Two-Stage Benzene Alkylation Process for Gasoline Refining
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Solution Overview
Problem
Current methods for reducing benzene content in gasoline, such as alkylation with light olefins, face challenges in controlling the formation of heavy components due to undesirable competing reactions like olefin oligomerization, which complicates meeting both benzene and residue content regulations.
Innovation Solution
Conducting the alkylation reaction in at least two stages with the olefin feed split between stages to maintain a molar ratio of alkylatable aromatic to alkylating agent at least 1.0 in each stage, using a catalyst like MWW zeolites, to minimize the formation of heavy components and achieve the desired benzene and residue levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If alkylation with light olefins is used to reduce benzene content, then benzene content is reduced, but heavy components are formed due to olefin oligomerization
Solution Approach 1:
The alkylation process is divided into two sequential stages. In the first stage, olefins are alkylated with aromatics at a molar ratio of 0.5-2.0:1 to produce mono-alkylated products. In the second stage, the effluent from stage 1 is further alkylated with additional olefins at the same molar ratio range to produce di-alkylated products. This segmentation prevents excessive oligomerization by controlling the olefin-to-aromatic ratio in each stage, thereby reducing heavy component formation while achieving the required benzene reduction to below 0.62 volume %.
2Device complexity
If single-stage alkylation is used to reduce benzene content, then process is simpler, but heavy components exceed 2 volume % due to uncontrolled oligomerization
Solution Approach 1:
The process is segmented into two alkylation stages with controlled olefin feed distribution. Stage 1 receives a portion of olefin feed to achieve partial conversion, and stage 2 receives the remaining olefin feed to achieve final benzene reduction. This segmentation allows each stage to operate at optimal aromatic-to-olefin ratios (0.5-2.0:1), preventing the runaway oligomerization that would occur in a single stage with high olefin concentrations, thus keeping heavies below 2 volume %.
Solution Approach 2:
The process controls the molar ratio of aromatic to olefin in the range of 0.5-2.0:1 in each stage, which is a critical parameter change from conventional single-stage processes. This parameter control ensures that olefins are consumed primarily for desired alkylation rather than oligomerization, while still achieving sufficient benzene conversion to meet regulatory requirements without excessive heavy component formation.
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 reduces benzene content below 0.62 volume % and limits heavy components to less than 2 volume %, meeting stringent regulatory requirements without the need for additional fractionation.
Implementation Method 1
The process involves contacting a benzene-containing gasoline blend stock with a C2 to C4 olefin stream in the presence of a catalyst containing the zeolite, SSZ-25, to produce an alkylated light hydrocarbon stream with reduced benzene content
Implementation Method 2
The alkylation reaction is carried out in the liquid phase with a catalyst which preferably comprises a member of the MWW family of zeolites, such as MCM-22, using a fixed catalyst bed
Data Source
AI summary
A process is described for alkylating benzene contained in a refinery gasoline stream, in which the refinery gasoline stream is contacted with an alkylating agent comprising one or more C2 to C5 olefins in an alkylation reaction zone under alkylation conditions to produce an alkylated effluent. The alkylation reaction zone comprises at least a first alkylation reaction stage and a second alkylation reaction stage and a portion of said alkylating agent is fed to each of said first and second alkylation reaction stages so that, although the molar ratio of alkylatable aromatic to alkylating agent in the total feed to the alkylation reaction zone is less than 1, the molar ratio of alkylatable aromatic to alkylating agent at the inlet of each of the first and second alkylation reaction stages is at least 1.0.