An interview with Darren Broom, product manager at Hiden Isochema, about the need for fast, accurate and reproducible laboratory gas and vapor sorption measurements using gravimetic techniques.
What does Hiden Isochema do?
Hiden Isochema manufactures instruments for measuring gas and vapor sorption by materials. Our instruments can determine both kinetics and thermodynamics, so that both the rate and total quantity of gas or vapor taken up by a material can be determined. Gases of industrial importance include hydrogen, nitrogen, methane, and carbon dioxide, while vapors include water and various organic compounds, such as benzene, toluene, and xylene.
Most of our instruments use the gravimetric technique. This means they determine the amount of gas or vapor absorbed or adsorbed by a material by measuring its weight change in response to exposure to a pressure of the species of interest. To do this, the weight must be measured very accurately, and this typically involves using a microbalance, which can measure microgram changes in the sample weight, as a function of time.
What type of practical industrial applications might Hiden Isochema instruments be used for and what data can be obtained?
The design and development of gas separation and purification processes is a very good example of an industrial application that our instruments can be used for. When using adsorption to separate gases – for industrial gas production, for instance – the most common processes are pressure swing adsorption (PSA) and temperature swing adsorption (TSA). Chemical engineers design the processes used industrially by combining the results of simulations and pilot plant testing. Such process design includes the selection of a suitable adsorbent – the material used in a separation column – and the most important information for gas separations is the amount of each gas adsorbed by the adsorbent as a function of temperature and pressure. This information can be provided by our instruments. It is also critical for process simulation. Without accurate input data, a simulation will itself be inaccurate.
What are the needs of your industrial customers when it comes to these instruments?
Chemical engineers require methods of quickly and easily measuring gas and vapor sorption, so that they can assess adsorbents for new processes. Accuracy is certainly important, but increasing sample throughput would be highly desirable in most cases. However, it really does depend on the customer. In research and development applications, flexibility – allowing the operator to make the measurements they require – is probably more important than ease of use. Of course, an instrument should always be relatively easy to use, but “push button” operation is of little use, in more demanding applications, if the instrument will then only perform a fixed set of measurements. On the other hand, one of our instruments, the IGAsorp Dynamic Vapor Sorption (DVS) analyzer, is widely used in quality control applications in the pharmaceutical industry. In this case, push button operation, ease of use, and the reliability and repeatability of the method and measurements are probably the most important priorities.
What are the challenges associated with measuring gas and vapor sorption in the laboratory?
Gravimetric gas and vapor sorption measurements are very simple in principle – they just involve measuring the weight change of a sample exposed to a defined pressure of gas or vapor. In practice, however, achieving high accuracy is a challenge; because results can be affected by the way the material is prepared for the measurement, by impurities in the gas or vapor supply, and by temperature measurement accuracy and stability. Measurements can also be rather time-consuming, particularly if the sorption kinetics – the rate at which the gas or vapor adsorbs – are slow. Speeding up the measurement process, while maintaining high accuracy, is therefore one of the most significant challenges for pure gas (single component) sorption measurements.
Another difficulty is ensuring the compatibility of gas and vapor sorption instruments for use with a range of different species. Hydrogen, for example – an industrially important gas – can attack or embrittle certain metals, including steels, under particular conditions of temperature and pressure. Gas handling component selection for instruments designed for hydrogen sorption measurement is therefore important and can restrict their operating range. Perhaps even more significantly, corrosive species can attack microbalance components, so this poses a challenge that requires special microbalance designs.
Most of our instruments are used to measure pure gas or vapor sorption. For separation applications, however, measuring the adsorption of mixtures of different gases is also important, and this is significantly more difficult. Measurements are usually laborious and require relatively large samples. Hiden Isochema has recently developed a new technique for this, which we call the Integral Mass Balance (IMB) method. This reduces measurement times and provides high accuracy measurements on relatively small samples.
What recent developments has Hiden Isochema made and how have they helped address some of the above challenges and needs?
One of our most significant developments in recent years was probably the introduction of the XEMIS. This is a gravimetric gas and vapor sorption analyzer that can operate up to gas pressures of 200 bar, but also with a number of toxic or corrosive species, including SOx, NOx, and ammonia. To do this, we developed a new type of microbalance that uses a conventional beam balance configuration, for measurement stability; however, all the sensitive detection and control mechanisms are mounted outside the chamber, so they cannot be attacked by the corrosive atmosphere.
Species compatibility is a key component of the flexibility of a sorption instrument, but some corrosive species are also of significant interest in gas separation and purification applications. If a gas or vapor can attack some of the components in a sorption instrument, then they are also likely to be harmful to humans, the environment, and industrial equipment. Methods of removing them from gas streams – using adsorption, for example – are therefore likely to be a focus in the chemical industry.
The other development is our recent introduction of the Integral Mass Balance (IMB) method for measuring multicomponent gas adsorption. This uses a new model in our IGA range of gravimetric sorption analyzers, the IGA-003-MC. Measuring multicomponent gas adsorption continues to be a challenge, even though such data are critical to the development and design of gas separation and purification processes. The IMB method allows the rapid, accurate measurement of binary gas adsorption isotherms on relatively small samples of only a few grams and is unique to Hiden Isochema instruments.
Where can our readers go to find out more?
For further information, please contact the Hiden Isochema sales and application team ([email protected]).
About Darren Broom
Darren Broom is a product manager for Hiden Isochema. He obtained a PhD in materials physics in 2002 from the University of Salford, UK, and then spent three years as a postdoctoral research fellow at the European Commission’s Institute for Energy in the Netherlands, working on hydrogen storage materials. He then returned to the UK to join Hiden Isochema in 2007.
In 2011, Springer published his book on the characterisation of hydrogen storage materials, and he has since broadened his interest in the analysis of gas-solid interactions to include the characterisation of porous adsorbents for gas separations.
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