Shell Higher Olefins Process E. F. Lutz Shell Development Company, P.O. Box 1380, Houston. TX 77251 Olefins, particularly ethylene, propylene, and butenes, have been key building blocks in the petrochemical industry since its inception. This stems from their ready availability, low cost, and reactivitv. which allows for simole conversion to a broad range of useful commercial prod;cts. Although this remains true today, a new class of higher molecular weight olefins has emerged over thelast 10 to 20 years. These are the linear alpha-alkenes, generally in the range of C6 through CzO,which impart unique and valuable characteristics to commercial products made from them. For example, when aloha-olefins. such as 1-hexene or 1-octene. are conolvmerized with ethileue, a stronger, tougher p&yeth;lene, called linear low density polyethylene, is produced and has superior properties as a packaging material. 1-Decene serves as the basis for automotive synthetic lubricating oils, which have extended change intervals to 12,000 miles. 1-Dodecene and higher-molecular-weight alpha-olefins are useful in making a variety of biodegradable surfactants which are widely used in household and industrial apolications. he earliest source of commercial of alphaolefins was the thermal cracking of petroleum-derived wax, a process introduced in the U S . by the Chevron Chemical Company about 20 years ago. Wax pyrolysis is performed a t over 500 OC a t a 5- to 15-8 contact time., oroducine about 90 wt% 1-alkenes a t a conversion of about 20-40 wt% per pass. Hieher conversion nroduces a substantial amount of aromatic:. Selectivities fdllow the pattern shown below.
-
.
0
wt %
Ca-Cs
33
4
8
12 16 Carbon Number
20
Figure 1. Olefin distribution as a function of carbon number
7
Cl0
25 35
C,I-CM
crc10
Typical analysis for a Cll/lz fraction is 93 wt% alpha, predominantly linear olefin, 5% dienes, and 2% paraffins. In recent times, wax cracking has largely been replaced by ethylene oligomerization processes, similar to that discovered by Ziegler and introduced in the U S . by the Gulf Oil Company about 20 years ago. The ethylene growth reaction producesa distribution of alpha-olefins as shown in Figure 1. The alpha-normal content of the alkenes is in the range of about 90-98 wt%, depending on carbon number with linearitv decreasing with increasing carbon number. -one of theumost difficult &oblems associated with all of the aloha-olefin mocesses is the oroduction of a broad ranee of alkenes, which find their way into a variety of mark& that are growing a t different rates. This can produce a shortage at imt- cnrln~nnumher and a surplus ar another, making prvduct mansgetxielit very difficult. Flexibilirs or the ability I
