Distribution hydrocarbon

Their satisfactory combustion requires no particular characteristics and the specifications are solely concerned with safety considerations (vapor pressure) and the C3 and C4 hydrocarbon distribution. 

These reactions are highly exothermic, for example one mole of -CH2- units generates 165 kj. The hydrocarbon distribution ranges from methane up to heavy waxes, depending on the nature of the catalyst and the reaction conditions. 

Figure 8.17. Hydrocarbon distribution of the products formed by Fischer-Tropsch synthesis over cobalt-based catalysts and by additional hydrocracking, illustrating how a two-stage concept enables optimization of diesel fuel yield. [Adapted from S.T. Sie,...

However, the detailed description of the FT product distribution together with the reactant conversion is a very important task for the industrial practice, being an essential prerequisite for the industrialization of the process. In this work, a detailed kinetic model developed for the FTS over a cobalt-based catalyst is presented that represents an evolution of the model published previously by some of us.10 Such a model has been obtained on the basis of experimental data collected in a fixed bed microreactor under conditions relevant to industrial operations (temperature, 210-235°C pressure, 8-25 bar H2/CO feed molar ratio, 1.8-2.7 gas hourly space velocity, (GHSV) 2,000-7,000 cm3 (STP)/h/gcatalyst), and it is able to predict at the same time both the CO and H2 conversions and the hydrocarbon distribution up to a carbon number of 49. The model does not presently include the formation of alcohols and C02, whose selectivity is very low in the FTS on cobalt-based catalysts. 

FIGURE 16.2 (a) CO conversion and (b) hydrocarbon distribution (in terms of ASF plot)... 

Figure 2. The effect of added HY zeolite on the hydrocarbon distribution Curve 1, Fes(CO)Ii-NaY + HY Curve 2, FeJCO)12-NaY initial pressure, 20 bar Hi/CO = 4/1 reaction temperature, 250°C...

McLaren R, Singleton DL, Lai JYK, et al. 1996. Analysis of motor vehicle sources and their contribution to ambient hydrocarbon distributions at urban sites in Toronto during the Southern Ontario oxidants study. Atmos Environ 30(12) 2219-2232. 

The distribution of ethers shifts towards more substituted species at constant temperature (80 °C) with the initial isobutene to glycerol ratio (Fig. 10.5). Changing the initial isobutene to glycerol ratio does not affect the by-product (Cg, C12 and Ci6 hydrocarbons) distribution. Temperature, however, has a clear effect on the hydrocarbon distribution the higher the temperature the smaller the fraction of C12 and CK, hydrocarbons of the total amount of hydrocarbons [8]. 

In the dimerization of isobutene, tertiary-butyl alcohol (TBA, 2-methyl-2-propanol) has a strong role in modifying the selectivity of the reaction to Cg hydrocarbons and limits further oligomerization to C12 and Ci6 hydrocarbons [34]. Also, in the etherification of glycerol with isobutene the addition of TBA has a clear effect on the selectivity and on hydrocarbon distribution. The selectivity to ethers increased and the fraction of the Cu and Ci6 hydrocarbons decreased while the concentration of TBA was increased from 0 to 2.6 mol.%. As a conclusion, the formation of C12 and C16 hydrocarbons can be prevented in two ways either TBA should be added to the reaction mixture or the reaction should be carried out at high temperatures [8]. 

McLaren, R D. L. Singleton, J. Y. K. Lai, B. Khouw, E. Singer, Z. Wu, and H. Niki, Analysis of Motor Vehicle Sources and Their Contribution to Ambient Hydrocarbon Distributions at Urban Sites in Toronto during the Southern Ontario Oxidants Study, Atmos. Environ., 30, 2219-2232 (1996a). 

The impression from the toted hydrocarbon distribution (Figure 1) is that both zeolites behave in a similar manner by producing C3-C5 products from C6+ hydrocarbons, the most significant difference being the ratio of C3/C4 yields. However, as is apparent from Figures 2-5, there are marked differences in paraffins and olefins for each zeolite. 

From a study of gasoline cver-cracking with either ZSM-5 or REHY, the resulting total hydrocarbon distributions by carbon number are grossly similar. In both cases, predominantly C2 - C5 products are formed from C6+ components. However, there are significant differences in detail, notably in hydrocarbon-type distributions. 

The saturated hydrocarbon distributions of the marl samples are dominated by long-chain n-alkanes of higher land plant origin (21) with a strong odd-over-even carbon number predominance. Hopanoid hydrocarbons are the next most abundant constituents, but other hydrocarbons particularly abundant in the laminite samples described hereafter are also clearly recognizable. 

Soroker, V., Lucas, C., Simon, T., Fresneau, D., Durand, J.-L. and Hefetz, A. (2003). Hydrocarbon distribution and colony odour homogenisation in Pachycondyla apicalis. Insect. Soc., 50, 212-217. 

Mitra, S., Dellapenna, T.M., and Dickhut, R.M. (1999a) Polycyclic aromatic hydrocarbon distribution within lower Hudson River estuarine sediments physical mixing vs. sediment geochemistry. Estuar. Coastal Shelf Sci. 49, 311-326. 

Stark, A., Abrajano, T., Hellou, J., and Metcalf-Smith, J.L. (2003) Molecular and isotopic characterization of polycyclic aromatic hydrocarbon distribution and sources at the international segment of the St. Lawrence River. Org. Geochem. 34, 225-237. 

Hydrocarbon distributions in the Fischer-Tropsch (FT) synthesis on Ru, Co, and Fe catalysts often do not obey simple Flory kinetics. Flory plots are curved and the chain growth parameter a increases with increasing carbon number until it reaches an asymptotic value. a-Olefin/n-paraffin ratios on all three types of catalysts decrease asymptotically to zero as carbon number increases. These data are consistent with diffusion-enhanced readsorption of a-olefins within catalyst particles. Diffusion limitations within liquid-filled catalyst particles slow down the removal of a-olefins. This increases the residence time and the fugacity of a-olefins within catalyst pores, enhances their probability of readsorption and chain initiation, and leads to the formation of heavier and more paraffinic products. Structural catalyst properties, such as pellet size, porosity, and site density, and the kinetics of readsorption, chain termination and growth, determine the extent of a-olefin readsorption within catalyst particles and control FT selectivity. 

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