# Amine-Appended Hyper-Crosslinked Polymers for Direct Air Capture of CO2

## TL;DR

This paper introduces a new type of polymer for capturing CO2 from the air, which could help reduce climate change by improving the efficiency of CO2 capture technologies.

## Contribution

The study demonstrates how varying polymerization duration affects pore structure and CO2 capture performance in hyper-crosslinked polymers.

## Key findings

- Reduced polymerization duration increases accessible micropore volume and CO2 uptake.
- The best sample achieved an equilibrium CO2 uptake of 0.43 mmol/g at 400 ppm and 298 K.
- The new adsorbent showed a CO2 sorption kinetics 5.5 times faster than the benchmark Lewatit VP OC 1065.

## Abstract

Capturing CO2 from the ambient atmosphere
is a promising
method to reduce the impact of climate change. Fast deployment and
scale-up of adsorption-based direct air capture (DAC) technologies
are needed to meet the IPCC target and rely, in part, on the development
of efficient and scalable low-cost adsorbents. While a benchmark DAC
adsorbent, the polymeric resin Lewatit VP OC 1065, has been established,
the reasons behind its performance and the potential for further optimization
remain largely unknown. Indeed, a fundamental understanding of the
relationship between adsorbent pore structure, chemistry, and DAC
performance, both equilibrium and kinetics, has yet to be formulated.
Here, we have built on the chemistry of Lewatit and synthesized a
hyper-crosslinked polymer (HCP) by grafting a microporous chlorine-functionalized
support with diethylenetriamine. We produced four different adsorbents
by varying the polymerization duration between 10 min and 19 h to
assess the impact of pore structure on CO2 uptake at 400
ppm. Reduced degrees of polymerization (i.e., shorter polymerization
durations) resulted in higher accessible micropore volume and consequentially
increased CO2 uptake and amine efficiency. The best sample
achieved an equilibrium uptake of 0.43 mmol/g (400 ppm of CO2, 298 K), which is about half that of the benchmark adsorbent Lewatit
VP OC 1065. We have then assessed the CO2 sorption kinetics
of this sample (grain size of 24–74 μm) at 400 ppm and
303 K using a gravimetric technique and have compared the results
to those of other amine-grafted polymeric adsorbents. We measured
a lower bound linear driving force constant (k
LDF) of 0.0120 ± 0.0004 s–1. This value
is 5.5 times faster than that of the benchmark adsorbent Lewatit VP
OC 1065 with the same grain size of 24–74 μm, highlighting
the importance of macropore diffusion in addition to the CO2 reaction kinetics. This study shows how synthesis operating conditions
alter the pore structures and adsorption behavior of porous polymers
and provides the foundation to design better and faster DAC adsorbents.