WO2014152291A1 - Carboxylated biochar compositions and methods of making and using the same - Google Patents

Abstract

Described herein are carboxylated biochar compositions and methods for creating advanced biochar materials with higher cation exchange capacity and free of potential toxic components for use as filtration materials and as biochar soil amendment and carbon sequestration agent to help control climate change for energy and environmental sustainability on Earth.

Description

CARBOXYLATED BIOCHAR COMPOSITIONS AND METHODS OF MAKING AND

USING THE SAME

CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority upon U.S. provisional application Serial No.

61 /781 ,080, filed March 14, 2013. This application is hereby incorporated by reference in its entirety for all of its teachings.

FIELD OF THE INVENTION

Described herein are carboxylated biochar compositions and methods for creating advanced biochar materials with higher cation exchange capacity and free of potential toxic components for use as filtration materials and as biochar soil amendment and carbon sequestration agent to help control climate change for energy and environmental sustainability on Earth.

BACKGROUND Smokeless biomass pyrolysis with utilization of biochar as a soil amendment is a potentially significant approach for renewable energy production and for carbon sequestration at giga tons of carbon (GtC) scales. Referring to Fig. 1 , this approach was co-initiated by Danny Day of Eprida Inc. and the inventor of the present invention (see WO 2004037747). This approach has received some recognition worldwide,¹'²'³'⁴'⁵ especially since certain biochar-related soil research results have also indicated the possibility of using biochar as a soil amendment for carbon sequestration.⁶'⁷'⁸'⁹'¹⁰ Recently, the approach of biochar soil application has been discussed at the United Nations Framework Convention on Climate Change (UNFCCC) for possible consideration as a potential climate mitigation technology in accounting carbon credit (International Biochar Initiative).

The central idea⁵'¹¹ is that biochar (Fig. 2, left), if produced cleanly and sustainably by pyrolysis of biomass wastes and used as a soil amendment, would "lock up" biomass carbon in a form that can persist in soils for hundreds to thousands of years; and at the same time, help to retain nutrients in soils and reduce the runoff of agricultural chemicals.

The capacity of carbon sequestration by application of biochar fertilizer in soils could be quite significant since the technology could potentially be applied in many land areas including croplands, grasslands and also a fraction of forest lands. The maximum capacity of carbon sequestration through biochar soil amendment in croplands alone is estimated to be about 428 GtC for the world.¹⁰ This capacity is estimated according to: (a) the maximal amount of biochar carbon that could be cumulatively placed into soil while still beneficial to soil environment and plant growth; and (b) the arable land area that the technology could potentially be applied through biochar agricultural practice. Globally, each year about 6.6 gigatons (Gt) of dry matter waste biomass¹² (e.g., crop stovers, dead leaves, waste woods, and rice straws) are produced. Deployment of an advanced biomass pyrolysis technology could turn this type of waste into valuable biochar, bio-syngas, and biofuel products in a distributed manner. Worldwide, this approach could result in a net reduction of greenhouse-gas emissions by about 1 .8 Gt of C0₂-C equivalent emissions per year, which is about 12% of the current global anthropogenic emissions.¹³ Advanced biomass pyrolysis coupled with biochar soil amendment is unique among carbon sequestration strategies in that it can simultaneously offset gigatons of C0₂ emissions and build sustainability into agricultural systems. This is a unique "carbon-negative" bioenergy system approach, which on a life-cycle basis could not only reduce but also reverse human effects on climate change.¹⁰

More scientific and technological development is needed before this approach can be considered for widespread commercial implementation. For example, a new generation of high-tech biochar materials with higher cation change capacity¹⁴'¹⁵ to retain soil nutrients is needed to serve as an effective soil amendment and carbon sequestration agent. Furthermore, biochar occasionally shows inhibitory effects on plant growth.¹⁶'¹⁷'¹⁸ Organic species including possibly inhibitory and benign (or stimulatory) chemicals¹⁹'²⁰ are produced as part of the biomass pyrolysis process.²¹'²² A number of organic compounds belonging to various chemical classes, including n-alkanoic acids, hydroxyl and acetoxy acids, benzoic acids, diols, triols, and phenols were recently identified in organic solvent extracts of biochar. Some of these biochar chemicals, including polycyclic aromatic hydrocarbons (PAHs), are potentially phytotoxic or biocidal, especially at high concentrations. More recently, using the techniques of electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) with Kendrick mass defect analysis, it has also been determined that the most likely biochar toxin species contain carboxyl and hydroxyl homologous series and that the phytotoxicity of biochar substances is most likely due to degraded lignin-like species rich in oxygen containing functionalities,²⁴ which is also part of the PAHs type of organic molecules. In addition, certain PAHs are suspected carcinogens.²⁵'²⁶'²⁷'²⁸ If biochar were to be globally used as a soil amendment and carbon sequestration agent at GtC scales, the release of potentially toxic compounds into soil and associated hydrologic systems might have unpredictable negative consequences in the environment. Therefore, it is essential to address some of these undesirable effects in order for biochar to be used as a soil amendment and carbon sequestration agent at gigaton scales. Any new technology that could produce an advanced biochar product that has high cation exchange capacity without any undesirable side effects would be highly desirable for this major mission of using biochar soil carbon sequestration to control climate change towards sustainability on Earth. SUMMARY OF THE INVENTION

Described herein are methods that innovatively apply a series of carbon dioxide- enhanced carboxylation and cleaning processes to create a new generation of clean carboxylated biochar materials with higher cation exchange capacity and free of undesirable potential toxic components, which represents a major technology improvement in this arena.

In one of the various embodiments, described herein are methods for producing a carboxylated biochar material possessing a higher cation-exchanging property. The cation-exchanging ability of a biochar is known to be predominantly dependent on the density of cation-exchanging groups mainly carboxyl (-COOH) groups in the biochar.

In another embodiment, a biochar source is reacted with an injected carboxylating (or decarboxylation-suppressing) C0₂ stream in a controlled manner such that the biochar source homogeneously acquires carboxy-containing cation-exchanging groups in a thermochemical biomass carbonization process that preferably retains carboxyl group on biochar surfaces. According to another embodiment, an increased C0₂ partial pressure, in a range from 0.15 to 300 atm through injection of a C0₂ stream suppresses the decarboxylation of the biochar materials during the biomass pyrolysis process, so that the biochar product will retain more carboxyl groups (thus higher cation exchange capacity).

In another embodiment, the said use of increased C0₂ partial pressure is realized by retaining the C0₂ gas generated in a thermochemical biomass carbonization in a sealed pressure-resistant reactor with fixed volume resulting in a thermo-physically auto-pressurized biomass pyrolysis process for production of biochar with higher cation exchange capacity.

According to yet another embodiment, the injection of C0₂-containing gas stream is performed preferably with nearly 100% or above 15% of C0₂ under 1 to 300 atmospheric (atm) pressure(s). The increased partial pressure of C0₂ through injected C0₂ stream can also lead to carboxylation of the biochar materials in some extent during the biomass pyrolysis, for example, by insertion of C0₂ into the C-H bonds of biochar materials. According to another embodiment, a catalyst can be used to enhance the insertion of C0₂ into the C-H bonds of biochar materials to produce carboxyl groups. In one aspect, the catalyst can be coated onto the surfaces of the reactor walls and mixing devices such as mixing balls and beads that will be in contact with biochar materials to facilitate the C0₂-driven carboxylation reaction for implantation of C0₂ into biochar materials for higher cation exchange capacity.

According to one of the various embodiments, the presence of the catalyst can facilitate the removal of potential biochar toxins through molecular structural destruction by the catalyst-assisted insertion of C0₂ into the C-H bonds of the toxic organic molecules including the phenolic-type phytotoxins and polycyclic aromatic hydrocarbons (PAHs). Therefore, the removal of potential biochar toxins and the carboxylation of biochar materials are accomplished simultaneously by the catalyst-enabled insertion of C0₂ into the C-H bonds of biochar materials and also into the C-H bonds of the potentially toxic organic molecules including polycyclic aromatic hydrocarbons (PAHs) so that the cation exchange capacity of biochar materials is enhanced and the potential biochar toxins are removed by molecular structural destruction through the catalytic C0₂ molecular implantation.

According to one of the various embodiment, the injected C0₂ stream is used also to purge the biochar materials in the catalyst-coated pyrolysis reactor so that the small organic molecules (typically at a molecular mass of about 500 Dalton or smaller) will be effectively removed from the biochar products and exit as part of the pyrolysis vapors that can be harvested for biofuel production. Therefore, the injection of C0₂ stream can be employed with the carboxylation catalyst to produce biochar materials with higher cation exchange capacity and free of biochar toxin. In one embodiment, the biochar source is treated with catalytic C0₂ plasma for

"C0₂-implantation" on the surfaces of the biochar materials. Preferably, the C0₂ plasma employed in one of the various embodiments is a type of low temperature plasma. Generally, the plasma process entails subjecting the biochar at reduced pressure to a source of ionized carbon dioxide or carbon dioxide radicals. The introduction of C0₂ into the biochar materials by a C0₂ plasma treatment increases the carboxylation or the 0:C ratios of these materials. The cation exchange capacity increases with the 0:C ratio of the biochar materials. The method includes C0₂ plasma treatment that improves cation exchange capacity by enhanced "carboxylation" of the biochar materials. Accordingly, use of relatively cold gas plasma can facilitate molecular re-engineering of biochar materials to impart unique surface properties such as the cation exchange capacity, without affecting the bulk properties of the biochar.

According to one of the various embodiments, carbon monoxide (CO) plasma can also be used to modify biochar carbon surfaces. For example, the treatment of carbon materials with carbon monoxide (CO) atmospheric plasma can result in tailorable surface O/C ratios as high as about 0.70:1 . According to another embodiment, the plasma-enabled CO and/or CO₂ molecular implantation process can be used also as a mechanism to remove potential biochar toxins by molecular structural destruction through the plasma-assisted implantation of CO and/or CO2 into the toxic organic molecules such as the phenolic- type phytotoxins and polycyclic aromatic hydrocarbons (PAHs). Therefore, the removal of potential biochar toxins and the enhancement of biochar cation exchange capacity are accomplished simultaneously through the use of catalytic carbon dioxide (CO₂) plasma and/or carbon monoxide (CO) plasma implanting CO₂ and/or CO into both the biochar materials and the toxic organic molecules including polycyclic aromatic hydrocarbons (PAHs) so that the cation exchange capacity of biochar materials is enhanced and the potential biochar toxins are removed by molecular structural destruction through the plasma-assisted molecular implantation of CO₂ and/or CO.

Finally, described herein are carboxylated biochar compositions having a particular, exceptional, or optimal set of characteristics, such as an optimal carboxyl contents, or optimal oxygen-to-carbon molar ratio, enhanced cation exchange capacity, surface area, composition, zero toxin content, and/or uniformity in any of these or other characteristics. The methods disclosed hereinare particularly suitable for producing these types of advanced biochar products with higher cation exchange capacity and free of potential toxic components, which can be used in many practical applications such as the use of the carboxylated biochars as filtration materials and as a biochar soil amendment and carbon sequestration agent.

The advantages of the materials, methods, and devices described herein will be set forth - in part in the description that follows - or may be learned by practice of the aspects described below. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive. BRIEF DESCRIPTION OF FIGURES

Fig. 1 shows the global carbon cycle and envisioned "carbon-negative" biomass- pyrolysis energy technology concept for biofuel and biochar production, and carbon dioxide capture and sequestration. Fig. 2 are photographs showing, from left to right, 10g biochar from pyrolysis of cornstover, 10g soil, and 10g mixture of biochar (10% W) and soil (90% W). The soil sample shown here is a surface soil from 0-15 cm deep at the University of Tennessee's Research and Education Center, Milan, Tennessee, USA (358560N latitude, 888430W longitude), which is also known as the Carbon Sequestration in Terrestrial Ecosystems site (CSiTE) supported by the U.S. Department of Energy.

Fig. 3 shows the application of C0₂ injection during biomass pyrolysis for production of biochar materials with higher cation exchange capacity.

Fig. 4 shows the application of C0₂ injection and carboxylation catalyst for production of biochar materials with higher cation exchange capacity and free of biochar toxin.

Fig. 5 shows the application of C0₂/water steam injection and carboxylation catalyst for production of biochar materials with higher cation exchange capacity and free of biochar toxin.

Fig. 6 shows the application of catalytic C0₂ plasma for production of biochar materials with higher cation exchange capacity.

Fig. 7 shows the application of quenching with C0₂/carbonated water for production of biochar materials with higher cation exchange capacity.

DETAILED DESCRIPTION

The compositions, methods, and articles described herein can be understood more readily by reference to the following detailed description. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a catalyst" includes mixtures of two or more catalysts. "Optional" or "optionally" means that the subsequently described event or circumstance can or cannot occur and that the description includes instances where the event or circumstance occurs and instances where it does not.

As used herein, the term "about" is used to provide flexibility to a numerical range endpoint by providing that a given value may be "a little above" or "a little below" the endpoint without affecting the desired result.

Described herein are methods for producing carboxylated biochar compositions with unique properties. The methods described herein apply a series of carbon dioxide- enhanced carboxylation and cleaning processes to create a new generation of clean biochar materials with higher cation exchange capacity and free of undesirable potential toxic substances, which represents a major technology improvement in this arena. The carboxylating agents and catalysts are used herein to convert biochar compositions to unique carboxylated compositions. Various aspects and embodiments of the methods herein are disclosed as follows.

In a first aspect, described herein is a method for producing a carboxylated biochar material possessing a higher cation-exchanging property. The cation- exchanging ability of a biochar is known to be predominantly dependent on the density of cation-exchanging groups mainly carboxyl (-COOH) groups in the biochar.

In one aspect, a biochar source is reacted with an injected carboxylating CO₂ stream, a carboxylating agent useful herein, (Fig. 3) in a controlled manner such that the biochar source homogeneously acquires carboxy-containing cation-exchanging groups in a thermochemical biomass carbonization process that retains carboxyl group on biochar surfaces. Examples of the thermochemical biomass carbonization process useful herein include, but are not limited to, ambient pressure biomass pyrolysis, slow biomass pyrolysis, fast biomass pyrolysis, biomass gasification process, pressurized biomass pyrolysis process, hydrothermal biomass conversion, and any combination thereof.

By being a "thermochemical biomass carbonization process" is meant that a significant portion of the total carbon content in the biochar source biomass remains (i.e., is not converted to oxide gases of combustion) after the carbonization described herein is completed. Oxide gases of thermochemical biomass carbonization typically include CO₂ and H₂O, as shown in the following example of biomass pyrolysis process reaction:

Biomass-CH(OH)-CH₂-COOH→ Biochar-CH=CH₂ + H₂O + CO₂ [1 ] According to one of the various embodiments, an increased CO₂ partial pressure in a range from 0.15 to 300 atm (atmospheric pressure unit) through injection of a CO₂ stream (Fig. 3) will thermodynamically suppress the decarboxylation of the biochar materials during the biomass pyrolysis process, so that the biochar product will retain more carboxyl groups (thus higher cation exchange capacity) as shown in the following example of a controlled biomass pyrolysis process reaction in the presence of high CO₂ partial pressure with the injection of a CO₂ stream:

Biomass-CH(OH)-CH₂-COOH → Biochar-CH=CH-COOH + H₂O [2]

In one of the various embodiments, the use of increased CO₂ partial pressure is realized by retaining the CO₂ gas generated during thermochemical biomass carbonization in a sealed pressure-resistant reactor with fixed volume resulting in a thermo-physically auto-pressurized biomass pyrolysis process for production of biochar with higher cation exchange capacity.

In another embodiment, the injection of a CO₂-containing gas stream is performed preferably with nearly 100% or above 15% of CO₂ under 1 to 300 atmospheric (atm) pressure(s). In one aspect, the C0₂-containing gas stream can be a C0₂/water steam stream, a 100% C0₂ stream, a 90% C0₂ stream, a 80% C0₂ stream, a 70% C0₂ stream, a 60% C0₂ stream, a 50% C0₂ stream, a 40% C0₂ stream, a 30% C0₂ stream, a 20% C0₂ stream, a 15% C02 stream, an artificial gas mixture including a C0₂-nitrogen (N₂) mixture, a C0₂-argon mixture, a C0₂-helium mixture, a C0₂-CO mixture, or an oxygen (0₂)-carbon dioxide (C0₂) mixture, and any combination thereof.

In certain aspects, the increased partial pressure of C0₂ through injected C0₂ stream (Fig. 3) can also, to some extent, lead to carboxylation of biochar materials during the biomass pyrolysis, for example, by insertion of C0₂ into the C-H bonds of biochar materials:

Biochar-CHs + C0₂→ Biochar-CH₂-COOH [3]

In this aspect, the carboxylated biochar product will have more carboxyl groups and thus higher cation exchange capacity, since the carboxyl groups readily deprotonate in water and result in more negative charge (Biochar-CH₂-COO^~) on the carboxylated biochar materials:

Biochar-CH₂-COOH→ Biochar-CH₂-COO^" + ΗΓ [4]

The injection of C0₂ gas is performed in either a continuous and/or pulsed mode to optimize the operation effects. In another aspect, the injected C0₂ stream can also function as a carrier gas to purge the biochar materials during the biomass pyrolysis process so that the small organic molecules (typically at a molecular mass of about 500 Dalton or smaller) will be effectively removed from the biochar products and exit as part of the pyrolysis vapors that can be harvested as bio-oils and syngas through condensation and filtration for biofuel production. As illustrated in Fig. 3, after the condensation of the pyrolysis vapors, which produces bio-oils liquid, the un- condensable portion of pyrolysis vapors/gases is filtered with a C0₂ membrane filtration system to recover C0₂ and separate the syngas product. The recovered C0₂ stream is recycled back into the C0₂ injection system to continue purging the biochar materials with the C0₂ gas stream in the pyrolysis reactor to effectively push the pyrolysis vapors (including small organic molecules) out of the pyrolysis reactor so that the biochar product will be more clean (containing much less residual pyrolysis bio-oils which could contain the potential biochar toxins including certain polycyclic aromatic hydrocarbons). So, in this case, the injected C0₂ stream also serve as a carrier gas to clean the biochar products as it is purging through the biochar particles in the pyrolysis reactor, in addition to its role on suppression of decarboxylation. It was recently identified that a certain biochar phytotoxic effect²⁹ is due to a type of small organic molecules including certain polycyclic aromatic hydrocarbons (PAHs) at a molecular mass of about 500 Dalton (Da) or smaller that are co-produced during biomass pyrolysis. The potential biochar toxins are typically soluble organic matters that include residual pyrolysis bio-oils, small organic molecules at a molecular mass of about 500 Dalton (Da) or smaller that are co- produced during biomass pyrolysis, polycyclic aromatic hydrocarbons, degraded lignin-like species rich in oxygen containing functionalities, phenolic type of phytotoxins with at least one carboxyl group, and combinations thereof. Therefore, the methods of C0₂ stream injection described herein can be employed to suppress decarboxylation and remove potential biochar toxins to produce advanced biochar materials with higher cation exchange capacity and free of the biochar toxin.

According to another embodiment (Fig, 4), a catalyst such as, for example, copper(l), silver(l), gold(l), zero-valent nickel (Ni), and Cu (ll)-exchanged montmorillonite K10 clay can be used to enhance the insertion of C0₂ into the C-H bonds of biochar materials. The coinage metal (copper, silver, gold) catalysts such as copper (I) and silver(l) may be in a number of forms including (but not limited to): copper(l) oxide (Cu₂0), copper(l) carbonate (Cu₂C0₃), copper(l) bicarbonate (CuHC0₃), copper(l) chloride (CuCI), copper(l) iodide (Cul), copper (I) hydroxide, copper(l) nitrate, silver oxide (Ag₂0), silver(l) carbonate (Ag₂C0₃), silver(l) bicarbonate (AgHC0₃), silver chloride (AgCI), silver(l) hydroxide, silver nitrate (AgN0₃), silver(l) iodide (Agl), AgOAc, (4,7-dichloro-1 ,10-phenanthroline)-bis(triphenylphosphine) copper(l) nitrate, zero-valent nickel (Ni) such as bis(cyclooctadiene)nickel(0) also known as Ni(cod)₂, low-valent nickel complexes, and their combinations thereof. In one aspect, the surfaces of the reactor walls and/or mixing devices such as mixing balls and beads that can be in contact with biochar materials are coated typically with the catalyst as shown in Fig. 4 to further facilitate the C0₂-drriven carboxylation reaction [3] for implantation of C0₂ into biochar materials for higher cation exchange capacity.

In one of the various embodiments, the surfaces of the reactor walls and mixing devices are coated first with the coinage metals such as, for example, a copper (Cu) film and then condition the metal film such as by heating it with controlled amount of oxidizer such as 0₂ in such a way that some of the coinage metal atoms on the surfaces are oxidized to the low-valent metal (I) state in order to activate the catalytic activity for carboxylation of biochar materials. In one of the various embodiments, the metallocatalyst conditioning and re-conditioning process is operated in combination with the biomass pyrolysis and C0₂/steam injection processes to achieve more desirable results. With certain metallocatalysts such as the copper or silver salts, especially in the presence of a mild base such as K₂C0₃, the carboxylation of biochar can occur even at quite mild conditions (temperature 30-50°C, 0.1 -5 atm of C0₂). Therefore, in one of the various embodiments, the catalytic carboxylation is used as a post-production processing technique to enhance the cation exchange capacity of biochar products as well.

According to one of the various embodiments, the catalyst-enabled carboxylation reaction [3] can be used also as a mechanism to remove potential biochar toxins through molecular structural destruction by the catalyst-enabled insertion of C0₂ into the C-H bonds of the toxic organic molecules such as the phenolic-type phytotoxins and polycyclic aromatic hydrocarbons (PAHs). Therefore, the removal of potential biochar toxins and the carboxylation of biochar materials are accomplished simultaneously by the catalyst-enabled insertion of C0₂ into the C-H bonds of biochar materials and also into the C-H bonds of the potentially toxic organic molecules including polycyclic aromatic hydrocarbons (PAHs) so that the cation exchange capacity of biochar materials is enhanced and the potential biochar toxins are removed by molecular structural destruction through the catalyst-assisted C0₂ molecular implantation.

In another aspect, the injected C0₂ stream is also used to purge the biochar materials in the catalyst-coated pyrolysis reactor so that the small organic molecules (at a molecular mass of about 500 Dalton or smaller) will be effectively removed from the biochar products and exit as part of the pyrolysis vapors that can be harvested for biofuel production. Therefore, the injection of C0₂ stream can be employed with the carboxylation catalyst to produce biochar materials with higher cation exchange capacity and free of biochar toxin (Fig. 4).

In one of the various embodiments (Fig. 5), injection of C0₂/water steam is used as a tool for both enhanced biochar cleaning and carboxylation during the biomass pyrolysis process to produce biochar materials with higher cation exchange capacity and free of biochar toxin. The injection of C0₂/water steam is operated with either a continuous or pulsed mode. The ratio of C0₂ to water (H₂0) steam in the injected gas stream is innovatively used to control the relative partial pressure of C0₂ during the biochar production process. Preferably, no more than about 20 percent by weight of the carbon contained in the biochar source biomass is converted to one or more oxide gases (C0₂, CO) of combustions except water (H₂O). More preferably, no more than about 10, 5, 2, or 1 percent by weight of the carbon contained in the biochar source is converted to one or more oxide gases of combustion except water (H₂O). In a particular embodiment, the methods herein are conducted as a combustionless process, i.e., such that substantially none (e.g., less than 0.5 or 0.1 percent by weight) of the carbon content of the biomass is converted to oxide gases of combustion except water (H₂O). Meanwhile, the injected CO₂/water steam is used to purge the biochar materials during the pyrolysis and the catalyzed carboxylation process so that the small organic molecules co-produced during pyrolysis will be effectively removed from the biochar products and exit as part of the pyrolysis vapors that can be harvested for biofuel production. Therefore, the injection of CO₂/water steam can be employed to produce biochar materials with higher cation exchange capacity and free of biochar toxin. The term "free of biochar toxin" herein means that the content of the potential biochar toxin (if any) is reduced to such a lower level that will no longer have any toxic effect to algal culture growth when tested with a standard concentration of biochar water-extracted substances measured as 0.189 grams of dissolved organic carbon (DOC) per liter.

As illustrated in Fig. 5, after the condensation of the pyrolysis vapors, which produces bio-oils liquid, the un-condensable portion of pyrolysis vapors/gases is filtered with C0₂ membrane filtration system to recover C0₂ and separate the syngas product. The recovered C0₂ stream is recycled back into the C0₂/water steam injection system to continue purging the biochar materials with the C0₂/steam stream in the catalyst- coated pyrolysis reactor to effectively push the pyrolysis vapors (including small organic molecules) out of the pyrolysis reactor so that the biochar product will be more clean (containing much less residual pyrolysis bio-oils). In one of the various embodiments, the un-condensable portion (the non-bio-oils part) of the pyrolysis vapors/gases including CO, CO₂, H₂, CH₄, and water vapor is also recycled back through the CO₂/water steam injection system into the biochar-producing reactor as a carrier gas to purge the biochar materials and push the pyrolysis vapors (including small organic molecules) out of the pyrolysis reactor so that the biochar product will be more clean (containing much less residual pyrolysis bio-oils which could contain the potential biochar toxins including certain polycyclic aromatic hydrocarbons). Therefore, the suppression of decarboxylation and the removal of potential biochar toxins are accomplished simultaneously by use of a CO₂-containing gas stream including the CO₂/water steam flowing through the pyrolysis reactor to purge the biochar products and effectively push the pyrolysis vapors (including small organic molecules) out of the reactor so that the biochar products will be more clean and free of potential biochar toxins. In contrast to the highly uncontrolled combustion processes known in the art, the methods described herein are a highly controlled biomass carbonization process that results in the suppression of decarboxylation or enhanced carboxylation of biochar material such that a biochar with a higher cation exchange property is produced while advantageously emitting much lower amounts of oxide gases of combustion. Moreover, due in large part to the controlled nature of the biomass carbonization and biochar carboxylation process, the methods described herein generally produce a substantially uniform (i.e., substantially homogeneous) carboxylated biochar. By being "substantially uniform" is generally meant, at minimum, that there is an absence in the carboxylated biochar of regions of non-carboxylated biochar (as commonly found in biochar material formed under uncontrolled conditions, such as in open pits). Preferably, a substantially uniform carboxylated biochar possesses different macroscopic regions (e.g., of at least 100 μιη², 1 mm², 10 mm², or 1 cm² in size) that vary by no more than 10%, 5%, 2%, 1 %, 0.5%, or 0.1 % in at least one characteristic, such as CEC, oxygen to carbon molar ratio, and/or surface area. The substantial uniformity of the carboxylated biochar advantageously provides a user with a biochar material that provides a consistent result when distributed into soil, either packaged or in the ground. Furthermore, a substantial uniformity of the carboxylated biochar ensures that a tested characteristic of the biochar is indicative of the entire batch of biochar.

In one aspect, a substantially uniform biochar is attained by an effective level of mixing of the biochar during the carboxylation process. For example, in one embodiment, biochar is agitated, shaken, or stirred either manually or mechanically during the C0₂-gas-driven carboxylation and purging process. In another embodiment, the biochar is reacted in an open or closed container (e.g., a kiln) containing a tumbling mechanism such that the biochar is tumbled during the carboxylation reaction with carbonates and/or bicarbonates. The biochar source considered herein can be any biochar material that could benefit by the carboxylation process of the inventive method. The biochar source could be, for example, a byproduct of a pyrolysis or gasification process, or material acquired from a biochar deposit and/or natural coal materials (coal mines) as well. In one aspect, the biochar is plant-derived (i.e., derived from cellulosic biomass or vegetation). Some particular examples of biomass materials useful herein include, for example, cornstover (e.g., the leaves, husks, stalks, or cobs of corn plants), grasses (e.g., switchgrass, miscanthus, wheat straw, rice straw, barley straw, alfalfa, bamboo, hemp), sugarcane, hull or shell material (e.g., peanut, rice, and walnut hulls), any woody biomasses including dead trees such as dead pine and dead oak, Douglas fir, woodchips, saw dust, paper or wood pulp, algae, aquatic plants, food waste, agricultural waste, and forest waste. In one embodiment, the biomass material is in its native form, i.e., unmodified except for natural degradation processes, before being converted to biochar. In another embodiment, the biomass material is modified by, for example, adulteration with a non-biomass material (e.g., plastic- or rubber-based materials) or by physical modification (e.g., mashing, grinding, compacting, blending, heating, steaming, bleaching, nitrogenating, oxygenating, or sulfurating), before being converted to biochar.

The one or more carboxylating agents considered herein are any compounds or materials known in the art that tend to be reactive by imparting carboxyl groups into organic materials. An example of a carboxylating agent is C0₂ or CO in the gas form in addition to the CO₂/water vapor stream. The CO₂ gas may also be in the form of an artificial gas mixture, such as a CO₂-nitrogen (N₂), CO₂-argon, CO₂-helium, CO₂-CO, or oxygen (O₂)-carbon dioxide (CO₂) mixture. An artificial gas mixture can be advantageous for the purposes of the invention in that the level of CO₂ can be precisely controlled, thereby further controlling the pyrolysis and carboxylation reactions to optimize the density and kind of oxygen-containing functional groups in the biochar. For example, in different embodiments, it may be preferred to use a CO₂-CO-containing gas mixture having at least, less than, or about, for example, 0.1 %, 0.5%, 1 %, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, or 99% by the volume of CO₂, or a range bounded by any two of the foregoing values. In another embodiment, a substantially pure source of CO₂ gas is used, i.e., greater than 99% of CO₂.

Some examples of other carboxylating agents useful herein include the carbonates and bicarbonates in the solid and/or liquid forms such as CaCO₃, Ca(HCO₃)₂, MgCO₃, Mg(HCO₃)₂, K₂CO₃, KHCO₃,NaHCO₃, Na₂CO₃, Cu₂CO₃, CuHCO₃, AgHCO₃, Ag₂CO₃ and Cs₂CO₃. In the metal-catalyzed cases, alkali carbonates such as K₂CO₃, Na₂CO₃, CaCO₃, Cs₂CO₃, and/or MgCO₃ may be used as the base. In this case, when the carboxylation reaction is carried out in the presence of a mild base such as K₂CO₃, a carboxylate salt is formed, which typically makes the overall reaction to be energetically more favorable ( A G = -10.1 kcal mol^-1). Alternatively, the carboxylating agent can be two or more chemicals that react with each other to form CO₂ or CO₂-CO gas in situ (such as carbonates plus hydrochloric acids). CO₂ and carbonates can be used together to produce the carboxylated biochar as well.

In another aspect (Fig 6), the biochar source can be treated with catalytic CO₂ plasma for "CO₂-implantation" onto the surfaces of the biochar materials as shown in Equation 3 above. Any of the CO₂ plasma processes known in the art, including high and low temperature plasma processes, can be used herein. The introduction of C0₂ into the biochar materials by a C0₂ plasma treatment increases the carboxylation or the 0:C molar ratios of these materials. The cation exchange capacity increases with the 0:C ratio of the biochar materials. The method includes C0₂ plasma treatment as a treatment that improves cation exchange capacity by enhanced "carboxylation" of the biochar materials. Accordingly, use of a relatively cold gas plasma can enable molecular re-engineering of biochar materials to impart unique surface properties such as the cation exchange capacity, without affecting the bulk properties of the biochar.

Preferably, the C0₂ plasma is low temperature (cold) plasma (e.g., 15 to 30°C). The plasma process entails subjecting the biochar at reduced pressure (i.e., in a vacuum chamber) to a source of ionized carbon dioxide or carbon dioxide radicals. The ionized source of C0₂ is typically produced by exposing C0₂ at a somewhat reduced pressures and/or atmospheric pressure in a range of about 0.05 to 760 Torr to an ionizing source, such as an ionizing microwave, radiofrequency, or current source. Commonly, a radiofrequency (or microwave) source (e.g., of 40 kHz, 13.56 MHz or 2.45 GHz at a RF or MW power of about 5-10,000 W) is used to ionize the C0₂. The particular C0₂ plasma conditions depend on several factors including the type of plasma generator, gas composition, power source capability and characteristics, operating pressure and temperature, the degree of carboxylation required, and characteristics of the particular biochar being treated (i.e., its susceptibility or resistance to carboxylation). Depending on several factors including those mentioned above, the biochar can be exposed to the ionized carbon dioxide for at least about 0.1 , 0.2, 0.5, 1 , 1 .5, 2, 2.5, 3, 4, or 5 minutes and up to 6, 8, 10, 12, 15, 20, 30, 40, 50, 60, 90 or 180 minutes. Although the biochar can be plasma treated within a temperature range of about 15 to 30°C, a lower temperature (e.g., less than 15°C) or a higher temperature (e.g., greater than 30 0, such as 40°C, 50*0, 60°C, 70°C, 80°C, 90°C, 100°C, 1 10°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200 °C, 210°C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C, 290 °C, 300 °C, 310°C, 320 °C, 330 °C, 340 °C, and 350 °C) may also be used. Not wishing to be bound by theory, the organic contaminants (potential toxins) adsorbed on biochar surfaces are removed by plasma-assisted chemical reaction with highly reactive carbon dioxide radicals and through ablation by energetic carbon dioxide ions. At the same time, certain plasma with moderate energetic carbon dioxide ions can promote surface carboxylation and sometimes also hydroxylation (possibly forming carboxyl COOH groups and hydroxyl OH on the biochar carbon surfaces), which will increase surface wettability and more importantly cation exchange capacity (CEC). Both the surface wettability and CEC are fundamentally important properties for biochar soil applications to better retain water and nutrients for improved soil fertility as well as reduction of agricultural chemicals runoff. In another embodiment, the method is practiced by treating a biochar source with one or more carboxylating agents at a temperature at which the carboxylating compound is reactive enough to impart carboxyl groups or oxygen-containing cation- exchanging groups to the biochar, i.e., at a suitably reactive temperature, wherein the amount of the carboxylating compound and/or time of reaction is appropriately adjusted such that the biochar acquires the cation-exchanging groups in a thermochemical biomass carbonization process with carboxylation and/or suppression of decarboxylation. In a particular embodiment, the reaction is conducted as a combustionless process because of the excess amount of CO₂. Highly reactive carboxylating process such as CO₂ plasma can typically function effectively at room temperature (e.g., 15 to 30°C) or even lower temperatures (e.g., less than 15°C). Moderately reactive carboxylating compounds (e.g., CO₂, O₂ and CO) with certain catalysts can typically function effectively at a temperature of at least 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900 or 950°C, or within a range bounded by any two of these values. It is understood that longer reaction times and high pressures generally yield a more carboxylated biochar whereas shorter reaction times generally yield a less carboxylated biochar. Therefore, it is also understood that a moderately reactive or substantially unreactive carboxylating compound may effectively carboxylate biochar by use of a temperature of or less than 200°C under certain pressures if a sufficient period of time is used, e.g., about or at least 3, 6, 12 hours, 24 hours, 36 hours, 48 hours, 72 hours, a week, two weeks, three weeks, a month, two months, or three months. In a particular embodiment, the carboxylating compound is reacted with biochar in a closed system (i.e., closed container) in order to ensure that the intended amount of carboxylating compound as measured, and no less and no more, is reacted with the biochar. When a carboxylating solid or liquid carboxylating compound (or a solution thereof) is used, the solid or liquid can be weighed into the closed container along with the biochar source and the contents homogeneously mixed or blended under conditions suitable for carboxylation of the biochar to take place. For example, the temperature of the mixed reactants in the container can be raised along with proper agitation until the solid or liquid becomes suitably vaporized in order to promote its reaction with the biochar in a uniform (i.e., homogeneous) manner. When a carboxylating gas (e.g., C0₂ plasma) is used, a selected volume of the gas corresponding to a calculated weight or moles of the gas can be charged into the closed system along with the biochar source.

In one aspect, when an artificial C0₂-gas mixture is used, the reactants are typically placed in a heatable closed system (i.e., a thermally-insulated chamber), such as an oven, kiln, or furnace. The heatable closed system can be any such systems known in the art typically operated or assisted by, for example, a flame (e.g., from a natural gas source), electricity, or microwaves. The kiln can be, for example, any of the downdraft, updraft, cross draft, fluid bed, or rotating kilns known in the art. The heatable closed system can also be one configured to adjust the moisture level of the biochar, i.e., either to decrease or increase the moisture level of the biochar. The moisture level can be suitably adjusted, for example, to a humidity level of about, at least, or no more than 1 %, 2%, 5%, 10%, 15, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, or a humidity level within a range bounded by any two of these values. In different embodiments, the reactants can be heated in the closed chamber to increase the internal pressure by raising a temperature to: 100°C, 150°C, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, or 550 °C, or a temperature within a range bounded by any two of the foregoing temperatures. In a particular embodiment, heating can advantageously be minimized or altogether dispensed with by reacting still hot biochar (i.e., as rendered hot by a biomass-to- biochar production process) under the carboxylating conditions of the invention. The still hot biochar preferably possesses a temperature of at least 450 °C, 400 °C, 350 °C, 300 °C, 250 °C, 200 °C, 150°C, or within a range bounded by any two of these values.

In one embodiment, the biochar and one or more carboxylating agents are reacted for a period of time necessary for substantially all of the carboxylating reactant in a closed container to be consumed. In another embodiment, conditions of temperature and/or time are selected such that a portion of the carboxylating reactant in a closed container is consumed.

In another particular embodiment, carboxylation of biochar materials is attained by conducting the carboxylating reaction in an open or closed container and rapidly quenching the reaction with C0₂-containing water (Fig. 7). The reaction can be quenched by, for example, contacting the reacting biochar with an excessive amount of C0₂-containing water such as C0₂/carbonated water, and/or inert substance, preferably when the biochar material is still hot, e.g., a temperature of at least 800°C, 750°C, 700 °C, 650 °C 600 °C 550 °C 500 °C, 450 °C, 400 °C, 350 °C, 300 °C, 250 °C, 200 °C, 150°C, 100°C, 50 °C, or within a range bounded by any two of these values, as produced from a biomass-to-biochar process. The inert substance can be, for example, carbonates, bicarbonate or a form of biomass (e.g., soil, plant-material, or the like). An excessive amount of C0₂/carbonated water and/or carbonates/inert substance is an amount that preferably covers all of the reacting biochar, or alternatively, functions as a bulk surface shield of the biochar, with the result that the carboxylating process is facilitated due to the addition of the excess C0₂ to the hot biochar preferably at a pressure higher than the ambient atmospheric pressure as shown in Fig 7. If an elevated temperature is being used in the carboxylating process, the quenching step also typically has the effect of rapidly reducing the temperature of the biochar.

The methods described herein can also include one or more preliminary steps for producing biochar (i.e., the biochar source or "produced biochar") from biomass before the biochar is carboxylated. The biomass-to-biochar process can be conducted within any suitable time frame before the produced biochar is carboxylated.

As shown in the Examples below, hydrothermal conversion (HTC) of biomass produces biochar materials with cation exchange capacity higher than that of ambient pressure biomass pyrolysis. HTC is a process of heating up biomass in a temperature range of 180-380 °C in the presence of water in a sealed pressure-tolerant reactor with fixed volume. As the biomass/water is heated up inside the sealed reactor, the inside pressure rise dramatically. For example, when the temperature is raised to 250-380 °C, the pressure inside can get as high as 7-30 MPa (i.e., 69-296 atm). The gas formed during the hydrothermal biomass carbonization is mainly C0₂.³° The concentration of C0₂ in the headspace of a hydrothermal biomass carbonization reactor can reach as high as 70-90%.³¹ Therefore, the C0₂ partial pressure during the hydrothermal biomass carbonization process can reach as high as 5.6-24 MPa (i.e., 55.2-236.8 atm). Not wishing to be bound by theory, an increased C0₂ partial pressure in the biomass carbonization process will suppresses decarboxylation and thus retain more carboxyl groups as described in the process reaction [2] above, resulting in a biochar product with higher cation exchange capacity.

In one embodiment, a biomass-to-biochar process is conducted in a non- integrated manner with the biochar carboxylating process. In the non-integrated process, biochar produced by a biomass-to-biochar process is transported to a separate location where the biochar carboxylating process is conducted. The transport process generally results in the cooling of the biochar to ambient temperature conditions (e.g., 15-30°C) before carboxylation occurs. Typically, the produced biochar is packaged and/or stored in the non-integrated process before carboxylation of the biochar. In another embodiment, a biomass-to-biochar process is conducted in an integrated manner with a biochar carboxylation process. In the integrated process, biochar produced by a biomass-to-biochar process is carboxylated in situ without first being cooled to ambient temperature. For example, in the integrated embodiment, freshly produced biochar can have a temperature of, for example, about or at least 450 °C, 400 °C, 350 °C, 300 °C, 250 °C, 200 °C, 150°C, 100°C, or 50 0, or a temperature within a range bounded by any two of these values, before being subjected to the carboxylation process. If desired, the freshly produced biochar can be subjected to additional heating to elevate and/or maintain its temperature before the carboxylation step. The biochar carboxylation process can be integrated with, for example, a biomass-to-fuel process, such as a low temperature or high temperature pyrolysis process. In such processes, typically about 40%, 50%, or 60% of the biomass carbon is converted into biochar while the remaining 60%, 50%, or 40% of carbon is converted to fuel (syngas and bio-oils). Furthermore, since it has been found that lower temperature pyrolysis processes generally yield a biochar material with even more improved fertilizer retention properties, in a particular embodiment, the biochar carboxylation process is integrated with a biomass pyrolysis process conducted at a temperature of no more than about 800 °C, 750 °C, 700 °C, 650 °C, 600 °C, 550 °C, 500 °C, 450 °C, 400 °C, 350 °C, or 300°C. In one embodiment, an integrated process is configured as a batch process wherein separate batches of produced biochar are carboxylated at different times. In another embodiment, the integrated process is configured as a continuous process wherein biochar produced by the biomass-to-biochar process is continuously subjected to a carboxylation process as it is produced. For example, produced biochar can be continuously transported either manually or by an automated conveyor mechanism through a biochar carboxylation zone. The automated conveyor mechanism can be, for example, a conveyor belt, gravity-fed mechanism, or air pressure mechanism.

In another aspect, the carboxylated biochar produced herein has a particular, exceptional, or optimal set of characteristics, such as a particular, exceptional, or optimal carboxyl contents, or optimal oxygen-to-carbon molar ratio, enhanced CEC, surface area, composition, zero toxin content, and/or uniformity in any of these or other characteristics. The methods described herein are particularly suitable for producing these types of advanced biochars.

In one embodiment, the CEC of the carboxylated biochar is at least moderate, e.g., about or at least 50, 60, 70, 80, 90, 100, 1 10, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240 mmol/kg, or within a particular range bounded by any two of the foregoing values. In another embodiment, the CEC of the carboxylated biochar is atypically or exceptionally high, e.g., about or at least 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1 100, 1200 mmol/kg, or within a particular range bounded by any two of the foregoing values. In another embodiment, the CEC of the carboxylated biochar is within a range having a minimum value selected from any of the exemplary moderate CEC values given above and a maximum value selected from any of the exemplary atypically high CEC values given above (for example, 50-1000 mmol/kg or 200-1200 mmol/kg). Preferably, the CEC value is substantially uniform throughout the biochar material.

The density of carboxy-containing cation-exchanging groups is typically proportional to the measured oxygen-to-carbon molar ratio of the biochar, wherein the higher the oxygen-to-carbon molar ratio, the greater the density of cation-exchanging groups in the biochar. In different embodiments, the oxygen-to-carbon molar ratio of the carboxylated biochar is at least 0.1 :1 , 0.2:1 , 0.25:1 , 0.3:1 , 0.35:1 , 0.4:1 , 0.45:1 , 0.50:1 , 0.60:1 , 0.70:1 , or within a range bounded by any two of the foregoing ratios. Preferably, the oxygenated biochar contains a substantially uniform density of the carboxy- containing cation-exchanging groups and a substantially uniform oxygen-to-carbon molar ratio throughout the biochar material. According to one of the various embodiments, carbon monoxide (CO) plasma can be used to modify biochar carbon materials. In this aspect, oxygen-containing carbon functional groups are created at the biochar carbon surfaces to enhance biochar cation exchange capacity. For example, the treatment of carbon materials with carbon monoxide (CO) atmospheric plasma can result in tailorable surface O:C molar ratios as high as about 0.70:1 at biochar carbon surfaces.

According to another embodiment, the plasma-enabled molecular implantation of CO and/or CO₂ into biochar carbon materials can be used also as a mechanism to remove potential biochar toxins through molecular structural destruction by the plasma- assisted implantation of CO and/or CO2 into the toxic organic molecules such as the phenolic-type phytotoxins and polycyclic aromatic hydrocarbons (PAHs). Therefore, the removal of potential biochar toxins and the enhancement of biochar cation exchange capacity are accomplished simultaneously through the use of catalytic carbon dioxide (CO₂) plasma and/or carbon monoxide (CO) plasma implanting CO₂ and/or CO into both the biochar materials and the potentially toxic organic molecules including polycyclic aromatic hydrocarbons (PAHs), so that the biochar cation exchange capacity is enhanced and the potential biochar toxins are removed by molecular structural destruction through the plasma-assisted C0₂ and/or CO implantation.

The carboxylated biochar can have any suitable specific surface area (SSA), as commonly determined by BET analysis. In different embodiments, the carboxylated biochar has an SSA value of about, or at least, or no more than 0.1 , 0.5, 1 , 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 80, 100, 200, 400, 600, or 800 m²/g, or an SSA value within a range bounded by any two of the foregoing values.

The carboxylated biochar can also have any suitable charge density. In different embodiments, the carboxylated biochar has a charge density of about, or at least, or no more than 1 , 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 1 10, or 120 mmol/ m², or a charge density within a range bounded by any two of the foregoing values.

The carboxylated biochar can also have any suitable carbon, nitrogen, oxygen, hydrogen, phosphorous, calcium, sulfur, ash, and volatile matter content. The carbon content can be about, at least, or no more than, for example, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 mole percent, or within a particular range therein. The nitrogen content can be about, at least, or no more than, for example, 0.1 , 0.25, 0.5, 0.75, 1 .0, 1 .25, 1 .5, 1 .75, 2.0, 2.25, 2.5, 2.75, 3.0, 3.25, 3.5, 3.75, 4.0, 4.5, 5.0, 6.0, 7.0, or 8.0 mole percent, or within a particular range therein. The oxygen content can be about, at least, or no more than, for example, 1 , 2, 5, 10, 15, 20, 25, or 30 mole percent, or within a particular range therein. The hydrogen content can be about, at least, or no more than, for example, 1 , 2, 5, 10, 1 5, 20, 25, or 30 mole percent, or within a particular range therein. The phosphorus or calcium content can independently be about, at least, or no more than, for example, 5, 10, 25, 50, 100, 500, 1000, 5000, 7500, 10000, 15000, 20000, or 25000 mg/kg, or within a particular range therein. The sulfur content can be about, at least, or no more than, for example, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, or 2000 ppm, or within a particular range therein. The ash content can be about, at least, or no more than, for example, 1 , 2.5, 5, 10, 15, 20, 30, 40, 50, 60, or 70%, or within a particular range therein. The volatile matter content can be about, at least, or no more than, for example, 1 , 2.5, 5, 10, 15, 20, 25, 30, 35, or 40%, or within a particular range therein.

The carboxylated biochar can also have any suitable particle size. In various embodiments, the carboxylated biochar can have a particle size of about, at least, or no more than, for example, 50, 100, 250, 500, 750, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, or 5000 μιτι, or a particle size within a particular range bounded by any two of the foregoing values. In certain applications (e.g., to ensure the biochar materials are resistant to becoming airborne in windy and/or desert areas), larger biochar particle sizes, such as 6000, 7000, 8000, 9000, 10,000, 20,000, 30,000, 40,000, 50,000 μιτι, or higher (for example, up to 100,000 μιτι), or a particle size within a particular range bounded by any two of the foregoing values, may be preferred. The biochar materials may also be in the form of an agglomeration, compaction, or fusion of biochar particles (e.g., pellets or cakes) for this type of application as well. The size of the pellets or cakes can correspond, for example, to any of the larger particle sizes given above.

The term "particle size" as used above for a particular value can mean a precise or substantially monodisperse particle size (e.g., within ±0-5% of the value) or a more dispersed particle size (e.g., greater than 5% and up to, for example, about 50% or 100% of the value). In addition, the biochar particles may have a size distribution that is monomodal, bimodal, or higher modal. The term "particle size" may also refer to an average particle size. If desired, the particle size of the carboxylated biochar can be appropriately modified by techniques known in the art. For example, the biochar particles may be ground, agglomerated, or sieved by any of the techniques known in the art. Furthermore, when the particles or pellets are substantially or completely spherical, the above exemplary particle or pellet sizes refer to the diameter of the particles or pellets. For particles or pellets that are non-spherical (e.g., elliptical, cylindrical, rod-like, plate-like, disc-like, rectangular, pyramidal, or amorphous), the above exemplary particle or pellet sizes can refer to at least one, two, or three of the dimensional axes of the particles or pellets.

The carboxylated biochar can also have any suitable pore size. In various embodiments, the oxygenated biochar can have a pore size of about, at least, or no more than, for example, 0.5, 1 , 1 .5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 100, 250, 500, 750, 1000, 1500, 2000, 2500, 5000, 6000, 7000, 8000, 9000, 10,000, 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000 or 100,000 nm, or a pore size within a particular range bounded by any two of the foregoing values.

The carboxylated biochar, such as produced by the method described above, may also be admixed (i.e., enriched) in one or more soil-fertilizing compounds or materials for use as a fertilizing biochar soil amendment and carbon sequestration agent. The soil-fertilizing compounds or materials can be, for example, nitrogen-based (e.g., ammonium-based), carbonate-based (e.g., CaC0₃), phosphate-based (e.g., the known phosphate minerals, such as in rock phosphate or triple superphosphate), and potassium-based (e.g., KCI). In a particular embodiment, the one or more soil-fertilizing compounds or materials includes at least one nitrogen-containing, and more typically, NH₄ ⁺-containing compound or material. Some examples of nitrogen-containing fertilizing compounds or materials include, for example, (NH₄)₂C0₃, NH₄HC0₃, NH₄N0₃, (NH₄)₂S0₄, (NH₂)₂CO, biuret, triazine-based materials (e.g., melamine or cyanuric acid), urea-formaldehyde resin, and polyamine or polyimine polymers. The fertilizer material may be inorganic, as above, or alternatively, organic. Some examples of organic fertilizer materials include peat moss, manure, insect material, seaweed, sewage and guano. The biochar material can be treated by any of the methods known in the art in order to combine the biochar material with a fertilizer. In a particular embodiment, the biochar material is treated with a gas stream of hydrated ammonia to saturate the biochar material. The biochar material may also be coated with fertilizer compounds or materials. The coating may also be suitably modified or optimized as known in the art to adjust the rate of release of one or more fertilizer compounds or materials into soil. In another embodiment, one or more of the above generic or specific soil-fertilizing compounds or materials are excluded from the carboxylated biochar composition.

In another embodiment, the invention is directed to a soil formulation containing, at minimum, soil admixed with the biochar composition described above. The soil can be of any type and composition. For example, the soil can have any of the numerous and diverse proportions of clay, sand, and silt. The sand, silt, and clay components can be independently present in an amount ranging from substantially absent (i.e., zero weight percent or in trace amounts) up to precisely or substantially 100 weight percent (e.g., exactly 100% or at least 98 or 99%). In different embodiments, one or more of the sand, silt, and clay components are in an amount of, independently, about, at least, or no more than, for example, 0.1 , 0.5, 1 , 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 weight percent of the total weight of the soil absent the biochar. The soil may also preferably have one or more of the sand, silt, and clay components present in an amount within a range bounded by any two of the foregoing exemplary weight percentages. The soil can also contain any amount of humus and humic substances (i.e., organic matter), humic acid, fulvic acid, cellulose, lignin, peat, or other such component, in any of the exemplary amounts or ranges given above.

According to one of the various embodiments, the carboxylated biochar can be used as filtration materials to remove various cations and pollutants in waters and air. This embodiment is also directed to a use of certain carboxylated biochar materials for other environmental and/or industrial applications such as the formulation and production of carboxylated biochar columns and/or filters for filtration of waters, other solvents and/or air streams. During the filtration process, various cations and/or pollutants in the medium such as waters and air will be in contact with the carboxylated biochars in the columns and/or filters thereby being removed through cation exchange binding and/or physical chemistry adsorption on the carboxylated biochar materials. In many cases, the used biochar columns and/or filters can be readily disposed by combustion cleanly back to air C0₂ and H₂0. For certain biochar columns and/or filters after used in removal of certain heavy metal ions such as, for example, Cu²⁺, they can also be combusted to retain their adsorbed heavy metal content in a relatively small amount of the resultant ash that can also be readily disposed by other proper ways as well. In other aspects, the biochar materials may be disposed by burying into soil at certain proper locations consistent with the practices of both waste dispose and biochar carbon sequestration. Since the biomass-derived and carboxylated biochar materials are completely renewable, the use of carboxylated biochar materials for filtration applications disclosed herein is another sustainable green-clean technology to remove various cations and pollutants in waters and air. Accordingly, carboxylated biochar columns and/or filters may be used to remove various cations, contaminants, and pollutants selected from the group consisting of ammonium (NH₄ ⁺), Li⁺, Ba²⁺, Fe²⁺, Fe³⁺, Cu⁺, Cu²⁺, Cd²⁺, Cs⁺, Sr²⁺, Ni²⁺, Zn²⁺, Cr³⁺, Pb²⁺, Hg²⁺, other metal ions including uranium ions, plutonium ions, osmium ions, platinum ions, gold ions, iridium ions, ruthenium ions, rhodium ions, cobalt ions, titanium ions, thallium ions, tin ions, indium ions, gallium ions, germanium species and germanium compounds, arsenic species and arsenic compounds, selenium species and selenium compounds, and organic and/or inorganic molecules including certain pollutants in waters, air and other environmental and industrial media as well.

EXAMPLES

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compositions and methods described and claimed herein are made and evaluated, and are intended to be purely exemplary and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperatures, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric, or in atmospheric pressure units (atm) and/or MPa. As specified above, by retaining the C0₂ gas generated during thermochemical biomass carbonization while thermo-physically auto- pressurized in a sealed pressure-resistant reactor with fixed volume, the C0₂ partial pressure during the hydrothermal biomass carbonization process can reach as high as 5.6-24 MPa (i.e., 55.2-236.8 atm). Numerous variations and combinations of reaction conditions, e.g., component concentrations, desired solvents, solvent mixtures, temperatures, pressures, and other reaction ranges and conditions can be used to optimize the product purity and yield obtained from the described process. Only reasonable and routine experimentation will be required to optimize such process conditions.

A series of non-limiting experiments discussed below demonstrate the difference between hydrothermal conversion (HTC) of biomass and ambient pressure biomass pyrolysis when preparing carboxylated biochar compositions using the methods described herein. A series of biochar materials for a comparative study were produced from pinewood, peanut shell, and bamboo biomass through hydrothermal conversion at 300°C and by ambient-pressure slow pyrolysis over a temperature range of 300, 400, and 500°C. The cation exchange capacity (CEC) of these biochar materials were measured using the previously reported method^{33 34} of compulsive barium loading followed by magnesium displacement for each sample.

As shown in Table 1 , the averaged CEC values of all HTC-produced biochars are higher than those of the ambient-pressure pyrolysis biochars for all biomass sources (pinewood, peanut shell, and bamboo). The biochar CEC values all showed somewhat dependence on pH at which the CEC values were measured. The biochar CEC values are generally higher at pH 8.5 than at pH 6.0. This feature is consistent with the understanding that the oxygen-containing functional groups such as carboxyl groups in biochar material are likely the major contributors to the CEC values. When the oxygen- containing functional groups are deprotonated at relatively lower proton concentration (such as pH 8.5) according to reaction [4], biochar surface will have more negatively charged functional groups, thus displaying a higher value of cation exchange capacity. Conversely when the proton concentration is raised (such as pH 6.0), some of the negatively charged functional groups may be protonated thus leading to a somewhat lower value of cation exchange capacity. More importantly, the averaged CEC value, as determined at pH 8.5, of the biochar produced from pinewood by HTC is 634.65 mmol kg^"1 , which is significantly higher than those (134.74, 89.91 , and 57.86 mmol kg^"1) of biochars produced from the same pinewood biomass by ambient-pressure pyrolysis at 300°C, 400°C, and 500°C, respectively. Similarly, the CEC value of biochar produced from peanut shell by HTC is 567.28 mmol kg^"1 , which is also significantly higher than those (371 .90, 130.14, and 121 .69 mmol kg^"1) of biochars produced from the same peanut shell materials by ambient-pressure pyrolysis at 300, 400, and 500°C, respectively. The same characteristic pattern of the HTC vs. ambient-pressure pyrolysis biochars can be seen from the measured CEC values of the bamboo derived biochars: the CEC value of biochar produced from bamboo by HTC is 415.97 mmol kg^"1 , which is also significantly higher than those (292.43, 183.97, and 121 .99 mmol kg^"1) of biochars produced from bamboo by ambient-pressure pyrolysis at 300, 400, and 500°C, respectively. Therefore, in one aspect, hydrothermal carbonization of biomass can be used for producing biochar materials with higher cation exchange capacity. The data in Table 1 also demonstrated that a higher pyrolysis temperature favors decarboxylation; a relatively lower pyrolysis temperature favors retention of carboxyl groups, thus resulting in a biochar product with higher cation exchange capacity. Note, the CEC value (134.74 mmol kg^"1) of biochar produced from pinewood by ambient- pressure pyrolysis at 300°C is higher than those (89.91 and 57.86 mmol kg^"1) of biochars produced from the same biomass by pyrolysis at 400 and 500°C, respectively. Similarly, the CEC value (371 .90 mmol kg^"1) of biochar produced from peanut shell by ambient-pressure pyrolysis at 300°C is also higher than those (130.14 and 121 .69 mmol kg^"1) of biochars produced from peanut shell by pyrolysis at 400 and 500°C, respectively. The same pattern is also true for the CEC value (292.43 mmol kg^"1) of biochar produced from peanut shell by ambient-pressure pyrolysis at 300°C which is also higher than those (183.97 and 121 .99 mmol kg^"1) of biochar produced by pyrolysis of peanut shell at 400 and 500°C, respectively. Therefore, in one of the various embodiments, a relatively mild pyrolysis temperature (e.g., 300, 350, 400, 450, and 500°C) is selected to produce biochar materials with higher cation exchange capacity. On the other hand, a higher thermochemical biomass carbonization temperature such as a higher pyrolysis temperature in a range from 600 °C to 800 °C is beneficial to vaporizing and removing residual pyrolysis bio-oils which could contain the potential biochar toxins including certain polycyclic aromatic hydrocarbons adsorbed on the biochar materials. Therefore, in one aspect, the removal of potential biochar toxins and the suppression of decarboxylation (i.e., retention of biochar cation exchange capacity) can be accomplished through the use of increased CO₂ partial pressure in combination with a proper thermochemical biomass carbonization temperature selected from the group consisting of 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, and 800 °C. Table 1. Measured Cation Exchange Capacity (CEC) values of biochars produced by hydrothermal conversion vs. ambient pressure pyrolysis. Each value was determined as an average of n=6 trials. CEC values presented here are in mmol kg^"1 as determined at the various pH shown.

Furthermore, the biochar oxygen to carbon (0:C) molar ratio as determined through elemental and proximate analysis demonstrated the correlation with biochar cation exchange capacity as expected. As listed in Table 2, the 0:C molar ratio of biochar produced from pinewood by HTC is 0.26:1 , which is significantly higher than those (0.15:1 , 0.05:1 , and 0.036:1 ) of biochars produced from pinewood by ambient- pressure pyrolysis at 300, 400, and 500°C, respectively. Note, the biochar 0:C molar ratio data (Table 2) here follows the same pattern as that of the pinewood-derived biochar cation exchange capacity values (Table 1 ). Therefore, biochar 0:C molar ratio is a characteristic indicator correlated with the biochar cation exchange capacity values in accordance with carboxylated biochar compositions produced by the methods described herein.

Table 2. Biochar Elemental and Proximate Analysis.

% % 0:C

% loss on volatile % fixed (molar

Sample drying matter Ash carbon C% H% N% o% ratio)

Pinewood

Char 300 4.08 27.89 4.93 67.18 74.17 3.76 <0.5 14.54 0.15

Pinewood

Char 400 4.88 19.57 3.99 76.44 81.64 2.69 <0.5 5.26 0.05

Pinewood

Char 500 4.29 11.67 2.37 82.11 83.2 2.74 <0.5 4.05 0.036

Pinewood

Char HTC 3.71 46.72 2.39 50.8 66.45 4.2 <0.5 22.84 0.26 In another non-limiting example, biochar samples were produced from pinewood under two different pyrolysis conditions at 400° C and ambient pressure: one with a constant flow of N₂ gas through the pyrolysis reactor which removed pyrolysis vapor and created an C0₂-depleted condition, designed as "400 N2 flow pinewood-derived biochar (Control)"; the other experiment using a constant flow of C0₂ gas through the pyrolysis reactor which removed pyrolysis vapor and created a C0₂-enriched environment, is designed as "400 C0₂ flow pinewood-derived biochar". The CEC values of these biochar materials were measured and comparatively analyzed. As shown in Table 3, the cation exchange capacity measured at pH 8.5 in the 400 C0₂ flow pinewood-derived biochar is significantly higher (174%) than that of the 400 N₂ flow pinewood-derived biochar (Control value, 100%). This experimental result again demonstrated that the use of an increased C0₂ partial pressure during biomass pyrolysis can indeed improve biochar cation exchange capacity value in accordance of the present invention.

In yet another non-limiting example, the 400 N2 flow pinewood-derived biochar was treated with atmospheric C0₂ plasma for 1 hour. The C0₂ plasma was generated using a commercially available C0₂ plasma generator (Diener Zepto plasma unit) using 5 watts of power with 40 kHz citation frequency. The cation exchange capacity of the C0₂ plasma-treated biochar is measured using the same method as described above. The data in Table 3 shows that the cation exchange capacity of the 400 N₂ flow pinewood-derived biochar treated with C0₂ plasma is the highest: 264% of the untreated biochar CEC value, which is better than that (174%) of the 400 C0₂ flow pinewood-derived biochar. This experimental result demonstrated that the use of C0₂ plasma can indeed improve biochar cation exchange capacity in accordance with the present invention.

Table 3. Cation exchange capacity (CEC) of biochars produced from pinewood under flow gases of either nitrogen or C0₂ as well as post production treatment with C0₂ plasma for 1 hour.

While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the invention claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept. REFERENCES CITED

Day, Danny, Robert J. Evans, James W. Lee, Don Reicosky (2005) "Economical C0₂, SOx, and NOx capture from fossil-fuel utilization with combined renewable hydrogen production and large-scale carbon sequestration," Energy 30:2558- 2579.

Day, Danny Marshal; Lee, James Weifu. "The production and use of a soil amendment made by the combined production of hydrogen, sequestered carbon and utilizing off gases containing carbon dioxide," PCT Int. Appl. (2004), 58 pp. WO 2004037747 A2.

E. Marris, Sequestration News Feature: Black is the new green, Nature 2006, 442:624-626.

J. Lehmann, Commentary: A handful of carbon, Nature 2007, 447:143-144.

Lee JW, Day DM (2012) Smokeless biomass pyrolysis for producing biofuels and biochar as a possible arsenal to control climate change. In: Advanced Biofuels and Bioproducts, Ed: Lee JW, Vol. I, Chapter 3, pages 23-34, Springer, New York.

Gundale, M. J. ; Thomas, H. ; DeLuca, T. H. Charcoal effects on soil solution chemistry and growth of Koeleria macrantha in the ponderosa pine/douglas fir ecosystem. Biol. Fertil. Soils 2007, 43, 303-31 1 .

Solomon, D. ; Lehmann, J. ; Thies, J. ; Schafer, T. ; Liang, B. ; Kinyangi, J. ; Neves, E.; Petersen, J. ; Luizao, F. ; Skjemstad, J. Molecular signature and sources of biochemical recalcitrance of organic C in Amazonian Dark Earths. Geochim. Cosmochim. Acta 2007, 71 , 2285-2298.

Lehmann, J. ; Gaunt, J. ; Rondon, M. Bio-char sequestration in terrestrial ecosystems A review. Mitigation Adaptation Strategies Global Change 2006, 1 1 , 403-427, 2006.

Adriana E. Downie, Lukas Van Zwieten, Ronald J. Smernik, Stephen Morris, Paul R. Munroe. Terra Preta Australis: Reassessing the carbon storage capacity of temperate soils, Agriculture, Ecosystems and Environment 140 (201 1 ) 137-147.

Lee, J. W.; Hawkins, B. ; Day, D. M. ; Reicosky, D. C. Sustainability: The capacity of smokeless biomass pyrolysis for energy production, global carbon capture and sequestration, Energy Environ. Sci. 2010, 3(1 1 ), 1609-1812. 1 1 . Lee JW, Hawkins B, Li X, Day DM (2012) Biochar fertilizer for soil amendment and carbon sequestration. In: Advanced Biofuels and Bioproducts, Ed: Lee JW, Vol. I, Chapter 6, pages 57-68. Springer, New York. 12. Krausmann F, Erb K, Gingrich S, Lauk C, Haberl H (2008) Global patterns of socioeconomic biomass flows in the year 2000. Ecological Economics 65:471 - 487.

13. Woolf D, Amonette JE, Street- Perrott FA, Lehmann J, Joseph S (2010)

Sustainable biochar to mitigate global climate change. Nature Communications,

DOI : 10.1038/ncomms1053.

14. Lee JW, Buchanan AC, Evans BR, Kidder M (2012) Oxygenation of biochar for enhanced cation exchange capacity. In: Advanced Biofuels and Bioproducts, Ed: Lee JW, Chapter 4, pages 35-45. Springer, New York.

15. Lee JW, Kidder M, Evans BR, Paik S, Buchanan AC, Garten C, Brown R (2010) Characterization of biochars produced from cornstover for soil amendment, Environ. Sci. Technol. 2010, 44, 7970-7974.

16. Rondon MA, Lehmann J, Ramirez J, Hurtado M (2007) Biological nitrogen

fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions. Biol Fertil Soils 43:699-708. 17. Rillig MC, Wagner M, Salem M, Antunes P, George C, Ramke HG, Titirici MM, Antonietti M (2010) Material derived from hydrothermal carbonization. Applied Soil Ecology 45:238-242.

18. Gundale MJ, Thomas H, DeLuca TH (2007) Charcoal effects on soil solution chemistry and growth of Koeleria macrantha in the ponderosa pine/douglas fir ecosystem. Biol. Fertil. Soils 43:303-31 1 .

19. Deenik JL, McClellan T, Uehara G, Antal MJ, Campbell S (2010) Charcoal

volatile matter content influences plant growth and soil nitrogen transformations. Soil Sci. Soc. Am. J. 74:1259-1270.

20. Spokas KA, Baker JM, Reicosky DC (2010) Ethylene: potential key for biochar amendment impacts. Plant Soil 333:443-452. DOI : 10.1007/s1 1 104-010-0359-5. 21 . Olsson M, Ramnas O, Petersson G (2004) Specific volatile hydrocarbons in

smoke from oxidative pyrolysis of softwood pellets. J. Anal. Appl. Pyrol. 71 :847- 854. 22. Song JZ, Peng PA (2010) Characterization of black carbon materials by pyrolysis-gas chromatography-mass spectrometry. J. Anal. Appl. Pyrol. 87:129- 137. 23. Ellen R. Graber, Yael Meller Harel, Max Kolton, Eddie Cytryn, Avner Silber, Dalia Rav David, Ludmilla Tsechansky, Menahem Borenshtein,Yigal Elad. Biochar impact on development and productivity of pepper and tomato grown in fertigated soilless media, Plant Soil (2010) 337:481 -496. 24. Smith CR, Sleighter R, Patrick H, Lee JW (2013) Molecular characterization of inhibiting biochar water-extractable substances using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, ACS journal: Environ. Sci. Technol. 47:13294-13302. 25. Clapp RW, Jacobs MM, Loechler EL (2008) Environmental and occupational cause of cancer" new evidence 2005-2007, Review of Environmental Health, 23(1 ):1 -37.

26. Daiwang Xu, Trevor M. Penning, Ian A. Blair, and Ronald G. Harvey (2009)

Synthesis of Phenol and Quinone Metabolites of Benzo[a]pyrene, a Carcinogenic

Component of Tobacco Smoke Implicated in Lung Cancer, J. Org. Chem. 2009, 74:597-604.

27. Rose, Alani; Ken, Drouillard; Kehinde, Olayinka; Babajide, Alo (2012)

Bioaccumulation of polycyclic aromatic hydrocarbons in fish and invertebrates of

Lagos Lagoon, Nigeria, Journal of Emerging Trends in Engineering and Applied Sciences, 3(2): 287-296.

28. J.D. Pleil, M.A. Stiegel, J.R. Sobus, S. Tabucchi, A.J. Ghio, M.C. Madden (2010) Cumulative exposure assessment for trace-level polycyclic aromatic

hydrocarbons (PAHs) using human blood and plasma analysis, Journal of Chromatography B, 878:1753-1760.

29. Smith CR, Buzan EM, Lee JW (2012) Potential impact of biochar water- extractable substances on environmental sustainability, ACS Sustainable Chem.

Eng. 2013, 1 , 1 18-126; DOI: 10.1021/sc300063f.

30. Axel Funke and Felix Ziegler (2010) Hydrothermal carbonization of biomass: A summary and discussion of chemical mechanisms for process engineering, Biofuels, Bioprod. Bioref. 4:160-177.

31 . H.-G. Ramke, D. Blohse, H.-J.Lehmann and J. Fettig (2009) Hydrothermal

carbonization of organic waste, in: COSSU, R. ; DIAZ, L. F. ; STEGMANN, R. (EDTS.), 2009: Sardinia 2009: Twelfth International Waste Management and Landfill Symposium, Sardinia, Italy, 05-09 October 2009, Proceedings, CISA Publisher.

Matthew D. Huff, Sandeep Kumar, James W. Lee (2014) Comparative analysis of pinewood, peanut shell, and bamboo biomass derived biochars produced via hydrothermal conversion and pyrolysis, Manuscript submitted for publication.

Lee, J. W.; Kidder, M. ; Evans, B. R. ; Paik, S. ; Buchanan lii, A. ; Garten, C. T. ; Brown, R. C, Characterization of biochars produced from cornstovers for soil amendment. Environmental science & technology 2010, 44, (20), 7970-7974.

Skjemstad, J. O. ; Gillman, G. P. ; Massis, A. ; Spouncer, L. R., Measurement of Cation Exchange Capacity of Organic-Matter Fractions from Soils using a Modified Compulsive Exchange Method. Communications in Soil Science and Plant Analysis 2008, 39, (5-6), 926-937.

Claims

CLAIMS What is claimed is:

1 . A carboxylated biochar composition produced by the method comprising reacting a biochar source with a carboxylating reagent in the presence of a catalyst in a thermochemical biomass process, wherein the biochar source is contacted with the carboxylating reagent at a pressure sufficient to (a) suppress decarboxylation of the carboxylated biochar composition; (b) produce a toxin-free carboxylated biochar composition; and (c) produce a carboxylated biochar composition having an optimal set of characteristics selected from the group consisting of optimal carboxyl content, optimal oxygen-to-carbon molar ratio, enhanced cation exchange capacity, surface area, composition, nutrient contents, biochar particle size, uniformity, and any combination thereof.

2. The biochar composition of claim 1 , wherein the carboxylating reagent comprises C0₂, CO, a CO₂/water vapor stream, a CO₂-N₂ mixture, a CO₂-Ar mixture, a CO₂-He mixture, a CO₂-CO mixture, a CO₂-O₂ mixture, CaCO₃, Ca(HCO₃) , MgCOs, Mg(HCO₃) , K₂CO₃, KHCO₃, NaHCO₃, Na₂CO₃, Cu₂CO₃, CuHCO₃, AgHCO₃, Ag₂CO₃, Cs₂CO₃, or any combination thereof.

3. The biochar composition of claim 1 , wherein the carboxylating reagent comprises catalytic CO₂ plasma and/or carbon monoxide (CO) plasma.

4. The biochar composition of claim 1 , wherein the carboxylating reagent comprises from 15% to 100% CO₂ and is injected at a partial pressure from 1 to 300 atmospheres in a heatable closed system.

5. The biochar composition of claim 1 , wherein the catalyst is coated on the surface of a reactor wall and/or a mixing device comprising mixing balls or beads.

6. The biochar composition of claim 1 , wherein the catalyst comprises copper(l), silver(l), gold(l), zero-valent nickel (Ni), Cu (ll)-exchanged montmorillonite K10 clay, copper(l) oxide (Cu₂O), copper(l) carbonate (Cu₂CO₃), copper(l)

bicarbonate (CuHCO₃), copper(l) chloride (CuCI), copper(l) iodide (Cul), copper (I) hydroxide, copper(l) nitrate, silver oxide (Ag₂O), silver(l) carbonate (Ag₂CO₃), silver(l) bicarbonate (AgHC0₃), silver chloride (AgCI), silver(l) hydroxide, silver nitrate (AgN0₃), silver(l) iodide (Agl), AgOAc, (4,7-dichloro-1 ,1 0-phenanthroline)- bis(triphenylphosphine) copper(l) nitrate, zero-valent nickel (Ni) such as bis(cyclooctadiene)nickel(0) also known as Ni(cod)₂, low-valent nickel complexes, or any combination thereof.

7. The biochar composition of claim 1 , wherein the said thermochemical biomass carbonization process is selected from the group consisting of ambient pressure biomass pyrolysis, slow biomass pyrolysis, fast biomass pyrolysis, biomass gasification, pressurized biomass pyrolysis, hydrothermal biomass conversion, and any combination thereof.

8. The biochar composition of claim 1 , wherein the biochar source comprises a

byproduct of a pyrolysis or gasification process, material acquired from a biochar deposit, natural coal materials, biomass, or a combination thereof.

9. The biochar composition of claim 8, wherein the biomass comprises corn stover, switchgrass, miscanthus, wheat straw, rice straw, barley straw, alfalfa, bamboo, hemp, sugarcane, nut shell material, grain hull material, woodchips, sawdust, paper or wood pulp, food waste, agricultural waste, forest waste, or a

combination thereof.

10. The biochar composition of claim 1 , wherein the suppression of decarboxylation and removal of toxins are accomplished simultaneously by use of a C0₂- containing gas stream flowing through the biomass carbonization reactor to purge the biochar products and effectively remove the toxins from the carboxylated biochar composition.

1 1 . The biochar composition of claim 1 , wherein the removal of toxins and the

suppression of decarboxylation are accomplished through the use of increased C0₂ partial pressure at a temperature of 300^0 to 800 °C.

12. The biochar composition of claim 1 1 , wherein the use of said increased C0₂

partial pressure is conducted in a sealed pressure-resistant reactor with fixed volume resulting in a thermo-physically auto-pressurized biomass pyrolysis process.

13. The biochar composition of claim 1 , wherein the potential biochar toxins are selected from the group consisting of residual pyrolysis bio-oils, small organic molecules having a molecular mass of less than or equal to 500 Dalton, polycyclic aromatic hydrocarbons, degraded lignin-like species rich in oxygen containing functionalities, phenolic type of phytotoxins with at least one carboxyl group, and any combination thereof.

14. The biochar composition of claim 1 , wherein during the process pyrolysis vapors are produced, wherein the pyrolysis vapors can be condensed to produce a bio- oil liquid or a syngas product.

15. The biochar composition of claim 14, wherein uncondensed pyrolysis vapors are filtered with a C0₂ membrane filtration system to recover C0₂, wherein the recovered C0₂ is re-used as a carboxylating reagent.

16. The biochar composition of claim 1 , wherein the carboxylated biochar

composition is produced by quenching with C0₂-containing water, an inert substance, or a combination thereof.

17. The biochar composition of claim 1 , wherein the carboxylated biochar

composition has a cation exchange capacity of at least 130 mmol/kg and is free of biochar toxins.

18. The biochar composition of claim 1 , wherein the carboxylated biochar

composition has an oxygen-to-carbon molar ratio of at least 0.15:1 and is free of biochar toxins.

19. The biochar composition of claim 1 , wherein the carboxylated biochar

composition has an oxygen-to-carbon molar ratio of at least 0.26:1 and is free of biochar toxins.

20. The biochar composition of claim 1 , wherein the carboxylating agent is carbon dioxide (C0₂)-plasma, where the carboxylated biochar composition has a cation exchange capacity of at least 264% of that of the untreated biochar and is free of biochar toxins.

21 . The method of claim 1 , wherein the carboxylating agent is carbon

monoxide(CO)-plasma, where the carboxylated biochar composition has a surface oxygen-to-carbon molar ratio up to 0.70:1 at the biochar carbon surface and is free of biochar toxins.

22. A carboxylated biochar composition, wherein the composition is (a) toxin-free, and (b) has an optimal set of characteristics selected from the group consisting of optimal carboxyl content, optimal oxygen-to-carbon molar ratio, enhanced cation exchange capacity, surface area, composition, nutrient contents, biochar particle size, uniformity, and any combination thereof.

23. The biochar composition of claim 22, wherein the carboxylated biochar

composition has a cation exchange capacity of at least 130 mmol/kg and is free of biochar toxins.

24. The biochar composition of claim 22, wherein the carboxylated biochar

composition has an oxygen-to-carbon molar ratio of at least 0.15:1 and is free of biochar toxins.

25. The biochar composition of claim 22, wherein the carboxylated biochar

composition has an oxygen-to-carbon molar ratio of at least 0.26:1 and is free of biochar toxins.

26. A method for making a carboxylated biochar composition the method comprising reacting a biochar source with a carboxylating reagent in the presence of a catalyst in a thermochemical biomass process, wherein the biochar source is contacted with the carboxylating reagent at a pressure sufficient to (a) suppress decarboxylation of the carboxylated biochar composition; (b) produce a toxin-free carboxylated biochar composition; and (c) produce a carboxylated biochar composition having an optimal set of characteristics selected from the group consisting of optimal carboxyl content, optimal oxygen-to-carbon molar ratio, enhanced cation exchange capacity, surface area, composition, nutrient contents, biochar particle size, uniformity, and any combination thereof.

27. A method of removing at least one contaminant from a medium, the method

comprising contacting the medium with the carboxylated biochar composition of claims 1 -25.

28. The method of claim 27, wherein the medium comprises water or air.

29. The method of claim 27, wherein the at least one contaminant comprises a

cation, an organic molecule, or an inorganic pollutant.

30. The method of claim 27, wherein the at least one contaminant comprises a cation and the cation comprises NH₄ ⁺, Fe²⁺, Fe³⁺, Cu²⁺, Cd²⁺, Sr²⁺, Ni²⁺, Zn²⁺, Cr³⁺, Pb²⁺, Hg²⁺, uranium ions, plutonium ions, osmium ions, platinum ions, gold ions, iridium ions, ruthenium ions, rhodium ions, cobalt ions, titanium ions, thallium ions, tin ions, indium ions, gallium ions, germanium compounds, arsenic compounds, selenium compounds, and any combination thereof.

31 . A filter comprising the carboxylated biochar composition of claims 1 -25.

32. A fertilizer comprising the carboxylated biochar composition of claims 1 -25.

33. A soil formulation comprising the carboxylated biochar composition of claims 1 - 25.