Waste Plastic Pyrolysis Oil Fractionation With Recycle Cracking
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Solution Overview
Problem
Existing methods for pyrolyzing waste plastics are limited in improving the yield of high-quality light hydrocarbon oil, as they often result in excessive production of heavy oil components and residual wax, and the separation of high-boiling point components is inefficient.
Innovation Solution
A method involving the use of one or more distillation columns connected in series to a pyrolysis reactor, where the pyrolyzed gaseous stream is separated by boiling point, with middle and heavy oils being recycled to a second reactor, and the middle oil is subjected to secondary pyrolysis, while heavy oil is recycled back to the first reactor, under gradually increasing temperature conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If catalytic cracking or contactor methods are used during pyrolysis, then pyrolysis efficiency is improved, but the yield of light hydrocarbon oil is still limited and heavy oil components remain excessive
Solution Approach 1:
The pyrolysis process is divided into multiple stages with different temperature conditions. The first pyrolysis stage operates at a lower temperature to produce initial pyrolysis oil, while the second pyrolysis stage operates at a higher temperature to convert heavy oil components into light hydrocarbon oil, thereby increasing the overall yield of light hydrocarbon oil while maintaining high pyrolysis efficiency
Solution Approach 2:
The invention changes the temperature parameter between pyrolysis stages. The first pyrolysis is conducted at a lower temperature (e.g., 400-500°C) and the second pyrolysis at a higher temperature (e.g., 500-700°C), allowing optimal conversion of different hydrocarbon components at appropriate temperatures, thus maximizing light hydrocarbon oil yield
2Manufacturing precision
If a contactor is disposed above the pyrolysis reactor to separate long-chain hydrocarbons, then selectivity for specific pyrolysis oil components is improved, but the overall pyrolysis efficiency and light hydrocarbon oil yield are not significantly enhanced
Solution Approach 1:
The contactor is used in the first pyrolysis stage to preliminarily separate and remove long-chain hydrocarbon components before the second pyrolysis stage. This preliminary action prevents these heavy components from interfering with the subsequent high-temperature pyrolysis, improving both selectivity and overall efficiency
Solution Approach 2:
The separated long-chain hydrocarbon components from the contactor are continuously circulated back to the pyrolysis reactor for second pyrolysis, ensuring that all hydrocarbon components are fully utilized to produce light hydrocarbon oil, thereby maintaining continuous useful action and maximizing yield
3Quantity of substance
If heavy oil components are recycled to the pyrolysis reactor, then the yield of light hydrocarbon oil is improved, but the process complexity increases
Solution Approach 1:
The recycling system merges the heavy oil component stream back into the pyrolysis reactor inlet stream, creating an integrated process where heavy components are continuously converted. This merging approach increases light hydrocarbon oil yield while managing process complexity through unified flow management
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 approach increases the yield of high-quality light hydrocarbon oil, reduces residual wax discharge, and enhances pyrolysis efficiency, while also reducing greenhouse gas emissions and improving energy consumption.
Implementation Method 1
when a waste plastic such as a polyethylene or polypropylene material is heated and pyrolyzed at a certain temperature
Implementation Method 2
heated and pyrolyzed at a certain temperature, a gaseous stream containing a mixture of non-condensable gas and liquid oil may be produced
Implementation Method 3
separating the upper gaseous stream according to boiling point to obtain a stream containing C 5-12 light oil (LO), a stream containing C 13-22 middle oil (MO), and a stream containing C 23 or higher heavy oil (HO)
Implementation Method 4
a gaseous stream containing a mixture of non-condensable gas and liquid oil may be produced
Data Source
Figure 1~2
AI summary
The present invention provides a method of preparing pyrolysis oil from waste plastics, the method including: (S1) feeding a waste plastic raw material to a first reactor, performing primary pyrolysis, and discharging a upper gaseous stream produced by the pyrolysis through an upper portion of the first reactor; (S2) feeding the upper gaseous stream of the first reactor to one or more distillation columns and separating the upper gaseous stream according to boiling point to obtain a stream containing C5-12 light oil (LO), a stream containing C13-22 middle oil (MO), and a stream containing C23 or higher heavy oil (HO), respectively; (S3) feeding a portion of the stream containing the middle oil (MO) separated in the distillation column to a second reactor, performing secondary pyrolysis, and feeding a gaseous stream produced by the pyrolysis to the distillation column; and (S4) recycling the stream containing the heavy oil (HO) separated in the distillation column to the first reactor.