Biochar and process for its preparation

Abstract

Compositions comprising biochar having exceptional permanence, conductivity and / or toxic compound content are disclosed as well as carbonization methods and applications of those compositions in a range of industrial fields.

Description

[0001] BIOCHAR AND PROCESS FOR ITS PREPARATION

[0002] TECHNICAL FIELD

[0003] The present application relates to novel processes for producing carbon from biomass (biochar) of exceptionally high quality, such biochar itself and applications of such biochar which benefit from the advantageous properties of the biochar.

[0004] BACKGROUND

[0005] The increased demand for energy and resources resulting from worldwide economic growth and development has contributed to an increase in concentration of greenhouse gases, particularly carbon dioxide, in the atmosphere. This is widely accepted as being one of the most important challenges of the 21st century. To mitigate the effects of carbon dioxide, efforts have been made to reduce the global carbon footprint.

[0006] Efforts to mitigate the release of carbon dioxide have led to a variety of technologies for carbon capture, carbon sequestration, and carbon storage. One such approach is the conversion of biomass into biochar. By doing so, carbon which would otherwise be converted via the carbon cycle into atmospheric carbon dioxide can be sequestered thus reducing the production of atmospheric carbon dioxide.

[0007] While such approaches have been quantifiably demonstrated as having a profound impact on carbon footprint, the products of such processes are by definition inert in order to limit their conversion (e.g. via microbes, plant respiration or the like) to atmospheric carbon dioxide.

[0008] Accordingly, the uses of such materials are typically limited to applications in which carbon content and inertness are of benefit. One major use of biomass-derived carbon materials (biochar) is as an additive to compost.

[0009] An issue that has been identified with this application, however, is that biochar derived from combustion processes typically comprises significant volatile organic compounds including polyaromatic hydrocarbons which can be harmful to plant growth and human and animal health.

[0010] Additionally, while such materials typically have a reasonable durability (i.e. a lifespan before they are broken down and converted into carbon dioxide) in the order of tens to hundreds of years, greater permanence of biochar is desirable to ensure that any reduction in atmospheric carbon dioxide concentrations achieved by the sequestration of carbon into biochar is as long- lasting as possible.

[0011] There is therefore a need for a biochar product which has functional properties broadening its utility and range of potential applications. The provision of biochar compositions exhibiting properties which permit their use in a range of applications, and particularly the replacement of materials or components which have a large carbon footprint, would be particularly advantageous.

[0012] There is also a need for a biochar product which has exceptional purity and permanence. Further, there is a need for a biochar product which has a composition which minimizes impact on plant, animal and human health. These and other issues are provided by the present invention.

[0013] SUMMARY OF THE INVENTION

[0014] According to a first aspect, there is provided a composition comprising biochar exhibiting one or more of the following characteristics:

[0015] 1 . Permanence, characterized by one or more of the following properties:

[0016] 1.1. At least about 95% by weight of the carbon present being comprised in the form of stable polycyclic aromatic carbon (SPAC),and I or

[0017] 1 .2. At least about 90% by weight of carbon present having a random reflectance of about 2% or higher,

[0018] 2. Conductivity, characterized by the following property:

[0019] 2.1. At least about 80% by weight of the biochar comprised in the composition has a conductivity of at least about 100mS / cm, and I or

[0020] 3. Low levels of non-permanent organic compounds, characterized by one or more of the following properties:

[0021] 3.1 . About 100mg / kg or lower of polycyclic aromatic hydrocarbons (PAH), and I or

[0022] 3.2. About 12% by weight or lower of volatile organic compounds.

[0023] In preferred embodiments, the composition of the invention comprises biochar exhibiting a conductivity of at least about 100mS / cm. According to a further aspect of the invention, there is provided a process of producing biochar comprising: a) providing biomass to a carbonization reactor, b) providing a gas comprising oxygen to the carbonization reactor via an inlet, c) flowing a gas from the carbonization reactor via an outlet, d) initiating an exothermic reaction in the carbonization reactor, and e) removing biochar produced in the exothermic reaction from the carbonization reactor, wherein: i) the flow of gas comprising oxygen into the carbonization reactor is adjusted to maintain the pressure in the carbonization reactor at a predetermined target pressure, and I or ii) the process further comprises f) conducting heat treatment on the biochar produced in the exothermic reaction.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow diagram detailing the set-up of a carbonization reactor for implementation of the method of the invention.

[0026] DETAILED DESCRIPTION

[0027] As noted above, according to one aspect of the present invention, there is provided a composition comprising biochar exhibiting one or more of the following characteristics:

[0028] 1 . Permanence, characterized by one or more of the following properties:

[0029] 1.1. At least about 95% by weight of the carbon present being comprised in the form of stable polycyclic aromatic carbon (SPAC),

[0030] 1.2. At least about 90% by weight of the carbon present having a random reflectance of about 2% or higher,

[0031] 2. Conductivity

[0032] 2.1. At least about 80% by weight of the biochar comprised in the composition has a conductivity of at least about 100mS / cm, and I or

[0033] 3. Low levels of non-permanent organic compounds, characterized by one or more of the following properties:

[0034] 3.1. About 100mg / kg or lower of polycyclic aromatic hydrocarbons (PAH), 3.2. About 12% by weight or lower of volatile organic compounds.

[0035] Additionally, the biochar comprised in the composition of the present invention may exhibit one or more of the following properties: a) A carbon content of at least about 90%, b) A molar ratio of oxygen to carbon of about 0.1 or lower, c) A molar ratio of hydrogen to carbon of about 0.4 or lower, d) About 1 % by weight of sulfur or lower, e) Less than 0.01% by weight of all of cadmium, lead, mercury and arsenic, f) A density of about <5 g / cm3, g) About 50% or greater macropores, h) About 40% or lower micropores, i) A ratio of macropores : micropores of about 1 :1 or higher, and I or j) A surface area of (BET) of at least about 50m2 / g.

[0036] As used herein, the term “biochar” is used to describe any carbon-rich material obtained from biomass via a process in which the ratio of carbon to oxygen is increased such that the obtained material has an elevated carbon content. Examples of such processes include carbonization and pyrolysis.

[0037] In embodiments, the biochar may be derived from any type of biomass. Examples include agricultural residues such as corncobs, olive pits, walnut shells, sunflower shells and husks, and sugar cane bagasse; wood materials such as wood logs, slabs, chips, and bark; openwater plants such as water hyacinths and seaweed; organic municipal solid wastes, sewage sludge, or other organic clarified solids; and animal residues.

[0038] The biochar comprised in the composition of the invention has high permanence. As those skilled in the art will recognize, the permanence of a biochar is used to describe its stability or resistance to degradation over time. There are multiple methods for determining the permanence of a biochar, including average random reflectance, aromatization of carbon, thermal stability (as determined by hydrogen pyrolysis) and duration.

[0039] Where reference is made herein to the percentage by weight or the proportion of a component of biochar by weight, the given values are relative to the weight of the biochar, excluding i) ash and ii) moisture. To determine the proportion of ash and moisture in samples of biochar (in order to exclude them from the assessment of levels of other materials or compounds in biochar), these determinations can be made in accordance with ASTM D 3174 (for the assessment of levels of ash) or ASTM D 3173 (for the assessment of moisture levels).

[0040] The permanence of biochar can be assessed by many methods. One such approach takes a geological perspective. Random reflectance (Ro) is an established method used to determine the maturity of sedimentary organic matter. Biochar with a random reflectance rate greater than 2% is considered geologically stable. This research is detailed by Sanei et al. (International Journal of Coal Geology, volume 281 , January 2024). Random reflectance (Ro) is the percentage of light reflected from the surface of materials, primarily coal and other high- carbon materials. In embodiments of the invention, a significant majority of the biochar comprised in the composition (e.g. at least about 90% by weight) has a mean random reflectance (Ro) of about 2% or higher, about 3% or higher, about 4% or higher or about 5% or higher. In some embodiments, at least about 95% by weight of the carbon present in the biochar comprised in the composition of the invention has a mean random reflectance (Ro) of about 2% or higher, about 3% or higher, about 4% or higher or about 5% or higher. In certain embodiments, at least about 98% by weight of the carbon present in the biochar comprised in the composition of the invention has a mean random reflectance (Ro) of about 2% or higher, about 3% or higher, about 4% or higher or about 5% or higher.

[0041] Notably, while the disclosure in the paper by Hanei et al. does disclose 10mg biochar samples having mean random reflectance values in the order of those recited in the previous paragraph, there is no disclosure as to how such materials were prepared.

[0042] Additionally, as is demonstrated in the accompanying examples, the process of the invention permits the bulk production of biochar exhibiting such exceptionally high random reflectance values. These reflectance values were also accompanied by hydrogen index values (which can also be determined using techniques disclosed in the Hanei et al. paper) which are advantageously low. Thus, according to one aspect of the present invention, there is provided a composition comprising biochar having a mean random reflectance (Ro) value of about 4% or higher and a hydrogen index (mg HC / TOC) of about 1 % to about 100% or about 1% to about 10%. In certain embodiments, there is provided a composition comprising biochar having a mean random reflectance (Ro) value of about 4.5% or higher and a hydrogen index (mg HC / TOC) of about 1% to about 100% or about 1% to about 10%. In some embodiments, there is provided a composition comprising biochar having a mean random reflectance (Ro) value of about 5% or higher and a hydrogen index (mg HC / TOC) of about 1 % to about 100% or about 1 % to about 10%. The aromatization of carbon in a material is also an indicator of its permanence. In simple terms, the degree of aromatization of carbon is the percentage of carbon which is present in aromatic carbon compounds. Further, the structure of those carbon compounds is also indicative of permanence with structures comprising multiple fused aromatic rings present having a greater degree of permanence. Aromatization of carbon in biochar can be determined by hydrogen pyrolysis.

[0043] Thus, in embodiments, the proportion of carbon present in the biochar comprised in the composition of the invention in the form of stable polycyclic aromatic carbon (SPAC) may be about 95% or higher, about 96% or higher, about 97% or higher, about 98% or higher, about 99% or higher or about 99.5% or higher. Further details regarding the SPAC content of biochars and how this can be assessed are provided by Meredith et al. in Chapter 17 of “Biochar: A Guide to Analytical Methods”, 2017, the contents of which are incorporated herein in their entirety.

[0044] As those skilled in the art will recognize, both reflectance and aromatization have been used to predict half-life of carbonaceous materials. For example, Howell et al. (Science of the Total Environment, 849, 2022, pages 1 to 11) stated that SPAC is projected to persist for >1000 years, while in the Hanei et al. paper referred to above, the authors stated that, inertinite biochar (i.e. having a random reflectance of >2.0) would be expected to exhibit geological permanence, indicating a conservative half life of approximately 100 million years at an average surface temperature of 30°C. Other methods for experimentally predicting the half life of carbonaceous materials are known to those skilled in the field, for example as discussed by Li et al. in Journal of Carbon Research, 2023, 9(3), 67. Accordingly, in embodiments of the invention the average half life of the biochar comprised in the composition of the invention is at least about 1 ,000 years, at least about 10,000 years or at least about 100,000 years.

[0045] In embodiments of the invention, the biochar comprised in the composition of the invention may be characterized by high reflectance and high aromatization as described above. In certain embodiments, the biochar comprised in the composition of the invention may be characterized by high reflectance and high half life as described above. In some embodiments, the biochar comprised in the composition of the invention may be characterized by high aromatization and high half life as described above. In preferred embodiments, the biochar comprised in the composition of the invention may be characterized by all of high reflectance, high aromatization and high half life as described above. In addition to, or instead of, to permanence, the composition of the invention may advantageously comprise biochar which is conductive. In embodiments, the majority (e.g. at least about 80% by weight) of the biochar comprised in the composition of the invention is highly conductive, e.g. it may have an average conductivity of about 100mS / cm or more, about 200 mS / cm or more, about 500mS / cm or more, or about 1000mS / cm or more.

[0046] For the purposes of the present invention, and unless otherwise stated, conductivity is measured by i) grinding a sample to a target average particle size of 500 microns, ii) weighing the sample to determine its mass, iii) placing the sample in a measurement holder between two piston electrodes, iv) placing the assembly into a press, iv) applying a predetermined pressure to one or both of the piston electrodes, such that a load of 1 .2 tons (determined by multiplying the applied pressure by the cross sectional area of the piston electrode) is exerted on the sample, v) measuring the electrical resistance between the electrodes, and v) converting the electrical resistance measurements to conductivity.

[0047] As demonstrated in the accompanying examples, steps performed in the process of the invention provide exceptionally high uniformity of conductivity. Thus, in some embodiments, at least about 90% by weight of the biochar comprised in the composition of the invention may have an average conductivity of about 100mS / cm or more, about 200 mS / cm or more, about 500mS / cm or more, or about 1000mS / cm or more. In certain embodiments, at least about 95% by weight of the biochar comprised in the composition of the invention may have an average conductivity of about 100mS / cm or more, about 200 mS / cm or more, about 500mS / cm or more, or about 1000mS / cm or more.

[0048] Those skilled in the art will appreciate that electrical resistance is inversely proportional to conductivity and thus a biochar having a low electrical resistance will be highly conductive. Thus, where, in the present disclosure, reference is made to a composition or biochar having low resistivity, such a material will be highly conductive.

[0049] A further advantage of the composition of the present invention is that the biochar comprised therein has very low levels of non-permanent organic compounds. Those skilled in the art will recognize that such compounds are undesirable byproducts of combustion processes and can pose toxicity or health risks. Advantageously, the biochar comprised in the composition of the invention comprises very low levels of polycyclic aromatic hydrocarbons (PAH). As used herein, “polycyclic aromatic hydrocarbons” or “PAHs” are the sixteen polycyclic aromatic hydrocarbon compounds identified by the U.S. Environmental Protection Agency with details on how to measure outlined in DIN EN 17503 (specifically naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, indeno(1 ,2,3-cd)pyrene, dibenz(a,h)anthracene and benzo(g,h,i)perylene), the levels of which can be determined by gas chromatography (GC) and high performance liquid chromatography (HPLC), in accordance with the methodology detailed in standard DIN EN 17503.

[0050] Thus, in embodiments of the invention, the biochar comprised in the composition of the invention may contain less than about 100 mg, , less than about 50 mg, less than about 20 mg, less than about 10 mg, or less than about 5 mg of PAHs per kilogram of biochar. In some embodiments, the biochar comprised in the composition of the invention comprises less than about 10 mg of PAHs per kilogram of biochar. In certain embodiments, the biochar comprised in the composition of the invention comprises less than 1 mg of PAHs per kilogram of biochar.

[0051] Additionally or alternatively, the biochar comprised in the composition of the invention may comprise low levels of volatile organic compounds (VOCs). DIN 51720: 2001-03 details methodology as to how the levels of VOCs in biochar can be determined.

[0052] For example, in embodiments of the invention, the biochar comprised in the composition of the invention contains less than about 12% by weight, less than about 10% by weight, less than about 8% by weight, less than about 6% by weight, less than about 4% by weight, or less than about 2% by weight of volatile organic compounds. In some embodiments, the biochar comprised in the composition of the invention comprises less than about 10% by weight VOCs. In certain embodiments, the biochar comprised in the composition of the invention comprises less than about 5% by weight VOCs.

[0053] In embodiments of the invention, the biochar comprised in the composition of the invention may be characterized by high permanence and high conductivity as described above. In certain embodiments, the biochar comprised in the composition of the invention may be characterized by high reflectance and low levels of volatile organic compounds as described above. In some embodiments, the biochar comprised in the composition of the invention may be characterized by high conductivity and low levels of volatile organic compounds as described above. In preferred embodiments, the biochar comprised in the composition of the invention may be characterized by all of high permanence, high conductivity and low levels of volatile organic compounds as described above.

[0054] Given that a primary objective with biochar production is to sequester carbon and prevent it from entering the atmosphere in the form of carbon dioxide, it is desirable to have the highest possible concentration of carbon present, with other components of biomass minimized to the greatest possible extent. As is apparent from the accompanying examples, exceptionally pure and uniform biochar is obtainable from the process of the invention.

[0055] Thus, in embodiments of the invention, the carbon content of the biochar comprised in the composition of the invention may be at least about 90% or greater, about 92% or greater, about 93% or greater or about 95% or greater by weight of the biochar. Additionally or alternatively, the molar ratio of hydrogen to carbon may be about 0.4% or lower, 0.3% or lower, 0.25% or lower, about 0.2% or lower, about 0.15% or lower or about 0.1 % or lower. In embodiments, the molar ratio of oxygen to carbon may be about 0.1% or lower, about 0.05% or lower, about 0.02% or lower or about 0.01% or lower.

[0056] The composition of the invention advantageously further comprises low levels of materials which may be undesirable depending on the application of the biochar, such as sulfur. Thus, in embodiments of the invention, the biochar comprised in the composition comprises about 1 % or less, about 0.5% or less, 0.25% or less, about 0.2% or less, about 0.15% or less, about 0.1 % or less, about 0.05% or less or about 0.03% or less by weight of sulfur.

[0057] As is also demonstrated in the accompanying examples, the biochar comprised in the composition of the present invention has a calculable density and porosity. Thus, in some embodiments, the biochar comprised in the composition of the invention has an average density of about <5 g / cm3, about <3 g / cm3, about <2 g / cm3, about <1.75 g / cm3or about <1.5 g / cm3.

[0058] Additionally or alternatively, the average percentage of macropores in the biochar comprised in the composition of the invention may be about 50% or greater, about 60% or greater, about 70% or greater or about 80% or greater. In embodiments, the average percentage of micropores in the biochar comprised in the composition of the invention may be about 40% or lower, about 30% or lower or about 25% or lower. In some embodiments, the ratio of macropores to micropores may be about 1 :1 or greater, about 2:1 or greater, about 3:1 or greater or about 4:1 or greater.

[0059] In embodiments, the biochar comprised in the composition of the invention may be in particulate form. In some embodiments, the particulate biochar may have an average particle size of about 10pm to about 1000pm, about 50pm to about 500pm, about 500pm to about 5000pm or about 1000pm to about 3000pm. Additionally or alternatively, in certain embodiments, the biochar comprised in the composition of the invention may have may have a mean surface area (BET) of at least about 50m2 / g, at least about 100m2 / g, at least about 150m2 / g, at least about 200m2 / g, at least about 250m2 / g, at least about 300m2 / g or at least about 500m2 / g.

[0060] In certain embodiments, the biochar comprised in the composition of the invention may be in bulk form, for example with at least 60% of the material by mass having a particle size greater than about 50mm. In certain embodiments, the mean average particle size of bulk biochar is about 25mm to about 500mm, about 30mm to about 300mm or about 40mm to about 100mm. In some embodiments, the biochar comprised in the composition of the invention may be in coarse aggregate form. For example, in such embodiments the biochar may have a mean average particle size of about 2mm to about 100mm, about 3mm to about 75mm or about 5mm to about 50mm

[0061] In embodiments, the biochar comprised in the composition of the invention may be in fine aggregate form. In such embodiments, the mean particle size of biochar fine aggregate may be about 100pm to about 10mm, about 250pm to about 7.5mm or about 500pm to about 5mm. In certain embodiments, the biochar comprised in the composition of the invention may be in powder form. In such embodiments, biochar powder may comprise biochar particles with a mean particle size of about 1 pm to about 500pm, about 2pm to about 300pm or about 5pm to about 100pm.

[0062] In some embodiments, the biochar comprised in the composition of the invention may be in fines form, for example having an average particle size of less than about 50pm, less than about 20pm, less than about 10pm, less than about 5pm, less than about 2pm or less than about 1 pm.

[0063] In certain embodiments, the composition of the invention may comprise two or more of the above grades of biochar, for example at least two of bulk biochar, coarse aggregate biochar, fine aggregate biochar, biochar powder or biochar fines.

[0064] In embodiments, the composition of the invention may consist essentially of biochar, i.e. it may contain only de minimis levels of other materials. In some embodiments, the composition may consist exclusively of biochar.

[0065] In certain embodiments, the composition may comprise biochar as the major constituent. For example, the composition of the invention may comprise biochar in an amount of about 50% by weight or more, about 60% by weight or more, about 70% by weight or more, about 80% by weight or more or about 90% by weight or more.

[0066] In alternative embodiments, the composition may comprise larger volumes of materials other than biochar. For example, the composition of the invention may comprise biochar in an amount of about 50% by weight or less, about 40% by weight or less, about 30% by weight or less, about 20% by weight or less, about 15% by weight or less or about 10% by weight or less.

[0067] In certain embodiments of the invention, the weight ratio of biochar : biomass from which the biochar was produced is at least about 1 :1 in the composition of the invention. In some embodiments, the weight ratio of biochar : biomass from which the biochar was produced is at least about 10:1 in the composition of the invention. In preferred embodiments, the weight ratio of biochar : biomass from which the biochar was produced is at least about 20:1 in the composition of the invention.

[0068] Unlike prior art processes for producing high quality biochar, as demonstrated in the accompanying examples, the process of the present invention permits the production of bulk quantities of biochar having uniformly exceptional properties. Based on annual production volumes, in embodiments of the invention, the composition may produce at least 10 tons / year, at least 100 tons / year or at least 1 ,000 tons / year.

[0069] In embodiments of the invention, the composition may comprise at least about 10g or biochar, at least about 100g, at least about 1 kg of biochar, at least about 10kg of biochar, at least about 100kg of biochar, at least about 200kg of biochar, at least about 500kg of biochar, at least about 1000kg of biochar, at least about 2000kg of biochar or at least about 5000kg of biochar. In some embodiments, the composition may comprise at least about 1kg of biochar. In certain embodiments, the composition may comprise at least about 10kg of biochar. In preferred embodiments, the composition may comprise at least about 500kg of biochar.

[0070] In some embodiments, the composition may compose at least 10,000 tons / year or at least 100,000 tons / year.

[0071] The composition of the invention may be comprised in a container. For example, the composition of the invention may be comprised in a reactor, a hopper, a barrel, a sack or similar. Thus, according to a further aspect of the invention, there is provided a container comprising the composition of the invention. In such embodiments, the composition of the invention may be provided in a contact zone of a container, e.g. in a tank, chamber, reactor or similar. In such embodiments, the contact zone may be provided with a fluid inlet (e.g. a gas inlet or a liquid inlet) which permits the flow of fluid into the contact zone. Additionally or alternatively, the contact zone may be provided with a fluid outlet (e.g. a gas outlet or a liquid outlet) which permits the flow of fluid out of the contact zone. In some embodiments, the contact zone may comprise an electrical conduit permitting the supply and I or removal of electrical energy from the contact zone.

[0072] In some embodiments, the composition of the invention may be provided in the earth, e.g. in a trench, hole, cave, chamber, cavern or similar. The composition may be partially or totally embedded in the ground. Additionally or alternatively, the composition may extend above the ground.

[0073] As noted above, the composition of the invention may be provided in particulate form. In certain embodiments, the composition may be provided in the form of a shaped body, e.g. in a cube, spherical, oblong or other shape. In such embodiments, the shaped body may be formed by compressing particulate biochar and other components of the composition and I or by providing the composition with a binder or similar material.

[0074] As is demonstrated via the accompanying examples, biochar exhibiting the advantageous properties detailed herein are obtainable via processes developed by the inventors. Thus, according to a further aspect of the invention, there is provided a process of producing biochar comprising: a) providing biomass to a carbonization reactor, b) providing a gas comprising oxygen to the carbonization reactor via an inlet, c) flowing a gas from the carbonization reactor via an outlet, d) initiating an exothermic reaction in the carbonization reactor, and e) removing biochar produced in the exothermic reaction from the carbonization reactor, wherein: i) the flow of gas comprising oxygen into the carbonization reactor is adjusted to maintain the pressure in the carbonization reactor at a predetermined target pressure, and I or ii) the process additionally comprises f) conducting heat treatment on the biochar produced in the exothermic reaction.

[0075] In arrangements in which part i) of the method is applied (i.e. in which the flow of gas comprising oxygen into the carbonization reactor is adjusted to maintain the pressure in the carbonization reactor at a predetermined target pressure), this may be achieved by setting a target pressure within the carbonization reactor and flowing gas comprising oxygen into the reactor such that the pressure in the carbonization reactor remains constant (e.g. within about 25 kPa, within about 10 kPa, within about 5 kPa, within about 2 kPa, within about 1 kPa, or within about 0.5 kPa of the predetermined pressure). The predetermined target pressure may or may not be re-set during or after step b).

[0076] The adjustment of the flow of gas into the carbonization reactor occurs in response to a detected difference in measured pressure within the carbonization reactor compared to the predetermined target pressure. Thus, in embodiments of the invention, the process comprises the step of measuring the pressure in the carbonization reactor and comparing the measured pressure to the predetermined target pressure and adjusting the flow of gas if a difference between those values exists. In embodiments, the pressure is measured in the carbonization reactor by pressure sensing means.

[0077] Those skilled in the art will recognize that in conventional exothermic biochar production systems, the reaction rate, and thereby the pressure in the reactor has been controlled by maintaining as steady a mass flow of oxygen containing gas into the reactor as possible. The assumption for doing so was that a steady mass flow would result in steady reaction rate. However, the inventors have now unexpectedly found that the rate of the exothermic reaction can be more effectively controlled by adjusting the flow of gas comprising oxygen fed into the carbonization reactor in response to increases in pressure (indicative of reaction rate) in the carbonization reactor.

[0078] Where reference is made to the flow of gas being adjusted, the adjustment of the gas flow is preferably not manually controlled. Instead, the adjustment is active. In some embodiments, the adjustment of the gas flow is automated. In embodiments of the invention, this adjustment is effected by flow adjustment means which automatically adjust the flow of oxygen containing gas into the carbonization reactor in response to the detected pressure level within the carbonization reactor being different to the predetermined target pressure.

[0079] In embodiments, if the pressure in the carbonization reactor is in excess of the predetermined target value, then the flow of oxygen containing gas into the carbonization reactor is reduced by the flow adjustment means until the predetermined target pressure is attained.

[0080] Additionally or alternatively, if the pressure in the carbonization reactor is below the predetermined target value, then the flow of oxygen containing gas into the carbonization reactor is increased by the flow adjustment means until the predetermined target pressure is attained. In such embodiments, the flow of oxygen containing gas may be additionally controlled such that the flow of oxygen-containing gas into the carbonization reactor does not exceed a maximum value in order to prevent excessive pressure build up.

[0081] Preferably, the adjustment of the gas flow in response to a detected difference in pressure in the carbonization reactor from the predetermined target value is rapid. In certain embodiments, the adjustment of the gas flow occurs in about 30 seconds or less, in about 10 seconds or less, in about 5 seconds or less, in about 2 seconds or less, in about 1 second or less or in about 0.5 seconds or less from the timepoint at which a difference in pressure in the carbonization reactor from the predetermined target value is detected.

[0082] Any apparatus that can adjust the flow of oxygen containing gas into the carbonization reactor may be employed as the flow adjustment means. In some embodiments, flow adjustment means may be employed to achieve this, which flow adjustment means optionally comprise a pressure regulator, for example a pressure reducing regulator. Pressure-reducing regulators may be self-operated, high flow, differential, vacuum, air-loaded and I or pilot-operated. Examples of such apparatus include, but are not limited to, diaphragm valves, sliding gate regulators, vacuum regulators, dome loaded regulators and balanced plug regulators.

[0083] In embodiments, the pressure-reducing regulator may be configured to regulate the flow of oxygen-containing gas at a predetermined target pressure downstream of the regulator. Thus, in embodiments in which the pressure-reducing regulator is immediately upstream of the carbonization reactor, the predetermined target pressure will be the pressure in the remainder of the oxygen-containing gas inlet and I or the portion of the carbonization reactor which is fed with oxygen-containing gas via the inlet.

[0084] In embodiments of the invention, the process comprises the step of setting the predetermined target pressure. This may be done before or after step d) of the process, i.e. prior to or following ignition of the biomass.

[0085] In some embodiments, the flow of gas comprising oxygen into the carbonization reactor is adjusted to maintain the pressure in the carbonization reactor at a predetermined target pressure for a portion of the carbonization reaction (e.g. at least about 50%, at least about 60%, at least about 70%, at least about 80% or at least about 90% of the duration of the carbonization reaction). For the avoidance of doubt, the process steps do not necessarily need to be conducted in the order in which they are set out above, save that step e) will necessarily be conducted after step d). In some embodiments, step d) may be performed before step c). In alternative embodiments, step c) may be performed prior to step d). In certain embodiments, the process steps may overlap. For example, in step c), gas is flowed from the carbonization reactor. Such a step may be initiated prior to step d) (ignition of the biomass) and continue after that step has been completed.

[0086] Those familiar with carbonization reactions will recognize that once step d) is performed and the exothermic reaction is initiated, this will result in the conversion of biomass to biochar. As used herein, the term ‘exothermic reaction’ is interchangeable with ‘carbonization reaction’. In embodiments of the invention in which the process is operated in a batchwise manner, the exothermic reaction will conclude once all or substantially all of the biomass is converted into biochar, or, for some other reason, the exothermic reaction ceases. In preferred embodiments, the exothermic reaction concludes once all or substantially all of the biomass is converted into biochar.

[0087] In embodiments of the invention, the reactor is provided with pressure sensing means which are in communication with the flow adjustment means in order to ensure that adjustments to the flow of oxygen containing gas into the carbonization reactor are as rapid and as accurate as possible. Those skilled in the art will recognize that the pressure in different zones in the carbonization reactor will vary during the carbonization reaction. For example, in a vertically oriented carbonization reactor (e.g. as described in WO2023 / 152426) the pressure in the headspace of the carbonization reactor above the biomass during the carbonization reactor may be higher than the pressure in the lower portion of the reactor below the biomass, owing to a pressure drop imparted by the body of biomass.

[0088] Thus, where reference is made herein to adjusting the flow of oxygen-containing gas to maintain the pressure in the carbonization reactor at a predetermined target pressure, this assessment should be made a fixed position within the carbonization reactor, for example in the headspace above the biomass, at the inlet into the carbonization reactor or at the downstream part of the flow adjustment means.

[0089] The pressure drop across the biomass feedstock may be controlled via the selection of biomass having a certain average particle size and I or moisture level and I or by control of the packing density of the biomass into the reactor. In embodiments, in step a) of the process of the invention, the biomass may be loaded into the carbonization reactor such that it has a packed density of about 100 to about 1000 kg / m3, about 200 to about 900 kg I m3or about 300 to about 800 kg / m3.

[0090] Additionally or alternatively, in step a) of the process of the invention, the biomass may be loaded into the carbonization reactor such that the pressure drop across the loaded biomass feedstock prior to step d) of the process of the invention is at least about 15 kPa, at least about 25 kPa or at least about 50 kPa.

[0091] Owing to the process and reactor optimizations discussed herein, carbonization temperatures well in excess of those disclosed in the literature have been attained, leading to the production of biochar having exceptional properties including permanence and low levels of nonpermanent volatile compounds. Thus, in embodiments of the invention, the carbonization reaction, following step d) of the process, proceeds at a temperature in excess of about 700°C, about 800°C, about 850°C, about 900°C, about 950°C or about 1000°C.

[0092] Carbonization reactors of the prior art are typically operated at or below atmospheric pressure. However, owing to the improved process control measures discussed herein, this permits carbonization to be performed at greater than atmospheric pressure which contributes to the enhanced product quality. Thus, in embodiments of the invention, the carbonization reactor is operated at greater than atmospheric pressure during the carbonization reaction.

[0093] In embodiments of the invention, the predetermined target pressure in the carbonization reactor may be at least about 100 kPa, at least about 150kPa, at least about 200 kPa, at least about 250 kPa, at least about 300 kPa, at least about 350 kPa or at least about 400 kPa. Additionally or alternatively, the predetermined target pressure in the carbonization reactor may be at least about 2000 kPa or lower, about 1500 kPa or lower, about 1200 kPa or lower, about 1000 kPa or lower, about 800 kPa or lower, about 750 kPa or lower or about 700 kPa or lower. In some embodiments, the target pressure in the carbonization reactor ranges from around about 300 to about 700 kPa or about 400 to about 600 kPa.

[0094] In some embodiments, passive pressure control means may be employed to control the flow of gas via the outlet of the carbonization reactor. The passive pressure control means may be positioned within the carbonization reactor, at its outlet or downstream thereof. As used herein, “passive pressure control means” is used to describe apparatus which is not capable of actively modulating the rate or pressure of gas flowing therethrough in response to pressure fluctuations. Instead, the passive pressure control means passively limits the flow of gas therethrough. The pressure control means may be adjustable, i.e. it may be adjusted to permit the flow of gas at a given pressure or flow rate, but will not actively adjust this in response to pressure fluctuations. Examples of pressure control means that may be employed in the present method include one or more control valves.

[0095] In embodiments of the invention in which passive pressure control means are employed to control the flow of gas via the outlet of the carbonization reactor, following step b) and I or prior to step d) of the process, the passive pressure control means may be adjusted to adjust the flow of gas at a given pressure or flow rate from the carbonization reactor via its outlet. Additionally or alternatively, the passive pressure control means may be adjusted to adjust the flow of gas at a given pressure or flow rate from the carbonization reactor via its outlet following step d). In such embodiments, for at least about 50%, at least about 60%, at least about 70%, at least about 80% or at least about 90% of the duration of the carbonization reaction following step d), no such adjustments are made.

[0096] In some embodiments, the flow of gas from the carbonization reactor is controlled by a pressure regulator located at its outlet or downstream thereof.

[0097] In the embodiments in which oxygen-containing gas is flowed into the carbonization reactor by a pressure-reducing regulator, other components or apparatus may additionally be positioned upstream of the inlet of the carbonization reactor to modulate and I or direct the flow of oxygen-containing gas, provided that no component or apparatus is located between the pressure-reducing regulator and the inlet of the carbonization reactor which fully negates the adjustments in pressure produced by the pressure-reducing regulator in the gas flowed into the carbonization reactor.

[0098] For example, one or more additional pressure regulators (aside from the pressure-reducing regulator) may be located upstream of the carbonization reactor. This may be a second pressure-reducing regulator or alternatively be a back pressure regulator.

[0099] Additionally or alternatively, a supply of oxygen-containing gas, for example a high pressure air supply source may be provided to supply oxygen-containing gas. In such embodiments, the supply of oxygen-containing gas is located upstream of the pressure-reducing regulator.

[0100] In some embodiments, a mass flow controller may be employed. In certain embodiments of the invention, a gas flow controller may be employed upstream of the carbonization reactor. In such embodiments, the gas flow controller may limit the maximum flow of oxygen-containing gas into the carbonization reactor.

[0101] The flow control means may be connected to the inlet of the carbonization reactor (directly or indirectly) and I or any other components described herein using piping or other types of conduit capable of relaying gas under pressure. Similarly, the outlet of the carbonization reactor may be connected to any components downstream thereof (e.g. the passive pressure control means) using piping or other types of conduit capable of relaying heated gas under pressure.

[0102] One shortcoming with prior art carbonization processes is the incomplete conversion of biomass to biochar, i.e. where a substantial amount of biomass (e.g. about 5% by weight or more) is not converted to biochar. Not only does this reduce the yield of biochar obtained, but this can also result in entire batches falling outside of target specifications, e.g. average carbon content, C:H ratio, C:O ratio, etc. This problem has been addressed by the present invention as the process control approaches described herein enable the conversion of biomass to biochar to be increased. Thus, in embodiments of the invention, at least about 50% by weight of biomass provided in the carbonization reactor is converted to biochar. In some embodiments, at least about 90% by weight of biomass provided in the carbonization reactor is converted to biochar. In some embodiments, at least about 95%, at least about 97% or at least about 99% by weight of biomass provided in the carbonization reactor is converted to biochar.

[0103] As is demonstrated in the examples, the design of a carbonization reactor as described herein advantageously permits the method of the present invention to be performed. Thus, according to a further aspect of the present invention, there is provided a carbonization reactor comprising a gas inlet and a gas outlet, wherein the gas inlet is in fluid communication with a flow control means as described herein and optionally, upstream of the flow control means, a source of oxygen-containing gas. In embodiments, the gas outlet of the carbonization reactor may be in fluid communication with passive pressure control means. The carbonization reactor of this aspect of the invention may comprise any of the features described herein in connection with other aspects of the invention.

[0104] As is also demonstrated in the accompanying examples, the biochar obtainable from certain prior art processes may exhibit a degree of conductivity. Following the removal and analysis of conductive biochar from such a process, the inventors found that conductivity across the biochar was not always uniformly consistent across multiple samples.

[0105] Following extensive research, the inventors unexpectedly found that not only did heat treatment improve the uniformity of conductivity of the biochar, it also enhanced conductivity. Additionally, as shown in the examples, the heat treatment step advantageously additionally resulted in further enhancements to the biochar, including reducing the content of VOCs and PAHs and increasing surface area.

[0106] Thus, in embodiments, the process of the invention additionally comprises f) heat treating the biochar produced in the exothermic reaction.

[0107] Further, according to an additional aspect of the invention, there is provided a process for enhancing the uniformity of conductivity and I or increasing the average conductivity of a composition comprising biochar comprising heat treating the composition.

[0108] In embodiments in which the biochar composition is subjected to a heat treatment step, the biochar composition may be removed from the carbonization reactor and provided in a heat treatment reactor and heat applied thereto.

[0109] Alternatively, the heat treatment step may be performed in the carbonization reactor, prior to step e) (removal of the biochar from the reactor). In such embodiments, the heat supplied to the biochar in order to conduct the heat treatment step may be residual heat from the carbonization reaction.

[0110] In embodiments, the biochar composition may be heated to a temperature of at least about 500°C, at least about 600°C, at least about 700°C or at least about 800°C in the heat treatment step.

[0111] Heat may be supplied to the biochar in the treatment step via any means. For example, hot gas (e.g. air or gas flowed from the carbonization reactor following step d) of the process of the invention) may be fed into the reactor. The hot gas may be generated by combustion of gas flowed from the carbonization reactor following step d).

[0112] In some embodiments, the reactor may be provided with one or more heating elements. Additionally or alternatively, heating of the biochar in the heat treatment step may be ohmic, i.e. by flowing electrical current through the conductive biochar. The heat treatment step may be performed in a gaseous environment, i.e. the reactor in which the heat treatment step is conducted (e.g. the heat treatment reactor or the carbonization reactor) may comprise a gas. In such embodiments, the gas may comprise oxygen. For example, the gas in the reactor may comprise at least about 70%, at least about 80% or at least about 90% air by volume. In such embodiments that contain an oxidizing gas the heat treatment will result in a net loss of mass. In certain embodiments, the reactor in which the heat treatment step is conducted may be supplied with gas flowed from the carbonization reactor following ignition of the biomass in step d), which has optionally been treated prior to such supply.

[0113] In other embodiments the gaseous environment has negligible amounts of oxygen or other oxidizing agents.

[0114] In certain embodiments, the atmosphere in the reactor in which the heat treatment step is conducted may be inert. For example, the heat treatment step may be conducted under vacuum. Additionally or alternatively, the heat treatment step may be conducted in the presence of inert gas / es such as nitrogen and I or noble gases..

[0115] In other embodiments the gaseous environment during heat treatment contains hydrocarbons such as methane that may react with the carbon material resulting in a net weight increase. Such hydrocarbons may be provided by gas flowed from the carbonization reactor following step d) of the process of the invention.

[0116] As noted above, in embodiments, the gaseous environment in which heat treatment is conducted may comprise gas flowed from the carbonization reactor following step d). In further embodiments a portion or the entirety of the gas flowed from the carbonization reactor following step d) is combusted to generate CO2, N2, and H2O which may be present in the gaseous environment.

[0117] In preferred embodiments, the gas in the reactor in which heat treatment is conducted (e.g. the heat treatment reactor or the carbonization reactor) is cycled with fresh gas such that contaminants such as PAHs and / or VOCs emitted from the biochar composition are removed from the reactor such that the probability these contaminants recondense onto the biochar is eliminated or minimized. Preferably, the biochar composition is heated such that the biochar comprised therein is uniformly raised to the desired temperature. In one embodiment, the amount of time required for heating is minimized, such that the rate of production can be as large as possible.

[0118] Advantageously, as demonstrated in the accompanying examples, profound positive changes to the properties of biochar compositions can be achieved even utilizing short heat treatment steps. Thus, in embodiments of the invention, the heat treatment step has a duration of less than about 100 minutes, less than about 60 minutes, less than about 30 minutes, less than about 20 minutes or less than about 10 minutes.

[0119] In embodiments of the invention, the heat treatment step may be carried out at atmospheric pressure. However, controlled pressures may also be employed. Thus, in some embodiments, the heat treatment step may be carried out under vacuum, e.g. a partial vacuum. In alternative embodiments, the heat treatment step may be carried out at elevated pressures.

[0120] When heating large quantiles of biochar, the uniformity of heating may be insufficient if the treatment time is too small. For example, if a large reactor of biochar fragments is placed inside a heat treatment reactor such as a furnace, the biochar fragments on the inside of the container may take a longer period of time to rise to the temperature of the furnace, as compared to the biochar fragments that are close to the outer perimeter of the furnace.

[0121] In one embodiment, the treatment time is extended, such that the temperature of the biochar comprised at the innermost part of the heat treatment reactor is raised to the minimum desired temperature for the predetermined amount of time.

[0122] In another embodiment, the biochar composition being heat treated is provided on a conveyor system optionally comprising a thin layer of biochar and / or a single layer of biochar fragments on the conveyor, such that heating time for all of the biochar fragments is nearly uniform.

[0123] Those skilled in the art will be familiar with carbonization reactor design. In embodiments of the invention, the reactor is generally cylindrical with a perforated conical base. Oxygencontaining gas (e.g. air) may be flowed into the upper end of the reactor under pressure and exhaust gases may be vented from the lower end of the reactor. Examples of such reactors are disclosed in WO2023 / 152426 and W02023 / 205081 , the contents of which are incorporated herein by reference in their entirety, but additionally comprising the additional optimized features recited in the accompanying process claims. The reactor employed in the process of the invention may be arranged for a carbonization reaction that occurs in the biomass during the time it traverses the reactor, e.g. by passing from the bottom of the reactor to the top, e.g. to a perforated cone at the lower end of the reactor. In embodiments, the biomass can be fed into the carbonization reactor and removed as the biochar.

[0124] In embodiments of the invention, the reactor has an upper end optionally comprising the gas inlet and / or a bottom end, optionally comprising the gas outlet.

[0125] The carbonization reactor may be configured and the method conducted to maintain the reaction front, at least relatively, stationary in the vertical direction of the reactor, for example by monitoring the temperature at the upper sensor(s) and at the lowers sensor(s). In certain optional embodiments of the invention, repeated and / or continuous temperature measurements may be obtained using the at least two temperature sensors mounted at different heights of the carbonization reactor.

[0126] In certain embodiments, the carbonization reaction may be operated in a continuous, semibatch or batch manner.

[0127] In certain embodiments, the internal volume of the carbonization reactor is at greater than atmospheric pressure during the carbonization reaction.

[0128] In certain embodiments, addition of biomass to the carbonization reactor is performed at greater than atmospheric pressure. As used herein, "greater than atmospheric pressure" refers to an absolute pressure of more than 1.01325 bar.

[0129] In certain embodiments, the pressure in the carbonization reactor may be between 3 and 20 bar.

[0130] In embodiments of the invention, the mass of air fed into the carbonization reactor is less than the mass of biomass present in the reactor prior to commencement of the carbonization reaction. In some embodiments, the mass of air fed into the carbonization reactor is about 90% or lower, about 80% or lower, about 70% or lower, about 60% or lower or about 55% or lower than the mass of biomass present in the reactor prior to commencement of the carbonization reaction. Additionally or alternatively, the mass of air fed into the carbonization reactor is about 20% or higher, about 30% or higher, or about 40% or higher than the mass of biomass present in the reactor prior to commencement of the carbonization reaction.

[0131] In embodiments of the invention, following initiation of the exothermic carbonization reaction, the carbonization reaction proceeds to completion, yielding biochar. In embodiments, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 97%, at least about 99% or at least about 99.5% by weight of the biomass present in the reactor is converted to biochar by the exothermic carbonization reaction.

[0132] In certain embodiments, the temperature of the exothermic carbonization reaction is at least about 500°C, at least about 600°C, at least about 700°C or at least about 800°C.

[0133] In certain embodiments, the biomass may be added to the carbonization reactor in a continuous manner. As used herein, the term "continuous manner" refers to the addition of biomass while the exothermic reaction is underway. In certain embodiments, the biomass may be added to the carbonization reactor in a semi-batch manner. As used herein, the term "semi-batch manner" refers to the addition of biomass before the initiation of the exothermic reaction.

[0134] In certain embodiments, the biochar may be removed from the carbonization reactor in a continuous, semi-batch or batch manner.

[0135] In certain embodiments, the gas comprising oxygen is added to the carbonization reactor at greater than atmospheric pressure.

[0136] In certain embodiments, the gas comprising oxygen may be air. In certain embodiments, the gas comprising oxygen may be a gas comprising more than 21% oxygen.

[0137] In certain embodiments, the gas comprising oxygen contains less than 21 % oxygen. In certain embodiments, the gas comprising oxygen may be a gas where at least a portion of said gas originates from the oxygen-deficient gas outlet of a carbonization reactor.

[0138] In certain embodiments the gas comprising oxygen comprises less than 78% nitrogen.

[0139] In certain embodiments, the biomass is added at a rate to maintain a constant level of feedstock in the reactor. In certain embodiments, the rate of adding biomass can be controlled during the process to maintain an efficient carbonization process in the reactor. In one embodiment, the addition of biomass is done under pressure. In one embodiment, the reactor is maintained at higher than atmospheric pressure when biomass is added.

[0140] In certain embodiments, the biomass may be derived from a biological process such as photosynthesis or chemosynthesis. Examples of biomass include agricultural residues such as corncobs, olive pits, walnut shells, sunflower shells and husks, and sugar cane bagasse; wood materials such as wood logs, slabs, chips, and bark; open-water plants such as water hyacinths and seaweed; organic municipal solid wastes, sewage sludge, or other organic clarified solids; and animal residues.

[0141] In certain embodiments, the biomass may be mixed with an inorganic material prior to addition to the reactor. In one embodiment, the process may include the step of impregnating the biomass with a functional additive, e.g. an aqueous solution of an inorganic salt prior to addition to the reactor. In one embodiment, the biomass may be wet impregnated with an aqueous solution containing a metal salt prior to addition to the reactor.

[0142] In certain embodiments, the means for initiating an exothermic reaction in the carbonization reactor is located at the opposite end of the carbonization reactor relative to the input of the gas comprising oxygen.

[0143] In certain embodiments, the means for initiating an exothermic reaction in the carbonization reactor may be an electric heating source. In certain embodiments, the means for initiating an exothermic reaction in the carbonization reactor may be any other means suitable for initiating the reaction. Non-limiting examples of suitable means are burners burning liquid or gaseous fuels.

[0144] In one embodiment, the energy required to initiate an exothermic reaction in the reactor is provided by leaving a remainder of the hot product in the bottom of the container.

[0145] In certain embodiments, the process comprises the step of continuously removing from the carbonization reactor. In one embodiment, the reactor may be maintained at higher than atmospheric pressure when removing the biochar. In one embodiment, the biochar is cooled or quenched with water during removal.

[0146] In certain embodiments, the process of the invention comprising maintaining pressure of the reactor by controlling the flow of the oxygen comprising gas relative to the flow of the oxygendeficient gas. In certain embodiments, the flow of oxygen comprising gas is controlled by adjusting the pressure of the oxygen comprising gas relative to the pressure of the carbonization reactor.

[0147] In an embodiment, the process of the invention comprises feeding biomass from means for adding organic feedstock to a carbonization reactor, such as a biomass hopper, for example at the top of the carbonization reactor.

[0148] The passage of the biomass into and out of the means for adding biomass to the carbonization reactor may be controlled by isolation valves mounted above and below the means for adding biomass to a carbonization reactor that allow biomass to be fed into the reactor at above atmospheric pressure. Such valves can be used to prevent pressure from leaking out of the carbonization pressure reactor.

[0149] The means for adding organic feedstock to the carbonization reactor may be provided as a feedstock supply channel, which may comprise a supply screw or auger and / or a supply conveyor belt for moving the feedstock towards and I or into the reactor. In embodiments in which the method is under continuous operation, the means for adding organic feedstock to the carbonization reactor, or the feedstock supply channel in particular, may be exposed to the carbonization reactor during operation, for example at all times.

[0150] In an embodiment, the method of the invention comprises the step of removing biochar from the carbonization reactor. Thus, the carbonization reactor may comprise means for removing biochar from the carbonization reactor. The method may further comprise the step of transporting the biochar removed from the carbonization reactor to a storage container. The passage of the biochar into the storage container may be controlled by an isolation valve .

[0151] The carbonization reactor may comprises a perforated cone, for example at the lower end. The perforated cone collects the biomass and stops it from falling to the bottom of the reactor. Feeding means may be employed to remove biochar from the reactor, for example at the bottom of the perforated cone, and transport it to a storage container. The passage of the biochar into the storage container may be controlled by an isolation valve. An isolation valve on the outlet of the storage container allows the carbonization product to be removed from the pressurized system .

[0152] Using isolation valves allows the reactor to be loaded and / or unloaded with increased speed. This may be particularly facilitating for the continuous operation. One or more isolation valve(s) may be arranged for pressure isolation for adding the organic feedstock to the carbonization reactor and / or for removing the carbonization product from the carbonization reactor . One or more isolation valve(s) may be arranged for temperature isolation, in particular for removing the carbonization product from the carbonization reactor .

[0153] The method may be controlled to automatically add the biomass and / or remove the biochar based on the control instruction. This may be done under continuous operation of the method. In an embodiment, the method comprises the step of cooling or quenching the biochar, e.g. with water during or following removal of the biochar from the carbonization reactor. For this purpose, the reactor may comprise a cooler arranged to apply cooling fluid, such as water, to the biochar at the at the carbonization reactor and / or at the means for removing the biochar from the carbonization reactor. The cooling fluid may be delivered into the carbonization reactor and / or the means for removing a biochar from the carbonization reactor, e.g. into a product discharge channel. The cooler may be, for example, a spray cooler arranged to spray the cooling fluid at the biochar.

[0154] The method may also comprise the step of carrying away steam from the cooling. This may be achieved by means such as piping connected to the carbonization reactor and / or the means for removing the biochar from the carbonization reactor for carrying away steam from the cooling.

[0155] In embodiments, the organic feedstock is fed into the carbonization reactor at greater than atmospheric pressure.

[0156] In certain embodiments, the oxygen-deficient gas comprises by volume:

[0157] • 0-60% nitrogen

[0158] • 10-50% CO2

[0159] • 0-50% H2

[0160] • 10-50% CO

[0161] • 0-20% CH4

[0162] • 0-5% Ethane

[0163] • 0-5% Ethylene

[0164] • 0-5% Heavier hydrocarbons.

[0165] In certain embodiments, the oxygen deficient gas comprises less than 5 % oxygen. As used herein, the term "heavier hydrocarbons" refers to hydrocarbons consisting of three or more carbon atoms. Non-limiting examples of heavier hydrocarbons are propane, butane, propene, and butene.

[0166] As used above, the percentages of the components of the oxygen-deficient gas refer, unless explicitly stated otherwise, to a molar percentage of the oxygen-deficient gas composition.

[0167] In certain embodiments, the gas comprising oxygen is added to the carbonization reactor at greater than atmospheric pressure.

[0168] In certain embodiments, the gas comprising oxygen may be air. In certain embodiments, the gas comprising oxygen may be a gas comprising more than 21% oxygen. In certain embodiments, the organic feedstock is added to the carbonization reactor in a continuous manner.

[0169] In certain embodiments, the organic feedstock may be mixed with an inorganic material prior to addition to the reactor.

[0170] In certain embodiments, the biochar is removed from the carbonization reactor in a continuous, semi-batch or batch manner.

[0171] In certain embodiments, the addition of biomass is done at a rate to maintain a constant level of biomass in the reactor.

[0172] As explained herein, the process of the invention advantageously permits the reliable production of a biochar composition having exceptional properties. Thus, according to a further aspect of the present invention, there is provided a composition comprising biochar obtainable from the process of the present invention. The composition may comprise any of the features or properties disclosed herein.

[0173] Owing to the advantageous properties of the biochar of the invention, its use in a range of applications is possible, including in agriculture, horticulture, energy storage, biocomposites, pigments, water treatment, soil remediation, biogas production, and more.

[0174] Multiple properties of the composition of the present invention make it attractive for use as a supplement for growing media in horticulture and soils in agriculture. For example, strong biochar permanence means that the composition will remain inert in growing media and will not be degraded (e.g. by microbes or plants) and converted into carbon dioxide. Additionally, the advantages of growing media exhibiting a degree of conductivity is of interest. More specifically, it is believed that the incorporation of a conductive biochar in growing media will improve the facilitation of electron transfer amongst different microorganisms. Additionally, this can reduce the amount of nitrate runoff and increase the efficiency of nitrogen fertilizers . Further, low levels of volatile organic compounds and I or polyaromatic hydrocarbons, which can be harmful to plants, animals and humans, are also preferable. Finally, a high percentage of macropores will allow for adsorption and storage of water, while a high percentage of micropores will allow for the adsorption of nutrients and impurities. Thus, in embodiments of the invention, the composition of the invention may be a supplement for growing media. In certain embodiments, there is provided a growing medium comprising the composition of the invention.

[0175] As used herein, the term “growing medium” is to be interpreted broadly to encompass all types of growing media, including compost, soil, soil additives, soil additions, mulch and the like.

[0176] The conductive and I or porosity properties of the biochar provided in the compositions of the present invention also make it specifically attractive to applications of energy storage, biocomposites, and pigments. The present invention can replace fossil fuel derived carbon products that are currently used within these industries.

[0177] Within energy storage, the compositions of the invention may be used in the electrodes of devices such as batteries and supercapacitors.

[0178] Thus, in embodiments of the invention, there is provided an electrode or other electrically conductive body comprising the composition of the invention. There is also provided a battery or supercapacitor comprising such an electrode or electrically conductive body.

[0179] Within biocomposites, the present invention can be embedded into the polymer matrix and used to create materials that optionally provide added consumer benefits, such as dissipating static build-up or transferring electric charge, providing electromagnetic interference shielding. Thus, in embodiments of the invention, there is provided a polymer biocomposite comprising the composition of the invention.

[0180] Within pigments, the present invention can replace fossil fuel derived carbons that are used to create pigments, including conductive pigments, such as conductive carbon inks. These inks can be deposited onto various substrates and used across a wide variety of applications. Thus, in embodiments of the invention, there is provided a pigment comprising the composition of the invention. Additionally, there is provided a substrate comprising such an ink, e.g. deposited thereon.

[0181] Additionally, the conductive and porosity properties of the compositions of the present invention also make them specifically attractive to applications of water treatment and soil remediation. In both of these applications, the present invention can be used to remove contaminants and pollutants in various materials, including water and soil . Water can include but is not limited to mean drinking water, wastewater, effluent from various processes, and naturally draining rainwater. The term soil here can also mean any type of earth, including but not limited to rock, sediment, dirt, and farming soils. The conductive and porous properties allow for cleaning of these types of materials by removing pollutants that include but are not limited to organic fertilizers, inorganic fertilizers, pharmaceuticals, chemicals, and oils. Thus, in embodiments of the invention, there is provided the use of the compositions of the invention for removing contaminants and I or pollutants from various materials, such as water and soil. There is also provided a method of removing contaminants and I or pollutants from various materials, such as water and soil using the compositions of the invention.

[0182] Additionally, the conductive properties of the composition of the present invention also make it specifically attractive to applications of biogas production. Where biogas digesters are utilized, the present invention can be implemented to further increase the production of biogas and improve the efficiency of the process. Thus, in embodiments of the invention, there is provided the use of the compositions of the invention for use in biogas digesters to increase the production of biogas. There is also provided a method of increasing the production of biogas by a biogas digester using the compositions of the invention.

[0183] The invention will now be further demonstrated by way of the following examples

[0184] EXAMPLE 1 - Optimized Reactor Pressure Control

[0185] Referring to Figure 1 , the biochar production system 1000 includes a high pressure air supply source 100, with an output pressure between 750 and 900 kPa, capable of delivering a mass flow rate of at least 120% of the operating mass flow rate. A first pressure restricting device (a diaphragm pressure regulator) 120 is located downstream of the air source and is connected to the air supply source 100 by means of gas supply entry piping 140. This first pressure reducing regulator 120 reduces the line pressure to between 575 kPa and 650 kPa, and is rated to deliver at least 110% of the operating mass flow rate. After the first pressure restricting device is an electronic mass flow controller 160 that is capable of controlling the mass rate of air flowing through the device, and thus through the gas supply entry piping 140, and is rated for at least 110% of the operating mass flow rate. Following the electronic mass flow controller 160 is a further pressure-reducing regulator (which, for the purposes of the description of the method of the present invention, adjusts the flow of oxygen containing gas into the carbonization reactor) (a diaphragm pressure regulator) 180 which reduces the line pressure to deliver a flow of air which maintains the pressure within the carbonization reactor at the predetermined set rate of 415 kPa.

[0186] Gas supply entry piping 140 is connected from the output of the second pressure restricting device 180 to the reactor entry port 190 on the reactor vessel 200 to deliver the air from the air supply source 100 to the reactant mass of biomass feedstock 220 within the reactor vessel 200. The biomass feedstock 220 is loaded within the reactor vessel 200 such that a pressure of at least 25 kPa is required to drive the operating mass flow rate through the bed of biomass feedstock 220.

[0187] The exit port 240 of the reactor vessel is connected to a high-pressure discharge line 260 that carries process gases out of the reactor vessel 200. A variable area control valve 280 is connected to the high-pressure discharge line 260 on the upstream side of the variable area control valve 280. On the downstream side, the variable area control valve 280 is connected to a low-pressure discharge line 300. Process gases exiting through the low-pressure discharge line 300 may be directed to atmosphere, collection tanks, environmental scrubbers, and / or other types of additional processing equipment, depending on the desired treatment of the process gases.

[0188] Production of biochar from the reactant biomass feedstock 220 is accomplished by first adjusting the size of the open flow area within the variable area control valve 280 for the predetermined mass flow of air through the system during production. Adjustment of the variable area control valve 280 is made until a steady state pressure condition is achieved at each of the device points. At steady state, the pressure drop across the biomass feedstock 220 is preferably greater than 25 kPa, and more preferably greater than 50 kPa. The pressure drop across the second pressure restricting device 180 is preferably greater than 300 kPa, more preferably greater than 350 kPa, and most preferably greater than 400 kPa. Next, the reactant biomass feedstock 220 is ignited and the carbonization reaction proceeds.

[0189] The duration of the carbonization reaction (from ignition of the biomass to completion of the carbonization reaction upon the biomass being fully converted to biochar) was around 240 minutes. Upon completion of the carbonization reaction being detected, the flow of air into the reactor was stopped. The predetermined pressure in the carbonization reactor was around 415 kPa during the carbonization reaction, and temperatures in excess of 800°C were recorded using thermocouples mounted on the walls of the carbonization reactor. It is understood that the temperature in the biomass positioned in the center of the reactor undergoing carbonization will be significantly higher.

[0190] The following tables show properties of product obtained from the process of Example 1 :

[0191] Percentage of Carbon Comprised in Biochar Present as SPAC - As explained above, one way to assess the permanence of biochar is to determine the proportion of carbon which is present in the form of stable polycyclic aromatic carbon (SPAC). The proportion of carbon present as SPAC in samples of biochar obtained from the process of Example 1 from different biomass materials was assessed using hydropyrolysis (HyPy) in accordance with the methodology detailed by Meredith et al., in Chapter 17 of the 2017 edition of “Biochar: A Guide to Analytical Methods”. The following results were obtained:

[0192] Random Reflectance of Biochar - As also explained above, random reflectance (Ro) is also a measure of permanence of biochar. The random reflectance of samples of biochar obtained from the process of Example 1 from different biomass materials was assessed using the methodology detailed by Hanei et al. (International Journal of Coal Geology, volume 281 , January 2024, pages 1 to 20) and the following results were obtained: Non-Permanent Organic Compound Content of Biochar - The biochar obtainable from the processes as disclosed herein advantageously comprise low levels of non-permanent organic compounds, particularly PAHs and VOCs as defined above. Samples of biomass obtained from the process of Example 1 were analyzed and the levels of PAHs and VOCs which were determined are set out in the following tables:

[0193] PAH Content:

[0194] VOC Content:

[0195] Further Compositional Analysis - Additional compositional data from samples obtained from the process of Example 1 are provided in the following tables:

[0196] *AII of arsenic, lead, cadmium and mercury were below detectable limits.

[0197] EXAMPLE 2 - Post-Production Biochar Heat Treatment

[0198] A refractory lined electric furnace with internal open dimensions of 15cm x 15cm x 15cm was programmed to maintain a temperature of 750°C. Temperature control of the furnace was achieved through a PID temperature controller connected to a type K thermocouple which terminated inside of the furnace open area. Power from the PID control output was delivered to resistive heating elements that were integrated with the refractory lining to provide a uniform heating of the furnace open area. An aluminum oxide plate was placed on the bottom of the open area to provide a surface for the biochar fragments. This plate was placed in the furnace prior to heating, to allow the plate to be heated from a cooled state. Typically, heating of the plate is performed from room temperature to the desired operating temperature over the course of about at least 30 minutes, to minimize deleterious effects that can easily present from thermal shock.

[0199] Ten biochar fragments from a batch of biochar that was produced in accordance with the process detailed in WO2023 / 152426 and were set aside for testing. First, the resistivity of each fragment was measured with a 2-probe resistance measurement method using a Keithly 2000 multifunction desktop meter. Metal contact probes were gently pressed into the surface of each sample; two probes are used at a spacing of 1 centimeter, while recording the value of resistance displayed on the meter display. Values were taken once the meter value being displayed settled. While this technique for measuring conductivity differed from the compressive approach (in which conductivity was assessed under a mass of 1.2t, as described above), the conductivity results below, as measured in resistance, are broadly comparable with those obtained from the compressive approach, save that the resistance results obtained from this method will be inversely proportional to those obtained using the compressive approach, and that the conductivity which is measured using this technique will be lower than if measured using the compressive approach.

[0200] Next, the fragments are placed onto a transfer plate for easy loading into the furnace. The door to the furnace was opened and the fragments were quickly transferred by sliding them off of the transfer plate onto the aluminum oxide plate that was resting on the bottom of the furnace open area. Little care was taken with the arrangement of the fragments, with some fragments isolated and some fragments overlapping another. The furnace door was then shut and the temperature indicated by the thermocouple was observed. With the door open, the indicated temperature dropped to about 500°C. The indicated temperature quickly recovered to 700°C within 1 minute of closing the door. The indicated temperature climbed to the control setpoint of 750°C by minute number 4. At minute number 5 the fragments were removed from the furnace by removing the aluminum plate.

[0201] After the fragments cooled to room temperature, resistivity of each fragment was measured with a 2-probe resistance measurement method as described above, in this example. The results of measurement are shown in the table below: As is demonstrated, prior to treatment, some fragments within the biochar batch had relatively low resistivity, i.e. modest conductivity while others had high resistivity, i.e. were not conductive.

[0202] Strikingly, however, post-treatment, not only was a high degree of consistency obtained for all samples, but the reduction in resistivity, i.e. the production of exceptionally conductive biochar was achieved via a short term heat treatment step using conventional apparatus.

[0203] In a separate test, a sample from a different batch of biochar obtained from a process of the present invention was subjected to a heat treatment step as described above. The results are shown in the following table:

[0204] ‘Conductivity was measured using the compressive (1.2t) approach described above.

[0205] The embodiments disclosed herein are not limited to the examples described above and may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment. A method or a system, disclosed herein, may comprise at least one of the embodiments described hereinbefore. It will be understood that the benefits and advantages described above may relate to selected embodiments or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item refers to one or more of that item. The term “comprising” is used in this specification to mean including the feature(s) or act(s) followed thereafter, without excluding the presence of one or more additional features or acts.

[0206] The disclosed embodiments are susceptible to various modifications and alternative forms, and specific examples thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the disclosed embodiments are not to be limited to the particular forms or methods disclosed, but to the contrary, the disclosed embodiments are to cover all modifications, equivalents, and alternatives.

[0207] EXAMPLE 3 - Effect of Pressure Control on Oxygen-Containing Gas Flow into Reactor To assess the impact of regulating the pressure of oxygen-containing gas flowed into a carbonization reactor, comparative studies were performed.

[0208] In the comparator study, a reactor design as detailed in Example 1 was set up, but included different pressure regulating apparatus on the supply line of the oxygen-containing gas, upstream of the carbonization reactor. Instead of the use of a pressure regulator configured to maintain pressure within the reactor at a given value immediately upstream of the reactor, a pressure regulator configured to provide a constant flow rate of oxygen-containing gas into the reactor was employed.

[0209] In accordance with conventional carbonization processes, the supply of oxygen-containing gas was maintained at a pressure higher than the reactor's nominal operating pressure, 750 kPa. This is done in conventional carbonization processes to ensure a constant mass flow of oxygen-containing gas can be delivered by the mass flow controller. The biomass to be carbonized was wood pellets.

[0210] The inventors identified that this high-pressure differential configuration is susceptible to process upsets. These upsets can be triggered by several factors, including physical disturbances within the fixed bed of biomass or, more commonly, when the reaction front moves towards the top of the reactor where it can encounter regions with higher oxygen availability. These conditions can lead to sudden, uncontrolled combustion events. Because the air supply pressure is so high, the system continues to force the set amount of air into the reactor during the spike, effectively "feeding" the excursion and worsening its severity.

[0211] The primary consequence of these pressure spikes is the non-complete carbonisation of biomass. More specifically, in this comparator example, the obtained product is non-uniform, including raw or partially pyrolyzed feedstock (brown, woody material). The presence of this unburnt material means that the fixed carbon percentage of those particles is reduced, as low as 50% for unburned material, as is the total fixed carbon percentage of the batch which averaged about 70%. This negates a primary objective of carbonisation — to maximize fixed carbon.

[0212] The process was subsequently operated using the apparatus of Example 1 , including the pressure regulating apparatus as set out above in that example. The pressure regulator immediately upstream of the reactor was configured to deliver a flow of air to maintain pressure within the carbonization reactor at a predetermined set rate of 500 kPa.

[0213] The process was operated with no pressure spikes observed which ensured a stable and complete reaction environment. This enhanced stability resulted in a verifiably superior biochar product which was free of uncarbonized biomass and was a uniform, high-quality material. Additionally, the fixed carbon values for both particles of that biomass and the batch as a whole was in excess of 90%, fulfilling a key performance metric for carbonisation.

Claims

CLAIMS1. A composition comprising biochar exhibiting one or more of the following characteristics:1.

1. Permanence, characterized by one or more of the following properties:1.1.

1. At least about 95% by weight of the carbon present being comprised in the form of stable polycyclic aromatic carbon (SPAC),1.1.

2. At least about 90% by weight of carbon present having a random reflectance of about 2% or higher, and I or1.

2. Conductivity, characterized by the following property:1.2.

1. At least about 80% by weight of the biochar comprised in the composition has a conductivity of at least about 100mS / cm, and I or1.

3. Low levels of non-permanent organic compounds, characterized by one or more of the following properties:1.3.

1. About 100mg / kg or lower of polycyclic aromatic hydrocarbons (PAH), and I or1 .3.

2. About 12% by weight or lower of volatile organic compounds.

2. The composition of Claim 1 , wherein at least about 80% by weight of the biochar comprised in the composition has a conductivity of at least about 100mS / cm.

3. The composition of Claim 1 or 2, wherein the biochar comprised in the composition has an average carbon content of at least about 90%.

4. The composition of any preceding claim, wherein the biochar comprised in the composition has an average molar ratio of oxygen to carbon of about 0.1 or lower.

5. The composition of any preceding claim, wherein the biochar comprised in the composition has an average molar ratio of hydrogen to carbon of about 0.4 or lower.

6. The composition of any preceding claim, wherein the biochar comprised in the composition has an average sulfur content of about 1 % by weight or lower.

7. The composition of any preceding claim, wherein the biochar comprised in the composition has an average content of lead, cadmium, arsenic and mercury of less than about 0.01% by weight.

8. The composition of any preceding claim, wherein the biochar comprised in the composition has an average density of about <5 g / cm3.

9. The composition of any preceding claim, wherein the biochar comprised in the composition has on average about 50% or greater macropores.

10. The composition of any preceding claim, wherein the biochar comprised in the composition has on average about 40% or lower micropores.11 . The composition of any preceding claim, wherein the biochar comprised in the composition has an average ratio of macropores : micropores of about 1 :1 or higher.

12. The composition of any preceding claim, wherein the biochar comprised in the composition has a mean surface area of (BET) of at least about 50m2 / g.

13. The composition of any preceding claim comprising at least about 1 kg of biochar.

14. The composition of any preceding claim comprising at least about 1000kg of biochar.

15. The composition of any preceding claim, wherein the weight ratio of biochar : biomass from which the biochar was produced is at least 20:1 .

16. A container comprising the composition of any preceding claim.

17. A growing medium, an electrode, a pigment, a polymer biocomposite18. A process of producing biochar comprising: a) providing biomass to a carbonization reactor, b) providing a gas comprising oxygen to the carbonization reactor via an inlet, c) flowing a gas from the carbonization reactor via an outlet, d) initiating an exothermic reaction in the carbonization reactor, ande) removing biochar produced in the exothermic reaction from the carbonization reactor, wherein: i) the flow of gas comprising oxygen into the carbonization reactor is adjusted to maintain the pressure in the carbonization reactor at a predetermined target pressure, and I or ii) the process further comprises f) conducting heat treatment on the biochar produced in the exothermic reaction.

19. The process of Claim 18, wherein the adjustment of the flow of gas is controlled by flow adjustment means.

20. The process of Claim 19, wherein the flow adjustment means comprise a pressure reducing regulator.21 . The process of any one of Claims 18 to 20, wherein the oxygen-containing gas is air.

22. The process of any one of Claims 18 to 21 , wherein step f) is conducted prior to step e).

23. The process of any one of Claims 18 to 21 , wherein step f is conducted following step e).

24. The process of any one of Claims 18 to 23, wherein the heat treatment step is conducted at a temperature of at least about 600°C.

25. Biochar obtainable from the process of any one of Claims 18 to 24.

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