This webpage contains three tabs
HOME (this page):
- How this method works (physical chemistry).
- How it can be used within distillation.
- A list of chemical mixtures, which can be distilled using this method.
- Refrigerants are oftenly mixtures of chemicals. Some refrigerants are azeotropic. This distillation method (using a pressure sensitive azeotropic mixture) could potentially also be used in refrigeration cycles (refrigerators, freezers and heat pumps).
As the spectrum of acceptable refrigerants from time to time is revised (global warming potential, ozone depletion potential, ...), giving (future) pressure-sensitive azeotropic refrigerants a thought could be of interest.
Please find, in the refrigeration tab, an image describing how it could be used in refrigeration cycles.
It is possible to shift/move (and possibly even remove) a pressure-sensitive azeotrope in a single volume without adding any entrainer.
From pressure-swing distillation (PSD) of azeotropes, it is known that a pressure-sensitive azeotrope changes composition as the dew pressure changes. In PSD, the dew pressure is set to be the distillation column total pressure and the dew pressure is changed by using two columns running at two different pressures.
In this new distillation method, an inert gas, e.g. CO2, N2, a noble gas, a superheated hydrocarbon, e.g. methane, is introduced and the distillation is carried out in a single column.
P(total) = P(dew) + P(inert gas)
Hence, the total pressure can be substantially constant throughout a column, while P(dew) can be chosen according to vapour-liquid equilibrium (VLE) data in order to break the azeotrope.
T(reboiler) is determined by vapour-liquid equilibrium (VLE)
T(condenser) is determined by vapour-liquid equilibrium (VLE)
...lower distillation heating and cooling temperatures are required. Thus, waste heat instead of high temperature quality heat can be used, which means...
... (profitability) - lower operating costs
... (sustainability) - possibly lower high quality energy consumption
As no entrainers are used in this method for distilling azeotropes, no traces of entrainers will remain in the customer's end product. This may come in handy when the customer needs an ultra-pure chemical e.g. for use in the food industry or for a chromatographic chemical analysis method.
COLUMN DESIGN PRESSURE
This method is very suitable for distillation of azeotropes at dew pressures lower than atmospheric pressure. The column total pressure can still be kept atmospheric. The column design pressure can thus be adapted to this.
PRESSURE-SWING DISTILLATION (PSD) @ VERY LOW PRESSURE (VLP)
Pressure-swing azeotropic distillation requires one low pressure (LP) and one high pressure (HP) column to circumvent an azeotrope. This new distillation method allows PSD to be carried out using:
- one very low pressure (VLP) column @ sub-ambient pressure
- one medium pressure (MP) column.
[Annual Saving] =
= [Total Annual Cost(normal PSD)] - [Total Annual Cost(VLP-PSD)] =
= [Capital cost(normal PSD) + Operating cost(normal PSD)]
- [Capital cost(VLP-PSD) + [Operating cost(VLP-PSD)]
- Very low pressure (VLP) and medium pressure (MP) columns require lower design pressures, thus less stringent requirements.
- Bigger diameters are needed for VLP/MP columns compared to LP/HP columns.
- A pipe, a compressor and heat exchange means to recuperate heat is needed for the circulating inert gas.
- very low pressure (VLP) and medium pressure (MP) columns are better at using waste heat.