Gas–liquid–liquid–solid
(GLLS) reaction systems
are often encountered in manufacturing of fine and specialty chemicals.
More often than not, such reaction systems involve multiple reactions,
and selectivity toward the desired component always poses challenges.
An adequate understanding of various parameters affecting GLLS reactor
performance is essential to develop strategies for realizing desired
selectivity. In this work, a comprehensive reaction engineering model
for simulating four phase hydrogenation reactions has been developed.
A generalized mixing cell based framework for a reaction system with
four interacting phases (gas [G], aqueous [L], organic [L], and solid
catalyst [S]) was developed. The model is written in a general way
so as to specify one of the liquid phases as a continuous phase, and
the other three phases are dispersed into it. In each cell, vapor
space is included. The model includes the possibility of evaporation
of solvent and internal condensation (in vapor space). The model can
also be applied for a dead end (from a perspective of reacting gas)
reactor. Model equations were solved using MATLAB. The equations and
solution methodology were verified by comparing numerical solutions
with available solutions of various limiting cases. A case of four
phase hydrogenation of nitrobenzene to para amino phenol and aniline
was considered to illustrate the application of the developed model.
Key findings from the model were validated by comparing with laboratory
scale experimental data. The model was then used to develop insights
and guidelines for enhancing selectivity toward desired product. The
developed model and presented results will be useful to develop general
guidelines for design and optimization of GLLS reactors.