Ethane Oxydehydrogenation for DCE Production
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Solution Overview
Problem
Current processes for manufacturing 1,2-dichloroethane (DCE) and vinyl chloride (VC) using ethylene with purity less than 99.8% face issues such as catalyst poisoning, uneconomic oxygen consumption, high heat generation, and increased production costs due to the presence of impurities, which complicates the oxychlorination process and requires costly reactor modifications.
Innovation Solution
A process involving catalytic oxydehydrogenation of ethane to produce a gas mixture containing ethylene, which is then chlorinated and further converted to DCE in an oxychlorination reactor, with optional absorption/desorption steps to isolate and recycle DCE, reducing impurity-related issues and optimizing ethylene conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ethylene with purity less than 99.8% is used for oxychlorination, then production costs are reduced by simplifying separation operations, but catalyst poisoning occurs and operating problems arise
Solution Approach 1:
The patent applies preliminary action by performing selective hydrogenation of impurities (acetylene, propylene, butylene) before the oxychlorination reaction. This pre-treatment step removes substances that would otherwise poison the oxychlorination catalyst, allowing the use of lower-purity ethylene (99.5-99.8%) without compromising catalyst performance. The hydrogenation reactor is positioned upstream to eliminate harmful impurities in advance of the main reaction process.
Solution Approach 2:
The patent uses an intermediary substance (hydrogen) and an intermediary reaction (hydrogenation) to resolve the conflict between using low-purity ethylene and protecting the catalyst. The hydrogenation step acts as a mediator that selectively converts harmful impurities into harmless or removable substances (ethylene, methane) before they can reach and poison the oxychlorination catalyst, thus enabling cost-effective operation with lower-purity feedstock.
2Productivity
If hydrogen is converted in the oxychlorination reactor, then oxygen consumption increases and high heat of reaction is released, but this conversion limits reactor capability and requires high investment in heat exchange area
Solution Approach 1:
The patent extracts the hydrogen conversion function from the oxychlorination reactor by performing selective hydrogenation of impurities in a separate upstream reactor. This separation of functions prevents hydrogen from accumulating and reacting in the oxychlorination reactor, thereby eliminating the need for excessive heat exchange capacity. The hydrogenation reactor handles hydrogen consumption separately, allowing the oxychlorination reactor to operate at optimal thermal conditions.
Solution Approach 2:
The patent segments the chemical processing into distinct functional stages: (1) selective hydrogenation of impurities in a first reactor, (2) oxychlorination of ethylene in a second reactor. This segmentation allows each reactor to be optimized for its specific function, preventing the thermal interference that would occur if hydrogen conversion and oxychlorination occurred simultaneously in the same reactor.
3Device complexity
If simplified cracking of ethane is used to produce ethylene, then separation operations are simplified and costs are reduced, but impurities are present that cause catalyst poisoning and operating problems
Solution Approach 1:
The patent converts the harmful effect of impurities into a beneficial process feature by using selective hydrogenation. The impurities (acetylene, propylene, butylene) that would normally poison the catalyst are instead selectively converted into useful products (ethylene, methane) through controlled hydrogenation. This transforms a harmful presence into a useful pre-treatment opportunity, allowing simplified cracking processes to feed the oxychlorination reactor without requiring complex separation units.
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 process reduces production costs by allowing the use of lower-purity ethylene, minimizing hydrogen generation, and avoiding costly reactor modifications, while maintaining efficient ethylene conversion and reducing by-product formation, thus enhancing process efficiency and safety.
Implementation Method 1
the stream of ethane is subjected to a catalytic oxydehydrogenation producing a gas mixture containing ethylene, unconverted ethane, water and secondary constituents
Implementation Method 2
the dry gas mixture is then conveyed to a chlorination reactor supplied with a flow of chlorine so that at least 10% of the ethylene is converted to 1,2-dichloroethane
Implementation Method 3
the stream of products derived from the chlorination reactor is conveyed to an oxychlorination reactor in which the majority of the balance of ethylene is converted to 1,2-dichloroethane
Implementation Method 4
during which the 1,2-dichloroethane formed in the chlorination reactor is optionally extracted
Implementation Method 5
absorption/desorption step e'), during which the 1,2-dichloroethane formed in the chlorination reactor is optionally extracted
Implementation Method 6
the 1,2-dichloroethane obtained is subjected to a pyrolysis thus producing VC
Data Source
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Figure 2
AI summary
Process for the manufacture of 1,2-dichloroethane starting from a stream of ethane according to which: a) the stream of ethane is subjected to a catalytic oxydehydrogenation producing a gas mixture containing ethylene, unconverted ethane, water and secondary constituents; b) said gas mixture is optionally washed and dried thus producing a dry gas mixture; c) after an optional addit io nal purification step, the dry gas mixture is then conveyed to a chlorination reactor supplied with a flow of chlorine so that at least 10% of the ethylene is converted to 1,2-dichloroethane; d) the 1,2-dichloroethane formed in the chlorination reactor is optionally isolated from the stream of products derived from the chlorination reactor; e) the stream of products derived from the chlorination reactor, from which the 1,2-dichloroethane has optionally been extracted, is conveyed to an oxychlorination reactor in which the majority of the balance of ethylene is converted to 1,2-dichloroethane, after optionally having subjected the latter to an absorption/desorption step e'), during which the 1,2-dichloroethane formed in the chlorination reactor is optionally extracted if it has not previously been extracted; f) the 1,2-dichloroethane formed in the oxychlorination reactor is isolated from the stream of products derived from the oxychlorination reactor and is optionally added to the 1,2-dichloroethane formed in the chlorination reactor; g) the stream of products derived from the oxychlorination reactor, from which the 1,2-dichloroethane has been extracted, optionally containing an additional stream of ethane previously introduced in one of steps b) to f), is optionally recycled to step a) after having been optionally purged of gases and/or after an optional addit ional treatment in order to eliminate the chlorinated products contained therein.