Biomass conversion to activated carbon

Abstract

Methods of producing activated carbon are disclosed, which proceed through the formation of a biochar intermediate having threshold quality characteristics that render it suitable for (i) direct use, such as a soil amendment, as well as (ii) subsequent activation to make the higher-value activated carbon. These characteristics, including a favorably high fixed carbon content, may be achieved in an efficient manner and often with the avoidance of certain processing steps that add complexity and expense. Representative methods comprise (a) a carbonization step to obtain the biochar, and (b) an activation step of contacting the biochar with steam or other oxidant to obtain the activated carbon having an increased surface area (e.g., at least about 750 m2 / g) relative to that of the biochar. Particularly advantageous results, in terms of process performance and product quality characteristics, are achieved with biomass comprising almond residues (e.g., almond shells and hulls) as a starting material.

Description

[0001] BIOMASS CONVERSION TO ACTIVATED CARBON

[0002] CROSS REFERENCE TO RELATED APPLICATION

[0003]

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 664,264, filed June 26, 2024, which is hereby incorporated by reference in its entirety.

[0004] FIELD OF THE INVENTION

[0005]

[0002] The disclosure is directed to methods for converting biomass such as almond residues to activated carbon, by utilizing a combination of carbonization and activation steps, which steps may be performed in the same or different locations.

[0006] BACKGROUND

[0007]

[0003] Activated carbon is typically produced by the activation of charcoal, a carbonaceous or carbonized material that may be derived from a suitable source of carbon such as biomass. Charcoal is normally produced through the heating of this carbon source in an environment with little or no oxygen, which results in the partial decomposition of its chemical structure and an increase in its elemental carbon content. When derived more particularly from biomass, such as plant or animal matter, the charcoal, or carbonized material, may be referred to as “biochar.” Biomass generally refers to biological material derived from living or deceased organisms and includes lignoccllulosic materials (e.g., wood), vegetable oils, carbohydrates (e.g., sugars), aquatic materials (e.g., algae, aquatic plants, and seaweed), and animal by-products and wastes (e.g., offal, fats, and sewage sludge).

[0008]

[0004] Biochar and other carbonized materials may be produced batchwise on a small scale or continuously on a larger scale in suitable reactors, such as kilns, drums, etc., with a substantial input of heat energy. According to a specific technique, a carbon-containing feed is charged into a rotary kiln or fluidized bed in a substantially oxygen-free environment and then heated to pyrolytically convert this feed to biochar. External heating is required to sustain the carbonization. Another production method utilizes small throughput batch reactors, such as pits, or otherwise stationary kilns or drums, into which the feed is input in the presence of limited oxygen and then ignited to cause pyrolytic conversion to charcoal or biochar. The energy from the partial combustion thereby helps to sustain the carbonization process, but product quality may be sacrificed in the absence of an additional heat supply.

[0009]

[0005] The activation of biochar or other carbonized material, to provide activated carbon having an enhanced economic value that is at least partly due to its high surface area and pore volume characteristics, may be performed according to a number of possible routes. Chemical activation, for example, may involve treatment with an acid, base, or salt. Physical activation, on the other hand, can be achieved by heating in an oxidizing environment, such as obtained in the presence of steam or carbon dioxide in a rotary kiln or fluidized bed reactor. A combination of methods may also be employed. As in the case of carbonization, activated carbon production may likewise proceed through small batch or larger scale continuous processing, with a suitably sized vessel (e.g., kiln or drum) for containing and heating the carbonized material, but in this case in an environment having at least some oxygen (e.g., 5 vol-%) or other oxidant. Exemplary temperatures of 400-600°C using Ch, or 800-1000°C using H2O and / or CO2, for activated carbon formation, may be attained through external heating by combustion of a fuel such as propane or natural gas.

[0010]

[0006] Any reduction in heat input to carbonization or activation can directionally lead to inefficiencies, such as those associated with obtaining a lower quality / higher ash content product. Both processes can also lead to the formation of significant byproducts, including toxic gases, reactive liquid products (bio-oil), and / or particulate matter as a result of thermal degradation and / or incomplete combustion. This adds to the expense, treating requirements, and overall complexity associated with the conversion of biomass and other carbon sources to activated carbon. The ail of activated carbon production, particularly from biomass materials that might otherwise have only limited alternative use / value, is continually seeking further advancements in terms of processing efficiency and flexibility, leading to improved overall economics. For example, almond residues accumulate in significant quantities at almond processing facilities, with only a fraction of these residues being typically needed to satisfy end uses such as animal feed or power generation (e.g., combustion). Stockpiles of the remaining residues provide sites of potential insect infestation. SUMMARY

[0011]

[0007] Aspects of the present disclosure relate to the discovery of methods of producing activated carbon, which address certain drawbacks encountered in the art. Methods disclosed herein, for example, may advantageously proceed through the formation of a biochar intermediate having threshold quality characteristics that render it suitable for (i) direct use, such as a soil amendment, and / or (ii) subsequent activation to activated carbon, thereby further increasing value. These characteristics, including a favorably high fixed carbon content, may be achieved in an efficient manner and often with the avoidance of certain processing steps that add complexity and expense. Such excluded steps may involve chemical treatment, according to which an intermediate biochar or subsequently-produced activated carbon is otherwise contacted with an acid or base to remove impurities and / or increase surface area. Such excluded steps may alternatively, or additionally, extend to physical alterations, such as crushing of either the biomass prior to carbonization or the biochar prior to activation, which might otherwise be necessary to meet certain particle size constraints.

[0012]

[0008] Associated with these and other improvements in process cfficicncy / simplicity, according to some embodiments, is the selection of biomass as a starting material and more particularly the type of biomass and its overall composition, for example in terms of its relative amounts of the cellulose, hemicellulose, and lignin components. Tn this regard, more particular aspects of the invention relate to the discovery of methods for producing biochar and / or activated carbon, which are facilitated as a result of using almond residues as this stalling material or feed that is input to the carbonization step. The ability to efficiently process almond residues is especially advantageous in view of the continuously increasing crops of almond nuts and large amounts of biomass residues generated in the commercial separation of the edible kernels. In the absence of upgrading, these residues might be best valued based on combustion heat. Processing improvements associated with methods described herein may reside in (i) reduced equipment and / or operating requirements to achieve desired quality characteristics of biochai' (e.g., fixed carbon content) and / or activated carbon (e.g., surface area, pore volume, and / or specific adsorption properties), and / or (ii) improved quality characteristics of these materials for a given extent of equipment and / or operating requirements. For example, a greater content of fixed carbon in biochar may be attained, thereby improving its stability for a commercial application (e.g., as a soil amendment) or for storage / transport, or otherwise rendering it more amenable to conversion to high-quality activated carbon.

[0013]

[0009] These and other advantages may be realized or even augmented, in specific embodiments, according to further selections of almond residues, in terms of the weight ratio of almond shells : almond hulls, in biomass that is subjected to carbonization to obtain biochar, which is thereafter optionally activated to obtain activated carbon. For example, such weight ratio may differ from a “natural” ratio of about 1:4, based on 0.6 kg shells : 2.5 kg hulls that arc generated per kilogram of almond kcmcl / nut meat. In some embodiments, for example, a weight ratio of almond shells : almond hulls may be unity or within a range encompassing unity, such as from about 1:2 to about 2: 1. Regardless of any particular weight ratio, important advantages associated with the processing of biomass comprising predominantly, substantially all, or all, almond shells and hulls are unexpected in view of the conventional understanding that such almond residues were problematic with respect to upgrading, due to their fibrous composition and other characteristics. Often, it was considered necessary to dilute almond residues with more easily processable types of biomass.

[0014]

[0010] Moreover, to the extent that the biochar obtained from a carbonization step, as described herein, has sufficient stability that is at least partially associated with a significant fixed carbon content, this material may be easily shipped over long distances and / or stored over long time periods. This promotes flexibility of its potential applications. For example, according to particular embodiments, steps of carbonization and activation may be performed at respective, first and second locations, between which the biochar is transported (e.g., by ship, train, or truck). Transportation distances, representing distances between which these steps arc performed, may be, for example, at least 100 km, at least 1 ,000 km, or at least 5,000 km. Representative times (e.g., transportation times and / or storage times), elapsing between these steps may be, for example, at least 1 day, at least 1 month, or at least 1 year. In some embodiments, a first portion of biochar made by a given step of carbonization may be utilized (e.g. , as a soil amendment or as a feed to a subsequent activation step) following a relatively short delay (e.g. , of less than 1 day), whereas a second portion of the biochar may be utilized (e.g., as a soil amendment or as a feed to a subsequent activation step, for example performed at a location distant from that for performing the carbonization) following a relatively long delay (e.g., of greater than 1 day).

[0011] Embodiments of the invention are directed to methods for producing activated carbon. Exemplary methods comprise: (a) a carbonization step, which includes subjecting biomass to carbonization conditions sufficient to obtain a biochar having threshold quality characteristics (e.g., a fixed carbon content of at least about 50 wt-%), and (b) an activation step, which comprises contacting the biochar with an oxidant under activation conditions that include an activation temperature greater than that used in step (a) to obtain an activated carbon having a surface area of at least about 750 square meters per gram (m2 / g). Further embodiments arc directed to the above methods for making biochar comprising step (a), to provide threshold quality characteristics of the produced biochar that are suitable for its transport from a first location at which the carbonization step is performed, to a second location for performing an activation step comprising contacting the biochar with an oxidant under activation conditions to obtain an activated carbon. Methods according to such further embodiments may therefore also comprise, subsequent to the carbonization step (a), transporting the biochar to the second location and performing activation. Yet further embodiments arc directed to the above methods for making activated carbon comprising step (b), for example under activation conditions that include an activation temperature of at least about 800°C, with the biochar being provided from subjecting biomass to carbonization conditions sufficient to obtain threshold quality characteristics suitable for transport of the biochar from a first location at which a carbonization step is performed, to a second location at which said activation step is performed. Methods according to such, yet further, embodiments may therefore also comprise, prior to the activation step (b), transporting the biochar from the first location to the second location and performing the activation step.

[0015]

[0012] Other embodiments are directed to activated carbon made by a method according to any of the above and other embodiments described herein. Still further embodiments are directed to a filter, such as a water filtration cartridge, comprising activated carbon that is made according to any of the above and other embodiments described herein.

[0016]

[0013] Yet other embodiments are directed to biochar made by a method according to a carbonization step (a) in any of the above and other embodiments described herein. Still further embodiments arc directed to fertilizer, comprising biochar that is made according to any of the above and other embodiments described herein. A representative method comprises subjecting biomass to carbonization conditions sufficient to obtain a biochar having threshold quality characteristics, including a fixed carbon content of at least about 50 wt-%, and typically at least about 70 wt-%.

[0017]

[0014] According to any of the above and other embodiments described herein, the biomass may comprise, or possibly consist of, almond residues, such as those having been separated in almond processing by removal of the edible kernel or nut, and optionally having a shell : hull weight ratio that is within a range as described herein.

[0018]

[0015] These and other aspects and embodiments relating to the invention, as well as their associated features and advantages, will be apparent from the following detailed description.

[0019] DETAILED DESCRIPTION

[0020]

[0016] As described above, a representative method for producing activated carbon comprises

[0021] (a) a carbonization step that includes subjecting biomass to carbonization conditions sufficient to obtain a biochar having threshold quality characteristics. These characteristics may impart stability for transport and / or may impart particular value for a number of applications, thereby potentially increasing flexibility in terms of how the biochar may be used. Certain applications, include the subsequent upgrading to activated carbon, or otherwise direct use, such as a fertilizer or soil amendment to increase soil nutrient density. The method may further comprise (b) an activation step that includes contacting the biochar with an oxidant under activation conditions to obtain an activated carbon having an increased surface area (e.g., at least about 750 m2 / g) relative to that of the biochar. The activation conditions generally include an activation temperature greater than that used in the carbonization step. As described above, according to more particular embodiments, the steps (a) and (b) may be performed at respective different, first and second locations, and the method may further comprise transporting the biochar obtained in step (a) from the first location to the second location. Representative distances between locations at which steps (a) and

[0022] (b) are performed, and / or times elapsing between when steps (a) and (b) are performed, are described above.

[0023]

[0017] “Biomass” refers to substances derived from organisms living above the earth’s surface or within the earth’s oceans, rivers, and / or lakes. Representative biomass can include any plant material, or mixture of plant materials, such as a hardwood (e.g., whitewood), a softwood, a hardwood or softwood bark, lignin, algae, and / or lemna (sea weeds). Energy crops, or otherwise agricultural residues (e.g., logging residues) or other types of plant wastes or plant-derived wastes, may also be used as plant materials. Specific exemplary plant materials include com fiber, corn stover, and sugar cane bagasse, in addition to “on-purpose” energy crops such as switchgrass, miscanthus, and algae. Short rotation forestry products, such as energy crops, include alder, ash, southern beech, birch, eucalyptus, poplar, willow, paper mulberry, Australian Blackwood, sycamore, and varieties of paulownia elongate. Almond residues represent a type of biomass of particular interest. Almond residues, which include almond shells and / or almond hulls, have unique characteristics in terms of ash content and / or density that pose technical challenges for their effective conversion to higher value commercial products such as biochar (e.g., for use as a fertilizer) and activated carbon (e.g., for use as a filter material).

[0024]

[0018] The biomass may be completely or substantially free of (e.g., may comprise less than about 5 wt-%, or less than about 1 wt-% of) non-biological materials (e.g.. plastics, metals, and metal oxides, including rocks and glass). In some examples, the biomass is not mechanically treated (e.g. crushed) and is carbonized in its existing form, size, and shape, without any pre-treatment, or without any pre-treatment that alters the size and / or shape of the biomass. The biomass may be, in particular embodiments, pretreated biomass (e.g., pretreated almond residues), having been subjected to one or more suitable pretreating steps, prior to use in carbonization step (a). A pretreating step may be a separation of undesired impurities, such as materials other than almond residues, or, more particularly, a separation of non-biological materials (e.g., plastics, metals, rocks, and / or glass). Mechanical separation devices for achieving such separation include those based on particle size (e.g., sieves or filters), based on gravity, centrifugation, or entrainment (e.g., cyclone separators), or based on other techniques (e.g., electrostatic precipitators). A pretreating step may alternatively, or in combination, be a biomass particle size adjustment to reduce or increase an average particle size of the biomass (e.g. , almond residues), and / or improve uniformity of this particle size (e.g., provide a narrower particle size distribution), but for the avoidance of doubt in some embodiments no such step (e.g. a palletization or solidification) occurs. For example, representative methods may comprise, prior to step (a), molding the biomass into forms, such as rectangular, cylindrical, or spherical forms, which may have at least one average dimension (e.g., average length or average diameter dimension) of greater than about 0.5 cm (e.g., from about 0.5 cm to about 10 cm), greater than about 1 cm (e.g., from about 1 cm to about 8 cm), or greater than about 2 cm (e.g., from about 2 cm to about 5 cm). In some examples, the biomass may have these sizes without any pre-treatment. In this regard, converting biomass from its initial form (which may be shells or hulls, or otherwise granules, shavings, or other smaller sized materials, into which shells and hulls are processed), may provide a pretreated form (e.g., cylinders) having favorable surface area to volume ratio characteristics for subsequent processing according to step (a) and optionally step (b) of representative methods described herein. According to a particular embodiment, molding may include pelletizing the biomass into forms, such as cylindrical forms, having such at least one average dimension, for example an average length dimension, within any of these ranges. In the case pelletizing into cylindrical forms, the average diameter of these forms may be from about 0.1 to about 20 mm, such as from about 1 mm to about 15 mm or from about 2 mm to about 10 mm. Another possible pretreating step is moisture removal from the biomass, such that exemplary methods may comprise, prior to step (a), drying the biomass to obtain a biomass moisture content of less than about 15 wt- %, and more preferably less than about 10 wt-%. Drying may be performed at ambient temperature, but drying conditions will typically include an elevated drying temperature of at least about 50°C, or possibly at least about 100°C. Drying may be aided by the use of a flowing gas, such as flowing air for convenience.

[0025]

[0019] If two or more pretreating steps, such as any two of those described above, arc used, these may be performed in any order, although overall efficiency is normally improved if the separation of impurities is performed prior to other pretreating steps (e.g. , biomass particle size adjustment and / or biomass moisture removal). According to other particular embodiments, representative processes may be simplified in the case of biomass not being subjected to one or more pretreating steps described above. For example one or both of (i) a separation of impurities as described above, and (ii) a biomass particle size adjustment as described above, may be avoided. Optionally in combination with avoiding (i) and / or (ii), a drying step may also be avoided according to yet further embodiments, depending on the moisture content of the biomass (e.g., almond residues), carbonization conditions, and threshold quality characteristics, including moisture content, of the produced biochar. Further benefits may arise with respect to producing biochar and / or activated carbon, according to embodiments in which, prior to step (a), the biomass is not chemically treated. In this regard, conventional conditioning or pretreatment steps, such as hydrolysis, acid treatment (e.g., contacting with phosphoric acid), and / or alkali treatment (e.g., contacting with calcium hydroxide) may be avoided in such embodiments.

[0026]

[0020] Preferably, the biomass comprises, consists essentially of, or consists of, almond residues. For example, almond residues may be present in the biomass in an amount of at least about 80 wt-%, at least about 90 wt-%, at least about 95 wt-%, or at least about 99 wt-%. According to other embodiments, the biomass may comprise both almond residues and rice husks in a combined amount of these weight percentages. In the case of biomass comprising any content of almond residues, these may comprise, consist essentially of, or consist of, almond shells and almond hulls. Tn some examples, the biomass consists of or and / or includes almond shell and hull material that is not mechanically processed or altered after removal of the almond, or is not mechanically processed or altered by any means that would change the size or shape of the biomass but may include ancillary processing such as filtering or separating undesired material from the biomass like non-ahnond biomass materials. In some embodiments, the biomass may have particle sizes of at least about 20 mm in one dimension, or at least about 25 mm in one dimension, or at least about 30 mm in one dimension (e.g. biomass sized at about 30x20x1.5mm for at least some biomass material), prior to carbonization given the lack of mechanical crushing or other size reduction techniques. Preferably, a weight ratio of almond shells : almond hulls in the almond residues, or in the biomass generally, may be from about 1: 10 to about 10:1, from about 1:5 to about 5: 1, from about 1 : 3 to about 3 : 1 , or from about 1 : 2 to about 2 : 1. In some embodiments , the weight ratio, or weight ratio range, of almond shells : almond hulls may exclude (z. e. , be outside of) a “natural” shell : hull weight ratio or weight ratio range that is characteristic of almonds in nature and therefore also normally obtained in residues from almond processing. Such natural ratio, which may be excluded, may be about 1 :4, or otherwise such weight ratio range, which may be excluded, may be from about 2:5 to about 1:5, or from about 1:3 to about 2:7. A weight ratio of almond shells : almond hubs, whether inclusive or exclusive of a natural ratio, may advantageously facilitate methods of making biochar and / or activated carbon as described herein, such as according to those methods in which certain conventional steps (e.g., chemical treatment) may be omitted.

[0021] The carbonization step (a), according to which biomass (e.g., almond resides, such as almond shells and almond hulls having been pelletized) is subjected to carbonization conditions, provides biochar having threshold quality characteristics. Biochar refers to the solid carbonaceous residue that remains after biomass and its components, such as cellulose, hemicellulose, and / or lignin, are thermally decomposed in an environment with little or no oxygen, for example via pyrolysis. Representative carbonization conditions include a peak or maximum temperature of generally at least about 400°C, typically at least about 500°C, and often at least about 600°C. The peak or maximum temperature is preferably less than about 800°C in any case. The average time at which the biomass is subjected to a temperature of at least about 400°C, at least about 500°C, or at least about 600°C may vary, depending on the specific type of biomass and its quality characteristics (e.g., moisture content), with representative average times being at least about 1 minute (e.g., from about 1 minute to about 300 minutes, at least about 5 minutes (e.g., from about 5 minutes to about 180 minutes), or at least about 10 minutes (e.g., from about 10 minutes to about 60 minutes), as needed to obtain threshold characteristics associated with a stable product suitable for intermediate or end uses described herein. Preferably, with respect to subjecting (or heating) biomass to the elevated temperatures described above, carbonization conditions may further include an anaerobic environment under which such temperatures are maintained. The oxygen content in such environment may be 0 vol-%, but is more generally limited to less than about 15 vol-%, typically less than about 10 vol-%, and often less than about 5 vol-%. These limited concentrations, while applicable to the concentration of O2 in particular, may likewise apply to the concentrations of other oxidants, such as to the concentration(s) of any one of more of O2, CO2, and / or H2O, alone or in combination, present in the environment to which biomass is exposed during carbonization. Processing of biomass (e.g., almond residues) by carbonization to biochar may be performed batchwise or continuously.

[0027]

[0022] An important threshold quality characteristic of biochai' provided in step (a) of representative processes described herein is its fixed carbon content, which is determined according to ASTM 3172 and refers to the amount of biochar remaining after heating to 925°C for removal of volatile matter, and also excluding from the biochar any amounts of moisture and ash (i.e., 100%-volatile matter%-moisture%- ash%). The fixed carbon content of the biochar is preferably at least about 50 wt-% and more preferably at least about 70 wt-%. Alternatively, or optionally in combination with such fixed carbon content, the ash content of the biochar is preferably less than about 25 wt-% and more preferably less than about 15 wt-%. Sufficiently high fixed carbon content and / or sufficiently low ash content can be important in terms of facilitating the subsequent production of activated carbon.

[0028]

[0023] Those skilled in the art, having knowledge of the present specification, will appreciate how carbonization conditions can impact fixed carbon content and other threshold quality characteristics, such as moisture and ash content, of the obtained biochar, given a particular type of biomass (e.g., almond residues) and its initial form and characteristics (e.g., moisture level). Such carbonization conditions include representative peak temperatures, as well as representative times at a given nominal temperature (e.g., at least about 400°C, at least about 500°C, or at least about 600°C), as described above, in addition to characteristics of a given temperature profile to which biomass is subjected, such as in terms of ramp rate, holding time, and cooling rate. Other carbonization conditions can include the RPM of rotating equipment used for the heating / carbonization of biomass in its initial form or a pretreated form as described above. Exemplary values of RPM are in a range from about 1 to about 25, such as from about 2 to about 10.

[0029]

[0024] Important aspects of the invention relate to performing carbonization step (a) with an advantageous combination of threshold biochar quality characteristics, as described herein, together with favorable performance characteristics, such as biochar yield, which combination may be specific for a particular type of biomass. For example, in the case of processing almond residues (e.g., almond shells and almond hulls having been pelletized) to obtain biochar having a favorable fixed carbon content (e.g., greater than about 50 wt-%, or greater than about 70 wt-%), the yield of such biochar is preferably at least about 15 wt-% (e.g., from about 15 wt-% to about 50 wt-%), more preferably at least about 20 wt-% (e.g., from about 20 wt-% to about 50 wt-%), and even more preferably at least about 30 wt-% (e.g., from about 30 wt-% to about 45 wt- %). The values for yield may be based on the weight of biomass input to carbonization step (a) and weight of biochar obtained (e.g., in the case of batchwise processing), or otherwise may be based on the weight flow of biomass input and weight flow of biochar obtained (e.g., in the case of continuous processing). In some embodiments, the above biochar yields may be representative of the biomass and biochar weights, or weight flows, on a moisture -free basis.

[0030]

[0025] The activation step (b), according to methods described herein, is used to obtain activated carbon, which refers to an upgraded form of carbon, having been processed (e.g., by steam activation) to have a significant pore volume. This may be, for example, generally greater than about 0.1 cubic centimeters per gram (cc / g) (e.g., from about 0.1 cc / g to about 0.2 cc / g such as about 0.13 cc / g or about 0.18 cc / g) or about 0.2 cubic centimeters per gram (cc / g) (e.g. , from about 0.2 cc / g to about 0.8 cc / g) for pores within the mesopore size range, namely those 2-50 nanometers (nm) in diameter, or about 0.2 cubic centimeters per gram (cc / g) or less, or about 0.15 to about 0.2 cubic centimeters per gram (cc / g), or about 0.05 to about 0.2 0.2 cubic centimeters per gram (cc / g). Tn some examples, pore volume may be generally greater than about 0.1 cubic centimeters per gram (cc / g) and / or greater than about 0.2 cubic centimeters per gram (cc / g) (e.g., from about 0.2 cc / g to about 0.8 cc / g or from about 0.1 -0.2 cc / g) for pores within the meso- and micro-pore size ranges, namely those of less than 50 nanometers (nm) in diameter. This combined carbon meso- and micro-pore volume may be, according to more particular embodiments, at least about 0.1 cc / g, at least about 0.2 cc / g, at least about 0.3 cc / g, or at least about 0.4 cc / g (e.g., from about 0.4 cc / g to about 0.7 cc / g). The pore volume of activated carbon, as well as that of biochar, are based on the Barrett, Joyner, and Halenda (BJH) method, determined according to ASTM D5160. The increased pore volume, due to activation, results in a high surface area, which renders the activated carbon suitable for a large number of adsorption and reactive adsorption applications, particularly in the fields of liquid and gas purification, for example in the processing of municipal drinking water as well as foods and beverages, odor removal, industrial pollution control, and filters for home use. In representative embodiments, activated carbon produced by methods described herein may have a surface area of greater than about 800 square meters per gram (m2 / g), as is favorable for air treatment (e.g., moisture and / or odor removal), and preferably greater than about 950 m2 / g, as is favorable for tap water and waste water treatment. The surface area of activated carbon, as well as that of biochar, are based on the Brunauer-Emmett-Teller (BET) method, determined by nitrogen adsorption according to ASTM D1993-03(2008).

[0031]

[0026] Further embodiments of the invention in this regard are directed to upgrading of biochar, for example obtained from performing carbonization step (a) as described above, to activated carbon. Analogous to pretreating steps described above, which may be performed to alter properties of biomass prior to step (a), representative methods may comprise, prior to step (b), adjusting a particle size of the biochar and / or removing moisture from the biochar. Tn general, physical and / or chemical properties may be altered by one or more of the following, intermediate treatment steps subsequent to step (a) and prior to step (b): (al) sizing, such as to reduce average particle size, for example to obtain an average biochai' particle size of less than about 10 mm, less than about 5 mm, or even less than about 2 mm; (a2) chemical treatment, including alkali treatment, such as to reduce biochar carbonization residue content and / or silica content, for example to obtain a content, of one or both of these (independently or in combination), of less than about 5 wt-%, less than about 1 wt-%, or even less than about 0.5 wt-%; and / or (a3) drying to reduce biochar moisture content, for example to obtain a biochar moisture content of less than about 10 wt-%, less than about 5 wt-%, or even less than about 2 wt-%. In the case of sizing to reduce biochar average particle size, in specific embodiments this may be achieved, for example, by ball milling, roll milling, or crushing. In the case of chemical treatment to reduce biochar carbonization residue and / or silica content, this may be achieved by contacting or extraction with a suitable agent (an acid or, in the case of alkali treatment, a base) to preferentially remove (e.g., dissolve) unwanted impurities. Alternatively to, or in addition to, silica, these impurities may include hydrocarbon or oxygenated hydrocarbon species (e.g. , phenols), or possibly other volatile and / or preferentially soluble materials. In the case of drying to reduce biochar moisture content, this may be achieved, for example as described above with respect to associated temperatures and the optional use of flowing gas.

[0032]

[0027] According to other particular embodiments, representative methods may be simplified in the case of biochar not being subjected to one or more of these intermediate treatment steps and / or, more generally, not being subjected to one or more conventional intermediate treatment steps. That is, upgrading or activation step (b) may advantageously be performed, in some cases, without (i.e., excluding) certain conventional, intermediate treatment steps used to prepare biochar for processing by activation. For example, according to certain embodiments, prior to step (b), the biochar is not chemically treated (e.g., is not subjected to alkali treatment), such that intermediate treatment step (a2) above, namely chemical treatment, including alkali treatment, may be avoided. In view of this and the foregoing description, some embodiments are therefore directed to methods that may be simplified or streamlined insofar as the use of chemicals (e.g., acids and / or bases) may be avoided in both the pretreatment of biomass and the intermediate treatment of biochar. In particular embodiments, biomass pretreatment steps and biochar intermediate treatment steps may be limited to particle size adjustment / sizing steps and / or drying steps as described above. In more particular embodiments, even these steps may be eliminated, such that no pretreatment or intermediate treatment steps are performed, with the possible exception of separating undcsircd impurities, for example non-biological materials.

[0033] 128] Some embodiments of the invention are therefore directed to upgrading biochar to activated carbon, according to an activation step (b) as described herein, optionally without the need for at least some of the material (e.g., chemical), utility (e.g., dryer heat), and / or capital (e.g., grinder / pulverizer) requirements of conventional methods. Activation may be performed in the same vessel as used for the carbonization step (a), although, as described above, the steps (a) and (b) may be performed in separate locations and consequently use separate vessels. For example, biochar obtained in step (a) may be introduced into a separate steam activation vessel, such as by feeding it into a bed of biochar particles contained in this vessel and being fluidized with hot steam, as a fluidizing activation gas.

[0034]

[0029] In general, activation step (b) comprises contacting biochar (e.g., obtained according to a carbonization step (a)) with an oxidant under activation conditions, which may include an activation temperature that exceeds a peak or maximum temperature used for carbonization. A representative oxidant for contacting in step (b) is steam (H2O), oxygen (O2), or carbon dioxide (CO2), or possibly any combination of these. The oxidant(s) can be used for upgrading biochar, having a relatively low surface area (e.g., generally less than about 500 m2 / g, and more typically less than about 400 m2 / g), to activated carbon, having a representative surface area of at least about 750 m2 / g (e.g., from about 750 m2 / g to about 1750 m2 / g), preferably at least about 800 m2 / g (e.g., from about 800 m2 / g to about 1750 m2 / g) and more preferably at least about 950 m2 / g (e.g., from about 950 m2 / g to about 1750 m2 / g), with higher surface areas being amenable to air and water treatment applications for the activated carbon, as described above. Such surface area levels may advantageously be combined with other desirable properties of the activated carbon for commercial use, including (i) an iodine number (or iodine adsorptive value), determined according to ASTM D4607- 14(2021), of at least about 500 mg / g (e.g., from about 500 mg / g to about 1000 mg / g), preferably at least about 650 mg / g (e.g., from about 650 mg / g to about 1000 mg / g), and more preferably at least about 800 mg / g (e.g., from about 800 mg / g to about 1000 mg / g) and / or (ii) a methylene blue adsorption, determined according to ASTM C1777-20, of at least about 150 mg / g (e.g., from about 150 mg / g to about 350 mg / g), preferably at least about 175 mg / g (e.g., from about 175 mg / g to about 350 mg / g), and more preferably at least about 225 mg / g (e.g., from about 225 mg / g to about 350 mg / g). Significantly, the iodine number provides a measure of the microporc content of activated carbon (e.g. , pore sizes of up to 2 nm) by adsorption of iodine from solution. This characteristic represents, more specifically, the milligrams of iodine adsorbed per gram of activated carbon when iodine in the residual filtrate has a concentration of 0.02N.

[0035]

[0030] As in the case of performing carbonization step (a), important aspects of the invention likewise relate to performing activation step (b) to obtain advantageous quality characteristics of activated carbon, such as any one or more of those characteristics described above (e.g., surface area, iodine number, and / or methylene blue adsorption, within any of the ranges given above), in combination with favorable performance characteristics, such as activated carbon yield. The combination may be specific for a particular type of biochar and / or particular type of biomass used to obtain the biochar. For example, in the case of processing biochar obtained from almond residues (e.g., almond shells and almond hulls having been pelletized) to provide activated carbon having any one or more of the quality characteristics described herein, the yield of such activated carbon is preferably at least about 20 wt-% (e.g., from about 20 wt-% to about 70 wt-%), more preferably at least about 30 wt-% (e.g., from about 30 wt-% to about 70 wt-%), and even more preferably at least about 50 wt-% (e.g., from about 50 wt-% to about 70 wt-%). The values for yield may be based on the weight of biochar input to activation step (b) and weight of activated carbon obtained (e.g., in the case of batchwise processing), or otherwise may be based on the weight flow of biochar input and weight flow of activated carbon obtained (e.g., in the case of continuous processing). In some embodiments, these activated carbon yields may be representative of the biochar and activated carbon weights, or weight flows, on a moisture-free basis. An overall yield of activated carbon obtained from step (b), on the basis of biomass input to carbonization step (a), and determined as described above with respect to yields for these individual steps, is preferably at least about 8 wt-%, more preferably at least about 12 wt-% and even more preferably at least about 25 wt-%. Insofar as the activated carbon is obtained from biomass, this end product may be further characterized as renewable activated carbon.

[0036]

[0031] In the particular case of an oxidant comprising steam (H2O), the upgrading of biochar to activated carbon, according to activation step (b) of representative methods, may be accomplished by subjecting the biochar to activation conditions, and in this case steam activation conditions, of sufficient residence time and temperature to effect the desired transformations, including significant increases in both porosity and surface area. In this case, activation conditions may include a steam pressure, or H2O partial pressure, from about 0.1 MPa to about 1 MPa, such as from about 0.1 MPa to about 0.3 MPa. Following its removal from the steam activation vessel and separation from the activation effluent gas, the activated carbon product may be cooled and passivated to an extent that allows for its contact with air. Other modifications to the active sites of the end product, such as impregnation with inorganic alkaline materials, may also be performed. In any event, the surface area of the activated carbon may be within ranges as described above, with the resulting value being influenced by the severity of the steam activation conditions.

[0037]

[0032] Regardless of the particular oxidant(s) used, activation conditions include a suitable temperature and residence time to yield highly porous, high surface area activated carbon. Representative activation temperatures, or otherwise peak or maximum temperatures used in the environment to which biochai' is subjected during activation step (b), arc generally at least about 600°C (e.g., from about 600°C to about 1200°C), typically least about 800°C (e.g., from about 800°C to about 1200°C and often at least about 1000°C e.g., from about 1000°C to about 1200°C). Representative activation residence times, or times for which biochar is maintained under a temperature within any of these minimum values or ranges, are generally at least about 15 minutes (e.g., from about 15 minutes to about 10 hours), typically at least about 30 minutes (e.g. , from about 30 minutes to about 5 hours), and often at least about 1 hour (e.g., from about 1 hour to about 4 hours).

[0038]

[0033] While fluidized beds may be utilized to promote uniform temperatures and flow distribution, activation (e.g. , steam activation) may also be performed with a fixed bed of biochar or using any suitable apparatus and configuration for carrying out gas-solid contacting. Activation (e.g., steam activation) may be performed batchwise, for example, with the continuous input and withdrawal of oxidant-containing (e.g., steamcontaining) activation gas and the batchwise input of solid biochar and batchwise withdrawal of activated carbon, such that the biochar / gas contacting time (or time between the input and withdrawal of the batches of solid particles) is according to the residence times described above. In the case of steam activation being performed batchwise, a flow rate of steam-containing activation gas, or otherwise a flow rate of steam (e.g., a flow rate of H2O), may be from about 0.1 kg / hr to about 10 kg / hr, such as from about 0.3 kg / hr to about 3 kg / hr, per kg of biochar being activated. That is, a weight hourly space velocity (WHSV) based on steam flow may be from about 0.1 hr 1 to about 10 hr1, such as from about 0.3 hr1to about 3 hr1. According to other embodiments, activation may be performed continuously, for example, with the continuous input and withdrawal of both gases and solids, such that the average the char / gas contacting time is according to the residence times described above. Regardless of whether batchwise or continuous contacting of biochar with oxidant is utilized, physiochcmical activating agents may be added during activation to increase activity of the resulting product and / or introduce desired chemical functional groups. Representative activating agents include alkali and alkaline earth metal hydroxides, organic amines, chlorides (including hydrochloric acid), nitrates (including nitric acid), and sulfates (including sulfuric acid).

[0039]

[0034] Other embodiments of the invention relate to processes for producing activated carbon, which benefit from important properties of biochai' that is in particular derived from almond residues e.g., having a weight ratio of almond shells : almond hulls as described above). For example, biochar derived from almond residues is superior in many respects to coal as a starting material for producing activated carbon, both in terms of its overall quality and in terms of its environmental impact. Even in comparison to biochar, and activated carbon, derived from other types of biomass (e.g., rice husks, coconut shells, chestnut shells, peanut shells, sunflower seeds, walnut shells, spent coffee grounds, cocoa, hazelnut shells, palm kernel shells) respective biochai' and / or activated carbon derived from almond residues may benefit from improved characteristics (e.g., surface area), or combinations of characteristics (e.g., surface area and ash content), including those having values within any of the ranges as described herein.

[0035] Biochar from almond residues represents a significantly “cleaner” starting material for activated carbon production, compared to coal. In fact, common impurities in mined carbon sources are not only detrimental to the performance of activated carbon (e.g., in terms of its adsorptive capacity), but also pose environmental and health concerns associated with their disposal. Depending on its source, coal may contain total, combined amounts of mercury (Hg), selenium (Se), beryllium (Be), cadmium (Cd), arsenic (As), and chromium (Cr) of 25 parts per million by weight (wt-ppm) or more. In contrast, biochar and activated carbon produced therefrom generally have a total content of these elements of less than about 5 wt-ppm, typically less than about 1 wt- ppm, and often less than about 0.5 wt-ppm. With respect to mercury, which poses significant health concerns associated with the combustion of coal, biochar and activated carbon produced therefrom generally have a total content of this element of less than about 10 parts per billion by weight (wt-ppb), and typically less than about 5 wt-ppb. This is in contrast to a typical mercury content of about 100 wt-ppb for coal. Amounts of these trace elements may be determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), according to ASTM D5600-09.

[0040]

[0036] The ash content of a solid combustible material refers to the percentage by weight of a sample of such material that does not combust at a temperature of 650°C. The ash content may be determined by a straightforward combustion method, for example ASTM D2866-ll(2018), in which the sample is burned thoroughly under specified conditions, and the yield of the resulting, non-combustible ash is expressed as a percentage of the original weight. In the case of coal, a typical range with respect to its ash content is 5-25% by weight (wt-%), whereas biochar derived from almond residues, as well as activated carbon produced therefrom, may have an ash content of generally less than about 15 wt-% and typically less than about 10 wt-%. Likewise, volatile matter of a solid combustible material may be measured according to ASTM D5832- 98(2021), for determining the percentage of volatile products, exclusive of moisture vapor, released during heating of the material under rigidly controlled conditions. This method is used as a basis for the classification of various coal types. Advantageously, biochar derived from almond residues may have a typical range of volatile products of less than about 10 wt-%, and often less than about 5 wt-%. Again, this contrasts sharply with coal, having significantly higher amounts of volatile products.

[0037] Further advantages arise from the scalability of methods described herein, in terms of commercially producing biochar and activated carbon with favorable product quality and / or performance characteristics as described herein, and preferably a combination of these characteristics. For example, the methods may be used for the processing almond residues or other biomass, and / or for the production of biochai' and / or activated carbon, on a scale of at least 100 kg (or at least 100 kg / day) of any of these starting materials, intermediates, or end products, for example over the course of a single production run. Preferably this scale is at least 1 metric ton (or at least 1 metric ton / day), more preferably at least 10 metric tons (or at least 10 metric tons / day), and even more preferably at least 100 metric tons (or at least 100 metric tons / day).

[0041]

[0038] Finally, as described above, all or substantially all of the carbon in biochar, in addition to the carbon of activated carbon made therefrom, is renewable carbon (e.g.. derived from biomass). This beneficially reduces the carbon footprint associated with activated carbon production, according to methods described herein.

[0042] EXAMPLES

[0043]

[0039] The following examples arc set forth as representative of certain aspects and advantages relating to the present disclosure. These examples are not to be construed as limiting the scope of the invention, as other equivalent embodiments will be apparent in view of the present disclosure and appended claims.

[0044]

[0040] Activated carbon was produced from almond residues, and in particular from a combination of almond shells and hulls, according to a method as described herein and including (a) a carbonization step of subjecting the almond residues to carbonization conditions sufficient to obtain biochar, and (b) an activation step of contacting the biochar with steam under activation conditions to obtain the activated carbon.

[0045]

[0041] According to one experiment, carbonized material, or biochar, from almond residues was activated in a small (5kg-level) pilot furnace using the following steps: (1) heating the furnace, containing the biochar, to 950°C, (2) increasing steam pressure to 0.3 MPa, (3) adjusting steam flow rate to about 3.5 kg / hr, to conduct steam for activation for 20 min. The activated carbon product yield was 0.7 kg, or 14% of the original 5 kg of biomass (raw almond material).

[0046]

[0042] Another particular method involved molding (e.g. , pelletizing) almond residues prior to carbonization. The obtained biochar was then subjected to crushing / sizing. For example, ball milling, hammer crushing, and rolling milling could be used to obtain respective average particle sizes of <5 mm, <10 mm, and <4 mm. Subsequently, alkali treatment was used to remove silica to <5 wt-%, as well as remove ignition residue from the biochar. This was followed by drying and then activation in rotary kiln or fluidized bed furnace. Surface area (BET) before activation was 360 m2 / g, compared to 1002 nr / g after activation. Mesopore volume (BJH) increased from 0.15 cm3 / g before activation, to 0.34 cmVg after activation. In a separate experiment, surface area increased from 400-500 m2 / g before activation, to 1000+ / -200 m2 / g after activation, and mesopore volume after activation was 0.50+ / -0.20 cm3 / g.

[0047]

[0043] Relevant properties / characteristics of activated carbon products were determined, and exemplary values obtained from larger-scale operations are provided in the following table, with the understanding that these individual properties / characteristics may be obtained in isolation, or in any combination, according to various embodiments:

[0048]

[0044] In some examples, the biochar and / or activated carbon has a density of about 0.1 g / ml or less, or about 0.15 g / ml or less, a particle size of about 50 microns or less (in an amount of at least 90% of the total material) or a particle size of about 75 microns or less (in an amount of at least 99.8% of the total material), a surface area of at least about 700 m2 / g, at least about 900 m2 / g, at least about 1100 m2 / g, at least about 1300 m2 / g, at least about 1400 m2 / g, or about 700 m2 / g or less, about 900 m2 / g or less, about 1100 m2 / g or less, about 1300 or less, m2 / g about 1400 or less (or bracketed with any of these values, e.g. about 700-1400 m2 / g). A mass production, on a commercial scale, of biochai- and then activated carbon from 100% almond residues (shells and hulls) was performed. The biochar obtained from this biomass, at 21% yield, was determined to have a fixed carbon content of 71.1 wt-%, 12.74 wt-% ash, and 11 wt-% moisture. A higher fixed carbon content could be obtained by increasing the carbonization peak temperature from 500°C to 600°C w th a slower rpm of 4-5 RPM / 22 minutes. In addition, it was determined that higher quality biochar, in terms of its fixed carbon content, normally required some sacrifice in terms of yield. The biochar, in turn, could be further processed into activated carbon with an iodine number of 954 mg / g, indicative of a high surface area, and 50% yield. This test established that premium iodine number / surface area characteristics, as required for a number of commercial applications, could be achieved. From 100% almond shells and hulls, activated carbon with the following characteristics could be obtained: iodine number >960 mg / g; methylene blue adsorption >175 mg / g; moisture = 9.5 wt-%, reduced to 5 wt-% after drying for 1 day, with 25 wt-% overall yield. A biochar to activated carbon yield of 50-60 wt-% could attained, with higher quality product (e.g., in terms of surface area) generally correlating with lower yields.

[0049]

[0045] The above results demonstrate that methods described herein are effective for producing activated carbon from almond residues with favorable properties / characteristics, which may exceed those of activated carbon from petroleum- derived materials (e.g., coal), or even derived from other biomass types. The above results are representative of activated carbon produced from both granular / natural forms of almond hulls and shells, as well as pelletized forms. Typical surface areas obtained were about 1,600 m2 / g. For comparative purposes, activated carbon made in the same manner from rice husks alone, as well as other biomass types, had a lower surface area and decreased absorptive properties.

[0050]

[0046] Overall, embodiments of the invention relate to methods for activated carbon production from biomass, with particular methods utilizing almond residues as a stalling material. Certain aspects are associated with the advantages gained from these methods, in terms of operational performance, intermediate and end product properties, environmental impact, and economic attractiveness. Those having skill in the art, with the knowledge gained from the present disclosure, will recognize that various changes can be made to these methods in attaining these and other advantages, without departing from the scope of the present disclosure. As such, it should be understood that particular features described herein are susceptible to modification, alteration, changes, or substitution without departing from the scope of this disclosure. The specific embodiments illustrated and described herein arc for illustrative purposes only, and not limiting of the invention as set forth in the appended claims.

Claims

1. WHAT IS CLAIMED IS:1 . A method for producing activated carbon, the method comprising:(a) subjecting biomass to carbonization conditions sufficient to obtain a biochar having threshold quality characteristics, and(b) contacting the biochar with an oxidant under activation conditions that include an activation temperature greater than that used in step (a) to obtain an activated carbon having a surface area of at least about 750 square meters per gram (m2 / g), wherein the biomass comprises almond residues that include almond shells and almond husks, and wherein a weight ratio of almond shells : almond hulls in the biomass is from about 1:2 to about 2: 1.

2. The method of claim 1 , wherein steps (a) and (b) are performed at first and second locations, respectively, the method further comprising transporting the biochar obtained in step (a) from the first location to the second location, prior to step (b).

3. The method of claim 1 or claim 2, wherein the threshold quality characteristics include a fixed carbon content of at least about 50 wt-%.

4. The method of any one of claims 1 to 3, wherein the carbonization conditions include a peak temperature of a least about 500°C for a time from about 10 to about 60 minutes.

5. The method of any one of claims 1 to 4, wherein the carbonization conditions include an anaerobic environment.

6. The method of any one of claims 1 to 5, wherein the oxidant in step (b) is H?O, O2, or CO2.

7. The method of claim 6, wherein the oxidant is H2O and the activation conditions further include a steam pressure from about 0.1 MPa to about 0.3 MPa and a steam flow rate from about 0.3 kg / hr to about 3 kg / hr, per kg of biochar.

8. The method of any one of claims 1 to 7, wherein the activation temperature is at least about 800°C.

9. The method of any one of claims 1 to 8, wherein a biochar yield in step (a), based on a weight or a weight flow of the biomass, is from about 20 wt-% to about 50 wt-%.

10. The method of any one of claims 1 to 9, wherein an activated carbon yield in step (b), based on a weight or a weight flow of the biochar, is from about 30 wt-% to about 70 wt-%.

11. The method of any one of claims 1 to 10, further comprising, prior to step (a), drying the biomass to obtain a biomass moisture content of about 15 wt-% or less.

12. The method of any one of claims 1 to 11, further comprising, prior to step (a), pelletizing the biomass into forms having at least one dimension of greater than about 1 cm.

13. The method of any one of claims 1 to 12, further comprising, prior to step (b), altering physical and / or chemical properties of the biochar by one or more of (al) sizing to obtain an average biochar particle size of less than about 10 mm, (a2) alkali treatment to obtain a biochar carbonization residue and / or silica content of less than about 5 wt-%, and / or (a3) drying to obtain a biochar moisture content of less than about 10 wt-%.

14. The method of any one of claims 1 to 13, wherein, prior to step (a), the biomass is not chemically treated and / or prior to step (b), the biochar is not chemically treated.1 . The method of any one of claims 1 to 14, wherein the surface area is greater than 950 m2 / g, wherein the activated carbon has an iodine number of at least about 500 mg / g, and / or wherein the activated carbon has a methylene blue adsorption of at least about 175 mg / g.

16. A method for producing activated carbon, the method comprising, in a carbonization step, subjecting biomass to carbonization conditions sufficient to obtain a biochar having threshold quality characteristics, wherein said threshold quality characteristics are suitable for transport of the biochar from a first location at which said carbonization step is performed, to a second location for performing an activation step comprising contacting the biochar with an oxidant under activation conditions to obtain an activated carbon, wherein the biomass comprises almond residues that include almond shells and almond husks, and wherein a weight ratio of almond shells : almond hulls in the biomass is from about 1:2 to about 2: 1.

17. A method for producing activated carbon, the method comprising, in an activation step, contacting a biochar with an oxidant under activation conditions that include an activationtemperature of at least about 800°C to obtain an activated carbon having a surface area of at least about 750 square meters per gram (m2 / g), wherein said biochar is provided from subjecting biomass to carbonization conditions sufficient to obtain threshold quality characteristics suitable for transport of the biochar from a first location at which a carbonization step is performed, to a second location at which said activation step is performed, wherein the biomass comprises almond residues that include almond shells and almond husks, and wherein a weight ratio of almond shells : almond hulls in the biomass is from about 1:2 to about 2: 1.

18. Activated carbon made by the method of any one of claims 1 to 19.

19. Biochar made by a method comprising subjecting biomass to carbonization conditions sufficient to obtain a biochar having threshold quality characteristics, including a fixed carbon content of at least about 50 wt-%, wherein the biomass comprises almond residues that include almond shells and almond husks, and wherein a weight ratio of almond shells : almond hulls in the biomass is from about 1:2 to about 2: 1.

20. The biochar of claim 19, wherein the fixed carbon content is at least about 70 wt-%.

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