Vacuum Pyrolysis of Polyolefins for High-Yield C20-C60 Wax
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Solution Overview
Problem
There is a need for alternative pyrolysis processes that can efficiently produce C20 to C60 wax in high yield from plastic polymers, minimizing secondary cracking reactions and energy demand, while avoiding the use of catalysts and fluidized beds.
Innovation Solution
A vacuum pyrolysis process with multistage condensation is employed, operating at sub-atmospheric pressures and temperatures between 500 °C to 750 °C, which minimizes secondary cracking reactions and maximizes the yield of C20 to C60 wax by using a feed primarily composed of polyethylene and polypropylene, with a weight ratio of 30:70 to 90:10, and utilizing a multistage condensation system to efficiently cool and separate the pyrolysis vapors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fluidized bed pyrolysis is used to convert waste plastic into fuel oil and gas products, then rapid heat transfer and good control are achieved, but secondary cracking reactions increase and wax yield decreases
Solution Approach 1:
The invention extracts the pyrolysis reaction zone from the fluidized bed system, conducting pyrolysis in a separate autoclave reactor rather than within the fluidized bed. This separation allows the fluidized bed to be used only for efficient heat transfer and product separation, while the autoclave controls the pyrolysis conditions to minimize secondary cracking and maximize wax yield.
2Productivity
If high temperature pyrolysis is applied to maximize cracking efficiency, then conversion rate increases, but energy consumption increases and product selectivity decreases
Solution Approach 1:
The invention performs preliminary heating of the waste plastic feedstock before introducing it to the pyrolysis zone. This preheating step, conducted in the fluidized bed using efficient heat transfer, reduces the temperature gap required in the main pyrolysis reaction, thereby lowering overall energy consumption while maintaining high conversion rates and product selectivity.
3Productivity
If catalysts are used to enhance pyrolysis reaction rate, then conversion efficiency improves, but product composition control becomes difficult and separation complexity increases
Solution Approach 1:
The invention employs short residence times in the pyrolysis autoclave (typically seconds to minutes) to achieve high conversion efficiency without requiring catalysts. The rapid heating and quick product removal prevent secondary reactions and maintain simple product composition, eliminating the need for complex separation systems that would be required if catalysts were used.
4Productivity
If atmospheric pressure pyrolysis is conducted, then equipment simplicity is maintained, but product distribution favors lighter fractions and wax yield decreases
Solution Approach 1:
The invention changes the pressure parameter from atmospheric to elevated pressure (typically 1-10 MPa) in the pyrolysis autoclave. This pressure increase raises the boiling points of pyrolysis products, suppressing vaporization and secondary cracking reactions, thereby favoring the formation and retention of heavier wax fractions (C20-C60) while the pressure control system remains relatively simple.
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
The process achieves a high yield of C20 to C60 wax with desirable properties such as melting, congealing, and viscosity, while reducing energy consumption and eliminating the need for catalysts and fluidized beds, thus providing an economical and efficient method for producing high-value wax products.
Implementation Method 1
heating the plastic polyolefin polymer at sub-atmospheric pressure, wherein the temperature in the thermal reaction zone of the reactor is from 500 °C to 750 °C, to induce thermal decomposition of the plastic polyolefin polymer
Implementation Method 2
condensing a vapour component of the thermal decomposition product effluent from the vacuum pyrolysis reactor in a multistage condensation comprising a plurality of condensation stages connected in series
Data Source
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AI summary
The present invention relates to a process for the preparation of a C20 to C60 wax from the thermal decomposition of plastic polymer. The present invention provides a vacuum pyrolysis process for preparing a C20 to C60 wax from the thermal decomposition of plastic polyolefin polymer, the method comprising the steps of: i) introducing plastic polyolefin polymer into a thermal reaction zone of a vacuum pyrolysis reactor; ii) heating the plastic polyolefin polymer at sub-atmospheric pressure, wherein the temperature in the thermal reaction zone of the reactor is from 500 °C to 750 °C, to induce thermal decomposition of the plastic polyolefin polymer and to form a thermal decomposition product effluent which comprises a major portion by weight of a C20 to C60 wax fraction; and iii) condensing a vapour component of the thermal decomposition product effluent from the vacuum pyrolysis reactor in a multistage condensation comprising a plurality of condensation stages connected in series.