Conversion of vegetable oils on Pt/Al2O3/SAPO-11 to diesel and jet fuels containing aromatics

Abstract

Vegetable oils are excellent feedstock for production of diesel and jet fuels. However, catalysts and processes published in the literature do not produce drop-in fuels. One of the major problems is the selectivity and stability of the catalysts. It is vital that the hydrotreating is tested after at least 200h on stream to measure the steady-state performance of the catalyst rather than its initial activity. The presence of aromatics is a critical issue. This study addresses specifically the issue of aromatics related to the composition of the vegetable oils. A novel Pt/Al2O3/SAPO-11 is used. Testing six different oils indicates that a certain level of poly-unsaturation of the fatty acids is required to produce relatively high aromatics content. This was further supported in specific tests of vegetable oils, fatty acids and C16 hydrocarbons dissolved in decane. Therefore, poly-unsaturated soybean, sunflower and camelina oils produce fuels containing about 15wt% aromatics while the content of aromatics in the product of palm or castor oils hydrotreating is 2wt%. A tentative reactions sequence was suggested leading to triglycerides aromatization on the basis of measured dependency of hydrotreated oil products on the process space time, structure of aromatic hydrocarbons and published chemical transformations of triglycerides. Three stage processes were proposed to produce jet fuels that meet the standards. 42–48wt% yield of the jet fuel is reported. This is a basis for commercial production of drop-in diesel and jet fuel.