Hydrofining

Hydrofining usually involves only minor molecular changes of the feed with hydrogen consumption in the range of about 100 to 1,000 cu.ft./bbl. Typical applications include desulfurization of a wide range of feeds (naphtha, light and heavy distillates, and certain residua) and occasional pretreatment of cat cracker feeds. 

Wax Manufacture - A waxy distillate cut from c.ude or the wax byproduct from lube oil dewaxing is first deoiled. Resulting low oil content wax is hydrofined for color improvement and fractionated into appropriate melting point grades. 

When the feed is desulfurized, the Hydrofining unit is commonly integrated with the Powerformer to conserve heat. The stripper on the hydrofiner product which removes HjS is combined with the Powerformer absorber used to recover C4+ from the tail gas. This tower is termed an absorber stripper. Powerformer tail gas is used to strip HjS from the hydrofiner product. The hydrofiner product in turn serves to absorb the C4 + from this tail gas and return it to the Powerformer. 

The Hydrofining process is acmally one of many processes that exist, but all are very similar in nature.The main difference in the various processes is in "know how". Each process differs by catalysts, equipment and/or methods, but these are rather narrow since the general field of hydrogenation is an old and well established art. 

While not shown here. Hydrofining also removes nitrogen from various nitrogen compounds. Nitrogen is one of the causes of instability. Removal of nitrogen is much more difficult than sulfur removal. 

Carbon monoxide has been found to poison cobalt molybdate catalysts. It causes not only instantaneous deactivation but a cumulative deactivation as well. It should be removed from treat gas entirely or at least reduced to a very low value. Carbon dioxide also must be removed since it is converted to CO in the reducing atmosphere employed in Hydrofining. Liquid water can damage the structural integrity of the catalyst. Water, in the form of steam does not necessarily hurt the catalyst. In fact 30 psig steam/air mixtures are used to regenerate the catalyst. Also, steam appears to enhance the catalyst activity in... 

As mentioned earlier. Hydrofining may be applied to a host of products to improve their quality. Subsequent paragraphs will show the results that can be obtained. 

Hydrofining is applied to virgin naphthas mainly in the form of a pretreatment step for the feed to catalytic reformers (Powerforming). Sulfur levels of 5 parts per million (ppm) or less are required to avoid deactivation of the platinum reforming catalyst. 

Virgin naphtha hydrofining processing conditions have been standardized at 550°F, 4 V/hr/V, 300-400 psig and 400-500 SCF/B of 70% H treat gas. Such conditions will make a 4 ppm sulfur product of most stocks of interest. 

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

Hydrofining has all the advantages of acid treating without the disadvantages. For example, acid treating does not readily remove refractory sulfur compounds such as thiophene the treated products must be rerun to remove polymers with a consequent yield loss and disposal of the acid sludges is a serious problem. 

Hydrofining has been applied to Varsols and various other solvents for the control of odor, sulfur, and corrosion characteristics. For example. Hydrofining of Iranian and Kuwait distillates demonstrated its effectiveness as a means of producing "White Spirit", a high-quality solvent naphtha distributed in the United Kingdom. 

With higher boiling stocks, mild Hydrofining of kerosene effects desulfurization, color improvement, and a reduction in wick char. Hydrofining improves odor and by reducing sulfur content makes the kerosene less corrosive. 

It should also be noted that this process does not alter the smoke point. Smoke point is a function of aromatics content and mild Hydrofining does not hydrogenate aromatics. To accomplish this, treating over a more active catalyst such as nickel tungstate at pressures of at least 800 psig is required. 

Hydrofining is employed to desulfurize high sulfur diesel stocks, both virgin and cracked. The stability of cracked diesel stocks is also improved. In the diesel range, operating conditions become more severe. Compared to naphthas, temperatures are increased from the 550-600°F level to 700°F. 

Conventional Hydrofining of diesel oils does not improve octane number because octane number improvement, like smoke point improvement in kerosenes, requires samration of aromatics. Higher pressures are needed to gain appreciable aromatics samration and cetane number improvement. 

The virgin naphtha feed after having been hydrofined over a cobalt molybdenum catalyst to remove sulftir compounds passes through the Powerformer. After stabilization, the aromatics are recovered by extracdon with... 

Plugging of a hydrofiner catalyst bed (some local codes consider catalyst... 

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