Ethylene recovery

The latest of three ethylene recovery plants was started in 1991. Sasol sold almost 300,000 t of ethylene in 1992. Sasol also produces polypropylene at Secunda from propylene produced at Sasol Two. In 1992 Sasol started constmction of a linear alpha olefin plant at Secunda to be completed in 1994 (40). Initial production is expected to be 100,000 t/yr pentene and hexene. Sasol also has a project under constmction to extract and purify krypton and xenon from the air separation plants at Sasol Two. Other potential new products under consideration at Sasol are acrylonitrile, acetic acid, acetates, and alkylamines. 

Fig. 7. FCC off-gas ethane/ethylene recovery process. C3 = propane refrigerant.

Cryogenic processes using turboexpanders facilitate high levels of ethylene recovery from refinery gas while producing byproducts of hydrogen- and methane-rich gas. In a cryogenic process, most of the ethylene and almost all of the heavier components are liquified and ethylene is separated from this liquid. 

The principal function of the ethylene recovery facilities is to recover high... 

The Cj plus bottoms from the demethanizer then go to the deethanizer. A propylene-propane bottoms product containing 90-92% propylene is obtained which may either be sold, used directly as propylene- 90, or further purified. The ethylene-ethane overhead from the deethanizer is separated in the splitter tower yielding a 99.8% overhead ethylene product at -25°F. The ethane bottoms at -l-18°F may either be sent to fuel gas or used as feed to an ethane cracking furnace. Overall ethylene recovery in these facilities is about 98%. The product is of very high purity with less than 50 parts per million of non-hydrocarbon contaminants and a methane plus ethane level below 250 ppm. 

Because of the high olefin yields and low light ends make, the MTO process does not require the high cost separation equipment of a conventional ethylene recovery unit. Figure 12.12 shows the overall process design, including product... 

Reactor effluent is chilled and light-ends are separated from the C2-hydrocarbons. The demethanizer overhead is processed for ethylene recovery while the bottoms is sent to ethylene/ethane separation. An open heat-pump splitter is applied, thus sending ethylene product to the gas pipeline from the discharge of the ethylene-refrigerant compressor. 

Minton, B. K, Ethylene recovery from refinery gas , AICHE 86th National Meeting. Hoastoa, Texas (1/5 April 1979V... 

Moving bed gas adsorbers also have been proposed and used, patterned after moving bed gas oil crackers. In the Hypersorber of Figure 15.28, flows of gas and solids are countercurrent in a single vessel. After saturation, the solid is stripped with steam and removed at the bottom of the tower, and gas is lifted to cooling and adsorption zones. The control mechanism for solids flow and typical performance for ethylene recovery from cracked gases also are shown with the figure. Partly because of attrition losses and the advent of competitive processes for ethylene recovery, the Hyper-... 

Uncondensed gases from the quench tower are recycled to the reactor, except for a purge stream to remove inerts. The purge stream goes through an ethylene recovery system to keep the over-all utilization of ethylene high—i.e., better than 95%. 

Steam cracking of ethane is the most widely used process for making ethylene. U.S. 6,578,378 (to Technip-Coflexip) gives a typical ethane cracker product composition and describes an improved separation process for ethylene recovery. U.S. 5,990,370 (to BP) gives yields for ethane, propane, and mixtures. U.S. 5,271,827 (to Stone Webster) gives details of furnace design and yields for a naphtha feed. Several other separation schemes for ethylene and propylene recovery are described in the literature. Estimate the cost of production for a new steam cracking facility that produces 1 million metric tons per year of ethylene and 600,000 metric tons per year of propylene. What feedstock would you recommend ... 

Stephenson, W.K. and Rowe, C.T., 1993, Fouling control in ethylene recovery systems. Heat Transfer - Atlanta A.I.Ch.E. Symposium Series, Vol. 89, pages 335 - 340. 

Ethylene oxide - Shell Global Solutions International B. K Ethylene oxide/ethylene glycols - Scientific Design Company, Inc. Ethylene recovery from refinery offgas with contaminant removal - The Shaw Group... 

Ethylene recovery from refinery offgas with contaminant removal... 

Description The ROG unit is broken down into sections including feed contaminant removal, ethylene recovery and propylene recovery. Feed contaminants including acid gases, oxygen, NO, arsine, mercury, ammonia, nitrites, COS, acetylenes and water must be removed. It is critical that the designer of the unit be experienced with feedstock pretreatment since many of the trace components in the offgas can have an impact on the ultimate product purity, catalyst performance and operational safety. 

The ROG unit can include an ethylene recovery section that produces either dilutant or polymer-grade ethylene. Otherwise, the purified offgas stream is directed into the ethylene plant for further purification and recovery. Depending on the capacity constraints of the ethylene plant or the offgas quantity of methane, nitrogen and hydrogen, the ROG unit may include a cold box, followed by a demethanizer, a deethanizer and for polymer-grade ethylene, a splitter as well. 

Another option is illustrated in Figure 17 [22]. This diagram shows a simplified process flow diagram for an oxygen-based fixed bed oxychlorination system with ethylene recovery. With this system, the ethylene-rich oxy-... 

Vapor gas separation in polyolefin and polyvinyl chloride production Hydrocarbon separations Ethylene recovery in ethylene oxide production Olefin/paraffin separation Air separation Air drying CO2 capture... 

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