carrier. It is feasible that a mixture of steam and another gas is used as the gas carrier, for example steam and an inert gas. It is possible that steam could be used in combination with one or more of nitrogen, hydrogen, carbon dioxide or carbon monoxide.

[0055] Critically, once the products are released as vapours, the products are removed from the reactor by the gas flow in less than 5 seconds, or ideally less than 1 second. This removes the vaporised sugars from the reactor before further decomposition occurs. Lignin char is also produced from the hydrolysis reaction and may be removed from the reactor as solid particulates. Lignin may be further processes to a high carbon solid referred to as biochar.

[0056] The reactor is run at below atmospheric pressure, ideally less than 1 bar(a) and preferably at 0.5 bar(a) or below. This is to accelerate the evaporation of the products before they decompose.

[0057] The vapour is then condensed in a single step S170 by bringing the gas flow into contact with water, preferably a water spray or mist, as the gas flow exits the reactor. This is to ensure the conditions are such that liquid water is present allowing the oligomeric sugars and anhydro-sugars to dissolve directly into the water to form an aqueous sugar solution.A further hydrolysis step S180 is performed to produce the hydrated forms of the sugars. This includes the addition of an acid to perform acid hydrolysis. This subjects the aqueous sugar solution to acidic conditions and temperatures above 100°C, or ideally 120°C. The hydrolysis conditions are chosen to minimise further decomposition of the sugars. This hydrolysis also completes the hydrolysis of any oligomers or anhydro-sugars that are still present in the solution.

[0058] The products of the further hydrolysis step, preferably glucose, levoglucosan, and levulinic acid, are then purified in step S190. For the use in certain applications such as fermentation to ethanol, it is necessary to purify the sugar solution to remove decomposition products such as furfural or organic acids. This is achieved by a combination of treatments such as, but not limited to, activated carbon filtration, ion exchange resins treatment or over liming.

[0059] In a second embodiment of the process as shown in Figure 2, referenced as 20, similar steps to the first embodiment are performed. In particular biomass is received in step S200, the biomass is preferably passed through a particle selection means in step S210, a slurry may be produced by the addition of water in step S211 and the biomass is pre-treated in step S220.

[0060] Excess acid from the pre-treatment of the biomass in step S220 may be extracted from the slurry in this embodiment for use at a later stage.

[0061] As in the first embodiment, the pre-treated biomass is preferably washed in step S230, de-watered in step S240 and dried in step S250.

[0062] The biomass is then subjected to a single hydrolysis step S260 with the addition of steam S261. The conditions of the hydrolysis in the second embodiment are the same as in the first embodiment. Solid lignin char is removed from the reactor.

[0063] The vapourised sugars are condensed in step S270.

[0064] A further hydrolysis step takes place in step S280. Instead of sourcing new acid for the reaction, the acid for the further hydrolysis is added in step S224 from the excess acid from the pre-treatment step S220. This allows the acid to be recycled for further use, removing the need to source a further volume of acid for the further hydrolysis reaction.

[0065] Once the further hydrolysis is complete, the products are purified in step S290.It is therefore possible to produce monomeric sugars such as glucose, levoglucosan, and levulinic acid, for example, using only one hydrolysis step rather than two prior to the condensation of vapourised sugars. The same products are therefore produced in one hydrolysis step compared to two hydrolysis steps of known processes before condensation occurs, and so less energy is required overall. The described process is therefore more energy efficient than known two-step hydrolysis processes.

[0066] The words ‘comprises / comprising’ and the words ‘having / including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps, or components, but do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

[0067] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features ofthe invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

[0068] The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims.

Claims

Claims1. A process (10; 20) for treating lignocellulosic biomass to produce organic chemicals, the process comprising:a) subjecting biomass having one or more alkaline components to a pretreatment step of introducing an acidic additive to the biomass, such that the biomass has a pH of less than or equal to 3 (S120; S220);b) subjecting the biomass to a single hydrolysis step before step c) (S170;S270) so as to hydrolyse cellulose and vaporise the resulting products of cellulose hydrolysis (S160; S260); andc) condensing the resulting vapours to form an aqueous solution containing the products of cellulose hydrolysis (S170; S270).

2. A process (10; 20) as claimed in claim 1, wherein during step a) (S120; S220) the pH of the biomass is between 1.9 and 2.1.

3. A process (10; 20) as claimed in any one of the preceding claims, further comprising a washing step between step a) (S120; S220) and b) (S160; S260) of washing the biomass, such that the biomass has a pH of between 5 and 7 (S130; S230).

4. A process (10; 20) as claimed in claim 3, wherein demineralised water is used in the washing step (S130; S230).

5. A process (10; 20) as claimed in any one of the preceding claims, further comprising a de-watering step between step a) (S120; S220) and b) (S160; S260) of de-watering the biomass (S140; S240).

6. A process (10; 20) as claimed in any one of the preceding claims, further comprising a drying step between step a) (S120; S220) and b) (S160; S260) of drying the biomass (S150; S250).

7. A process (10; 20) as claimed in claim 6, wherein the biomass is dried to have less than 10% water by weight of the biomass after the drying step (S150; S250).

8. A process (10; 20) as claimed in claim 6 or claim 7, wherein the drying step (S150; S250) is carried out at less than 1 bar(a).

9. A process (10; 20) as claimed in any of the preceding claims, wherein step b) (S160; S260) occurs in a reactor in which the vapour residence time is less than 5 seconds.

10. A process (10; 20) as claimed in claim 9, wherein step b) (S160; S260) occurs in the reactor in which the vapour residence time is less than 1 second.

11. A process (10; 20) as claimed in any one of the preceding claims, wherein step b) (S160; S260) occurs in a reactor in which the solid residence time is greater than 30 seconds.

12. A process (10; 20) as claimed in claim 11, wherein step b) (S160; S260) occurs in the reactor in which the solid residence time is greater than 5 minutes.

13. A process (10; 20) as claimed in any one of the preceding claims, wherein step b) (S160; S260) occurs in a reactor at a pressure of less than 1 bar(a).

14. A process (10; 20) as claimed in any one of the preceding claims, wherein during step b) (S160; S260), steam ata temperature of at least 350°C is utilised.

15. A process (10; 20) as claimed in any one of the preceding claims, wherein there is a step prior to step a) (S120; S220) of providing the biomass having a maximum particle size of less than a predetermined value (S110; S210).

16. A process (10; 20) as claimed in claim 15, wherein the predetermined value is a maximum particle size of less than 10mm.

17. A process (10; 20) as claimed in claim 16, wherein the predetermined value is a maximum particle size of less than 6mm.

18. A process (10; 20) as claimed in any one of claims 15 to 17, wherein the predetermined value is predetermined by a particle selection means.

19. A process (10; 20) as claimed in any one of claims 15 to 18, further comprising a step prior to step a) (S120; S220) of grinding the biomass.

20. A process (10; 20) as claimed in any one of the preceding claims, wherein there is a step prior to step a) (S120; S220) of adding the biomass to water to make a slurry (S111; S211).

21. A process (10; 20) as claimed in any one of the preceding claims, further comprising a step d) (S180; S280) following step c) (S170; S270) of a further hydrolysis step to hydrolyse any unreacted biomass from the hydrolysis step b) (S160; S260).

22. A process (20) as claimed in claim 21, wherein there is a step (S224) of extracting excess acid from step a) (S220) and adding the excess acid to the further hydrolysis reaction of step d) (S280).

23. A process (10; 20) as claimed in any one of the preceding claims, wherein the condensation step (S170; S270) is a single step process where water is introduced to the resulting vapours such that the resulting vapours dissolve directly into water.

24. A process (10; 20) as claimed in any one of the preceding claims, further comprising a step e) (S190; S290) of purifying the products of cellulose hydrolysis.

25. A process (10; 20) as claimed in any one of the preceding claims, wherein after step b) (S160; S260) and prior to step c) lignin char is removed from the reactor, the lignin char being further processed to produce biochar.

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