Process and catalyst for selective hydrogenation of dienes and acetylenes

Abstract

A process for the selective hydrogenation of dienes and acetylenes in a mixed hydrocarbon stream from a pyrolysis steam cracker in which a front end a one step acetylene hydrogenation is carried out using catalyst comprising (A) 1 to 30 wt. % based on the total weight of the catalyst of a catalytic component of nickel only or nickel and one or more elements selected from the group consisting of copper, rhenium, palladium, zinc, gold, silver, magnesium, molybdenum, calcium and bismuth deposited on (B) a support having the a BET surface area of from 1 to about 100 m2 / gram, total nitrogen pore volume of from 0.2 to about 0.9 cc / gram and an average pore diameter of from about 110 to 450 Å under conditions of temperature and pressure to selectively hydrogenate acetylenes and dienes. The process hydrogenates the dienes and acetylenes to olefins without loss of ethylene and propylene in the light and heavy products which eliminates the need for further processing of the heavier stream. In addition the amount of polymerization in the lower part of the distillation column reactor is reduced.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a process and catalyst for the selective hydrogenation of dienes and acetylenes in a hydrocarbon stream containing hydrogen, methane, and C2s to C8s and heavier. More particularly the invention relates to a process wherein the hydrocarbon stream is fed between catalyst beds contained within a distillation column reactor. More particularly the invention relates to a process which utilizes a novel catalyst. [0003] 2. Related Art [0004] The vapor product stream from the quench system of a hydrocarbon steam cracker typically consists mainly of hydrogen, methane, C2-C6 olefins and paraffins, C2-C6 acetylenes and dienes, benzene, toluene, xylenes, and other C6+ components. Separation and recovery of the products according to carbon number is generally accomplished in a sequential distillation system after the first separation of hydrogen from the methane in a high pressure cold box system....

AI Technical Summary

Benefits of technology

[0006] It is an advantage of the present invention that novel catalyst has been developed to make a one step front end acetylene hydrogenation operable without the loss of ethylene. A particular advantage of the process is that the acetylenes and dienes in both the heavy and light products will be hydrogenated thus eliminating the need for further processing of the heavy products. It is a further advantage that the amount of polymerization in the lower portion of the distillation column reactor is reduced. It is also an advantage of the present process that ethylene and propylene contents are not reduced in the treated streams.

[0007] The present invention is a novel catalyst and the hydrogenation process using the novel catalyst for removing acetylenes and dienes contained within a product stream from a pyrolysis plant in a single step. Briefly the present process for the selective hydrogenation of acetylenes and dienes in a mixed hydrocarbon stream containing C1 to C8 hydrocarbons comprising contacting a mixed hydrocarbon stream containing C1 to C8 hydrocarbons, including ethylene, acetylenes and dienes and hydrogen with a catalyst comprising (A) 1 to 30 wt. % based on the total weight of the catalyst of a catalytic component of nickel only or nickel and one or more elements selected from the group consisting of copper, rhenium, palladium, zinc, gold, silver, magnesium, molybdenum, calcium and bismuth deposited on (B) a support having the a BET surface area of from 1 to about 100 m2 / gram, total nitrogen pore volume of from 0.2 to about 0.9 cc / gram and an average pore diameter of from about 110 to 450 Å under conditions of temperature and pressure to selectively hydrogenate acetylenes and dienes.

[0008] In one embodiment the selective hydrogenation of the acetylenes and dienes is carried out in a distillation column reactor wherein the charge gas from the pyrolysis plant is fed between two beds of hydrogenation catalyst with additional hydrogen added as needed below the beds. The added hydrogen is controlled such that a minimum of hydrogen exits the distillation column reactor in the overheads to reduce the load on the downstream processing equipment.

[0009] The catalyst used is nickel alone or in combination with an element selected from the group consisting of copper, rhenium, palladium, zinc, gold, silver, magnesium, molybdenum calcium and bismuth. The amount of the copper, rhenium, palladium, zinc, gold, silver, magnesium, molybdenum calcium and bismuth modifiers on the catalyst is relatively small compared to the amount of Ni, i.e., less than about 5% of based on the Ni component on the support. The metals (or oxides thereof) are deposited on a support having a BET surface area of from about 1 to about 100 m2 / g, total nitrogen pore volume of from 0.2 to about 0.9 cc / g, and an average pore diameter of 110 to 450 Å. The support is selected from the group consisting of alumina, silica, zirconia, talcite, silica alumina, and charcoal. Alumina is a preferred support, preferably alumina that has been calcined at a temperature in the range of 700 to 1200° C. The preferred catalyst will have at least 30%, more preferably at least 50% of the pores larger the 100 Å diameter and a total pore volume from about 0.2 cc / g to about 0.9 cc / g and ABD (apparent bulk density) from about 035 to about 0.75 g / cc.

Problems solved by technology

The design of the distillation system is complicated by the fact that the differences in relative volatility of the olefins, acetylenes, and dienes of the same carbon number are small making it difficult to produce the pure olefin products.

However, the patentees did not disclose a specific catalyst only “hydrogenation catalyst”.

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