(690c) Structure H Hydrate Formation with Lmgs and CO2, in Ice and Water

Structure
H hydrate formation with LMGS and CO₂,
in Ice and Water

Namrata
Gaikwad¹,
Omkar S. Kushwaha¹,
Praveen Linga³,
Jitendra Sangwai²,
Rajnish Kumar¹*

¹
Department of Chemical Engineering, Indian Institute of Technology,
Chennai, 600036, India

²
Department of Ocean Engineering, Petroleum Program, Indian Institute
of Technology, Chennai, 600036, India

³
Department
of Chemical and Biomolecular Engineering, National University of
Singapore, 117585, Singapore

Corresponding
author: rajnish@iitm.ac.in

Keywords:
Gas
hydrates, CO₂
Capture, CH₄
Storage, Hydrate Kinetics, Hydrate Dissociation.

Abstract

Van
der Waals radius of carbon dioxide molecules are significantly larger
than methane and thus it is a reluctant help gas for sH hydrate
formation. A successful attempt has been made to form structure H
(sH) hydrate at low pressure from four different types of experiments
in ice and water by employing methane and carbon-dioxide as a small
molecule guest substance (SMGS) and polar tert butyl methyl ether
(TBME) and hydrophobic cyclo-octane as a large molecule guest
substance (LMGS). One of the ideas was to use different LMGS such
that the effect of oxygen molecule containing LMGS which are slightly
polar could be studied with those LMGS which are completely
non-polar. Type-1 experiments were carried out to study the kinetics
of sH hydrate formation and dissociation for methane as SMGS for two
identified sH formers at 274K. Type-2 experiments were performed to
study the kinetics of carbon dioxide sH hydrate formation and
dissociation at 274K i.e, sH hydrate formation with liquid water,
such data are very rare in literature! Type-3 experiments were
studied to understand the formation and dissociation kinetics for
carbon dioxide sH hydrate at 266K, the literature suggests that sH
hydrate formation with CO₂
and LMGS is possible only at sub-zero temperature, i.e., with solid
water. Type-4 experiments were done to study the effect of driving
force on carbon dioxide sH hydrates formation in ice at 266K.
Experimental data on avg. gas uptake, water to hydrate conversion,
kinetics of methane and carbon dioxide sH hydrate formation and
dissociation at low pressure has been obtained. This study shows that
kinetics of gas uptake and water to hydrate conversion depends on the
type of LMGS and driving force used. Experiments with TBME as a LMGS
have shown higher gas uptake and rapid hydrate formation for methane.
However, the rate of hydrate growth for CO₂
hydrate was faster with TBME in ice and cyclo-octane in water. It is
observed that CO₂
molecules interact strongly with TBME in the liquid phase which might
be acting as an inhibitor in the formation of hydrate. The system
containing TBME as a LMGS has displayed a higher dissociation rate
compared to cyclo-octane for both methane and carbon-dioxide gas.