Thermal Cracking Mixed Waste Plastic Methane Hydrogen
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Solution Overview
Problem
Existing methods for producing lower hydrocarbons from mixed waste plastic (MWP) face challenges such as high coke formation, broad product ranges, reduced ethylene yield, and increased methane production due to hydrogenation, especially under high pressure and hydrogen-rich conditions, leading to inefficient and potentially hazardous reactions.
Innovation Solution
A thermal cracking method involving the co-conversion of MWP with methane and hydrogen at controlled ratios, pressures, and temperatures to maximize the yield of C2-C3 hydrocarbons by controlling methane as an initial heat source and radical activation, thereby reducing hydrogen consumption and preventing runaway reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If 100% MWP pyrolysis oil is used in catalytic cracking processes, then plastic waste is recycled, but high amounts of coke formation occur in feed nozzles during preheating
Solution Approach 1:
The patent changes the chemical composition parameters of the feed by blending MWP pyrolysis oil with virgin naphtha in specific ratios (30-70 wt% MWP oil, 70-30 wt% virgin naphtha). This parameter adjustment prevents coke formation while maintaining waste recycling benefits, as virgin naphtha acts as a diluent reducing the concentration of coke-prone components.
Solution Approach 2:
The invention creates a composite feed mixture combining MWP pyrolysis oil with virgin naphtha. This composite material leverages the properties of both components: MWP oil provides waste recycling and valuable hydrocarbons, while virgin naphtha provides stability and prevents coke formation, achieving synergistic effects.
2Productivity
If 100% MWP pyrolysis oil is used as cracker feed, then waste plastic is converted, but formation of heavier products (fuel oil and tar) is high
Solution Approach 1:
The patent adjusts the feed composition parameter by introducing virgin naphtha to modify the molecular weight distribution and chemical composition of the cracker feed. This parameter change promotes cracking reactions that produce lighter hydrocarbons while suppressing formation of heavy fuel oil and tar, optimizing product distribution.
3Object-generated harmful factors
If high amount of hydrogen is used in thermal cracking, then coke formation is reduced, but separation cost increases and valuable olefins are hydrogenated into less valuable aliphatic hydrocarbons
Solution Approach 1:
The patent optimizes the hydrogen partial pressure parameter within a specific range (0.1-5 MPa) rather than using high amounts of hydrogen. This controlled parameter adjustment sufficiently suppresses coke formation while minimizing excessive hydrogenation reactions, preserving olefin values and reducing separation costs.
Solution Approach 2:
The invention uses virgin naphtha as a model compound to replicate the desirable properties of pure hydrocarbon feeds. By copying the molecular structure and reactivity characteristics of virgin naphtha into the MWP feed blend, the system achieves low coke formation and high olefin yield without requiring excessive hydrogen.
4Productivity
If hydrogenation reaction proceeds vigorously at high temperature, then methane production is accelerated, but runaway reaction may occur and ethylene yield is reduced
Solution Approach 1:
The patent optimizes multiple parameters including temperature (700-900°C), pressure (0.1-5 MPa hydrogen partial pressure), and residence time (10-300 milliseconds). These parameter adjustments control the hydrogenation reaction rate to prevent runaway while maintaining productive methane and olefin formation.
Solution Approach 2:
The invention employs continuous rapid cooling (quenching) immediately after the reactor to continuously terminate the hydrogenation reaction. This continuous action prevents temperature runaway and maintains reaction stability while preserving the useful products formed during the controlled reaction period.
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 method enhances the yield of ethylene and propylene by up to 40% and avoids coking, ensuring a stable reaction process with controlled temperatures and pressures, thus improving the economic viability and safety of the process.
Implementation Method 1
thermal cracking of mixed waste plastic (MWP) under pressure and in the presence of methane and hydrogen
Implementation Method 2
in the presence of methane and hydrogen... methane as an initial heat source
Implementation Method 3
valuable olefins produced by the reactions are deeply hydrogenated by the hydrogen resulting in the conversion into aliphatic hydrocarbons
Data Source
AI summary
A method for producing lower hydrocarbons by a thermal cracking reaction from mixed waste plastic (MWP) is disclosed herein. The method includes: a. forming a mixed gas comprising methane and hydrogen, b. combining the mixed gas with the MWP to form a reaction mixture, c. reacting the reaction mixture in a reactor at a pressure of 1 to 40 bars, a temperature of 800° C. to 1200° C. and a residence time of 10 to 300 milliseconds in the reactor, and d. producing a lower hydrocarbon product stream through the outlet of the reactor. The methane/hydrogen mol ratio in the mixed gas is from 0.1 to 5.