(394d) Process Intensification Via Thin Film Evaporation for Simultaneous Reaction and Separation in Dispersants Production

Process intensification (PI) aims to drastically improve the efficiency of chemicals manufacturing, while reducing emissions and minimizing costs. One of the ways of achieving PI is to combine reaction and product separation steps into a single unit operation thereby improving the conversion and yield, and at the same time reducing the overall cost and footprint of the system. In this study we demonstrate the use of an agitated thin-film evaporator (TFE) for simultaneous dehydration and reaction in a continuous process for dispersant production. This is part of a larger effort in which we are exploring the batch-to-continuous transition in specialty chemicals production.

In the process of interest, dispersants are produced via reaction between poly-isobutylene succinic anhydride (PIBSA) and various polymeric amines. The reaction occurs via two steps: first the amination of the succinic anhydride to produce an intermediate amide, followed by the dehydration of the amide to the final succinimide product and water. In the industrial batch process, both reaction steps occur in the same reactor at conditions above the boiling point of water, and water vapor is hence continuously purged from the head space of the batch reactor. Our prior kinetic analysis had shown that the overall process is controlled by mass transfer, i.e. by the slow evaporation of water from the very large batch volume (typically 1,000s of gallons). In contrast, the absence of a purged head space in a continuous tubular reactor results in significant equilibrium limitations for the dehydration step, increasing the demand on water removal in a subsequent drying step. Hence, design of an efficient, continuous water evaporation step is a key requirement for successful transition from batch to continuous processing.

Among the options for continuous water evaporation, thin film evaporators (TFE) are particularly well-suited for the high-viscosity liquids typical for dispersant production. In TFE, blades of a spinning rotor result in formation of a thin film on the inner surface of a heated cylinder. The turbulent liquid film enables very high heat transfer from the outer surface to the liquid, as well as a large liquid-vapor interfacial area for evaporation, i.e. it simultaneously overcomes heat and mass transfer limitations faced by conventional evaporators.

In the present study, we develop performance models to analyze the use of a TFE to remove water from the product stream of a continuous flow reactor for dispersants production. Since water evaporation in the TFE simultaneously pushes the dehydration reaction to completion, reaction kinetics are coupled with mass and energy balances. The model incorporates physical properties (specific heat, viscosity, density, thermal conductivity etc) of the reacting species, operating conditions (pressure, temperature, rotor speed), reactor geometry and reaction kinetics to predict conversion, yield and water removal in the TFE. Correlations for heat and mass transfer coefficients are adapted from literature and validated experimentally. This performance model will be used to evaluate a configuration in which the continuous tubular reactor is completely replaced by a TFE unit to assess the efficiency of utilizing a TFE directly as a separative reactor. To our knowledge, the potential of using TFE as a reactive distillation unit has been little explored to-date. The results of the modeling study will be used to identify ranges of design and operating conditions that are promising for TFE utilization in continuous production of dispersants.