Extractive Distillation of Aromatics via Hydrofining
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Solution Overview
Problem
Existing processes for recovering aromatic hydrocarbons like benzene, toluene, and xylenes from naphtha streams using extractive distillation face issues with heavy hydrocarbon contaminants accumulating in the solvent phase, leading to increased energy consumption and decreased unit reliability, as these contaminants co-boil with the solvent and cannot be effectively removed by traditional regeneration processes.
Innovation Solution
The process involves a two-stage hydrofining and divided wall column approach to separate and remove heavy hydrocarbon contaminants from the naphtha stream before extractive distillation, using a first stage hydrofiner to remove dienes and styrenes, followed by a divided wall column to produce a twice hydrofined C6+ stream that is then processed through an extractive distillation unit, reducing the need for costly solvent purification steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional extractive distillation is used to separate aromatic hydrocarbons from naphtha, then aromatic compounds can be separated from non-aromatics, but heavy feed compounds accumulate in the solvent phase causing increased energy consumption and decreased unit reliability
Solution Approach 1:
The patent applies preliminary action by removing heavy compounds from the naphtha feedstock before the extractive distillation process through hydrofining and catalytic cracking. This prevents heavy compounds from entering the extractive distillation unit and accumulating in the solvent, thereby maintaining unit reliability and energy efficiency throughout operation.
Solution Approach 2:
The patent segments the processing into distinct stages: (1) hydrofining to remove dienes and styrenes, (2) catalytic cracking to break heavy compounds into lighter fractions, and (3) extractive distillation for aromatic separation. This segmentation ensures heavy compounds are eliminated before the extractive distillation step, preventing solvent contamination and associated energy increases.
2Productivity
If heavy compounds are allowed to accumulate in the solvent phase, then the extractive distillation process can continue operating, but unit capacity and reliability decrease
Solution Approach 1:
By implementing hydrofining and catalytic cracking before extractive distillation, the system performs preliminary removal of heavy compounds that would otherwise accumulate and reduce unit capacity. This maintains both productivity and reliability by preventing solvent degradation and process inefficiencies.
3Reliability
If additional purification steps are added to remove heavy compounds from the feed, then solvent performance is maintained, but device complexity and cost increase
Solution Approach 1:
The patent implements preliminary hydrofining and catalytic cracking steps that efficiently remove heavy compounds before extractive distillation. While this adds processing steps, it prevents the need for complex continuous purification systems and maintains solvent performance throughout operation, ultimately simplifying the overall process design.
4Loss of substance
If traditional regeneration processes are used, then very heavy byproduct compounds are removed, but heavy feed compounds that co-boil with the solvent cannot be effectively removed
Solution Approach 1:
The patent applies preliminary hydrofining to remove dienes and styrenes, followed by catalytic cracking to break heavy feed compounds into lighter fractions that do not co-boil with the solvent. This preliminary treatment ensures that only truly heavy byproducts remain, which can then be effectively removed by traditional regeneration processes, making the overall system highly effective.
Solution Approach 2:
The patent changes the chemical structure of heavy feed compounds through catalytic cracking, converting them into lighter fractions with different boiling points. This parameter change (molecular weight and boiling point reduction) enables effective separation from the solvent during regeneration, overcoming the limitation of traditional processes that cannot remove co-boiling compounds.
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 effectively prevents the buildup of heavy compounds in the extractive distillation unit, enhancing energy efficiency and reducing equipment requirements, thereby improving the separation of aromatic hydrocarbons while minimizing the need for additional purification steps.
Implementation Method 1
a first stage hydrofiner to remove dienes and styrenes
Implementation Method 2
a divided wall column to produce a twice hydrofined C6+ stream
Implementation Method 3
a stream rich in C6-8 hydrocarbons is then passed to an extractive distillation unit to recover a product comprising (i) benzene and/or toluene and (ii) xylene
Data Source
AI summary
The present invention relates to an improved extractive distillation process for recovering aromatic hydrocarbons from non-aromatic hydrocarbons in naphtha streams containing heavy hydrocarbon contaminants wherein each contaminant is characterized as having a boiling point in the range of between that of the separated non-aromatic hydrocarbons and the extractive distillation solvent utilized to recover and purify the aromatic hydrocarbons.