I/EC REPORTS &
INTERPRETS
BASF Cracker Makes Ethylene from Crude Oil :
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German unit avoids reactor-regenerator duplication, gives high yields of olefins and few by-products M
Major components of the process are housed in this structure 26 A
INDUSTRIAL AND ENGINEERING CHEMISTRY
ORE DETAILS about
the newer
E u r o p e a n processes for petrochemical olefin production continue to become available. Latest case in point is t h e fluidizcd bed crude oil cracking process developed by Badische Anilin- & Soda-Fabrik, Ludwigshafen, West G e r m a n y {C&EN, N o v . 9, 1959, p . 50). Badische has been r u n n i n g its unit nonstop for more t h a n two years now, a n d has accumulated sufficient confidence in its design to begin talking in more d e p t h a b o u t it. Significance of its n e w process, Badische points out, lies in its ability to h a n d l e a wide variety of crude a n d residual oils, its high yield of ethylene, propylene, a n d Cj's, a n d its operating ease. A n d as a result of the operating knowledge it h a s gained, Badische c a n increase c a p a c ity—i.e., one unit can process 200,000 metric tons per year of crude t o 50,000 tons of ethylene, 30,000 tons of propylene, a n d more than 12,000 tons of C^s. Like fluid coking, this BASF process is basically a d a u g h t e r of t h e Winkler process, developed by Badische i n t h e twenties a n d c o m mercialized by Esso Research a n d Engineering in t h e U . S. Badische has some 40 years experience w i t h fluidized bed roasting, best exemplified by its application to pyrites roasting ( I / E C , O c t o b e r 1958, p . 1500). It differs from fluid coking in that it uses only o n e vessel for b o t h cracking a n d r e g e n e r a t i o n a n d t h a t it is aimed at m a k i n g gaseous olefins i n stead of liquid products. T h u s it operates a t considerably higher temperatures.
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The Chemical World Today H o w It Works
I n t o a fluidized bed of petroleum coke at about 750° C. go steam, oxygen, and the crude oil. T h e steam a n d oxygen enter below t h e b e d ; the oil goes in about 2 feet above the grid fixed a t the lower level of the bed. I n the lower p a r t of the bed, some of the coke is burned in the steamoxygen stream to provide heat for the endothermic cracking reaction. T h e heated coke particles rise in the bed to t h e reaction zone, where they yield their heat. Circulation is so good that the t e m p e r a t u r e of the bed (within the limits of measurement) is uniform from top to bottom, Badische says. All the oxygen is used u p in the combustion process by the time the gas stream reaches the height where c r u d e oil enters. Hence, the cracking reactions a r e not complicated by oxidation reactions, the c o m p a n y points out. Cracking time, controlled by the flow rate of steam plus oxygen, is more t h a n one second—a long time for a cracking reaction. I t is closely interrelated with cracking temperature which, a t a r o u n d 750° C , is lower t h a n most cracking processes. Changing t h e oxygen rate changes the cracking t e m p e r a t u r e . U n d e r these conditions—one second contact time at 720° to 750° C — the m a i n cthylcne-forming fractions are "correctly cracked," as Badische puts it. Smaller molecules won't crack optimally, but in crude oil they are present only in small quantities. Some larger molecules undergo secondary reactions to yield soot a n d asphalts. These mostly stick to the coke particles in the bed, though, a n d are carried back down to the oxidizing zone a n d burned off to supply some of the heat of reaction. Contact time and bed t e m p e r a t u r e c a n be varied widely. T h u s , crude oils from m a n y different sources d e m a n d i n g different conditions for o p t i m u m cracking c a n be readily processed, BASF h a s found. T h e
These Are Typical Yields when 1 Ton o f a Minas Crude O i l Is Fed t o the BASF Cracker (Using about 10,000 cu. ft. of Oxygen per ton) 1,1). Ethylene Propylene C4's Hydrogen Methane Ethane Propane Acetylene
co
C O2
Light oil Aromatic fraction Coke
507 276 132 18 265 99 15 2 871 220 309 88 99
unit can even handle oil fractions as light as straight n a p h t h a s a n d as heavy as the heaviest residual oils. After Cracking
Cracked gases, containing some soot, tars, oils a n d other contaminants, enter a cyclone directly after leaving the cracking zone. T h e r e any entrained coke particles arc separated a n d returned to the coke bed. Next, the gases flow to a quencher, where they are cooled to about 300 e C. as they flow through a spray of recir-
culated " c o l u m n sump oil." T h e quenching also removes most of the residual carbon dust a n d asphaltic constituents, so that the gases are relatively clean when they leave. T h e 300° C. gas stream goes next to a fractionating column with a head temperature maintained a t about 100° C. Oils boiling above 100° C. are condensed and fractionated, yielding a high-boiling c u t (column sump oil) taken from the bottom of the column and a highly aromatic cut taken from about the middle. T h e column sump oil not used in the quencher is recycled directly back into the coke bed, sticks to the coke particles, is carried down into the oxidation area, a n d burned. T h e aromatic fraction, rich in n a p h t h a l e n e , is an end product. Oils boiling below 100° C. go overhead with the gases, arc condensed with the steam in a cooler, a n d arc separated as a light oil fraction, part of which goes back to the top of the fractionating column, t h e excess being d r a w n off as a n end product. Uncondensed gases leaving the cooler contain hydrogen, carbon monoxide a n d dioxide, m e t h a n e ,
Simplified flow d i a g r a m shows basic steps in process VOL. 53, NO. 11 ·
NOVEMBER 1961
27 A
PHYSICAL
PROPERTIES
ORTHO-ANISALDEHYDE MOLECULAR BOILING MELTING
WEIGHT...
POINT
136.14
(at 760 mm Hg)..
.238°C
38-39"C (2) 3"C SPECIFIC GRAVITY (liquid) 25° 126".. .1.1274 SPECIFIC GRAVITY (solid) 25°/25°.. . 1.258 REFRACTIVE INDEX η 20°/D.. .1.5608 ODOR. . .Burned, slightly phenolic SOLUBILITY in H20-Slightly soluble APPEARANCE... White to light tan solid *Exists
POINTS*...(1)
in two crystalline
forms
ANSUL CHEMICAL COMPANY, MARINETTE, WISCONSIN ώ INDUSTRIAL CHEMICALS ·γ· REFRIGERATION PRODUCTS
