Introduction
Gas
sorption analysis is important in many fields of materials science and consumer
product development. Some examples of current hot areas of technology involving
gas-solid (or gas liquid) interactions include the development of energy
storage materials, improved catalysts for petrochemical processing, advanced
pharmaceuticals and food industries. At present, there is tremendous interest
in the development of innovative materials for the transition to renewable
energy. The science of gas sorption has become particularly critical in the
advancement of materials for storing fuel gases such as hydrogen or natural
gas, as well as for sequestration of greenhouse gases. Some exciting prospects
for the chemical storage of gases include high-surface area and nanomaterials
(graphitic carbons, CNT, zeolites, Metal-Organic-Framework MOFs). In the field of hydrogen-storage, a
host of novel materials are being developed including high-pressure
metalhydrides, light-weight complex hydrides, destabilized multicomponent chemical
hydrides and amides, and other crossover materials such as ammonia borane
encapsulated into mesoporous silica scaffolding.
Of
prime interest in the discovery of these and many other new materials is the
characterization of gas absorption, adsorption and desorption kinetics,
capacity, thermodynamic properties, as well as cycling performance of
reversible materials. Also important is the ability to measure the tolerance of
catalyst, chemicals, and consumer products to air, moisture and low-level contaminants.
These wide-ranging requirements and the need to perform analysis at both a
research and a production level (milligrams to kilograms) have driven the
development of the H-Sorb 2600,
the ultimate tool for gas sorption analysis.
Careful
analysis of physical and chemical interactions between gases and solids (or
liquids) require extremely precise measurements. Several techniques are
employed for gas sorption measurements the most common of these being
gravimetric and volumetric methods. In volumetric methods the amount of gas
sorbed is typically determined by a change in pressure within a calibrated
volume containing the sample. In gravimetric methods, the amount of sorbed gas
is determined by measuring the apparent mass change of the sample. In
volumetric methods, the amount of gas sorbed is typically determined by a
change in pressure within a calibrated volume containing the sample. We believe
the volumetric method offers several distinct advantages over the gravimetric
method, and of the volumetric instruments available, the Gold APP Instruments
H-Sorb 2600 offers the best state-of-the-art measurements.
The Volumetric Method
One
of the most common and versatile types of volumetric instruments is the
Sieverts Apparatus. Simply put, a Sieverts Apparatus is an instrument
containing two reservoirs of known volume connected by an isolation valve, as
shown in Figure 1. The sample for
measurement is loaded into the sample volume and the initial pressure reading
is taken. For absorption the reservoir is filled with the sorption gas to a
predetermined pressure above that of the initial pressure in the sample volume.
The isolation valve between the two volumes is opened and the gas is allowed to
equilibrate between the reservoir and sample volume. By knowing the initial gas
pressures and the volumes of the system, the quantities of absorbed or desorbed
gas can be determined.
Figure
1. Schematic of a Sieverts Apparatus.
By
applying the Sievert’s approach to a system using a wide range of calibrated
volumes, advanced pressure control, pressure measurements, and temperature
control, it is possible to make a full suite of analyses with one device. Such
analyses include:
Capacity
The
total amount of gas absorbed or desorbed by a sample is pressure and
temperature dependent and therefore requires precise measurements of both. In
the volumetric method, capacity is directly related to pressure change. Small
amounts of impurities in the test gas may be strongly absorbed by the sample.
This can be very problematic in gravimetric methods as this uptake can cause
significant weight change that might be misinterpreted. In the volumetric
method, low levels of impurities may impact the performance of the material,
but will not produce significant pressure changes.
Kinetics
Kinetics
consists of the dynamic measurement of the change in moles of sorbed gas versus
time. An advanced sorption analyzer should consist of multiple reservoirs with
a wide range of volumes to match sample size and a wide range of sorption
conditions associated with each different type of material. Additionally,
sorption reactions generally involve significant endothermic or exothermic
reactions. Heat transfer from the sample is a critical aspect of proper
kinetics measurements. In a gravimetric instrument the sample is suspended from
a microbalance that does not allow direct contact of temperature measuring
probes or provide good heat transfer, limiting its usefulness.
Pressure-Composition
Isotherms
Pressure-Composition
Isotherms (PCT or PCI) is one of the most informative sorption measurements.
The result is a plot of the equilibrium absorbed gas concentration in the
material as a function of pressure and temperature.
The
volumetric approach to PCI measurements consists of adding (or removing) gas to
the sample volume in a small dose from one of the calibrated reservoirs and
waiting for the resulting gas/solid equilibrium. The PCI curve is produced from
the concentration of gas sorbed and the final pressure of each dose in a series
of many doses that either increase (absorption) or decrease (desorption) in
pressure. This is essentially a gas titration process.
The
PCI plot will typically show an equilibrium plateau associated with the
co-existence of the remaining unreacted material and the gas-reacted material,
thus providing a complete phase diagram. For example, metal hydride materials
that reversibly react with hydrogen show a well-defined plateau between the
solid solution a-phase, where
hydrogen is randomly dissolved within the solid matrix, and the b-phase, where hydrogen is in distinct
structural sites and has bonded to the host solid material. In addition, precise dosing PCI
measurements can provide detailed information on the presence of crystal
structure changes, new phases and sorption kinetics as a function of gas
concentration.
H-Sorb 2600 high pressure gas adsorption parameters
Analysis
Method: static volumetric, high pressure gas sorption
Versatility:
adsorption/desorption isotherms measurement (cryogenic to 500℃), Gibbs supercritical adsorption measurement
Data
Reduction: Langmuir model regression isotherm,
PCT(Pressure-Composition-Temperature) diagram/curve/isotherm measurement,
Langmuir maximum adsorption constant L and adsorption pressure constant B
measurement; Langmuir correction model loading-ratio correlation regression
(LCR) isotherm; Ono-Kondo (OK) lattice model isotherm regression; adsorptive
gas density and vapor-liquid equilibrium accuracy calculation under different
pressures and temperatures
Measuring
Ranges: continuous adsorption and desorption measurement from normal to 200Bar
pressure
Accuracy:
repeatability errors <3%
Temperature
Range: cryogenic to 500℃, accuracy±0.1℃
Sample
Ports: two samples analyzing and two degassing, stainless-steel micro welding
sample cells, software integrated temperature PID adjustment
Transducer
Accuracy: imported high precision transmitter, accuracy can reach 0.05% of F.S.
(full-scale), long-duration usage stability is 0.025% of F.S.
Ultimate
Vacuum: 4x10-2 Pa (3x10-4 Torr), molecular pump system (1x10-6 Pa) is optional
Adsorbate
Gas: high purity nitrogen, CO2 or others (Ar, Kr, H2, CH4 etc.)
Data
Acquisition: high-precision and high integration data acquisition modules,
minimal error, strong anti-interference ability
Specifications:
Height 22.05 inches (56cm)* Width 20.87 inches (53cm)*Depth 23.62 inches
(60cm); 132 pound (60kg); 220V/5A
H-Sorb 2600 high pressure gas adsorption features:
Control System: imported VCR
interface high pressure pneumatic valve can realize auto on-off within 200Bar,
sealing performance is top to 1x10-10 Pa.m3/s, can be used more than 500
million times; programmable logic controller (PLC) system, high integration and
sound anti-interference, improve stability and prolong life
Analysis Management: parameters
be set by software, fully automated, unattended operation at night; H-Sorb mode
is available for accurate control gas charging pressure points, gain ideal data
points
Manifold System: imported 316L
stainless steel thick-walled manifolds, micro welding sealing can reduce dead space
largely; metal VCR connection is convenient for installation and uninstallation
Safety
Measures: H-Sorb asymptotic technology realizes auto gas-charging and
degassing, prevents high pressure dangers caused by artificial misoperation,
and also minimizes large differential pressure’s impact to pressure transducer
Our
policy of continuous development may cause the information and specifications
contained herein to change without notice or liability.
