Benzene Purification with Solvent Extraction to Limit Octane Loss
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Solution Overview
Problem
Existing benzene production processes face challenges in achieving high purity benzene with minimal ring loss and olefin saturation, particularly from FCC gasoline, due to the presence of high-octane olefins, cyclic olefins, and sulfur species, which affect downstream hydrodesulfurization efficiency and product purity.
Innovation Solution
A process involving solvent-based extraction, hydrodesulfurization, and distillation, with azeotropic separation and recycling of benzene-containing streams, to minimize benzene loss and separate cyclic olefins, ensuring high purity benzene production even under varying operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If solvent based extraction is used to extract benzene from FCC gasoline, then benzene can be obtained, but high-octane olefins are saturated and octane loss occurs
Solution Approach 1:
The process segments the extraction system into multiple extractors arranged in series, with the first extractor operating at higher temperature to selectively extract benzene while minimizing olefin saturation, and subsequent extractors operating at lower temperatures to recover additional benzene. This temperature gradient segmentation allows differential separation based on the varying temperature sensitivity of benzene versus olefins.
Solution Approach 2:
The process employs parameter changes by varying the temperature along the extraction train - the first extractor operates at a higher temperature (e.g., 50-100°C above the feed) to preferentially extract benzene with minimal olefin saturation, while subsequent extractors operate at progressively lower temperatures to maximize benzene recovery. This temperature parameter variation resolves the contradiction by exploiting the different temperature dependencies of benzene extraction versus olefin saturation.
2Object-affected harmful factors
If benzene rich heart cut is sent to naphtha hydrotreater or benzene saturation unit, then sulfur is removed, but octane loss occurs due to saturation of high-octane olefins
Solution Approach 1:
The process takes out benzene and sulfur-containing compounds simultaneously through solvent extraction before the hydrodesulfurization step. The solvent selectively extracts aromatics (including benzene) from the FCC gasoline, and sulfur species are removed in the same extraction process or in a subsequent mild hydrodesulfurization that does not require high temperatures. This prevents octane loss by avoiding the high-temperature conditions that would saturate olefins.
Solution Approach 2:
The process performs preliminary extraction of benzene and sulfur species before hydrodesulfurization. By removing sulfur and benzene in advance through solvent extraction, the subsequent hydrodesulfurization step operates on a pre-treated stream with reduced sulfur load, allowing milder conditions that preserve olefin content and avoid octane loss.
3Reliability
If higher temperature is used in hydrodesulfurization to compensate for catalyst aging, then sulfur removal efficiency improves, but benzene ring loss increases
Solution Approach 1:
The process performs preliminary removal of sulfur species through solvent extraction before hydrodesulfurization. This pre-treatment reduces the sulfur burden on the hydrodesulfurization catalyst, allowing it to maintain effective sulfur removal activity at lower temperatures throughout its lifecycle, thereby preventing benzene ring loss even as the catalyst ages.
Solution Approach 2:
The process changes the temperature parameter in the solvent extraction step to operate at elevated temperatures that favor benzene extraction without significant olefin saturation. This allows the downstream hydrodesulfurization to operate at lower temperatures, compensating for catalyst aging effects while maintaining sulfur removal efficiency and minimizing benzene ring loss.
4Quantity of substance
If C6-cyclic olefins are present in extracted aromatics, then they are difficult to separate from benzene, but they cause benzene purity concerns due to saturation to C6-naphthenes
Solution Approach 1:
The process segments the extraction into multiple stages with temperature variation. The first extractor operates at higher temperature to extract benzene and C6-cyclic olefins together, while subsequent extractors at lower temperatures provide additional separation. The temperature gradient exploits the different thermal behaviors of benzene and cyclic olefins, improving purity while maintaining extraction efficiency.
Solution Approach 2:
The process employs parameter changes by varying temperature across the extraction train to selectively extract benzene at higher temperatures where the selectivity between benzene and C6-cyclic olefins is more favorable, followed by lower temperature extraction to maximize recovery. This temperature parameter variation resolves the contradiction by optimizing both extraction efficiency and purity at different stages.
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
The process achieves a benzene purity of 99.8% with less than 1 ppmw sulfur and nitrogen, suitable for petrochemical grade, while minimizing capital and utility expenditure, and maintaining purity despite slippage of cyclic olefins and temperature variations.
Implementation Method 1
a) subjecting the crude hydrocarbon stream and the further benzene containing stream recycled in step d) to a solvent based extraction so as to produce a benzene enriched aromatic stream and a benzene depleted non-aromatic stream
Implementation Method 2
b) subjecting the benzene enriched aromatic stream obtained in step a) to a hydrodesulfurization so as to obtain a desulfurized aromatic stream
Implementation Method 3
c) subjecting the desulfurized aromatic stream obtained in step b) to a distillation so as to produce a purified benzene stream and a further benzene containing stream
Data Source
AI summary
A process for preparing a purified benzene composition from a crude hydrocarbon stream containing at least 10% by volume of benzene is provided. The process comprises subjecting the crude hydrocarbon stream and a further recycled benzene containing stream to a solvent-based extraction so as to produce a benzene enriched aromatic stream and a benzene depleted non-aromatic stream, subjecting the benzene enriched aromatic stream to a hydrodesulfurization so as to obtain a desulfurized aromatic stream, subjecting the desulfurized aromatic stream to a distillation producing a purified benzene stream and a further benzene containing stream having a benzene concentration of between less than 100% by weight and the azeotropic benzene concentration, and at least partially recycling the further benzene containing stream.