Normalized hydrocarbon product distribution

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... 

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.

Various SAPO-n zeolite-supported Pd catalysts were recently investigated and compared in CO hydrogenation reactions (365). Although the acidic narrow channel (chabazite type) Pd/SAPO-34 catalyst produces mainly normal Cl—Cs alkanes, the ratios of branched hydrocarbons to normal hydrocarbons are quite high (6.7 for C4 and 10.8 for C5) on less acidic Pd/ SAPO-5, which has wide, unidimensional channels of 7.3 A cross section diameter. The comparison of product distribution on Pd/SAPO-5 and Pd/SAPO-11 catalysts is particularly interesting because in TPD of NH3, these zeolites reveal similar acid profiles and their IR spectra are similar. SAPO-11 has narrower unidimensional channels (6.3 x 3.9 A) than SAPO-5, but it produces only methane and oxygenates. The lack of higher hydrocarbons with Pd/SAPO-11 in comparison to Pd/SAPO-5 has been ascribed to shape selectivity due to the smaller pore size (365). 

Recently, FT synthesis reactions were shown to be independent of metal dispersion on Si02-supported catalysts with 6-22% cobalt dispersion (103). Turnover rates remained nearly constant (1.8-2.7 x 10 s ) over the entire dispersion range. Dispersion effects on reaction kinetics and product distributions were not reported. These tests were performed at very low reactant pressures (3 kPa CO, 9 kPa H2), conditions that prevent the formation of higher hydrocarbons and lead to methane with high selectivity and to CO hydrogenation turnover rates 10 times smaller than those obtained at normal FT synthesis conditions and reported here. These low reactant pressures also lead to kinetics that become positive order in CO pressure. Thus, the reported structure insensitivity (103) may agree only coincidentally with the similar conclusions that we reach here on the basis of our results for the synthesis of higher hydrocarbons on Co. 

Selectivity Product distribution ratio of Normal Branched hydrocarbons. References... 

Shown in Table 1 [1] is a typical MTG hydrocarbon product analysis. The selectivity can of course be varied by changing reaction conditions, as shown later. The hydrocarbon distribution displays some noteworthy features little or no hydro n, methane, or ethane is produced the carbon number range is limited mainly to C ClO (it is fortuitous that ClO is also the normal end point of conventional gasoline) the fraction contains significant amounts of isobutane, which will be useful for alkylate synthesis under conditions in which light olefins are brought into balance with isobutane and the aromatics are nearly exclusively methyl substituted. 

The determination of the carbon number distribution of petroleum waxes and the normal and non-normal hydrocarbons in each can be used for control of production... 

The termination step for 1-alkene formation is now the reaction of the surface alkenyl with surface H instead of the p-elimination step. Chain branching can proceed by the involvement of allylic intermediates. Since this new mechanism involves different types of reactions to form C2 and C2< hydrocarbons, it is not expected that the amounts of C2 products will lie on the normal curve of the Ander-son-Schulz-Flory distribution. 

The BP process [7] is based on a sand fluidized-bed pyrolysis reactor. The cracking temperature is kept at 400-600°C. Low-molecular hydrocarbons can be obtained. The process mainly involves converting waste plastics into normal linear hydrocarbons, the average molecular weight of which is 300-500. Most plastics can be treated by this process. Polyolefins are decomposed into small molecules with the same linear structure. PS is converted into styrene monomers and PET into mixture of hydrocarbons, carbon monoxide and carbon dioxide. A maximum of 2% PVC is allowed in this process, and the content of chlorine in the products is lower than 5 ppm. The distribution of alkene products in this process is like that in petroleum pyrolysis. The BP process was industrialized in 1997. 

The ZSM-5 family of zeolites show further interesting shape-selective effects. Both normal and methyl-substituted paraffins have access to interior sites, so both hexane and 3-methylpentane are cracked by ZSM-5, but steric constraints cause hexane to be cracked faster than 3-methylpentane. Further shape selectivity was found between 3-methylpentane and 2,3-dimethylbutane. No window effect with paraffin chain length was found with ZSM-5. In the conversion of methanol to hydrocarbons over ZSM-5 catalysts, the distribution 94,152,195 of aromatic products ends at Cio- The distribution of tetramethylbenzenes is not far from equilibrium, but has excess 1,2,4,5-tetramethylbenzene. Measurements of diffusion coefficients of alkyl benzenes show rapid decrease, by orders of magnitude, as ring substitution increases. 

Another proposal for explaining the two slope distributions is very consistent with the peculiarities of the Fischer Tropsch system The products of Fischer Tropsch synthesis do usually provide a liquid phase and a gaseous phase under reaction conditions.The gaseous compounds leave the reactor normally within a few seconds. The liquid does need a day or more until it elutes from the catalyst bed. Solubility of paraffinic hydrocarbon vapours in a paraffinic hydrocarbon liquid increases by a factor of about 2 for each carbon number of the product (ref. 27). Thus it needs only an increase of a very few carbon numbers of the product molecules to have them leaving the reactor mainly with the gas phase or with the liquid phase. With increasing residence time in the reactor the chance of readsorption increases and correspondingly the probability of chain prolongation increases. The kinetic scheme of this model is shown in Fig. 14. This model is very consistent with the experimental distributions. 

Production of Higher-Molecular-Weight Hydrocarbons. Kinetics, Surface Science, and Mechanisms The hydrogenation of carbon monoxide over iron, cobalt, and ruthenium surfaces produces a mixture of hydrocarbons with a wide range of molecular-weight distribution. Most of the hydrocarbons produced are normal paraffins however, olefins and alcohols in smaller concentrations are also obtained. 

Results were also obtained for the conversion of syngas containing C-labeled eth-ene or propene using a precipitated promoted iron catalyst. In addition, a fused iron catalyst was employed in a run with labeled ethene at 20 atm pressure. They found that the cracking reaction of ethene was of secondary importance with the iron catalyst, unlike the case with cobalt. The distribution of the synthesis products from C-ethene showed that about 50 percent of the transformation was to the C3 product the transformation to higher hydrocarbons decreased much quicker than for the cobalt normal pressure synthesis (Figure 33). With the addition of C-ethene the iso-paraffins had a lower activity than the normal paraffins this is consistent with the data for cobalt (Figure 34). 

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