erosion in this area. Instead, increased frequency
and extent of glacially dammed lakes (11) may inhibit exhumation and therefore cooling rates, potentially explaining this inverse trend.
Although the effect of climate cooling on surface processes during the Quaternary has been
documented, validation of an influence of surface
processes on tectonics remains elusive. Using multi-OSL thermochronometry of feldspar, we modeled
sub-Quaternary cooling rates of the Namche
Barwa massif. The data are inconsistent with a
spatially stationary model of exhumation for the
massif, which has been proposed to reflect feedbacks between river incision and tectonics (6).
Instead, our data support a continued northeastern
migration of exhumation (22). These results demonstrate that although surface processes and tectonics
may appear to be tightly coupled, stream power has
not necessarily engaged in a positive feedback
with tectonics in pinning the locus of exhumation
within the core of the eastern Himalayan syntaxis.
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This research was funded by Swiss National Fund grants PP00P2-
38956 and 200021-127127 and Netherlands Organisation for
Scientific Research (NWO) Veni grant 863.15.026. R. Lambert,
P. Valla, S. Willett, and O. Korup are thanked for insightful
discussions. J.-P. Burg is thanked for providing samples and
feedback. All of the raw data are available in the supplementary
materials. The comments of three anonymous reviewers
substantially improved the manuscript.
Materials and Methods
Figs. S1 to S22
Tables S1 to S10
Databases S1 to S64
15 January 2016; accepted 28 July 2016
Reverse osmosis molecular
differentiation of organic liquids using
carbon molecular sieve membranes
Dong-Yeun Koh,1 Benjamin A. McCool,2 Harry W. Deckman,2 Ryan P. Lively1*
Liquid-phase separations of similarly sized organic molecules using membranes is a major
challenge for energy-intensive industrial separation processes. We created free-standing
carbon molecular sieve membranes that translate the advantages of reverse osmosis
for aqueous separations to the separation of organic liquids. Polymer precursors were
cross-linked with a one-pot technique that protected the porous morphology of the
membranes from thermally induced structural rearrangement during carbonization.
Permeation studies using benzene derivatives whose kinetic diameters differ by less
than an angstrom show kinetically selective organic liquid reverse osmosis. Ratios of
single-component fluxes for para- and ortho-xylene exceeding 25 were observed and
para- and ortho- liquid mixtures were efficiently separated, with an equimolar feed
enriched to 81 mole para-xylene, without phase change and at ambient temperature.
Molecular separation processes are essen- tial in the production of clean water, pharmaceuticals, commodityand spe- cialtychemicals, andfuels. Approximately 40 to 60% of the energy used in the
production of these materials is spent on separation and purification processes (1). In downstream chemical processes, selective removal of
high-value alkyl-aromatics is required for the production of synthetic fibers, solvents, and films and
is performed with energy-intensive techniques
such as crystallization and simulated moving
bed adsorption (2). The separation of xylene isomers is especially challenging because of the
similarities in physical properties [i.e., boiling
point, molecular weight, and kinetic diameters
(3)]. Membrane-based processes may reduce the
energy intensity of these separations if effective
separation materials can be developed.
Organic solvent nanofiltration has emerged as
a separation process for purification of liquid
organic solvents from high-value products such
as pharmaceuticals (4). However, organic solvent
nanofiltration membrane materials do not have
the necessary molecular specificity to efficiently
separate molecules of similar size. Thus, we ex-
plore the potential for organic solvent reverse
osmosis (OSRO) using asymmetric carbon molec-
ular sieve (CMS) hollow fiber membranes.
CMS membranes possess molecularly sized
slit-like transport pathways that are provided
by the disordered two-dimensional (2D), sp2-
hybridized carbon structure (figs. S1 and S2 and
table S1). These result in higher productivity
than that of cage-like zeolite structures while
providing similar molecular selectivities (5–8).
Selectivity is the driving-force–normalized rela-
tive ratio of the mass transport rates of different
molecules permeating through the membrane
(see eqs. S1 to S16 for discussion on the devel-
opment of the selectivity eq. S17) and is considered
to be an intrinsic property of the membrane. The
term “separation factor” is an engineering param-
eter often used in membrane separation processes
and is the ratio of permeate composition over
the feed composition (eq. S18) (9). CMS mem-
branes have proved effective at reducing energy
1School of Chemical and Biomolecular Engineering, Georgia
Institute of Technology, Atlanta, GA 30332, USA. 2Separations
and Process Chemistry, Corporate Strategic Research, ExxonMobil
Research and Engineering, Annandale, NJ 08801, USA.
*Corresponding author. Email: email@example.com