Cracked naphthas

Olefins are produced primarily by thermal cracking of a hydrocarbon feedstock which takes place at low residence time in the presence of steam in the tubes of a furnace. In the United States, natural gas Hquids derived from natural gas processing, primarily ethane [74-84-0] and propane [74-98-6] have been the dominant feedstock for olefins plants, accounting for about 50 to 70% of ethylene production. Most of the remainder has been based on cracking naphtha or gas oil hydrocarbon streams which are derived from cmde oil. Naphtha is a hydrocarbon fraction boiling between 40 and 170°C, whereas the gas oil fraction bods between about 310 and 490°C. These feedstocks, which have been used primarily by producers with refinery affiliations, account for most of the remainder of olefins production. In addition a substantial amount of propylene and a small amount of ethylene ate recovered from waste gases produced in petroleum refineries. 

Catalytic Reforming. Worldwide, approximately 30% of commercial benzene is produced by catalytic reforming, a process ia which aromatic molecules are produced from the dehydrogenation of cycloparaffins, dehydroisomerization of alkyl cyclopentanes, and the cycHzation and subsequent dehydrogenation of paraffins (36). The feed to the catalytic reformer may be a straight-mn, hydrocracked, or thermally cracked naphtha fraction ia the... 

Residues (petroleum), coker scrubber, condensed-ring-arom-containing Residues (petroleum), hydrogenated steam-cracked naphtha, atm tower, vacuum, light... 

On cracked naphthas. Hydrofining provides not only desulfurization, but also improvements in gum, stability, and engine cleanliness characteristics. 

In treating cracked stocks such as steam cracked naphtha or visbreaker naphtha, which are highly olefinic in nature, nickel molybdate or nickel tungstate catalysts are generally employed. These catalysts have much higher activity for olefin samration reactions than does cobalt molybdate. 

Depending upon the refinery needs, the raw C5 plus steam cracked naphtha may be sent to isoprene extraction, treated to remove gum forming diolefins and sent to the refinery gasoline pool, or else completely hydrogenated and then fed to an aromatics extraction unit. 

A high purity hydrogen and a low purity methane stream result. The 95% hydrogen may be used directly to hydrogenate steam cracked naphtha or directly consumed elsewhere in the refinery. The methane stream goes to fuel. 

A Cj to Cg cracked naphtha cut is heated imder pressure in a soaking drum. Dimers and codimers of cyclopentadiene, methylcyciopentadiene, and isoprone are formed. This is followed by distillation, leaving a dimer concentrate bottoms. 

The direct counter-current contact of a hot gas with a cool immiscihle liquid is effectively used in certain hydrocarbon cracking processes for the quenching of hot gases/vapors. Sometimes, the liquid used is oil and followed hy water quench, as is typical in ethylene plants cracking naphtha or other hydrocarbon as feed stock. 

Products from coking processes vary considerably with feed type and process conditions. These products are hydrocarbon gases, cracked naphtha, middle distillates, and coke. The gas and liquid products are characterized by a high percentage of unsaturation. Hydrotreatment is usually required to saturate olefinic compounds and to desulfurize products from coking units. 

Reactor temperature is also a function of the feedstock used. Higher molecular weight hydrocarhons generally crack at lower temperatures than lower molecular weight compounds. For example, a typical furnace outlet temperature for cracking ethane is approximately 800°C, while the temperature for cracking naphtha or gas oil is about 675-700°C. 

Products from steam cracking naphtha at high severities ... 

Transpolypentamer (TPR) is produced by the ring cleavage of cyclopentene. Cyclopentene is obtained from cracked naphtha or gas oil, which contain small amounts of cyclopentene, cyclopentadiene, and... 

Distillates (petroleum), light steam-cracked naphtha... 

Gas oils (petroleum), catalytic-cracked naphtha depropanizer overhead, C3-rich acid-free... 

Residues (petroleum), steam-cracked naphtha distn... 

Dianor [Diamond Alkali, Oronozio de Nora] A process for cracking naphtha to ethylene, adapted for small-scale operation so that polyvinyl chloride could be made by developing nations. Developed in the 1970s by Chem Systems and the two named companies, but not commercialized. 

In Chapter 4 you II find a complete discussion of the manufacture of ethylene and propylene by cracking naphtha or gas oil in an olefin plant. One of the by-products of cracking those feedstocks is benzene. The term by-product may not be appropriate anymore, since about a third of the benzene supply in the United Stares now comes from olefins plants. 

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. 

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]. 

Aluminum Chloride Processing A refining method using aluminum chloride as a catalyst to improve the appearance and odor of steam cracked naphtha streams. Aluminum chloride functions as a catalyst for the polymerization of olefins into higher-molecular-weight, less-problematic compounds. 

Clay Treating A process used to improve the color of cracked naphthas and light distillates. It is also used to remove surface active agents which can negatively impact the WSIM rating of jet fuel. 

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