Hydrotreating processes feedstocks

Hydrotreating reduces the sulfur content of all the products. With hydrotreated feeds, more of the feed sulfur goes to coke and heavy liquid products. The same sulfur atoms that were converted to H S in the FCC process are also being removed first in the hydrotreating process. The remaining sulfur compounds are harder to remove. The heavier and more aromatic the feedstock, the greater the level of sulfur in the coke (Table 2-7). 

In principle, the flowsheet of an industrial facility is similar to those of the different hydrotreating processes (Figure 5.2-42) [61]. The feedstock C4 cut rid of water is pressurized to about 15 to 20 bar by pumping, injected with a hydrogen-rich gas and then, preheated by heat exchange with the reaction effluent and by steam. In a downflow stream, it then enters the reactor, which operates in a gas-liquid mixed phase with one or more catalyst beds (palladium, rhodium on inert alumina). After cooling, the isomerization products are flashed... 

Hydrotreating processes have two definite roles (1) desulfurization to supply low-sulfur fuel oils and (2) pretreatment of feed residua for residuum fluid catalytic cracking processes. The main goal is to remove sulfur, metal, and asphaltene contents from residua and other heavy feedstocks to a desired level. 

The Chevron deasphalted oil hydrotreating process is designed to desulfurize heavy feedstocks that have had the asphaltene fraction removed by prior application of a deasphalting process (Chapter 7). The principal product is a low-sulfur fuel oil that can be used as a blending stock or as a feedstock for a fluid catalytic unit (Table 9-7). 

Unicracking hydrodesulfurization (Unicracking/HDS) process a fixed-bed, catalytic process for the hydrotreating heavy feedstocks. 

Table 1 Typical hydrotreating process conditions for various feedstocks...

Production of cresols and xylenols from spent caustic washes of the petroleum refineries has been confined mostly to the Untied States since cresolates feedstocks have been inadequate in other countries. Besides as a result of use of UOP s Merox process of sweetening which does not use NaOH solution, or of hydrotreating process, less and less cresols... 

Feedstocks for this very flexible process are usually vacuum distillates, deasphalted oils, residues (hydrotreated or not), as well as by-products from other processes such as extracts, paraffinic slack waxes, distillates from visbreaking and coking, residues from hydrocracking, converted in mixtures with the main feedstock. 

Older rerefining units used 2-5 kg/L of activated clay at 40—70°C and higher temperatures in place of TEE to clean the oil (80). More elaborate chemical and hydrotreating of used engine oils without a distillation step has been developed by Phillips Petroleum for processing 40,000 /yr (10 X 10 gal/yr). Establishment of a reflable feedstock supply is a critical consideration for larger rerefining plants. 

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