Method for preparing polycarbonate powder

Abstract

The invention provides a method for processing a gel layer of polycarbonate from a solution and further preparing polycarbonate powder when the polycarbonate is prepared by an interfacial polycondensation method. The method comprises the following steps that a polycarbonate solution and hot water are conveyed into a container in the same direction, part of a solvent is heated and evaporated, polycarbonate forms gel with the density lower than that of water, the gel is continuously spread on the flowing water surface to form a gel layer under the driving effect of water flow, wherein the content of the residual solvent is 10-70% of the weight of carbonic ester; the gel layer is separated at an outlet of the container and then is crushed to obtain wet powder containing polycarbonate, a solvent and a small amount of water, and then the wet powder is dried to remove the residual solvent and water to obtain powder. The method is simple in process, the moisture content of the treated powder is low, energy consumption can be reduced during drying, good process economy is achieved, the dried powder has high stacking density, the fine powder content is low, and the method is suitable for being applied to the downstream industry.

Description

technical field [0001] The invention relates to a method for processing polycarbonate powder from a solution. Background technique [0002] The preparation of polycarbonate by the interfacial phosgene process requires the removal of the solvent, usually dichloromethane, in the post-treatment process. The method for removing methylene chloride in polycarbonate solution, disclosed main several categories include: [0003] US 4568418 discloses a steam precipitation process, that is, the polycarbonate solution and superheated steam are sprayed into the pipeline at high speed, the dichloromethane in the solution evaporates rapidly, and the polycarbonate is also sheared into powder by the high-speed steam. This process needs to consume a large amount of superheated steam, and the bulk density of the prepared powder is low, which is not conducive to downstream use. [0004] CN 1733819 discloses a method, crushing the gel obtained after concentrating the polycarbonate solution, an...

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Problems solved by technology

However, this method requires a tower with a height of 25-30 meters and a huge space, and the space utilization efficiency is low, and the amount of hot water required to process the polycarbonate per unit weight is relatively large

[0007] In addition, these methods present additional problems when dealing with polycarbonate species with reduced crystallinity

The steam precipitation process is prone to wire drawing problems; the particle size of the powder prepared by kneading and crushing is usually too large, the bulk density is low, and it is not suitable for downstream use; the poor solvent precipitation usually results in a paste, and the powder cannot be obtained; the hot water tower The flocs generated by this method are easy to stick into large pieces, and there are also problems in the control of the particle size of the powder

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