Steam cracking of ethane

As a constituent of natural gas, ethane is normally burned with methane as a fuel gas. Ethane s relation with petrochemicals is mainly through its cracking to ethylene. Ethylene is the largest end use of ethane in the U.S. while it is only 5% in Western Europe. Chapter 3 discusses steam cracking of ethane. 

Table 8.1 shows the stochastic model solution for the petrochemical system. The solution indicated the selection of 22 processes with a slightly different configuration and production capacities from the deterministic case, Table 4.2 in Chapter 4. For example, acetic acid was produced by direct oxidation of n-butylenes instead of the air oxidation of acetaldehyde. Furthermore, ethylene was produced by pyrolysis of ethane instead of steam cracking of ethane-propane (50-50 wt%). These changes, as well as the different production capacities obtained, illustrate the effect of the uncertainty in process yield, raw material and product prices, and lower product... 

As can be seen, there is a small portion of ethylene produced in the gas. This small amount of olefin was sufficient for the early days of the chemical industry but soon became displaced by the larger production volume of olefins by steam cracking of ethane, LPG and naphtha from oil and gas sources. 

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 ... 

Ethylene production by steam cracking of ethane Eonr cases with two or three objectives from (1) maximization of ethane conversion, (2) maximization of ethylene selectivity, and (3) maximization of ethylene flow rate. NSGA-n Reactor inlet temperatnre and length were observed to be the most important decision variables. Tarafder et al. (2005b)... 

H-Oil unit are processed for sulfur recovery and then sent for separation through the gas recovery facilities associated with the steam cracker. Remaining unconverted residue from the H-Oil operation is used as a fuel oil component for plant fuel. Ethylene is manufactured by steam cracking of ethane, propane, naphtha, and distillate, and products from these operations are separated in conventional gas recovery facilities. Hydrogen for H-Oil is partially supplied by by-product recovery from steam cracker and H-Oil off-gases supplemented by steam reforming of methane. The heavy oils produced in steam cracking of naphtha and distillate are blended with the H-Oil residue to yield plant fuel. 

Ethylene is the largest volume organic chemical product, with world production over 50 billion pounds per year. It is normally produced by steam cracking of ethane or heavier hydrocarbons. This process is quite energy and capital intensive. 

It can also be obtained by steam cracking of ethane at temperatures above 1200°C. Nowadays acetylene has generally been replaced by alkenes as a chemical feedstock. India and East European countries however, continue to use some acetylene technology as they have adequate coal reserves but are oil importers. 

The specific raw material used in cracking processes depends on the natural resources from each geographic region, and this determines the final distribution of olefins.Thus, in Europe and Asia, ethylene is produced from naphtha, gas oil, and natural gas condensates (co-producing propylene, C4-olefins and aromatic compoimds), whereas in the US, Canada, and the Middle East, steam cracking of ethane and propane is mainly employed. One aspect to be considered is the fact that for the production of 1 ton of ethylene in a typical naphtha cracker, 3.3 tons of naphtha are required," while when using ethane only 1.7 tons of feed are needed. 

To date, some of the best results reported for steam cracking of ethane are i) selectivity to ethylene of 84% for ethane conversion of 54% (at 800 C, residence time of 0.79 s, ethane partial pressure of 154 kPa, and 0.3 kgwater/kgraw) ii) selectivity to ethylene of 78% for ethane conversion of 69% (at 833°C, residence time of 0.75 s, ethane partial pressure of 154 kPa, and 0.3 kgwater/kgraw). Therefore, neither the energy efficiency (reaction temperatures of 800°C and above in an endothermic reaction) nor the productivity are optimal in the steam cracking processes. 

---