PETROLEUM — FIELD 247 



which is concerned chiefly with the new catalytic processes — the defini- 

 tion will be narrowed to identify processes which decompose the sulfur- 

 hydrocarbon compounds in the gasoline, and evolve the sulfur as hydro- 

 gen sulfide or possibly as sulfur dioxide. 



Isomerization. — Inasmuch as saturated hydrocarbons can exist as 

 either straight- or branched-chain compounds, and as the branched 

 chain compounds in the gasoline boiling range have higher antiknock 

 qualities than the straight-chain compounds (e. g., iso-octane vs. nor- 

 mal heptane, the 100 and 0, respectively, of our antiknock scale), in- 

 terest in controlled changing of straight chains to branched chains 

 (isomerization) increased sharply as practicable methods were dis- 

 covered. Isomerization, as now available for our study as an isolated 

 process, is confined to butane and pentane conversion to the correspond- 

 ing iso-compounds; but inasmuch as the extremely high octane-number 

 increase obtained during certain catalytic-dehydrogenation operations 

 on gasoline can best be accounted for by assuming some isomerization 

 to have occurred, it is the opinion in many quarters that catalysts and 

 conditions will be found eventually which will extend isomerization 

 as a controlled process into the broad gasoline boiling range. 



Aromatization. — For present purposes let us define aromatization as 

 the conversion of saturated hydrocarbons to aromatic hydrocarbons, 

 e. g., conversion of hexane to benzol, heptane to toluol, etc. Processes 

 using catalysts at relatively high temperatures and moderate pressures 

 have accomplished such conversions with surprisingly high yields. 



Catalytic cracking and reforming. — As mentioned previously, crack- 

 ing involves dehydrogenation of the type defined as destructive. In 

 the rupturing of the hydrocarbon chains, there are created fragments 

 which are extremely active chemically. In the course of reacting to 

 attain chemical stability, these fragments apparently, to some degree, 

 engage in practically all of the reactions which we have been discuss- 

 ing. The use of a catalyst during cracking has the interesting effect 

 of decreasing the amount of polymerization to tar and at the same 

 time encouraging aromatization and isomerization of the cracked 

 fractions into the gasoline boiling range. As a result, material of high 

 antiknock value is produced. In catalytic reforming a different effect 

 is sought. Here aromatization and isomerization are encouraged by 

 different operating conditions and catalysts, but every effort is made 

 to suppress the chain rupture which would cause excessive conversion 

 of gasoline to gas. In figure 4 catalytic reforming is classified as de- 

 hydrogenation, but merely for convenience, and does not infer that the 

 dehydrogenation phase is considered predominant. 



Coking. — The operation of coking, whether thermal or catalytic, 

 consists of heat-treating heavy hydrocarbons, usually crude residuum 

 or cracked tar, in order to increase the ultimate yield of gasoline from 



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