Industrial Research 



149 



stock in a 24-hoiir day. In contrast to this, the largo 

 combination cracking and distiUation units now in 

 operation range in capacity to over 35,000 barrels per 

 day, and the operating time between shut-downs for 

 cleaning and repairs has increased from 1 day to 3 

 months or more. The severity of service conditions 

 for the equipment employed has been a constant 

 stimulus to metallurgists to produce more endm'ing 

 materials of construction. This is an ever present 

 problem because the petroleum technologist is always 

 ready to employ conditions of temperature and pres- 

 sure exceeding those possible with the latest develop- 

 ments in special alloj's and steels. 



The developments in cracking have not been confined 

 to increasing gasoline yield but have also led to marked 

 improvement m qualit5\ By way of illustration, it 

 has become possible to vaiy the volatility within wide 

 limits by changing the ratio of low- to high-boiling 

 material produced, a matter of considerable importance 

 from the standpoint of adjusting fuel performance to 

 meet seasonal requirements. Within reasonable limits, 

 it is now also possible to alter the chemical composition 

 bj' controlling the degree of branchiness, the unsatura- 

 tion, and the aroma ticity of the hj'drocarbons boiling 

 in the gasoline fractions, which in turn gives products 

 of improved antilcnock performance commonly 

 expressed in terms of octane number. 



A further advance, improving fuel quality, resulted 

 from the introduction of reforming. The reforming 

 operation is similar to cracking except that it is con- 

 cerned with raising gasoline quality rather than yield. 

 By the application of heat, the higher boiling naptha 

 fractions of low octane numbers are converted through 

 the processes of isomerization, cyclization, and de- 

 hydrogenation, into compounds of higher octane 



MlLLrON 

 BARRELS 



1921 1923 1925 1927 1929 I9JI I9J3 1935 1937 1939 



Figure 36. — The Production of Domestic Gasoline in tlie 

 United States, 1921-39 



numbers, with some attendant decrease in boiling 

 range and production of gaseous degradation products. 



The extensive use of cracking and reforming intro- 

 duced a new problem to the industry, because of the in- 

 stability toward oxidation and i)olymerization of cer- 

 tain of the unsaturated compounds produced. To 

 avoid formation of gum in gasoline, it became necessary 

 to develop new and improved treating methods. And 

 besides treating methods, oxidation inhibitors were 

 developed which when added in minute quantities 

 would greatly improve the stability of gasoline. 



Closely related to cracking is the high pressure hydro- 

 genation process for producing gasoline from heavier 

 hydrocarbon fractions. It is capable of wide varia- 

 tions in operating conditions and in results produced. 

 Such destructive hydrogenation can cither be directed 

 toward the production of gasoline yields far in excess of 

 those which can be obtained by any cracking process, 

 or toward producing gasoline containing aromatic 

 type products of very high octane number. 



Efforts to replace thermal with catalytic cracking 

 I)rocesses are already producing promising results. 

 Because of the milder operating conditions and the 

 selective action of the catalysts employed, it is possible 

 in this manner to obtain better over-all yields of desir- 

 able products and a gasoline of improved octane num- 

 ber. Although much of the experience gained in 

 thermal cracking can be applied directly here, numerous 

 new problems have been and are still encountered in the 

 development of both catalysts and operating conditions. 



Synthetic Fuels 



The need for higher gasoline yields and the trend 

 toward gasolines of improved performance with respect 

 to octane rating and volatility, both worked in the direc- 

 tion of more extensive as well as more intensive crack- 

 ing. Intensive cracking in turn, meant a gradually 

 increasing production of gaseous byproducts, which in 

 addition to the amounts already available as natural 

 gas, became a serious problem to the industry. A 

 variety of methods for converting at least some of these 

 gaseous hydrocarbons back into higher molecular 

 weight compounds boiling in the gasoline range have 

 been developed in recent years as a result of a vast 

 amount of research work. Some of the methods employ 

 straight thermal polymerization under conditions more 

 severe than those normally employed in cracking opera- 

 tions. Other methods depend upon the use of catalysts 

 which selectively polymerize the imsaturated constit- 

 uents. Still another method known as alkylation 

 depends upon the combining of an olefin with an iso- 

 paraffin. The alkylation process can be carried out 

 either by the use of high temperatures and pressures, or 

 at lower temperatures and pressures, by employing 

 sulfuric acid as a catalyst. 



