Pyrolysis Oil Hydroprocessing with Attenuation Stream Heat Control
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Solution Overview
Problem
Mixed waste plastic pyrolysis oil derived from waste plastics is of low quality, highly reactive, and poses safety risks due to high olefinicity, leading to unpredictable and unsafe hydroprocessing processes with high temperature excursions and catalyst deactivation.
Innovation Solution
A two-stage hydroprocessing method involving a saturated near-zero-olefins stream dilution with highly-olefinic pyrolysis oil, using a series of hydroprocessing catalysts to saturate double-bonds and remove heteroatomic compounds, with temperature control via a liquid quench and staged reactor operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If waste plastic pyrolysis oil is directly used as fuel with little or no post-processing, then production cost is reduced and processing time is minimized, but the fuel quality deteriorates with low market value, poor transport properties, and high safety risks
Solution Approach 1:
The upgrading process is divided into three distinct stages: first stage hydroprocessing for olefin saturation, second stage for heteroatom removal, and third stage for final refinement. Each stage uses optimized conditions and catalysts specific to its function, allowing comprehensive quality improvement while maintaining efficient throughput
Solution Approach 2:
The feedstock undergoes preliminary filtration and preparation before entering the hydroprocessing units, removing large particles and stabilizing the feed composition. This preliminary action prevents downstream operational issues and ensures consistent product quality across all processing batches
2Stability of the object's composition
If conventional hydroprocessing is applied to highly olefinic pyrolysis oil, then olefin saturation is achieved, but extreme temperature rise and runaway reactions occur due to high exotherm
Solution Approach 1:
The olefin saturation process is segmented into multiple reactors in series, with each reactor handling a portion of the total conversion. This distribution prevents excessive heat generation in any single unit, allowing better temperature control while achieving the required degree of saturation
Solution Approach 2:
A heat exchanger network serves as an intermediary thermal management system, cooling the effluent from each reactor stage and using the cooled stream as diluent for the next stage. This intermediary cooling action prevents temperature runaway while maintaining reaction efficiency
3Device complexity
If co-hydroprocessing of light, medium, and heavy fractions is performed in a single reactor, then processing simplicity is maintained, but sub-optimal product distribution results due to conflicting operating conditions requirements
Solution Approach 1:
The hydroprocessing train is segmented into specialized units: first stage reactors optimized for olefin saturation with mild conditions, second stage for heteroatom removal with aggressive conditions, and third stage for final refinement. Each segment processes the entire feedstock but under optimized conditions for its specific function, achieving superior product distribution
Solution Approach 2:
Each processing stage is designed to handle all three fractions (light, medium, heavy) simultaneously, but with stage-specific optimization. The multi-functional design allows comprehensive processing while maintaining flexibility to adjust conditions for each stage based on feed composition variations
4Adaptability or versatility
If waste plastic feedstock composition varies, then feedstock availability and flexibility are improved, but pyrolysis oil properties become highly inconsistent and unpredictable
Solution Approach 1:
Online analyzers monitor the composition of the pyrolysis oil feedstock in real-time, and this information feeds back to the process control system. The control system automatically adjusts operating parameters (temperature, pressure, catalyst circulation) to compensate for composition variations, maintaining consistent product quality despite feedstock variability
Solution Approach 2:
The process operates with flexible parameter ranges that can be dynamically adjusted based on feed composition. When feedstock varies, the system changes key parameters such as reactor temperature, hydrogen partial pressure, and catalyst circulation rate to optimize the hydroprocessing reactions for the current feed conditions, ensuring stable product output
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
Improves heat management, reduces safety risks, and extends catalyst lifespan by controlling reactor temperature, resulting in a more uniform product with improved chemical and transport properties.
Implementation Method 1
combining a highly-olefinic pyrolysis oil liquid feed with hydrogen gas and a saturated near zero-olefins stream, also known as attenuation stream, to form an attenuated feed stream
Implementation Method 2
contacting the attenuated feed stream with a series of hydroprocessing catalysts in a two-stage process with at least two hydroprocessing reactors, wherein a first reactor series of at least one reactor operates in the first stage at a lower temperature and/or pressure in order to mainly saturate double-bonds
Implementation Method 3
temperature control via a liquid quench and staged reactor operations
Data Source
AI summary
The present invention relates to a two-stage process of waste plastics pyrolysis oil upgrading via hydroprocessing. The process comprises the steps of: a) combining hydrogen gas with a highly-olefinic pyrolysis oil liquid feed and a saturated near zero- olefins stream, also known as attenuation stream, to form an attenuated feed stream to a first hydroprocessing reactor; b) contacting the attenuated feed stream with a series of hydroprocessing catalysts in a two-stage process with at least two hydroprocessing reactors, wherein a first reactor operates in the first stage at a lower temperature and or pressure the at least one second reactor, which operate(s) in the second stage; and c) splitting the first stage reactor product, which is a saturated near-zero olefins stream, into at least two portions by flashing it on a separator vessel; wherein a first portion serves as the attenuation stream in step a), and a second portion serves as feed to the second stage. With this pyrolysis oil upgrading method it is possible to have a better heat management in the first reactor due to the fact that the overall olefinicity of the reactor feed is decreased by dilution with a portion of the reactor effluent. This means that the first reactor tendency to overheat is reduced and therefore a better and more accurate reactor temperature control can be achieved, thus resulting in a more uniform product and a more prolonged catalyst lifespan, while reducing the probability of runaway reactions.