Higher compression ratio automobiles of the future will require higher octane number motor fuels.
Since the virgin naphtha portion of the present gasoline pools is the lowest octane number constituent, hydroforming virgin naphtha is an attractive method of increasing the over-all octane number. The octane number of the virgin naphtha is improved in hydrof orming by dehydrogenation of naphthenes to aromatics, isomerization of normal paraffins to isoparaffins, and hydrocracking of paraffins to lower molecular weight hydrocarbons. The gasoline is low in Sulfur and stable. Operating temperatures are in the order of 900-1000~ F. and pressures in the range of 200-300 psig.
Extensive studies of the technology of hydroforming have indicated that thermal precracking of the naphtha feed has an unfavorable effect on the yieldoctane number relationship in subsequent catalytic processing. Substantial elimination of precracking by limiting the maximum temperature and time of contact in the furnace as well as in the void spaces in a fixed bed reactor has shown 4.59% higher yield of gasoline for the same octane number.
The dehydrogenation reactions in hydroforming are endothermic and would cause as much as 250' F. temperature drop through a single adiabatic fixed bed reactor. Laboratory isothermal reactors made possible by external heating of the reactor walls have shown 5.5% yield improvement for the same octane number over adiabatic operations.
The Fluid catalyst technique has been demonstrated in commercial Fluid catalytic cracking plants. X Fluid hydro former is similar to a catalytic cracking unit in that it has a Fluid reactor and a regenerator, the latter being smaller than in a cracking unit because of the lower carbon production. Catalyst is circulated between the two vessels to remove carbon deposits by air combustion and catalyst losses are controlled by means of cyclones and a hydrocarbon * Standard Oil Development Company. vapor scrubber. The continuous flow of reactants and catalysts through the two vessels makes possible a simple and flexible plant. The highly turbulent mixing of catalyst and vapors in the body of the reactor maintains isothermal conditions during the reaction. This together with supply of heat in the regenerated catalyst, avoids high temperatures in the oil preheater. Thus, the yield advantages of no precracking and isothermal processing are combined.
The Fluid technique as compared with the best improved fixed bed processing methods has been shown in pilot units to give a 5.5% yield advantage when producing a 95 CFRR O.N. clear gasoline.
Plant estimates for the two units show the Fluid process to cost 40% less than the fixed bed unit. When producing 85 CFRR clear octane number hydroformates, the investment is in the order of $ 250 per BlSD of feed. This investment is considerably less than thermal equipment to produce the same quality and quantity of ga
