Monomer-Solvent Recycle Process for Propylene Polymerization
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Solution Overview
Problem
Advanced solution and supercritical polymerization processes face challenges in monomer separation and recycle due to reduced solvency at higher monomer concentrations, leading to fouling issues and increased costs, particularly in homogeneous polymerization systems where higher temperatures are limited by the reduced solvency of reactor effluents.
Innovation Solution
The implementation of a monomer/solvent separation and recycle process that involves pressurizing a polymer-lean stream, splitting it into two recycle streams, heating one stream, and combining it with the reactor effluent before passing through a pressure let-down valve to facilitate phase separation and recycle, thereby avoiding fouling and optimizing heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If higher monomer concentrations are used in advanced solution and supercritical polymerization processes, then polymerization productivity and product quality are improved, but solvency of the reactor effluent is reduced leading to fouling and operational problems
Solution Approach 1:
The recycle stream is divided into two separate streams: a first recycle stream and a second recycle stream. The first stream is heated to high temperature (150-250°C) to evaporate solvent and monomer, while the second stream is cooled to condense these components. This segmentation allows each stream to perform a specific function, preventing fouling while maintaining high monomer concentrations in the reactor.
Solution Approach 2:
The invention changes the temperature parameter of the first recycle stream to a high range (150-250°C) to alter its physical properties and enable effective evaporation of volatile components. This parameter change resolves the solvency issue by removing volatile monomer and solvent before recycling, allowing higher monomer concentrations in the reactor without fouling problems.
2Manufacturing precision
If higher temperatures are applied to reactor effluent to remove solvent and monomer, then separation efficiency is improved, but polymer-rich phase forms causing heat exchanger fouling
Solution Approach 1:
The recycle stream is segmented into two separate streams with different temperature treatments. The first stream undergoes high-temperature heating to evaporate volatiles, while the second stream is cooled for condensation. This segmentation prevents the polymer-rich phase from forming in the heat exchanger by controlling the temperature profile, thereby avoiding fouling while maintaining separation efficiency.
Solution Approach 2:
The first recycle stream is pre-heated to high temperature before combining with the reactor effluent. This preliminary heating action evaporates solvent and monomer in advance, preventing them from causing fouling in subsequent heat exchangers. The preliminary action removes the harmful volatile components before they can accumulate and cause operational problems.
3Manufacturing precision
If increased heating is applied to reactor effluent to cover enthalpy of evaporation and maintain polymer moltenness, then product quality is improved, but maximum temperature is limited by reduced solvency at higher temperatures
Solution Approach 1:
The heating process is segmented into two stages: first, the first recycle stream is heated to high temperature (150-250°C) to evaporate volatile components; second, the heated stream is combined with the reactor effluent. This segmentation allows the system to achieve the necessary heating for product quality without being limited by solvency constraints, as the volatile components are removed in the first stream before mixing.
Solution Approach 2:
The first recycle stream acts as an intermediary medium that carries the volatile components (solvent and monomer) away from the reactor effluent. By heating this intermediary stream separately, the system can remove volatile components without directly heating the polymer-rich reactor effluent to temperatures that would compromise solvency. The intermediary stream facilitates the removal of volatiles while protecting the main reaction system from excessive temperature.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process enhances the separation efficiency of monomers and solvents, reduces fouling risks, and lowers operational costs by maintaining polymer moltenness and improving heat transfer properties, allowing for higher monomer concentrations without compromising product quality or increasing VOC levels.
Implementation Method 1
pressurizing a polymer-lean stream from the gravimetric separator to form a high-pressure polymer-lean recycle stream
Implementation Method 2
heating one of the high-pressure polymer-lean recycle streams to form a heated high-pressure polymer-lean recycle stream
Implementation Method 3
passing the heated high-pressure reactor effluent mixed stream through a pressure let-down valve to form a heated low-pressure reactor effluent mixed stream
Implementation Method 4
a downstream gravimetric separator fluidly connected to the one or more reactors
Data Source
AI summary
Monomer/solvent separation and recycle processes for continuous supercritical, solution and advanced solution polymerization processes for propylene-containing polymers and their blends are provided. The advantageous monomer/solvent separation and recycle process includes heating a polymer-lean recycle stream coming from a gravimetric separator positioned downstream of the reactor to form a heated polymer-lean recycle stream, and subsequently combining the heated polymer-lean recycle stream with the one or more homogenous reactor effluent streams to form a heated reactor effluent mixed stream. The heated reactor effluent mixed stream may then be passed through a pressure let-down valve followed and a gravimetric separator, such as to provide for reduced fouling propensity of the polymer-rich phase and sufficient heating of the polymer-rich phase to be able to pass through the remainder of the processing steps to form a propylene based polymer product without additional heat.