The chemical process industry faces the challenge of supplying a fast growing and ever more demanding global population with the products we need.

This results in the increased consumption of the non-renewable resources on which the vast majority of those products is based. At the same time, the average efficiency with which these resources are converted into final products remains dramatically low; according to the World Resources Institute, lower than 25 per cent. It is a very worrying figure and ‘factor 4’, ‘factor 10’ or even ‘factor 20’ are nowadays frequently quoted terms indicating the scale of improvement needed.

Switching to renewable raw materials, such as cellulose, sugar cane or crops will surely help the sustainability problem but will not resolve it completely. Besides, biotechnological processes usually suffer from low product yields. So being ‘green’ will not be enough; we need to be ‘green’ and efficient. One of the paths leading to this goal is process intensification (PI).

Miniaturisation is a hallmark of PI. Equipment miniaturisation significantly increases the safety of chemical processes. It is obvious that smaller is safer and by making inventories smaller many disastrous accidents in the chemical industry could have been avoided.

It has been shown, for instance, that implementing PI principles at the Union Carbide plant at Bhopal could have prevented the worst industrial disaster in the history of mankind and the deaths of thousands of people. The inventory of poisonous methyl isocyanate at the plant could have been reduced from 41tonnes to less than 10kilogrammes! But PI is not only about miniaturisation and not only about safety. It has clearly also other sustainability-related dimensions, reducing material usage, energy consumption and waste generation. Producing much more with much less is the clue to PI.

A bolder attitude

One must realise, however, that the required substantial technological changes in the process industry will not be possible without a bolder attitude towards process innovation in the industry itself and more daring, imagination-driven chemical engineering research in academia.

For the time being, a risk-avoiding culture still dominates the scene. We avoid the risk of innovation as if we have forgotten that real breakthroughs can only be achieved by undertaking the risk, and that failure presents an inherent part of true scientific progress. Such an attitude within the industry does not help the universities either in daring to undertake risky research themes. Also, in universities, evolutionary, small-step, low-risk subjects are often chosen. Assessed on ‘productivity’ and publication statistics, we tend to retreat to safe but not spectacular research: research that brings more of the same results in published papers and in conference presentations.

The chair of PI at Delft University of Technology is one of the world’s first in this field. It has been established in the Process and Energy Laboratory. This is a very good and logical choice, because both process and energy are keys to the research programme of the chair in the coming years: I have decided to focus on intensification of chemical and biochemical processes using locally controlled energy from alternative sources.

Alternative sources and forms of energy present a field full of scientific unknowns and tremendous research challenges and, as you can see from the examples shown in Table 1, their application in chemical processing can result in spectacular intensification effects. Often, intensification by two or even three orders of magnitude is possible and most of these effects have a clear sustainability dimension. For instance, the high-gravity field utilised in the so-called spinning disk reactor and applied to one of the processes at GlaxoSmithKline resulted in 1000-fold reduction of the processing time, 100-fold reduction of equipment inventory and 12-fold reduction of the by-products level.

The big three

Three alternative energy forms particularly attract my research interest: microwaves, light and supersonic shockwave.

A microwave is a form of electromagnetic energy, nowadays known to almost everyone from kitchen appliances. It falls at the lower end of the electromagnetic spectrum, and is defined in the frequency range of 300 to about 300000MHz. Polar molecules subjected to microwave irradiation exhibit dipole rotation trying to align with the rapidly changing electric field of the microwave. The rotational motion of the molecule results in a transfer of energy. Additionally, in substances where free ions or ionic species are present, the energy is also transferred by the ionic motion in an oscillating microwave field. As a result of both these mechanisms the substance is heated directly and almost evenly. Heating with microwaves is therefore fundamentally different from conventional heating by conduction.

Microwaves are known to accelerate chemical reactions, often by factors of hundreds and in many cases significantly better product yields are reported. The exact mechanism behind the above phenomenon is still being disputed.

Despite obvious intensification effects of microwave irradiation on chemical reactions and other advantages such as energy savings, mild treatment in case of temperature-sensitive products or absence of fouling, as yet no microwave-assisted process has been commercialised. There is a clear need to develop understanding, engineering models and methodology for scale-up and design of continuous microwave reactors and I intend to start systematic investigations in this area. I hope to create a situation in which the fine chemical or pharmaceutical industries abandon the traditional, stirred-vessel-based ‘cooking recipe’ route of process development and will reach for much more efficient intensive equipment.

Microreactors are often seen as a most extreme form of PI. But can a microreactor be further intensified? I am strongly convinced that it can. Alternative sources and forms of energy open up new possibilities here. Microwaves coupled with microtechnology offer a perfect opportunity to increase process selectivity by an instantaneous heating-up of the reactants and a fast quenching of the reaction products.

We will investigate microwave-assisted microprocessing (so-called ‘µ2’) in the coming years. Fundamental challenges here include equipment materials and their interaction with microwave radiation, application of microwave energy to micro-volumes, modelling and optimisation of microwave-driven process in microequipment.

Other fascinating research opportunities open up in integrated systems, such as multifunctional reactors.

I expect that with microwave irradiation fast,

low-temperature processes with significant selectivity increase and energy savings could be realised, using either local heat interaction with the catalytic sites or the plasma formation. I would like to enter this area and undertake an attempt to develop a small-volume process for microwave-supported hydrogen production for fuel cell applications. The ultimate goal and our ambition here is a portable unit for low-temperature reforming of biofuels and purification of hydrogen. Such a highly integrated system would signify a breakthrough in the development of portable

emission-free hydrogen sources for automotive applications or for distributed power generation..

Molecular effects

The influence of the molecular effects induced by the microwave field on transport and interfacial phenomena in multiphase separation systems, such as distillation, extraction or crystallisation, presents another exciting and largely unexplored research area. Scarce literature data, for instance, indicate that microwave heating can drastically accelerate batch distillation processes. I am interested in studying new concepts of continuous horizontal distillation units, in which the traditional spot-input of heat via the reboiler is replaced by a spatially distributed microwave energy input. Realisation of such concepts could mean an important step on the way to compact, ‘under-the-roof’ chemical plants.

Then there is that other form of electromagnetic energy – light. The use of light, either artificial or solar, in catalysis can lead to unprecedented high product selectivities.

However, in current types of photocatalytic reactors, a significant portion of emitted light is absorbed or dissipated before it reaches the catalytic site. This results in high energy demands and makes photocatalytic reactors often economically unattractive. An ideal photocatalytic reactor should be able to emit photons exactly where and when they are needed, that is in the direct vicinity of the catalytic site and upon contact of the reacting molecules with that site. This requirement presents a tremendous research challenge and I intend to address it in a long-term collaborative research programme that will initially focus on the use of controlled luminescence in photocatalysis.

Finally, utilising the energy of a supersonic shockwave also presents a largely unexplored area of great practical potential. Industrial data clearly confirm substantial effects in terms of mass transfer achieved by the use of supersonic flow in multiphase systems. The influence of the supersonic shockwave on phase dispersion and contacting presents an interesting fundamental research problem and I intend to investigate this problem, both theoretically and experimentally.

Professor Dr Ir Andrzej Stankiewicz is also senior scientist with DSM Research, Geleen, The Netherlands.