Mixed Waste Plastic Pyrolysis for Stable Hydrocracker Feed
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Solution Overview
Problem
Current methods for converting mixed waste plastic into valuable petrochemicals are inefficient, as they often result in unstable feedstocks for hydrocrackers, high methane production, and limited scalability, with previous attempts focusing on small-scale, modular plants that are not suitable for continuous large-scale operations.
Innovation Solution
A process involving the pyrolysis of mixed waste plastic to produce a gaseous and liquid stream, where the liquid stream is separated into high and low aromatics content streams, with the low aromatics stream being fed to a hydrocracking unit, along with a hydrocracker feed, to produce additional valuable petrochemicals, while maintaining a stable feedstock and reducing asphaltenes and sulfur content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If mixed waste plastic is directly pyrolyzed and fed to hydrocracker, then petrochemicals can be produced, but the feedstock becomes unstable and asphaltenes precipitate
Solution Approach 1:
The pyrolysis liquid is separated into two distinct fractions based on boiling point: a light fraction (boiling below 205°C) and a heavy residual fraction (boiling above 205°C). This segmentation allows the light fraction to be used as stable hydrocracker feed while the heavy fraction undergoes further processing, preventing asphaltenes precipitation and feedstock instability.
Solution Approach 2:
The unstable heavy residual fraction containing asphaltenes is extracted and removed from the hydrocracker feed stream. By taking out this problematic fraction and processing it separately (e.g., through coking or asphaltene precipitation), the stability of the remaining feedstock is maintained while still allowing petrochemical production from the light fraction.
2Quantity of substance
If conventional pyrolysis methods are used, then plastic waste can be converted, but methane production is high and valuable petrochemicals yield is limited
Solution Approach 1:
The pyrolysis process parameters are optimized to favor the production of light hydrocarbons suitable for hydrocracking over methane formation. By controlling temperature, residence time, and heating rate, the process maximizes the yield of C5+ hydrocarbons while minimizing methane, thereby increasing valuable petrochemicals yield and reducing substance loss.
3Ease of manufacture
If small-scale modular plants are used for pyrolysis, then conversion can be achieved, but scalability to continuous large-scale operations is limited
Solution Approach 1:
The process design integrates multiple functions into a unified continuous processing system. The pyrolysis unit, separation system, and hydrocracking unit are connected to form an integrated plant that can operate continuously at large scale, eliminating the limitations of small-scale modular approaches while maintaining ease of manufacture through standardized equipment design.
4Productivity
If the entire pyrolysis liquid is fed to hydrocracker, then maximum conversion is achieved, but asphaltenes precipitate and sulfur content remains high
Solution Approach 1:
The pyrolysis liquid is segmented into light and heavy fractions, with only the light fraction being fed to the hydrocracker. This segmentation prevents asphaltenes precipitation and reduces sulfur content in the hydrocracker feed, while the heavy fraction is processed separately to recover valuable components and remove harmful substances.
Solution Approach 2:
The heavy residual fraction containing asphaltenes and high sulfur content, which would be harmful to the hydrocracker, is converted into a separate processing stream. This fraction can be treated through coking or other processes to remove sulfur and recover hydrocarbons, thereby converting a harmful waste stream into a potential source of additional petrochemicals while protecting the hydrocracker from damage.
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 integrated process significantly increases the yield of petrochemicals like ethane, propane, butane, ethylene, propylene, and aromatics, while maintaining a stable hydrocracker feed, reducing asphaltenes and sulfur content, and improving the economic viability of steam cracker operations by producing a feedstock with a boiling curve similar to whole crude oil.
Implementation Method 1
feeding mixed waste plastic (MWP) to a pyrolysis reactor, converting said MWP into a gaseous stream and a liquid stream
Implementation Method 2
converting said liquid stream, together with said hydrocracker feed, through hydrocracking into at least one gaseous stream and a liquid stream
Data Source
AI summary
A process for converting mixed waste plastic (MWP) into valuable petrochemicals including feeding MWP to a pyrolysis reactor, converting the MWP into a gaseous stream and a liquid stream, and further processing the gaseous stream into valuable petrochemicals.