Controlled flow instrument for microwave assisted chemistry with high viscosity liquids and heterogeneous mixtures
A controlled-flow microwave instrument for chemical synthesis using heterogeneous or highly viscous starting materials includes a microwave source for generating electromagnetic radiation in the microwave frequencies, a microwave cavity in wave communication with the source for exposing compositions placed therein to microwave radiation, a microwave-transparent pressure resistant reaction vessel in the cavity, a source reservoir for starting materials and related compositions, a pump in communication with the source reservoir for pumping heterogeneous or highly viscous materials from the source reservoir to the reaction vessel, and a pressure-resistant valve between the pump and the reaction vessel for isolating the reaction vessel from the pump and the source reservoir during application of microwave energy to compositions in the vessel and from any resulting high pressures generated therein.
1. A method of conducting microwave assisted chemical reactions using high viscosity liquids or heterogeneous mixtures of liquids and solids, the method comprising:
pumping a discrete portion of a composition selected from the group consisting of high viscosity liquids and heterogeneous mixtures of liquids and solids to a microwave-transparent pressure resistant reaction vessel at ambient pressures of between about atmospheric pressure and about 30 psi;
isolating the discrete portion in the pressure resistant vessel;
applying microwave radiation to the isolated discrete portion in the reaction vessel to initiate and maintain a chemical reaction at a pressure of at least about 175 psi while preventing the vessel from releasing higher-pressure gases generated by a chemical reaction in the vessel;
releasing pressure from the vessel following desired completion of the chemical reaction; and
pumping the reaction products of the discrete portion from the vessel at ambient pressures of between about atmospheric pressure and about 30 psi following the pressure release.
2. A method according to claim 1 comprising pumping a second discrete portion after the first has been pumped out and thereafter carrying out the steps of isolating the second portion, applying microwave radiation to the second portion, releasing pressure from the vessel, and pumping reaction products from the vessel.
3. A method according to claim 2 comprising rinsing the reaction vessel with a solvent between the steps of pumping the reaction products and pumping the second discrete portion.
4. A method according to claim 3 comprising driving the rinsing solvent with an inert gas.
5. A method according to claim 1 comprising stirring the discrete portion in the reaction vessel during the step of applying microwave radiation.
6. A method according to claim 1 wherein the step of applying microwave radiation comprises applying single mode radiation.
7. A method according to claim 1 wherein the step of applying microwave radiation comprises applying dual mode radiation.
8. A method according to claim 1 comprising maintaining the reaction vessel at a constant temperature for extended portions of a chemical reaction.
9. A method according to claim 1 comprising measuring the temperature of the reaction vessel and adjusting the application of microwave radiation in response to the measured temperature.
10. A method according to claim 1 comprising measuring the temperature of the reaction vessel and cooling the reaction vessel in response to the measured temperature.
11. A method according to claim 1 comprising maintaining the pressure in the reaction vessel at between about 175 and 250 psi.
12. A method according to claim 1 comprising mixing the composition from components selected from the group consisting of solids, liquids, solutions, solid phase catalysts and solid-supported reagents prior to the step of pumping the composition to the reaction vessel.