Continuous process for producing anionic clay

#This invention involves the continuous preparation of anionic clays and the preparation of Mg—Al solid solutions by heat-treatment of the anionic clay. Anionic clays have a crystal structure which consists of positively charged layers built up of specific combinations of metal hydroxides between which there are anions and water molecules. Hydrotalcite is an example of a naturally occurring anionic clay, in which carbonate is the predominant anion present. Meixnerite is an anionic clay wherein hydroxyl is the predominant anion present.

#In hydrotalcite-like anionic clays the brucite-like main layers are built up of octahedra alternating with interlayers in which water molecules and anions, more particularly carbonate ions, are distributed. The interlayers may contain anions such as NO3−, OH, Cl−, Br−, I−, SO42−, SiO32−, CrO42−, BO32−, MnO4−, HGaO32−, HVO42−, ClO4−, BO32−, pillaring anions such as V10O26−6 and Mo7O246−, monocarboxylates such as acetate, dicarboxylates such as oxalate, alkyl sulphonates such as laurylsulphonate.

#It should be noted that a variety of terms are used to describe the material which is referred to herein as an anionic clay. Hydrotalcite-like and layered double hydroxide are interchangeably used by those skilled in the art. Herein the materials are referred to as anionic clays, comprising within that term hydrotalcite-like and layered double hydroxide materials.

#FIG. 1 shows a PXRD pattern of commercially available Mg—Al carbonate anionic clay.

#FIG. 2 shows a PXRD pattern of a Mg—Al carbonate anionic clay prepared by coprecipitation.

#FIG. 3 shows a PXRD pattern of a Mg—Al acetate anionic clay prepared by the process according to the invention, wherein gibbsite and MgO are reacted at 65° C.

#This invention involves the continuous preparation of anionic clays. In particular it describes a process for the preparation of an anionic clay wherein an aluminum source and a magnesium source are fed to a reactor and reacted in aqueous suspension to obtain an anionic clay, the aluminum source being aluminum trihydrate or its thermally treated forms. The magnesium source may be composed of a solution of a magnesium salt, a solid magnesium-bearing compound or a mixture of the two. Reaction between the Mg source and aluminum trihydrate or its thermally treated form results in the direct formation of an anionic clay. The reaction takes place at room temperature or higher. At temperatures higher than 100° C., the reaction is preferably carried out under autogeneous conditions. In the method according to the invention carbonate, hydroxyl. or other anions or mixtures thereof, either provided within the reaction medium for example by feeding a soluble salt to the reactor or absorbed during the synthesis from the atmosphere, are incorporated into the interlayer region as the necessary charge-balancing anion.

#Anionic clays prepared by this method exhibit the well known properties and characteristics (e.g. chemical analysis, powder X-ray diffraction pattern, FTIR, thermal decomposition characteristics, surface area, pore volume, and pore size distribution) usually associated with anionic clays prepared by the customary and previously disclosed methods.

#Upon being heated, anionic clays generally form Mg—Al solid solutions, and at higher temperatures, spinels. When used as a catalyst, an adsorbent (for instance a SOx adsorbent for catalytic cracking reactions), or a catalyst support, the anionic clay according to the invention is usually heated during preparation and is thus in the Mg—Al solid solution form. During use in a FCC unit, the catalyst or adsorbent is converted from an anionic clay into Mg—Al solid solutions.