Secondary Cracking and Upgrading of Shale Oil from Pyrolyzing Oil Shale over Shale Ash

Abstract

Considering oil shale pyrolysis with a solid heat carrier, this article investigated the effect of shale ash, as the bed material for secondary reactions of pyrolysis volatile, on final product distribution and quality of oil shale pyrolysis in a laboratory dual-stage fixed bed reactor. The examined factors included the residence time of pyrolysis volatile in a shale ash bed and the temperature of shale ash (i.e., cracking temperature). Prolonging the pyrolysis volatile residence time in the shale ash bed from 0 to 10 s decreased the shale oil yield by 31.0% but increased the fraction of gasoline and diesel (boiling point <623 K) by 46.4%. A part of heavy oil (boiling point >773 K) was cracked to increase the yields of light oil and pyrolysis gas (especially H2 and CH4). The shale ash bed temperature was the key factor affecting the product distribution. The catalytic effect of shale ash lowered the shale oil cracking temperature for achieving the same degree of oil cracking. The catalytic activity of shale ash for cracking shale oil was shown to be closely dependent on the metal oxides in the ash. While CaO and Na2O tended to inhibit the formation of coke and to promote catalytic reforming, Fe2O3 showed good activity in cracking shale oil and forming coke.