High Temperature Final Dehydration Reactor for Ethylene
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Solution Overview
Problem
The existing processes for converting ethanol to jet fuel face challenges in minimizing the production of diethyl ether impurities, which affects the selectivity and efficiency of ethylene production, particularly due to lower reactor outlet temperatures leading to diethyl ether formation.
Innovation Solution
A process involving the division of the ethanol feed stream into two portions, with one portion being heated with steam and subjected to dehydration in a series of reactors, including a high-temperature third reactor to minimize diethyl ether formation, achieving an effluent with less than 10 mol ppm diethyl ether.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lower reactor outlet temperatures are used in ethanol dehydration, then energy consumption is reduced, but diethyl ether formation increases
Solution Approach 1:
The dehydration process is divided into multiple reactor stages (first dehydration reactor, second dehydration reactor, and final dehydration reactor) with intermediate heating. This segmentation allows the process to use lower temperatures in initial stages (reducing energy consumption) while applying high temperature only in the final stage (preventing diethyl ether formation), thus resolving the contradiction between energy efficiency and product purity.
Solution Approach 2:
The process performs preliminary dehydration at lower temperatures in the first and second reactors, converting most ethanol to ethylene before the final high-temperature stage. This preliminary action reduces the ethanol load on the final reactor, allowing it to operate at high temperature for a shorter duration, thereby minimizing diethyl ether formation while controlling overall energy consumption.
2Object-generated harmful factors
If a single high temperature reactor is used for ethanol dehydration, then diethyl ether production is minimized, but energy consumption increases
Solution Approach 1:
Instead of using a single high-temperature reactor, the process segments the dehydration into multiple stages with intermediate heating. The final dehydration reactor operates at high temperature (400-450°C) to minimize diethyl ether, but the preceding reactors operate at lower temperatures, reducing the cumulative energy requirement compared to maintaining high temperature throughout a single reactor.
Solution Approach 2:
The process recovers heat from the effluent of the final dehydration reactor and uses it to preheat the feed stream entering the first dehydration reactor. This heat recovery reduces the energy input required in subsequent heating stages, thereby reducing overall energy consumption while maintaining the high-temperature final dehydration needed to minimize diethyl ether.
3Object-generated harmful factors
If multiple reactors with intermediate heating are used, then diethyl ether formation is reduced, but device complexity increases
Solution Approach 1:
The dehydration process is segmented into three reactors with intermediate heating, which reduces diethyl ether formation by ensuring complete conversion and preventing equilibrium limitations. While this increases device complexity compared to a single reactor, the segmentation allows for better control of reaction conditions at each stage, improving overall process efficiency and product quality.
Solution Approach 2:
The process combines the dehydration and heating functions into an integrated multi-reactor system with heat exchange between stages. The effluent from one reactor serves as the feed for the next, and heat is recovered and reused within the system. This merging of functions reduces the need for separate heating equipment and simplifies the overall process configuration despite the multiple reactors.
4Object-generated harmful factors
If steam is extensively used in ethanol dehydration, then diethyl ether formation is suppressed, but utility consumption increases
Solution Approach 1:
The process recovers heat from the hot effluent stream and uses it to generate steam or preheat feed streams. This heat recovery reduces the utility consumption required to generate the steam needed for suppressing diethyl ether formation in the dehydration reactors, thereby resolving the contradiction between ether suppression and energy consumption.
Solution Approach 2:
The process uses the heat generated from the exothermic dehydration reaction itself to produce the steam required for the process. The effluent heat is utilized to generate steam for the reactors, making the system partially self-sufficient and reducing external utility consumption while maintaining adequate steam levels to suppress diethyl ether 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 significantly reduces diethyl ether formation, enhancing ethylene selectivity and efficiency, with the third reactor maintaining high temperatures to prevent ether formation and optimizing steam usage, resulting in a process with improved energy recovery and reduced utility consumption.
Implementation Method 1
sending the first portion to a reactor through a charge heater; mixing steam with the first portion at the charge heater
Implementation Method 2
subjecting the ethanol/steam mixture to sufficient conditions to dehydrate the ethanol to produce an effluent comprising ethylene and water
Implementation Method 3
sending product effluents from the first reactor and the second reactor to a third reactor about 450-475° C. and the effluent from the third reactor contains less than 10 mol ppm diethyl-ether
Data Source
AI summary
A process of converting an ethanol feed stream to ethylene comprising sending portions of said ethanol feed stream to two reactors in parallel and then sending the combined product to a third reactor that is operated at a higher temperature to prevent the formation of ethers such as diethyl ether.