With a continuous reduction in limited oil resources and also a drastic increase in oil demand due to growth of emerging developing countries, an imbalance of supply and demand in the market is caused, resulting in high oil prices. Furthermore, irreversible greenhouse gas generated by indiscriminate use of oil may incur serious environmental problems such as global warming.
Countries around the world already have made many efforts to replace oil resources through biomass which is recyclable and reusable, and biofuels such as bioethanol, biodiesel, etc., and bioplastic monomers such as lactic acid, propanediol, etc. are industrially produced and thus replace transportation fuels or petrochemical materials.
As part of these efforts, materials which are recently spotlighted are exemplified by biomass-derived furan-based compounds, that is, 5-hydroxymethyl-2-furfural (HMF) and 5-alkoxymethyl-2-furfural (AMF) as an alkyl ether derivative thereof.
HMF and AMF may be converted into 2,5-furan dicarboxylic acid (FDCA) via oxidation, and FDCA is known to be an alternative to terephthalic acid (TPA) which is a monomer of PET (Poly(ethylene terephthalate)) widely useful in vessels for beverages and food, etc. PET is obtained from ethylene glycol (EG) and TPA monomers through polycondensation. Currently, in order to prepare biomass-based PET, the EG monomer is being industrially produced from bioethanol-based bioethylene, but TPA is not yet obtained from any biomass-based material.
Also, AMF is known to be a next-generation biofuel, and has an energy density equal to or more than that of gasoline, and has no problems related to extended storage and corrosion due to low hygroscopicity, unlike bioethanol. Moreover, in the case of bioethnaol produced through an enzyme conversion process, it essentially emits 2 equiv. carbon dioxide from 1 equiv. hexose in the process (C6H10O6→2CH3CH2OH 2CO2↑), whereas AMF may be produced using a complete carbon-neutral process without carbon loss.
5-hydroxymethyl-2-furfural (HMF) and 5-alkoxymethyl-2-furfural (AMF) may be obtained from polysaccharide materials composed of hexoses such as sugars, starch, cellulose, agar (red algae) among carbohydrate components present in biomass. Specifically, polysaccharide materials composed of hexoses such as sugars, starch, cellulose, agar (red algae) are converted into monosaccharide materials such as fructose, glucose and galactose through saccharification based on hydrolysis, and 3 equiv. water molecules are removed from the monosaccharide materials thus converted under dehydration conditions, thus producing HMF or AMF.
The hexose compound of the monosaccharide such as fructose, glucose or galactose includes two kinds of structural isomers, for examples, ketose and aldose. Ketose and aldose may be sorted depending on the position of the carbonyl group, wherein ketose is a ketone compound having a carbonyl group at C2, and aldose is an aldehyde compound having a carbonyl group at C1.
Also, the hexose compound exists while forming an equilibrium relation between a linear structure and a ring structure depending on pH conditions. As such, ketose forms a five-membered ring structure, and aldose forms a six-membered ring structure.
Thus, when obtaining HMF and AMF as furan-based compounds having a five-membered ring structure from the hexose compound of the monosaccharide, ketose is known to be much easier in terms of conversion, compared to aldose. Hence, to produce HMF or AMF, fructose which is ketose is generally used as a starting material.
However, most of hexose compounds existing in nature are aldose such as glucose or galactose, and ketose such as fructose is limitedly present in sugars, milk, etc. Methods of converting glucose into fructose through enzyme conversion are known, and such glucose is mass produced in the form of high-concentration fructose and is thus utilized in food additives, etc. However, compared to direct use of glucose, additional process costs are required and about 50% glucose is present even in high-concentration fructose.
Thus, research into directly obtaining HMF and AMF from aldose such as glucose that is the hexose compound very abundant in nature is ongoing currently.
With the goal of directly producing HMF and AMF from aldose, isomerization conditions for converting aldose into ketose are required. The most typical method known to date is the use of a Cr(II) or Cr(III) catalyst in the presence of an imidazolium type ionic liquid solvent (Science 2007; 316; 1597-1600). However, this method is undesirable in terms of profitability upon industrial mass production because the ionic liquid solvent used is expensive.
Another method is reported to be a method of maximizing conversion efficiency through real-time extraction of a produced furan-based compound using a biphasic system (Science, 2006; 312; 1933-1937). However, because this method provides no additional isomerization conditions, it is mainly effectively applied to fructose which is ketose rather than aldose, and in order to maintain the biphasic system during the reaction, the selection of the solvent is limited, and the use of a heterogeneous catalyst is difficult. Also, the furan-based product resulting from both the methods as above is limited to HMF. Furthermore, HMF, which is unstable compared to AMF, is partially decomposed in the course of recovery from the reaction mixture, which is undesirable.
International Patent Application No. WO 2007/104514 discloses a method of synthesizing AMF, comprising converting a hexose compound using a solid acid catalyst in the presence of an alcohol solvent. However, because this method provides no additional isomerization conditions like the biphasic system conversion method, it is mainly effectively applied to fructose which is ketose. Also, the concentration of the hexose compound which is the substrate under reaction conditions is as low as about 1% (wt/V), undesirably increasing production and recovery process costs.