Patent Description:
Furfural plays an important role in the chemical industry as a precursor of furan and derivatives of furan, including furfuryl alcohol. Also, furfural is used for the production of resins by condensation reaction of furfural with formaldehyde, phenol, acetone or urea. In addition, furfural can be used as a solvent, vulcanization enhancer, insecticide, fungicide, germicide, or in the production of such compounds, as well as for use as a potential fuel.

Furfural is an attractive compound because it can be produced from renewable resources. One potential source of renewable (non-fossil) feedstock for the production of furfural are substances selected from the group consisting of xylose, oligosaccharides comprising xylose units and polysaccharides comprising xylose units originating from cellulose-containing biomass.

Xylose is a monosaccharide also referred to as wood sugar which belongs to the group of pentoses. Oligo- and polysaccharides which comprise xylose units typically occur in plants, especially in woody parts of plants, in straw, and in the seeds or the shells of the seeds of several plants. Oligo- and polysaccharides which consist of xylose units are generally referred to as xylans. Oligo- and polysaccharides which consist of xylose units and other monosaccharide units are generally referred to as heteroxylans. Xylans and heteroxylans belong to the group of polyoses. Polyoses (earlier also referred to as hemicellulose) are polysaccharides which in plant biomass typically occur in a composite wherein said polyoses and lignin are incorporated between cellulose fibres. Dry plant biomass (water content below <NUM> wt. %) which comprises cellulose, polyoses and lignin is also referred to hereinabove and hereinbelow as lignocellulose.

One general process to produce furfural from xylose in biomass material is "aqueous dehydration" using batchwise or continuous acid-catalysed dehydration. This type of aqueous dehydration process provides a yield of about <NUM>-<NUM> mol% furfural (meaning only <NUM> - <NUM> % of the total moles of xylose is converted to furfural) (Furfural - a promising platform for lignocellulosic biofuels by <NPL>). With such low yields, it degrades <NUM>-<NUM> mol% of the valuable xylose into undesirable by-products that foul equipment and contaminate the water stream.

Another general process which has improved yields over aqueous dehydration is "biphasic dehydration," which adds a water-insoluble solution to the aqueous dehydration to extract the furfural into an organic phase to protect it from further degradation, and optionally a salt in the aqueous phase to further assist the extraction of furfural into the water-insoluble solution (Lange et al. While biphasic dehydration can increase the yield to <NUM> to <NUM> mol%, it still degrades <NUM> to <NUM> mol% of the valuable xylose into undesirable by-products that foul equipment and build up in the solvent recycle stream.

Yet another process with improved yields over biphasic dehydration is to extract and recover xylose as a solid product from hydrolysis of biomass and subjecting the recovered xylose in a dehydration reaction (<NPL>;<NPL>). Because the xylose is not in solution, the dehydration reaction can be carried out in a single phase under conditions favourable to the furfural conversion, such as using polar aprotic solvents which can provide furfural yields of <NUM> mol%. However, this process requires isolation of the xylose from the hydrolysate, e.g., by distilling out all the water, which can be highly energy demanding. Such isolation process to recover the xylose in solid form can further concentrate contaminants of the xylose streams in the solid xylose end product.

Although there are processes to provide improved isolation xylose from hydrolysate, such as (<CIT>), these processes nonetheless, are directed to providing the xylose in dry form to allow the xylose to then be converted and/or used in the production of a C5 sugar-platform of biochemical and biofuels.

<CIT> discloses a method for producing furfural, comprising: enzymatically isomerizing xylose to xylulose in an aqueous solution; extracting both xylose and xylulose with an immiscible non-aqueous phase containing a water-insoluble boronic acid (such as a phenyl boronic acid or a naphthalene boronic acid) which forms diboronate esters with the two isomers and drives the isomerisation reaction towards formation of more xylulose; extracting xylulose from the immiscible non-aqueous phase with a mixture of acidic aqueous and aprotic solvents such as DMSO; heating the mixture from previous step, containing extracted xylulose, to dehydrate xylulose to furfural.

It would, therefore, be advantageous to provide a process for the production of furfural from a xylose-containing aqueous solution with a relatively higher yield without expensive isolation of xylose in dry form.

Accordingly, the present invention provides a process for a method for producing furfural comprising:.

The present disclosure also provides for a method for producing furfural comprising:.

Optionally, step (i) comprises providing at least a portion of the second non-aqueous phase from (h) to a distillation process to recover an overhead product comprising furfural and a bottom product comprising water-insoluble solvent and water-insoluble boronic acid. Optionally, the method further comprises providing at least a portion of the bottom product for use as part of the extraction solution. Optionally, at least a portion of the first aqueous phase in (c) comprises water-soluble solvent, water-insoluble solvent, and water-insoluble boronic acid, said method further comprising: separating at least a portion of the first aqueous phase in (c) from the first combined solution; and further processing at least a portion of the separated first aqueous phase to recover at least one of water-soluble solvent, water-insoluble solvent, and water-insoluble boronic acid.

Optionally, the method further comprises performing at least a portion of steps (c) and (d) in a liquid-liquid extraction unit in counter-current operation, wherein the xylose-containing solution is provided at a higher temperature than the temperature of the extraction solution.

Optionally, the method further comprises providing at least a portion of the second aqueous phase from (h) to a distillation process to recover an overhead product comprising water and furfural and an acidic bottom product comprising water and water-soluble solvent, wherein the bottom product has a pH of less than <NUM>. Optionally, the method further comprises providing at least a portion of the acidic bottom product for use as part of the conversion solution.

Optionally, the method further comprises providing at least a portion of the second aqueous phase from (h) to a solvent-extraction process to recover furfural, wherein at least a portion of solvent used in the extraction process comprises the distillation bottom product comprising water-insoluble solvent and water-insoluble boronic acid.

Optionally, the xylose-containing solution is a hydrolysate. Optionally, the water-insoluble boronic acid has up to <NUM> wt. % solubility in water at <NUM>. Optionally, the water-insoluble boronic acid is selected from the group consisting of phenylboronic acid, <NUM>-biphenylboronic acid, <NUM>-butylphenyl boronic acid, <NUM>-tert-Butylphenyl boronic acid, <NUM>-ethylphenyl boronic acid, <NUM>-naphthylboronic acid, naphthalene-<NUM>-boronic acid, o-tolylboronic acid, m-tolylboronic acid, (<NUM>-methylpropyl) boronic acid, butylboronic acid, octylboronic acid, phenethyl boronic acid, cyclohexyl boronic acid, and any combination thereof. Optionally, the water-insoluble solvent has up to <NUM> wt. % solubility in water at <NUM>. Optionally, the water-insoluble solvent is selected from the group consisting of benzoic acid, cresol (m), di-isopropyl ether, terephthalic acid, diethylene glycol diethyl ether, anisole, salicylic acid, <NUM>,<NUM> xylenol, 4Et-phenol, toluene, benzofuran, ethylbenzene, octanoic acid, <NUM>-methylnaphtalene, nitrobenzene, guaiacol, heptane, <NUM>-octanol, and methylisobutyl ketones, an any combination thereof. Optionally, at least one of the water-insoluble boronic acid and water-insoluble solvent has a boiling point higher than that of furfural, preferably at least <NUM> higher. Optionally, the water-soluble solvent has a logP (octanol-water partition co-efficient) in a range from (-<NUM>) to <NUM>. Optionally, the water-soluble solvent is selected from the group consisting of dimethyl sulfoxide, diglyme, sulfolane, gamma butyrolactone, succinic acid, nMe-acetamide, dioxane, nMe-pyrrolidone, gamma valerolactone, acetone, Acetic acid, and any combination thereof. Optionally, the water-soluble solvent has a boiling point higher than that of water, preferably at least <NUM> higher.

The present invention will now be described in detail with reference to embodiments thereof as illustrated in the accompanying drawings. References to "one embodiment", "an embodiment" "an example embodiment", etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which would be apparent to those skilled in the art, are within the scope of the invention.

Although the description herein provides numerous specific details that are set forth for a thorough understanding of illustrative embodiments, it will be apparent to one skilled in the art that embodiments may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. The features and advantages of embodiments may be better understood with reference to the drawings and discussions that follow.

In addition, when like elements are used in one or more figures, identical reference characters will be used in each figure, and a detailed description of the element will be provided only at its first occurrence. Some features or components of the systems or processes described herein may be omitted in certain depicted configurations in the interest of clarity. Moreover, certain features such as, but not limited to pumps, valves, gas bleeds, gas inlets, fluid inlets, fluid outlets and the like have not necessarily been depicted in the figures, but their presence and function will be understood by one having ordinary skill in the art. Similarly, the depiction of some of such features in the figures does not indicate that all of them are depicted.

The present inventors have surprisingly found that xylose in an aqueous solution can be extracted as xylose-diboronate ester (BA<NUM>X) into the non-aqueous phase of an extraction solution comprising a water-insoluble solvent and a water-insoluble boronic acid, and the non-aqueous phase can be separated for conversion or dehydration of the xylose-diboronate ester (BA<NUM>X) into furfural with an acidic conversion solution comprising water and a water-soluble solvent. The furfural can then be recovered using any suitable methods. Optionally, instead of or in addition to making furfural, the xylose-diboronate ester (BA<NUM>X) in the separated non-aqueous phase can be back-extracted into xylose to recover the xylose away from impurities or other undesired compounds that may be present in the initial xylose solution.

As used herein, "aqueous solution" has its ordinary meaning, which is a solution in which a solute is dissolved in a solvent, and the solvent is water. "Water-insoluble" also has its ordinary meaning, which describes the low solubility of a substance in water. Low solubility means preferably up to <NUM> wt. % solubility at <NUM>, including up to <NUM> wt. % solubility, up to <NUM> wt. % solubility, up to <NUM> wt. % solubility, or up to <NUM> wt. % solubility. Alternatively, "water-insoluble" as used herein describes a substance with an octanol-water partition coefficient LogP (also called LogKow) of at least <NUM>, including at least <NUM>, or at least <NUM>. "Water-soluble" as used herein describes a substance with a LogP in a range from (-<NUM>) to <NUM>, preferably from (-<NUM>) to (-<NUM>), more preferably (-<NUM>) to (-<NUM>). "Aqueous phase" has its ordinary meaning, which describes a liquid phase in which the concentration of water is greater than the concentration of water-insoluble liquid component(s). "Non-aqueous" has its ordinary meaning, which describes a liquid phase in which the concentration of water-insoluble liquid component(s) is greater than the concentration of water.

The present disclosure provides for a process for producing furfural comprising:.

In addition, the present disclosure also provides for a method for producing furfural comprising:.

Referring to <FIG>, the process comprises providing a xylose-containing aqueous solution <NUM> comprising xylose in an amount of greater than or equal to <NUM> wt. %, including preferably greater than or equal to <NUM> wt. %, more preferably greater than or equal to <NUM> wt. %, or most preferably greater than or equal to <NUM> wt.

The process described herein can be suitable for use with a xylose-containing aqueous solution with any pH, from <NUM> to <NUM>. That is, the process described herein can be used with xylose-containing aqueous solution <NUM> that is acidic with a pH in a range from <NUM> to <NUM>, xylose-containing aqueous solution <NUM> that is basic with a pH in a range of <NUM> to <NUM>, or xylose-containing aqueous solution <NUM> that is neutral with a pH from greater than <NUM> to less than <NUM>.

While any xylose-containing solution as described herein may be provided for use in the process, a suitable xylose-containing solution <NUM> can include one that is derived from a pre-treatment step in which a cellulosic biomass is hydrolysed by methods known by one of ordinary skill in the art, including hot water at neutral pH (e.g. steam explosion), hot water at acidic pH e.g. by addition of organic or inorganic acids (e.g. dilute acid and reversible-acid pre-treatment), or hot water at basic pH e.g. by addition of organic or inorganic base (e.g. kraft pulping), as described e.g. by <NPL>, as well as those methods that employ ionic liquids.

In a preferred embodiment the term "cellulosic biomass" refers to biomass comprising a) cellulose as well as b) one or more substances selected from the group consisting of polyoses and other sources of xylose units. For example, lignocellulose is cellulosic biomass that can serve as a source of xylose units. Suitable cellulosic biomass, particularly lignocellulose, includes any material and/or agricultural biomass having a lignocellulose (or hemicellulose) concentration of at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, or at least <NUM>%. Exemplary lignocellulosic biomasses that can be used in this regard include, but are not limited to: corn cobs, crop residues such as corn husks, corn stover, grasses, wheat, wheat straw, barley straw, hay, rice straw, switchgrass, waste paper, sugar cane bagasse, sorghum, components obtained from milling of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers and animal manure, soy hulls from soybean processing, rice hulls from rice milling, corn fibre from wet milling or dry milling, bagasse from sugarcane processing, pulp from sugar beets processing, distillers grains, and the like.

Suitably, the pretreatment step as described in <CIT> and <CIT> can be used to hydrolyse cellulosic biomass to produce a xylose-containing solution that may be used in the process described herein. As noted above, such product of hydrolysis may be referred to as a hydrolysate, which comprises xylose in an amount of at least <NUM> wt. %, including preferably at least <NUM> wt. %, at least <NUM> wt. %, or most preferably at least <NUM> wt.

Preferably, xylose-containing aqueous solution <NUM> may be a product of an acidic pre-treatment based on diluted H2SO4 or concentrated HESA as acid, as described in <CIT>.

Xylose-containing solution <NUM> is an aqueous solution, which means it is a solution in which the solvent is liquid water.

Referring to <FIG>, the process further comprises providing an extraction solution <NUM> comprising an organic or water-insoluble boronic acid (BA: R-B(OH)<NUM>) and a water-insoluble solvent.

A suitable water-insoluble boronic acid is one with low water solubility, preferably up to <NUM> wt. % solubility (meaning the selected water-insoluble boronic acid is soluble up to <NUM> wt. % in water at <NUM>), including up to <NUM> wt. % solubility, up to <NUM> wt. % solubility, up to <NUM> wt. % solubility, or up to <NUM> wt. % solubility. Alternatively, a suitable water-insoluble boronic acid is one with an octanol-water partition coefficient LogP (also called LogKow) of at least <NUM>, including at least <NUM>, or at least <NUM>.

In a preferred embodiment, a suitable water-insoluble boronic acid has an atmospheric boiling point that is higher than the atmospheric boiling point (Tb) of furfural, which is <NUM>, to allow for use of distillation as an option for recovery of furfural as an overhead product. Preferably, the suitable water-insoluble boronic acid has an atmospheric boiling point that is at least <NUM> higher (i.e., atmospheric boiling point of at least 164C), more preferably at least <NUM> (i.e., atmospheric boiling point of at least 167C).

For instance, one exemplary suitable water-insoluble boronic acid is phenyl boronic acid, which has a water solubility of <NUM> wt. % at <NUM> and a logP of <NUM> and an atmospheric boiling point Tb of <NUM>. Other substituted phenyl boronate compounds are also suitable, such as alkyl phenyl boronate, naphthanyl boronate and substituted naphthanyl boronate, and any combination thereof. For example, one suitable example is <NUM>-napthyl boronic acid, which has a water solubility of <NUM> wt. % at <NUM> and a logP of <NUM> and a Tb of <NUM>. Another example is octylboronic acid which is reported as water-insoluble and has a logP of <NUM> and a Tb of <NUM>.

Table <NUM> below shows examples of suitable water-insoluble boronic acid that can be used in extraction solution <NUM>, along with their solubility description and/or LogP, and atmospheric boiling point (Tb).

One or more (such as two or more) suitable water-insoluble boronic acid as described here can be used in extraction solution <NUM> as described herein based on design choices by one of ordinary skill in the art. While certain descriptions may refer to "a water-insoluble boronic acid," "the water-insoluble boronic acid," or "the boronic acid," it is understood that such reference can include more than one (such as two or more) water-insoluble boronic acids, as applicable.

Referring to <FIG>, extraction solution <NUM> further comprises a water-insoluble solvent. A suitable water-insoluble solvent is one with low water solubility to lower the likelihood of dissolution in water, preferably up to <NUM> wt. % solubility (meaning the selected water-insoluble solvent is soluble up to <NUM> wt. % of in water at <NUM>), including up to <NUM> wt. % solubility, up to <NUM> wt. % solubility, up to <NUM> wt. % solubility, or up to <NUM> wt. % solubility. Alternatively, a suitable water-insoluble solvent is one with an octanol-water partition coefficient LogP (also called LogKow) of at least <NUM>, including at least <NUM>, or at least <NUM> and up to <NUM>, up to <NUM>, or up to <NUM>, preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, and most preferably from <NUM> to <NUM>.

In a preferred embodiment, a suitable water-insoluble solvent has an atmospheric boiling point that is higher than the atmospheric boiling point of furfural, which is <NUM>, to allow for use of distillation as an option for recovery of furfural as an overhead product. Preferably, the suitable water-insoluble boronic acid has an atmospheric boiling point that is at least <NUM> higher (i.e., atmospheric boiling point of at least <NUM>), more preferably at least <NUM> (i.e., atmospheric boiling point of at least <NUM>).

In a preferred embodiment, the water-insoluble solvent has a good affinity for the xylose-diboronate ester and a good affinity for furfural. By affinity we mean a high partition coefficient of the BA<NUM>X or furfural between extraction solution <NUM> and water in first combined solution <NUM> (described further below), including such partition coefficient of at least <NUM>, preferably at least <NUM>, preferably at least <NUM>, and most preferably at least <NUM>.

Examples of suitable water-insoluble solvent that have good affinity for the xylose-diboronate ester and a good affinity for furfural include aromatic hydrocarbons, preferably toluene and most preferably methyl naphthalene or aromatic mixtures rich in alkylbenzene or alkyl-naphthalene components. Water-insoluble solvent also include aromatic components that carry heteroatoms such as nitrobenzene, anisole, guaiacol, cresols, as well as aliphatic components free of heteroatoms (e.g., heptane and other alkanes) or containing heteroatoms (e.g., <NUM>-octanol, methylisobutyl ketones).

Table <NUM> below shows examples of suitable water-insoluble solvents that can be used in extraction solution <NUM>, along with their solubility (LogP) and atmospheric boiling point (Tb).

One or more (such as two or more) suitable water-insoluble solvents as described here can be used in extraction solution <NUM> as described herein based on design choices by one of ordinary skill in the art. While certain descriptions may refer to "a water-insoluble solvent" or "the water-insoluble solvent," it is understood that such reference can include more than one (such as two or more) water-insoluble solvents, as applicable.

Suitably, extraction solution <NUM> can comprise at least <NUM> wt. %, including at least <NUM> wt. %, at least <NUM> wt. %, or at least <NUM> wt. % of the water-insoluble boronic acid and up to <NUM> wt. %, including up to <NUM> wt. %, up to <NUM> wt. %, or up to <NUM> wt. % of the water-insoluble solvent.

Referring to <FIG>, the process further comprises combining an amount of xylose-containing solution <NUM> with an amount of extraction solution <NUM> to provide first combined solution <NUM>, wherein the ratio of boronic acid to xylose in first combined solution <NUM> is at least <NUM>:<NUM> molar, respectively, preferably at least <NUM>:<NUM> and most preferably at least <NUM>:<NUM>. It is understood that one of ordinary skill would be capable of (i) determining the amount of xylose in xylose-containing solution <NUM> (if such amount is unknown) using methods such as high-pressure liquid chromatography (HPLC), (ii) preparing extraction solution <NUM> with a suitable amount of water-insoluble boronic acid and water-insoluble solvent, in accordance with the description provided herein, and (iii) determining the amount of such extraction solution <NUM> to be added to a particular amount of xylose-containing solution <NUM> so that the ratio of boronic acid to xylose in first combined solution <NUM> is at least <NUM>:<NUM> molar.

When xylose-containing solution <NUM> is combined with extraction solution <NUM> to form first combined solution <NUM>, at least a portion of the xylose from solution <NUM> comes into contact with at least a portion of organic boronic acid from solution <NUM>. This contact allows the xylose to be converted to xylose monoboronate and subsequently xylose-diboronate ester, which has low solubility in water, so it has a greater affinity toward the water-insoluble solvent of solution <NUM> that is in solution <NUM>. As more xylose is converted to xylose-diboronate esters, non-aqueous phase <NUM> comprising (i) boronic acid and water-insoluble solvent from extraction solution <NUM> and (ii) xylose-diboronate esters begins to form. Correspondingly, aqueous phase <NUM> with less xylose than xylose-containing solution <NUM> begins to form as well.

After an amount of time, which can be determined or selected by one of ordinary skill to achieve certain desired objectives, first combined solution <NUM> comprises aqueous phase <NUM> and a non-aqueous phase <NUM>, said non-aqueous phase comprising at least a portion of the xylose from xylose-containing solution <NUM> as xylose-diboronate ester (BA<NUM>X). Preferably, non-aqueous phase <NUM> comprises at least <NUM> mol% of the xylose from xylose-containing solution <NUM> as xylose-diboronate ester, more preferably at least <NUM> mol%, including at least <NUM> mol% or at least <NUM> mol%.

Preferably, first combined solution <NUM> is mixed using suitable methods, such as mixing, stirring, static mixer, turbulent flow, jet loop, etc to allow xylose and organic boronic acids molecules to interact, thereby improving the yield of xylose-diboronate-ester that forms. Examples of suitable methods for mixing can additionally or alternatively include internal components of the separation or extraction units noted above. Suitably, the mixing may be performed for at least <NUM> minutes, preferably at least <NUM> minutes, and most preferably at least <NUM> minutes.

Referring to <FIG>, the process further comprises separating at least a portion of non-aqueous phase <NUM> from first combined solution <NUM>. While <FIG> shows aqueous phase <NUM> also being separated, this is optional and is included in <FIG> to illustrate the two phases (<NUM> and <NUM>) being described. While the steps of forming first combined solution <NUM> and separating non-aqueous phase <NUM> can be performed separately, they can suitably be carried out at least partially (and/or fully) together via a liquid-liquid extraction or separation process as further described below.

After at least a portion of the xylose in first combined solution <NUM> has been allowed to react to form xylose-diboronate esters and first combined solution <NUM> comprises aqueous phase <NUM> and non-aqueous phase <NUM>, the phases <NUM> and <NUM> can be separated using suitable methods, such as liquid-liquid extraction or separation methods, suitably in co-current flow and preferably counter-current flow. It is understood by one of ordinary skill that aqueous phase <NUM> can contain an amount of water-insoluble boronic acid and water-insoluble solvent from extraction solution <NUM> but the concentration of water in aqueous phase <NUM> is higher than the concentration of water-insoluble components from extraction solution <NUM>. Similarly, it is understood that non-aqueous phase <NUM> can contain an amount of water but the concentration of water-insoluble boronic acid and water-insoluble solvent in non-aqueous phase <NUM> is higher than the concentration of water.

Such extraction or separation methods can be performed using a series of mixers-decanters but can also be performed in a unit or series of units that integrates mixing and decanting and is preferably operated in counter current flow. Such unit can optionally contain internal components to facilitate the mixing and decanting, including stationary components (trays, random or structured packings) or agitators (e.g., rotating or oscillating disks).

Referring to <FIG>, forming of first combined solution <NUM> and separating of non-aqueous phase <NUM> can be performed at ambient temperature (at least <NUM>), and optionally either or both can be performed at elevated temperature, such as at least <NUM>, at least <NUM>, or at least <NUM>. One exemplary factor to consider in selecting an elevated temperature is that higher temperatures will allow shorter extraction times to facilitate the rate of reaction of xylose with boronic acid, and correspondingly, the conversion from xylose to xylose-diboronate ester in first combined solution <NUM>. There are other factors for consideration known to one of ordinary skill in selecting conditions to perform step <NUM> and/or step <NUM>, such as energy requirements.

In one embodiment, forming of first combined solution <NUM> and separating of non-aqueous phase <NUM> can be performed isothermally (e.g., temperature is the same for both steps). Additionally, or alternatively, they can be performed under a temperature gradient. One suitable way of providing a temperature gradient is to provide xylose-containing solution <NUM> at a higher temperature than extraction solution <NUM>. For instance, the temperature of xylose-containing solution <NUM> can be at least <NUM> higher than the temperature of extraction solution <NUM>, preferably at least <NUM> higher, more preferably at least <NUM> higher, and most preferably at least <NUM> higher. Referring to <FIG>, the at least a portion of non-aqueous phase <NUM>, preferably at least <NUM>% of non-aqueous phase <NUM>, is separated from first combined solution <NUM> using one or more suitable separation methods as described above. More preferably, at least <NUM>%, including at least <NUM>%, or at least <NUM>% of non-aqueous phase <NUM> is separated from first combined solution <NUM>. Preferably, such separation is achieved using at least liquid-liquid separation via gravity whereby phases <NUM> and <NUM> are retained in a separator at least an amount of time that allows phases <NUM> and <NUM> to separate by the differences in density of phases <NUM> and <NUM>, with aqueous phase <NUM> typically being above non-aqueous phase <NUM>. It is known to one of ordinary skill that such separation via liquid-liquid separation can also be facilitated by enhanced gravity using, for example, hydrocyclone and centrifugation devices. It is understood that one of ordinary skill would be capable of selecting the suitable separator specifications (such as size, configuration, including whether and which internal components to include to facilitate mixing and decanting, arrangement, including whether to use dedicated units (e.g., mixer-decanter) and/or integration with the extraction unit, and whether and which enhanced gravity devices to include) and suitable amount of time to achieve an equilibrium condition between phases <NUM> and <NUM> at the temperature and pressure of separation of first combined solution <NUM> to allow for separation and/or removal of at least a portion of non-aqueous phase <NUM> from first combined solution <NUM>, which effectively removes non-aqueous phase <NUM> from aqueous phase <NUM>. As noted above, the xylose-diboronate ester has lower solubility in water, which means non-aqueous phase <NUM> comprises a greater portion of the xylose-diboronate ester than aqueous phase <NUM>. Separation of non-aqueous phase <NUM> also separates or removes a greater portion of the xylose-diboronate ester from first combined solution <NUM>.

Referring to <FIG>, the process further comprises combining at least a portion of the separated portion of non-aqueous phase <NUM> with conversion solution <NUM> to form second combined solution <NUM>, wherein conversion solution <NUM> comprises a water-soluble solvent and water and has a pH of less than or equal to <NUM>. Preferably, at least <NUM>% of the separated non-aqueous phase <NUM> is combined with conversion solution <NUM>, more preferably at least <NUM>%, including at least <NUM>%, at least <NUM>%, or all of the separated non-aqueous phase <NUM> is combined with conversion solution <NUM>. The ratio of conversion solution <NUM> to non-aqueous phase <NUM> in second combined solution <NUM> is in a range from <NUM> to <NUM>, preferably from <NUM> to <NUM>, and more preferably from <NUM> to <NUM>, by weight, respectively. Notably, second combined solution <NUM> comprises four major components: water-insoluble boronic acid and water-insoluble solvent from extraction solution <NUM>, and water-soluble solvent and water from conversion solution <NUM>.

Conversion solution <NUM> comprises water and a water-soluble solvent. Suitably, the amount of water-soluble solvent in conversion solution is in a range of <NUM> wt. % to <NUM> wt. %, preferably from <NUM> wt. % to <NUM> wt. %, more preferably from <NUM> wt. % to <NUM> wt. %, and most preferably from <NUM> wt. % to <NUM> wt. Suitably, the water-soluble solvent has a LogP (octanol-water partition co-efficient) in a range from (-<NUM>) to <NUM>, preferably from (-<NUM>) to (-<NUM>), more preferably (-<NUM>) to (-<NUM>), which facilitate solubilizing of the water-insoluble solvent in water.

One or more water-soluble solvents may be used in aqueous conversation solution <NUM> as described herein based on design choices by one of ordinary skill in the art. While certain descriptions may refer to "a water-soluble solvent" or "the water-soluble solvent," it is understood that such reference can include more than one (such as two or more) water-insoluble solvents, as applicable. Examples of suitable water-soluble solvent include dioxane, GVL (gamma-valerolactone), dimethyl sulfoxide (DMSO), and sulfolane, and any combination thereof.

Table <NUM> below shows examples of suitable water-soluble solvents that can be used in conversion solution <NUM>, along with their solubility (LogP).

Conversion solution <NUM> has a pH of less than or equal to <NUM>, preferably less than or equal to <NUM>. Any suitable acid, preferably inorganic acid (or combination of suitable acids) can be used to lower the pH of conversion solution <NUM> to the desired acidic pH. Examples of suitable acids include: H<NUM>SO<NUM>, HCl, H<NUM>PO<NUM>, methane sulfonic acid, formic acid, acetic acid, trifluoro acetic acid, trichloro acetic acid, and any combinations thereof.

Referring to <FIG>, the process further comprises heating the second combined solution to a temperature Th at or above which the second combined solution consists essentially of a homogeneous liquid phase, wherein such heating converts at least a portion of the xylose-diboronate ester into furfural. At least an aqueous phase and a non-aqueous phase of the second combined solution become a homogeneous liquid phase.

Referring to <FIG>, when the xylose-diboronate esters from non-aqueous phase <NUM> in second combined solution <NUM> come into contact and react with water molecules generally from conversion solution <NUM>, the xylose-diboronate esters are converted to furfural via a dehydration reaction.

Preferably at least <NUM> mol% of the xylose-diboronate ester in second combined solution <NUM> is converted into furfural, more preferably at least <NUM> mol%, including at least <NUM> mol% or at least <NUM> mol%, of the xylose-diboronate ester is converted into furfural. By heating second combined solution <NUM> to temperature Th where it consists essentially of a homogenous liquid phase, at least <NUM> mol% of the xylose-diboronate ester in second combined solution <NUM> is converted into furfural, preferably at least <NUM> mol%.

Suitably, second combined solution <NUM> may be heated at temperature Th for at least <NUM> minute, preferably at least <NUM> minutes, more preferably at least <NUM> minutes, most preferably at least <NUM> minutes, and preferably up to <NUM> hours, more preferably up to <NUM> hours, and most preferably up to <NUM> hours. For instance, the amount of time second combined solution <NUM> is preferably heated at temperature Th is in a range from <NUM> minutes to <NUM> hours, more preferably from <NUM> minutes to <NUM> hours, and most preferably from <NUM> minutes to <NUM> hours.

This Th temperature depends at least on (i) the properties and concentration of the water-soluble solvent in conversion solution <NUM> and the water-insoluble solvent in non-aqueous phase <NUM> and (ii) the properties and concentration of the boronic acid that is bound to xylose and/or free from xylose in second combined solution <NUM>. As such, it is within the knowledge of one of ordinary skills to determine the Th for the particular conditions of a certain process as designed by such one of ordinary skills in accordance with the disclosures herein, such as composition of second combined solution <NUM> which depends on composition of upstream elements. Preferably, Th is in a range from at least <NUM>, more preferably at least <NUM>, and most preferably at least <NUM> degrees.

Referring to <FIG>, second combined solution <NUM> is preferably mixed at least a portion of the time it is heated at temperature Th, said mixing is performed using suitable methods such as at least those described herein. Such mixing can further facilitate contact between water molecules and the xylose-diboronate esters for conversion to furfural. Suitable mixing methods include mixing, stirring, static mixer, turbulent flow, jet loop, etc. Suitably, the mixing may be performed for at least <NUM> minutes, preferably at least <NUM> minutes, and most preferably at least <NUM> minutes.

Referring to <FIG>, process <NUM> further comprises cooling down heated second combined solution <NUM> to a temperature at or below which the homogenous liquid phase separates into an aqueous phase (not shown) and a non-aqueous phase (not shown) in cooled second combined solution <NUM>. Such temperature may be referred to as Ts. In particular, cooled second combined solution <NUM> comprises an aqueous phase comprising water, water-soluble solvent, and furfural and a non-aqueous phase comprising boronic acid, water-soluble solvent, and furfural. Preferably, the temperature Ts is at least <NUM> below Th, more preferably at least <NUM> below Th, including at least <NUM>, at least <NUM>, or at least <NUM> below Th.

While process <NUM>, particularly heating of second combined solution <NUM> to temperature Th, may be preferred to provide an optimal rate of conversion of xylose-diboronate ester to furfural, such heating is not necessary to produce furfural in accordance with the processes and systems disclosed herein. <FIG> depicts process <NUM> which involves heating of second combined solution to temperature below temperature Th, meaning the aqueous and non-aqueous phases of such heated second combined solution does not become a homogenous phase. As noted above, when like elements in <FIG> are also in <FIG> or other figures, identical reference characters will be used in each figure. Detailed description of these elements, whether disclosed below or above, apply equally for each figure, and will not be repeated verbatim for readability.

Referring to <FIG>, process <NUM> comprises heating second combined solution <NUM> to a temperature from <NUM> to convert at least a portion of the xylose-diboronate ester into furfural, wherein heated second solution <NUM> comprises an aqueous phase (not shown) comprising water, water-soluble solvent, and furfural and a non-aqueous phase (not shown) comprising boronic acid, water-soluble solvent, and furfural.

Suitably, second combined solution <NUM> may be heated for at least <NUM> minute, preferably at least <NUM> minutes, more preferably at least <NUM> minutes, most preferably at least <NUM> minutes, and preferably up to <NUM> hours, more preferably up to <NUM> hours, and most preferably up to <NUM> hours. For instance, the amount of time second combined solution <NUM> is preferably heated at a temperature of at least <NUM> is in a range from <NUM> minutes to <NUM> hours, more preferably from <NUM> minutes to <NUM> hours, and most preferably from <NUM> minutes to <NUM> hours.

Preferably at least <NUM> mol% of the xylose-diboronate ester in second combined solution <NUM> is converted into furfural, more preferably at least <NUM> mol%, and most preferably least <NUM> mol% of the xylose-diboronate ester is converted into furfural.

Referring to <FIG>, second combined solution <NUM> is preferably mixed at least a portion of the time it is heated, said mixing is performed using suitable methods such as at least those described herein. Such mixing can further facilitate contact between water molecules and the xylose-diboronate esters for conversion to furfural. Suitable mixing methods include mixing, stirring, static mixer, turbulent flow, jet loop, etc. Suitably, the mixing may be performed for at least <NUM> minutes, preferably at least <NUM> minutes, and most preferably at least <NUM> minutes.

It is understood by one of ordinary skill that aqueous phases <NUM> and <NUM> can contain an amount of water-insoluble boronic acid and water-insoluble solvent, but the concentrations of water and water-soluble solvent are higher than those in non-aqueous phase <NUM>. Similarly, it is understood that non-aqueous phases <NUM> and <NUM> can contain an amount of water and water-soluble solvent but the concentrations of water-insoluble solvent and water-insoluble boronic acid are higher than those in conversion solution <NUM>.

Non-aqueous phase <NUM> or <NUM> comprises at least a portion of the produced furfural in second combined solution <NUM>/<NUM> or <NUM>, respectively, including at least <NUM> wt. %, preferably at least <NUM> wt. %, more preferably at least <NUM> wt. %, and most preferably at least <NUM> wt. At least a portion of the furfural in non-aqueous phase <NUM> or <NUM> can be recovered by suitable methods, such as distillation where the furfural is part of an overhead product.

Referring to <FIG> and <FIG>, processes <NUM> and <NUM> enable conversion of at least a portion of the xylose-diboronate ester in second combined solution <NUM>/<NUM> and <NUM>, respectively, into furfural. Preferably at least <NUM>% of the xylose-diboronate ester in second combined solution <NUM> or <NUM> is converted to furfural, more preferably at least <NUM> mol%, including at least <NUM> mol% and at least <NUM> mol%.

Referring to <FIG> and <FIG>, process <NUM> and <NUM> further comprise recovering at least a portion of the produced furfural using any suitable methods known to one of ordinary skills. For instance, referring to <FIG>, at least non-aqueous phase <NUM> and aqueous phase <NUM> may be separated from cooled second combined solution <NUM>, and referring to <FIG>, at least non-aqueous phase <NUM> and aqueous phase <NUM> may be separated from heated combined solution <NUM>. At least a portion (preferably greater than <NUM>%) of non-aqueous phase <NUM> or <NUM> may be provided to a distillation unit to recover at least a portion of the furfural as overhead product <NUM> while leaving a majority (greater than <NUM>%) of non-aqueous phase <NUM> or <NUM> comprising boronic acid and water-insoluble solvent as bottom product <NUM>. Suitably, additionally, or alternatively, permeation or affinity separation (not shown) can be used to recover at least a portion of the produced furfural.

Referring to <FIG> and <FIG>, bottom product <NUM> comprises at least a portion of water-insoluble boronic acid and water-insoluble solvent from extraction solution <NUM>. Optionally, at least a portion of bottom product <NUM> can be recycled (i.e., reused) as part of extraction solution <NUM>. That is, optionally, extraction solution <NUM> can comprise at least a portion of bottom product <NUM>, including at least <NUM> wt. %, preferably at least <NUM> wt. %, more preferably at least <NUM> wt. %, and most preferably at least <NUM> wt. % or at least <NUM> wt.

In addition to water-insoluble solvent and water-insoluble boronic acid, bottom product <NUM> or <NUM> can further comprise an amount of water-soluble solvent (such as, at least <NUM> wt. % to <NUM> wt. %, preferably <NUM> wt. % to <NUM> wt. %, and more preferably <NUM> wt. % to <NUM> wt. If an amount of bottom product <NUM> or <NUM> is recycled for use as part of extraction solvent <NUM>, at least some of the water-soluble solvent in bottom product <NUM> or <NUM> can be in aqueous phase <NUM>, along with other components from bottom product <NUM> or <NUM>. That is, aqueous phase <NUM> can comprise (i) water-soluble solvent, (ii) water-insoluble solvent, and (iii) water-insoluble boronic acid. Optionally, aqueous phase <NUM> may be further processed (not shown) to recover at least one of such water-soluble solvent, water-insoluble solvent, and water-insoluble boronic acid. Suitable further processing of aqueous phase <NUM> may include adsorption, such as if the water-soluble solvent comprises sulfolane, then activated carbon may be used to adsorb a portion of the sulfolane. Such adsorption bed may also be used recover a portion of water-insoluble solvent and water-insoluble boronic acid from aqueous phase <NUM>.

Referring to <FIG> and <FIG>, aqueous phase <NUM> or <NUM> also comprises furfural from second combined solution <NUM> or <NUM>, respectively, and may be further processed to recover at least a portion of that furfural using suitable methods known to one of ordinary skills. For instance, aqueous phase <NUM> or <NUM> may be provided to a distillation unit to recover the furfural as overhead product <NUM> (in vapour form) which comprises water and furfural since furfural forms a heterogeneous azeotrope with water. By water-furfural heterogeneous azeotrope, we mean a mixture of water and furfural that are co-distilled at about <NUM>:<NUM> weight ratio as top product and separate into a water-rich and a furfural-rich phase upon condensation. The furfural in overhead product <NUM> may be optionally recovered by cooling overhead product <NUM> to allow it to condense from vapour phase to liquid phase and separate into an aqueous phase (not shown) and a non-aqueous phase comprising more furfural than the aqueous phase of condensed overhead product <NUM>. Accordingly, process <NUM> or <NUM> can optionally comprise cooling at least a portion of overhead product <NUM> to temperature Tc to allow such condensation and separation. Preferably, Tc is less than <NUM> at <NUM> atmospheric pressure, preferably less than <NUM>, and more preferably less than <NUM>.

Aqueous phase <NUM> comprises (i) water in a range from <NUM> to <NUM> wt. %, preferably about 92wt% and (ii) at least <NUM> wt. %, preferably at least <NUM> wt. % and most preferably about <NUM> wt. % furfural, and non-aqueous phase <NUM> comprises (i) furfural in a range from <NUM> to <NUM> wt. % and (ii) at least <NUM> wt. % water, preferably <NUM> wt. Aqueous phase <NUM> and non-aqueous phase <NUM> may be separated for further furfural recovery using suitable separation methods such as liquid-liquid separation as described herein. Referring to <FIG> and <FIG>, bottom product <NUM> from such distillation comprises water and water-soluble solvent originally in conversion solution <NUM> and is acidic (i.e., has pH less than <NUM>). Preferably, as shown, at least a portion (at least <NUM>%, preferably at least <NUM>%) of bottom product <NUM> may optionally be recycled (i.e., reused) as part of conversion solution <NUM>.

Alternatively or additionally to providing aqueous phase <NUM> to a distillation unit for further processing to recover at least a portion of the residual furfural in aqueous phase <NUM>, the residual furfural may be extracted with a water-insoluble solvent as known to one of ordinary skill, including those described herein. Optionally, such water-insoluble solvent may comprise at least a portion of bottom product <NUM> or <NUM>. That is, at least a portion of bottom product <NUM> or <NUM> can be used in extraction of furfural in aqueous phase <NUM>.

As described, referring to <FIG> and <FIG>, aspects of processes <NUM> and <NUM> allow for recycling of at least a portion (preferably greater than <NUM>%) of (i) bottom product <NUM> in extraction solution <NUM> and/or (ii) bottom product <NUM> in conversion solution <NUM>. Such recycling reduces the consumption of costly chemicals, particularly water-insoluble solvent and water-insoluble boronic acid of extraction solution <NUM> and/or water-soluble solvent and inorganic acid of conversion solution <NUM>.

<FIG> illustrates one exemplary suitable embodiment of system <NUM> for producing furfural from xylose in accordance with this disclosure, such as process <NUM>. <FIG> similarly illustrates one exemplary suitable embodiment of system <NUM> for performing certain aspects of the processes described herein, such as process <NUM>. As shown in <FIG> and <FIG>, xylose-containing solution <NUM> and extraction solution <NUM> are provided to and combined in extraction unit <NUM> to form first combined solution <NUM>. Extraction unit <NUM> is designed to perform liquid-liquid extraction, preferably in counter-current, and perform separation to separate non-aqueous phase <NUM> as described above. As shown in <FIG> and <FIG>, system <NUM> allows for the steps of forming first combined solution <NUM> and separating non-aqueous phase <NUM> to be carried out at least partially (and/or fully) together via extraction unit <NUM>. Extraction unit can be performed in co-current flow and preferably counter-current flow.

Extraction unit <NUM> can be operated isothermally for a desired amount of time at a constant temperature. Additionally or alternatively, extraction unit <NUM> can be operated with a temperature gradient for a desired amount of time by providing xylose-containing solution <NUM> at a temperature that is at least <NUM>, at least <NUM>, at least <NUM>, or at least <NUM>, higher than the temperature of extraction solution <NUM>. If extraction unit <NUM> is operated in counter-current mode with a temperature gradient, such operation can combine a higher extraction rate associated with the warmer section that is in close proximity with the inlet of extraction unit <NUM> for xylose-containing solution <NUM> (which translates to higher concentration of xylose in the portion of first combined solution <NUM> at that location) with low loss of extraction solution <NUM> in the water-rich effluent in the cooler section in close proximity with an outlet for aqueous phase <NUM>.

Referring to <FIG> and <FIG>, aqueous phase <NUM> and non-aqueous phase <NUM> are separated via extraction unit <NUM>. Non-aqueous phase <NUM> comprises at least <NUM> mol% (and preferably more than <NUM> mol%) of the xylose in the xylose containing solution <NUM> initially provided to form first combined solution <NUM>. The processes described herein, such as process <NUM> in <FIG> which can be performed with system <NUM> in <FIG>, can be designed to have at least <NUM>% selectivity for xylose, which means in such an embodiment, non-aqueous phase <NUM> comprises at least <NUM>% and aqueous phase <NUM> comprises less than <NUM>% of the xylose originally in xylose-containing solution <NUM>.

Referring to <FIG> and <FIG>, non-aqueous phase <NUM> is provided to dehydration unit <NUM>. Conversion solution <NUM> is also provided to dehydration unit <NUM>, and non-aqueous phase <NUM> and conversion solution <NUM> are combined in unit <NUM> to form second combined solution <NUM> or <NUM>, respectively. Referring to <FIG> and <FIG>, second combined solution <NUM> and <NUM>, respectively, are heated while preferably being mixed at least a portion (or substantially all) of the time being heated in dehydration unit <NUM> by a suitable method and corresponding component(s) as described above. In one embodiment, second combined solution <NUM> and <NUM> are heated to a temperature of at least <NUM> in dehydration unit <NUM> to convert xylose-diboronate ester to furfural.

Referring to <FIG>, second combined solution <NUM> is heated to temperature Th in dehydration unit <NUM> where second combined solution <NUM> consists essentially of a homogeneous liquid phase, the duration of which and optional mixing are in accordance with the descriptions provided herein. Such heated second combined solution <NUM> is provided to cooling unit <NUM> for cooling to temperature Tc, thereby forming cooled second combined solution <NUM> which comprises an aqueous phase comprising water, water-soluble solvent, and furfural, and a non-aqueous phase comprising water-insoluble boronic acid, water-insoluble solvent, and furfural. At least a portion of such aqueous and non-aqueous phases of cooled second combined solution <NUM> can be separated as stream <NUM> and <NUM>, respectively, using suitable methods such as those described herein, including liquid-liquid separation.

Referring to <FIG>, second combined solution <NUM> is heated in dehydration unit <NUM> to a temperature below temperature Th, where heated second combined solution <NUM> comprises an aqueous phase comprising water, water-soluble solvent, and furfural, and a non-aqueous phase comprising water-insoluble boronic acid, water-insoluble solvent, and furfural. At least a portion of such aqueous and non-aqueous phases of second combined solution <NUM> can be separated as stream <NUM> and <NUM>, respectively, using suitable methods such as those described herein, including liquid-liquid separation. In system <NUM>, dehydration unit <NUM> is also capable of performing liquid-liquid separation (or extraction) to separate aqueous phase <NUM> and non-aqueous phase <NUM> from second combined solution <NUM>.

Referring to <FIG> and <FIG>, aqueous phases <NUM> and <NUM>, respectively, are provided to distillation unit <NUM>, which is preferably operated under conditions configured to recover residual furfural contained in aqueous phases <NUM> and <NUM> that was produced in dehydration unit <NUM>. For instance, unit <NUM> can be operated slightly above ambient pressure (e.g., <NUM> atm) and with a top temperature of unit <NUM> at about <NUM> to <NUM>. At least a portion of the furfural in aqueous phases <NUM> and <NUM> is recovered as top product <NUM>, which comprises water and furfural. Bottom product <NUM> is acidic (i.e., has pH less than <NUM>) and comprises an amount of water-soluble solvent from conversion solution <NUM>. Preferably, as shown, at least a portion (at least <NUM>%, preferably at least <NUM>%) of bottom product <NUM> is recycled (i.e., reused) as part of conversion solution <NUM>.

Referring to <FIG> and <FIG>, overhead product <NUM> of distillation unit <NUM> comprises water and furfural since furfural forms a heterogeneous azeotrope with water. As shown, overhead product <NUM> is provided to cooling unit <NUM> to be cooled to temperature Tc, which is the temperature at or below which the water/furfural azeotrope in overhead product <NUM> (exiting unit <NUM> at a temperature in a range from <NUM> -<NUM> at <NUM> atmosphere) to condense and separate into aqueous phase <NUM> comprising (i) water in a range from <NUM> to <NUM> wt. %, preferably about <NUM>% and (ii) at least <NUM> wt. %, preferably about <NUM> wt. % furfural, and non-aqueous phase <NUM> comprising (i) furfural in a range from <NUM> to <NUM> wt. % and (ii) at least <NUM> wt. % water, preferably <NUM> wt. Cooling unit <NUM> is preferably capable of performing liquid-liquid separation to separate aqueous phase <NUM> and non-aqueous phase <NUM> from each other.

Referring to <FIG> and <FIG>, non-aqueous phase <NUM> or <NUM>, respectively, is provided to distillation unit <NUM> for recovery of furfural in overhead product stream <NUM>. As shown, at least a portion (at least <NUM>% or substantially all) of bottom product stream <NUM> can be recycled (or reused) as part of extraction solvent <NUM>.

Optionally, in addition to or as an alternative to using distillation for unit <NUM> to remove furfural from aqueous phase <NUM> to provide bottom product stream <NUM>, unit <NUM> can comprise a suitable liquid-liquid extraction process using a suitable water-insoluble solvent to extract furfural into the water-insoluble solvent. Such water-insoluble solvent for use in this optional aspect of unit <NUM> can comprise at least a portion of bottom product stream <NUM> or <NUM>.

Preferably, embodiments of the processes and systems as described herein are carried out or operated continuously for an amount of time, such as at least <NUM> hours.

<FIG> shows process <NUM> which can be used to isolate xylose from xylose-containing solution <NUM> for other further processing, including subsequent evaporation of water to produce the xylose in powder form. Referring to <FIG>, nonaqueous phase <NUM> is combined with back extraction solution <NUM> to form BA<NUM>X-containing solution <NUM> and to convert the xylose-diboronate esters (BA<NUM>X) back into xylose. Back extraction solution <NUM> is preferably an aqueous and acidic solution with a pH of less than or equal to <NUM>, preferably less than or equal to <NUM>, and more preferably less than or equal to <NUM>. BA2X-containing solution <NUM> preferably comprises back extraction solution <NUM> and non-aqueous phase <NUM> in a ratio by weight of in a range from <NUM> to <NUM>, preferably from <NUM> to <NUM>, and more preferably from <NUM> to <NUM>, respectively. BA<NUM>X-containing solution <NUM> may be heated to a temperature in a range from <NUM> to <NUM>, preferably from <NUM> to <NUM>, and more preferably from <NUM> to <NUM>, for an amount of time of at least <NUM> minute, preferably at least <NUM> minutes, and more preferably at least <NUM> minutes. Optionally, BA<NUM>X-containing solution <NUM> may be mixed at least a portion of the time it is heated.

In BA<NUM>X-containing solution <NUM>, the xylose-diboronate esters react with water, which converts the xylose-diboronate esters to into boronic acid and xylose, which is more soluble in aqueous phase than non-aqueous phase. As more xylose-diboronate esters dissociate into xylose, an aqueous phase comprising xylose and water and a non-aqueous phase comprising boronic acid and water-insoluble solvent from extraction solution <NUM> begin to form, wherein the concentrations of water and xylose in such aqueous phase is higher than those in such non-aqueous phase of solution <NUM>. Such aqueous and non-aqueous phases can be recovered from solution <NUM> as aqueous phase <NUM> and non-aqueous phase <NUM> using suitable separation methods, such as those described herein.

Aqueous phase <NUM> is substantially free of contaminants potentially present in xylose-containing solution <NUM> which may have presented challenges to isolation of the xylose from solution <NUM>. For instance, if xylose-containing solution <NUM> were a hydrolysate, evaporation of water from solution <NUM> would have left a solid product containing xylose along with other contaminants, particularly with the amount of xylose being a small percentage of the solid product. In aqueous-phase <NUM>, however, the amount of xylose would be significantly more than other contaminants from xylose-containing solution <NUM> because of the selectivity of boronic acid to xylose to form xylose-diboronate esters, which are extracted with extraction solution <NUM>. At least a portion of the xylose in aqueous phase <NUM> may be recovered in solid or powder form using methods known to one of ordinary skill, including evaporation of water.

If process <NUM> is selected to recover xylose in addition or as an alternative to furfural production as described with <FIG>, extraction solution <NUM> may be designed to comprises a water-insoluble solvent that has moderate affinity for the xylose-diboronate esters (i.e., the BA<NUM>X has moderate solubility in the selected water-insoluble solvent) (e.g., heptane instead of toluene) to balance extraction and back extraction. That is, the higher the affinity for xylose-diboronate esters (meaning more of the xylose-diboronate ester resides in the water-insoluble solvent as compared to another solvent that could be selected), the greater amount of back conversion solution <NUM> is needed to drive the reaction to the xylose.

Embodiments of the processes and systems described herein can be further illustrated by the following exemplary, non-limiting examples.

In Example <NUM>, nine experiments were conducted with different water-insoluble solvent and pH as shown in Table <NUM> below. General experimental conditions for these nine experiments include:.

The aqueous phases and non-aqueous phases from Example <NUM> were analysed by means of <NUM>-NMR using a <NUM> Bruker spectrometer. The aqueous phases were measured in a <NUM>:<NUM><NUM>O/D<NUM>O mixture (in which D2O is deuterated water also called heavy water or heavy water used for the analysis) with Trimethylsilyl propanoic acid (TMSP) as the internal standard and the non-aqueous phases were measured in a <NUM>:<NUM> mixture of toluene and toluene-d8 with dioxane as the internal standard. These mixtures of aqueous and non-aqueous phases being analysed are composed by equal volumes (<NUM>µL) of the particular aqueous or non-aqueous phase and the deuterated solvent, containing the standard.

The experiments of Example <NUM> show recovery of xylose using toluene, <NUM>-methylnaphthalene, n-heptane, and octanol as water-insoluble solution, with PBA as the water-insoluble boronic acid.

In experiments <NUM> and <NUM>-<NUM>, the molar ratio of boronic acid to xylose was <NUM>:<NUM>. Experiments <NUM> and <NUM> demonstrate a potential correlation between extraction efficiency and ratio of boronic acid to xylose, particularly that a higher molar ratio of boronic acid can produce a higher extraction rate (experiment <NUM>) while a lower molar ratio of boronic acid also results in extraction of xylose but at a lower rate (experiment <NUM>).

In addition, these experiments show that embodiments of the processes and systems described herein allow for xylose extraction from acidic and basic xylose-containing solutions. The experiments also demonstrate that embodiments of the processes and systems described herein allow for xylose extraction using aromatic solvents and aliphatic solvents, although the aromatic solvents (toluene and <NUM>-methylnaphthalene) provide a better rate of extraction than the aliphatic solvents (n-heptane and octanol). The non-aqueous phase of experiments <NUM>-<NUM> of Example <NUM> can either be back extracted to xylose as described above (particularly with respect to <FIG>), and/or further combined with a conversion solution to produce furfural (dehydration reaction) as described herein (such as conversion solution <NUM>). Example <NUM> below shows experiments of such dehydration reaction.

In Example <NUM>, experiments were conducted under different conditions as set forth in Table <NUM> below. General experimental conditions for the <NUM> experiments include:.

The various second combined solutions as shown in Table <NUM> below were provided to a heavy glass wall cylindrical pressure vessel having a total volume <NUM>, which was sealed with a Teflon cap, and heated at <NUM> for various amounts of time shown in Table <NUM>.

The pressure vessel for each experiment was cooled, and the liquid product was separated into a bottom aqueous phase and a top toluene-rich phase. The resulting concentrations of residual xylose diboronate ester (BA<NUM>X), xylose (X) and furfural (F) were quantified in each phase using <NUM>H-NMR analysis in the presence of internal standard as described above. The sum of the molar yields of furfural found in the aqueous and organic phase for each experiment are shown below in Table <NUM>. In addition, Table <NUM> shows the conversion mol%, which indicates the mol% of free xylose or BA<NUM>X that was converted to furfural.

The experiments of Example <NUM> show furfural production in accordance with embodiments of the processes and systems described herein. Such furfural yields can be improved with at least one of (i) using a <NUM>:<NUM>:<NUM> volume ratio of water-insoluble solvent: acidic water : water-soluble solvent (see experiments <NUM> and <NUM> as compared to experiment <NUM> in which lower yields were observed with lower ratio of water-soluble solvent), (ii) selecting a longer reaction time (see experiment <NUM> vs. <NUM> in which lower furfural yields were observed with shorter reaction time, or experiments <NUM> - <NUM>, in which similar correlation between yields and reaction time was observed), and (iii) solvent selection (see experiment <NUM> vs. <NUM> in which toluene vs. benzene was used with DMSO, or experiments <NUM> - <NUM> in which the combination of <NUM>-MN and sulfolane is more effective than toluene and GVL dioxane, all of which indicates aromatic water-insoluble solvent can be preferred for use with DMSO or sulfolane as water-soluble solvent (vs. GVL or dioxane).

In Example <NUM>, additional experiments <NUM> - <NUM> as shown in Table <NUM> were carried out to demonstrate the desirable effect of converting the BA<NUM>X to furfural under conditions that allow the formation all the reaction components to merge into a single phase during the reaction (e.g., heating the second combined solution to temperature Th). These experiments were carried out under the same general conditions as described above for experiments <NUM> - <NUM> of Example <NUM> with the representative second combined solution comprising toluene-water-sulfolane mixture in <NUM>:<NUM>:<NUM> volume ratio and PBA but with varying either the reaction temperature or the PBA concentration to switch between monophasic and bi-phasic conditions, which was witnessed by visual inspection. The variation in PBA concentration was executed by replacing the xylose-diboronate ester (PBA<NUM>X) with an equal molar amount of free xylose and a varying molar amount of free PBA.

Similar to above, experiments <NUM> - <NUM> show furfural production in accordance with embodiments of the processes and systems described herein. Such furfural yield can be improved by heating second combined solution to temperature Th at or above which the second combined solution consists essentially of a homogenous phase. For instance, experiments <NUM> - <NUM> show that furfural production yields of at least about <NUM>% were observed under conditions that allow the two liquid phases observed at room temperature fuse into a single liquid phase at reaction temperature as compared to when the representative second combined solution has two phases at reaction temperature.

We first analysed one non-aqueous phase comprising methylnaphthalene (MN) (such as one potential embodiment of non-aqueous phase <NUM> or <NUM> of <FIG>, respectively) and one aqueous phase comprising water and sulfolane (S) (such as one potential embodiment of aqueous phase <NUM> or <NUM> of <FIG>, respectively) that are separated in the decanter after the dehydration reaction (such as those in Example <NUM> and/or one embodiment of second combined solution <NUM> or <NUM> of <FIG>, respectively). Table <NUM> below reports the distribution of the main components over the two phases at room temperature. The distribution between polar and apolar phases is reported as ratio of concentrations Kd and ratio of absolute amounts Pmol. It should be noticed that volume of the polar phase of water + sulfolane is twice as large as that of the apolar phase, which results in Pmol being twice as large as Kd.

Table <NUM> shows that the addition of sulfolane improves the solubility of both MN (water-insoluble solvent) and PBA in the aqueous phase. Accordingly, the aqueous phase that consists essentially of water and sulfolane also contains traces of furfural (<<NUM> wt. %), PBA (<<NUM> wt. %) and MN (<<NUM>. Optionally, furfural can be recovered as described, for instance as overhead product <NUM> by providing the polar phase to unit <NUM> in <FIG> or <FIG>, and the MN and PBA remaining, such as in bottom product <NUM> of <FIG>, can be recycled to the dehydration reaction as part of the conversion solution.

The non-aqueous phase that is rich in MN (water-insoluble solvent), meaning greater concentration of MN as compared to the aqueous phase, contained much (<NUM>%) of the overall furfural produced and initial PBA (boronic acid). As described, furfural can be recovered from this non-aqueous phase in an overhead product of a distillation process. The remaining bottom product (e.g., <NUM> or <NUM>) comprising MN and PBA can be recycled as part of the extraction solution. Because the non-aqueous phase also contained some sulfolane (water-soluble solvent, 4wt%), which may get lost in the aqueous phase of first combined solution if the bottom product comprising MN and PBA is recycled as described. Optional further processing of the aqueous phase of first combined solution (such as aqueous phase <NUM> of <FIG>) may be employed to reduce such potential loss.

As described, the present disclosure provides processes and systems to produce furfural from an aqueous xylose-containing solution without isolation of xylose in dry form, which can be costly. In particular, certain embodiments of the processes and systems described herein (such as process <NUM> and system <NUM>) are capable of and can be designed to produce such furfural at a relatively higher yield of at least <NUM> mol%, preferably at least <NUM> mol%, more preferably at least <NUM> mol%, and most preferably at least <NUM> mol% (meaning at least <NUM>, <NUM>, <NUM>, or <NUM> mol% of xylose is converted to furfural) without isolation of xylose in dry form. Although other embodiments (such as process <NUM> and system <NUM>) may not provide such high yields, they nonetheless can still provide various benefits described herein. One of ordinary skills can design various embodiments as described herein to achieve the desired yields in light of various factors (such as energy demands, equipment costs, etc.).

Embodiments of the processes and systems described herein allow for less formation of undesirable by-products (such as humins) from the various reactants and/or furfural degradation, which allows for furfural production with marginal fouling of equipment and marginal contamination of various product and solvent streams. The selectivity of water-insoluble boronic acid for xylose (in contrast with other sugars such as glucose and mannose) in first combined solution <NUM> allows for extraction of xylose as described while the majority (greater than <NUM>%) of other sugars remain in solution <NUM> after non-aqueous phase <NUM> comprising xylose-diboronate esters is separated. Non-aqueous phase <NUM> comprising less contaminants (i.e., non-xylose components such as other sugars and lignin) means less contaminants that are subject to dehydration reactions, such as those described for second combined solution <NUM>, <NUM>, and/or <NUM>, and/or carried out in unit <NUM>, which would degrade these contaminants to humins and other fouling components.

Furthermore, various embodiments of the processes and systems describe herein enable recovery of furfural using distillation of water-insoluble components in non-aqueous phase <NUM> or <NUM>, which is, broadly speaking, simpler as compared to distillation of an aqueous solution containing furfural. For instance, various embodiments described herein allow one of ordinary skill to optionally select a water-insoluble solvent with a boiling point above the boiling point of furfural. Such solvent selection can further reduce energy demands of the corresponding process or system by enabling recovery via distillation of the minor component, furfural, as an overhead product (such as <NUM> or <NUM>) of the distillation column instead of distilling the major component, the water-insoluble solvent.

Moreover, optional recovery of furfural from aqueous phase <NUM> or <NUM> is made possible. It can include post-distillation processing to separate the furfural and water from the water-furfural azeotrope that forms in overhead product <NUM>. However, it can also consist of extraction using at least a portion of bottom product <NUM> or <NUM> comprising water-insoluble solvent and boronic acid.

Claim 1:
A method for producing furfural comprising:
a. providing a xylose-containing solution comprising xylose in an amount of greater than or equal to <NUM> wt.%, wherein the xylose-containing solution is an aqueous solution;
b. providing an extraction solution comprising a water-insoluble boronic acid (BA: R-B(OH)<NUM>) and a water-insoluble solvent;
c. combining the xylose-containing solution with the extraction solution to provide a first combined solution, wherein the ratio of boronic acid to xylose in the first combined solution is greater than <NUM>:<NUM> molar, respectively, and wherein the first combined solution comprises a first aqueous phase and a first non-aqueous phase, said non-aqueous phase comprising at least a portion of the xylose as xylose-diboronate ester (BA<NUM>X);
d. separating at least a portion of the first non-aqueous phase from the first combined solution;
e. providing a conversion solution comprising a water-soluble solvent and water, said conversion solution has a pH of less than or equal to <NUM>;
f. combining at least a portion of the non-aqueous phase from (d) with the conversion solution in a ratio of conversion solution to the non-aqueous phase in a range from <NUM> to <NUM> by weight, respectively, to form a second combined solution;
g. heating the second combined solution to a temperature Th at or above which the second combined solution consists essentially of a homogeneous liquid phase, wherein such heating converts at least a portion of the xylose-diboronate ester into furfural,
h. cooling down the heated second combined solution such that the cooled second combined solution comprises (i) a second aqueous phase comprising water, water-soluble solvent, and furfural and (ii) a second non-aqueous phase comprising water-insoluble solvent, water-insoluble boronic acid, and furfural; and separating at least a portion of the second non-aqueous phase from the cooled second combined solution; and
i. recovering at least a portion of the furfural in the second non-aqueous phase.