Application: The CDHydro process is used to selectively hydrogenate diolefins in the top section of a hydrocarbon distillation column. Additional applications including mercaptan removal, hydroisomerization and hydrogenation of olefins and aromatics are also available.
Description: The patented CDHydro process combines fractionation with hydrogenation. Proprietary devices containing catalyst are installed in the fractionation column’s top section (1). Hydrogen is introduced beneath the catalyst zone. Fractionation carries light components into the catalyst zone where the reaction with hydrogen occurs. Fractionation also sends heavy materials to the bottom. This prevents foulants and heavy catalyst poisons in the feed from contacting the catalyst. In addition, clean hydrogenated reflux continuously washes the catalyst zone. These factors combine to give a long catalyst life. Additionally, mercaptans can react with diolefins to make heavy, thermally-stable sulfides. The sulfides are fractionated to the bottoms product. This can eliminate the need for a separate mercaptan removal step. The distillate product is ideal feedstock for alkylation or etherification processes.
The heat of reaction evaporates liquid, and the resulting vapor is condensed in the overhead condenser (2) to provide additional reflux. The natural temperature profile in the fractionation column results in a virtually isothermal catalyst bed rather than the temperature increase typical of conventional reactors.
The CDHydro process can operate at much lower pressure than conventional processes. Pressures for the CDHydro process are typically set by the fractionation requirements. Additionally, the elimination of a separate hydrogenation reactor and hydrogen stripper offers significant capital cost reduction relative to conventional technologies.
Feeding the CDHydro process with reformate and light-straight run for benzene saturation provides the refiner with increased flexibility to produce low-benzene gasoline. Isomerization of the resulting C5 / C6 overhead stream provides higher octane and yield due to reduced benzene and C7+ content compared to typical isomerization feedstocks.
Economics: Fixed-bed hydrogenation requires a distillation column followed by a fixed-bed hydrogenation unit. The CDHydro process eliminates the fixed-bed unit by incorporating catalyst in the column. When a new distillation column is used, capital cost of the column is only 5% to 20% more than for a standard column depending on the CDHydro application. Elimination of the fixed-bed reactor and stripper can reduce capital cost by as much as 50%.