This report contains the results of the investigation of the state of the art of the abatement systems of volatile organic compounds (VOCs) from gas streams of industrial processes. Most of the studies related to photocatalytic processes concern applications for the removal of indoor VOCs, with VOC concentrations often lower than ppb. In the case of industrial processes, the VOC concentrations to be treated are of the order of ppm and the flow rates to be processed are thousands of m3/h; furthermore, applying an emission control technique to an industrial process requires the development of continuous reactors capable of obtaining a high removal efficiency through a single step.

Pollutant treatment is an aspect that significantly impacts the overall efficiency of a process, both due to the technical complexity introduced by the treatment method itself and its impact on energy consumption. Consequently, the introduction of efficient abatement techniques with reduced energy consumption is an important factor in the development of a competitive, technologically advanced and increasingly environmental sustainable industrial context, which can significantly contribute to climate change mitigation objectives. In this work, the different types of techniques currently available have been taken into consideration, highlighting for each one, the advantageous aspects and limitations in order to identify possible margins for improvement within which to propose more energy-efficient technological solutions.

The techniques considered are divided into two macro-categories: destructive techniques and non-destructive techniques. Destructive techniques involve the complete transformation of VOCs, present in the gas stream to be treated, into combustion products, namely carbon dioxide and water. Among the destructive techniques, the following were considered: oxidation, thermal or catalytic, biofiltration and photocatalysis. Among the non-destructive techniques, the following were discussed: adsorption, absorption, condensation and separation with membranes. Of all the technologies for the reduction of VOCs listed above, most industrial processes involve the use of regenerative oxidation techniques (about 90%), followed by adsorption (3%). However, the two most widely used techniques feature high energy consumption, due to the need to heat the gas stream to high temperatures in the case of oxidative processes and to the regeneration of the sorbent—by heating or depressurisation—in the case of adsorption. Furthermore, these processes, although theoretically they can be used to treat even very diluted currents, are not very efficient in certain applications.

Photocatalysis is one method that can potentially overcome the limitations of the abatement processes currently used, since it is a process suitable for treating all types of gaseous currents, even very diluted ones, and can be conducted at room temperature, resulting in significantly lower energy consumption. Furthermore, since photocatalysis is currently a laboratory-scale technology (TRL3-4), it is susceptible to significant improvements, both from the point of view of process development and material fine-tuning. Such margins of improvement could extend photocatalysis from a method tested on a laboratory scale to a method applicable on an industrial scale.