Dense CO2 Decontamination Using Surfactants and Complexing Agents
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Solution Overview
Problem
Current decontamination processes using dense pressurized fluids, particularly supercritical CO2, are ineffective in removing solid radioactive particulate inorganic contaminants like PuO2 due to nonpolar nature of CO2, leading to inefficient transfer and redeposition of contaminants, and generate significant aqueous effluents posing criticality risks and environmental concerns.
Innovation Solution
A process using a water-free extraction medium comprising dense pressurized CO2, nonhalogenated surfactants such as block copolymers of PEO and PPO, and complexing agents like TBP, subjected to mechanical action to enhance contaminant transfer and prevent redeposition, thereby reducing effluent generation and criticality risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If dense pressurized CO2 is used for decontamination, then environmental benefits and reduced effluent generation are achieved, but the nonpolar nature of CO2 causes inefficient transfer and redeposition of polar contaminants like PuO2
Solution Approach 1:
The patent introduces cosolvents (alcohols, ketones, carboxylic acids) and surfactants as intermediary substances that bridge the polarity gap between nonpolar CO2 and polar contaminants. These intermediaries form complexes with the contaminants, enabling their transfer from the solid substrate into the CO2 phase, thus resolving the contradiction between environmental benefits and decontamination effectiveness.
Solution Approach 2:
The patent modifies the physical-chemical parameters of CO2 by adjusting pressure and temperature to achieve supercritical or dense liquid states, enhancing its solvent capacity. Additionally, by adding cosolvents and surfactants, the polarity parameter of the CO2 medium is changed, allowing efficient interaction with polar contaminants while maintaining the environmental advantages of CO2-based systems.
2Reliability
If cosolvents and surfactants are added to increase polarity of CO2, then extraction of polar contaminants improves, but process complexity and cost increase
Solution Approach 1:
The patent employs small amounts (0.01-5 wt%) of cosolvents and surfactants, applying partial action rather than complete substitution. This partial addition suffices to achieve the necessary polarity enhancement for effective contaminant extraction, avoiding the complexity of fully developing alternative solvent systems while still resolving the extraction efficiency issue.
3Reliability
If conventional solvents are used for decontamination, then contaminant dissolution is achieved, but large volumes of contaminated liquid effluents are generated requiring additional treatment
Solution Approach 1:
The patent extracts contaminants from the solid substrate into the CO2 phase using supercritical or dense liquid CO2 as the extraction medium. This extraction process transfers contaminants from the solid phase directly into the gas/supercritical phase, avoiding the formation of large volumes of liquid waste effluents that characterize conventional solvent-based methods, thus resolving the contradiction between decontamination capability and waste generation.
4Reliability
If aqueous media are used for decontamination, then contaminant removal is achieved, but criticality risks and environmental concerns increase
Solution Approach 1:
The patent uses CO2 as an inert, non-aqueous extraction medium that creates an inert environment during the decontamination process. This inert atmosphere eliminates the criticality risks associated with water-based systems, particularly when handling radioactive materials, while still achieving effective contaminant removal through the enhanced solvent capacity and polarity modification techniques employed in supercritical CO2 systems.
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
Achieves high decontamination effectiveness without water or fluorinated surfactants, minimizing effluent generation and criticality risks, allowing for efficient extraction and recovery of radioactive contaminants in a nuclear medium with reduced pressure and temperature conditions.
Implementation Method 1
using dense pressurized CO2, in particular supercritical CO2
Implementation Method 2
CO2 is the fluid most commonly used for supercritical fluid extraction as CO2 is inert and non-flammable
Implementation Method 3
In the case of the extraction of polar inorganic compounds, it is necessary to add cosolvents or third substances or additives in order to increase the solubility of the polar molecules in CO2. The cosolvents are generally alcohols, while the third substances or additives are provided in the form of surfactants or ligands
Implementation Method 4
the said solid substrate and/or the extraction medium is/are subjected, simultaneously with the contacting operation, to a mechanical action
Implementation Method 5
CO2 is the fluid most commonly used for supercritical fluid extraction as CO2 is inert and non-flammable. Beyond its critical point (Tc=31.1° C. or 294.1 K and Pc=7.4 MPa), CO2 is said to be supercritical and its physicochemical properties change and lie between those of gases and of liquids
Data Source
AI summary
Process for decontaminating, cleaning a solid organic substrate contaminated by solid radioactive particulate inorganic contaminants, in which:the said solid substrate is brought into contact with an extraction medium, devoid of water, comprising:dense pressurized CO2;at least one nonhalogenated surface-active compound chosen from block copolymers of poly(ethylene oxide) PEO and poly(propylene oxide) PPO, such as (EO)x-(PO)y diblock copolymers, (EO)x-(PO)y-(EO)x triblock copolymers and (PO)x-(EO)y-(PO)x, triblock copolymers, where x and y are integers from 2 to 80 with x other than y; and polydi(1 to 6C)alkylsiloxanes, such as polydimethylsiloxane (PDMS); andat least one complexing agent chosen from tributyl phosphate (TBP), crown ethers, tributylphosphine oxide, triphenylphosphine oxide and tri(n-octyl)phosphine oxide;the solid substrate and/or the extraction medium is/are subjected, simultaneously with the contacting operation, to a mechanical action.