Catalytic Transformation Of Biomass-derived α-angelica Lactone To γ-valerolactone In Ionic Liquids At Mild Conditions

The shortage of fossil fuels and environmental consideration arouse interest inthe conversion of biomass-derived carbohydrates to fuels and chemicals. Additionally,the effective utilization of bio-based products has many advantages compared tofossil fuel. In this aspect, γ-valerolactone (GVL), which can be produced fromlignocellulosic biomass, has drawn increasing attention because of its benignproperties and versatile functions in recent years. The starting materials for obtainingGVL are always levulinic acid (LA) and its esters, but the reaction conditions are verydrastic, such as higher temperature and toxic organic solvents employed. Thus, newsynthetic methods need to be developed in order to meet the requirements of lowenergy consumption and emissions reduction.Ionic liquids (ILs) as novel solvents with favorable environmental and technicalfeatures hold great potential as replacements for traditional volatile organic solventsand have been shown to be a viable medium for numerous types of reactions,especially in the conversion of biomass-derived carbohydrates. Therefore, a newprocess for the conversion of α-angelica lactone (α-AL) to GVL was carried out byusing a series of ILs as solvents in a batch-type reactor. Among these ILs,[Bmim]PF6showed the best performance on the selective hydrogenation at60°C with a reactiontime of20min. Interestingly, it was found that the reaction can also take place at atemperature as low as room temperature with complete conversion and nearly100%selectivity, which greatly reduces the energy required for the production of GVL. Thereaction system of ionic liquid/catalyst showed good reusability. There was noobvious decrease in conversion and selectivity after10uses. Furthermore, the kineticsof the catalytic hydrogenation reaction of α-AL was studied to elucidate the reactionprofile. Systematic kinetics experiments were carried out by varying the reactiontemperature from20to100°C at4.0MPa, and the simulated data fits well with thefirst-order reaction law with the reaction activation energy27.9kJ/mol. Meanwhile,the mechanism of α-AL hydrogenation was also been predicted.In order to reduce the cost of using noble metal as catalyst, several amorphousalloy catalysts with different components were used in the hydrogenation reaction of α-AL, the results showed that Ni-Mo-Al has the best activity and selectivity. WithNi-Mo-Al as catalyst, BmimPF6has a remarkable influence on the selectivity of α-ALhydrogenation and catalyst stability. Moreover, a good result was obtained withBmimPF6/Ni-Mo-Al system at80oC, hydrogen pressure of6.0MPa, reaction time of8h and catalyst loading of5wt%, which gave the highest yield of94.3%andselectivity of93.2%. Based on the optimization study, the kinetics of the catalytichydrogenation reaction of α-AL was studied. It was found that the reaction activationenergy was32.2kJ/mol and the pre-exponential factor was595.6. Thus, the catalyticactivity of Ni-Mo-Al was lower when compared with Pd/C catalyst, but good resultswere also achieved with Ni-Mo-Al at mild conditions, it declared that usingnon-noble metal catalyst to replace noble metal catalyst in α-AL hydrogenationreaction is feasible.The product was separated by diethyl ether, which is very volatile and toxic, thusa new green separation method need to be developed for the selectivity hydrogenationof α-AL. Considering ILs/CO2can present an interesting phase behavior at highpressure, which has mechanistic and practical implications for both reaction andseparation systems, thus a reaction-separation coupling system was developed to beused in the selectivity hydrogenation of α-AL, where one phase (IL) is acting as the(stationary) catalytic phase, and the other phase (CO2) takes part as carrier and/orextracting agent. Firstly, we investigated the phase behavior ofBmimPF6/CO2/methanol, with the increasing pressure, a second liquid phaseappeared, and the three phases are IL-rich phase, methanol-rich phase and rich in CO2with some methanol, then the methanol-rich phase disappeared. Under this condition,the hydrogenation of α-AL reactions were carried out, and the obtained resultsshowed that α-AL has a considerable conversion with99.0%at room temperature for5h. Moreover, the upper phase contained no detectable α-AL, but GVL almostexisted in upper phase so the pure product can be recovered by removal of methanoland CO2.