Microwave apparatus (Microwave Accelerated Reaction System (MARS 5), CEM Corpora­tion) shown in Figure 9 was used to study the effect of carrying out experiments in a sealed reactor under high pressure and high temperature. The microwave apparatus operates at
2.45 GHz frequency, while the microwave output can be manipulated up to maximum pow­er of 1,200 Watts. This apparatus also consists of a fluoropolymer-coated microwave cavity, a cavity exhaust fan and tubing to vent fumes and a digital computer programmable for 100 programs consisting of up to five stages each. Inside the cavity is an alternating turntable system which can hold up to 13 reactor vessels, thus performing simultaneous experiments on 13 samples is possible.

The sealed Teflon-reactor vessel can handle pressures up to 5MPa and temperatures up to 250 oC. The reactor can be connected to the pressure and temperature control mechanisms of the MARS 5, for online monitoring and for operational safety. Some of the experiments were also carried out in a similar apparatus (Ethos) manufactured by Milestone General Co, Ltd.

Inside Cavity

Microwave Apparatus

Tmax = ~240 °С Pmax = ~5MPa

Sealed Reactor

Figure 9. Microwave apparatus for pressurized synthesis of ETBE in a sealed reactor vessel (MARS5, CEM Corporation, Japan)

In a typical experiment, about 0.25 mol each of the reactants (TBA and ETOH) were placed inside the vessel, and mixed with 20g of Amberlyst 15 catalysts. The reactor was sealed and connected to temperature and pressure sensors, then microwave was irradiated until the set irradiation time has elapsed. After cooling the vessel to reach a temperature below 50 oC, the reactor was opened and an aliquot part of the products was taken for analysis.

Figure 10 shows the yields of ETBE using MW at various power at irradiation time of 1 min. A maximum yield of about 87% was obtained at MW power of 350W. At this condition, the attained temperature was around 87oC as shown in Figure 11, higher than the boiling points of the two alcohols. The yield was also found to be dependent on the amount of catalysts, reaction time and microwave power.