Method for preventing or inhibiting fouling in a gas-phase polyolefin polymerization process

#The present invention generally relates to a method for preventing or inhibiting fouling in a gas-phase polyolefin polymerization process.

#In a continuous gas-phase, fluidized-bed polyolefin polymerization process, it was found that process equipment such as the gas loop piping and heat exchangers would foul to such an extent that a shutdown was periodically required to clean the equipment. Investigation into this problem led to the surprising discovery that internal equipment surfaces that were made to “sweat” (i.e., condense liquids on the internal surfaces) and kept wet had a reduced tendency to foul and remained clean for long periods of time. Modification of equipment and/or operating conditions such that the surfaces of the equipment that are exposed to the process gas could be made to “sweat” or condense liquids on all or nearly all of their surfaces has greatly reduced the rate of fouling experienced in the loop and the loop heat exchangers. In addition, “sweating” of the internal pipe surfaces of a tubular, loop, gas-phase polymerization reactor greatly reduces the fouling rate experienced in the reactor.

#The invention provides for a method for preventing or inhibiting fouling in a gas-phase polyolefin polymerization process. In one embodiment, the method comprises passing a gas mixture having an average temperature above its dew point temperature through process equipment, and maintaining the inside surface temperature of the equipment below the dew point temperature of the gas mixture.

#The method of the invention can be applied to any gas-phase polyolefin polymerization process that is susceptible to fouling. Such processes include those using gas-phase tubular loop reactors or fluidized bed reactors.

#In a first embodiment, the method of the invention comprises passing a gas mixture having an average temperature above its dew point temperature through process equipment, and maintaining the inside surface temperature of the equipment below the dew point temperature of the gas mixture.

#The gas mixture typically contains olefin monomers, hydrogen, nitrogen, and optionally one or more inert condensable compounds. Typical olefin monomers include one or more of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-dodecene, etc. Exemplary inert condensable compounds include saturated hydrocarbons such as butane, pentane, hexane, or mixtures thereof.