PNNL-13501 - Pacific Northwest National Laboratory

Study Control Number: PN00065/1472
Microchannel Distillation
Ward E. TeGrotenhuis, V. Susie Stenkamp
The Department of Energy has established goals for the chemical industry to reduce by 30% material use, energy
consumption, water consumption, toxic dispersion, and pollution dispersion. Advances in distillation technology are
critical for achieving these goals, because distillation is the most often used technology for separations in the chemical
process industry. Microchannel distillation may substantially reduce the size of equipment and improve energy
efficiency.
Project Description
The objective of this project was to evaluate the
feasibility of microchannel distillation devices using
proof-of-concept testing and predictive modeling. These
devices have the potential to significantly reduce the
energy and the size of equipment needed to produce a
wide array of chemicals and fuel. A test device was built
and charged with a mixture of acetone and methanol and
operated in total reflux mode. The temperature profile
along the length of the heat pipe and the operating
pressure were measured and used to determine
composition profiles at different heat inputs. Vapor and
liquid equilibrium curves were subsequently used to
calculate the number of theoretical stages and the height
equivalent of a theoretical plate. Results indicate a
substantial reduction in the height equivalent of a
theoretical plate over commercially available advanced
structured packings. Progress was also made in
developing a predictive model and initial designs were
developed for incorporating the concepts into high
interfacial area, multi-channel microchannel devices.
Introduction
For several years, Pacific Northwest National Laboratory
has been developing microchemical and thermal systems
that are compact and efficient in comparison to
conventional process technology.
The typical order of magnitude or more reduction in
hardware volume and mass over conventional technology
is achieved through rapid heat and mass transfer rates that
can be accomplished in microchannel devices. The
potential for reduced capital and operating costs over
conventional distillation technologies due to reduction in
equipment size and improved thermal efficiency would
have a dramatic impact on the petrochemical industry.
The key aspects for demonstrating microchannel
distillation capability are to achieve high mass transfer
efficiency between counter-flowing gas and liquid
streams while providing means for condensation and
reboiling.
Results and Accomplishments
Distillation was successfully demonstrated within the heat
pipe configurations that were built and tested, thereby
establishing the capability for microchannel distillation.
Axial temperature profiles are shown in Figure 1 for a
range of heat inputs. The starting composition was
5 mol% acetone in a mixture of acetone and methanol and
the device was operated in total reflux mode. Assuming
constant pressure along the length of the device and
assuming the gas and liquid are at equilibrium at the
measured temperatures, composition profiles are
constructed from the vapor-liquid equilibrium curve.
Composition profiles are shown in Figure 2 for the
temperature profiles shown in Figure 1. Finally, the
degree of separation, as determined from the composition
profile, is used to calculate the number of theoretical
stages that when divided into the length gives the height
equivalence of a theoretical plate. Figure 3 gives the
number of theoretical stages and the height equivalence as
a function of heat input.
The results indicate there exists optimal heat input where
the maximum separation of components is achieved.
Values achieved for height equivalence within the devices
tested as represented by Figure 3 are 4 to 10 times smaller
than commercially available advanced structured packed
columns (Humphrey and Keller 1997) shown in Table 1.
Separations and Conversions 427