8.1 Introduction

• • In this lecture, we present a brief overview of the hydroprocessing operations in the petroleum refinery.The hydroprocessing operations mainly involve hydrotreating and hydrocracking units.

• From reforming and cracking reactions, the gasoline yields have been predominantly increased. However, their quality has not been addressed.

• Gasoline and other products from intermediate operations have good number of undesired materials.

• The undesired materials mainly include (a) organic sulphur containing compounds (b) organic nitrogen containing compounds and (c) metals.

• Other undesired materials include olefins (double bond compounds) and metals.

• The sulphur removal from various refinery intermediate process streams is desired for several reasons.  Firstly, the fuel specifications with lower sulphur content should be met. Secondly, the shelf life of sulphur sensitive platinum catalysts need to be increased.

• Similarly, nitrogen removal from various process streams is desired to improve yields, reduce catalyst poisoning, reduce NO_x formation in combustion etc.

• The metals such as Vanadium and Nickel need to be removed as they tend to poison the catalyst and can cause environmental problems after combustion.

• The olefin removal is primarily desired to obtain clean products after combustion. Other than this, the formation of polymeric (gum type) compounds in fuel combustion be avoided.

• Aromatics removal is desired primarily to meet the desired specifications.

8.2 Definitions of hydroprocessing, hydrotreating and hydrocracking

• • In hydroprocessing, feedstocks are sent to a catalytic reactor in the presence of hydrogen.

• Depending upon the intensity of the hydroprocessing operation, the hydroprocessing is termed as hydrotreating or hydrocracking.

• During hydrotreating, sulphur and nitrogen concentration in the final products is reduced along with the saturation of olefins and aromatics.  However, boiling range of the final products will be similar to that of the feed stock.

• During hydrocracking, heavier molecules react with hydrogen to generate lighter hydrocarbons.