Production of light olefins from aliphatic hetero compounds

The process of making light olefins containing 2 to 4 carbon atoms which comprises contacting a feedstock comprising one or more aliphatic hetero compounds with a silicoaluminophosphate molecular sieve comprising a molecular framework of [AlO.sub.2 ], [PO.sub.2 ] and [SiO.sub.2 ] tetrahedral units, at effective process conditions to produce said light olefins wherein the silicoaluminophosphate molecular sieve comprises a microporous crystalline silicoaluminophosphate whose unit empirical formula in the as-synthesized and anhydrous form is

• mR:
• (Si.sub.x Al.sub.y P.sub.z)O.sub.2
• wherein "R" represents at least one organic templating agent present in the intracrystalline pore system;
• "m" has a value of from 0.02 to 0.3;
• "m" represents the moles of "R" present per mole of (Si.sub.x Al.sub.y P.sub.z)O.sub.2 ;
• "x", "y" and "z" represent the mole fractions of silicon, aluminum and phosphorus respectively, present as tetrahedral units, said mole fractions being such that they are within the pentagonal compositional area defined by points A, B, C, D and E of the ternary diagram which is FIG. 1.