There are many well known processes for the production of ethylene and propylene from feedstocks containing saturated hydrocarbons. One such process is thermal or steam cracking. By this method, a hydrocarbon feed stream is heated in an externally fired reactor to a temperature to effect conversion of a portion of the feedstream to gaseous unsaturated hydrocarbons. A particular example of this type of process is described in U.S. Pat. No. 3,764,634. In this process a hydrocarbon feedstock is introduced to an externally heated tubular cracking furnace together with a particulate abrasive material. The mixture is heated to a temperature in the range from about 600.degree. to about 900.degree. C. to convert a substantial portion of the feedstock to gaseous, unsaturated hydrocarbons. The resulting fluidized vaporous reaction mixture containing suspended abrasive particles is circulated through the cracking furnace to a quenching zone, whereby the scouring action of the abrasive particles prevents the deposition of by-product coke on the inner surface of the furnace.
Additional hydrocarbon steam cracking methods are described in U.S. Pat. Nos. 3,720,600 and 3,708,552.
A second method of producing ethylene and propylene from ethane and propane is by dehydrogenation. U.S. Pat. No. 3,113,984 describes a method for the dehydrogenation of hydrocarbons to produce olefins having from three to five carbon atoms per molecule from a feedstock having the same number of carbon atoms per molecule. According to this process, a reactant gas stream consisting of a hydrocarbon feedstock, steam, oxygen and inert gas is produced. The volume ratios of the hydrocarbon feed, steam and oxygen in the reactant stream are controlled within a certain prescribed range. The reactant gas stream is passed though a bed of activated charcoal granules to produce a product stream containing olefins having the same number of carbon atoms as the feedstock.
U.S. Pat. No. 3,647,682 discloses a dehydrogenation process for producing olefins from petroleum feedstocks rich in saturated hydrocarbons using zeolitic molecular sieve catalysts. This process provides for catalyticaly cracking paraffinic hydrocarbons to produce ethylene and propylene.
There are also a number of other dehydrogenation processes which are used in the art. In one process, fresh feed is mixed with unconverted hydrocarbon recycle feed and hydrogen-rich recycle gas and converted to the desired product over a noble metal catalyst such as platinum over alumina, at about atmospheric pressure.
Other processes use multiple metal promoted catalysts over highly calcined supports. Fresh feed and unconverted hydrocarbon recycle is passed over the catalyst at pressures from about 1 to 8 atmospheres and temperatures above about 475.degree. C. in the presence of at least 2 to 3 moles of steam per mole of feed for dilution. Examples of dehydrogenation processes using metal promoted catalysts are described in U.S. Pat. Nos. 3,641,182 and 3,880,776.
Still another process uses a Chromia catalyst under vacuum and at a temperature effective for dehydrogenating the propane.