Mastering the Microwaves

ControlAccording to Professor Andrzej Stankiewicz, Chair of Intensified Reaction and Separation Systems (IRS) and Director of the Delft Pro-cess Technology Institute (DPTI) at TU Delft, the challenge is clear: “We need to ensure that microwaves act only at the site where they are needed and that their effects are uniform; and much of this comes down to designing the right equipment.” And this is where IRS has been highly successful, developing viable options for using microwaves in chemical processes. For instance, IRS has demonstrated the over-riding importance of orientation of electromagnetic fields with respect to the material; microwave heating occurs in one plane but not the other. This new insight about heating patterns has en-abled IRS to design and scale-up novel micro-wave application systems based on standing- or travelling-wave concepts.

Microwave GasificationIRS is also using microwaves as part of a Bill Gates Project to ‘Reinvent the Toilet’, converting human waste into synthesis gas, a mixture of hydrogen and carbon monoxide, which can then be used to generate electricity. Using micro-waves to induce non-equilibrium plasma, the human waste can be ‘gasified’ very efficiently, reaching almost 200% energy recovery. “This is partially a matter of process design”, says project leader Dr Guido Sturm, “but also thermal management because at 1000s of degrees C, the plasma is hot enough to melt the reactor in 10 seconds. As we want to run the process con-tinuously, this was something of a challenge.”

Ultimately IRS has shown that you can make scalable equipment for industrial processes that brings the microwaves under control, delivering heating that is uniform, highly effective and ma-terial-selective, at energy efficiencies exceeding 90%.

Microwaves have distinct advantages over other types of energy; they heat things quickly and highly selectively. So microwaves have the potential to intensify many reaction and separation processes within industry e.g. gas-solid catalyt-ic reactions, liquid-phase organic syntheses, polymerisation, distillation, crystallisation and membrane separation. The problem is that microwaves are difficult to control and their effects are non-uniform, so they have been of limited use in industry. Either they are used to heat or dry things quickly but unevenly, as in domestic ovens or industrial driers, or they are used to heat very small volumes, which is of little relevance to large-scale processes.

Prof Andrzej StankiewiczA.I.Stankiewicz@tudelft.nl

+31 15 27 82147