Method for seed bed treatment before a polymerization reaction

Abstract

In some embodiments, a method in which at least one continuity additive (“CA”) and a seed bed are pre-loaded into a reactor, and a polymerization reaction is optionally then performed in the reactor. In other embodiments, at least one flow improver, at least one CA, and a seed bed are pre-loaded into a reactor. Pre-loading of a reactor with a CA can significantly improve continuity of a subsequent polymerization reaction in the reactor during its initial stages, including by reducing sheeting and fouling. The CA can be pre-loaded in dry form (e.g., as a powder), or in liquid or slurry form (e.g., as an oil slurry). To aid delivery of a dry CA to the reactor and combination of the dry CA with a seed bed in the reactor, the dry CA can be combined with a flow improver and the combination of CA and flow improver then loaded into the reactor. Alternatively, the CA and flow improver can be sequentially loaded into the reactor, and then mixed together (and mixed with a seed bed) in the reactor after both the CA and flow improver have been separately loaded into the reactor.

Description

FIELD OF THE INVENTION [0001] The invention pertains to methods for seed bed treatment before performance of a polymerization reaction (e.g., an olefin polymerization reaction) to improve continuity of the reaction. BACKGROUND OF THE INVENTION [0002] One commonly used method for producing polymers is gas phase polymerization. During operation to produce polyolefins by polymerization, a conventional gas phase fluidized bed reactor contains a fluidized dense-phase bed including a mixture of reaction gas, polymer (resin) particles, catalyst, and catalyst modifiers. Before such a polymerization reaction, a “seed bed” is typically loaded into the reactor or is present in the reactor from a previous polymerization operation. The seed bed is (or consists essentially of) granular material that is or includes polymer material. The polymer material can but need not be identical to the desired end product of the reaction. An example of seed bed material is metallocene polyethylene. [0003] It i...

AI Technical Summary

Benefits of technology

[0018] Pre-loading of the reactor in accordance with the invention can significantly improve continuity of the polymerization reaction during at least one initial stage (before the reaction has stabilized), including by reducing sheeting and fouling. The initial stage (or stages) of a polymerization reaction are the most critical in the sense that there is typically a higher tendency for operability problems to occur before the reaction has stabilized than after it has stabilized.

[0025] In preferred embodiments in this class, pre-loading the reactor (in step (b)) with the CA or combination eliminates or significantly reduces sheeting and fouling that would otherwise occur (if the reactor were not pre-loaded with the CA or combination) during at least one initial stage of the polymerization reaction, and optionally also otherwise improves continuity during at least one initial stage of the polymerization reaction.

[0031] In a class of preferred embodiments, a CA is pre-loaded in dry form (e.g., as a powder) into the reactor. In other preferred embodiments, the CA is pre-loaded into the reactor in liquid or slurry form (e.g., as an oil slurry) or as a component of a mixture of solids, liquids, or at least one solid and at least one liquid. For example, a solid and / or a liquid CA can be pre-loaded (in accordance with some embodiments) with a carrier liquid (e.g., a hydrocarbon or hydrocarbon oil) into a reactor. To aid delivery of a dry CA to a reactor and combination of the dry CA with a seed bed in the reactor, the dry CA can be combined with a flow improver and the combination of CA and flow improver then loaded into the reactor. Alternatively, a CA and a flow improver can be sequentially loaded into the reactor, and then mixed together (and mixed with a seed bed) in the reactor after both the CA and flow improver have been separately loaded into the reactor. The improved flow properties of the combined CA and flow improver allow for delivery of the CA as a solid (e.g., to pre-load the reactor with a specific, predetermined amount of CA for smooth start up operation).

Problems solved by technology

However, the present inventors have recognized that a reactor can be vulnerable to sheeting and / or fouling during the critical initial stage(s) of a polymerization reaction (before the reaction has stabilized) even if each such initial stage is performed in the presence of a CA, if the concentration of the CA is low.

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