C2-C4 hydrocarbons

Studies were conducted at Gulf Research Development Company by Janezic (1979) to investigate the anaerobic microbial evolution of C -C hydrocarbons upon decomposition of various organic substrates including green plant branches, grass 

1 - Liter Modified SOHNGEN Flask Substrate Added 

The experimental scheme for anaerobic decomposition is shown in Fig. 5-4. Exactly 1.5 g of each substrate was added to a modified 1 litre Sohngen flask and autoclaved at 120°C and 15 psi to ensure sterility, after which each flask was filled to capacity with a sterile inorganic nutrient medium and pH adjusted. Next 50 ml of a heterogeneous innoculum prepared from muds from a local lake was injected into each flask as inoculates , while 50 ml. of sterile nutrient medium was used for control samples. Headspace C1-C4 hydrocarbons were measured prior to incubation to provide baseline concentrations. Minimum detection limits were 3 ppb on a volume basis using a high-sensitivity gas chromatograph equipped with a flame ionisation detector. Samples were incubated at 25°C and 36°C over a five week period. 

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Comparison of the volume/volume composition data with the relative pressure data shows that although C2-C4 hydrocarbons are present to the greatest volume percent, their actual pressures are an order of magnitude lower than the C5 plus hydrocarbons. Hence, the C5 plus hydrocarbons would be adsorbed in preference to the C2-C4 hydrocarbons and would displace them over a number of cycles. It is apparent therefore that the C5 plus hydrocarbons must be considered the primary target gases for pre-adsorption in guard bed systems... 

The severity of these problems is quite sensitive to the nature of the particular organic, as expected, and likely to the particular sampling configuration and conditions as well. For example, Calogirou et al. (1997) showed that saturated oxygenated terpenes adsorbed on Tenax were not affected by the presence of 100 ppb 03 whereas as much as 80-90% of the most reactive, unsaturated compounds reacted. Indeed, no a-terpinene was observed when ozone was present. On the other hand, Koppmann et al. (1995) report no significant interference problems with 03 for the C2-C4 hydrocarbons which were sampled using a heated stainless steel inlet line, which destroys as much as half of the initial ozone, and then cryotrapped. 

Longer life and better activity were obtained with catalysts composed of chro-mia and alumina.151 While pure alumina has little dehydrogenation activity, the incorporation of as little as 3% or as much as 60% chromia provides effective catalysts the most widely used commercial catalyst usually contains 20% chromia. Chromia-alumina is used in the dehydrogenation of C2—C4 hydrocarbons to the corresponding alkenes.152-154 1,3-Butadiene may also be manufactured under appropriate conditions (see Section 2.3.3). 

Microwave heating was also used to induce catalytic oligomerization of methane to afford C2-C4 hydrocarbons.571 Changing the catalysts and the applied power and the use of diluent gas (He) allowed significant alteration of product selectivities. Selectivity to benzene over nickel powder or activated carbon was 24 and 33%, respectively. 

Natural gas naturally occurring gas with a heat content over 1000 Btu/ft3, consisting mainly of methane but also containing smaller amounts of the C2-C4 hydrocarbons as well as nitrogen, carbon dioxide, and hydrogen sulfide. 

Ratte M., Plass-Dulmer C., Koppmann R., Rudolph J., and Denga J. (1993) Production mechanism of C2-C4 hydrocarbons in seawater— Field-measurements and experiments. Global Biogeochem. Cycles 7, 369—378. 

Hence, for example, Dollimore etal have considered thermodynamic aspects of the adsorption of organic vapours on graphites and carbon blacks. Heats of adsorption and entropies of adsorbed vapours were determined, and the authors came to the conclusion that mobile adsorption appeared to be very important in the systems. In some ways the observation that C2-C4 hydrocarbons were adsorbed flat on a graphite surface tends to support this conclusion, although Hoory and Praunitz prefer to explain their results in terms of double bond interaction with the graphite.Jonas et al. find... 

While natural gas reforming is the primary process for the industrial production of H2, the reforming of other gaseous hydrocarbons such as ethane, propane, and n-butane have been explored for the production of H2 for fuel cells.52,97 The reforming of propane and n-butane received particular attention in recent years, because they are the primary constituents of liquefied petroleum gas (LPG), which is available commercially and can be easily transported and stored on-site. LPG could be an attractive fuel for solid oxide fuel cells (SOFCs) and PEMFCs for mobile applications.98 01 The chemistry, thermodynamics, catalysts, kinetics, and reaction mechanism involved in the reforming of C2-C4 hydrocarbons are briefly discussed in this section. 

The Ni-based catalysts known for the steam reforming of natural gas are also active for the steam reforming of C2-C4 hydrocarbons. However, carbon deposition and... 

Table 2.11. A Few Selected Catalysts Reported Recently for the Steam Reforming of C2-C4 Hydrocarbons... 

Pd23Zr73, Os25Zr73, Ir2JZr75 Fe82.2Bl7.8 (C2—C4 hydrocarbons) [4.17, 18]... 

Rimmelin et al. [22] treated TMO+SbClg- with the strong hindered base 2,2,0,0-tetramethylpiperidyl-lithium (TMPLi) and obtained MeOEt as well as C2-C4 hydrocarbons (Table 1). The TMO ion appears therefore at least plausible as an intermediate in C-C bond formation. A Stevens rearrangement would also be plausible but not proven. When t-butyllithium was used in place of TMPLi, isopentane rather than MeOEt was formed, showing the criticality of a sterically hindered base. 

Landfill gases, particularly methane, C2-C4 hydrocarbons, hydrogen, and oxygen, are sampled via a sampling probe pushed into the deposited refuse (Figure 13.17). The gases at the required depth are evacuated via a vacuum pump and a sample put into a gas bulb for GC analysis. 

Analysis of Products. The three fractions collected from each sample were analyzed by gas chromatography. The noncondensable fraction, containing hydrogen and methane, was analyzed on silica gel at room temperature. The fraction containing C2-C4 hydrocarbons was analyzed at 75 °C. on silica gel treated with didecyl phthalate. Aliquots of the liquid fraction were analyzed on three columns of different selectivity Bentone-34-didecyl phthalate silicone SE-30 and m-polyphenyl ether (five-ring). Products were identified, and their yields were determined by comparison of retention volumes and peak areas with values for known amounts of authentic samples. 

It is well known that nickel has an outstanding activity for methanation. Thus, it is worth mentioning the observation that in CO hydrogenation an amorphous Nij0Nbj0 alloy produced C2-C4 hydrocarbons with a selectivity of 46% (39% ethene and propene) together with only 40% methane (523 K, H CO = 1) (55). 

Lombardo and co-workers published a series of papers between 1980 and 1986 on the hydrogenation and hydrogenolysis of C2-C4 hydrocarbons over reduced LaCoC>3 and LaCo(>3 supported on La2C>3. They concluded that these reactions occur over metallic centers (Co0) generated either during reaction or hydrogen pretreatment of the catalyst. 

Temperature profiles of the individual gases from pyrolysis of Pittsburgh vitrain are shown in Figure 3. The molar percentages of C02, CH4, and the C2-C4 hydrocarbons decrease with increasing reaction temperature. The functional dependence of H2 and CO on temperature is more complex. H2 production starts at 31.5 mole % at 700°C and increases to a maximum of 67.0 mole % at 990°C. Further increase in temperature causes a small but real decrease in its concentration. CO concentration changes in an opposite manner to H2. A minimum CO value of 12.0 mole % is achieved at about the same temperature at which the maximum H2 concentration occurred. The gas composition data are given on a H20-02-N2-free basis. 

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