Process and catalyst for the selective hydrogenation of compounds having a carbonyl carbon atom

Abstract

A selective hydrogenation process is disclosed that can upgrade impure feeds, such as those obtained from biomass containing several small (e.g., 2-6 carbon atoms) molecules with aldehyde and / or ketone carbon atoms. For example, glycolaldehyde and its methylated derivative, hydroxyacetone (acetol), are both high-value intermediates for certain downstream processing reactions, but they are typically recovered in the condensate from the pyrolysis of carbohydrates (e.g., aldose-containing sugars) along with glyoxal and its methylated derivative, pyruvaldehyde. Selective hydrogenation of compounds with two carbonyl carbon atoms without overhydrogenation to ethylene glycol and propylene glycol can increase the concentration of desired intermediates. The beneficial effects of such selective hydrogenation can be achieved through the use of hydrogenation catalysts containing precious metals, such as Ru and Pt.

Description

[Technical field]

[0001] In one aspect, the present invention relates to a process and catalyst for the selective hydrogenation of compounds having at least two carbonyl carbon atoms, which may be aldehyde and / or ketone carbon atoms. In another aspect, the present invention relates to a process and catalyst for increasing the amount of selectively hydrogenated analogs, such as, for example, glycolaldehyde from the selective hydrogenation of glyoxal (both of which may be initially present in impure feeds). [Background technology]

[0002] The long-term trend of increasing costs for many hydrocarbon feedstocks has been a major motivation to explore alternative sources of petroleum-based carbon for the production of many important and valuable chemical products. Biomass (material derived from living or recently living organisms) is considered a readily available and inexpensive source of renewable non-petroleum-based carbon from which many such known high-value chemicals can be derived. The ability to convert biomass into fuels, chemicals, energy, and other materials is expected to strengthen local economies, reduce dependency on oil and gas resources, and reduce air and water pollution. The production of energy and chemicals from renewable resources such as biomass also reduces the net release of carbon dioxide (a greenhouse gas) into the environment from fossil-based sources, carbon that would otherwise be "sequestered."

[0003] Nevertheless, the development of sustainable technologies for producing chemicals from renewable resources that have traditionally been made exclusively from petroleum-based carbon remains a significant challenge. For example, in recent years, the biodiesel industry has provided an abundance of crude glycerol as a by-product of the refining of triglycerides in vegetable oils and animal fats. This glycerol can be refined to serve as a feedstock for producing propylene glycol (1,2-propanediol), a known high-value chemical of the same carbon number from non-renewable resources. However, the steps required to properly refine glycerol for this purpose are quite costly, and the biodiesel industry relies heavily on tax credits and other forms of government subsidies for its profitability.

[0004] Pyrolysis of biomass is being actively investigated as a potential route to generate smaller so-called "platform" molecules that can serve as building blocks for commercially desirable products. An important example of such a molecule is glycolaldehyde (C2H4O2), which has significant utility as a reactive intermediate in that it is the smallest molecule with both aldehyde and hydroxyl carbon atoms. This molecule offers a potential synthetic route for the production of bio-based monoethanolamine (MEA) and diethanolamine (DEA), both of which have significant industrial applications, via reductive amination. Glycolaldehyde can be obtained from the conversion of aldose monosaccharides (e.g., glucose) via the initial formation of an aqueous solution, followed by pyrolysis ("aqueous thermolysis"), and then condensation of the evolved steam. Such processes are described, for example, in WO 02 / 40436. These and other pyrolysis processes, also referred to in the art as pyrolysis and cracking processes, result in a variety of mixtures of compounds. Isolation of more valuable useful materials such as glycolaldehyde is complicated by the number of other compounds present in the condensate, and the similarity of their boiling points (relative volatility) reduces the efficiency of usable distillation.

[0005] The overall economic attractiveness of a given synthetic route based on renewable carbon precursors depends heavily on its total utility and energy requirements, such as the conversion of glycolaldehyde to MEA and DEA described in U.S. Pat. No. 6,534,441, U.S. Pat. No. 8,772,548, and U.S. Pat. No. 8,742,174. These requirements are in turn heavily influenced by the upstream economics associated with purifying impure feedstocks to obtain precursor products such as glycolaldehyde with suitable purity. Thus, progress in the ongoing effort to replace fossil-derived chemicals with their renewable carbon counterparts will depend heavily on improvements in upstream processing efficiency, particularly improvements realized from improved reaction selectivity, intermediate and final product quality, and / or component separation. All of these have the potential to reduce production costs to a commercially viable extent. Summary of the Invention [Means for solving the problem]

[0006] An aspect of the present invention relates to the discovery of a selective hydrogenation process that can significantly benefit or upgrade impure feeds obtained from biomass, e.g., feeds containing several small (e.g., 2-6 carbon atoms) molecules with aldehyde and / or ketone carbon atoms. For example, both glycolaldehyde and its methylated derivative hydroxyacetone (acetol) are high-value intermediates for certain downstream processing reactions, but they are usually recovered in the condensate together with glyoxal and its methylated derivative pyruvaldehyde from the pyrolysis of carbohydrates (e.g., aldose-containing sugars). The latter more reactive species can interfere with the desired downstream reactions, e.g., reductive amination of glycolaldehyde to MEA and / or DEA. For example, under conditions otherwise favorable for this reaction, these more reactive species can cause the production of undesirable imidazole derivatives. More specifically, in the presence of water or methanol as a solvent, ammonia in a high pressure hydrogen environment can combine with glycolaldehyde and the more reactive species, either glyoxal or pyruvaldehyde, according to the undesirable cyclization reaction as follows: [ka]

[0007] These and other reactions can not only significantly reduce the utilization of glycolaldehyde and other desired intermediates such as hydroxyacetone (acetol), but can also concomitantly produce by-products that require downstream separation and thus additional production costs.

[0008] However, it has been advantageously discovered that the more reactive species generated in pyrolysis and other biomass conversion processes can be selectively hydrogenated to analogs, particularly hydroxyl carbon atom analogs, that do not result in the above-mentioned potential for interfering with synthetic pathways involving desired intermediates (e.g., glycolaldehyde or hydroxyacetone). In fact, according to some embodiments, the selectively hydrogenated analogs may actually correspond to these desired intermediates themselves, so that selective hydrogenation, as described herein, can increase the amount of desired intermediates in a given product, thereby improving their effective utilization in downstream processing, while reducing the potential for harmful by-product formation from the more reactive species or starting compounds.

[0009] Certain aspects of the present invention relate to the discovery of process conditions and catalysts for carrying out selective hydrogenation of one or more starting compounds to form products having increased amounts of one or more desired intermediates (e.g., glycolaldehyde and / or hydroxyacetone) corresponding to selectively hydrogenated analogs (e.g., hydroxyl carbon atom analogs). Thus, advantageously, selective hydrogenation is generally accompanied by a reduction in the amount of one or more starting compounds (e.g., glyoxal and / or pyruvaldehyde) that can potentially reduce the effective availability of such desired intermediates (e.g., via the formation of undesirable by-products as described above). The starting compounds that are selectively converted (selectively hydrogenated) are typically those that exhibit high reactivity by having at least two (and often only two) carbonyl carbon atoms, which may be aldehyde carbon atoms, ketone carbon atoms, or a combination thereof.

[0010] For example, the starting compound glyoxal has two aldehyde carbon atoms, while the starting compound pyruvaldehyde has an aldehyde carbon atom and a ketone carbon atom. Selective hydrogenation of glyoxal produces glycolaldehyde as a selectively hydrogenated analog by converting one of its two aldehyde carbon atoms to a hydroxyl carbon atom. Selective hydrogenation of pyruvaldehyde produces hydroxyacetone as a major selectively hydrogenated analog by converting its (more reactive) aldehyde carbon atom to a hydroxyl carbon atom. Another minor selectively hydrogenated analog, namely 2-hydroxypropanal, can also be produced by converting its (less reactive) ketone carbon atom to a hydroxyl carbon atom. Exemplary impurity feeds can include other compounds, such as compounds having only one carbonyl carbon atom (e.g., a single aldehyde carbon atom or a single ketone carbon atom) that can be converted to a hydroxyl carbon atom in the selective hydrogenation process described herein. An example of such a compound is 5-hydroxymethylfurfural, which can be converted to 2,5-dihydroxymethylfuran.

[0011] Advantageously, the use of the selective hydrogenation conditions and catalysts described herein can provide a favorable reaction environment in which the most reactive compounds in the impure feed, and therefore the compounds most susceptible to hydrogenation, are converted to the more desirable (higher value) intermediates described above. However, these intermediates themselves, whether produced by this selective hydrogenation or originally present in the impure feed, are hydrogenated to a minimal or even negligible extent. Thus, the overall effect of subjecting the impure feed to a hydrogenation reaction environment is generally to form a product having a net increase or additional amount of one or more of these more valuable selectively hydrogenated analogs. That is, further conversion (hydrogenation) of these more desirable intermediates to more fully or completely hydrogenated analogs in which additional or all carbonyl carbon atoms are converted to hydroxyl carbon atoms is limited or substantially absent.

[0012] For example, glyoxal may be substantially converted to glycolaldehyde, but the further conversion (hydrogenation) of glycolaldehyde (whether produced from glyoxal or already present in the impure feed) to ethylene glycol may be minimized or negligible. Similarly, pyruvaldehyde may be substantially converted to hydroxyacetone and / or 2-hydroxypropanal, but the further conversion (hydrogenation) of one or both of these selectively hydrogenated analogs to propylene glycol may be minimized or negligible.

[0013] Using the teachings herein, one skilled in the art can determine the optimal hydrogenation environment (i.e., adjust the hydrogenation conditions) to achieve selective conversion of one or more compounds in a given impure feed that have a relatively high susceptibility to hydrogenation to one or more higher-value intermediates that have a relatively low susceptibility to hydrogenation. This allows for the formation of products with increased amounts of such intermediates, preferably without significant further conversion of such intermediates. Thus, the selective hydrogenation described herein can, in some embodiments, include "selective stabilization," whereby the impure feed is beneficially stabilized by selective hydrogenation of the most reactive compounds, thereby (i) limiting undesirable side reactions of such compounds in downstream processing, and (ii) producing additional amounts of higher-value intermediates from such compounds for use in the downstream processing. Thereby, the overall economics associated with providing intermediates in the synthesis of chemicals from renewable carbon sources can be significantly improved.

[0014] An additional benefit of the selective hydrogenation process and its associated conditions and catalysts is the conversion of starting compounds to the selectively hydrogenated analogs described above with significantly different relative volatilities. The difference in boiling points of the higher value intermediates can improve downstream gas / liquid separation efficiency, for example by distillation. With this in mind, a further aspect of the present invention relates to a synthetic method including downstream and optionally upstream processing steps that benefit from selective hydrogenation to increase the effective utilization of one or more of the higher value intermediates described above. The method may include, for example, upstream pyrolysis of carbohydrates (e.g., aldose-containing sugars) and cooling to condense the liquid mixture subjected to selective hydrogenation. The method may include downstream distillation of the product obtained from selective hydrogenation to recover a fraction enriched in higher value intermediates (e.g., glycolaldehyde and / or hydroxyacetone).

[0015] Overall, selective hydrogenation using the heterogeneous catalysts and conditions described herein can play an important, even essential, role in establishing the economic feasibility needed for commercial-scale production of renewable carbon-based chemicals. Selective hydrogenation is beneficial due to its environmental compatibility and the resulting reduced generation of hazardous waste compared to alternative routes, such as reduction processes that rely on stoichiometric amounts of reducing agents, e.g., alkali metal borohydrides.

[0016] These and other aspects, embodiments and attendant advantages will become apparent from the following detailed description. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Detailed Description of the Embodiments A particular embodiment of the present invention relates to a process for the selective hydrogenation of at least a first starting compound present in an impure feed, where the first starting compound has at least two carbonyl carbon atoms. The term "impure feed" is intended to mean that the starting compound is generally not present in its pure form, but may be a mixture, often with other compounds, resulting from a given application, such as the pyrolysis of carbohydrates. The term does not impose any restrictions with respect to purity, and in fact the selective hydrogenation process described herein is equally applicable to high purity feeds, such as feeds containing 99 wt% or more of a given starting compound described herein, or feeds containing one or more starting compounds and an aqueous or organic solvent (e.g. methanol) in a combined amount of 99 wt% or more.

[0018] A representative method includes contacting an impure feed with a hydrogenation catalyst under hydrogenation conditions to selectively hydrogenate a first starting compound to at least a major first selectively hydrogenated analog. That is, the analog is produced by converting one of at least two carbonyl carbon atoms to a hydroxyl carbon atom while retaining the other one of at least two carbonyl carbon atoms. Thus, preferably, the remainder of the molecule of the first starting compound remains unchanged (retained) except for the conversion of a single carbonyl carbon atom to a hydroxyl carbon atom. The selective hydrogenation thereby forms a product having an increased amount (e.g., increased concentration or weight percent) of at least a major first selectively hydrogenated analog. This "increased amount" as described above means an increased total amount or an increased net amount, taking into account any loss of the analog due to further conversion (hydrogenation) to a more or completely hydrogenated analog (wherein additional or all carbonyl carbon atoms are converted to hydroxyl carbon atoms). Thus, since the molecules of a given compound in the feed are generally indistinguishable based on their origin, such further conversion may be of an analogue produced from the first starting compound or that was already present in the impure feed. Similarly, the product may have a reduced amount (e.g., reduced concentration or weight percent) of the first starting compound.

[0019] The "carbonyl carbon atom" of a given compound refers to a carbon atom that is double-bonded to an oxygen atom, as recognized in the art. Thus, the carbonyl carbon atom can refer to a carbon atom that forms an aldehyde group, which is further bonded to both other carbon atoms and a hydrogen atom, i.e., the "aldehyde carbon atom" referred to herein. The carbonyl carbon atom can also refer to a carbon atom that forms a ketone group, which is further bonded to two other carbon atoms, i.e., the "ketone carbon atom" referred to herein.

[0020] [Starting compound and its selectively hydrogenated analogue] A selective hydrogenation analog of a starting compound refers to a compound formed by hydrogenation of one or more, but not necessarily all, of the carbonyl carbon atoms of the starting compound. This hydrogenation results in the conversion of one or more carbonyl carbon atoms to one or more corresponding hydroxyl carbon atoms. In many cases, the molecular structure of the starting compound is retained for the remainder of the selective hydrogenation analog other than this conversion of one or more carbonyl carbon atoms. By "hydroxyl carbon atom" is meant the carbon atom bonded to a hydroxyl (-OH) group, as recognized in the art. In many cases, the starting compound has two carbonyl carbon atoms (e.g., two aldehyde carbon atoms, an aldehyde carbon atom and a ketone carbon atom, or two ketone carbon atoms), and selective hydrogenation will convert one of the two carbonyl carbon atoms to the corresponding hydroxyl carbon atom.

[0021] To emphasize that a variety of starting compounds having the characteristics of the "starting compound" described above may be present in a given impure feed, these may be referred to as a "first starting compound," a "second starting compound," etc. Thus, a "first starting compound" has at least two carbonyl carbon atoms as described above, e.g., at least two aldehyde carbon atoms, at least one aldehyde carbon atom and at least one ketone carbon atom, or at least two ketone carbon atoms. However, any "starting compound" so designated may be selectively hydrogenated to form a selectively hydrogenated analog (e.g., an aldehyde carbon atom may be converted to a hydroxyl carbon atom and a ketone carbon atom may be retained) in the same manner and with the same performance criteria (e.g., in terms of yield obtained), as described herein.

[0022] To emphasize that a variety of selectively hydrogenated analogs may be produced from a given starting compound, such as, for example, a variety of selectively hydrogenated analogs that may be produced from a "first starting compound" or a variety of selectively hydrogenated analogs that may be produced from a "second starting compound," these various selectively hydrogenated analogs may be referred to as "major first selectively hydrogenated analogs" or "minor first selectively hydrogenated analogs" (when produced from a first starting compound), or as "major second selectively hydrogenated analogs" or "minor second selectively hydrogenated analogs" (when produced from a second starting compound). The designations "major" and "minor" may, in some embodiments, but are not necessarily, intended to refer to selectively hydrogenated analogs that are produced in relatively greater and lesser amounts (e.g., with higher and lower selectivities and corresponding yields), respectively.

[0023] For example, a "major first selectively hydrogenated analog" may be produced from the conversion of a more reactive aldehyde carbonyl carbon atom of a first starting compound to a corresponding hydroxyl carbon atom while retaining the less reactive ketone carbon atom, whereas a "minor first selectively hydrogenated analog" may be produced from the conversion of a less reactive ketone carbon atom of the same first starting compound to a corresponding hydroxyl carbon atom while retaining the more reactive aldehyde carbon atom. In a manner similar to such an embodiment in which the impure feed comprises a first starting compound having both aldehyde and ketone carbon atoms, and the conversion of the former produces a major first selectively hydrogenated analog and the conversion of the latter produces a minor first selectively hydrogenated analog, the impure feed may further comprise other starting compounds having the characteristics of the "starting compound" described above. For example, the impure feed may further comprise a second starting compound that is different from the first starting compound but still has at least two carbonyl carbon atoms. Contacting the impure feed with a hydrogenation catalyst under hydrogenation conditions described herein may selectively hydrogenate the second starting compound to at least a major second selectively hydrogenated analog, in this case by converting one of the at least two carbonyl carbon atoms of the second starting compound to a hydroxyl carbon atom while preserving the other one of the at least two carbonyl carbon atoms of the second starting compound.

[0024] According to a particular embodiment, two of the at least two carbonyl carbon atoms of the first starting compound are aldehyde carbon atoms, and a specific example of such a first starting compound is glyoxal. For such a first starting compound, a first selectively hydrogenated analog (or a major first selectively hydrogenated analog) can be produced by converting one of these aldehyde carbon atoms to a hydroxyl carbon atom while retaining the other aldehyde carbon atom (e.g., a product having an increased amount of the first selectively hydrogenated analog can be formed). According to a specific example, the selective hydrogenation of glyoxal produces glycolaldehyde as a selectively hydrogenated analog according to the following reaction: [ka]

[0025] According to another specific embodiment, one of the at least two carbonyl carbon atoms of the first starting compound is an aldehyde carbon atom and another of the at least two carbonyl carbon atoms is a ketone carbon atom, and a specific example of such a first starting compound is pyruvaldehyde. For such a first starting compound, a major first selectively hydrogenated analog can be produced by converting the aldehyde carbon atom to a hydroxyl carbon atom while retaining the ketone carbon atom (e.g., a product having an increased amount of the major first selectively hydrogenated analog can be formed). According to a specific example, selective hydrogenation of pyruvaldehyde produces hydroxyacetone as the major first selectively hydrogenated analog according to the following reaction: [ka]

[0026] For such a first starting compound having both aldehyde and ketone carbon atoms (e.g., pyruvaldehyde), it is also possible to produce a minor first selectively hydrogenated analog (e.g., to form a product having an increased amount thereof) by converting the ketone carbon atom to a hydroxyl carbon atom while retaining the aldehyde carbon atom. According to a specific example, selective hydrogenation of pyruvaldehyde produces 2-hydroxypropanal as a minor first selectively hydrogenated analog according to the following reaction: [ka]

[0027] Particular examples of starting compounds (e.g., first and / or second starting compounds) present in the impure feed are those resulting from pyrolysis of carbohydrates, including sugars such as those in the category of aldose-containing sugars (e.g., glucose) and / or oligosaccharides (e.g., disaccharides such as sucrose). Such pyrolysis produces smaller molecules. In an exemplary embodiment, the first starting compound, or optionally both the first starting compound and the second starting compound, have 2-5 carbon atoms. In a further exemplary embodiment, the first starting compound, or optionally both the first starting compound and the second starting compound, have two carbonyl carbon atoms, e.g., only two carbonyl carbon atoms (e.g., only two aldehyde carbon atoms, only one aldehyde carbon atom and only one ketone carbon atom, or only two ketone carbon atoms). According to particular embodiments, the impure feed may include both glyoxal and pyruvaldehyde as first and second starting compounds, each having the characteristics of a "starting compound" described herein.

[0028] [Impure feed / product / starting compounds and conversion of other compounds] The starting compound (e.g., the first starting compound) or mixture of starting compounds (e.g., the first starting compound and the second starting compound) may be present in the impure feed in an amount or combined amount corresponding to a liquid mixture condensed from a gas phase product of a carbohydrate pyrolysis, such as, but not limited to, the carbohydrate pyrolysis described in WO 02 / 40436 referenced above. However, whether the impure feed is obtained from pyrolysis or not, the amount or combined amount may generally be between 1 wt% and 75 wt%, typically between 2 wt% and 50 wt%, and often between 5 wt% and 30 wt%. As described above, contacting the impure feed with a hydrogenation catalyst under hydrogenation conditions converts (or more specifically selectively hydrogenates) at least the first starting compound to form a product having an increased amount of selectively hydrogenated analog. According to a more particular embodiment, this increased amount is relative to the initial amount of selectively hydrogenated analog present in the impure feed. For example, a selective hydrogenation analog of a given starting compound (e.g., a major first selective hydrogenation analog and / or a minor first selective hydrogenation analog of a first starting compound) may be present in the impure feed in an amount or combination of amounts within the ranges set forth above for the starting compound or mixture of starting compounds. An increased amount of selective hydrogenation analog (e.g., in the case of a first starting compound, an increased amount of the major first selective hydrogenation analog, an increased amount of the minor first selective hydrogenation analog, or an increased amount of a combination of these selective hydrogenation analogs) may represent a yield resulting from conversion (or more specifically selective hydrogenation) of the starting compound of at least 60% (e.g., 60% to 100%), at least 75% (e.g., 75% to 99%), or at least 85% (e.g., 85% to 99%) of the theoretical yield.

[0029] As understood in the art, the yield of one or more given compounds refers to the product of the conversion and the selectivity, where selectivity refers to the fraction (or percentage) of the compound or converted products that occur as such compounds. In determining a given yield, one skilled in the art will recognize, using the teachings herein, that a given starting compound, selectively hydrogenated analog, or fully hydrogenated analog may be in various forms, such as dimeric, oligomeric, hydrated, etc., depending on the particular composition in which the compound and / or analog is contained (e.g., in the presence of an aqueous or organic solvent). For example, glycolaldehyde may be in either dimeric, oligomeric, or hydrated form. Glycolaldehyde dimer is a particularly predominant form, which is also known as the cyclic structure 2,5-dihydroxy-1,4-dioxane. Thus, for purposes of determining yields as described herein, one mole of a dimeric compound or analog is considered equivalent to two moles of such compound or analog, one mole of a trimeric compound or analog is considered equivalent to three moles of such compound or analog, and so forth.

[0030] For illustrative purposes, an exemplary impure feed may contain 100 moles of pyruvaldehyde as the first starting compound. In this case, an increased amount of (i) 80 moles of hydroxyacetone (acetol) as the major first selective hydrogenation analog, or (ii) 80 moles of 2-hydroxypropanal as the minor first selective hydrogenation analog, or (iii) 80 moles of a combination of these selective hydrogenation analogs in the product would represent 80% of the theoretical yield of hydroxyacetone (acetol), 2-hydroxypropanal, or a combination, respectively, obtained from the conversion of pyruvaldehyde. In this case, these yields associated with the increased amounts are obtained regardless of whether the impure feed further contains an initial amount of either the first selective hydrogenation analog (in this case hydroxyacetone (acetol)) and / or the minor first selective hydrogenation analog (in this case 2-hydroxypropanal).

[0031] Advantageously, as described above, the increased amounts associated with "selective" hydrogenation relate to the discovery of hydrogenation conditions that do not result in a significant degree of more complete hydrogenation of the desired selectively hydrogenated analog, whether originally present in the impure feed or produced from its respective starting compound. In representative embodiments, the amount of more completely or fully hydrogenated analog (wherein additional or all carbonyl carbon atoms are converted to hydroxyl carbon atoms) in the product represents a yield of such analog of less than 5% (e.g., 0.001% to 5%), less than 2% (e.g., 0.001% to 2%), or less than 1% (e.g., 0.01% to 1%) of the theoretical yield. Such amounts of more completely or fully hydrogenated analog may be obtained in combination with increased amounts of selectively hydrogenated analog (or combinations of selectively hydrogenated analogs) that represent a yield within any of the ranges described above. For illustrative purposes, the exemplary impure feed described above, which includes 100 moles of pyruvaldehyde as the first starting compound, may further include 20 moles of hydroxyacetone (acetol) as the major first selectively hydrogenated analogue and 10 moles of 2-hydroxypropanal as the minor first selectively hydrogenated analogue. Full hydrogenation of this first starting compound and the first selectively hydrogenated analogue can theoretically produce 130 moles of the fully hydrogenated analogue propylene glycol. Thus, the amount of 1 mole of propylene glycol in the product would represent a yield of 0.77% (1 / 130) of the theoretical yield, assuming that the impure feed does not include an initial amount of this fully hydrogenated analogue. In the case of an impure feed that includes an initial amount of fully hydrogenated analogue, the increased amount (based on the initial amount) would represent a yield within the range given above (e.g., less than 2% of the theoretical yield).

[0032] In view of the above, according to some embodiments, the impure feed may include one or more selective hydrogenation analogs (e.g., a major first selective hydrogenation analog and / or a minor first selective hydrogenation analog) in an amount or combined amount within the ranges given above (e.g., 1 wt % to 75 wt %) based on the amount or combined amount of the starting compound or mixture of starting compounds. Alternatively, the one or more selective hydrogenation analogs may be substantially absent from the impure feed, and for example, the one or more selective hydrogenation analogs (e.g., a major first selective hydrogenation analog and / or a minor first selective hydrogenation analog) may be present in the impure feed in an amount or combined amount of less than 1 wt % or less than 0.5 wt %. The impure feed may also contain one or more fully hydrogenated analogs (e.g., ethylene glycol when the starting compound is glycolaldehyde, propylene glycol when the starting compound is pyruvaldehyde) in amounts or combined amounts within the ranges given above (e.g., 1 wt % to 75 wt %) based on the amount or combined amount of the starting compound or mixture of starting compounds. Alternatively, the one or more fully hydrogenated analogs may be substantially absent from the impure feed, and, for example, the one or more fully hydrogenated analogs may be present in the impure feed in amounts or combined amounts of less than 1 wt % or less than 0.5 wt %.

[0033] In addition to the starting compound, the impure feed may contain one or more compounds (different from the starting compound) having only a single carbonyl carbon atom, either an aldehyde carbon atom or a ketone carbon atom. Under the hydrogenation conditions described herein (conditions for contacting the impure feed with a hydrogenation catalyst), such compounds may be hydrogenated to the corresponding hydrogenated analogs by converting the single carbonyl carbon atom to a hydroxyl carbon atom. According to specific examples of compounds having only a single carbonyl carbon atom, the hydrogenation of furfural or 5-hydroxymethylfurfural may produce 5-hydroxymethylfuran or 2,5-dihydroxymethylfuran as the corresponding hydrogenated analogs, respectively, based on the following reaction: [ka]

[0034] According to some embodiments, under hydrogenation conditions suitable for substantially converting a starting compound (e.g., a first starting compound) to one or more selectively hydrogenated analogs (e.g., a major first selectively hydrogenated analog and / or a minor first selectively hydrogenated analog), one or more compounds having only a single carbonyl carbon atom may be partially converted to their corresponding hydrogenated analogs. For example, one or more corresponding hydrogenated analogs may be produced (forming products having increased amounts) in an amount that represents a yield obtained from the conversion (hydrogenation) of such compounds, generally 10% to 90%, typically 15% to 75%, and often 20% to 60% of the theoretical yield. In such embodiments, the increased amount of one or more selectively hydrogenated analogs may represent a yield obtained from the conversion of one or more starting compounds, as described above (e.g., at least 60% of the theoretical yield). The amount or combined amount of one or more compounds having only a single carbonyl carbon atom in the impure feed may be within the ranges given above (e.g., 1 wt % to 75 wt %) based on the amount or combined amount of the starting compound or mixture of starting compounds. Alternatively, one or more compounds having only a single carbonyl carbon atom may be substantially absent from the impure feed, and, for example, such compounds may be present in the impure feed in amounts or combined amounts of less than 1 wt % or less than 0.5 wt %.

[0035] Regardless of whether one or more compounds having only a single carbonyl carbon atom are present or substantially absent in the impure feed, the impure feed may contain one or more corresponding hydrogenated analogs of such compounds (e.g., 5-hydroxymethylfuran or 2,5-dihydroxymethylfuran as the corresponding hydrogenated analogs of furfural or 5-hydroxymethylfurfural, respectively) in amounts or combined amounts within the ranges given above (e.g., 1 wt. % to 75 wt. %) based on the amount or combined amount of the starting compound or mixture of starting compounds. Alternatively, one or more corresponding hydrogenated analogs may be substantially absent from the impure feed, and, for example, one or more corresponding hydrogenated analogs may be present in the impure feed in amounts or combined amounts less than 1 wt. % or less than 0.5 wt. %.

[0036] In other further embodiments, value may be derived from the conversion (hydrogenation) of one or more such compounds having only a single carbonyl carbon atom (e.g., furfural and / or 5-hydroxymethylfurfural) in the absence or even substantial absence of the conversion (selective hydrogenation) of one or more starting compounds as described herein. According to such embodiments, starting compounds as defined herein may be substantially absent from the impure feed, and for example, starting compounds (e.g., compounds having at least two carbonyl carbon atoms, e.g., those having only two carbonyl carbon atoms) may be present in the impure feed in an amount or combination of less than 1 wt.% or less than 0.5 wt.%. In such embodiments, the amount or combination of one or more compounds having only a single carbonyl carbon atom in the impure feed may be within the ranges given above (e.g., 1 wt.% to 75 wt.%).

[0037] More specific embodiments relate to a method for increasing the amount or effective availability of glycolaldehyde, which is typically initially present in an impure feed, but may alternatively be absent or substantially absent from the impure feed. The impure feed may further include, for example, glyoxal, pyruvaldehyde, and hydroxyacetone (acetol). Upon contacting the impure feed with a hydrogenation catalyst under hydrogenation conditions described herein, at least a portion of the glyoxal is converted (selectively hydrogenated) to form a product having an increased amount of glycolaldehyde as a first selectively hydrogenated analog. For example, the increased amount of glycolaldehyde may represent a yield obtained from the conversion (selective hydrogenation) of glyoxal within any of the ranges given above for the selectively hydrogenated analog (e.g., at least 60% of theoretical yield). Advantageously, the selective hydrogenation may be carried out without any recognition of the net formation of a more fully or completely hydrogenated analog in which additional or all carbonyl carbon atoms are converted to hydroxyl carbon atoms. For example, the amount of such analogs (e.g., ethylene glycol and / or propylene glycol) in the product may represent the yields described above (e.g., less than 5%, less than 2%, or less than 1% of the theoretical yield). Importantly, therefore, the exemplary selective hydrogenation process can be carried out with little or no conversion of a valuable intermediate, such as hydroxyacetone (acetol), to its fully hydrogenated analog, such as propylene glycol. In effect, contacting under hydrogenation conditions may selectively hydrogenate at least a portion of pyruvaldehyde as the second starting compound to form an increased amount of hydroxyacetone (acetol) as the major second selectively hydrogenated analog in the product along with an increased amount of glycolaldehyde.

[0038] [Hydrogenation catalyst and conditions] Particular embodiments relate to the above-described process for selective hydrogenation, which contacts an impure feed with a hydrogenation catalyst under hydrogenation conditions. Exemplary hydrogenation catalysts are precious metal-containing catalysts, meaning that they contain at least one precious metal. For example, the hydrogenation catalyst may contain ruthenium or platinum as the precious metal, or may contain both of these precious metals. The hydrogenation catalyst may contain one or both of these precious metals or other precious metals, generally in an amount of 0.1 wt% to 15 wt%, typically 0.5 wt% to 10 wt%, based on the weight of the catalyst, or in a combination amount. Regardless of the amount, the hydrogenation catalyst may be a solid supported precious metal-containing catalyst, meaning that the precious metal is supported on a solid support, which may be substantially refractory (inert) under hydrogenation conditions, or may itself be functional (e.g., if it provides acidic or basic sites to provide or promote catalytic activity). Carbon, including activated carbon, is an exemplary solid support.

[0039] Noble metal is understood to mean a group of oxidation-resistant metal elements. In an exemplary embodiment, the at least one noble metal of the hydrogenation catalyst can be selected from the group consisting of platinum (Pt), rhodium (Rh), ruthenium (Ru), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir) and gold (Au), and according to a specific embodiment, the term "consisting of" is used to merely represent the group member from which the noble metal is selected, and does not exclude the addition of other noble metals and / or other metals in general. Thus, a hydrogenation catalyst containing a noble metal encompasses a catalyst containing at least two noble metals, and even a catalyst containing at least three noble metals, as well as a catalyst containing two noble metals and a third non-noble metal, such as a cocatalyst metal (e.g., a transition metal). According to a preferred embodiment, the noble metal is present in an amount or combination of amounts within the ranges given above. Alternatively, when at least two precious metals are present, they may each be present independently in an amount of 0.05 wt% to 12 wt%, 0.3 wt% to 10 wt%, or 1 wt% to 7.5 wt%, based on the weight of the catalyst. Alternatively, the first precious metal may be present in an amount falling within any of these ranges, and the second precious metal may be present in a smaller amount relative to the first precious metal. For example, the second precious metal may be present in an amount of 0.03 wt% to 10 wt%, 0.1 wt% to 5 wt%, or 0.3 wt% to 3 wt%, based on the weight of the catalyst.

[0040] For example, a representative hydrogenation catalyst may include two precious metals, Ru and Pt, and Ru and Pt may be independently present in any of these ranges (e.g., 1 wt% to 7.5 wt%). That is, either Ru may be present in such amounts, Pt may be present in such amounts, or Ru and Pt may both be present in such amounts. In other embodiments, Ru may be present in any of the ranges described above for a first precious metal (e.g., 1 wt% to 7.5 wt%), and Pt may be present in any of the ranges described above for a second precious metal (e.g., 0.3 wt% to 3 wt%), except that Pt is present in a smaller amount compared to Ru.

[0041] In addition to one or more precious metals (e.g., Ru and Pt in the amounts described above), exemplary hydrogenation catalysts may further include a non-precious metal, such as a metal selected from Groups 13-15 of the Periodic Table (e.g., Ga, Ge, In, or Sn). Such non-precious metals may be present in amounts within the ranges given above for precious metals (e.g., 0.05 wt% to 12 wt%, 0.3 wt% to 10 wt%, or 1 wt% to 7.5 wt%, based on the weight of the catalyst). A preferred non-precious metal is Sn.

[0042] In an exemplary embodiment, a single precious metal (e.g., either Ru or Pt) or two precious metals (e.g., both Ru and Pt) may be present in the hydrogenation catalyst substantially solely with a non-precious metal (e.g., Sn) selected from Groups 13-15 of the periodic table, e.g., any other metals may be present in an amount or combination of less than 0.1 wt% or less than 0.05 wt% based on the weight of the hydrogenation catalyst. In a further exemplary embodiment, a single precious metal or two precious metals may be present in the hydrogenation catalyst substantially solely with a non-precious metal (e.g., Sn) selected from Groups 13-15 of the periodic table, excluding metals that may be present in the solid support (e.g., aluminum is present in the solid support as aluminum oxide). Thus, in the case of a support composed substantially entirely of carbon, a single precious metal or two precious metals may be present in the hydrogenation catalyst substantially solely with a non-precious metal (e.g., Sn) selected from Groups 13-15 of the periodic table. For example, any other metals than the single precious metal or two precious metals, together with a non-precious metal selected from Groups 13-15 of the Periodic Table (e.g., Sn) and the metal of the solid support (if any), may be present in an amount or combined amount of less than 0.1 wt % or less than 0.05 wt %, based on the weight of the hydrogenation catalyst. Any metal present in the catalyst, including the precious metal, may generally have a metal particle size within the range of 0.3 nanometers (nm) to 20 nm, typically 0.5 nm to 10 nm, and often 1 nm to 5 nm.

[0043] The hydrogenation-active noble and non-noble metals (e.g., Sn) of the exemplary hydrogenation catalysts may be supported or deposited on a solid support, which is intended to include catalysts in which the metals are present on the support surface and / or within the porous internal structure of the support. Thus, in addition to such hydrogenation-active metals, the exemplary hydrogenation catalysts may further include a solid support, with exemplary solid supports including carbon and / or one or more metal oxides. Exemplary metal oxides are selected from the group consisting of aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, strontium oxide, tin oxide, and the like. The solid support may be entirely or substantially entirely composed of one or more such metal oxides, for example, one or more metal oxides are present in an amount or combination of at least 95 wt% of the solid support. Alternatively, carbon, such as activated carbon, may be present in an amount of at least 95 wt% or at least 99 wt% of the solid support. Activated carbon refers to a form of carbon after any of several possible treatments (e.g., high-temperature steaming) to increase porosity. Activated carbon also refers to forms obtained by chemical treatment (eg, with an acid or base) that alters properties such as the concentration of acidic sites.

[0044] The precious and non-precious metals (e.g., Sn) can be incorporated into the solid support according to known techniques of catalyst preparation, including sublimation, impregnation, or dry mixing. In the case of impregnation, an impregnation solution of soluble compounds of one or more metals in a polar (aqueous) or non-polar (e.g., organic) solvent can be contacted with the solid support, preferably under an inert atmosphere. For example, the contacting can be carried out in an ambient atmosphere of nitrogen, argon, and / or helium, preferably with stirring, or in a non-inert atmosphere such as air. The solvent can then be evaporated from the solid support, for example, using heat, flowing gas, and / or vacuum conditions, leaving a dry metal-impregnated support. For example, in the case of two precious metals (e.g., Ru and Pt), the metals can be impregnated into the solid support and one non-precious metal (e.g., Sn) can be simultaneously impregnated by dissolving both in the same impregnation solution, or impregnated separately using different impregnation solutions and contacting steps. In either case, the metal impregnated support may be subjected to further preparation steps, such as solvent washing to remove excess precious metal and impurities, further drying, and calcination to provide the hydrogenation catalyst.

[0045] The solid support itself can be prepared according to known methods, such as extrusion to form cylindrical particles (extrudates), oil dropping or spray drying to form spherical particles. Regardless of the particular shape of the solid support and the resulting catalyst particles, the amount of precious and non-precious metals present in the hydrogenation catalyst described above refers to the average weight of such metals in a given catalyst particle (e.g., any shape, such as cylindrical or spherical), regardless of the particular distribution of the metals within the particle. In this regard, it is understood that different preparation methods can provide different distributions, such as deposition of the metals primarily on or near the surface of the solid support, or a uniform distribution of the metals throughout the solid support. In general, the weight percentages described herein based on the weight of the solid support or based on the weight of the hydrogenation catalyst can refer to the weight percentages in a single catalyst particle, but more typically refer to the average weight percentages over a number of catalyst particles, such as the number in a hydrogenation reactor that forms the catalyst bed used in the process described herein.

[0046] An aspect of the present invention relates to a method for selective hydrogenation of starting compounds such as glyoxal and pyruvaldehyde using the noble metal-containing hydrogenation catalyst and hydrogenation conditions described herein. Advantages associated with this method are described above, including the formation of additional amounts of the desired selectively hydrogenated analogs without any perceived further conversion (hydrogenation) of such analogs to more fully or completely hydrogenated analogs. For any given impure feed, the amount and specific type of noble metal-containing hydrogenation catalyst and the strength of the hydrogenation conditions can be determined by one of skill in the art using knowledge gained from this disclosure to achieve an optimal balance of selective hydrogenation of the starting compound without complete hydrogenation of the generated selectively hydrogenated analog. Under hydrogenation conditions, the impure feed, including any solvent such as water and / or methanol, can be present in combination with any hydrogenation catalyst or combination of catalysts described above to form a reaction mixture. The amount or combination of hydrogenation catalysts in such a reaction mixture can be 0.1 wt% to 10 wt%, 0.3 wt% to 8 wt%, or 0.5 wt% to 5 wt%. For a continuous process, the hydrogenation catalyst may be present in the reaction mixture in an amount required to achieve the Weight Hourly Space Velocity (WHSV) described below.

[0047] Typical hydrogenation conditions include elevated total pressure and hydrogen partial pressure, the latter of which is often at least about 3 megapascals (MPa) (435 psi). This hydrogen partial pressure, in combination with a noble metal-containing hydrogenation catalyst, can provide the performance criteria described above (e.g., with respect to a relatively high yield of one or more selectively hydrogenated analogs and a relatively low yield of one or more fully hydrogenated analogs). Pressure can be included in the hydrogenation reactor used to contact an impure feed (e.g., an impure feed containing glyoxal and / or pyruvaldehyde) with the heterogeneous (solid) noble metal-containing hydrogenation catalyst described above to obtain a product having an increased amount of a selectively hydrogenated analog (e.g., glycolaldehyde or hydroxyacetone (acetol)). The reaction mixture containing the catalyst and subjected to hydrogenation conditions can be aqueous (containing water as a solvent) or organic (e.g., containing methanol as a solvent) and generally contains dissolved hydrogen under these conditions. In the case of a continuous process, impure feed may be added continuously to the reaction mixture and product may be withdrawn continuously from the reaction mixture (eg, following separation from the catalyst).

[0048] The hydrogenation conditions under which the reaction mixture is maintained during the conversion of the starting compounds to their respective selectively hydrogenated analogues generally include absolute reactor pressures in the range of 300 psi to 3500 psi, typically 500 psi to 3000 psi, and often 750 psi to 1500 psi. The reactor pressure may be generated primarily or substantially from hydrogen, and these total pressure ranges may also correspond to ranges of hydrogen partial pressures. However, the contribution of the vapor pressure of the reaction mixture to the total pressure under hydrogenation conditions will generally result in a reduced hydrogen partial pressure compared to the total pressure, so for example the hydrogen partial pressure may generally be in the range of 1.38 MPa (200 psi) to 22.4 MPa (3250 psi), typically 3.00 MPa (435 psi) to 20.0 MPa (2901 psi), and often 4.82 MPa (700 psi) to 9.31 MPa (1350 psi).

[0049] Other hydrogenation conditions present in the hydrogenation reactor include temperatures generally between 20°C (68°F) and 200°C (392°F), typically between 50°C (122°F) and 150°C (302°F), and often between 50°C (122°F) and 75°C (167°F). The reaction time, i.e., the time during which the reaction mixture is maintained under any target value or target subrange of pressure and temperature within any of the pressure and temperature ranges given above (e.g., a target total pressure value of 8.27 MPa (1200 psi) and a target temperature of 65°C (149°F)), is generally between 0.25 hours and 15 hours, typically between 0.25 hours and 5 hours, and often between 0.5 hours and 3 hours, for batch reactions. In continuous processes, these reaction times correspond to the reactor residence time. An additional parameter that is relevant for continuous processes is the weight hourly space velocity (WHSV), which is understood in the art as the weight flow rate of the feed (e.g., impure feed containing starting compounds) to the reactor divided by the weight of the catalyst (in this case, a noble metal-containing hydrogenation catalyst). This parameter therefore represents the equivalent catalyst bed weight of the feed processed per hour and is related to the inverse of the reactor residence time. According to an exemplary embodiment, the hydrogenation conditions are generally within 0.01 hr -1 ~20hr -1 , typically 0.05hr -1 ~5hr -1 , often 0.5hr -1 ~3hr -1 Includes WHSV.

[0050] Using the teachings herein, one skilled in the art can adjust the hydrogenation conditions to an optimal strength for a given impure feed and hydrogenation catalyst such that the starting compound is selectively hydrogenated to the corresponding selectively hydrogenated analog described herein without being substantially converted to the corresponding more fully or fully hydrogenated analog. For example, the hydrogenation strength can be increased by increasing any one or more of the hydrogen partial pressure, temperature, and residence time (or by decreasing the WHSV in the case of a continuous process). Conversely, the hydrogenation strength can be decreased by decreasing any one or more of these hydrogenation conditions (or by increasing the WHSV in the case of a continuous process). Thus, representative embodiments relate to selective hydrogenation processes described herein that further include monitoring the composition of the product (e.g., to determine the concentration of a given starting compound, selectively hydrogenated analog, and / or fully hydrogenated analog) and adjusting the hydrogenation strength to improve or optimize the composition based on such composition (e.g., to decrease or minimize the concentration of the starting compound or fully hydrogenated analog, or to increase or maximize the concentration of the selectively hydrogenated analog).

[0051] The impure feed may be charged to the hydrogenation reactor in a batchwise manner or may be added continuously to the reactor. In either case, the use of a heterogeneous (solid) hydrogenation catalyst facilitates the separation of the product, which is generally obtained as a liquid (after cooling), from the reaction mixture containing the catalyst. In the case of a batchwise operation, after charging the selective hydrogenation reactor with the impure feed and the hydrogenation catalyst, the reactor may be sealed and purged with an inert gas (e.g., nitrogen), and then purged and pressurized with hydrogen. In the case of a continuous operation, the impure feed may be added continuously (e.g., pumped) to the reactor after such purging and pressurization. A fresh hydrogen stream may also be added continuously, and this fresh hydrogen stream may be optionally combined with a recycle gas stream containing hydrogen, so that the combined (fresh and recycle) hydrogen stream may be added continuously to the reactor (e.g., using one or more compressors, such as a feed compressor and a recycle compressor). The recycle gas stream may be all or a portion of the vapor fraction separated from the product (e.g., following removal of a vent or purge gas stream to prevent excessive accumulation of undesirable impurities) and is continuously withdrawn from the reactor in the same manner as the product. For example, the vapor fraction comprising the recycle gas stream and the liquid fraction comprising the product may be withdrawn together from the reactor in a substantially catalyst-free reactor effluent stream. To improve the recovery of condensable species (e.g., selectively hydrogenated analogs and / or unconverted starting compounds) in the liquid fraction / product, the reactor effluent stream may be cooled (e.g., using a condenser) prior to separating the vapor fraction from the liquid fraction (e.g., in a flash separator). According to some embodiments, a portion of the product may be similarly recycled to the reactor (e.g., following one or more downstream separation steps) to improve the overall conversion of a given starting compound to a selectively hydrogenated analog. In the case of a batch reaction, hydrogen is generally present in the reactor in excess of the molar hydrogen requirement of stoichiometric amounts for the complete conversion of one or more starting compounds to their selectively hydrogenated analogs. For example, the stoichiometric excess can represent at least 1.5 times, at least 5 times, or at least 10 times the molar hydrogen requirement.For continuous reactions, hydrogen is generally added in excess of such stoichiometric amounts (eg, in a fresh hydrogen stream or in a combined hydrogen stream).

[0052] The product recovered from the hydrogenation reactor may be subjected to any of several possible separation steps to provide a purified product stream, such as one enriched in any of the selectively hydrogenated analogs described herein (e.g., glycolaldehyde, hydroxyacetone (acetol), and / or 2-hydroxypropanal). Such separation steps may include one or more of phase separation, extraction (e.g., with an organic solvent having preferential affinity for the selectively hydrogenated analogs), and distillation, sequentially in any order. Extraction and distillation may alternatively be combined in a single extractive distillation step. As described above, one particular advantage of the selective hydrogenation methods described herein is the conversion of the starting compound to a selectively hydrogenated analog that has a significantly different relative volatility, such as in the case of the high boiling fraction obtained by distillation, and is therefore more easily separable. For example, the starting compound glyoxal has a normal boiling point of 51° C. (124° F.), while its selectively hydrogenated analog glycolaldehyde has a significantly higher normal boiling point of 131° C. (268° F.). The starting compound pyruvaldehyde has a normal boiling point of 72° C. (162° F.), while the selectively hydrogenated analog hydroxyacetone (acetol) has a significantly higher normal boiling point of about 146° C. (295° F.), and the selectively hydrogenated analog 2-hydroxypropanal also has a significantly higher normal boiling point of about 122° C. (252° F.) As with the recycle gas stream, any of the separated liquid product streams, particularly such streams enriched in one or more unconverted starting compounds, may similarly be recycled to the hydrogenation reactor.

[0053] According to further embodiments, the production of one or more selectively hydrogenated analogs, such as glycolaldehyde and / or hydroxyacetone (acetol), may be combined with upstream and / or downstream processing steps, such as, for example, a process of pyrolysis of a carbohydrate (e.g., an aldose-containing sugar). Thus, the upstream processing may include pyrolysis of an aqueous solution of a carbohydrate in a pyrolysis reactor under pyrolysis conditions including elevated temperatures (e.g., 500° C. (932° F.) or higher) to provide a gas-phase pyrolysis product including pyrolysis products of an aldose-containing sugar. This may further include cooling the gas-phase pyrolysis product, for example, in a condenser, to condense a liquid mixture including glyoxal, pyruvaldehyde, glycolaldehyde, and hydroxyacetone (acetol) as such pyrolysis products. The condensed liquid mixture obtained from such an upstream processing step may then correspond to the impure feed described herein.

[0054] Thus, the process may further comprise contacting the condensed liquid mixture with a hydrogenation catalyst under hydrogenation conditions to selectively hydrogenate (i) at least a portion of the glyoxal, (ii) at least a portion of the pyruvaldehyde, or (iii) both (i) and (ii) to form a product having, respectively, (i) an increased amount of glycolaldehyde, (ii) an increased amount of hydroxyacetone (acetol), or (iii) both (i) and (ii). These selectively hydrogenated analogs, i.e., glycolaldehyde and hydroxyacetone (acetol), may be conveniently separated by distillation of the product due to their increased boiling points compared to their respective starting compounds glyoxal and pyruvaldehyde. In particular, downstream processing may include distilling the product to recover a fraction such as a bottoms fraction or a relatively high boiling fraction enriched in (i) glycolaldehyde (glycolaldehyde-enriched fraction), (ii) hydroxyacetone (acetol) (hydroxyacetone-enriched fraction), or (iii) both (i) and (ii) (glycolaldehyde- and hydroxyacetone-enriched fraction), respectively. In this case, the term "enriched in" means at least an increased concentration or weight percent of (i), (ii), or (iii) relative to the product (which in this case may correspond to the feed to the distillation). Distillation of the product may further recover a fraction such as an overhead fraction or a relatively low boiling fraction depleted in (i) glycolaldehyde (glycolaldehyde-depleted fraction), (ii) hydroxyacetone (acetol) (hydroxyacetone-depleted fraction), or (iii) both (i) and (ii) (glycolaldehyde- and hydroxyacetone-depleted fraction), respectively. In this case, the term "depleted in" means at least a reduced concentration or weight percent of (i), (ii), or (iii) compared to the product (which in this case may correspond to the feed to the distillation). In some embodiments, such overhead fractions or relatively low boiling fractions may be enriched in one or more of the respective starting compounds compared to the product. For example, they may be enriched in (iv) unconverted glyoxal, (v) unconverted pyruvaldehyde, or (vi) both (iv) and (v).Depending on the particular concentration or weight percentage of (iv), (v), or (vi), overall conversion and process economics may be improved by recycling at least a portion of such overhead fraction or relatively low boiling fraction, or at least a portion of any other fraction obtained in the above-described production processes having sufficient concentration or weight percentage of (iv), (v), or (vi) to justify its recycling to the hydrogenation reactor.

[0055] The following examples are given as representative of the present invention, but should not be construed as limiting the scope of the invention, since other equivalent embodiments will become apparent in view of this disclosure and the appended claims. EXAMPLES

[0056] Example 1 [Hydrogenation of furfural] A liquid mixture of 24 grams of furfural and 62 grams of methanol solvent was charged to a 300 cc high pressure reactor (Parr Instrument Company). To this mixture was added 2.05 grams of particulate solid catalyst with a metal content of 2 wt% Ru / 2 wt% Sn / 0.5% wt% Pt supported on a carbon support. The reactor was purged with hydrogen while continuously stirring the reaction mixture at 800 rpm. The reactor was then pressurized to 8.3 MPa (1200 psi) with hydrogen and the reaction mixture was heated to 65° C. and maintained at this temperature for 1 hour. The reaction mixture was then cooled to room temperature and the reactor was opened. The solid and liquid contents were removed from the reactor and filtered by vacuum filtration to separate the catalyst. The filtrate was subjected to rotary evaporation to remove the methanol solvent. The composition of the remaining liquid was analyzed using nuclear magnetic resonance (NMR) spectroscopy and found to contain furfural alcohol (5-hydroxymethylfuran) and unreacted furfural.

[0057] Thus, the hydrogenation catalyst and conditions were sufficient to hydrogenate a portion of the furfural to its corresponding hydrogenated analogue, 5-hydroxymethylfuran.

[0058] Example 2 [Selective hydrogenation of pyruvaldehyde] A liquid composition of 15.1 grams of pyruvaldehyde concentrated to 40 wt% in water was added to 86 ml of water, and the resulting mixture was charged into a 300 cc high pressure reactor (Parr Instrument Company). To this mixture was added 1.96 grams of particulate solid catalyst with a metal content of 2 wt% Ru / 2 wt% Sn / 0.5% wt% Pt supported on a carbon support. The reactor was purged with hydrogen while the reaction mixture was continuously stirred at 800 rpm. The reactor was then pressurized to 8.3 MPa (1200 psi) with hydrogen, and the reaction mixture was heated to 65°C and maintained at this temperature for 1 hour. The reaction mixture was then cooled to room temperature and the reactor was opened. The solid and liquid contents were removed from the reactor and filtered by vacuum filtration to separate the catalyst. The composition of the filtrate was analyzed using NMR spectroscopy and found to contain mainly (>80%) hydroxyacetone (acetol) and a small amount of unconverted pyruvaldehyde.

[0059] Thus, the hydrogenation catalyst and conditions were sufficient to selectively hydrogenate pyruvaldehyde to its selectively hydrogenated analogue hydroxyacetone (acetol).

[0060] Example 3 [Selective hydrogenation of glyoxal] A liquid composition of 15.1 grams of glyoxal concentrated to 40 wt% in water was added to 85 ml of water, and the resulting mixture was charged into a 300 cc high pressure reactor (Parr Instrument Company). To this mixture was added 2.17 grams of particulate solid catalyst with a metal content of 2 wt% Ru / 2 wt% Sn / 0.5% wt% Pt supported on a carbon support. The reactor was purged with hydrogen while continuously stirring the reaction mixture at 800 rpm. The reactor was then pressurized to 8.3 MPa (1200 psi) with hydrogen, and the reaction mixture was heated to 60° C. and maintained at this temperature for 1 hour. The reaction mixture was then cooled to room temperature and the reactor was opened. The solid and liquid contents were removed from the reactor and filtered by vacuum filtration to separate the catalyst. The composition of the filtrate was analyzed using NMR spectroscopy and found to contain glycolaldehyde (14% based on NMR) and unconverted glyoxal.

[0061] Thus, the hydrogenation catalyst and conditions were sufficient to selectively hydrogenate glyoxal to its selectively hydrogenated analog, glycolaldehyde.

[0062] Example 4 [Selective hydrogenation of glyoxal and pyruvaldehyde] 100 ml of a liquid composition containing 7 wt% glycolaldehyde and also containing glyoxal and pyruvaldehyde was charged into a 300 cc high pressure reactor (Parr Instrument Company). To this mixture was added 2.05 grams of a particulate solid catalyst with a metal content of 2 wt% Ru / 2 wt% Sn / 0.5% wt% Pt supported on a carbon support. The reactor was purged with hydrogen while continuously stirring the reaction mixture at 800 rpm. The reactor was then pressurized to 8.3 MPa (1200 psi) with hydrogen and the reaction mixture was heated to 60° C. and maintained at this temperature for 1 hour. The reaction mixture was then cooled to room temperature and the reactor was opened. The solid and liquid contents were removed from the reactor and filtered by vacuum filtration to separate the catalyst. The composition of the filtrate was analyzed using NMR spectroscopy and found to contain glycolaldehyde and hydroxyacetone (acetol). Ethylene glycol was also detected, but only at trace levels, less than 100 parts per million (ppm) by weight.

[0063] Thus, the hydrogenation catalyst and conditions were sufficient to selectively hydrogenate glyoxal to its selectively hydrogenated analog, glycolaldehyde, and also to selectively hydrogenate pyruvaldehyde to its selectively hydrogenated analog, hydroxyacetone (acetol). Under the same conditions, very little of the fully hydrogenated analog of glyoxal, i.e., ethylene glycol, was produced.

[0064] Generally, aspects of the present invention relate to the use of selective hydrogenation to increase the concentration of certain desired intermediates, such as glycolaldehyde and hydroxyacetone (acetol), in impure feeds, such as liquid mixtures recovered from carbohydrate pyrolysis, thereby improving the efficiency and associated economics of synthetic routes to high value chemicals from renewable feeds via such desired intermediates.

Claims

1. 1. A process for the selective hydrogenation of at least a first starting compound present in an impure feed, said first starting compound having two carbonyl carbon atoms and being glyoxal or pyruvaldehyde; The method further comprising: selectively hydrogenating said first starting compound to at least a major first selectively hydrogenated analog by contacting said impure feed with a hydrogenation catalyst under hydrogenation conditions to convert one of said two carbonyl carbon atoms to a hydroxyl carbon atom while preserving the other one of said two carbonyl carbon atoms; forming a product having an increased amount of said at least major first selectively hydrogenated analog; Including, the impure feed is a mixture of the first starting compound and other compounds resulting from pyrolysis of carbohydrates, the mixture further comprising the major first selectively hydrogenated analog; the hydrogenation catalyst comprises ruthenium, platinum, and tin; (i) the first starting compound is glyoxal and the major first selectively hydrogenated analog is glycolaldehyde; (ii) the first starting compound is pyruvaldehyde and the major first selectively hydrogenated analog is hydroxyacetone (acetol); method.

2. 2. The method of claim 1, wherein one of the two carbonyl carbon atoms of the first starting compound is an aldehyde carbon atom and the other of the two carbonyl carbon atoms of the first starting compound is a ketone carbon atom, and a minor first selective hydrogenation analog results from converting the ketone carbon atom to the hydroxyl carbon atom and retaining the aldehyde carbon atom.

3. the impure feed further comprises a second starting compound different from the first starting compound and having two carbonyl carbon atoms, and the contacting selectively hydrogenates the second starting compound to at least a major second selectively hydrogenated analog by converting one of the two carbonyl carbon atoms of the second starting compound to a hydroxyl carbon atom while preserving the other one of the two carbonyl carbon atoms of the second starting compound; the second starting compound is a compound having 2 to 5 carbon atoms obtained from the pyrolysis of a carbohydrate, (a) two of the two carbonyl carbon atoms of the second starting compound are aldehyde carbon atoms; or (b) one of the two carbonyl carbon atoms of the second starting compound is an aldehyde carbon atom and the other of the two carbonyl carbon atoms of the second starting compound is a ketone carbon atom, and the major second selective hydrogenation analog results from converting the aldehyde carbon atom to the hydroxyl carbon atom and retaining the ketone carbon atom; The method according to claim 1 or 2.

4. 3. The method of claim 2, wherein the first starting compound is pyruvaldehyde, and the major first selectively hydrogenated analog is hydroxyacetone (acetol) and the minor first selectively hydrogenated analog is 2-hydroxypropanal.

5. 4. The method of claim 3, wherein the first and second starting compounds are glyoxal and pyruvaldehyde.

6. 6. The method of any one of claims 1 to 5, wherein the impure feed comprises compounds having only a single carbonyl carbon atom, either an aldehyde carbon atom or a ketone carbon atom, and wherein the contacting hydrogenates the compounds to the corresponding hydrogenated analogs by converting the single carbonyl carbon atom to a hydroxyl carbon atom.

7. 7. The method of claim 6, wherein the compound having only a single carbonyl carbon atom is furfural or 5-hydroxymethylfurfural, and the corresponding hydrogenated analog is 5-hydroxymethylfuran or 2,5-dihydroxymethylfuran, respectively.

8. 8. The process of any one of claims 1 to 7, wherein the hydrogenation conditions comprise a temperature of from 20°C (68°F) to 150°C (302°F), a hydrogen partial pressure of from 3 MPa (435 psi) to 18 MPa (2610 psi), and a residence time of from 0.25 hours to 5 hours.

9. 9. The method of any one of claims 1 to 8, wherein the impure feed comprises glyoxal, pyruvaldehyde, glycolaldehyde, and hydroxyacetone (acetol), and the method comprises contacting the impure feed with a hydrogenation catalyst under hydrogenation conditions to selectively hydrogenate at least a portion of the glyoxal to form a product having an increased amount of glycolaldehyde.

10. 10. The process of claim 9, wherein said contacting under hydrogenation conditions selectively hydrogenates at least a portion of said pyruvaldehyde to form an increased amount of hydroxyacetone along with an increased amount of glycolaldehyde in said product.

11. The method further comprising: conducting pyrolysis of an aqueous solution of an aldose-containing sugar in a pyrolysis reactor under pyrolysis conditions including an elevated temperature to provide a gas phase pyrolysis product comprising a pyrolysis product of the aldose-containing sugar; cooling the gas phase pyrolysis product to condense a liquid mixture comprising glyoxal, pyruvaldehyde, glycolaldehyde, and hydroxyacetone (acetol); contacting the liquid mixture with a hydrogenation catalyst under hydrogenation conditions to selectively hydrogenate (i) at least a portion of the glyoxal, (ii) at least a portion of the pyruvaldehyde, or (iii) both (i) and (ii) to form a product having, respectively, (i) an increased amount of glycolaldehyde, (ii) an increased amount of hydroxyacetone (acetol), or (iii) both (i) and (ii); distilling the product to recover a fraction enriched in (i) glycolaldehyde, (ii) hydroxyacetone (acetol), or (iii) both (i) and (ii), respectively; The method according to any one of claims 1 to 10, comprising:

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