Distribution hydrocarbons, product

Huang, X. W., Elbashir N. O., and Roberts, C. B. 2004. Supercritical solvent effects on hydrocarbon product distributions from Fischer-Tropsch synthesis over an alumina-supported cobalt catalyst. Industrial Engineering Chemistry Research 43 6369-81. 

FIGURE 13.3 Typical hydrocarbon product distribution of a Fe-LTFT catalyst. 

In a recent publication, Chang and Silvestri have discussed this reaction in detail (109). They reported that under conditions of low (ca. 10%) conversion substantial amounts of dimethyl ether, formed by the reversible dehydration of methanol, are present and 78% of the primary hydrocarbon product consists of C2-C4 olefins. Also, if dimethyl ether, in the absence of water, is used instead of methanol, essentially the same hydrocarbon product distribution is obtained. On the basis of these observations, Chang and Silvestri suggest the reaction path shown below ... 

X. Huang, N. O. Elbashir and C. B. Roberts, Supercritical Solvent Effects on Hydrocarbon Product Distributions from Fischer-Tropsch synthesis over an Alumina-Supported Cobalt Catalyst, Ind. Eng. Chem. Res., 2004, 43, 6369-6381. 

Steady-state operation was quickly achieved under SCF conditions and the SCF-FT process has a marked effect on the hydrocarbon product distribution with a shift to higher carbon number products owing to enhanced heat and mass transfer from the catalyst surface. In addition, an obvious difference in the olefin content was observed where the 1-olefin content in the SCF phase was always higher than in the gas phase. Based on the experimental observations, a mechanistic explanation is provided for the difference of the reaction behavior under supercritical and gas-phase environments. 

Metal molybdates421 and cobalt-thoria-kieselguhr422 also catalyze the formation of hydrocarbons. It is believed, however, that methanol is simply a source of synthesis gas via dissociation and the actual reaction leading to hydrocarbon formation is a Fischer-Tropsch reaction. Alumina is a selective dehydration catalyst, yielding dimethyl ether at 300-350°C, but small quantities of methane and C2 hydrocarbons423 424 are formed above 350°C. Heteropoly acids and salts exhibit high activity in the conversion of methanol and dimethyl ether.425-428 Acidity was found to determine activity,427 130 while hydrocarbon product distribution was affected by several experimental variables.428-432... 

Figure 2. Variation in the normalized hydrocarbon product distribution with time on stream in the conversion of C2H2 (WHSV = 0.48 hr1) over pure H-ZSM-5 at 400 °C. Figure shows both total aromatic and, separately, fused-ring aromatic component of total aromatics.

Table I. Variation of the Normalized Hydrocarbon Product Distribution with Extended Time on Stream at 310 °C Over a 13% Ni/ZSM-5/Al203 Catalyst.

Figure 5. Illustration of the long-term normalized hydrocarbon product distribution obtained in the conversion of C2H2 + H2O mixtures over a 13% Ni/ZSM-5/Al203 catalyst at 310 °C. [H20]/[C2H2] = 0.6. WHSV(C2H2) = 3.2 hr1.

Figure 6. Variation of the normalized hydrocarbon product distribution as a function of catalyst contact time at 350 °C at a fixed [H2OMC2H2] of 0.6 and added He to vary the total VHSV.

Table n. Variation of Normalized Hydrocarbon Product Distribution at 350 °C as a Function of [H20]/[C2H2] Ratio All Other Reaction Variables Held Constant... 

The effect of reaction temperature on hydrocarbon product distribution is illustrated in Figure 7 for runs carried out at a constant C2H2 WHS V of 3.2 hr1 and a [H2OMC2H2] value of 0.4 and temperatures ranging from 175 to 450 °C. 

Figure 7. Effect of reaction temperature on % conversion of the C2H2 at a fixed reactant ratio of [H2OMC2H2] = 0.4 and a C2H2 WHSV of 3.2 hr1 (left ordinate). Normalized hydrocarbon product distribution as a function of reaction temperature (right ordinate). Catalyst employed was 13% Ni/ZSM-5/Al203.

Table V. Comparison of Hydrocarbon Product Distributions Obtained in Conversions of C2H2/H2O and C2H2/CH3CHO Under Comparable Reaction Conditions at 350 °C Over a 13% NVZSM-5/AI2O3 Catalyst...

Recently, we reported detailed descriptions of hydrocarbon chain growth on supported Ru catalysts (7,8) we showed that product distributions do not follow simple polymerization kinetics and proposed a diffusion-enhanced olefin readsorption model in order to account for such deviations (7,8). In this paper, we describe this model and show that it also applies to Co and Fe catalysts. Finally, we use this model to discuss a few examples from the literature where catalyst physical structure and reaction conditions markedly influence hydrocarbon product distributions. 

A striking similarity observed between the hydrocarbon product distributions in the photolysis of dimethylcyclobutanones and the photolysis of dimethylpyrazolines has been noted (52,158). 

We also studied the effect of ion exchange with on the catalytic activity of acid-treated Bent (H -Bent ), sometimes called activated clay. The results are given in Table IV. H" -Bent is virtually the same as H -Bent in catalytic activity. However, the catalytic activity of Ti -Bent for methanol conversion to hydrocarbons is much higher than that of Ti -Bent. The hydrocarbon yield reaches 90%, and the products, in addition to methane, are primarily olefins lower than Ce. The selectivity for olefin formation is estimated to be 90% or higher based on C2 and C3 hydrocarbon product distribution. Ti -Bent appears to surpass the phosphorus compound-modified zeolite proposed by Kaeding and Butter (31) in selective activity for olefin formation, and has the potential to exceed H-Fe-silicate (32) and Ni-SAPO-34 (33), proposed recently by Inui et al. 

Fig. 37. Hydrocarbon product distribution in CO hydrogenation on solvated metal atom-grafted Co,-NaY catalysts (mol%). Curve A 520 K, CO/Hj ratio 1/2, 0.02% conversion the distribution of C products is 1-butane (33%), isobutane (3%), le -2-butene (18.5%), and cis-2-butene (15.5%). Curve B 563 K, 0.04% conversion.

Hydrocarbon product distributions on the zeolite-supported catalyst are shown in Table 1. The product distribution did not change greatly after deposition at 400 C, but the olefin fraction obviously increased. The shift in selectivity of paraffins to olefins is attributed to be due to the reduced capacity of the deactivated catalyst 10 hydrogenate primary olefins to the con-espondiiig paraffins. Similar results were also obtained with the alumina-supported catalysts. 

Hydrocarbon product distribution for CO hydrogentaion on zeolite-supported cobalt at 21(fC... 

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