Cracked gases Composition

Table 9. BASF Process Consumptions and By-Product Yields and Cracked Gas Composition, ...

The cracked gas composition is shown ia Table 10 for the water queach operatioa (16). Oae thousand cubic meters of methane and 600 m of oxygen produce 1800 m of cracked gas. If a naphtha quench is used, additional yields are produced, consuming 130 kg of naphtha/1000 of methane... 

A comparison of cracked gas compositions for a number of cracking processes has been presented by Sachanen (72), as shown in Table IX. 

Fig II 13 Calculation results for the example of hydrogen separation from cracked gas Composition is given in Table 113 (a) Purge ratio of inert gas ( l/ h) = 011 and (b) 0 I... 

The composition of the cracked gas with methane and naphtha and the plant feed and energy requirements are given in Table 9. The overall yield of acetylene based on methane is about 24% (14). A single burner with methane produces 25 t/d and with naphtha or LPG produces 30 t/d. The acetylene is purified by means of /V-methy1pyrro1idinone. 

Figure 13. Effect of hydrotreating severity on catalytic cracking light gas composition -- low severity cracking.

The catalytic cracking of four major classes of hydrocarbons is surveyed in terms of gas composition to provide a basic pattern of mode of decomposition. This pattern is correlated with the acid-catalyzed low temperature reverse reactions of olefin polymerization and aromatic alkylation. The Whitmore carbonium ion mechanism is introduced and supported by thermochemical data, and is then applied to provide a common basis for the primary and secondary reactions encountered in catalytic cracking and for acid-catalyzed polymerization and alkylation reactions. Experimental work on the acidity of the cracking catalyst and the nature of carbonium ions is cited. The formation of liquid products in catalytic cracking is reviewed briefly and the properties of the gasoline are correlated with the over-all reaction mechanics. 

The cracking at 500° C. of both monocyclic and bicyclic cyclohexane-type naphthenes, which are important components of petroleum, again displays uniformity in gas compositions, approaching that of the n-paraffins. The gaseous products shown here as mole percentage amount to 26 to 52 weight % of the total feed reacted. 

The main objective in FCC catalyst design is to prepare cracking catalyst compositions which are active and selective for the conversion of gas-oil into high octane gasoline fraction. From the point of view of the zeolitic component, most of the present advances in octane enhancement have been achieved by introducing low unit cell size ultrastable zeolites (1) and by inclusion of about 1-2 of ZSM-5 zeolite in the final catalyst formulation (2). With these formulations, it is possible to increase the Research Octane Number (RON) of the gasoline, while only a minor increase in the Motor Octane Number (MON) has been obtained. Other materials such as mixed oxides and PILCS (3,4) have been studied as possible components, but there are selectivity limitations which must be overcome. 

Light gas compositions are shown in Table VIII for hexadecane cracking at constant 50% conversion. Results are reported as iso-to-normal and olefin-to-paraffin ratios for C4 products. 

A practical approach we have used in the past is to define a simple empirical model for the decomposition of feedstock (single or mixed feeds). Then yields, product gas composition, expansion on cracking, partial pressure, and so forth, are all calculated by using a back-up program which relates yields to decomposition or other internal measures of severity and to the other conditions of cracking (reaction time, average partial pressure). 

The results obtained can be explained by considering the reactions involved in the processes. We can assume that the main reactions in catalytic pyrolysis are catalytic cracking of tars and light hydrocarbons, which will explain the increase in gas yields when the catalyst is present in the reaction bed (18). Steam reforming of tars (reac. 1), methane (reac. 2) and Cj (reac. 3), and the water-gas shift reaction (reac. 4) can explain the final gas composition generated in catalytic steam gasification. 

For the wood volatiles an average of the compositions measured by Chan [17], who performed pyrolysis experiments with Oregon lodgcpole pine pellets, was used. The tar fraction was assumed to crack and give a secondary gas composition equal to the primary gas composition. The assumed volatiles composition for the fuel is summarized in Table /. 

The produced combustible gas of the demonstration plant has a different composition from that of the small pilot plant. The former includes more carbon monoxide and less carbon dioxide than the latter. The difference in gas composition between the two tests seems to come from the fact that in case of the larger reactor, supplied solid waste is heated up promptly and over-cracking is prevented. Because of the high carbon monoxide content, the calorific value of the demonstration plant is higher than that of the small reactors. Sampling of the combustible gas for... 

Pyrolysis of Pulp and Paper Sludge. The filter cake containing about 80% moisture was supplied for the cracking reactor without predrying. Heavy oil was fed to the incinerator as the auxiliary fuel. This is different from the case of municipal refuse, but the combustible gas composition and calorific value, flue gas composition and ash were similar to that of municipal refuse. The chemical analysis of combustible gas and flue gas are shown in Tables IX and X. 

In studies of tar cracking using a separate catalyst bed, two types of tar sources are applied, one directly drawn from a biomass gasifier and the other from model compounds. According to VTTs work [12], the tar consists mainly of highly stable compounds such as benzene (60-70 wt %), naphthalene (10-20 wt %), and other polyaromatic hydrocarbons (10-20 wt %), which can amount to 15-20 g of tar/Nm in biomass gasification. So, benzene and naphthalene were used in this work as tar model compounds with a fixed concentration of 15 g/Nm (4300 ppm) for benzene and 5 g/Nm (875 ppm) for naphthalene, respectively. The gas composition used was 50 vol % N2, 12 vol % CO, 10 vol % H2, 11 vol % CO2, 12 vol % H2O, 5 vol % CH4, 4300 ppm benzene (or 875 ppm naphthalene), which is a typical composition of the product gas from a biomass fluidised bed gasifier operated with air. The reaction tests were performed under three filtration gas velocities 2.5, 4 and 6 cm/s. All experimental points were monitored for at least 60 min after the reaction reached an apparent steady state at the selected operation condition. 

Figure 8. Product gas composition vs. cracking temperature with Incoloy 800. Key O, ethane X, methane , ethylene and A, propylene.

Figure 2. Exit gas composition from steam cracking of propane in quartz reactor with steel (Sandvik 15RelO) as the foil material after 10 min on stream. Conditions temperature range, 800-870°C feed gas composition, 29 mol% C3Ha, 32% HtO, and 39% N3 and total feed rate, 0.42 L gas/min.

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