WO2012177138A1

WO2012177138A1 - Process for the liquid-phase reforming of lignin to aromatic chemicals and hydrogen

Info

Publication number: WO2012177138A1
Application number: PCT/NL2012/050446
Authority: WO
Inventors: Joseph John ZAKZESKI; Pieter Cornelis Antonius BRUIJNINCX; Bert Marc Weckhuysen
Original assignee: Universiteit Utrecht Holding B.V.
Priority date: 2011-06-23
Filing date: 2012-06-25
Publication date: 2012-12-27

Abstract

A process for the liquid-phase reforming of lignin into monomeric, dimeric, and oligomeric aromatic chemicals, hydrogen, and other light gases is provided using components from a second-generation lignocellulosic biorefinery whereby a lignin containing feed is solubilized in water-alcohol containing solvents followed by the liquid-phase reforming in the optional presence of a superacid, acid, or base co- catalyst. The resulting isolated aromatic components, the gases, and the solvent following the process can be tuned based on reaction conditions in particular on the catalyst and co-catalyst, and therefore the product distribution is highly tunable depending on chemical demand. The aromatic products consist of alkylated phenol, guaiacol, catechol, and syringolmonomers, dimers, and oligomers, and the ethanol solvent is recoverable either as ethanol, ethyl ether, or higher alcohols including n- butanol or n-hexanol with the particular distribution based on the reaction conditions employed.

Description

Title: Process for the liquid-phase reforming of lignin to aromatic chemicals and hydrogen

Field of the invention

The present invention relates to processes for the conversion of lignin-containing feeds using transition metal catalysts to produce hydrogen, light hydrocarbons and platform aromatic chemicals. More specifically, the present invention relates to a catalytic process for the conversion of lignin-containing feeds into monomeric aromatic chemicals, hydrogen, and light gases, including methane and ethane.

Background of the invention

With the depletion of fossil fuels as a source of fuels, chemicals, and energy, the fraction of energy and chemicals supplied by renewable resources such as biomass can be expected to increase in the foreseeable future [1 ]. One particular opportunity to realize the full potential of biomass-derived feedstocks is through the development of biorefineries. Current biorefineries are transitioning from using sugars obtained from sugarcane or corn as feedstocks to lignocellulosic materials, which are cheaper, more abundant, and do not directly compete with food production. Vast quantities of cellulose, hemicellulose, and lignin are processed by the modern biorefinery. The conversion of the cellulose and hemicellulose component of these materials to transportation fuels, primarily ethanol, has received considerable attention recently and has met some successes [2-1 1 ]. In part because of its recalcitrance, the valorization of the lignin component has received little attention relative to cellulose. Lignin comprises between 15-30% of lignocellulosic biomass by weight and about 40% by energy [12] and consists of methoxylated phenylpropene structures that confer strength and rigidity to plants [13-15]. Isolated lignin is usually obtained by deployment of a pretreatment method, such as the kraft and organosolv methods, which degrade the extended polymer to smaller compounds and, depending on the method, causes other chemical transformations such as sulfur incorporation [1 ]. As of 2004, the pulp and paper industry alone produced 50 million tons of extracted lignin, but only approximately 2% of the lignin available is used commercially with the remainder used as a low value fuel [16]. With its unique structure and chemical properties, a wide range of bulk and fine chemicals, particularly aromatics, and fuels are potentially obtainable from lignin with the development of appropriate catalytic technology. Such developments represent an opportunity to improve the chemical and energy integration of the modern biorefinery.

The depolymerization of the complicated lignin polymer into smaller molecules is an important aspect of lignin valorization. Previous methods to depolymerize lignin include pyrolysis, catalytic hydrogenation, oxidation, or hydrocracking [1 , 17-20]. US Patent No. 6172272 B1 to Shabtai et al. discloses a two-stage catalytic process that utilizes a base-catalyzed depolymerization followed by selective hydrocracking with a superacid catalyst [21 ]. US Patent Application Nos. 20090218061 A1 and

20090218062 A1 to Schinski et al. disclose a process for the hydrotreating of lignin [22,23]. The disadvantages of these processes include high reaction temperatures (often T > 538°C) and the need for a hydrogen feedstock in the case of

hydrocracking.

The aqueous-phase reforming (APR) of biomass-derived oxygenated compounds, such as methanol, glycol, glycerol, sorbitol, xylose, and glucose, at relatively low temperatures (T < 538°C) have been reported for the production of hydrogen at temperatures considerably lower than that required for gasification or pyrolysis [24]. Several patents and manuscripts have been published in the field of aqueous-phase reforming (APR) of biomass-derived oxygenated compounds for the production of hydrogen and chemicals. For example, the preferred catalysts for these systems comprise Group VIII transition metals, including alloys and mixtures, with platinum, ruthenium, or rhodium giving the most favorable results as disclosed by U.S. Pat. Nos. 6953873 and 7618612 to Cortright and Dumesic [25, 26]. The catalyst support is preferably selected from the group consisting of alumina, boron nitride, carbon, ceria, silica, silica-alumina, silica nitride, titania, zirconia, or mixtures thereof, which silica the preferential support [27, 28]. In most reports of APR reactions, fluidized-bed tubular reactors were used, and a decrease in void-space, defined as portions of the reaction that contain no solid catalyst, resulted in higher hydrogen production [29].

To date, all studies of APR have focused on the use of model compounds that could be derived from biomass, such as sorbitol and glucose. Only recently a process for the APR of actual biomass consisting of Southern pine sawdust for the production of hydrogen was disclosed by U.S. Pat. Application No. 20080103344 to Jones and Agrawal [30]. Only a small fraction of the lignin in the southern pine sawdust was acid soluble, and depolymerization occurred to a limited extent due to the formation of some acid-labile bonds, such as a- and β-ether linkages [31 ]. Earlier reports of the treatment of lignin under acidic conditions describe the cross-linking effect of sulfuric acid resulting in the formation of higher molecular weight polymeric products [31 -33]. A prior process for the aqueous-phase reforming of lignin resulted in the production of isolated monomeric aromatic compounds and hydrogen, although the system was plagued by extensive solid formations caused by lignin recondensation and relatively low yields [34].

Tokarev et al. [35] described the beneficial effect of co-reforming of the substrates ethanol and sorbitol for the production of hydrogen .

Although the patents and processes described above indicate that biomass-derived compounds can be converted to hydrogen via the aqueous-phase reforming reaction, there is no disclosure of the liquid-phase reforming of lignin for the production of hydrogen, light alkanes, and aromatic chemicals. Moreover, there is no disclosure of a process that uses chemical components readily obtained from a lignocellulosic biorefinery for the liquid-phase reforming of lignin for increased chemical and energy integration. Accordingly, a readily-integrated process under moderate conditions for the conversion of lignin into hydrogen, light alkanes, and monomeric aromatic products in the biorefinery scheme is highly desirable.

One of the objects of the present invention is to provide a process for the valorization of lignin for the production of monomeric aromatic compounds, hydrogen, light alkanes, and other useful components in the biorefinery scheme.

Another object of the present invention is to provide a process that operates under milder conditions than thus far employed in this field.

Another object of the present invention is to minimize unwanted side-products, such as highly recalcitrant solids formed during conventional aqueous-phase reforming reactions. Summary of the invention

A process for the liquid-phase reforming of lignin into monomeric, dimeric, and oligomeric aromatic chemicals, hydrogen, and other light gases is provided. The process uses components readily obtained from a second-generation lignocellulosic biorefinery and improves the chemical and energy integration of the biorefinery scheme. In the first component of the process, lignin obtained from a selected pretreatment method is solubilized in water-containing solvents followed by the catalytic liquid-phase reforming in the optional presence of a co-catalyst. The characteristics of the isolated aromatic components, the gases, and the solvent following the process depend heavily on the reaction conditions employed, particularly the presence of the catalyst and co-catalyst, and therefore the product distribution is highly tunable depending on chemical demand. The aromatic products consist of alkylated phenol, guaiacol, catechol, and syringol monomers, dimers, and oligomers with the particular distribution based on the reaction conditions employed. The invention provides a catalytic process for the liquid-phase reforming of lignin to monomeric aromatic compounds, hydrogen, light alkanes, and other useful chemicals that readily integrate into the biorefinery scheme. The one-step process of the invention involves the solubilization of lignin in water-containing solvents and contacting with a group VIII transition metal catalyst. Surprisingly, it was been found that the presence of a water-alcohol solvent mixture in the process of the invention suppresses side reactions and produces lignin solutions with very little residual solid material compared to conventional processes of aqueous phase reforming.

Detailed description of the invention

Thus in a first aspect, the invention pertains to a process for treating a lignin- containing feed with a transition metal catalyst in a water-alcohol containing solvent. The process has the advantage of providing a convenient and efficient one-step, one- pot conversion of lignin into aromatics and gases without the need for separating intermediate products. The process has the advantage of using components readily obtained in the lignocellulosic biorefinery scheme to produce valuable platform chemicals (i.e. chemicals that can be used as a starting point for other chemicals) thereby increasing the chemical and energy integration of the biorefinery scheme. Moreover, the process operates under conditions milder than that used in gasification or pyrolysis, with temperatures of approximately 498 K. Unwanted solid formation is suppressed, which facilitates the development of continuous rather than batch or semi-batch industrial processing. This is unexpected when looking at the general aqueous phase reforming literature and processes that usually deals with feeds in aqueous phase reforming such as glycerol and sorbitol where the formation of recalcitrant solids is not so much an issue. The distribution of particular products desired, including aromatic compounds, light gases, and solvents, are readily tuned. The lignin-containing feed can be in its broadest form from any lignin source, but is preferably selected from the group consisting of kraft lignins, organosolv lignins, lignins obtained from agricultural products or waste, and lignins obtained from sugarcane bagasse, and combinations thereof. The nature of the lignin used as a feed during the liquid-phase reforming process may vary. There is a preference for isolated lignin. The structure of lignin varies considerably from plant to plant, especially with regards to the number of methoxy groups present on the aromatic ring along with the type and abundance of the many linkages present in the lignin polymer. Lignin obtained from hardwoods, for example, tends to constitute approximately equal proportions of coniferyl and sinapyl alcohols. In contrast, lignin obtained from softwoods contains approximately 90% of coniferyl alcohols whereas lignin from grasses contains mostly p-coumaryl alcohols. In addition, the pretreatment method used to obtain extracted lignin drastically influences the functional groups and linkages present in the isolated polymer. The kraft process, which is extensively deployed throughout the pulp and paper industry and thus exhibits infrastructural advantages relative to other processes, yields abundant, readily available, renewable, accessible, but also recalcitrant kraft lignin. Other sources of lignin, such as those obtained from the organosolv pretreatment method, confer different properties to the extracted lignin, including the nature of the linkages and functional groups present in the extracted lignin and the extent of sulfur and other elemental incorporation into the lignin polymer. With the broad distribution of plant-derived lignocellulosic biomass and existing lignin pretreatment infrastructure, the type and variety of lignin received by the biorefinery will vary considerably depending on geographical location. A general and readily deployable process capable of valorizing such broad feed distributions is therefore advantageous.

The catalyst can consist of materials generally used for aqueous-phase reforming, including but not limited to precious (e.g. Pt, Rh, Ru, Ir) and non-precious metals (e.g. Ni, Co) supported (on, for example, AI2O3 or C) or unsupported, pelletized or powdered.

As the catalyst in the process of the present invention, any catalyst used in the liquid- phase reforming can be used, with preference for catalysts containing group VIII elements, in particular selected from the group of consisting of iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, including alloys and mixtures thereof, preferably platinum, ruthenium, or rhodium and mixtures thereof. The transition metal catalyst is present in an amount of 0.01 to 25 wt% relative to the feed, preferably from 0.1 to 15 wt%, more preferably from 0.5-10 wt%

The catalyst material used in the present invention may be a heterogeneous catalyst. The use of a heterogeneous catalyst allows easier processing or regeneration of the catalyst or the use of a heterogenous catalyst allows for an easier recycling, for instance in a continuous process. In certain preferred embodiment, the catalyst may be provided on a carrier. Preferred carriers for catalysts to be used in the process of the invention are selected form the group consisting of alumina, boron nitride, carbon, ceria, silica, silica-alumina, silica nitride, titania, zirconia, and mixtures thereof. There is a preference for a Pt/AI₂O3 or Pt/C catalyst-carrier combination.

The alcohol used in the process of the present invention can be any alcohol that is miscible with water. There is a preference for the lower alkanols, preferably selected from the group consisting of methanol, ethanol, propanol, isopropanol, n-butanol, 2- butanol, tert-butanol and mixtures thereof, more preferably ethanol and mixtures of ethanol with other lower alkanols. One of the additional advantages is that ethanol can be used in the form of bioethanol which adds to the green character of the present invention. Other solvents that are possible are solvents that are formed during the reaction, such as diethyl ether.

The lignin-containing feed is preferably mixed with the water/alcohol combination in about 1 wt-% to about 200 wt-% water/solvent with respect to the weight of the lignin material.

Specifically, the process involves the solubilization of the lignin component in aqueous alcohol (composed of water and alcohol) mixtures. The mixtures consist of from 0%-100% alcohol ('from 0%' thus excluding 0 as a value), preferably from 5 to 95% alcohol by weight (and hence 95 to 5% water, respectively), more preferably from 25 to 75% and a higher preference for about 40-60% alcohol. As a solvent ethanol being most preferred and preferably at a range of 40-60% by weight. The water and alcohol content of the solvent in certain embodiments is based on added solvent, preferably not including water and or alcohol that is present in the feed or in cocatalyst such as sulfuric acid, The advantages of this process in the biorefinery scheme is that the lignin used as a feed need not be dry, and the alcohol (such as ethanol) need not be pure, as the preferred alcohol content (ethanol) is far from the azeotrope point and thus readily obtained in the lignocellulosic biorefinery scheme. In the process of the present invention, a co-catalyst can be used. Thus, the solubilized lignin is subjected to the liquid-phase reforming in the presence of a reforming catalyst and a co-catalyst.

The co-catalyst present during the liquid-phase reforming reaction aids in the hydrolysis or general disruption of the linkages present in the lignin polymer. These co-catalysts can comprise superacids, acids, or bases depending on the distribution of products desired during the reforming of the lignin. Examples of each category include phosphotungstic acid, mineral acids such as sulfuric acid, and bases including NaOH.

The co-catalyst can be selected from the group consisting of a superacid, an acid, and a base co-catalyst. The superacid co-catalyst can comprise phosphotungstic acid. The acid co-catalyst can comprise sulfuric acid. When sulfuric acid is used as cocatalyst, it can be added in the form of oleum, or the water content of the sulfuric acid is not taken into account in the alcohol-water ratio of the solvent. The base co- catalyst can be an alkaline or earth alkaline hydroxide base, preferably an alkaline hydroxide, more preferably selected from the group consisting of sodium, potassium, cesium, calcium or lithium hydroxide. Alternatively solid superbases can be used such as high-temperature treated MgO, MgO-Na₂0, CsX-type zeolite, and combinations thereof. The cocatalyst can be present in an amount up to 6 wt%, preferably up to 3 wt% based on the feed, i.e. lignin source.

The process can be performed in a continuous or batch mode. The process is preferably performed in a temperature range from about 100 to about 250°C, preferably from about 150 to about 240°C, more preferably from about 200 to about 230°C.

The process can be performed under autogeneous pressure in a batch reactor or it can be performed under additional pressure. The process can be performed semi- batch at a pressure of 50-60 bar. In certain embodiments additional pressure can be provided by a gas that is selected form the group consisting of helium, argon, carbon dioxide or nitrogen.

The reaction time for the process of the invention is preferably from about 30 s to about 90 min in batch mode. The process provides isolated monomeric aromatic chemicals, which consist of alkylated phenols and alkylated alkoxyphenols, and catechol, alkylated catechols, and alkylated alkoxycatechols with the characteristics of the alkyl side-chain depending on the co-catalyst employed. During this process light molecules, including hydrogen, methanol, and light alkanes, such as methane and ethane, are produced. The ethanol component of the solution is retained, converted to ethyl ether, or converted to useful higher alcohols, such as butanol and hexanol.

Description of the figures:

Figure 1 : The principle features of the process of the invention for the integrated lignin valorization process for the lignocellulosic biorefinery scheme are shown in the schematic diagram, which is discussed in further detail below. In the first component of the process, lignocellulosic biomass is received and processed in the

lignocellulosic biorefinery. In the first section, a pretreatment step, which may depend on existing infrastructure and available technology, separates the biomass into cellulose, hemicellulose, and lignin component streams. Valorization of the cellulose and hemicellulose components yields valuable chemicals and fuels including ethanol, a portion of which is diverted for the solubilization of the lignin component in

approximately 50 vol% in water. The specific details regarding the solubilization of lignin are described in the examples herein elsewhere. The lignin is mixed into the ethanol/water solution and subjected to heating to 40-225°C until the lignin material dissolves. Small quantities of residual solid can be removed by decantation and filtration before further processing. Following the solubilization, the dissolved lignin can be mixed with a specified quantity of co-catalyst consisting of superacids, acids, or bases, including but not limited to H₂S0₄, polyphosphoric tungstic acid, or NaOH. Additional details including the quantities of co-catalyst added to the

lignin/ethanol/water solution is described herein elsewhere.

The components of the reaction mixture, including the lignin, catalyst, and co-catalyst, can be introduced to the ethanol/water solution in the reactor sequentially and in any order. The ethanol component of the solvent is preferably mixed with water before introduction of other materials to enhance solubility and suppress lignin side reactions (e.g. recondensation). The lignin used in this process may originate from

lignocellulosic plant materials including but not limited to grasses, softwoods or hardwoods from trees or shrubs, sugarcane, mixtures of these categories and combinations thereof. The lignin may be isolated through a pretreatment process including but not limited to the kraft, lignosulfonate, or organosolv lignin processes. The reaction solution and catalyst can be charged to an enclosed reaction vessel, which can be sealed to collect gases produced during the process or equipped with a back-pressure regulator to allow continuous, semi-batch collection of gaseous products. The enclosed reaction mixture, consisting of lignin, ethanol, water, catalyst, and co-catalyst can be heated at a rate of 5-15°C/min to a specified reaction temperature, preferably 225°C, and held approximately or precisely at this

temperature for 0-1 .5 h or until reactions involving lignin are complete. The pressure of the sealed vessel will initially reach the vapor pressure of the ethanol/water solution but then steadily increase as gases are produced from reforming of the lignin and solvent. For semi-batch operation, the autoclave can be pressurized with an inert gas (such as helium, argon or nitrogen) to preferably 55-58 bar to prevent evaporation and loss of the solvent. The enclosed vessel can be equipped with a stirring mechanism to enhance contact of the solubilized lignin with the catalyst. The reaction vessel will consist of devices to record temperature and pressures, such as thermocouples, thermistors, gauges, or pressure transducers and external heating mechanisms. The vessel can also contain gas and liquid sampling valves for introduction or removal of reactants or products to or from the reaction vessel, respectively, during either semi-batch or continuous processing.

Figure 2 provides a schematic overview of the lignin valorization.

Examples

The experimental procedures applied as well as the yield of isolated aromatic products, light gases, and solvent under various reaction conditions are provided in the following non-limiting examples, which illustrate the liquid-phase reforming of lignin process of the invention. Experimental and Analytical Methods

Materials

Three different lignin samples were used in this study. The alcell lignin (66.47% C, 5.96% H, 0.15% N, 27.43% O by difference) was isolated by the organosolv extraction method and obtained from Wageningen University. The INDULIN AT kraft lignin (63.25% C, 6.05% H, 0.94% N, 1 .64% S, 28.12% 0 by difference), provided by ECN, was obtained from pine and is free from all hemicellulosic materials. The lignin from sugarcane bagasse (58.90% C, 4.90% H, 0.14% N, 1.53% S, 34.53% O by difference) is derived from Brazilian sugarcane and was obtained from the Dow Chemical Company.

Apparatus

The lignin solubilization studies were conducted in a semi-batch 200 ml_ autoclave equipped with quartz windows, thermocouple, pressure gauge and transducer, magnetic driver (750 rpm), and back-pressure regulator set at 58 bar. Lignin samples were stored in a desiccator prior to use. During a typical treatment, 0.200 g lignin (either kraft, alcell, sugarcane bagasse, or soda) was added to the autoclave with 100 ml_ H₂0 and 100 ml_ ethanol. The autoclave was then sealed, purged and charged with 58 bar He, and finally heated at approximately 4 K/min to 498 K. The liquid phase reforming and reductions reactions were conducted in a semi-batch 40 mL Parr autoclave equipped with a thermocouple, a pressure transducer and gauge, a magnetic driver (750 rpm), and a back-pressure regulator set at 58 bar. Procedure

Lignin samples were stored in a desiccator prior to use. During a typical liquid phase reforming reaction, 0.125 g lignin (either kraft, alcell, or sugarcane bagasse) was added to the autoclave along with 0.125 g Pt/Al₂0₃ (1 % Pt), 5.5 g H20, 5.5 g ethanol, and either 0.58 g H₂S0₄, 0.3 g phosphotungstic acid hydrate (Sigma-Aldrich,

99.995%) or NaOH (Sigma-Aldrich, 97%). The autoclave was then sealed, purged with He, and then 58 bar He was charged to the autoclave. The autoclave was then rapidly heated to 498 K in the course of about 15 min. Gas sampling was conducted using a dual-column Galaxie micro gas chromatography unit. After the designated time (typically 1 .5 h), the autoclave was cooled in an ice water bath and vented. At the conclusion of the reactions, the autoclaves were vented, the liquid phase was separated from solids, and finely dispersed solids were isolated by centrifugation if necessary.

Analysis Products contained in the liquid phase were isolated by three sequential extractions using approximately 9 g dichloromethane, the quantity of which was subsequently reduced using a rotary evaporator at 310 K until dichloromethane no longer evaporated from the extracted solution. Chemical composition of the isolated yields was determined by a Varian GC equipped with a VF-WAXms capillary column and a Galaxie GC equipped with a CP-WAX capillary column, each equipped with an FID detector. Syringaldehyde was used as an internal standard. The quantity of unknown products was estimated using the response factor determined for guaiacol. Product identification was conducted using a Shimadzu GCMS-QP2010 equipped with either a VF-WAXms or CP-WAX capillary column and by comparison with pure compounds when available.

Experimental Example 1 :

A summary of the kraft lignin liquid-phase reforming results, including the most abundant isolated monomeric aromatic products, gases formed, and products obtained from the ethanol solution, are provided in Table 1.

The liquid-phase reforming reactions were conducted with a Pt/AI₂0₃ reforming catalyst in the presence of either acid or base co-catalysts. In the case of the H₂S0₄, guaiacol was the most abundant isolated monomeric aromatic product followed by ethylcatechol and methanol, which were formed via the acid-catalyzed hydrolysis of ethylguaiacol. The proportion of isolated monomeric aromatic products obtained via the liquid-phase reforming of lignin in ethanol/water mixtures exceeded by an order of magnitude that obtained from similar conditions with just water as the solvent, with up to 17.6% of the original lignin mass converted to monomeric isolated products.

Moreover, in contrast to the lignin aqueous-phase reforming, the formation of solids was suppressed; the only solid material recovered at the conclusion of the reaction was the catalyst. During the liquid-phase reforming, useful light gases, including H₂ and CO2, along with CH₄, and C2H6, were obtained, and CO was not detected.

Several reaction pathways for the formation of alkanes are favorable under the reaction conditions employed and may include the Bransted acid-catalyzed

dehydration reactions, or through the reaction of H₂ and CO or CO2 to form alkanes. In addition to the reaction of the lignin, a significant quantity of the ethanol used in the processes was converted to diethyl ether, a process catalyzed by H₂SO₄ at elevated temperatures. Substitution of H₂S0₄ with tungstophosphoric acid resulted in higher yields of guaiacol and ethoxylated guaiacol products relative to the case in which H₂S0₄ was used as the co-catalyst. The formation of the latter product provides evidence that the ethanol aids the valorization process by serving as a capping agent for the phenolic functionality of the depolymerized lignin, which is otherwise susceptible to

repolymerization with other lignin molecules. In contrast to the case of H₂S0₄, no H₂ was observed in the gas phase, although light alkanes were still observed in lesser quantities. The ethanol solvent was also significantly more stable in the presence of this co-catalyst, with reduced quantities of diethyl ether detected at the conclusion of the reaction.

Use of NaOH as a co-catalyst also resulted in yields of isolated monomeric products, corresponding to approximately 12.8% conversion of the original kraft lignin mass. However, the product distribution differed from the cases in which acids were used. Although guaiacol was still obtained in relatively high yields, benzyl alcohol and related species were obtained. These products were not observed when an acidic co- catalyst was used. As in the case of H₂S0₄, H₂ production was observed in the presence of NaOH, although the basic conditions resulted in reduced alkane production relative to the acidic conditions. The reactivity of the ethanol solvent also differed relative to the acidic cases. 1 -Butanol, which has a high energy content, low miscibility with water, low volatility and can replace or be blended into gasoline without the need to modify engine technology, was obtained as the primary product along with lesser quantities of 1 -hexanol, 1 -but-3-enol, and similar products, thus representing a method to produce transportation fuels simultaneously during the lignin valorization.

Table 1 : Example of liquid-phase reforming of kraft lignin. Reaction conditions: 124.5 mg kraft lignin, 5.5 g H20, 5.5 g ethanol, 124.5 mg 1 wt% Pt/Al₂0₃, T = 498 K, t = 90 min, P = 58 bar He. Co-catalyst: 0.58 g H₂S0 or 0.33 g tungstophosphoric acid (HPA) or 0.3 g NaOH

Experimental Example 2:

The following is an example of the liquid-phase reforming of alcell organosolv lignin using the process of the invention. A summary of the results are given in Table 2. A summary of the results are given in Table 2. In the case of the organosolv lignin, 94% of the original starting mass was solubilized with the residual quantity recovered as a solid. In the case in which H₂S0₄ was used as the co-catalyst, the most abundant products consisted of propeneguaiacol and ethylcatechol followed by guaiacol and syringol. Approximately 9% of the lignin starting material was recovered as isolated monomeric aromatic products. Both hydrogen and light alkanes, consisting of methane and ethane, were obtained, consisting of about 4.5 and 0.7% of the gas in the autoclave headspace at the conclusion of the reaction. As in the case of

Experimental Example 1 , diethyl ether was produced in large quantities. When tungstophosphoric acid was used as the co-catalyst, lower yields of isolated monomeric products were obtained, but the proportion of syringol and guaiacol increased relative to the case in which H₂S0₄ was used as the co-catalyst. Light alkanes, consisting of methane and ethane, were detected, although hydrogen was not detected during the process. Use of NaOH as the co-catalyst resulted in isolation of dialkoxytoluene, acetovanillone, and propylbenzyl alcohol as the most abundant products with total isolated monomeric yields corresponding to about 1 1 % based on the quantity of lignin starting material. Hydrogen and light alkanes, consisting of methane, ethane, and propane, were obtained. Butanol and hexanol were observed in similar concentrations as that given in Experimental Example 1 .

Table 2: Example of liquid-phase reforming of alcell organosolv lignin. Reaction conditions: 124.5 mg organosolv lignin, 5.5 g H₂0, 5.5 g ethanol, 124.5 mg 1 wt% Pt/Al₂0₃, T = 498 K, t = 90 min, P = 58 bar He. Co-catalyst: 0.58 g H₂S0 or 0.33 g tungstophosphoric aci (HPA) or 0.3 g NaOH.

Experimental Example 3:

A summary of the results are given in Table 3. The following is an example of the liquid-phase reforming of lignin from sugarcane bagasse using the process of the invention. A summary of the results are given in Table 3. In the case of the sugarcane bagasse lignin, 91 % of the original starting mass was solubilized with the residual quantity recovered as a solid. In the case in which H₂S0₄ was used as the co- catalyst, the most abundant products consisted of ethylphenol and 1 -ethoxy-4- methoxybenzene. Approximately 16% of the lignin starting material was recovered as isolated monomeric aromatic products. As in the case of Experimental Example 1 , diethyl ether was produced in large quantities. Both hydrogen and light alkanes, consisting of methane and ethane, were obtained, consisting of about 6.0 and 0.8% of the gas in the autoclave headspace at the conclusion of the reaction. When

tungstophosphoric acid was used as the co-catalyst, similar aromatic product distributions were obtained relative to the case in which H₂S0₄ was used as the co- catalyst, although no hydrogen was detected in the autoclave headspace. Light alkanes, consisting of methane and ethane, were detected, although hydrogen was not detected during the process. Use of NaOH as the co-catalyst resulted in the lowest quantity of isolated aromatic products, which consisted of ethylphenol, methylacetophenone, and ethoxyphenol as the most abundant products with total isolated monomeric yields corresponding to about 2% based on the quantity of lignin starting material. Hydrogen and light alkanes, consisting of methane, ethane, and propane, were obtained. Butanol and hexanol were observed in similar concentrations as that given in Experimental Example 1 . Experimental Example 4

Comparative reactions were performed analogous to Experiment 1 at 58 bar, with and without alcohol in the solvent, with and without sulfuric acid and with two different commercially available reforming catalysts (1 % Pt/AL₂0₃ and 1 % Pt/C, both from Sigma Aldrich. Total isolated yields were compared.

Total Isolated Yield

(Pt/AI₂03)/H₂0/H₂S0 1 .3 %

(Pt/AI₂0₃)/H₂0/EtOH/H₂S0 3.4 %

(Pt/C)/H₂0/EtOH/H₂S0 4.7 % (Pt/C)/H₂0/EtOH 1 .5%

From these results, the positive quantitative effect from the alcohol in the solvent mixture and the cocatalyst on the yield are clear, aside from more qualitative advantageous effects such as less residue. The same effect is observed with another conventional reforming catalyst at the same catalyst load, indicating that the effect originates in the use of alcohol and/or cocatalyst.

Table 3: Example of liquid-phase reforming of lignin derived from sugarcane bagasse. Reaction conditions: 124.5 mg sugarcane bagasse lignin, 5.5 g H₂0, 5.5 g ethanol, 124.5 mg 1 wt% Pt/Al₂0₃, T = 498 K, t = 90 min, P = 58 bar He. Co-catalyst: 0.58 g H₂S0 or 0.33 g tungstophosphoric acid (HPA) or 0.3 g NaOH.

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Claims

C L A I M S

1 . A process for treating a lignin-containing feed comprising contacting a lignin-containing feed with a transition metal catalyst in a solvent comprising water and alcohol.

2. The process according to claim 1 , wherein the lignin-containing feed is selected from the group consisting of kraft lignins, organosolv lignins, lignins obtained from agricultural products or waste, and lignin obtained from sugarcane bagasse, and combinations thereof.

3. The process according to claims 1 -2, wherein the transition metal catalyst is selected from the group consisting of iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, including alloys and mixtures thereof, preferably platinum, ruthenium, or rhodium.

4. The process according to claim 1 -3, wherein the transition metal catalyst is present in an amount of 0.01 to 25 wt% relative to the feed

5. The process according to claim 1 -4, wherein the alcohol is selected from the group consisting of lower alkanols, preferably methanol, ethanol, propanol, isopropanol, more preferably ethanol.

6. The process according to claim 1 -5, wherein the amount of alcohol in the solvent is from 0 to 100% by weight.

7. The process according to claim 1 -6, wherein the ratio solvent/ lignin- containing feed weight ratio is between about 100 and 0.

8. The process according to claim 1 -7, wherein the transition metal catalyst is provided on a carrier, selected from the group consisting of alumina, boron nitrite, carbon, ceria, silica, silica-alumina, silica nitride, titania, zirconia, and mixtures thereof.

9. The process according to claim 1 -8, wherein the catalyst-carrier is Pt/Al₂0₃ or PT/C.

10. The process according to claim 9, wherein a co-catalyst is present, selected from the group consisting of superacid, acid, or base co-catalyst.

1 1 . The process according to claim 10, wherein the superacid co-catalyst comprises tungstophosphoric acid.

12. The process according to claim 10, wherein the acid co-catalyst comprises sulfuric acid.

13. The process according to claim 10, wherein the base co-catalyst comprises alkali hydroxide.

14. The process according to claim 10-13, wherein the co-catalyst is present in an amount of up to 6 wt%, preferably up to 3%.

15. The process according to claim 1 -14, wherein the process is carried out from about 100 to about 250°C, preferably from about 150 to about 240°C, more preferably from about 200 to about 230°C.