September 1947
1105
INDUSTRIAL AND ENGINEERING CHEMISTRY
975" F.1 results in cracked gasolinea that are very olefinic; and despite the advantage of ,
I OCT4NE NUMBER 1 I,. higher aromatic concentrat,ion, such gasolines may bc too low in lean-mixture octane rating. IIowever, the over-all advantages of high tcmpwature cracking as practiced on the fluid catalyst cracking units were clonvincingl>- greatnamely, higher plant rapacity because of mor? convr.rsion for a given carbon yield and much d pt~oduction of normal butcmes and enc. The production cf these olefins ha5 tieen oi trc,nipndous importaiici, t o the, synt lit tic rubhcr and aviation gasolinci proI I gral11,s. I I n viviv of tlic. over-all tlesirability of high I tt~mpcraturecracking in tht! fluid C A I alyst units, this probleni reso1vt.d itself to one of finding the, AROMATICS\ \ hest method for improving the lean-misture \ o ~ ~ i : + rating nt~ of the aviation gasoliii~without HVDROGENATED ___ h diatrinic*nt to rich-mixture perfornianw. The UNHYDROGENATED - - - - - \ rcrrt~iting of catalytic gasoline by a s x o n d \ H\ p:tw over the crac1;iiig catalyst was one ans\vcr I O L E F I NS/ 5 t o t h i s problem. However, i n the _. oli~finicgasolincv produced a t elevated craclting a teinpvrarurcs, it considerable loss of product was involved. .Isan alternatv it appeared that I simple hydrogemtion of the catalytically 156 I75 200 225 250 275 300 iU0 125 M I D B O I L I N G P O I N T OF F R A C T I O P ' , ~ F cracked gasoline might bc a desirable process if conditions were used to saturatc the olefins Figure 1. Effect of High Preisure Hjdrogenation on Octane Uumber, witlii)ut hydrogenation of the aroniarics. .Is Olefin Content, and 4roniatic Content of i \ i a t i o n Cawline Fractions will he pointed out, this type of hydrogenation from High Temperature, Fluid Catalyst Cracking of 'I'insley Gas Oil proccw proved hoth feasible and desirable, since v i t h S?nthetic Catalyst it gave about lOOV, volumetric yield of satuin leanrated uroduct. .Z large - iniurovement . mixture octane rating of the' leaded gasoline wab obtained coiltent. If hydrogenation capacity is limii mg, this procedure allo\vr a more efficient utilization of given hydrogenation facilities without any loss in rich-mixture performance. The reason for this improvement, is t h a t t,he olefins in the catalytic naphtha arid a greater over-all production of aviation gasoline. Another are prcdoininaritly of branched structure and arc thus conadvantage for acid treatment of the high boiling aromatic fractions lies in the improved rich-mixture rating which in general has verted into isoparaffins of high octane number. The laboratory dovelopment and the large scale application of this process not bcen found to occur upon hydrogenation are discussed later. I n the following discussion t,he lean-mixture octane rating of gasolines is expressed as t.he octane number determined by t,he A.S.T.M. aviation method. Rich-mixture ratings TABLE I. -4CID T R E A T M E N T O F 233-325' F. FR.4CTION O F AVIATION GASOLINE FROM HIGH TEMPER.4TURE, FLUID CATALYST are expressed as I.U.E.P. (indicated mean effective pressure) CRACKING OF COASTAL GAS OIL WITH SYNTHETIC CATALYST determined on the C.F.R. supercharged aviation engine. (II
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LABORATORY DEVELOPMEYT
Figure 1 shows t,ypical d a t a on the composition and octane rating of aviation gasoline boiling range fractions from the high temperature fluid catalyst cracking of a gas oil from a mixed basts crude (Tinsky), both before and after hj-drogenation for renioval of olefins. Aromatic concentration incrc'ases and olefin concentration decrcascs nit,li increase in boiling point. Hydrogenation, as carried out, in this process for almost complete removal of olefins, has practically no effect on the aromatics present in the crackcd material. The lower boiling fractions Os high olefin content shon, after addition of lead, a niuch greater improvement in lean-misturc octane number upon hydrogenation than do the higher boiling fractions which are less olefinic and inore aromatic in nature. Since the greatest improvement, based on octane rating alone, is ohtaiiied by thc li>-drogenationof the light naphtha, the higher boiling fractions may he by-passed around the hydrogenation stage with little loss in total product, quality. The improved stability, which is character ic of fully hydrogenated products, may be maintained in this case by acid treatment of the high boiling by-passed fractions. Table I demonstrates the improvement, in stability of high boiling, catalytically cracked fractions following acid treatment. Only low treating losses occur by this procedure since thc fraction to be acid-treated is initially low in olefin
Acid t r e a t , lb. 98% acid/barrel Yield, v o l u m e % Bromine n u m b e r , cg./gram Copper-dish g u m mg./100 ml. 5-ho:ir army gum', mg./100 ml. hlodified 16-hour army g u m , mg./100 ml.
