(601d) Relay Simulated Moving Bed Chromatography: Concept and Design Rules

Relay Simulated Moving Bed Chromatography:
Concept and Design Rules

Jose P. B. Mota

Requimte/CQFB, Departamento
de Quimica, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa,
2829-516 Caparica, Portugal

Corresponding author email: pmota@fct.unl.pt

We present a new class of multicolumn chromatographic processes
that change the classical way of handling the product outlets of simulated
moving-bed (SMB) chromatography to avoid the use of flow controllers or an
extra pump—the objective is to have just two- or three-way valves at a
column outlet—while maintaining the analogy with the SMB in terms of
displaced volumes of fluid per switch interval. In this class of processes the
flow through a zone (or column) is always in one of three states: (i) frozen, (ii) completely directed to the next zone (or
column), or (iii) entirely diverted to a product line. We use the term relayed stream to refer to this particular type
of manipulation of the outflow from a column.

For this class of processes we derive a SMB analog—the R-SMB
process—and demonstrate, under the framework of the equilibrium theory,
that this process has the same separation region as the classical SMB for
linear adsorption systems. In addition, the results from the equilibrium theory
show that the R-SMB process consists of two distinct cycles that differ only in
their intermediate sub-step (Fig. 1): one cycle (R-SMB^-) for values of the selectivity, α, smaller than (3 + 5^1/2)/2
and another cycle (R-SMB⁺) for larger values of α; in the
former case no product stream is collected during the intermediate sub-step,
whereas in the latter case both product streams are collected. The selectivity
is defined as α = V₂/V₁, where V_i = [ϵ + (1-ϵ)K_i]V, ϵ is the bed porosity, K_i is the Henry constant of
component i
and V is the column volume.

We also examine the R-SMB process under conditions of finite column
efficiency and compare its performance against those of the classical open- and
closed-loop SMBs. Our simulation results (Fig. 2) show that the R-SMB process
requires less desorbent and is more productive than
the standard SMB processes under conditions of finite column efficiency and
that the comparison increasingly favors the R-SMB as the column efficiency
decreases. We provide an experimental proof-of-concept for two linear
separation problems.