Green Chemistry Processes To Reduce Production'S Negative Impact

The world production of industrial and biological waste is constantly increasing. Undoubtedly, recycling programs and an improvement of industrial efficiency have brought certain positive results, but not enough to compensate for the dramatic global waste growth. Therefore, new waste recycling and recovery technologies are needed. For example, the recovery of biomass for biodiesel production is quite developed and has already had industrial success.

However, waste recovery and biomass applications for the production of chemical products such as catalysts or high added-value compounds are still under development. In fact, the biggest limitation for these types of processes is to create technologies with low environmental impact and low energy costs, so that they can be competitive with petroleum products. Indeed, the current limits of waste and biomass valorization are excessive energy consumption, variable product quality, low efficiency and limited flexibility. As a result, the development of new competitive technologies is a priority.

In recent years, in bibliography several researches are reported concerning processes of recovery and valorization of biomass and wastes. In fact, numerous research groups are involved in the use of biomass and wastes for the synthesis of new materials, motivated by the multiple advantages that these wastes show compared to petroleum products or other conventional sources. For instance, by-products from the agricultural industry has been used in order to obtain high value-added products according to the principles of green chemistry [1], or end-of-life vehicle waste has been used to produce photocatalysts [2].

With this in mind, the current doctoral thesis proposes the development of sustainable methodologies for the valorization of biomass and wastes through low energy and environmental impact techniques such as microwave, mechanochemistry and flow chemistry.

Indeed, over the last ten years, the use of alternative energies, such as microwaves, has been identified as a new methodology with the potential to intensify chemical synthesis in terms of energy efficiency. These innovative technologies are interesting partners with green chemistry towards sustainability [3-7]. In fact, the use of microwave irradiation allows to perform chemical reactions in a very short time, minimizing or suppressing side reactions, reducing solvents waste and energy consumption, using low volumes of solvents.

Mechanochemistry technique offers more promising paths than the conventional ones, allowing nanoparticles production and the accomplishment of reactions under solvent-free conditions and avoiding conventional heating and any addition of toxic reagents. Moreover, mechanochemical assisted protocols are less expensive and faster than traditional processes.

Lastly, flow-chemistry offers numerous advantages in good agreement with green metrics such as minimization of reaction times, reduction of waste production. Furthermore, this technology leads to achieve good yields and selectivities and is characterized by an outstanding cost and energy efficiency.

Specifically, the current doctoral thesis was aimed at the development of new materials derived from industrial wastes or biomass (such scrap waste automotive converter catalysts or pig bristles) and its applications through microwave heating, mechanochemistry and flow chemistry processes. In particular, new waste-based materials were synthesized together with transition metals. In all cases, various synthesis and reaction parameters were analyzed, with greater attention to times and performances, and with a special focus on the production of no toxic waste.