Spray Oxidation Process for Selective Aromatic Conversion
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Solution Overview
Problem
Industrial oxidation processes, such as the Mid-Century Process for producing terephthalic acid, face challenges with inadequate oxygen mass transfer rates in the liquid phase, leading to reduced product purity and increased waste due to solvent oxidation.
Innovation Solution
A spray process where small droplets of a liquid reaction mixture containing an oxidizable reactant, catalyst, and solvent are introduced into a gaseous reaction zone with oxygen, allowing for enhanced oxygen permeation and reaction control, thereby improving mass transfer and reducing solvent combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If air is vigorously bubbled through the liquid phase reactor, then oxygen mass transfer is enhanced, but the process still suffers from inadequate oxygen mass transfer rate
Solution Approach 1:
The liquid reaction mixture is segmented into small droplets (0.1-2.0 mm diameter) that are sprayed into the gas phase reactor. This segmentation dramatically increases the total surface area of liquid exposed to oxygen, enhancing mass transfer from gas to liquid phase while maintaining efficient reaction rates.
Solution Approach 2:
The conventional liquid-phase reactor with gas bubbling is inverted to a gas-phase reactor with liquid spraying. Instead of forcing gas through liquid, the liquid is dispersed into the gas phase, fundamentally changing the mass transfer direction and improving oxygen availability to the catalyst.
2Reliability
If conventional liquid phase oxidation is used, then reaction selectivity is maintained, but solvent oxidation (burning) occurs leading to waste
Solution Approach 1:
The reaction parameters are changed by operating at lower liquid hourly space velocities (LHSV) and controlling droplet residence time in the gas phase. This allows selective oxidation to proceed while minimizing the conditions that lead to solvent burning and unwanted byproducts.
Solution Approach 2:
The sprayed droplets continuously pass through the oxygen-rich gas phase, maintaining continuous contact between reactants and oxygen. This continuous action ensures complete conversion of the substrate to desired products while preventing accumulation that could lead to solvent oxidation.
3Productivity
If acetic acid solvent is used in the liquid phase reactor, then reaction proceeds, but roughly 5% of the acetic acid is oxidized (burned)
Solution Approach 1:
The acetic acid solvent is segmented into small droplets that are quickly processed through the reactor. This segmentation reduces the total residence time of the solvent in the high-temperature zone, minimizing the opportunity for acetic acid oxidation while maintaining efficient substrate conversion.
Solution Approach 2:
The reaction system rushes through the critical temperature zone quickly by controlling droplet size and residence time. This allows the oxidation reaction to complete before the acetic acid solvent can significantly decompose or burn, reducing solvent loss.
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 increases the yield and purity of products like terephthalic acid, reduces waste, and enhances safety by minimizing solvent oxidation, achieving higher throughput and tighter temperature control.
Implementation Method 1
introducing small droplets of a liquid reaction mixture having an oxidizable reactant, a catalyst, and a solvent into a gaseous reaction zone containing oxygen
Implementation Method 2
an inadequate or non-optimal O2 mass transfer rate in the liquid phase. The mass transfer is accomplished in a stirred liquid phase reactor, wherein the air is vigorously bubbled through the liquid phase
Implementation Method 3
oxidizing the reactant with the oxygen at a suitable reaction temperature and a suitable reaction pressure to produce an oxidized product
Data Source
Figure 1
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AI summary
Oxidation process can include: introducing small droplets of liquid reaction mixture having oxidizable reactant, catalyst, and solvent into a reaction zone containing oxygen and diluent gas; and oxidizing the reactant with the oxygen at a suitable reaction temperature and a suitable reaction pressure to produce an oxidized product. The liquid reaction mixture can have an aromatic feedstock having an oxidizable substituent as the oxidizable reactant. The oxidized product can include an aromatic compound having at least one carboxylic acid. For example, the aromatic feedstock can include a benzene ring having at least one oxidizable alkyl substituent, furan hetero-ring having at least one oxidizable alkyl substituent, a naphthalene poly-ring having at least one oxidizable alkyl substituent, derivatives thereof, and mixtures thereof.