Cracking naphtha yield

When naphtha or gas oil is cracked, imagine the limitless combinations possible. Naphthas are made up of molecules in the C5 to Cio range gas oils from Cio to perhaps C30 or C40. The structures include everything from simple paraffins (aliphacics) to complex polynuclear aromatics, so a-much wider range of possible molecules can form. Ethylene yields.froin..cracking naphtha or gas oil are much smaller than those from ethane or propane, as you can see from Table 5-1- But to compensate the plant operator, a full range of other hydrocarbons is produced as by-products also. 

The base-load supply of butadiene is from olefins plants simply because butadiene is coproduced with the other olefins. There s not much decision on whether or not to produce it. It just comes out, but in a small ratio compared CO ethylene and propylene. Cracking ethane yields one pound of butadiene for every 45 pounds of ethylene cracldng the heavy liquids, naphtha or gas oil, produces one pound of butadiene for every seven pounds of ethylene. Because of the increase in heavy liquids cracldng, about 75% of the butadiene produced in the United States is coproduced in olefin plants. 

The naphtha yield was lower for Catalyst B than for the reference and this illustrates the necessity to have enough zeolite surface area in the catalyst to be able to crack all the components in the feed, both those that can be cracked directly and those that must be precracked on the matrix before they can be cracked by the zeolite. Catalyst C had a slightly higher naphtha maximum than the reference catalyst, despite its high matrix surface area. The high matrix surface area of Catalyst C,... 

Figure 5.3 shows light olefin yields of DCC process in four refineries with different feedstocks at reaction temperatures of 545-565°C. The propylene yield can reach 23 wt% with paraffinic feed, and about 18-19 wt% with intermediate-based feed. The propylene/ethylene ratio is about 3.5-6.2, much higher than that of steam cracking. The DCC operation can be modified to further increase the yield of propylene. For example, recycling a part of DCC cracked naphtha to the reactor resulted in a propylene yield increment of 3.5 wt % in Jinan Refinery [16]. 

Thiophene-type sulfur is found in cracked naphthas and is not removed in most gasoline-treating processes, except with very high losses in liquid yield. 

Table 7 shows the yield distribution of the C4 isomers from different feedstocks with specific processing schemes. The largest yield of butylenes comes from the refineries processing middle distillates and from olefins plants cracking naphtha. The refinery product contains 35 to 65% butanes olefins plants, 3 to 5%. Catalyst type and operating severity determine the selectivity of the C4 isomer distribution (41) in the refinery process stream. Processes that parallel fluid catalytic cracking to produce butylenes and propylene from heavy cmde oil fractions are under development (42). 

Installation of more conversion equipment both in new refinery construction and as additions to existing hydroskimming facilities is already a trend. The production of more naphtha by providing new conversion units would, of course, make the additional naphtha more costly. In this connection a number of studies both our own and others (4) have attempted to determine the cost of incremental naphtha production. These indicate that in typically sized European hydroskimming refinery (operating on either Libyan or Arabian crudes) gasoline plus petrochemical naphtha yields can be increased by about 50% by installation of catalytic cracking. Based on today s prices for the other refinery products, the cost... 

Table 23 gives the main physicochemical properties of a number of naphtha cuts derived from Kirkuk and Hassi-Messaoud crudes. The steam cracking of these naphthas yields a wide variety of products, ranging from hydrogen to highly aromatic heavy liquid fractions. 

Thermal cracking of naphtha yields the following gas, which is to be separated by a distillation train into the products indicated. If reasonably sharp separations are to be achieved, determine by heuristics two good sequences. 

The reaction temperature in DCC is higher than that of conventional FCC but much lower than that of steam cracking. Propylene yields over 20 wt% are achievable with paraffinic feeds. Ethylene yield is much higher than the conventional FCC process. The DCC-mixed C s stream also contains increased amounts of butylenes and iso-C s as compared to an FCC. The high olefin yields are achieved by deeper cracking into the aliphatic components of the naphtha and ECO. The dry gas produced from the DCC process contains approximately 50% ethylene. The cracking reactions are endothermic, and compared to FCC, a higher coke make is required to satisfy the heat balance. Table 1 summarizes typical olefins yields for DCC with FCC. 

Description The most predominant feed used to produce ethylene today is naphtha, as more than half of the world s ethylene is currently derived from cracking naphtha feed. The Advanced Catalytic Olefins (ACO) process is an alternative process that catalytically converts naphtha feed and is thus able to produce higher ultimate yields of light olefins (propylene plus ethylene) and at a higher P/E production ratio relative to steam cracking, typically about 1 1. 

Figure 3.33 Naphtha yield from catalytic cracking of various hydrocarbon mixtures...

Figure 4.10 Naphtha cracking. Typical yields as a function of KSF. Zdonik et al. [533]. Reproduced with the permission of Elsevier.

Piperylene occurs in the Cs cut of a cracked naphtha fraction alongside, but in smaller amounts than isoprene. At least one isopentane dehydrogenation process used for making isoprene also yields some piperylene. 

In a single stage, without liquid recycle, the conversion can be optimized between 60 and 90%. The very paraffinic residue is used to make lubricant oil bases of high viscosity index in the range of 150 N to 350 N the residue can also be used as feedstock to steam cracking plants providing ethylene and propylene yields equal to those from paraffinic naphthas, or as additional feedstock to catalytic cracking units. 

The feedstocks used ia the production of petroleum resias are obtaiaed mainly from the low pressure vapor-phase cracking (steam cracking) and subsequent fractionation of petroleum distillates ranging from light naphthas to gas oil fractions, which typically boil ia the 20—450°C range (16). Obtaiaed from this process are feedstreams composed of atiphatic, aromatic, and cycloatiphatic olefins and diolefins, which are subsequently polymerized to yield resias of various compositioas and physical properties. Typically, feedstocks are divided iato atiphatic, cycloatiphatic, and aromatic streams. Table 2 illustrates the predominant olefinic hydrocarbons obtained from steam cracking processes for petroleum resia synthesis (18). 

Farbwerke Hoechst AG and Hbls AG have cooperated in the development of industrial-scale plasma units up to 10,000 kW (7). Yields of acetylene of 40—50 wt % with naphtha feedstock, and about 27 wt % with cmde oil feedstock, have been obtained. Acetylene concentration in the cracked gas is in the 10—15 vol % range. 

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. 

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... 

As is indicated in Figure 4, saturates contribute less to the vacuum gas oil (VGO) than the aromatics, but more than the polars present at percentage, rather than trace, levels. VGO itself is occasionally used as a heating oil but most commonly it is processed by catalytic cracking to produce naphtha or by extraction to yield lubricant oils. 

The main limitation to thermal conversion is that the products can be unstable. Thermal cracking at low pressure gives olefins, particularly in the naphtha fraction such olefins yield an unstable product that tends to form gum as well as heavier products that form sediments (5). 

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