Fluorine-Containing Alkene Production via Segmented Catalytic Process
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Solution Overview
Problem
Existing methods for producing fluorine-containing alkenes with terminal -CF=CH2 groups face issues such as by-product formation, low yield, and catalyst instability, particularly with chromium oxide and antimony catalysts, which complicate purification and reduce efficiency.
Innovation Solution
A two-step process using a chlorine-containing alkene or alkane as starting material, with a first reaction step under increased pressure in the presence of a chromium oxide or fluorinated chromium oxide catalyst to produce a fluorine-containing alkane, followed by a dehydrohalogenation step under lower pressure to enhance selectivity and reduce by-product formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chromium oxide or fluorinated chromium oxide catalyst is used for fluorination reaction, then the catalyst stability and ease of handling are improved, but by-product production increases and target yield decreases
Solution Approach 1:
The reaction process is divided into two separate stages: fluorination reaction stage and dehydrohalogenation stage. Each stage uses optimized conditions and catalysts appropriate for its specific purpose, allowing the fluorination to proceed with stable chromium oxide catalyst while the dehydrohalogenation uses conditions that maximize target product formation and minimize by-products.
Solution Approach 2:
The patent employs different temperature and pressure parameters for each reaction stage. The fluorination reaction occurs at lower temperatures (200-400°C) and higher pressures to favor adduct formation, while the dehydrohalogenation stage uses higher temperatures to promote elimination reactions and form the desired terminal alkene product with minimal by-products.
2Productivity
If reaction temperature is raised to increase starting material conversion, then productivity is improved, but by-product production increases
Solution Approach 1:
Conversion is achieved in two stages rather than one high-temperature stage. The first stage at moderate temperatures achieves partial conversion with minimal by-products, and the second dehydrohalogenation stage completes the conversion to target product without generating significant by-products, thus maintaining high overall productivity without the harmful effect of elevated by-product formation.
3Object-generated harmful factors
If antimony chloride catalyst is used for fluorination reaction, then by-product production is suppressed, but catalyst stability and ease of operation deteriorate due to moisture sensitivity and deactivation
Solution Approach 1:
The patent uses chromium oxide or fluorinated chromium oxide catalysts that, while producing more by-products in single-stage reactions, are stable, non-sensitive to moisture, and can be used continuously without deactivation. The two-stage process compensates for the by-product issue, allowing use of these robust, easy-to-handle catalysts without requiring the complex moisture protection and reactivation procedures needed for antimony chloride.
4Productivity
If starting material and intermediates are recycled from reactor outlet, then productivity is improved, but non-reusable by-products concentrate and hinder the producing process
Solution Approach 1:
The two-stage reaction design allows for selective removal and separation of by-products between stages. The fluorination stage produces intermediates that can be separated from by-products, and the dehydrohalogenation stage converts these intermediates to target product. This staged approach prevents by-product accumulation that would occur in continuous recycling, while still allowing efficient recycling of unreacted starting materials and intermediates.
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 achieves high selectivity and efficiency in producing fluorine-containing alkenes while minimizing by-product production, using easily handled catalysts and allowing for effective recycling of unconverted materials.
Implementation Method 1
reacting at least one chlorine-containing compound... with anhydrous HF as a fluorinating agent under an increased pressure of 0.3-5 MPa in a gas phase in the presence of at least one fluorination catalyst selected from chromium oxide and fluorinated chromium oxide
Implementation Method 2
heating the product of step (i) containing a compound of the formula CF3-(CX2)n-CF2-CH3... under a pressure in the range of from atmospheric pressure to 0.3 MPa and lower than that of step (i) to dehydrohalogenate the compound (5)
Data Source
Figure 1
AI summary
The present invention provides a process for producing a fluorine-containing alkene of the general formula CF3 (CX2)nCF=CH2, wherein X each independently represents F or Cl, and n is an integer of 0 to 2. The process includes a first reaction step of allowing a specific chlorine-containing compound to react with a fluorinating agent under increased pressure in a gas phase in the presence of at least one fluorination catalyst selected from the group consisting of chromium oxide and fluorinated chromium oxide, and a second reaction step of heating the product of the first reaction step in a gas phase under a pressure lower than the pressure in the first reaction step. The process of the present invention can produce a fluorine-containing alkene with a high selectivity with the use of a catalyst that can be easily handled, while suppressing production of by-products that cannot be easily converted into the target or separated.