This invention relates to catalytic reactor operation wherein a liquid phase is treated with a gaseous reactant. In particular it relates to a technique for contacting multi-phase reactants in a fixed porous catalyst bed under continuous operating conditions, including methods and apparatus for controlling transverse fluid flow in the reactor.
Chemical reactions between liquid and gaseous reactants present difficulties in obtaining intimate contact between phases. Such reactions are further complicated when the desired reaction is catalytic and requires contact of both fluid phases with a solid catalyst. In the operation of conventional co-current multiphase reactors, the gas and liquid tend to travel different flow paths. The gas phase flows in the direction of least pressure resistance; whereas the liquid phase flows by gravity in a trickle path over and around the catalyst particles. Channel flow and gas frictional drag tend to make the liquid flow non-uniformly, thus leaving portions of the catalyst bed underutilized due to lack of adequate wetting.
Various attempts have been made to avoid maldistribution, such as the provision of multiple layers of catalyst with interlayered redistributors located along the reactor longitudinal axis. Numerous multi-phase reactor systems have been developed wherein a fixed porous bed of solid catalyst is retained in a reactor. Typically, fixed bed reactors have been arranged with the diverse phases being passed cocurrently over the catalyst, for instance as shown in U.S. Pat. Nos. 4,126,539 (Derr et al), 4,235,847 (Scott), 4,283,271 (Garwood et al), and 4,396,538 (Chen et al). Other known techniques for contacting liquid-gas mixtures with solid catalysts include slurry catalyst, ebullated bed, crosscurrent and countercurrent systems, such as disclosed in U.S. Pat. Nos. 2,717,202, 3,186,935, 4,221,653, and 4,269,805. The above cited patents are incorporated herein by reference.
In the petroleum refining industry, multi-phase catalytic reactor systems have been employed for dewaxing, hydrogenation, desulfurizing, hydrocracking, isomerization and other treatments of liquid feedstocks, especially distillates, lubricants, heavy oil fractions, residuum, etc. In a preferred hydrodewaxing process the catalyst comprises a medium pore siliceous zeolite having a constraint index of about 1 to 12, for example, an acidic ZSM-5 type pentasil aluminosilicate having a silica to alumina mole ratio greater than 12.
While prior reactor systems are satisfactory for certain needs, efficient multi-phase contact has been difficult to achieve for many fixed bed applications. It is an object of the present invention to provide a unique reactor system, including crosscurrent operating techniques and apparatus, for improved treatment of liquid with a gaseous reactant in a reactor containing a porous fixed bed of solid catalyst. It is a further object to provide a technique for operating multi-phase reactors under controlled flow conditions to maintain substantially uniform gas-liquid contact, while minimizing flow maldistribution patterns and providing horizontal gas motion simultaneously with a downwardly gravitating liquid motion.