Petrochemical processing, high-temperature

TfflS SECTION INCLUDES TESTS for determining the materials of construction requirements for equipment used for manufacturing chemicals. This includes both bulk chemicals, which are typically manufactured in dedicated equipment in large quantities, and specialty chemicals, which are most often made in smaller quantities and often in equipment used for more than one process. Tests for both organic and inorganic chemicals eure included. Because some tests require the presence of an electrolyte, they are not suitable for many pure organic processes. Equipment intended for use in the pharmaceutical, petrochemical, or high-temperature gas phase or molten salt processes have special requirements that are not included in this section. 

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). 

Spent Sulfuric Field. Spent sulfuric acid recovered from petrochemical and refinery processes can be fed to a high temperature furnace at 870—1260°C, where it is transformed kito sulfur dioxide, water, and other gaseous products. After suitable scmbbkig and drykig, the gases are passed to a conventional contact sulfuric acid plant (263). 

The principal use of the alkylation process is the production of high octane aviation and motor gasoline blending stocks by the chemical addition of C2, C3, C4, or C5 olefins or mixtures of these olefins to an iso-paraffin, usually isobutane. Alkylation of benzene with olefins to produce styrene, cumene, and detergent alkylate are petrochemical processes. The alkylation reaction can be promoted by concentrated sulfuric acid, hydrofluoric acid, aluminum chloride, or boron fluoride at low temperatures. Thermal alkylation is possible at high temperatures and very high pressures. 

Uses. Solvent for high-temperature resins petrochemical processing, in the microelectronics fabrication industry, dyes and pigments, industrial and domestic cleaning compounds agricultural and pharmaceutical formulations... 

The man-made catalysts, mostly solids, usually aim to cause the high-temperature rupture or synthesis of materials. These reactions play an important role in many industrial processes, such as the production of methanol, sulfuric acid, ammonia, and various petrochemicals, polymers, paints, and plastics. It is estimated that well over 50% of all the chemical products produced today are made with the use of catalysts. These materials, their reaction rates, and the reactors that use them are the concern of this chapter and Chapters 19-22. 

For illustration, a number of high-temperature gas-phase processes are discussed in some detail in this and the following chapter. Low-temperature applications such as atmospheric chemistry are outside the scope of this book. High-temperature gas-phase reactions are important in combustion, incineration, flue gas-cleaning, petrochemical processes, as well certain processes in chemical synthesis and materials production. While the details of these systems may vary significantly, they share some characteristics that are common for all gas-phase reaction mechanisms. 

Sulfur chemistry is important both in combustion and in the petrochemical industry. Most fossil fuels contain sulfur, and also biofuels and household waste have a sulfur content. As a consequence sulfur species are often present in combustion processes. Knowledge of gas-phase sulfur chemistry occurring in combustion has bearing on pollutant emissions and on system corrosion. Air pollution by SO2 still constitutes a major environmental concern and search for control techniques has motivated research also on high-temperature homogeneous sulfur chemistry. However, more recent work on sulfur chemistry has been concerned mainly with the effect of sulfur on other pollutant emissions, such as NO and CO, and with the SO3/SO2 ratio, which is important for the corrosive potential of the flue gas and for formation of sulfur containing aerosols. 

In the petrochemical industry, gas-phase sulfur chemistry is important in the Claus pro-cess[141], which is used to remove sulfur from acid gas streams generated in oil and gas operations. In this process a high-temperature furnace (1200-1500 K) is used to oxidize about a third of the H2S in the acid gas to SO2. Subsequently the remaining H2S reacts with the SO2 over a catalyst (440-640 K) to form free sulfur. The process can be described in terms of the overall reactions... 

Nickel alloys containing chromium and iron of the composition given in Table 4.38 are used widely in chemical, petrochemical and other high-temperature processes. 

The high temperature process is the only commercially proven process for the production of olefins and liquids from coal. Current developments favour a low temperature process which is commercially proven to produce liquids and wax from coal or gas. The low temperature process produces a waxy synthetic crude oil which is cracked to produce diesel of high cetane and naphtha. The naphtha, which has high level of Unear paraffins, is sold on the petrochemical naphtha market rather than conversion into gasoline. The conversion of this naphtha into olefins by steam cracking has been addressed in previous chapters. 

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