Split Feed Naphtha Reforming for Paraxylene Yield
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Solution Overview
Problem
Current methods for refining hydrocarbons from naphtha feeds are inefficient in isolating and maximizing paraxylene production, as they often reject heavy aromatic compounds and do not optimize the separation of aromatic components.
Innovation Solution
A method involving the split-processing of hydrotreated naphtha into light, middle, and heavy fractions, followed by separate reforming, dealkylation, transalkylation, and isomerization steps to enhance paraxylene production, utilizing different reformer severities and catalysts to maximize aromatic yields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional whole-feed naphtha reforming is used, then the process is simple, but the aromatic compound separation efficiency is low and paraxylene yield is limited
Solution Approach 1:
The naphtha feed is divided into three distinct fractions (light, middle, and heavy) based on boiling point ranges, with each fraction processed through separate reforming units. This segmentation allows optimized separation and processing of different aromatic compounds, particularly enhancing paraxylene yield from the middle fraction while maintaining process manageability through modular architecture.
Solution Approach 2:
Each reforming unit is configured with specific catalysts and operating conditions tailored to its designated fraction: the light fraction unit uses conditions optimized for benzene production, the middle fraction unit employs conditions favoring paraxylene synthesis, and the heavy fraction unit uses conditions suitable for heavier aromatics. This localized optimization maximizes overall paraxylene yield while keeping each individual unit relatively simple.
2Quantity of substance
If heavy aromatic compounds are rejected, then the separation process is simplified, but the total aromatics yield is reduced
Solution Approach 1:
The process segments heavy aromatic compounds into a dedicated heavy fraction that is processed separately through a dedicated reforming unit. Instead of rejecting these compounds, the system captures and processes them to produce heavier aromatics and additional paraxylene through transalkylation reactions, thereby increasing total aromatics yield while maintaining clear process boundaries.
Solution Approach 2:
The heavy fraction is processed with modified reforming conditions (different temperature, pressure, and catalyst composition) compared to the light and middle fractions. These parameter changes enable the heavy fraction to undergo transalkylation reactions that convert heavy aromatics into lighter aromatic compounds and paraxylene, increasing overall yield without requiring complex separation equipment.
3Productivity
If different reformer severities are applied to different fractions, then the aromatic production is optimized, but the process control complexity increases
Solution Approach 1:
The reforming system is segmented into three independent units, each handling a specific fraction with its own optimized severity conditions. This modular approach allows each unit to be controlled and optimized independently, maximizing aromatic production for each fraction while simplifying overall process control through standardized unit designs and independent operation parameters.
Solution Approach 2:
Each reforming unit is equipped with locally optimized catalysts and operating conditions matched to its specific fraction: the light fraction unit operates at conditions favoring benzene formation, the middle fraction unit uses conditions optimized for paraxylene production, and the heavy fraction unit employs conditions suitable for heavier aromatics. This localized optimization maximizes aromatic yield while maintaining straightforward control through standardized unit operations.
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 weight percentage of aromatic compounds recovered, particularly paraxylene, compared to traditional whole-feed naphtha reforming processes, as demonstrated by Aspen HYSYS simulations, improving research octane number and total aromatics yield.
Implementation Method 1
The light fraction is processed with a first reformer to yield a light reformate. The middle fraction is processed with a second reformer to yield a middle reformate. The heavy fraction is processed with a third reformer to yield a heavy reformate.
Implementation Method 2
The heavy reformate is processed with a dealkylation unit to yield a dealkylated heavy aromatics stream.
Implementation Method 3
The first mixed heavy aromatics stream is processed with a transalkylation unit to yield a transalkylation effluent stream.
Implementation Method 4
The middle reformate is processed with a PX separator to yield a PX product stream, a PX separator effluent stream, or both.
Implementation Method 5
The PX separator effluent stream is processed with a xylene isomerization unit to yield a xylene isomerization effluent stream.
Data Source
AI summary
Increased paraxylene production through the use of a split feed reforming process, wherein hydrotreated naphtha is split into light, middle and heavy fractions. Each fraction is reformed separately to generate streams containing aromatic compounds. These streams can further be processed and can undergo dealkylation, transalkylation, disproportionation, isomerization, and separation steps to maximize paraxylene production. In addition, some streams are recycled or recombined in order to maximize paraxylene production.