Principle of preparation of organic bentonite
The principle of preparation of organic bentonite is montmorillonite mineral: montmorillonite is a unique aluminosilicate mineral, consisting of two layers of SiO tetrahedral sheets sandwiched by a layer of AIO (OH) octahedral pieces of lamellar minerals. The Si·+ in the montmorillonite structural unit layer can be replaced by A13+, and the AP+ in the octahedral layer is often replaced by multivalent ions such as Mg2+, Fe3+, and Zn2+, so that the charge in the crystal lattice is unbalanced, resulting in residual negative charge. It has the ability to adsorb cations and exchange anions, and has high hydration energy. The interaction between the oxygen layer and the oxygen layer between the crystal layers of the C-axis (layer stacking direction) is small, and good dissociation can be formed. In the surface, the layers are easily immersed in water molecules or other polar molecules, causing expansion in the C-axis direction. This is a property not found in other non-swelling clays. Due to this property, the montmorillonite layer is filled with nH:O interlayer water and exchangeable cations, which are the driving force for the expansion of montmorillonite. However, for bentonites with different ore-forming conditions, the types of exchangeable cations between the montmorillonite layers and the exchange capacity (CEC) are quite different. Among them, the interlayer valence cation (Ca2+, Mg2+, etc.) montmorillonite double layer hydration film is thin, the expansion ratio is low; the low-cost cation (Na+, K+, etc.) hydrated film thickness, high expansion ratio. Therefore, Na + montmorillonite is then reacted with an organic covering agent. The organic covering agent is usually a kind of cationic surfactant with a carbon chain length of more than 12, and the Na+ exchange with the montmorillonite crystal layer realizes an ion exchange reaction to change the hydrophilic montmorillonite into a hydrophobic montmorillonite: Na+-montmorillonite+[NHa·R4-a]CI-[NHa·R4-a]-montmorillonite+NaCI
Organic bentonite is prepared by three methods: wet method, pre-gel method and dry method. Among these three methods, the dry method is simple, the production efficiency is high, and the prepared organic bentonite is suitable as a thickener for oil-based drilling fluid, but this method has more dust and is more polluted by the environment; the key steps of the wet method Whether the particle size of the particles in the suspension meets the requirements, and impurities in the bentonite, especially whether the quartz is removed, is directly related to the performance of the organic bentonite. It is worth noting that the preparation of organic bentonite must be sodium bentonite, but not calcium bentonite, because Na has a larger hydrated ionic radius than Ca, which increases the interlayer spacing d(001) of bentonite, which is beneficial to organic cations. Ion exchange.
Organic bentonite has been produced and applied in China for more than 30 years and is widely used in the production of industrial coatings and release agents. Organic bentonite is a suspension and thickener for industrial coatings. The specific use method is as follows: firstly, the organic bentonite is made into an organic bentonite paste (or organic bentonite gel), and then the organic bentonite paste is used as a coating and a release agent. The manufacturing process of the organic bentonite paste is as follows: (using a high-speed dispersing machine) )
Feeding amount (mass percentage)
Solvent (solvent oil)
2. Organic bentonite
3. Polar activator
Mix for 5 minutes
Mix for 5 minutes
The solvent is first introduced, the mixing is started, the organic bentonite is added for 4-5 minutes, and the polar activator (polar additive) is added to continue mixing for 4-5 minutes. The amount of organic bentonite can be increased or decreased, and for the convenience of operation, 10% is the highest amount. Through testing, the best polar additives are 95% methanol, 95% ethanol and propylene carbonate. The correct dosage is as follows:
Methanol/water (95/5) 33% of organic bentonite
Ethanol/water (95/5) 50% of organic bentonite
Propylene carbonate, 33% of organic bentonite
In order to obtain optimum activation efficiency, both methanol and ethanol contain 5% water, and using methanol or ethanol containing water, the viscosity rises rapidly, while anhydrous methanol or ethanol is used, and there is no gel effect.