Research Projects

Continuous manufacturing in fine and specialty chemicals and pharmaceutical industry has gained significant attention over the last decade or so. It offers excellent advantages viz. rapid synthesis, consistent product quality, high efficiency over batch operation amongst many others. During the synthesis of several specialty chemicals and intermediates, the amount of solvent used is 20 - 100 times the product mass. This also implies that for making a process economical and environmentally feasible the solvents need to be recycled and reused, which is an energy intensive operation and 5% of solvent is lost in every cycle. Since a large quantity of solvents is needed to keep the reactants in dissolved conditions, the effective volume of the reactor reduces significantly if the solvents are eliminated. To obviate these issues, it is necessary to carry out reactions in near solvent free conditions in continuous mode of operation, also known as reactive extrusion using screws (single or twin type) that can handle even viscous and sticky mass. Despite the robustness of the screw for extrusion kind of applications, the reliable design approach for carrying out reactions (endothermic or exothermic single phase or multiphase reactions) and subsequent scale-up remains a knowledge gap. Over last 4 years, a large number of published reports are seen in the area of mechanochemical synthesis with some excellent papers on batch mechanochemistry using various mills well as a few papers on continuous mechanochemistry. The initial results are encouraging and clearly support an important way towards sustainable manufacturing, where one minimizes or avoids the use of solvents completely. The project will explore the following: (i) Effect of various screw designs (single screw and twin-screw) on transport coefficients (mixing, mass & heat transfer) in different orientations. (ii) The effect of particle property variations on transport coefficients and reaction rates. (iii) Develop a detailed understanding on the validity of Arrhenius equation for solid-phase reactions to correlate rate and energy as the present formulation assumed collision at molecular scale. (iv) Understanding mixing in such systems is complex, especially, when the reacting particles are not similar in terms of size and shapes. This becomes the most important part when the reaction is needed to be carried out with mixtures of two or three different particle sizes and moreover in exact stoichiometric ratios. (v) Develop a detailed understanding of the mean residence time on the screw design and screw rotation speed. (vi) Develop a quantitative data and design approach for predicting the influence of the design parameters on the overall conversion and yield for specific reactions (viz. aromatic nitration of naphthalin, fluorination with KF or TBAF, chlorination of solids with thionyl chloride, diazotization using diazonium salts etc.) at 3 different scales of operation.