Naphtha pyrolysis

HDA [Hydrodealkylation] A proprietary dealkylation process for making benzene from toluene, xylenes, pyrolysis naphtha, and other petroleum refinery intermediates. The catalyst,... 

In setting the prices for the premium cases, we have incorporated a sliding price scale on some by-products hence, a range of prices appears in some rows of Table V. These price variations reflect differences in the composition of a particular by-product which result from cracking different feedstocks. By way of example, the aromatics content of a pyrolysis naphtha depends on the specific feedstock from which it is derived. The premium price of the particular pyrolysis naphtha thus depends on its BTX concentration. The nonaromatic content of the pyrolysis naphtha is valued the same as naphtha. Further details can be found in Table VI. 

The nature of the specific additional processing that will be installed will be specific to each individual refinery s base situation, but in general the effect will be to increase the value of several of the by-products associated with ethylene production. These include propylene, butylene, and the aromatics in the pyrolysis naphtha. The prices of the two olefins will tend to rise as additional alkylation units are installed to boost gasoline octanes, thus making these chemicals more valuable to the... 

Table XII. Basis for Determining Value of Aromatics-Rich Pyrolysis Naphtha...

Value of aromatics-rich pyrolysis naphtha determined by value of its components as finished chemicals, and the costs incurred in treating and separation required to produce them from pyrolysis naphtha. Breakdown of pyrolysis naphtha is as follows ... 

The cost incurred in treating and separating the pyrolysis naphtha into its constituent parts is approximately 0.6 f5/lb of pyrolysis naphtha. 

Ross and Shu [38] report a model for naphtha pyrolysis. Naphtha feed is treated as a single lumped constituent A, which decomposes by a pseudo-elementary process of the first order into products By, viz. 

HDA [HydroDeAlkylation] A proprietary dealkylation process for making benzene from toluene, xylenes, pyrolysis naphtha, and other petroleum refinery intermediates. The catalyst, typically chromium oxide or molybdenum oxide, together with hydrogen gas, removes the methyl groups from the aromatic hydrocarbons, converting them to methane. The process also converts cresols to phenol. Developed by Hydrocarbon Research with Atlantic Richfield Corporation and widely licensed worldwide. 

In the present study, silicon and transition metal substituted aluminophosphate molecular sieves have also been evaluated for activity and selectivity for para-xylene production via Cg aromatic isomerization. In commercial practice, Cg aromatic cuts are obtained from reformate gasoline and from pyrolysis naphtha streams. Both feeds contain a significant fraction of ethylbenzene which is difficult to separate from xylenes by physical techniques,... 

In the USA, and to some extent in Great Britain and Norway, ethane is the dominant feedstock for steam cracking. It is recovered from wet natural gas and gives high yields of ethylene, hydrogen and methane. From naphtha, the preferred feedstock in Europe and Japan, additional principal products are propylene, C4 hydrocarbons and pyrolysis naphtha as well as highly aromatic pyrolysis tar. 

Table 4.3 Typical data for hydrogenated pyrolysis naphtha...

Xylenes. The main appHcation of xylene isomers, primarily p- and 0-xylenes, is in the manufacture of plasticizers and polyester fibers and resins. Demands for xylene isomers and other aromatics such as benzene have steadily been increasing over the last two decades. The major source of xylenes is the catalytic reforming of naphtha and the pyrolysis of naphtha and gas oils. A significant amount of toluene and Cg aromatics, which have lower petrochemical value, is also produced by these processes. More valuable p- or 0-xylene isomers can be manufactured from these low value aromatics in a process complex consisting of transalkylation, eg, the Tatoray process and Mobil s toluene disproportionation (M lDP) and selective toluene disproportionation (MSTDP) processes isomerization, eg, the UOP Isomar process (88) and Mobil s high temperature isomerization (MHTI), low pressure isomerization (MLPI), and vapor-phase isomerization (MVPI) processes (89) and xylene isomer separation, eg, the UOP Parex process (90). 

The separation train of the plant is designed to recover important constituents present in the furnace effluent. The modem olefin plant must be designed to accommodate various feedstocks, ie, it usually is designed for feedstock flexibiUty in both the pyrolysis furnaces and the separation system (52). For example, a plant may crack feedstocks ranging from ethane to naphtha or naphtha to gas oils. 

Significant products from a typical steam cracker are ethylene, propylene, butadiene, and pyrolysis gasoline. Typical wt % yields for butylenes from a steam cracker for different feedstocks are ethane, 0.3 propane, 1.2 50% ethane/50% propane mixture, 0.8 butane, 2.8 hill-range naphtha, 7.3 light gas oil, 4.3. A typical steam cracking plant cracks a mixture of feedstocks that results in butylenes yields of about 1% to 4%. These yields can be increased by almost 50% if cracking severity is lowered to maximize propylene production instead of ethylene. 

The combination of low residence time and low partial pressure produces high selectivity to olefins at a constant feed conversion. In the 1960s, the residence time was 0.5 to 0.8 seconds, whereas in the late 1980s, residence time was typically 0.1 to 0.15 seconds. Typical pyrolysis heater characteristics are given in Table 4. Temperature, pressure, conversion, and residence time profiles across the reactor for naphtha cracking are illustrated in Figure 2. 

The primary sources of toluene and xylenes are reformates from catalytic reforming units, gasoline from catcracking, and pyrolysis gasoline from steam reforming of naphtha and gas oils. As mentioned earlier, solvent extraction is used to separate these aromatics from the reformate mixture. 

The pyrolysis reactor is an important processing step in an olefin plant. It is used to crack heavier hydrocarbons such as naphtha and LPG to lower molecular weight hydrocarbons such as ethylene. The pyrolysis reactor, in this study, consists of two identical sides each side contains four cracking coils in parallel (see Fig. 2). 

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