Methane absorption

The reflection spectrum of the atmosphere is a measure of the albedo of the planet (Figure 10.4) and, despite the strong methane absorption in the red, Titan s disc looks orange principally due to scatter from the surface of dense methane-hydrocarbon clouds. Scatter from aerosol particles within the thick clouds obscures the surface of the moon although the radar analysis reveals considerable Chapman layer structure within the atmosphere and some interesting surface features. 

The data illustrated in Fig. 4(a) are methane absorption lines (0.02 cm-1 wide) observed with a four-pass Littrow-type diffraction grating spectrometer. For these data also, 256 points were taken. The data were obtained at low pressure, so that Doppler broadening is the major contributor to the true width of the lines. The straightforward inverse-filtered estimate with 15 (complex) coefficients retained is shown in Fig. 4(b). Figure 4(c) shows the restored function. The positions and intensities of the restored absorption... 

Fig. 31 Experimentally obtained methane absorption lines in the infrared spectral region, (a) Two isolated methane spectral lines. A smooth curve is fitted to the base line, (b) Replotted lines. All points on the smooth curve were assigned the value of zero, and all values on the spectral lines are adjusted accordingly.

Products of these reactions, aldehydes and ketones, undergo photodissociations under tropospheric sunlight. Aldehydes absorb actinic UV-A radiation and methanal absorption extends out to approximately 370 nm, whereas the heavier aldehydes absorb only to approximately 345 nm. Methanal has two photodissociation paths ... 

As the brown dwarfs cool to temperatures below 1400 K, a drastic change occurs between 1400 K to 1200 K when CH4 bands become strong while CO band weaken. The CH4 bands are extremely broad in near infrared and they even modify the near infrared broad band colors. Strong methane absorption at 1.6 and 2.2 //, reduces more than half flux from H and K pass-band giving them unrealistic colors. 

The results of speetropolarimetric measurements in methane absorption bands at the center of the planetary disk allow us to determine, with simplicity and high accuracy, the methane eoncentration along the line of sight [33] ... 

Several years later the spectropolarimetry was used by Kucherov et al. [27] to study the vertical stracture of planetary atmospheres from observations of polarization within absorption bands. A method was developed to estimate the abundance of absorbing gas in a layer of planetary atmosphere above the cloud deck by analyzing the variation of the polarization across an absorption band profile (Fig.4). The observations were performed at the center of Jupiter s disk in two methane absorption bands in 1986 with 60 cm telescopes at the soviet field station in Bolivia and on Mt Maidanak in Uzbekistan. Using the... 

Figure 4. Average values of (a) the percentage polarization p and (b) the Stokes parameter Q measured at the center of the Jovian disk in the 727 nm methane absorption band. Dots correspond to measurements on 26/27 June and 10/11 July 1986 (phase angle a 11 ) circles are for data on October 8/9, 13/14, 14/15 (a 6. 9) crosses are for October 1/2, 2/3 (a 4. 6). The wavelength resolution is 2.5nm. The error of measurements remains constant within the band, and is indicated by a vertical bar for each phase angle [27].

Colorless gas, characteristic unpleasant odor. B.p. —20.2°C m.p. —161.5°C ( ock and Zeidler). Ignites and burns with a green flame on exposure to air. Not attacked by water at room temperature. At higher temperatures, reaction with water in a sealed tube yields methyl borates and methane. Absorption by aqueous KOH and NH3 solutions is violent. Ammonia and its derivatives give addition products with trimethylboron. 

An interesting point is that infrared absorptions that are symmetry-forbidden and hence that do not appear in the spectrum of the gaseous molecule may appear when that molecule is adsorbed. Thus Sheppard and Yates [74] found that normally forbidden bands could be detected in the case of methane and hydrogen adsorbed on glass this meant that there was a decrease in molecular symmetry. In the case of the methane, it appeared from the band shapes that some reduction in rotational degrees of freedom had occurred. Figure XVII-16 shows the IR spectrum for a physisorbed H2 system, and Refs. 69 and 75 give the IR spectra for adsorbed N2 (on Ni) and O2 (in a zeolite), respectively. 

The butane-containing streams in petroleum refineries come from a variety of different process units consequently, varying amounts of butanes in mixtures containing other light alkanes and alkenes are obtained. The most common recovery techniques for these streams are lean oil absorption and fractionation. A typical scheme involves feeding the light hydrocarbon stream to an absorber-stripper where methane is separated from the other hydrocarbons. The heavier fraction is then debutanized, depropanized, and de-ethanized by distillation to produce C, C, and C2 streams, respectively. Most often the stream contains butylenes and other unsaturates which must be removed by additional separation techniques if pure butanes are desired. 

The second CO2 removal is conducted using the same solvent employed in the first step. This allows a common regeneration stripper to be used for the two absorbers. The gases leaving the second absorption step stiU contain some 0.25—0.4% CO and 0.01—0.1% CO2 and so must be methanated as discussed earlier. The CO, CO2, and possibly small amounts of CH, N2, and Ar can also be removed by pressure-swing adsorption if desired. 

Total carbon in beryUium is determined by combustion of the sample, along with an accelerator mixture of tin, iron, and copper, in a stream of oxygen (15,16). The evolved carbon dioxide is usuaUy measured by infrared absorption spectrometry. BeryUium carbide can be determined without interference from graphitic carbon by dissolution of the sample in a strong base. BeryUium carbide is converted to methane, which can be determined directly by gas chromatography. Alternatively, the evolved methane can be oxidized to carbon dioxide, which is determined gravimetricaUy (16). 

The influence of Zn-deposition on Cu(lll) surfaces on methanol synthesis by hydrogenation of CO2 shows that Zn creates sites stabilizing the formate intermediate and thus promotes the hydrogenation process [2.44]. Further publications deal with methane oxidation by various layered rock-salt-type oxides [2.45], poisoning of vana-dia in VOx/Ti02 by K2O, leading to lower reduction capability of the vanadia, because of the formation of [2.46], and interaction of SO2 with Cu, CU2O, and CuO to show the temperature-dependence of SO2 absorption or sulfide formation [2.47]. 

The reaction produces additional hydrogen for ammonia synthesis. The shift reactor effluent is cooled and tlie condensed water is separated. The gas is purified by removing carbon dioxide from the synthesis gas by absorption with hot carbonate, Selexol, or methyl ethyl amine (MEA). After purification, the remaining traces of carbon monoxide and carbon dioxide are removed in the methanation reactions. 

Absorption recovers valuable light components such as propane/propylene and butane/ butylene as vapors from fractionating columns. These vapors are bubbled through an absorption fluid, such as kerosene or heavy naphtha, in a fractionating-like column to dissolve in the oil while gases, such as hydrogen, methane, ethane, and ethylene, pass through. Absorption is effectively performed at 100 to 150 psi with absorber heated and distilled. The gas fraction is condensed as liquefied petroleum gas (LPG). The liquid fraction is reused in the absorption tower. 

The rich gas from the absorption operation is usually stripped of the desirable components and recycled back to the absorber (Figure 8-57). The stripping medium may be steam or a dry or inert gas (methane, nitrogen, carbon oxides—hydrogen, etc.). This depends upon the process application of the various components. 

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