Pyrolysis gasoline operation

The depropanizer bottoms are further processed in the debutanizer for separation of product from light pyrolysis gasoline. The debutanizer operates at a moderate pressure of 0.4 to 0.5 MPa, and is a conventional fractionator with steam heated reboders and water cooled condensers. 

DISTAPEX A process for removing aromatic hydrocarbons from pyrolysis gasoline or coke-oven benzole by extractive distillation with added N-methyl pyrrolidone. The operating temperature is at least 170°C. Developed by Lurgi. First announced in 1961 by 1993, 22 plants had been built. 

Pyrotol A process for making benzene from pyrolysis gasoline by hydrocracking. Developed by Houdry Process and Chemical Company. In 1987, 13 units were operating worldwide. 

A vast range of techniques are available for the treatment of reforming and pyrolysis gasolines, designed to isolate the aromatic hydrocarbons needed by the chemical industry. Since these operations produce the diflerent constituents in proportions that do not matdi demand, supplementary conversions (of compounds whose petrochemical uses are limited to those of greater necessity) avoid the problematic upgradings of surplus misure a better adjustment of production to requirements, and hence improve overall productivity. 

The high concentration of these components makes separation of the BTX an attractive proposition and many naphtha cracking operations now separate BTX rather than produce pyrolysis gasoline. 

A major portion of the world s BTX is made by naphtha reforming. The technology and economics of this route is well reported in petroleum refinery handbooks. Often this route uses extractive distillation to extract aromatics prior to distillation. Reforming operations are often integrated with ethylene cracking operations to maximise benzene production from reformate and pyrolysis gasoline. ... 

Table 7.2 presents the data for a plant which extracts propylene and pyrolysis gasoline, but recycles the rest of the products. Of the byproducts the mixed C4 stream is recycled to the feed-side of the cracker furnaces, with the hydrogen and methane recycled to the fuel-side. The same quantum of operating allowances for feed and fuel are included in the statistics. 

A CLOSED operation can be modelled in which all products other than ethylene, propylene and pyrolysis gasoline are recycled. The propane and C4 streams are recycled to the feed side of the pyrolysis furnace and the hydrogen, methane and fuel oil to the fuel side of the furnace. This offsets some of the need for fuel but reduces the by-product credits to 482 million/year and this raises the production cost to 1227/toime and reduces the operating margin to 211/tonne as valuable by-products are reduced to fuel value. The comparative cost breakdown is illustrated in Eigure 9.4. 

Gas oil cracking has all of the characteristics of naphtha cracking. The typical statistics are given in Table 9.4. Relative to naphtha, the gas oil cracking requires considerably more feed for the same ethylene output (500 kt/y) and at the same time produces increased volumes of pyrolysis gasoline and more particularly pyrolysis fuel oil. This requires an increase in the fixed capital to naphtha for the same scale of operation. 

The economic evaluation cases previously mentioned examine the points suggested with respect to several configurations of the petrochemical refinery. Case 01 is the basic olefins unit (Figure 2) which disposes of its C5-C9 fractions as a semihydrogenated "pyrolysis gasoline. The higher boiling fractions are sold as fuel oil. Butadiene separation is considered to be a part of the basic olefins operation. 

The requirement for benzene is over 6Mt per annum in the U.S.A., somewhat lower in western Europe. Coal-tar operations make only modest contributions. In western Europe the main source is pyrolysis gasoline, whereas catalytic reforming (section 12.2.2.3) is the main source in the U.S.A., where the catalytic (clay) or thermal hydrodealkylation of toluene is also more important. 

The Kureha/ Union Carbide process operates at a higher temperature than the BASF method (Figure 3.46). It uses steam as a heat carrier, at a temperature of 2,000 °C. Preheated crude oil is fed into the superheated steam in an adiabatic reactor, from which 30% ethylene is recovered. Reaction time is only 15 to 20 msec. This process also produces an aromatics-rich oil of relatively high naphthalene content which boils above the pyrolysis gasoline. The aromatic pyrolysis tar concurrently produced can be used to manufacture medium-modulus carbon fibers. 

Figure 4.2 shows the benzene plant operated by Mitsubishi Petrochemical Co, in Kashima/Japan, which refines 175,000 tpa of pyrolysis gasoline by hydrogenation and extraction using the Sulfolane process (see Chapter 4.2.1.1). 

EP2 was a commercially success story and the byproduct processing has added substantively to its benefits such that the project payback was achieved after the first 12 months of operations with all parties involved gaining commercially. In the first year, sales of propane and butane were exceeding 70,000 tons benefiting from sales prices in excess of US 700/MT and sales of pyrolysis gasoline exceeded 40,000 tons providing SEEF with a low cost feedstock to increase their economic benefits. 

---