Natural Gas and Refined Products Jane B. Hooper Petroleum Technology Center, Marathon Oil Company, 7400 South Broadway, Littleton, Colorado 80 122 The layout for this article is similar to the review in 1993. The section headers describe the petroleum product type. The subcategories are arranged by analytical test. There were hundreds of articles written over the last two years on analytical testing of natural gas and refined petroleum products. The types of articles included in this review are as follows: those presenting new, more sophisticated techniques that combine different types of analytical instrumentation into one analysis; those that have intentionally simplified standard methods to give more rapid run times and ease of analysis; those that have modified existing methodology to improve the accuracy or scope of the methods; those that describe on-line techniques and the accompanying computer models that are used to develop correlations for numerous fuel properties by measuring only a few individual parameters. NATURAL GAS AND NATURAL GAS LIQUIDS Calorific Value. There are a variety of analytical techniques used to measure the caloriiic value (or energy content) of natural gas. Unique gas chromatographic methods include Annino's online process unit with a plug-in cartridge chromatograph with capillary capabilities for a quick analysis (El) and Tompkins' totally portable gas chromatograph (GC) weighing only 23 lb (E2). Brown and Lo use a near-infrared (near-IR) fiber-optic system for on-line monitoring (E3). King et al. make nuclear magnetic resonance (NMR) free-induction decay and relaxation time measurements to determine the calorific value of fuel gases (E4). For a review of chromatographic methods, see Cox ( E a . Sowell discusses the industrial uses of calorimeters (E@. For a comparison of calorimetry and gas chromatographic methods in a European study, refer to Vandendriessche et al. ( E n . Compressibility Factors. For natural gas mixtures, Li and Guo use a RUSKA apparatus with a modified OU/GRI equation of state to more accurately predict supercompressibility and compressibility factors (Et?). For a review of references relating to supercompressibility and compressibility, see Starling (E9). Hydrocarbon Components. For the separation of natural gas into its hydrocarbon constituents, gas chromatographic techniques are described in the literature. Low uses an automated on-line GC to analyze mixtures of natural and liquefied gases. It is specially designed to sample under high pressure in an effort to overcome problems associated with phase changes in on-line sampling (EM).There are two mass spectrometry (MS) methods discussed: Lindinger et al. uses ion/molecule reaction MS instead of electron impact ionization. There is less fragmentation of the reactant gases with their method ( E l l ) .Baylis et al. use capillary GC/combustion isotope ratio MS for a quicker analysis and headspace sampling capabilities (El2). Phase Equilibrium. There are a couple of new developments relating to the behavior and composition of gadliquid phases: Chylinski et al. have a new, automated instrument for studying two-and three-phase equilibrium fluids in gas condensate systems at pressures of
