Due to the exhaustion of traditional energy sources together with an increase in the global energy demand, impetus is currently being given to the development of alternative energy sources. Among them, biomass is renewable quantitative biological resource that attracts a great deal of attention.
Among biomass-based industrial raw materials, isosorbide (C6H10O4) that is prepared by dehydration of sorbitol (C6H14O6) attracts attention as an environmentally friendly raw material for preparing polycarbonate (PC) as a substitute for bisphenol A (BPA), an epoxy monomer or an environmentally friendly plasticizer. Namely, isosorbide, a material that can be obtained by simple dehydration of sorbitol, is attracting attention as a monomer required for synthesis of next-generation, high-performance, environmentally friendly materials that can replace conventional polymer products, and many studies thereon have been conducted.
Environmentally friendly materials generally show poor properties compared to petrochemical-based materials, whereas isosorbide advantages in that it is environmentally friendly and, at the same time, shows excellent properties compared to conventional petrochemical-based materials. In addition, isosorbide may be used as an additive that can make plastic materials stronger and tougher, and that is also used as an agent for treating cardiac diseases by being boded to nitrate.
When D-glucose obtained from biomass by pretreatment is hydrogenated in the presence of a catalyst, sorbitol is produced. Isosorbide is produced by double dehydration of sorbitol. This cyclization reaction is influenced by various reaction conditions, including temperature, pressure, solvent, catalyst, etc.
Technologies of removing water using vacuum reactions or azeotropic solvents are mainly known. As a technology of removing water under a vacuum, U.S. Pat. No. 7,649,099 discloses a process of producing isosorbide using two reactors including a first reactor and a second reactor, wherein a heterogeneous solid catalyst is introduced into the first reactor and a homogeneous catalyst is introduced into the second reactor and wherein a reaction is carried out at a controlled temperature under a vacuum. However, the above US patent has a disadvantage in that, because the two reactors are used, the investment for the vacuum reaction process is high. Meanwhile, a technology that uses an azeotropic solvent is disclosed in U.S. Pat. No. 6,639,067. The latter US patent discloses a process in which anhydrosugar alcohol is produced by dehydration in the presence of an acid catalyst and an organic solvent, and then separated by azeotropic distillation. However, the process disclosed therein has disadvantages in that it is difficult to control the reaction temperature, because a single azeotropic solvent is used, and in that the reaction temperature is determined according to the boiling point of the solvent used.
Thus, there is a need for a method capable of more efficiently controlling the reaction temperature, unlike the method that uses the single azeotropic solvent.
Accordingly, the present inventors have found that, when a solvent comprising at least two components that form an azeotrope with water and that have significantly different boiling points is used in a process that produces isosorbide from sorbitol, the reaction temperature can be efficiently controlled and the yield of isosorbide can be increased, thereby completing the present invention.