(40c) Design of Resin Polymers for the Adsorption of Metal Ions Using Computer Aided Molecular Design (CAMD)

Design of resin polymers for the adsorption of metal ions using computer
aided molecular design (CAMD)

AIChE Annual Meeting, Salt
Lake City, Utah, Nov. 8-13, 2015

For
submission to "Adsorbent
Materials"

Rajib Mukherjee and Urmila
M. Diwekar

Vishwamitra Research Institute,
Center for Uncertain Systems:

Tools for Optimization and Management
(VRI-CUSTOM),

2714 Crystal Way, Crystal Lake, IL
60012

Abstract:

            The
advancement and economic viability of vertical drilling technology has lead to
the expansion of gas production with hydraulic fracturing of sedimentary rocks
known as shale formations. A huge amount of water is used in the process. The flowback water from the process of hydraulic fracturing may contain a variety of formation materials, including
brines, heavy metals, natural occurring
radioactive material (NORM), and organics, which
can make wastewater treatment difficult and expensive. One of the easiest and
common practices for the removal of heavy metals and radionuclides from water is the use of ion exchange resin polymers.

            Commonly
occurring NORM in hydraulic fracking includes radium
and barium. NORM and other heavy metals can be removed using cation exchange resins by adsorption. The adsorption
mechanism depends on the difference in activities of NORM and other heavy
metals in adsorbents and the bulk fluid phase. The activity coefficients can be
obtained using the group contribution methods. In the present work, the
activity coefficient in the adsorbent resin polymers is obtained using group
contribution methods. For example, polystyrene
sulfonate is a cation
exchange resin. It
contains sulphonic acid functional group as cation exchanger. Other functional
groups can also act as cation exchangers includes carboxylic acid, phosphonic
acid, phosphinic acid, phenolic, arsonic acid, silinonic acid etc. that can act
as a strong acid or weak acid cation exchangers. Keeping the same polymer backbone,
different functional group for cation exchange shows different adsorption
capacity of the resin polymer. For the backbone polymer, other than polystyrene, different poly venyl
aryl compounds can also be used. The monomer units of the polymers can also be divided
into structural and functional groups with varied interaction parameters with
NORM and other heavy metals. Thus, the activity coefficient in a complex
adsorbent can be obtained using group contribution method.

            The
UNIFAC group contribution is generally used for different compounds. In case of
polymer, a free volume of polymer has been added. The
modified UNIFAC method is used for estimating activities of adsorbents in the
polymer phase. In our research, the interaction parameters of NORM and other heavy
metals with structural and functional groups obtained from different resin
polymers used as cation exchange resins are obtained
using the modified UNIFAC method. The
interaction parameters are found by solving an optimization problem where the
goal is to minimize the percentage error in the theoretical estimation of adsorption
with the experimental results obtained from adsorption isotherm.

            The interaction parameters and other group properties obtained
with modified UNIFAC group contribution method can be used in a computer-aided
molecular design (CAMD) methodology for optimal design of novel resin polymers
for NORM and other heavy metals removal.
In this work, optimal design of novel
polymer is solved as a mixed integer nonlinear programming problem. A new
algorithm called efficient ant colony optimization (EACO) is used to solve the
problem. The algorithm for CAMD of adsorption resin polymer design maximizes
the adsorption capacity of the adsorbent subject to structural feasibility,
thermodynamic property correlations, process conditions and process
constraints.

            In
this work we have developed a technology for the design of novel resin polymers
useful for the removal of heavy metals and NORM from water. Polymers can be
divided into structural and functional groups. The structural and functional
property of a polymer depends on these groups. We have used the adsorption
theory and develop new group contribution methods (GCMs) to predict interaction
properties of each group present in the adsorbents based on their
thermodynamics. We have also used a novel CAMD framework to design adsorbent polymers
with improved properties using properties of the structural and functional groups
that have been developed by the group contribution methods.