Multi-Stage Oxidative Dehydrogenation with Inter-Stage Cooling
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Solution Overview
Problem
Existing oxidative dehydrogenation processes are energy intensive due to high steam and nitrogen recirculation rates, and they are impurity-sensitive, with a need to increase conversions and yields per pass.
Innovation Solution
A multi-stage oxidative dehydrogenation process with inter-stage cooling, using up to six successive reaction zones and a reduced steam-to-dehydrogenation reactant molar ratio, along with the use of a moderator gas to replace air and improve heat recovery, and the inclusion of an acetylene and aldehyde removal catalyst to manage oxygen levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a large flow of steam is used to control the exotherm in oxidative dehydrogenation, then temperature control is improved, but energy consumption increases due to large amounts of energy required for superheating and vaporization
Solution Approach 1:
The single reaction zone is divided into multiple reaction zones (first reaction zone, second reaction zone, etc.) with inter-stage cooling. Each zone operates at optimized conditions and the exotherm is managed across multiple stages rather than one large stage, reducing the steam flow rate required in each zone while maintaining overall temperature control.
Solution Approach 2:
A cooling zone is introduced as an intermediary between reaction zones to remove heat from the effluent stream. This cooling zone acts as a heat sink, allowing the reaction zones to operate at higher temperatures without requiring excessive steam for temperature control, thereby reducing energy consumption.
2Productivity
If a large flow of steam is used in oxidative dehydrogenation, then per pass yield is improved by reducing partial pressures, but steam usage increases requiring large amounts of energy for superheating and vaporization
Solution Approach 1:
The process is segmented into multiple reaction zones where each zone operates with optimized steam-to-hydrocarbon ratios. The cumulative effect of multiple stages achieves the desired conversion and yield per pass without requiring excessively high steam flow rates in any single zone, thus reducing overall steam usage and associated energy costs.
3Ease of manufacture
If air is used as the oxygen source in oxidative dehydrogenation, then oxygen supply is simplified, but nitrogen recycle is required increasing complexity and energy consumption
Solution Approach 1:
The nitrogen component is extracted and removed from the oxygen source. Instead of using air (which contains nitrogen), pure oxygen is supplied to the reaction zones. This eliminates the need for nitrogen recycle systems and associated complexity while maintaining the simplicity of oxygen supply.
Solution Approach 2:
The composition of the gas feed is changed from air-based (with nitrogen) to oxygen-based (without nitrogen). This parameter change in the feed composition eliminates the need for nitrogen management and recycle systems, simplifying the overall process while reducing energy consumption associated with nitrogen handling.
4Device complexity
If a single stage reactor system is used, then device complexity is reduced, but conversion and yield per pass are limited
Solution Approach 1:
The single reactor is segmented into multiple reaction zones arranged in series. Each zone contains catalyst and operates under controlled conditions, allowing progressive conversion of the hydrocarbon to the desired product. This segmentation increases conversion and yield per pass while maintaining manageable complexity through modular zone design.
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 reduces steam usage and associated energy costs, increases conversion by 10% or more and yield by up to 15% per pass, while minimizing nitrogen recycle and improving heat recovery.
Implementation Method 1
oxidative dehydrogenation of a dehydrogenation reactant in a plurality of successive oxidative dehydrogenation reaction zones
Implementation Method 2
adiabatic, catalytic reaction zone
Implementation Method 3
cooling the effluent stream in a heat exchanger to a second-stage inlet temperature
Implementation Method 4
adiabatic reaction zones... intensely exothermic reaction
Implementation Method 5
The oxidative dehydrogenation reaction is intensely exothermic
Implementation Method 6
superheated steam to dehydrogenation reactant molar ratio
Implementation Method 7
Steam also acts as a heat sink in an adiabatic reaction system to moderate temperature rise
Data Source
AI summary
A method of oxidatively dehydrogenating a dehydrogenation reactant includes providing a first gaseous feed stream to a first adiabatic, catalytic reaction zone with less than a stoichiometric amount of oxygen and superheated steam, oxidatively dehydrogenating dehydrogenation reactant in said first adiabatic, catalytic reaction zone and subsequently cooling the effluent, adding additional oxygen and reacting the effluent stream in at least one subsequent adiabatic reaction zone. The dehydrogenation system enables higher conversion and yield per pass and in some cases greatly reduces steam usage and energy costs. In a preferred integrated process, ethylene is converted to n-butene which is then oxidatively dehydrogenated to butadiene.