Silica Aerogel Production via pH-Triggered Surfactant Separation
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Solution Overview
Problem
Current methods for producing silica aerogel are costly and environmentally impactful due to the need for solvent exchange and the use of high-pressure supercritical drying, as well as the requirement for fluorine solvents, which complicates the process and increases costs.
Innovation Solution
A method involving the addition of monoalkyltrialkoxysilane to an acidic aqueous solution with a surfactant to form a sol, followed by gelation and separation in a solvent mixture of immiscible solvents to remove the surfactant, then drying at conditions below the critical temperature and pressure of the solvent, reducing contraction and porosity while using less organic solvent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solvent exchange is performed multiple times to remove surfactant before drying, then the surfactant removal is improved, but the production cost and environmental impact increase due to large amounts of organic solvent (especially fluorine solvent) usage
Solution Approach 1:
The invention utilizes liquid-liquid phase separation by adjusting the pH of the aqueous solution. When pH is adjusted to 2.0 or lower, the surfactant separates from the aqueous phase, allowing easy removal through decantation or filtration. This phase transition approach eliminates the need for multiple solvent exchange steps using organic solvents, significantly reducing production cost and environmental impact while maintaining effective surfactant removal.
Solution Approach 2:
The invention changes the pH parameter of the aqueous solution from neutral/basic to strongly acidic (pH 2.0 or lower). This parameter change triggers the surfactant to precipitate or separate from the aqueous phase, enabling simple removal without requiring multiple solvent exchange operations. The pH adjustment is achieved by adding acid to the gel, transforming the system state to facilitate surfactant removal.
2Strength
If drying is performed under supercritical conditions using carbon dioxide, then the framework strength is improved to prevent breaking, but the device complexity and capital investment increase due to high-pressure equipment requirements
Solution Approach 1:
The invention changes the drying parameters from supercritical conditions (high pressure and temperature) to ambient or mild conditions. By adjusting the pH to 2.0 or lower before drying, the surfactant is removed and the silica framework is stabilized, allowing drying to be performed without high-pressure equipment. This parameter change enables simple atmospheric drying while maintaining framework integrity.
Solution Approach 2:
The invention performs preliminary pH adjustment and surfactant removal before the drying step. By removing the surfactant and stabilizing the framework structure in advance (when pH is 2.0 or lower), the gel becomes resistant to collapse during drying. This preliminary action eliminates the need for supercritical drying equipment, as the framework is already strengthened before the drying process begins.
3Productivity
If the gel is dried without complete surfactant removal, then the production process is simplified, but the porosity decreases due to contraction during drying
Solution Approach 1:
The invention uses pH adjustment as a control parameter to achieve complete surfactant removal before drying. By setting pH to 2.0 or lower, the surfactant quantitatively separates from the aqueous phase, ensuring complete removal. This parameter control maintains the porous structure during drying, preventing contraction while keeping the process simple through single-step pH adjustment rather than multiple solvent exchange steps.
Solution Approach 2:
The invention replaces the mechanical process of multiple solvent exchange operations with a chemical parameter adjustment (pH change). Instead of mechanically removing solvent repeatedly, the pH adjustment causes chemical phase separation of the surfactant, which can be removed in a single step. This substitution maintains porosity while simplifying the process, achieving both complete surfactant removal and high productivity.
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 method simplifies the production process, reduces environmental impact, and lowers costs by eliminating the need for supercritical drying and fluorine solvents, resulting in silica aerogel with high rigidity, flexibility, and excellent heat insulation properties.
Implementation Method 1
immersing the wet gel in a solvent mixture of a first solvent and a second solvent immiscible with the first solvent to move the surfactant contained in the wet gel to a phase of the second solvent while moving the wet gel to a phase of the first solvent
Implementation Method 2
a solvent mixture of a first solvent and a second solvent immiscible with the first solvent
Implementation Method 3
drying the wet gel having moved to the phase of the first solvent in the separation step at a temperature lower than a critical temperature of the first solvent under a pressure lower than a critical pressure of the first solvent to remove the first solvent from the wet gel
Data Source
AI summary
A method for producing a silica aerogel includes a gelation step of adding a monoalkyltrialkoxysilane to an acidic aqueous solution containing a surfactant to prepare a sol, and then gelating the sol to prepare a wet gel. The method further includes a separation step of immersing the wet gel in a solvent mixture of a first solvent and a second solvent immiscible with the first solvent. The first solvent has an ETN value of 0.5 or less, and the second solvent has an ETN value between those of the first solvent and water. The method further includes a drying step of drying the wet gel at a temperature lower than a critical temperature of the first solvent under a pressure lower than a critical pressure of the first solvent to remove the first solvent from the wet gel.