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Ph. D. ThesisPh. D. Thesis 4. Experiments, Setups and Data Sets 4. Experiments, Setups and Data Sets 4.5. Data Sets 4.5. Data Sets 4.5.1. Refrigerants R22 and R134a4.5.1. Refrigerants R22 and R134a
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Ph. D. Thesis
  Table of Contents
  1. Introduction
  2. Theory Fundamentals of the Multivariate Data Analysis
  3. Theory Quantification of the Refrigerants R22 and R134a: Part I
  4. Experiments, Setups and Data Sets
    4.1. The Sensor Principle
    4.2. SPR Setup
    4.3. RIfS Sensor Array
    4.4. 4l Miniaturized RIfS Sensor
    4.5. Data Sets
      4.5.1. Refrigerants R22 and R134a R22 and R134a by the SPR Setup R22 and R134a by the RIfS Array and the 4l-Setup
      4.5.2. Homologous Series of the Low Alcohols
  5. Results Kinetic Measurements
  6. Results Multivariate Calibrations
  7. Results Genetic Algorithm Framework
  8. Results Growing Neural Network Framework
  9. Results All Data Sets
  10. Results Various Aspects of the Frameworks and Measurements
  11. Summary and Outlook
  12. References
  13. Acknowledgements
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4.5.   Data Sets

4.5.1.   Refrigerants R22 and R134a

For more than four decades a chlorofluorocarbon known as R22 (chlorodifluoromethan) has been the refrigerant of choice for application in freezers, refrigerators and air-conditioners. Yet, in the early 70s, Rowland and Molina showed that the chlorine of chlorofluorocarbons and hydrochlorofluorocarbons is released when the molecules are exposed to ultraviolet radiation in the stratosphere. A free chlorine atom in the stratosphere can act as catalyst for breaking down many stratospheric ozone molecules [180]-[182]. Consequently, in 1987 the Montreal Protocol was signed by almost all industrial countries. The Montreal Protocol is an international agreement on the phase-out of refrigerants based on chlorofluorocarbons. The Montreal Protocol is carried out in national laws of all participating countries like the "Clean Air Act, Title VI" in the United States [183] or the "FCKW-Halon-Verbotsverordnung" in Germany [184].

In consequence, national laws [185],[186] regulated the substitution of the chlorofluorocarbons and hydrochlorofluorocarbons by hydrofluorocarbons, which do not deplete the ozone layer. Among these substitutes, the hydrofluorocarbon R134a (1,1,1,2-tetrafluoroethane) plays the most important role. According to the "Alternative Fluorocarbons Acceptability Study" [187] the portion of R134a among the worldwide sold refrigerants for air-conditioners and refrigerators increased from 0% to 31% in the period from 1990 to 2000. In the same time, the portion of the hydrochlorofluorocarbons decreased from 95% to 64% whereby in 2000 practically no hydrochlorofluorocarbons except of R22 were sold for the use in refrigerants and air-conditioners.

This gradual substitution process of the refrigerants and the resulting diversity of the refrigerants found in old freezers, refrigerators and in air-conditioners prevent a reuse of the refrigerants. At the moment, the recycling process is a downcycling process whereby the refrigerants are converted to hydrogen chloride and hydrogen fluoride. A high quality recycling is not possible since the refrigerants are sometimes returned with no labels or wrong labels and since the refrigerants are often mixtures originating from different refrigerators or even were used as blends like the so-called R400 and R500 series. On the other hand, an analysis of the refrigerants of each refrigerator by a laboratory is too expensive. This results in the need of a detection method, which enables a fast, durable and economical on-line quantification of different mixtures of refrigerants. As sensor setups can come up to these requirements, data sets were recorded to examine how feasible an application of sensor setups for the quantification of R22 and R134a in mixtures in air is. Additionally several polymers were investigated to find an optimal polymer respectively an optimal combination of polymers for the discrimination of the refrigerants R22 and R134a (see chapter 3).

figure 14: 3D ball and sticks molecular models of the refrigerants R22 and R134a.

The gas mixtures of R22, R134a and air were generated using a gas mixing station with computer-driven mass-flow controllers (MKS, Munich, Germany). A 4-way valve before the cell ensured that the path length was the same for all analytes. Dry synthetic air was used as carrier gas. All measurements were performed at a constant flow rate.

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