Two-step thermal process to control the formation of furfural from the conversion of pentoses or pentosan-rich lignocellulosic biomass using alcoholic-acid eutectic mixtures

Abstract

The present invention refers to a thermal process of two consecutive steps to control the formation of furfural in the valorization of lignocellulosic biomass rich in pentosans using alcoholic-acid eutectic mixtures. This process of two steps allows the control of secondary reactions and subsequent formation of inhibitor products in biomass pretreatment, improving the performance of further biomass transformations, such as the enzymatic and fermentative conversion of polysaccharides. The first step consists of the selective and high conversion of pentoses into pentosides in the presence of an alcoholic-acid eutectic mixture, in the absence of water, and at low temperature, inhibiting the occurrence of dehydration reactions of pentoses that lead to furfural formation. After separating the resulting liquid phase from the solid fraction enriched in cellulose, a second step relies on the conversion of formed pentosides into furfural using the same eutectic mixture in the presence of water and at elevated temperatures

Description

Two-step thermal process to control the formation of furfural from the conversion of pentoses or pentosan-rich lignocellulosic biomass using alcoholic-acid eutectic mixtures

[0001] The present invention describes a two-step thermal process to control the formation of furfural from pentoses (e.g., xylose and arabinose from hydrolysis of hemicelluloses) or lignocellulosic biomasses containing pentosans. The process aims at integrating a selective conversion of pentoses into pentosides during the pretreatment step of lignocellulosic biomasses, and subsequent conversion of pentosides into furfural after the filtration of pretreated biomass. A specific aspect of this invention relies on using alcoholic-acid eutectic mixtures as ecologically benign solvents and capable of promoting the above conversions in a combination of pretreatment, fractionation, and conversion of lignocellulosic biomass, such as agriculture and forest residues and agro-industrial waste. Therefore, the present invention falls on the development of chemical processes for the conversion of lignocellulosic biomass into new chemicals in the frame of biorefinery processes, bioeconomy and circular economy strategy.

[0002] Lignocellulosic biomass is the most abundant renewable resource on Earth and is mainly composed of polysaccharides (cellulose and hemicelluloses) and lignin that can be used in the production of energy, fuels, materials, and chemicals. However, pretreatment of lignocellulosic biomass, a crucial step that allows the breakdown of covalent and intermolecular bonds between its components, is necessary to produce these products. Pretreatment is essential to reduce biomass recalcitrance and thus increase the efficiency of the fractionation and conversion processes of the main biomass components, especially those involving the enzymatic hydrolysis of polysaccharides into monosaccharides and their subsequent conversion by fermentation into biofuels (bioethanol, biobutanol, among others) and other bioproducts (organic acids, biopolymers, enzymes, among others).

[0003] The most used procedures in the pretreatment of lignocellulosic biomass involve physical, mechanical, biological, chemical, or combinations of these methods. Among these, chemical pretreatments involve the use of acids, bases, or organic solvents capable of cleaving the intermolecular covalent bonds between the biomass components, facilitating their fractionation. However, these pretreatments generally require high-temperature conditions and / or reagent concentrations, resulting in undesired degradation of economically relevant biomass components and the formation of products that inhibit other relevant reactions in biomass processing. In addition, many of these pretreatments have disadvantages, such as high energy consumption, significant CO2emissions, use of toxic and non-biodegradable reagents, high equipment costs, among others. Furthermore, constraints on the conversion efficiency of sugars that are associated with the formation of inhibitors are frequently observed. Therefore, new, highly efficient, and versatile processes that exhibit reduced energy consumption, minimized CO2emissions, and lower environmental impact for the pretreatment of biomass are required. In this sense, a promising approach is the use of green solvents, namely eutectic mixtures.

[0004] Eutectic mixtures (or eutectic solvents-ES) are usually composed of two or more components (solid or liquid) that are combined in specific proportions to form a liquid mixture with a melting point lower than any of the individual components that made up the mixture. The ease of preparation of these eutectic mixtures and the possibility of adjusting their physicochemical properties by the combination of different components, or their proportions, make them an attractive class of solvents for multiple applications, including pretreatment, fractionation, and conversion of biomass into new chemicals.

[0005] The application of eutectic mixtures in biomass processing is quite recent. One of the first related studies, published in 2012, demonstrated the ability of these eutectic mixtures to dissolve lignin. For instance, cholinium chloride (ChCl) and lactic acid (LA) in a molar ratio of 1:9 demonstrated the best performance in the dissolution of technical lignin. Since then, multiple studies upon biomass delignification (partial depolymerization of lignin and its subsequent dissolution) using eutectic mixtures have been developed .

[0006] Among several eutectic mixtures tested, those with acid character, such as ChCl:LA or ChCl:oxalic acid (OA), presented the best performances in biomass delignification. The acidity of these solvents is the dominant factor in promoting the disruption of the lignocellulosic matrix and cleavage of chemical bonds present in the lignin structure, particularly the ether bonds β-O-4, essential for delignification. This process allows the selective separation of lignin from cellulose fibers present in biomass. For example, ChCl:LA showed the highest selectivity in delignification, extracting 62 to 84 % of the initial lignin content in poplar wood after treatment at 130 ºC or 145 ºC for 6 hours, respectively . Alvarez-Vasco et al. (NPL1) related the selectivity in the delignification using ChCl:LA with its ability to break the β-O-4 ether bonds present in lignin (NPL1). Some studies have effectively addressed the mechanisms related to the interaction of eutectic mixtures with lignin and their capacity for biomass delignification. In particular, a superior delignification mediated by the ChCl:LA mixture was demonstrated when compared to only LA, suggesting a positive role of ChCl in the delignification mechanism, even at low content in the eutectic mixture (NPL3). Subsequently, another study revealed that the presence of chloride ions increased the efficiency of β-O-4 bond cleavage (NPL4). The main reason for this efficiency lies in the nucleophilic substitution of the neighboring hydroxyl groups of the ether bond by the chloride ion, allowing the formation of an intermediate that favors the cleavage of the respective ether bond (NPL4). Unlike ionic liquids, acidic eutectic mixtures maintain the crystallinity of cellulose fibers after the delignification process. However, the size of these fibers is reduced due to acid hydrolysis of the amorphous sections of these fibers.

[0007] In particular, ChCl:LA has shown better performance in delignification for higher LA molar ratios, such as 1:5 and 1:10 . However, an excess of organic acid can exhibit a negative impact on the chemical structure of the extracted lignin. For example, condensation reactions among lignin macromolecules can be promoted, compromising and limiting the application of extracted lignin. In addition, the preservation of hemicelluloses in the solid is inefficient. Part of the hemicellulosic fraction is hydrolyzed into pentoses, which in turn are dehydrated into furfural. This last participates in several secondary reactions forming degradation products, such as humins. On the other hand, eutectic mixtures based on alcohols, such as those containing ethylene glycol (EG) and glycerol (Gly), despite having lower efficiency in the delignification process, demonstrate considerable benefits in biomass fractionation, including high lignin dissolution capacity, lower corrosivity, and greater compatibility with the subsequent use of fractionated streams in biotechnological processes involving microorganisms. Therefore, the use of alcoholic-acid eutectic mixtures capable of maintaining the high capacity of delignification and avoiding the degradation of other biomass components has been disclosed in literature.

[0008] For example, Kandanelli et al. (2018) have developed a more efficient delignification process (~50 %) for different biomass varieties (rice husk, rice straw, and wheat straw) using an alcoholic-acid eutectic mixture by combining ChCl:AO withn-butanol, in the molar ratio ChCl:AO:n-butanol of 2:2:1, in a pretreatment at 120 ºC for 60 minutes (NPL6). Yao et al. (2022) also observed a better delignification of different lignocellulosic biomasses using an alcoholic-acid eutectic mixture composed of ChCl:LA:ethanol (1:2:1), at pretreatment conditions of 160 ºC for 60 minutes (NPL7). Li et al. (2022) used an alcoholic-acid eutectic mixture based on ChCl:AO:EG in the pretreatment of bamboo residues at 130 ºC for 6 hours and observed an improvement in delignification of about 1.7 times when compared to the respective binary eutectic mixture (ChCl:OA) (NPL8). Poy et al. (2023) also showed the effectiveness of a eutectic mixture composed of ChCl:LA:EG (1:5:5) in the pretreatment of rice straw (120 ºC, 4 h) towards biobutanol. Although authors mentioned the hemicellulosic fraction was preserved in the pretreated solid enabling much higher conversion of sugars into biobutanol, yielding 95.7 g butanol / kg biomass, one of the highest values reported in literature (NPL9). Yet, very low delignification yield was achieved, which means that the fractionation ability of the eutectic mixture is reduced.

[0009] In all these processes that used alcohol-acid eutectic mixtures, the biomass pretreatment temperatures were always above 100 ºC. Despite minimizing the degradation of lignin structure compared to acid eutectic mixtures (e.g., ChCl:LA), the degradation levels of hemicelluloses are still high. Hemicelluloses degrade more easily when submitted to pretreatment under acidic conditions, especially at elevated temperatures (above 100 ºC).

[0010] The formation of oligomeric saccharides (oligosaccharides) and monomeric saccharides (monosaccharides), especially pentoses (xylose and arabinose) and hexoses (glucose, mannose and galactose) are usually observed during hemicellulose hydrolysis. When the pretreatment of lignocellulosic biomass containing xylans is performed in an acidic medium, the xylans are hydrolyzed in xylooligosaccharides and xylose, which in turn may suffer dehydration forming furfural and other degradation products, including humins. The latter are macromolecular structures resulting from secondary reactions between the various saccharides and furanic compounds and are strongly inhibitory of subsequent valorization steps of the fractionated materials. Furfural is a chemical compound belonging to the class of furanic aldehydes and is widely used in the chemical industry as an intermediate (pivot) compound in the synthesis of other chemicals. For example, furfural is used in the production of furanic derivatives, such as acids and alcohols, which have applications in the manufacture of plastics, resins, solvents, and pharmaceuticals, as well as direct additive to gasoline.

[0011] When the main objective is to convert the lignocellulosic biomass, particularly cellulose, into biofuels (ethanol, butanol, among others) through enzymatic and fermentation processes, the presence of furfural impairs the performance of the process. Furfural inhibits the cell growth of microorganisms and inhibits the functioning of hydrolytic enzymes of polysaccharides, reducing the productivity of these biofuels. Therefore, removing or reducing the presence of furfural before enzymatic saccharification and microbial fermentation by detoxification processes is usually necessary.

[0012] There are different strategies to minimize the presence of furfural or to mitigate its inhibitory effects and improve enzymatic saccharification and fermentation. The type of biomass pretreatment can be modified to reduce furfural formation. For example, Rajan et al. (2014) emphasize that the conditions of the pretreatment step have a significant impact on the formation of inhibitors, such as furfural. The study highlights the importance of carefully controlling pretreatment temperature, reaction time, and acid concentration to optimize bioethanol production and minimize inhibitor generation (NPL10). Besides, pretreatments using acids, peroxide or alkaline pretreatments are also reported before enzymatic saccharification and fermentation. In the latter approaches, furfural is not generated in appreciable amounts, although the pretreatment performance is relatively less efficient when compared to the acidic pretreatment (NPL11).

[0013] Another approach to improve enzymatic saccharification and fermentation is the use of yeasts and bacteria more tolerant to the presence of furfural (NPL12). Patent US20150275187A1 features modified microbial strains expressing a furfural resistant gene. The resistant gene described in this patent was identified and isolated from a microbial strain resistant to furfural. This gene can confer furfural resistance to other microbial strains when introduced in and expressed by them. These strains can be used in several industrial processes, such as bioethanol production from lignocellulosic biomasses, without significant inhibition of furfural (PTL1).

[0014] Additives that neutralize the negative effects of furfural or detoxification processes through extraction, filtration, adsorption, or washing of the pretreated material can also be used. For example, Deng et al. (2018) used activated carbon to remove furfural and other inhibitors after the pretreatment of sugarcane bagasse. These authors obtained 100 % removal of furfural and 10 % loss of sugars (NPL13). In the examples cited, the removal or inhibition of furfural formation before enzymatic saccharification and microbial fermentation, involves additional steps, which increase the cost of the process, the wastewater and the loss of soluble sugars, compromising the efficiency of the whole process. In addition, many of these processes do not allow the recovery and use of furfural.

[0015] Another approach to promote the inhibition of furfural formation was presented by Bouxin et al. (2014), where a variety of pretreatments of Sitka spruce (Picea sitchensis) using ethanol / water with dilute sulphuric acid was applied to generate new products and improve the yield of saccharification. In the most efficient condition (1 %(w / w) of sulphuric acid in 60 %(v / v) of ethanol in water, 60 minutes at 180 ºC) was observed the formation of ethylxylosides with a yield of 2.2 % from biomass. This formation of ethylxylosides prevented the subsequent degradation of xylose into furfural. The conversion of xylose into furfural requires that xylose is in open chain form and since the xylosides formed are in the form of cyclic acetals, which are not in equilibrium with the open form, the conversion into furfural is not favored. It has also been suggested that the amount of acid and the reaction time do not influence the percentage of xylose formed. On the other hand, the concentration of ethanol has a direct effect on the yield of these products. The authors also emphasized that these products have potential as intermediates in the production of high-value chemicals (NPL14).

[0016] A similar approach to inhibit the formation of humins was proposed by Hu et al. (2012). The study investigated the acid pretreatment of xylose in methanol / water, using Amberlite 70 as a heterogeneous acid catalyst. The results showed that xylose was mostly converted to methylxylosides, while humin content was reduced (below 130 ºC). The authors proposed that xylose conversion into methylxylosides protected it from dehydration reactions and consequent formation of degradation products (NPL15).

[0017] Although xylosides are presented in some studies as intermediate compounds in the conversion of xylose to furfural, the control of their formation has never been well explored. Furthermore, it has never been demonstrated how the manipulation of this reaction can be useful in the development of an efficient biomass pretreatment process with impact on the entire biomass valorization chain, including the saccharification and fermentation steps.

[0018] In a first aspect the invention refers to a two-step thermal process to convert pentoses or biomass containing pentosans into furfural comprising the steps of (i) reacting a pentose and / or biomass containing pentosans with an alcoholic-acid eutectic mixture, wherein the alcoholic-acid eutectic mixture comprises at least one organic salt, one organic or inorganic acid, and one alcohol, at a temperature within the range of 10 and 100 ºC, during a period of time between 30 minutes and 8 hours, under constant stirring, to form pentosides; and (ii) reacting the reactional liquid obtained from step (i) with water or a two-phase mixture containing water and immiscible organic solvent, at a temperature within the range of 100 to 200 ºC, during a period of time between 30 minutes and 24 hours, under constant stirring, to form furfural.

[0019] In a particular aspect of the invention, the biomass is selected from wood, straw, bark, bagasse, seeds, and logs, among other agricultural waste and agro-industrial waste rich in pentosan-type hemicelluloses.

[0020] In another particular aspect of the invention, the organic salt of step (i) is preferably a quaternary ammonium halide, quaternary phosphonium halide, imidazolium halide, pyridinium halide, pyrrolidinium halide, and more preferably quaternary ammonium halide, and more preferably cholinium chloride or cholinium bromide.

[0021] In another particular aspect of the invention, the acid in the alcoholic-acid eutectic mixture is a strong organic or inorganic acid with a pKa of less than 2,5.

[0022] In a most particular aspect of the invention, the acid in the alcoholic-acid eutectic mixture is selected fromp-toluenosulfonic acid, 4-hydroxybenzenesulfonic acid, sulfosalicylic acid, maleic acid, oxalic acid, nitric acid, sulphuric acid, hydrochloric acid, hydrobromic acid or phosphoric acid.

[0023] In another particular aspect of the invention, the alcohol in the alcoholic-acid eutectic mixture is a monoalcohol, a diol, or a polyol.

[0024] In a most particular aspect of the invention, the alcohol in the alcoholic-acid eutectic mixture is a monoalcohol selected from a monoalcohol with a carbon chain between C1-C12 long, preferably methanol, ethanol, propanol or butanol.

[0025] In a most particular aspect of the invention, the alcohol in the alcoholic-acid eutectic mixture is a diol selected from ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, or diols with longer carbon chain length, such as polyethylene glycol.

[0026] In a most particular aspect of the invention, the alcohol in the alcoholic-acid eutectic mixture is a polyol selected from a polyol with a carbon chain between C1-C20 long, preferably glycerol, xylitol, mannitol, erythritol or sorbitol.

[0027] In another aspect of the invention, the temperature at which the reaction of step (i) takes place is within the range of 40 to 90 ºC, preferably at 80 ºC.

[0028] In another aspect of the invention, the reaction of step (i) occurs during a time period between 2 and 6 hours, preferably during 4 hours.

[0029] In another aspect of the invention, the pentose and / or biomass containing pentosans, to alcoholic-acid eutectic mixture mass ratio of step (i) is comprised within the range of 1:5 to 1:10.

[0030] In another aspect of the invention, the resultant mixture of step (i) is separated by filtration or ultrafiltration before step (ii).

[0031] In another aspect of the invention, the temperature at which the reaction of step (ii) takes place is within the range of 110 to 150 ºC, preferably at 120 ºC.

[0032] In another aspect of the invention, the reaction of step (ii) occurs during a time period between 4 and 20 hours, preferably during 16 hours.

[0033] In another aspect of the invention, the immiscible organic solvent of step (ii) is selected from xylene, methyl isobutyl ketone, cyclohexanone, anisole, methyl isoamyl ketone.

[0034] Conversion of pentoses or biomass containing pentosans is often incomplete due to the presence of furfural. Existing methods provide alternative approaches to improve the yield of conversion by resorting to chemicals and several step processes. There is a need for a simpler and better rate of conversion process.

[0035] The present invention comprises a two-step thermal process that allows the control of the formation of furfural from the conversion of pentoses and / or lignocellulosic biomass, using alcoholic-acid eutectic mixtures, consisting of at least one acid component, an alcohol component, and an organic salt component

[0036] The two-phase process of the invention inhibits furfural formation in step (i) and enables the extraction of furfural in step (ii) from the organic phase, while other compounds remain in the aqueous phase. The process herein disclosed provides a suitable process for industrial application with improved pentose or pentosans containing biomass conversion yields.

[0037] The current invention establishes control over the formation of furfural from pentoses (xylose and arabinose) or lignocellulosic biomasses containing pentosans using alcoholic-acid eutectic mixtures, offering significant economic and environmental advantages. This approach enables enhanced valorization of low-cost biomass, including agricultural and forestry residues, and agro-industrial waste, among others. Pretreatment with these alcoholic-acid eutectic mixtures followed by separation of a cellulose-rich solid fraction from the liquid fraction containing lignin and pentosides reduces the possibility of inhibition phenomena occurring in subsequent biotechnological processes, making cellulose more accessible for its conversion into bioproducts.

[0038] From an environmental point of view, one of the great advantages of these eutectic mixtures is that they allow the pretreatment to be carried out at lower temperatures compared to other existing methods and this can lead to a reduction in the energy consumption required in the process. In addition, the use of these eutectic mixtures brings two other advantages: on one hand, converting hemicelluloses into pentosides, which are separated together with lignin from the cellulose-rich solid fraction, reduces the potential for inhibition reactions (resulting from the presence of furfural) during the enzymatic hydrolysis of cellulose and the subsequent fermentation of glucose for the formation of biofuels; and on the other hand, reduces the formation of inhibitors of microbial fermentation, contributing to the more efficient conversion of fermentable sugars into bioproducts (e.g. biofuels). With less inhibition, enzymes have better performance in enzymatic hydrolysis, and microorganisms have better performance in converting sugars into bioproducts, resulting in higher yield and productivity of the entire value chain.Fig.1

[0039] Example of the chemical structure of the isomers (anomers) of the xylosides formed from the reaction between xylose and ethylene glycol present in the eutectic mixture.

[0040] Example of the general chemical structure of xyloside isomers (anomers) formed from the reaction between xylose and alcohol (monoalcohol, diol, or polyol) present in the eutectic mixture.

[0041] General scheme of a two-step representative thermal process for controlling the formation of furfural from pentoses.

[0042] General scheme of a representative two-step thermal process for the control of furfural formation from biomass containing pentosans.

[0043] GC-MS chromatogram acquired by gas chromatography of a sample after the xylose conversion into xylosides using ChCl:pTSA:EG (1:1:9) at 80 ºC for 30 minutes (derivatization with trimethylsilylation for GC-MS analysis). The sample presents high yield of xylosides in contrast to initial xylose.

[0044] The present invention comprises a two-step thermal process that allows the control of the formation of furfural from the conversion of pentoses and / or lignocellulosic biomass, using alcoholic-acid eutectic mixtures, consisting of at least one acid component, an alcohol component, and an organic salt component.

[0045] In particular, the invention lies in a first step, herein also referred to as step (i), that envisages the inhibition of furfural formation, due to the production of pentosides (intermediate compounds, most commonly xylosides) in a process at low temperature (10-100 ºC) and in the absence of water. Pentosides are formed through the chemical reaction (Fischer glycosylation) of the alcohol component from the eutectic mixture with pentoses (xylose or arabinose). This reaction is catalyzed by a strong organic or inorganic acid, also present in the eutectic mixture. When applied to lignocellulosic biomass, the process enables pretreatment of biomass, hydrolysis of hemicelluloses (pentosan type) and followed by the selective inhibition of furfural formation through the conversion of pentoses into pentosides. This prevents secondary reactions of dehydration / degradation of furfural, preserving the total content of pentoses for its subsequent recovery in the context of biorefinery processes. It should be noted that the chemical environment provided by this type of eutectic mixture favors the transformation of pentoses into pentosides at lower temperatures than any other process described in the literature.

[0046] In the second step, herein also referred to as step (ii), the pentosides are selectively converted into furfural by applying high temperatures (100-200 ºC) and in the presence water. If the initial material is lignocellulosic biomass, a filtration shall be carried out to separate the eutectic mixture containing pentosides (and lignin) from the cellulose-enriched solid preceding the second step of the process. Therefore, the present invention describes a process for the selective inhibition and reversible production of furfural in different stages. This is a technical advantage over the existing methods tackling the inhibition of furfural formation, where furfural cannot be produced and recovered at the end of the process.

[0047] More particularly, pentoses (xylose or arabinose) or lignocellulosic biomass containing pentosans (for example, wood, straw, bark, bagasse, seeds, logs, among other agriculture and forest residues and agro-industrial waste) are added to an alcoholic-acid eutectic mixture in a solid-liquid mass ratio between 1:0.1 and 1:20, in absence of water, and consisting of at least three components. A first component of the alcoholic-acid eutectic mixture shall be a strong organic or inorganic acid (pKa less than 2,5), such asp-toluenosulfonic acid (pTSA), 4-hydroxybenzenesulfonic acid, sulfosalicylic acid, maleic acid, oxalic acid, nitric acid, sulphuric acid, hydrochloric acid, hydrobromic acid, perchloric acid, phosphoric acid, and others. A second component of the alcohol-acid eutectic mixture shall be an alcohol such as methanol, ethanol, propanol, butanol or alcohols with longer carbon chain lengths, most preferably between C1-C12, a diol such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol or diols with longer carbon chain lengths, such as polyethylene glycol, or polyols such as glycerol, xylitol, mannitol, erythritol, sorbitol or polyols with longer carbon chain lengths, most preferably between C1-C20. A third component of the eutectic alcohol-acid mixture shall be used in the fractionation processes of lignocellulosic biomass, in particular an organic salt, namely quaternary ammonium, phosphonium, pyridinium or pyrrolidinium halides, and preferably cholinium chloride or cholinium bromide. The reaction mixture is then placed at a low temperature (10 ºC - 100 ºC) for a defined period (30 min to 8 hours). This process allows the inhibition of furfural production due to the formation of stable intermediates in these reaction conditions, namely pentosides.

[0048] In the second step, distilled water or a two-phase system containing distilled water and an immiscible organic solvent (for example, xylene, methyl isobutyl ketone, cyclohexanone, anisole, or methyl isoamyl ketone) is added to the final liquid mixture obtained in the first step. The resulting mixture is heated at elevated temperatures (100 ºC - 200 ºC) over a defined period (30 min to 24 hours), allowing to selectively convert pentosides into furfural with high yields.

[0049] In addition, the process allows subsequent enzymatic hydrolysis of the solid fraction separated in the first step (essentially cellulose) and the subsequent microbial fermentation of the hydrolyzed sugars can be carried out without the risk of being inhibited by the presence of furfural, which is only formed in the second step. In this way, the overall efficiency of the valorization of biomass carbohydrates is substantially improved.

[0050] Inis represented, in a schematic and simplified perspective, the general process of this invention, namely the inhibition of furfural formation simultaneously with the pretreatment of biomass and the final recovery of furfural.

[0051] Moreover, the two-phase system used in the second step allows the extraction of furfural to the organic phase, while other compounds remain in the aqueous phase. In this way, the presented process is a new and more suitable process for industrial application compared to any existing process.

[0052] Materials

[0053] The appropriate sugars for this process are pentoses (xylose and arabinose). Pentosan-rich lignocellulosic biomass (for example, wood, straw, bark, bagasse, seeds, logs, among other agricultural waste and agro-industrial waste) can be ground with a knife mill to a size of 0.5-3.5 mm.

[0054] The most suitable alcoholic-acid eutectic mixtures for experiments are those that have alcohols and strong acids in their formulation, such as cholinium chloride:p-toluenosulonic acid:ethylene glycol (ChCl:pTSA:EG). Before the process, alcoholic-acid eutectic mixtures are prepared as described in the literature (NPL16). In the second step, for the formation of furfural, distilled water or a two-phase system composed of distilled water and an immiscible organic solvent (for example, xylene, methyl isobutyl ketone, cyclohexanone, anisole, or methyl isoamyl ketone) were used for the recovery of furfural.

[0055] Analytical techniques – Gas chromatography coupled to mass spectrometry (GC-MS)

[0056] Before the analysis by gas chromatography coupled to mass spectrometry (GC-MS), the samples were derived by silylation. For this, 20 mg of sample was dissolved in 250 μL of pyridine containing 0.6 mg of tetracosane (used internal standard) and then 250 μl of N,O-bis(trimethylsilyl)trifluorocacetamide and 50 μL of trimethylsilyl chloride were added at room temperature. Subsequently, the mixture was placed in a bath at 70 ºC for 30 minutes.

[0057] The derived samples were analyzed by GC-MS using a Trace Gas Chromatograph (2000 series) equipped with a Thermo Scientific DSQ II mass spectrometer (Waltham, Massachusetts, USA). The compounds were separated into a capillary column DB-1 J&W (30 m x 0.32 mm internal diameter, 0.25 μm thick, Santa Clara, California, USA), using helium as a carrier gas (35 cm s-1). The temperature program was as follows: initial temperature, 80 ºC for 5 min; 4 ºC min-1to 260 ºC; 2 ºC min-1to 285 ºC, which was maintained for 8 minutes. The injector and transfer line temperatures were 250 ºC and 290 ºC, respectively, while the division ratio was 1:33. The mass spectrometer was operated in the mode of electron impact with energy of 70 eV, and the data were collected in a range of m / z 33-700. The ion source was maintained at 250 ºC. The compounds were identified based on their mass spectra and fragmentation patterns.

[0058] Analytical techniques – High performance liquid chromatography

[0059] Before high performance liquid chromatography (HPLC) analysis, the samples were diluted in distilled water to an adequate volume and filtered using nylon filters with a pore diameter of 0.45 µm.

[0060] The samples (10 µL) were injected into the HPLC system consisting of a L-2130 pump (Hitachi, Chiyoda, Japan), an L-2200 automatic sampler (Hitachi, Chiyoda, Japan), and two detectors, a photodiode matrix detector (DAD) L-2455 (Chiachi, Japan) and a refractive index detector (RI) L-2490 (Hitachi, Chiyoda, Japan). The compounds were separated into an ion exchange column Rezex ROA-Organic Acid H+ 8% (300 x 7.8 mm; particle size 8 µm), preceded by a Carbo-H (3 mm internal diameter), both supplied by Phenomenex (Torrance, CA, USA) and maintained at 65 ºC (oven Gecko 2000, CIL Cluzeau, Sainte-Foy-la-Grande, France). The eluent used was a 0.005 N solution of sulphuric acid, eluted at a flow of 0.5 mL min-1. Calibration curves were used to determine the concentration of sugars and furfural.

[0061] Process to control the inhibition and formation of furfural with alcoholic-acid eutectic mixtures

[0062] The process herein disclosed is described in detail inand. The first step of the procedure (inhibition of furfural) may be carried out in any glass or metal container to ensure the preparation of a mixture of pentose or lignocellulosic biomass containing pentosans with the alcohol-acid eutectic mixture (between 1:0.1 and 1:20 mass ratio, preferably between 1:1 and 1:15, or more preferably 1:10) for a certain time (between 30 min and 10 hours, preferably between 30 min and 8 hours, or more preferably 4 hours) and at an established temperature (between 10 ºC and 100 ºC, preferably between 50 and 90 ºC, or more preferably at a temperature of 80 ºC), with stirring.

[0063] For the formation of furfural, distilled water (ratio of 1:3 relative to the eutectic mixture) or a two-phase system (ratio of 2.5:1.5 relative to the eutectic mixture) containing distilled water and an organic solvent, such as xylene, methyl isobutyl ketone, cyclohexanone, anisole or methyl isoamyl ketone (ratio of 1:4) are added to the previous mixture prepared during the first step in any glass or metal container for a certain time (between 30 min and 24 hours, preferably between 4 and 20 hours, or more preferably at 16 hours) and at an established temperature (between 100ºC and 200 ºC, preferably between 110 ºC and 150 ºC, or more preferably at a temperature of 120 ºC), with stirring.

[0064] In the case of using lignocellulosic biomass as initial material, after the first step of inhibition of furfural formation and simultaneous pretreatment of biomass, the obtained cellulose-rich solid and the resulting liquid fraction containing mainly the products of pentose reaction (pentosides) and lignin, are separated by vacuum filtration prior to second step. Afterwards, the liquid fraction containing the products can be further used in the second step to convert pentosides into furfural as described above.Examples

[0065] Examples 1-5 demonstrate the effect of the alcohol component from the eutectic alcohol-acid mixture on the first step of the process.

[0066] Examples 6 and 7 demonstrate the effect of the acid component from the eutectic alcohol-acid mixture on the first step of the process.

[0067] Examples 8 and 9 demonstrate the effect of the absence of the organic salt component from the alcohol-acid eutectic mixture on the first step of the process.

[0068] Example 10 demonstrates the effect of lower temperature (25 ºC) on the first step of the process.

[0069] Example 11 demonstrates the effect of increasing the amount of xylose on the first step of the process.

[0070] Example 12 demonstrates the effect of replacing xylose with arabinose on the first step of the process.

[0071] Examples 13-15 demonstrate the effect of the solvent (distilled water or two-phase system) on the second step of the process.

[0072] Example 16 demonstrates the first step of the process using lignocellulosic biomass (rice straw) as initial material.

[0073] Examples 17-18 demonstrate the second step of the process using lignocellulosic biomass (rice straw) as initial material and the effect of the solvent (distilled water or two-phase system).

[0074] EXAMPLE 1 –Process example comprising the first step of control of furfural formation by the conversion of xylose into xylosides in the presence of ChCl:pTSA:ethylene glycol (1:1:9) at 80 ºC

[0075] Approximately 4.507 g of ChCl:pTSA:ethylene glycol (1:1:9) were added to a 15 mL bottle containing a magnetic stirrer and 0.5054 g of xylose. The mixture was maintained at 80 ºC and under continuous agitation for 30 minutes, 1 hour, and 2 hours. Two products (Anomers 1 and 2 - Table 1) are obtained from the reaction of xylose with ethylene glycol, identified as two xyloside isomers, as identified by GC-MS. The quantification of these compounds was later performed by HPLC analysis and the percentages are relative to the initial content of xylose, according to Table 1.

[0076] Table 1. Results of the conversion of xylose into xylosides and furfural in the presence of ChCl:pTSA:ethylene glycol (1:1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural(%)0.56.7031.4557.300.2416.4030.8656.840.3426.3031.4657.020.68

[0077] EXAMPLE 2 – Process example comprising the first step of control of the furfural formation by the conversion of xylose into xylosides in the presence of ChCl:pTSA:hexanediol (1:1:9) at 80 ºC

[0078] Approximately 4.632 g of ChCl:pTSA:hexanediol (1:1:9) were added to a 15 mL bottle containing a magnetic stirrer and 0.499 g of xylose. The mixture was maintained at 80 ºC and under continuous agitation for 30 minutes, 1 hour, and 2 hours. Two products (Anomers 3 and 4 - Table 2) are obtained from the reaction of xylose with hexanediol and are identified as two xyloside isomers, as identified by GC-MS. The quantification of these compounds was later performed by HPLC analysis and the percentages are relative to the initial content of xylose, according to Table 2.

[0079] Table 2. Results of the conversion of xylose into xylosides and furfural in the presence of ChCl:pTSA:hexanediol (1:1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Xylose (%)Anomer 3 (%)Anomer 4 (%)Furfural (%)0.512.0839.6148.140.1617.0235.1757.620.1826.6932.2660.670.37

[0080] EXAMPLE 3 – Processexample comprising the first step of control of the furfural formation by the conversion of xylose into xylosides in the presence of ChCl:pTSA:butanol (1:1:9) at 80 ºC

[0081] Approximately 4.584 g of ChCl:pTSA:butanol (1:1:9) were added to a 15 mL bottle containing a magnetic stirrer and 0.4947 g of xylose. The mixture was maintained at 80 ºC and stirred continuously for 30 minutes. Two products (Anomers 5 and 6 - Table 3) are obtained from the reaction of xylose with butanol and are identified as two xyloside isomers, as identified by GC-MS. The quantification of these compounds was later performed by HPLC analysis and the percentages are relative to the initial weight of xylose, according to Table 3.

[0082] Table 3. Results of the conversion of xylose into xylosides and furfural in the presence of ChCl:pTSA:butanol (1:1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Xylose (%)Anomer 5 (%)Anomer 6 (%)Furfural (%)0.515.7528.9152.600.93

[0083] EXAMPLE 4 – Processexample comprising the first step of control of the furfural formation by the conversion of xylose into xylosides in the presence of ChCl:pTSA:hexanol (1:1:9) at 80 ºC

[0084] Approximately 4.640 g of ChCl:pTSA:hexanol (1:1:9) were added to a 15 mL bottle containing a magnetic stirrer and 0.501 g of xylose. The mixture was maintained at 80 ºC and stirred continuously for 30 minutes. Two products (Anomers 7 and 8 - Table 4) are obtained from the reaction of xylose with hexanol and are identified as two xyloside isomers, as identified by GC-MS. The quantification of these compounds was later performed by HPLC analysis and the percentages are relative to the initial weight of xylose, according to Table 4.

[0085] Table 4. Results of the conversion of xylose into xylosides and furfural in the presence of ChCl:pTSA:hexanol (1:1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Xylose (%)Anomer 7 (%)Anomer 8 (%)Furfural (%)0.522.9026.4151.700.48

[0086] EXAMPLE 5 –Process example comprising the first step of control of the furfural formation by the conversion of xylose into xylosides in the presence of ChCl:pTSA:ethanol (1:1:9) at 80 ºC

[0087] Approximately, 4.703 g of ChCl:pTSA:ethanol (1:1:9) were added to a 15 mL bottle containing a magnetic stirrer and 0.505 g of xylose. The mixture was maintained at 80 ºC and stirred continuously for 30 minutes. Two products (Anomers 9 and 10 - Table 5) are obtained from the reaction of xylose with ethanol and are identified as two xyloside isomers, as identified by GC-MS. The quantification of these compounds was later made by HPLC analysis and the percentages are relative to the initial content of xylose, according to Table 5.

[0088] Table 5. Results of the conversion of xylose into xylosides and furfural in the presence of ChCl:pTSA:ethanol (1:1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Xylose (%)Anomer 9 (%)Anomer 10 (%)Furfural (%)0.516.4028.4550.871.06

[0089] EXAMPLE 6 –Process example comprising the first step of control of the furfural formation by the conversion of xylose into xylosides in the presence of ChCl:H2SO4:ethylene glycol (1:1:9) at 80 ºC

[0090] Approximately 4.778 g of ChCl:H2SO4:ethylene glycol (1:1:9) were added to a 15 mL bottle containing a magnetic stirrer and 0.545 g of Xylose. The mixture was maintained at 80 ºC and stirred continuously for 30 minutes. Two products (Anomers 1 and 2 - Table 6) are obtained from the reaction of xylose with ethylene glycol and are identified as two xyloside isomers, as identified by GC-MS. The quantification of these compounds was later performed by HPLC analysis and the percentages are relative to the initial content of xylose, according to Table 6.

[0091] Table 6. Results of the conversion of xylose into xylosides and furfural in the presence of ChCl:H2SO4:ethylene glycol (1:1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)0.57.0230.3256.760.67

[0092] EXAMPLE 7 – Processexample comprising the first step of control of the furfural formation by the conversion of xylose into xylosides in the presence of ChCl:oxalic acid:ethylene glycol (1:1:9) at 80 ºC

[0093] Approximately 5.204 g of ChCl:oxalic acid:ethylene glycol (1:1:9) were added to a 15 mL bottle containing a magnetic stirrer and 0.5178 g of xylose. The mixture was maintained at 80 ºC and stirred continuously for 30 minutes. Two products (Anomers 1 and 2 - Table 7) are obtained from the reaction of xylose with ethylene glycol and are identified as two xyloside isomers, as identified by GC-MS. The quantification of these compounds was later performed by HPLC analysis and the percentages are relative to the initial content of xylose, according to Table 7.

[0094] Table 7. Results of the conversion of xylose into xylosides and furfural in the presence of ChCl:oxalic acid:ethylene glycol (1:1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)0.549.7531.3217.210.08

[0095] EXAMPLE 8 –Process example comprising the first step of control of the furfural formation by the conversion of xylose into xylosides in the presence of H2SO4:ethylene glycol (1:9) at 80 ºC

[0096] Approximately 4.744 g of H2SO4:ethylene glycol (1:9) were added to a 15 mL bottle containing a magnetic stirrer and 0.537 g of xylose. The mixture was maintained at 80 ºC and stirred continuously for 30 minutes. Two products (Anomers 1 and 2 - Table 8) are obtained from the reaction of xylose with ethylene glycol and are identified as two xyloside isomers, as identified by GC-MS. The quantification of these compounds was later made by HPLC analysis and the percentages are relative to the initial weight of xylose, as shown in Table 8.

[0097] Table 8. Results of the conversion of xylose into xylosides and furfural in the presence of H2SO4:ethylene glycol (1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)0.56.8030.5461.360.30

[0098] EXAMPLE 9 – Processexample comprising the first step of control of the furfural formation by the conversion of xylose into xylosides in the presence of pTSA:ethylene glycol (1:9) at 80 ºC

[0099] Approximately 4.703 g of pTSA:ethylene glycol (1:9) were added to a 15 mL bottle containing a magnetic stirrer and 0.505 g of xylose. The mixture was maintained at 80 ºC and stirred continuously for 30 minutes. Two products (Anomers 1 and 2 - Table 9) are obtained from the reaction of xylose with ethylene glycol and are identified as two xyloside isomers, as identified by GC-MS. The quantification of these compounds was later made by HPLC analysis and the percentages are relative to the initial weight of xylose, according to Table 9.

[0100] Table 9. Results of the conversion of xylose into xylosides and furfural in the presence of pTSA:ethylene glycol (1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)0.56.1132.8163.590.08

[0101] EXAMPLE 10 – Processexample comprising the first step of control of the furfural formation by the conversion of xylose into xylosides in the presence of ChCl:pTSA:ethylene glycol (1:1:9) at 25 ºC

[0102] To analyze the effect of the process temperature, the procedure of the first step was performed in the same way as described in Example 1, but with a temperature of 25 ºC and same reaction time as before (30 min, 1, 2, and 6 hours). Two products (Anomers 1 and 2 - Table 10) are obtained from the reaction of xylose with ethylene glycol, identified as two isomers of xyloside, as identified by GC-MS. The quantification of these compounds was later made by HPLC analysis and the percentages are relative to the initial weight of xylose, according to Table 10.

[0103] Table 10. Results of the conversion of xylose into xylosides and furfural in the presence of ChCl:pTSA:ethylene glycol (1:1:9) in a solid-liquid mass ratio of 1:10 at 25 ºCTime (h)Xylose (%)Anomer 1(%)Anomer 2 (%)Furfural(%)0.577.716.705.810173.779.709.000265.7416.1911.000454.1225.3620.060

[0104] EXAMPLE 11 –Process example comprising the first step of control of the furfural formation by the conversion of 2 g of xylose into xylosides in the presence of ChCl:pTSA:ethylene glycol (1:1:9) at 80 ºC

[0105] To analyze the effect of the amount of xylose used in the first step of the process, 2.104 g of xylose were used and the procedure was performed in the same way as described in Example 1. The results are presented in Table 11 and the percentages are relative to the initial weight of xylose.

[0106] Table 11. Results of the conversion of 2 g of xylose into xylosides and furfural in the presence of ChCl:pTSA:ethylene glycol (1:1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)0.57.9326.2845.690.19

[0107] EXAMPLE 12 – Processexample comprising the first step of control of the furfural formation by the conversion of arabinose into pentosides in the presence of ChCl:pTSA:ethylene glycol (1:1:9) at 80 ºC

[0108] Approximately 4.334 g of ChCl:pTSA:ethylene glycol (1:1:9) were added to a 15 mL bottle containing a magnetic stirrer and 0.401 g of arabinose. The mixture was maintained at 80 ºC and stirred continuously for 30 minutes. Two products (Anomers 11 and 12 - Table 12) are obtained from the reaction of arabinose with ethylene glycol and are identified as two isomers of pentosides derived from arabinose, as identified by GC-MS. The quantification of these compounds was later made by HPLC analysis and the percentages are relative to the initial weight of arabinose, according to Table 12.

[0109] Table 12. Results of the conversion of arabinose into pentosides and furfural in the presence of ChCl:pTSA:ethylene glycol (1:1:9) in a solid-liquid mass ratio of 1:10 at 80 ºCTime (h)Arabinose (%)Anomer 11 (%)Anomer 12 (%)Furfural (%)0.514.1011.5471.470.16

[0110] EXAMPLE 13 –Process example comprising the second step of the process to promote the formation of furfural by adding water to the reaction system after the first step and setting the temperature to 120 ºC

[0111] For the second step of the process, about 1.5 mL of distilled water was added to the final mixture obtained from the first step prepared in Example 1 (reaction at 0.5 h). The mixture was maintained at 120 ºC and under continuous agitation for 30 minutes, 1, 2, 4, 8, and 16 hours. After 16 hours it is possible to notice that the degradation of furfural begins and, for this reason, no higher times were used. The quantification of the compounds obtained was made by HPLC analysis and the percentages of Anomers 1 and 2 and furfural are relative to the initial weight of xylose in the first step. The amount of xylose presented here comes from the degradation of xylosides (Anomers 1 and 2) produced in the previous step. The results are shown in Table 13.

[0112] Table 13. Results of the conversion of xylosides into furfural in the presence of water at a temperature of 120 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)0.512.1527.2945.159.72111.5022.8538.8615.7629.2420.0133.9423.2747.0516.3326.8531.4986.1713.3420.8635.29163.4112.1017.4220.26

[0113] EXAMPLE 14 –Process example comprising the second step of the process to promote the formation of furfural by adding water and xylene to the reaction system after the first step and setting the temperature to 120 ºC

[0114] The procedure of the second step was performed in the same way as described in example 13 but with the addition of 1.5 mL of distilled water and 6 mL of xylene to the final mixture obtained from the first step prepared in Example 1 (reaction at 0.5 h). The percentages of Anomers 1 and 2 and furfural are relative to the initial content of xylose in the first step. The amount of xylose presented here comes from the hydrolysis of xylosides (Anomers 1 and 2) produced in the previous step. The results are shown in Table 14.

[0115] Table 14. Results of the conversion of xylosides into furfural in the presence of water and xylene at a temperature of 120 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)28.9517.2626.0923.0948.0614.7022.2747.5285.1713.8720.6646.11160.111.943.0634.89

[0116] EXAMPLE 15 –Process example comprising the second step of the process to promote the formation of furfural by adding water and methyl isobutyl ketone to the reaction system after the first step and setting the temperature to 120 ºC

[0117] The procedure of the second step was performed in the same way as described in example 13 but with the addition of 1.5 mL of distilled water and 6 mL of methyl isobutyl ketone to the final mixture obtained from the first step prepared in Example 1 (reaction at 0.5 h). The percentages of Anomers 1 and 2 and furfural are relative to the initial content of xylose in the first step. The amount of xylose presented here comes from the degradation of xylosides (Anomers 1 and 2) produced in the previous step. The results are presented in Table 15.

[0118] Table 15. Results of the conversion of xylosides into furfural in the presence of water and methyl isobutyl ketone at a temperature of 120 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)213.5020.9134.1513.58411.0319.8330.7926.0083.4911.2817.1137.61160.156.329.4835.34

[0119] EXAMPLE 16–Process example comprising the pretreatment of rice straw with simultaneous inhibition of furfural formation by the conversion of xylose into xylosides in the presence of ChCl:pTSA:ethylene glycol (1:1:9) at 80 ºC

[0120] For the pretreatment of rice straw, 0.5 g of dry biomass was added to a 15 mL bottle containing a magnetic stirrer and 4.5 g of ChCl:pTSA:ethylene glycol (1:1:9). The mixture was maintained at 80 ºC and under continuous agitation for 30 min, 1, 2, 4, 6, and 8 hours. After pretreatment, the flasks were cooled and 10 g of ethanol was added to decrease the viscosity of the liquid fraction while maintaining the components of the extracted biomass dissolved. The liquid fraction and the solid fraction were separated by vacuum filtration. Two products (Anomers 1 and 2 - Table 16) are obtained during the pretreatment of rice straw due to the reaction of xylose with ethylene glycol and are identified as two isomers of pentosides derived from xylose, as identified by GC-MS. The quantification of these compounds was later made by HPLC analysis and the percentages are relative to the percentage of xylan (17.6 %) present in the biomass, according to Table 16.

[0121] Table 16. Results of rice straw pretreatment in the presence of ChCl:pTSA:ethylene glycol (1:1:9) at 80 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)0.55.607.8011.770.00113.0317.1725.630.20215.5819.8831.640.62418.7022.6234.681.17623.3126.9540.911.74817.0818.8228.072.14

[0122] EXAMPLE 17 – Process example comprising the second step of the process to promote the formation of furfural by adding water to the reaction system after the first step, using rice straw and setting the temperature to 120 ºC

[0123] For the second step of the process using rice straw as initial raw material, about 1.5 mL of distilled water was added to the final mixture obtained from the first step prepared in Example 16 (reaction at 6 hour). The mixture was maintained at 120 ºC and under continuous agitation for 2, 4, 8, 16, and 24 hours. The quantification of the compounds obtained was made by HPLC analysis and the percentages of Anomers 1 and 2 and furfural are relative to the percentage of xylan that stays in the liquid fraction after biomass pretreatment (9.6 %). The amount of xylose presented here comes from the degradation of xylosides (Anomers 1 and 2) produced in the previous step (Example 16). The results are shown in Table 17.

[0124] Table 17. Results of the conversion of xylosides into furfural using rice straw in the presence of water at a temperature of 120 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)217.9913.1814.579.68418.8711.9911.8218.3089.235.074.7227.21166.422.851.8039.02245.532.441.4823.98

[0125] EXAMPLE 18 – Process example comprising the second step of the process to promote the formation of furfural by adding water and xylene to reaction system after the first step using rice straw and setting the temperature to 120 ºC

[0126] For the second step of the process using rice straw as initial raw material, about 1.5 mL of distilled water and 6 mL of xylene were added to the final mixture obtained from the first step using the 6 hours reaction prepared in Example 16. The mixture was maintained at 120 ºC and under continuous agitation for 2, 4, 8, 16, and 24 hours. The quantification of the compounds obtained was made by HPLC analysis and the percentages of Anomers 1 and 2 and furfural are relative to the percentage of xylan that stays in the liquid fraction after biomass pretreatment (9.6 %). The amount of xylose presented here comes from the degradation of xylosides (Anomers 1 and 2) produced in the previous step (Example 16). The results are shown in Table 18.

[0127] Table 18. Results of the conversion of xylosides into furfural using rice straw in the presence of water and xylene at a temperature of 120 ºCTime (h)Xylose (%)Anomer 1 (%)Anomer 2 (%)Furfural (%)217.0512.0014.8022.95416.7510.3311.4830.2889.574.594.4852.67164.181.720.8672.77243.821.630.6831.07

[0128] The information and examples presented here are intended to be illustrative of the present invention and not be considered limiting. Other variations / changes are possible within the scope of this invention and will be evident to experts.

[0129] The process herein disclosed can be used in the production of energy, fuels, materials, and chemicals.Patent Literature

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Claims

1.Two-step thermal process to convert pentoses or biomass containing pentosans into furfural comprising the steps of:reacting a pentose and / or biomass containing pentosans with an alcoholic-acid eutectic mixture, wherein the alcoholic-acid eutectic mixture comprises at least one organic salt, one organic or inorganic acid, and one alcohol, at a temperature within the range of 10 and 100 ºC, during a period of time between 30 minutes and 8 hours, under constant stirring, to form pentosides; andreacting the reactional liquid obtained from step (i) with water or a two-phase mixture containing water and immiscible organic solvent, at a temperature within the range of 100 to 200 ºC, during a period of time between 30 minutes and 24 hours, under constant stirring, to form furfural.2.Process according to claim 1, wherein said biomass is selected from wood, straw, bark, bagasse, seeds, and logs, among other agricultural waste and agro-industrial waste rich in pentosan-type hemicelluloses.3.Process according to claims 1 or 2, wherein said organic salt is preferably a quaternary ammonium halide, quaternary phosphonium halide, imidazolium halide, pyridinium halide, pyrrolidinium halide, and more preferably quaternary ammonium halide, and more preferably cholinium chloride or cholinium bromide.4.Process according to any of the preceding claims, wherein the acid in the alcoholic-acid eutectic mixture is a strong organic or inorganic acid, with a pKa of less than 2,5.5.Process according to claim 4 wherein the acid is selected fromp-toluenosulfonic acid, 4-hydroxybenzenesulfonic acid, sulfosalicylic acid, maleic acid, oxalic acid, nitric acid, sulphuric acid, hydrochloric acid, hydrobromic acid or phosphoric acid.6.Process according to any of the preceding claims, wherein the alcohol in the alcoholic-acid eutectic mixture is a monoalcohol, a diol, or a polyol.7.Process according to claim 6, wherein the monoalcohol is selected from a monoalcohol with a carbon chain between C1-C12 long, preferably methanol, ethanol, propanol or butanol.8.Process according to claim 6, wherein said diol is selected from ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, or diols with longer carbon chain length, such as polyethylene glycol.9.Process according to claim 6, wherein the polyol is selected from a polyol with a carbon chain between C1-C20 long, preferably glycerol, xylitol, mannitol, erythritol or sorbitol.10.Process according to any of the preceding claims, wherein the temperature of step (i) is within the range of 40 to 90 ºC, preferably at 80 ºC.11.Process according to any of the preceding claims, wherein the reaction of step (i) occurs during a time period between 2 and 6 hours, preferably during 4 hours.12.Process according to any of the preceding claims, wherein the pentose and / or biomass containing pentosans, to alcoholic-acid eutectic mixture mass ratio of step (i) is comprised within the range of 1:5 to 1:10.13.Process according to any of the preceding claims, wherein the resultant mixture of step (i) is separated by filtration or ultrafiltration before step (ii).14.Process according to any of the preceding claims, wherein the temperature of step (ii) is within the range of 110 to 150 ºC, preferably at 120 ºC.15.Process according to any of the preceding claims, wherein the reaction of step (ii) occurs during a time period between 4 and 20 hours, preferably during 16 hours.16.Process according to any of the preceding claims, wherein the immiscible organic solvent of step (ii) is selected from xylene, methyl isobutyl ketone, cyclohexanone, anisole, methyl isoamyl ketone.

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