aluminum citrate is an acid-soluble aluminum compound that can be used to make a water-blocking gel in subterranean formations. The aluminum citrate product can be prepared by a number of different methods and is generally used in liquid form, but also in dry form where it is mixed with an aqueous solution of the polymer to make a single blended product that is then injected into the subterranean formation.
Dry form of aluminum citrate can be produced on a large scale using either a drum dryer or by spray drying. This process is relatively straightforward and produces a very dense product that is easily transported and handled on a large scale.
The aluminum concentration in the final dry product depends on the aluminum source in the liquid product and the molar ratio of aluminum to citrate. A mixture of aluminum chlorohydrate and citrate with a molar ratio of about 1.9:1 yields a product that contains about 12.0-13.5 percent by weight aluminum, depending on the drying conditions.
The aluminum concentration in the final dry product can be increased by drying at higher temperatures. However, this increases the hygroscopicity of the product and decreases its solubility, making it more difficult to transport on a large scale. For these reasons, a stable product with a moisture content of about 3-5 percent is preferred. The optimum temperature range for the drying of this material is about 45deg C. to 105deg C., but it is possible to increase the drying temperature above 105deg C to produce a product with a greater moisture content.