Biochar

Abstract

The present invention relates to biochar, and particularly, although not exclusively, to the carbonisation of a photosynthetic organism to generate biochar. The invention extends to methods for converting a photosynthetic organism into biochar, and encompasses apparatus and / or reactors used to perform such methods.

Description

[0001] BIOCHAR

[0002] The present invention relates to biochar, and particularly, although not exclusively, to the carbonisation of a photosynthetic organism to generate biochar. The invention extends to methods for converting a photosynthetic organism into biochar, and encompasses apparatus and / or reactors used to perform such methods.

[0003] Biochar is the product of thermal treatments of biomass. Biochar is relatively resistant to chemical and microbial degradation, and is a stable form of carbon-rich material.

[0004] Furthermore, biochar can survive in the soil organic matter reservoir for thousands of years. The relative stability of biochar has led to proposals for its use in carbon sequestration to mitigate climate change. Biochar can also be used in industrial and agricultural applications.

[0005] The transformation of biomass into biochar involves heat-induced chemical changes. Ideally, the biomass, which is the source material, has high ratios of hydrogen to carbon, and oxygen to carbon. Early chemical changes in response to heating involve a reduction of oxygen contents as water and carbon dioxide are produced. Later chemical changes in response to heating involve a reduction of hydrogen contents as methane and other hydrocarbons are released. The loss of hydrogen corresponds to the formation of stable aromatic and polycyclic aromatic rings in the developing biochar.

[0006] Different types of biomass can be used as the source material for biochar generation. Moreover, the thermal processes used to generate biochar vary widely in temperature, pressure, time, and reagents. Choice of source materials and conditions for biochar production can lead to biochar products with different physical properties, chemical architectures, yields, and efficiencies.

[0007] There is, therefore, a need to identify both a biomass starting material, and associated carbonisation processes that are efficient, sustainable, and scalable for biochar production. The products can then be used for a range of purposes, including various industrial, agricultural, and climate change mitigation applications.

[0008] In order to address the above problem, the inventor investigated the use of algae and the photosynthetic bacterium, Spirulina spp., as biomass source materials for producing biochar. Both algae and photosynthetic bacteria have advantages as a source of biomass owing to their rapid growth rate and opportunities for offshore aquaculture. In particular, microalgae are a promising biomass feedstock for the production of biochar owing to their high productivity and non-consumption of soil or arable land. In addition, current biochar generation processes require certain laborious stages before carbonisation can be performed. An initial mechanical, cold system drying stage, such as centrifugation, is performed to remove a portion of the water from the biomass. Thermal drying of the biomass may then be performed to remove any remaining water in the biomass prior to the carbonisation process. However, thermal drying is an energy-intensive process, as it requires heating of the biomass.

[0009] In view of such limitations, the inventor investigated alternative methods of dewatering the biomass starting material. The inventor surprisingly discovered that, rather than cold system centrifugation and energy-intensive thermal drying, hydrothermal carbonisation (HTC) not only effectively dewaters the algae in one step, but also creates a hot system, i.e., an exothermic reaction. As such, the use of HTC does not require additional heat, and is therefore more energy efficient than existing dewatering processes used in the biochar generation field. In addition, this initial HTC step provides a mechanism to break labile bonds and liberate some biologically limiting elements, including nitrogen, phosphorus, and potassium, that can be re-used for algal growth. The products of HTC then undergo anhydrous carbonisation, as they do in current biochar generation processes.

[0010] The inventor has now developed a two-step process involving hydrothermal carbonisation followed by anhydrous carbonisation to generate biochar from a photosynthetic organism, for example, algae or photosynthetic bacteria. The process allows (I) significant nutrient recovery (allowing algal growth to occur in a sustainable and scalable fashion), (ii) efficient water removal from biomass, and (iii) a positive heat budget for the overall process.

[0011] Accordingly, in a first aspect of the invention, there is provided a method of converting a photosynthetic organism into biochar, the method comprising subjecting a photosynthetic organism to hydrothermal carbonisation (HTC) to produce hydrochar, and subjecting the hydrochar to anhydrous carbonisation to produce biochar.

[0012] It will be appreciated that hydrothermal carbonisation (HTC) of a material involves the application of heat, water, and pressure to the material. It will also be appreciated that anhydrous carbonisation of a material involves the application of heat to the material in the absence of oxygen.

[0013] It will be appreciated that photosynthetic organisms are able to convert light energy into chemical energy, which is stored in organic compounds that can later be metabolised through cellular respiration to fuel the organism's activities. It will also be appreciated that photosynthetic organisms include certain plants, algae, and bacteria.

[0014] In one embodiment, the photosynthetic organism is an algae.

[0015] In another embodiment, the photosynthetic organism is a plant.

[0016] In yet another embodiment, the photosynthetic organism is a photosynthetic bacteria, for example cyanobacteria.

[0017] In one embodiment, the photosynthetic organism is obtained from a source, including: a wastewater treatment system, an open-water system comprising eutrophication and / or algal biomass growth, and / or waste from the nutraceutical industry.

[0018] Advantageously, the method of the invention provides efficiency, operating cost efficiency, and economic benefits over the conventional methodology for producing biochar.

[0019] Capital cost efficiency benefits derive from the reduced need for dehydration units. Operating cost efficiency is derived from the reduced need for external energy to provide thermal energy. The combination of capital and operating efficiency results in economic benefits.

[0020] Thus, in one embodiment, the method comprises a two-step carbonisation process in which a first step comprises converting a photosynthetic organism into hydrochar via the hydrothermal carbonisation (HTC), and a second step comprises concerting the hydrochar to anhydrous carbonisation to produce biochar.

[0021] Advantageously, the method of the invention may involve converting algae into biochar. Algae have advantages as a source of biomass owing to their rapid growth rate and opportunities for offshore aquaculture. In particular, microalgae are a promising biomass feedstock for the production of biochar owing to their high productivity and nonconsumption of soil or arable land.

[0022] In one embodiment, the photosynthetic organism is harvested by filtration, flocculation, flotation, sedimentation, centrifugation, or any combination thereof. In one embodiment, the algae are fresh-water or marine-based algae. Typically, however, the algae are fresh-water algae.

[0023] In one embodiment, the algae may be selected from a group of algae consisting of: Division - Chlorophyta (green algae), genus Acetabularia (mermaid's wine glass class Charophyceae, order Desmidiales (desmids), order Charales (stoneworts), genus Chlamydomonas, genus Chlorella, genus Cladophora, genus Codium, genus Hydrodictyon (water net), genus Oedogonium, genus Pediastrum, genus Pleurococcus, genus Scenedesmus, genus Spirogyra, genus Ulothrix, genus Ulva (sea lettuce), genus Volvox, Division Chromophyta, class Phaeophyceae (brown algae), genus Fucus, genus Laminaria, genus Macrocystis, genus Pelagophycus, genus Sargassum (gulfweed), class Bacillariophyceae (diatoms), class Chrysophyceae (golden algae), class Xanthophyceae (yellow-green algae), genus Vaucheria, Division Cryptophyta, class Cryptophyceae, Division Rhodophyta (red algae), genus Batrachospermum , genus Callophyllis, species Chondrus crispus (Irish moss), species Palmaria palmata (dulse), genus Porphyra (laver), and genus Nitophyllum.

[0024] Typically, the algae comprise microalgae.

[0025] Most typically, the algae comprise Chlorella.

[0026] In an embodiment, the algae may be selected from a group of algae consisting of: Chlorella autotrophica, Chlorella colonials, Chlorella lewinii, Chlorella minutissima, Chlorella pituita, Chlorella pulchelloides, Chlorella pyrenoidosa, Chlorella rotunda, Chlorella singularis, Chlorella sorokiniana, Chlorella variabilis, Chlorella volutis, and Chlorella vulgaris.

[0027] Typically, the algae comprise Chlorella vulgaris.

[0028] In one embodiment, the method of the invention may involve converting photosynthetic bacteria into biochar.

[0029] Typically, the photosynthetic bacteria comprise cyanobacteria.

[0030] Most typically, the photosynthetic bacteria comprise Spirulina spp..

[0031] Thus, in another embodiment, the photosynthetic bacteria may be selected from a group of bacteria consisting of: Spirulina abbreviate, Spirulina agilis, Spirulina agilissima, Spirulina albida, Spirulina ardissoni, Spirulina baltica, Spirulina bayannurensis, Spirulina breviarticulata, Spirulina cabrerae, Spirulina caldaria, Spirulina cavanillesiana, Spirulina condensate, Spirulina corakiana, Spirulina flavovirens, Spirulina funiformis, Spirulina gessneri, Spirulina gomontiana, Spirulina gomontii, Spirulina gordiana, Spirulina gracilis Spirulina innatans, Spirulina labyrinthiformis, Spirulina laxa, Spirulina laxissima Spirulina legitima, Spirulina magnified, Spirulina major, Spirulina margaritae, Spirulina mariae, Spirulina massartii, Spirulina maxima, Spirulina miniata, Spirulina minima, Spirulina mukdensis, Spirulina nodosa, Spirulina nordstedtii, Spirulina okensis, Spirulina oscillarioides, Spirulina platensis, Spirulina princeps, Spirulina pseudotenuissima, Spirulina robusta, Spirulina rosea, Spirulina schroederi, Spirulina sigmoidea, Spirulina socialis, Spirulina spirulinoides, Spirulina subsalsa, Spirulina subtilissima, Spirulina supersalsa, Spirulina tenerrima, Spirulina tenuior, Spirulina tenuis, Spirulina tenuissima, Spirulina thermalis, Spirulina turfosa, Spirulina versicolor, Spirulina weissii, Spirulina spp, Arthrospira spp., and associated Prochiorophytes.

[0032] In a preferred embodiment, the photosynthetic bacteria comprises Spirulina, such as Arthrospira platensis, Arthrospira fusiformis, and / or Arthrospira maxima.

[0033] In an embodiment, the method comprises use of hydrothermal carbonisation (HTC) in order to convert the photosynthetic organism into hydrochar.

[0034] Hydrothermal carbonisation (HTC) is a relatively recently developed approach to treating wet organic waste. HTC, which may be referred to as "wet pyrolysis", is being considered also for the valorisation of polymeric waste, such as biomass. The technology itself is a way of mimicking the natural phenomena of mineralisation in aqueous media, found in natural biomass. The use of HTC in the valorisation of polymeric waste is gaining popularity. Modern HTC applications have used various waste forms of biomass, municipal solid waste, plastics, and bulk textiles as reactants, in order to produce solid carbon, various gases (such as CO2, CO, CH4, and C2H4), and oil products.

[0035] The HTC process may use a solvent in order to regulate the pressure to the desired reaction conditions inside the reactor. In the case of water or other organic solvents, these can be reactants at the same time, having a double function. Moreover, when water is utilised, it has an autocatalytic effect towards carbonisation.

[0036] Therefore, in one embodiment, the HTC process comprises the use of a solvent. The solvent may be an organic solvent. Water is a suitable solvent for hydrothermal conversion processes, due to its low cost, non-toxicity, and abundance. Organic materials are hydrolysed into low molecular weight molecules during HTC. Due to the intermediate molecules' instability and reactivity, they re-polymerise into high molecular weight compounds.

[0037] Therefore, typically the solvent is water.

[0038] In one embodiment, the HTC process comprises a water to photosynthetic organism biomass ratio of between 1: 1 and 20: 1, or between 2: 1 and 10: 1, or between 3: 1 and 5: 1. In an embodiment, the HTC process comprises a water to photosynthetic organism biomass ratio of about 4: 1.

[0039] The HTC process may be batch, fed-batch, continuous, or semi continuous.

[0040] In the case of a batch hydrothermal reactor, the advantages of this reactor design, as previously mentioned, lie with the exothermic nature of the reaction enabling lower temperature operation, as well as the ability to easily process wet feedstocks, for example, a photosynthetic organism, such as algae, harvested from wastewater treatment systems, and / or open water eutrophication blooms, which is then concentrated to approximately 20% by weight.

[0041] Typically, the HTC process is continuous or semi continuous.

[0042] In one embodiment, the HTC process comprises a catalyst or does not comprise a catalyst.

[0043] The experiments discussed in the Examples were conducted in the absence of a catalyst. Typically, therefore, the HTC process does not comprise a catalyst.

[0044] In one embodiment, the HTC reaction may be performed at a temperature range of between 50 °C and 500 °C. The HTC reaction may be performed at a temperature range of between 60 and 400 °C, between 70 and 300 °C, between 80 and 250 °C, or between 90 and 200 °C.

[0045] In an embodiment, the HTC reaction is performed at a temperature range of between 100 and 180 °C, between 110 and 160 °C, or between 115 and 150 °C. The inventor has discovered that increasing pressure helps break chemical bonds at lower temperatures; importantly, these pressures do not require expensive equipment.

[0046] In a preferred embodiment, the HTC reaction is performed at a temperature range of between 120 and 140 °C, or between 125 and 135 °C.

[0047] It will be appreciated that any of the above temperature ranges can be combined to result in a temperature range defined by lower and upper temperature limits.

[0048] It will also be appreciated that the temperatures and pressures of the HTC reaction are set by the stainless steel vessel and the bond breaking temperature-pressure relationship. For example, extra time may be added to counteract reduced temperature and pressure.

[0049] It will also be appreciated that the temperature can be anywhere above 100 °C, and the pressure can be anywhere above 1 bar.

[0050] The HTC reaction may be performed such that it has a residence time of between 5 seconds and 24 hours. In an embodiment, the HTC reaction has a residence time of between 10 seconds and 23 hours, 15 seconds and 22 hours, 30 seconds and 21 hours, 45 seconds and 20 hours, 1 minute and 19 hours, 2 minutes and 18 hours, or 3 minutes and 17 hours. Typically, the HTC reaction has a residence time of between 4 minutes and 16 hours, 5 minutes and 16 hours, 6 minutes and 15 hours, 7 minutes and 14 hours, 8 minutes and 13 hours, 9 minutes and 12 hours, or 10 minutes and 11 hours.

[0051] In an embodiment, the HTC reaction is performed such that it has a residence time of between 1 minute and 30 minutes. Typically, the HTC reaction is performed such that it has a residence time of 8 minutes, 10 minutes, and / or 12 minutes.

[0052] The HTC reaction may be performed at a pressure which may vary depending on the temperature. For example, a pressure of 0 bar (gauge) may be used at 100 °C, while a pressure of more than 1.4 bar (gauge) may be used at 140 °C.

[0053] Accordingly, in one embodiment of the invention, the HTC reaction may be performed at a pressure of between atmospheric pressure and 100 bar (gauge) or 50 bar (gauge). Typically, the HTC reaction is performed at a pressure of between 0.1 and 20 bar, 0.5 and 15 bar, 0.8 and 10 bar, or 1 and 5 bar. Most typically, the HTC reaction is performed at a pressure of 1.1 bar (gauge). The optimum conditions discovered by the inventor through experimentation in the Examples as a proof-of-concept were 129 °C, 1.1 bar (gauge), 10 minutes.

[0054] The method may comprise the use of a purging gas during the HTC process to purge the reactor of any air which may be present. The purging gas may be an inert gas, such as nitrogen or argon.

[0055] In an embodiment, however, the purging gas is nitrogen.

[0056] The HTC process results in "hydrochar", which is recovered by vacuum filtration. The hydrochar is friable and suitable for downstream handling. The hydrochar represents mainly hydrothermally transformed proteins which are the major component in algae.

[0057] Typically, the hydrochar is recovered from the HTC process by vacuum filtration.

[0058] Typically, the hydrochar comprises, in part, hydrothermally transformed proteins.

[0059] The liquids recovered by HTC contain liberated nutrients that can be reused for growth of additional photosynthetic organism feedstock. The HTC conditions release carbohydrates and lipids from the photosynthetic organism; the release of lipids provides a source of potential fuel for combustion purposes.

[0060] Thus, in an embodiment, the method may comprise an additional step of feeding nutrients liberated from the photosynthetic organism during the HTC step back into a growing photosynthetic organism biomass which acts as a feedstock for the photosynthetic organism.

[0061] The method can comprise growth of the photosynthetic organism to produce the photosynthetic organism biomass.

[0062] Typically, the photosynthetic organism is grown in a suitable medium, which may comprise: warm water, an appropriate nutrient profile, light, and / or atmospheric air, in order to optimise system productivity.

[0063] Typically, the photosynthetic organism is grown in a medium comprising liberated nutrients recovered from the HTC of the photosynthetic organism. The photosynthetic organism may be grown in a medium comprising carbohydrates recovered from the HTC of the photosynthetic organism.

[0064] In an embodiment, the method can comprise using lipids liberated from the photosynthetic organism during HTC as a fuel source for the HTC and / or the anhydrous carbonisation processes.

[0065] The method may comprise anhydrous carbonisation of the hydrochar into biochar.

[0066] Typically, the method comprises anhydrous carbonisation following the hydrothermal carbonisation step in order to achieve the conversion of the photosynthetic organism into biochar.

[0067] Thus, the second step comprises subjecting the previously produced hydrochar to anhydrous carbonisation, also known as post-hydrothermal carbonisation (PHTC), to generate a carbon-rich biochar that meets market needs.

[0068] In another embodiment, the hydrochar produced by the HTC process undergoes anhydrous carbonisation.

[0069] In one embodiment, the hydrochar is heated progressively from room temperature to 700 °C (e.g., a rate of 20 to 300 °C at 20 °C / min), and held for a fixed period of time (e.g., 30 min).

[0070] In another embodiment, the hydrochar is heated in the absence of oxygen.

[0071] In yet another embodiment, the hydrochar is heated in the absence of oxygen, whereby the oxygen is excluded by a non-oxidising atmosphere.

[0072] In another embodiment, the hydrochar is heated in the presence of nitrogen and / or helium.

[0073] In another embodiment, the hydrochar is heated in a vacuum.

[0074] In one embodiment, the anhydrous carbonisation process comprises heating the hydrochar. Typically, the anhydrous carbonisation process comprises heating of the hydrochar produced by hydrothermal carbonisation. In another embodiment, the anhydrous carbonisation process involves progressively heating the hydrochar from 0 °C to 1000 °C, from 5 °C to 950 °C, from 10 °C to 900 °C, or from 15 °C to 850 °C.

[0075] In an embodiment, the anhydrous carbonisation process involves progressively heating hydrochar from 18 °C to 750 °C. Typically, the anhydrous carbonisation process involves progressively heating hydrochar from 20 °C to 700 °C.

[0076] In another embodiment, the anhydrous carbonisation process involves progressively heating hydrochar at a rate of 1 to 100 °C / min.

[0077] Typically, the anhydrous carbonisation process involves progressively heating hydrochar at a rate of 10 to 50 °C / min. In an embodiment, the anhydrous carbonisation process involves progressively heating hydrochar at a rate of 15 to 30 °C / min. In some embodiments, the anhydrous carbonisation process involves progressively heating hydrochar at a rate of 20 °C / min.

[0078] In one embodiment, the anhydrous carbonisation process involves heating the hydrochar at a fixed temperature for a fixed period of time.

[0079] In an embodiment, the hydrochar is heated at a fixed temperature for a fixed period of time after being heated at progressively increasing temperatures.

[0080] In one embodiment, the hydrochar is heated at between 500 and 900 °C for 5 minutes to 10 hours.

[0081] In an embodiment, the hydrochar is heated at between 600 and 800 °C for 10 minutes to 5 hours. In an embodiment, the hydrochar is heated at between 650 and 750 °C for 10 minutes to 2 hours. In an embodiment, the hydrochar is heated at between 675 and 725 °C for 15 minutes to 45 minutes. Typically, the hydrochar is heated at 700 °C for 30 minutes.

[0082] The reaction may be continuously fed with an inert gas (e.g., nitrogen) to provide an inert atmosphere. Hence, the method may comprise the use of a purging gas during the anhydrous carbonisation process to purge the reactor of any air which may be present. The purging gas may be an inert gas, such as nitrogen or argon.

[0083] In an embodiment, however, the purging gas is nitrogen. As shown in Figures 1 and 2, the product of the methods of the invention is biochar.

[0084] Accordingly, in a second aspect of the invention, there is provided biochar obtained, or obtainable, by the method according to the first aspect.

[0085] The biochar may comprise a range of forms and compositions. The biochar form may comprise a fine powder, flakes, a friable solid, and / or an agglomerated mass. The biochar composition may comprise variable proportions of nutrients, and / or hydrogen to carbon ratio, and / or oxygen to carbon ratio.

[0086] The transformation of photosynthetic organisms into biochar involves heat-induced chemical changes. Algae, for example, has high ratios of hydrogen to carbon, and oxygen to carbon. Early chemical changes in response to heating involve a reduction of oxygen contents as water and carbon dioxide are produced. Later chemical changes in response to heating involve a reduction of hydrogen contents as methane and other hydrocarbons are released. The loss of hydrogen corresponds to the formation of stable aromatic and polycyclic aromatic rings in the developing biochar.

[0087] As shown in Example 4, Table 3, the inventors have determined the elemental composition of the biochar products.

[0088] In one embodiment, therefore, the biochar may comprise carbon (C) at between 1 and 100 (wt. %), between 20 and 95 (wt. %), between 30 and 90 (wt. %), between 35 and 80 (wt. %), or between 40 and 75 (wt. %). In another embodiment, the biochar may comprise carbon (C) at between 45 and 74 (wt. %), between 46 and 73 (wt. %), between 47 and 72 (wt. %), between 48 and 71 (wt. %), or between 49 and 70 (wt. %). Typically, the biochar comprises carbon (C) at between 49.9 and 66.9 (wt. %).

[0089] In another embodiment, therefore, the biochar may comprise carbon (C) at between 1 and 65.8 (wt. %), between 10 and 65.8 (wt. %), between 20 and 65.8 (wt. %), between 30 and 65.8, between 35 and 65.8 (wt. %), or between 40 and 65.8 (wt. %). In another embodiment, the biochar may comprise carbon (C) at between 45 and 65.8 (wt. %), between 46 and 65.8 (wt. %), between 47 and 65.8 (wt. %), between 48 and 65.8 (wt.

[0090] %), or between 49 and 65.8 (wt. %). Typically, the biochar comprises carbon (c) at between 49.9 and 65.8 (wt. %). In another embodiment, the biochar may comprise carbon (C) at less than 100 (wt. %), less than 95 (wt. %), less than 90 (wt. %), less than 80 (wt. %), or less than 75 (wt. %). In another embodiment, the biochar may comprise carbon (C) at less than 74 (wt. %), less than 73 (wt. %), less than 72 (wt. %), less than 71 (wt. %), or less than 70 (wt. %). In another embodiment, the biochar may comprise carbon (C) at less than 69 (wt. %), less than 68 (wt. %), less than 67 (wt. %), less than 65 (wt. %), or less than 64 (wt. %).

[0091] In one embodiment, the biochar may comprise a carbon (C) to hydrogen (H) ratio of between 10: 1 and 1 : 1, between 9: 1 and 1.5: 1, between 8: 1 and 2: 1, between 7: 1 and 2.5: 1, or between 6: 1 and 3: 1. In another embodiment, the biochar may comprise a carbon (C) to hydrogen (H) ratio of between 5: 1 and 3.1: 1, between 4: 1 and 3.15: 1, or between 3: 1 and 3.19: 1. Typically, the biochar may comprise a carbon (C) to hydrogen (H) ratio of around 3.2: 1.

[0092] As shown in Example 5, Table 4, the inventors have determined the sulfur contents of the biochar products.

[0093] In one embodiment, the biochar may comprise sulfur (S) at less than 0.5 (mean %), less than 0.4 (mean %), less than 0.3 (mean %), less than 0.2 (mean %), or less than 0. 1 (mean %). Typically, the biochar comprises 0% (mean %) sulfur.

[0094] In a third aspect of the invention, there is provided an apparatus for performing the method according to the first aspect.

[0095] In one embodiment, the apparatus is configured to convert a photosynthetic organism into biochar under conditions that are suitable to convert the photosynthetic organism into biochar. In another embodiment, the apparatus is configured to convert a photosynthetic organism into hydrochar under conditions that are suitable to convert the photosynthetic organism into hydrochar. In another embodiment, the apparatus is configured to convert hydrochar into biochar under conditions that are suitable to convert hydrochar into biochar.

[0096] In one embodiment, the apparatus is configured to subject a photosynthetic organism to hydrothermal carbonisation. In another embodiment, the apparatus is configured to subject hydrochar to anhydrous carbonisation. The apparatus may comprise a furnace or a heat exchanger. The apparatus may comprise at least one reaction vessel in which the hydrothermal carbonisation and / or anhydrous carbonisation process takes place. The apparatus may comprise at least one reaction vessel in which the hydrothermal carbonisation process takes place, and at least one reaction vessel in which the anhydrous carbonisation process takes place.

[0097] In one embodiment, the reaction vessel in which the hydrothermal carbonisation process takes place is separate from the reaction vessel in which the anhydrous carbonisation process takes place. In another embodiment, the reaction vessel in which the hydrothermal carbonisation process takes place is connected to the reaction vessel in which the anhydrous carbonisation process takes place.

[0098] The reaction vessel in which the hydrothermal carbonisation process takes place may be connected to the reaction vessel in which the anhydrous carbonisation process takes place by a conduit along which the hydrochar is fed from the reaction vessel in which the hydrothermal carbonisation process takes place to the reaction vessel in which the anhydrous carbonisation process takes place. In some embodiments the hydrothermal carbonisation and anhydrous carbonisation may be carried out in the same vessel.

[0099] The inventor has exemplified that HTC at 130 °C and 2 bar does not require specialised high temperature and pressure equipment, and can therefore be achieved using stainless steel equipment with rubber or silicone gaskets.

[0100] In one embodiment, therefore, the apparatus comprises stainless steel.

[0101] In another embodiment, the apparatus comprises rubber, and / or silicone components.

[0102] In a fourth aspect of the invention, there is provided a reactor for performing the method according to the first aspect.

[0103] In one embodiment, the reactor may comprise a batch reactor. In another embodiment, the batch reactor comprises a temperature and / or pressure controller.

[0104] Biochar is a carbon-rich residue generated by the thermal decomposition of biomass in an oxygen-limited atmosphere. Biochar is relatively resistant to chemical and microbial degradation, and is a stable form of carbon-rich material. Furthermore, biochar can survive in the soil organic matter reservoir for thousands of years. As such, these biochar materials have a wide range of utilities in agriculture or industry. Accordingly, in a fifth aspect, there is provided use of the biochar according to the second aspect, in agriculture or industry.

[0105] For example, the biochar may be used in carbon sequestration, optionally to mitigate climate change by removing carbon from the atmosphere and storing it in a relatively stable material that has a lifetime of thousands of years. Biochar may also be used in industrial and agricultural applications, for example through its addition to materials such as soil, concrete, asphalt, and / or battery systems, thus delivering more short term performance benefits. In addition, the biochar may be used as a carbon sink, soil additive, medium for water retention, animal food, concrete additive, sorbent, fuel, energy store, electrode materials, and / or catalyst. The biochar may be an ingredient.

[0106] In one embodiment, therefore, the biochar is used as a soil amendment, concrete additive, asphalt additive, battery ingredient, carbon sink, soil additive, medium for water retention, animal food, concrete additive, sorbent, fuel, energy store, electrode materials, and / or catalyst.

[0107] Typically, however, the biochar is used as a soil amendment, concrete additive, asphalt additive, carbon sink, soil additive, medium for water retention, animal food, fuel, and / or electrode material.

[0108] By-products of the present disclosure include lipids and nutrients, which in turn offer numerous opportunities.

[0109] All of the features described herein (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0110] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying Figure, in which:-

[0111] Figure 1 is a flow diagram comparing one embodiment of the biochar generation process according to the invention with the conventional prior art approach. Figure 2 is a flow diagram showing one embodiment of the biochar generation process according to the invention.

[0112] Examples

[0113] The inventor has developed a novel method of converting a photosynthetic organism (e.g., algae) into biochar, which comprises a two-step carbonisation process. This method, which involves a first step comprising hydrothermal carbonisation (HTC), and a second step comprising anhydrous carbonisation, has been shown by the inventor to provide scalability, efficiency, and economic benefits over conventional methodology.

[0114] Example 1 - A two-step method of converting alaae into biochar

[0115] Referring to Figures 1 and 2, there are shown flow diagrams of the method of the invention for producing biochar from algae, used by the inventor as a proof-of-concept for photosynthetic organisms in general. The method involves a first step comprising hydrothermal carbonisation (HTC) of the algal biomass to produce hydrochar, and a second step comprising anhydrous carbonisation of the hydrochar to produce the biochar product.

[0116] Step 1 - Hydrothermal carbonisation (HTC) of algae to form hydrochar

[0117] The first step of the method involves hydrothermal carbonisation (HTC) of algal biomass to produce hydrochar.

[0118] The algal biomass is obtained from a number of sources, including wastewater treatment systems, open-water systems suffering eutrophication and algal biomass growth, and / or waste from the nutraceutical industry.

[0119] The HTC step is carried out at moderate temperatures (e.g., 130 °C) and pressures (e.g., 2 bar / 30 psi Wh) in a vessel made of suitable material (e.g., stainless steel).

[0120] The residence time explored by the inventor was 1 hour, and the water to biomass ratio was 4: 1, although the inventor envisages and expects other reasonably similar conditions to produce similar results.

[0121] The liquids recovered by HTC contain liberated nutrients that can be reused for growth of future algal feedstock. The HTC conditions release carbohydrates and lipids from the algae. The release of lipids provides a source of potential fuel for combustion purposes. HTC at 130 °C and 2 bar does not require specialised high temperature and pressure equipment, and can be achieved using stainless steel equipment with rubber or silicone gaskets.

[0122] The remaining "hydrochar" is recovered by vacuum filtration. It will be appreciated that vacuum filtration (suction filtration) is a standard technique used for separating a solidliquid mixture when the goal is to retain the solid. This a low cost solution that is enabled by the friable solid product. The hydrochar is friable and suitable for downstream handling. It will be appreciated that HTC followed by vacuum filtration provides energy savings compared to direct thermal drying, as used in the prior art method (see Figure 1). The hydrochar represents mainly hydrothermally transformed proteins which are the major component in algae.

[0123] Step 2 - Anhydrous carbonisation of the hydrochar to form biochar

[0124] The second step of the method of the invention involves subjecting the hydrochar to anhydrous carbonisation, which, in this instance, could also be referred to as posthydrothermal carbonisation (PHTC), to generate a carbon-rich biochar that meets market needs.

[0125] It will be appreciated that anhydrous carbonisation of a material involves the application of heat to the material in the absence of oxygen. It will also be appreciated that posthydrothermal carbonisation (PHTC) involves the application of dry heat after HTC.

[0126] The hydrochar is heated progressively from room temperature to 700 °C (e.g., a rate of 20 to 300 °C at 20 °C / min), and held for a fixed period of time (e.g., 30 min). The reactor is continuously fed with nitrogen to provide an inert atmosphere.

[0127] Example 2 - Properties of Chlorella and Soirulina

[0128] The inventor used Chlorella (Chlorella vulgaris) as their test microalgae, and Spirulina (Arthrospira platensis) as their test cyanobacteria, as a proof-of-concept for photosynthetic organisms in general. The chemical properties of starting materials and products as identified by the experimentation of the inventor are shown in Table 1, which shows the elemental compositions and carbon yields for the biochars produced by the inventor's method.

[0129] Table 1. Source materials, elemental compositions, and carbon yields for biochars. (DAF: Dry Ash Free; Mol : Molar). *P and K contents were determined on biochar that was subjected to HTC at 200 °C.D. / D. . C% H% C H H / C N% P% K%

[0130] Biomass / Biochar (DAF) (DAF) Mol Mol (Mol) (DAF) * *

[0131] Cyanobacteria

[0132] Spirulina starting52 7 7 24.4 7.2 1.64 11.3 1.2 1.4 material

[0133] Spirulina drying-68 5 1 5 5 7 1 5 0.26 9.5 3.6 3.6 carbonisation

[0134] Spirulina HTC-69 8 1 9 5 8 1 9 0.33 9.1 4.8 2.6 carbonization

[0135] Microalaae

[0136] Chlorella starting 7 i 2 4 6 7 2 1 56 10 31.3 Q.2 material

[0137] Chlorella drying-68 7 1 5 5 7 1 5 0.26 8.1 0.4 0.1 carbonisation

[0138] Chlorella HTC-70g1 >9 5 i9 1 >9 0i 32 10 1 2i9 0i 3carbonization

[0139] The biochars generated by the HTC-carbonisation process of the invention have high N contents, 8-10 wt. %, as shown in Table 1, indicating the retention of protein in the biochar. In addition, the biochars generated by the HTC-carbonisation of the invention process have P and K contents in the range 4.6-0.1 wt. %, with K contents being higher in the microalgae biochars.

[0140] Furthermore, lipid yields from HTC exceed those from laboratory carbonisation, indicating that the HTC process of the invention removes all lipids from the starting materials. The inventor can predict, therefore, that microalgae and cyanobacteria, or indeed any photosynthetic organism, with low lipid contents would give rise to higher biochar yields relative to their more lipid-rich counterparts.

[0141] The inventor also notes that the final H / C ratio listed for the HTC-carbonisation biochar in Table 1 is far better than the minimum criteria set by certifying organisations for carbon credits.

[0142] Example 3 - Comparison of hydrothermal carbonisation and thermal drying carbonisation

[0143] The initial HTC stage prior to the subsequent anhydrous carbonisation step was incorporated by the inventor in order to provide energy savings relative to conventional thermal drying at 105 °C (see Figure 1), thus providing a more energy-efficient methodology. The inventor has also surprisingly discovered through their experimentation that both thermal drying at 105 °C and HTC at 130 °C generate a friable material suitable for laboratory carbonisation.

[0144] In addition, the inventor has discovered that the bulk densities and porosities for the HTC-carbonisation-produced biochar are similar to those generated by the conventional thermal drying-carbonisation process, as shown in Table 2.

[0145] Table 2 - Densities and porosities of biochar produced bv drvina-carbonisation and HTC- carbonisation

[0146] Bulk density (g / cm3) Porosity (%)

[0147] Spirulina drying-carbonization 0.29 84

[0148] Spirulina HTC-carbonization 0.32 82

[0149] Chlorella drying-carbonization 0.33 81

[0150] Chlorella HTC-carbonization 0.29 83

[0151] For all samples, concentrations of the alkali and alkaline metals, Na, Mg, and Ca were in the range 0.1-0.6 wt.%, while Fe reached 0.2 wt.%, and Cr, Cu, Ni, and Zn were below 70 ppm. Concentrations for Co, Cd, As, Zn, Co, and Pb were less than 1 ppm.

[0152] These data are significant with regards to uses of the biochar, as biochar surface area is important for its use as a soil amendment and as a chemical reactant / adsorbent.

[0153] Example 4 - Comparison of biochars which result from processes comprising hydrothermal carbonisation (HTC) or thermal drying carbonisation

[0154] The results of a comparison of the inventor's innovative new protocol to a more conventional direct carbonisation (DC) process are shown in Table 3.

[0155] It will be appreciated that direct carbonization (DC) involves single step application of dry heat.

[0156] Table 3 - Elemental compositions and carbon yields for the biochars.

[0157] Sample ID

[0158] Two samples, SN23S1 and SN23C1, were subjected to direct carbonisation (DC) at 700 °C and direct carbonisation at 700 °C after (post-) hydrothermal carbonisation (PHTC) at 130 °C and 200 °C. One sample of SN231C1 was treated with water at 105 °C and then dried (SN23ClDriedlO5 °C). Carbon yields and H / C ratios for PHTC 130 °C (SN23S1PHTC130 & SN23C1PHTC130) are similar to more conventional direct carbonisation at 700 °C (SN23S1DC130 & SN23C1DC130).

[0159] The inventor has discovered that the final carbon yields of their new and innovative two- step carbonisation protocol are 32-35% for algae, where the loss of carbohydrates and lipids make up the remainder. The inventor has also discovered that the yields are not affected by the choice of either direct thermal drying, as used in the conventional methodology, at 105°C, or HTC, as described in the present disclosure, at 130°C.

[0160] The inventor's comparisons of the two-step carbonisation process (i.e., Step 1 and Step 2) with direct anhydrous carbonisation at 700 °C (i.e., no Step one HTC; direct to Step 2) reveal that there are no impacts on carbon yields, indicating that the benefits of the two-step process are provided without removing any product yield advantages of the one step (direct to Step 2) process.

[0161] Furthermore, the inventor predicts that the liquids recovered by HTC contain liberated nutrients that can be reused for growth of future photosynthetic organism feedstock. As shown in the Examples, the HTC conditions release carbohydrates and lipids from the photosynthetic organism; the release of lipids provides a source of potential fuel for combustion purposes. As shown in Figure 1, therefore, the method can comprise an additional step of feeding any liberated nutrients resulting from the production of the hydrochar back into the biomass, and / or using any liberated lipids as a fuel source for HTC and / or anhydrous carbonisation. Therefore, the inventor has discovered that the replacement of an initial thermal drying stage with a HTC stage to the carbonisation process adds only benefits, which pertain to scalability, and assisting efficiency and economics.

[0162] Example 5 - Sulfur contents

[0163] The inventors also measured the sulfur contents (mean %) of starting materials and biochar products following different experimental conditions as shown in Table 4.

[0164] Table 4 - Sulfur contents (mean %) of starting materials and biochar products following different experimental conditions.

[0165] As shown, the inventors innovative two-step carbonisation protocol (Ch lorel la / Spi ru 11 na HTC at 130 °C followed by pyrolysis (post-carbonisation) at 700 °C) results in biochar with 0% (mean %) sulfur.

[0166] Conclusions

[0167] The inventor has developed an innovative and effective method of producing biochar from algae. The inventor's method of converting photosynthetic organisms into biochar comprises a two-step carbonisation process. This method, which involves a first step comprising hydrothermal carbonisation (HTC), and a second step comprising anhydrous carbonisation, has been shown by the inventor to provide benefits over conventional methodology. Furthermore, the inventor has identified that photosynthetic organisms, such as algae, have advantages over conventional alternative biomass, such as those sourced from food waste, anaerobic digestate waste, and sewerage solid waste as a source of biomass, owing to their rapid growth rate and opportunities for large scale production. This choice of biomass works in synergy with the two-step carbonisation process described in the present disclosure, which provides capability for nutrient recovery to assist scalability, efficient water removal from biomass to assist efficiency, and energy benefits to assist economics though achieving a positive heat budget for the overall process.

[0168] To summarise, the inventor has surprisingly developed a method:

[0169] (i) for a two-step carbonisation process to generate biochar from photosynthetic organisms;

[0170] (ii) where the invention allows significant nutrient recovery, thus allowing photosynthetic organism growth to occur in a sustainable and scalable fashion;

[0171] (iii) where the invention allows efficient water removal from biomass; and

[0172] (iv) which provides a positive heat budget for the overall process.

[0173] References

[0174] Ahmad, M., Rajapaksha, A., Lim, J., Zhang, M., Bolan, N., Mohan, D., Vithanage, M., Lee, S., Ok, Y. Biochar as a sorbent for contaminant management in soil and water: a review. Chemosphere, 99 (2014), pp. 19-33.

[0175] Cha, J., Park, S., Jung, S., Ryu, C., Jeon, J., Shin, M., Park, Y. Production and utilization of biochar: A review. J. Ind. Eng. Chem., 40 (2016), pp. 1-15.

[0176] Fang, J., Zhan, L., Ok, Y., Gao, B. Minireview of potential applications of hydrochar derived from hydrothermal carbonization of biomass. J. Ind. Eng. Chem., 57 (2018), pp. 15-21.

[0177] Funke, A., Ziegler, F. Hydrothermal carbonization of biomass: A summary and discussion of chemical mechanisms for process engineering. Biofuels Bioprod Biorefin., 4 (2010), pp. 160-177.

[0178] Kambo, H., Dutta, A. A comparative review of biochar and hydrochar in terms of production, physico-chemical properties and applications. Renew. Sust. Energ., 45 (2015), pp. 359-378.

[0179] Karhu, K., Mattila, T., Bergstrom, I., Regina, K. Biochar addition to agricultural soil increased CH4 uptake and water holding capacity - Results from a short-term pilot field study. Agriculture, Ecosystems & Environment 140 (2011), pp. 309-313.

[0180] Lee, J., Kim, K., Kwon, E. Biochar as a Catalyst. Renew. Sust. Energ., 77 (2017), pp. 70-79. Lehmann, J., Joseph, S. (2009). Biochar for Environmental Management. Science and Technology. 1stEdition. Routledge.

[0181] Matovic, D. Biochar as a viable carbon sequestration option: Global and Canadian perspective. Energy, 36 (2011), pp. 2011-2016.

[0182] Mendez, A., Barriga, S., Fidalgo, J., Gasco, G. Adsorbent materials from paper industry waste materials and their use in Cu(II) removal from water. Journal of Hazardous Materials, 165 (2009), pp. 736-743.

[0183] Sohi, S., Krull, E., Lopez-Capel, E., Bol, R. A Review of Biochar and Its Use and Function in Soil. Adv. Agron., 105 (2010), pp. 47-82.

[0184] Xiong, X., Yu, I., Cao, L., Tsang, D., Zhang, S., Ok, Y. A review of biochar-based catalysts for chemical synthesis, biofuel production, and pollution control. Bioresour. Technol., 246 (2017), pp. 254-270.

[0185] Yu, K., Lau, B., Show, P., Ong, H., Ling, T., Chen, W., Ng, E., Chang, J. Recent developments on algal biochar production and characterization. Bioresour. Technol., 246 (2017), pp. 2-11.

Claims

Claims1. A method of converting a photosynthetic organism into biochar, the method comprising:(i) subjecting a photosynthetic organism to hydrothermal carbonisation (HTC) to produce hydrochar; and(ii) subjecting the hydrochar to anhydrous carbonisation to produce biochar.

2. The method according to claim 1, wherein the photosynthetic organism is:(i) an algae;(II) a plant; or(ill) a photosynthetic bacteria.

3. The method according to either claim 1 or claim 2, wherein the photosynthetic organism is obtained from a wastewater treatment system, an open-water system comprising eutrophication and / or algal biomass growth, and / or waste from the nutraceutical industry.

4. The method according to any preceding claim, wherein the photosynthetic organism is harvested by filtration, flocculation, flotation, sedimentation, centrifugation, or any combination thereof.

5. The method according to any one of claims 2-4, wherein the algae are fresh-water or marine-based algae.

6. The method according to any one of claims 2-5, wherein the algae is selected from a group of algae consisting of:Division - Chlorophyta (green algae), genus Acetabularia (mermaid's wine glass / , class Charophyceae, order Desmidiales (desmids), order Charales (stoneworts), genus Chlamydomonas, genus Chlorella, genus Cladophora, genus Codium, genus Hydrodictyon (water net), genus Oedogonium, genus Pediastrum, genus Pleurococcus, genus Scenedesmus, genus Spirogyra, genus Ulothrix, genus Ulva (sea lettuce), genus Volvox, Division Chromophyta, class Phaeophyceae (brown algae), genus Fucus, genus Laminaria, genus Macrocystis, genus Pelagophycus, genus Sargassum (gulfweed), class Bacillariophyceae (diatoms), class Chrysophyceae (golden algae), class Xanthophyceae (yellow-green algae), genus Vaucheria, Division Cryptophyta, class Cryptophyceae, Division Rhodophyta (red algae), genus Batrachospermum , genus Callophyllis, speciesChondrus crispus (Irish moss), species Palmaria palmata (dulse), genus Porphyra (laver), and / or genus Nitophyllum.

7. The method according to any one of claims 2-6, wherein the algae comprise microalgae and / or Chlorella.

8. The method according to any one of claims 2-7, wherein the algae is selected from a group of algae consisting of: Chlorella autotrophica, Chlorella colonials, Chlorella lewinii, Chlorella minutissima, Chlorella pituita, Chlorella pulchelloides, Chlorella pyrenoidosa, Chlorella rotunda, Chlorella singularis, Chlorella sorokiniana, Chlorella variabilis, Chlorella volutis, and Chlorella vulgaris.

9. The method according to any one of claims 2-8, wherein the photosynthetic bacteria comprise cyanobacteria and / or Spirulina spp..

10. The method according to any one of claims 2-9, wherein the photosynthetic bacteria are selected from a group of bacteria consisting of: Spirulina abbreviate, Spirulina agilis, Spirulina agilissima, Spirulina albida, Spirulina ardissoni, Spirulina baltica, Spirulina bayannurensis, Spirulina breviarticulata, Spirulina cabrerae, Spirulina caldaria, Spirulina cavanillesiana, Spirulina condensate, Spirulina corakiana, Spirulina flavovirens, Spirulina funiformis, Spirulina gessneri, Spirulina gomontiana, Spirulina gomontii, Spirulina gordiana, Spirulina gracilis, Spirulina innatans, Spirulina labyrinthiformis, Spirulina laxa, Spirulina laxissima, Spirulina legitima, Spirulina magnified, Spirulina major, Spirulina margaritae, Spirulina mariae, Spirulina massartii, Spirulina maxima, Spirulina miniata, Spirulina minima, Spirulina mukdensis, Spirulina nodosa, Spirulina nordstedtii, Spirulina okensis, Spirulina oscillarioides, Spirulina platensis, Spirulina princeps, Spirulina pseudotenuissima, Spirulina robusta, Spirulina rosea, Spirulina schroederi, Spirulina sigmoidea, Spirulina socialis, Spirulina spirulinoides, Spirulina subsalsa, Spirulina subtilissima, Spirulina supersalsa, Spirulina tenerrima, Spirulina tenuior, Spirulina tenuis, Spirulina tenuissima, Spirulina thermalis, Spirulina turfosa, Spirulina versicolor, Spirulina weissii, Spirulina spp, Arthrospira spp., and / or associated Prochiorophytes.

11. The method according to any one of claims 2-10, wherein the photosynthetic bacteria comprise Arthrospira platensis, Arthrospira fusiformis, and / or Arthrospira maxima .

12. The method according to claim 1, wherein the HTC process comprises the use of a solvent, optionally wherein the solvent is an organic solvent or water.

13. The method according to claim 12, wherein the HTC process comprises a water to photosynthetic organism biomass ratio of between 1 : 1 and 20 : 1, between 2: 1 and 10: 1, between 3: 1 and 5: 1, or of about 4: 1.

14. The method according to any preceding claim, wherein the HTC process is batch, fed-batch, continuous, or semi continuous.

15. The method according to any preceding claim, wherein the HTC process comprises a catalyst or does not comprise a catalyst.

16. The method according to any preceding claim, wherein the HTC reaction is performed at a temperature range of between 50 °C and 500 °C, between 60 and 400 °C, between 70 and 300 °C, between 80 and 250 °C, between 90 and 200 °C, between 100 and 180 °C, between 110 and 160 °C, between 115 and 150 °C, between 120 and 140 °C, or between 125 and 135 °C.

17. The method according to any preceding claim, wherein the HTC reaction is performed such that it has a residence time of between 5 seconds and 24 hours, 10 seconds and 23 hours, 15 seconds and 22 hours, 30 seconds and 21 hours, 45 seconds and 20 hours, 1 minute and 19 hours, 2 minutes and 18 hours, 3 minutes and 17 hours, 4 minutes and 16 hours, 5 minutes and 16 hours, 6 minutes and 15 hours, 7 minutes and 14 hours, 8 minutes and 13 hours, 9 minutes and 12 hours, 10 minutes and 11 hours, 1 minute and 30 minutes, of 8 minutes, of 10 minutes, and / or of 12 minutes.

18. The method according to any preceding claim, wherein the HTC reaction is performed at a pressure of between atmospheric pressure and 100 bar (gauge) or 50 bar (gauge), between 0.1 and 20 bar, 0.5 and 15 bar, 0.8 and 10 bar, 1 and 5 bar, or at a pressure of 1.1 bar (gauge).

19. The method according to any preceding claim, wherein the HTC process comprises the use of a purging gas, optionally wherein the purging gas is an inert gas, optionally wherein the inert gas is nitrogen or argon.

20. The method according to any preceding claim, wherein the hydrochar is recovered from the HTC process by vacuum filtration.

21. The method according to any preceding claim, wherein the method comprises an additional step of:(ill) feeding nutrients liberated from the photosynthetic organism during the HTC step back into a growing photosynthetic organism biomass which acts as a feedstock for the photosynthetic organism.

22. The method according to any preceding claim, wherein the photosynthetic organism is grown in a medium comprising warm water, an appropriate nutrient profile, light, atmospheric air, liberated nutrients, optionally comprising liberated nutrients recovered from the HTC of the photosynthetic organism, and / or carbohydrates recovered from the HTC of the photosynthetic organism.

23. The method according to any preceding claim, wherein lipids liberated from the photosynthetic organism during HTC are used as a fuel source for the HTC and / or the anhydrous carbonisation processes.

24. The method according to any preceding claim, wherein the hydrochar is heated in the absence of oxygen, optionally wherein the oxygen is excluded by a non-oxidising atmosphere, and / or wherein the hydrochar is heated in the presence of nitrogen and / or helium, and / or wherein the hydrochar is heated in a vacuum.

25. The method according to any preceding claim, wherein the anhydrous carbonisation process involves progressively heating the hydrochar from 0 °C to 1000 °C, from 5 °C to 950 °C, from 10 °C to 900 °C, from 15 °C to 850 °C, from 18 °C to 750 °C, or from 20 °C to 700 °C.

26. The method according to any preceding claim, wherein the anhydrous carbonisation process involves progressively heating hydrochar at a rate of 1 to 100 °C / min, 10 to 50 °C / min, 15 to 30 °C / min, or at a rate of 20 °C / min.

27. The method according to any preceding claim, wherein the anhydrous carbonisation process involves heating the hydrochar at a fixed temperature for a fixed period of time, optionally after being heated at progressively increasing temperatures.

28. The method according to any preceding claim, wherein the hydrochar is heated at between 500 and 900 °C for 5 minutes to 10 hours, at between 600 and 800 °C for 10 minutes to 5 hours, at between 650 and 750 °C for 10 minutes to 2 hours, at between 675 and 725 °C for 15 minutes to 45 minutes, or at 700 °C for 30 minutes.

29. The method according to any preceding claim, wherein the method comprises the use of a purging gas during the anhydrous carbonisation process, optionally wherein the purging gas is an inert gas, optionally wherein the inert gas is nitrogen or argon.

30. Biochar obtained, or obtainable, by the method according to any preceding claim.

31. The biochar according to claim 30, wherein the biochar comprises a fine powder, flakes, a friable solid, and / or an agglomerated mass.

32. An apparatus suitable for performing the method according to any one of claims 1- 29.

33. The apparatus according to claim 32, wherein the apparatus comprises stainless steel, rubber, and / or silicone components.

34. A reactor suitable for performing the method according to any one of claims 1-29.

35. Use of biochar according to claim 30 in agriculture or industry.

36. The use according to claim 35 as a soil amendment, concrete additive, asphalt additive, battery ingredient, carbon sink, soil additive, medium for water retention, animal food, concrete additive, sorbent, fuel, energy store, electrode materials, and / or catalyst.

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