Vapor Pressure Measurements of Pentane at Low Temperatures (-160 ºC to -50 ºC) using Cost-Effective Equipment

Abstract

Certain extraterrestrial environments like ocean worlds and icy satellites, are promising astrobiological places that can host a plethora of organic compounds trapped in their ices. The vapor pressure curves derived from theoretical calculations and experimental measurements aid in the construction of phase diagrams, which can help us better understand the behavior of organic molecules under the extraterrestrial conditions that aren’t found on Earth. In this work, a novel method was developed to measure vapor pressures at low temperatures (-160 ºC to -50 ºC) using cost-effective instrumentation. Following the development of the approach, vapor pressure of n-pentane was measured at temperatures ranging from -160 ºC to -50 ºC. Very few experimental measurements exist for n-pentane and for many other organics, especially at low temperatures. Vapor pressure measurements from the novel experimental procedure were difficult to compare to theoretical n-pentane phase diagrams; but, were comparable to past experimental measurements for n-pentane. The calculated enthalpy of fusion value from experimental run 1 was almost one order of magnitude lower as compared to literature value. The calculated enthalpy of vaporization value from experimental run 1 was about one and half orders of magnitude lower than the literature value. The development of this approach to measure vapor pressures at low temperatures is a first step to design a system that can be used for organic liquids samples (like n-pentane) using cost-effective equipment. It also has the potential to be further modified and enhanced to also measure vapor pressure of gaseous organics at low temperatures.