Patent GB-820986-A (GB)
Title: Process for preparing a silica-magnesia hydrocarbon cracking catalyst
Inventor: JR CHARLES P WILSON
IPC: B01J21/14
Filed: 1957-04-25
Abstract: Silica-magnesia catalysts, suitable for cracking reactions, are prepared by a process which comprises reacting a colloidal dispersion of a complex of magnesia and a magnesium salt (oxysalt) with a silica hydrogel, recovering the resulting silica-magnesia complex formed thereby, dispersing the complex into an aqueous slurry containing free magnesium ions, thereby increasing the content of free magnesium ions, ageing the slurry for a short period of time at 60 DEG  to 65 DEG  C., sufficient to induce a compacted density of 0.40 to 0.88 gm./cm.3 in the final catalyst, separating the solids from said slurry, reslurrying the solids with a solution of a fluorine compound of sufficient concentration to provide 0.5 to 5 wt. of residual fluorine in the final catalyst, and washing and drying the resulting composite.  The silica hydrogel may be obtained by treating an alkali metal silicate such as a sodium silicate having a silica : soda ratio of about 3.3 : 1, an SiO2 content of 5 to 10 wt. % and the balance water, with a mineral acid such as sulphuric or hydrochloric, preferably in two stages, sufficient acid to form a hydrogel structure supporting the un-neutralized silicate and then, after a short interval adding sufficient acid to neutralize about 80% or more of the Na2O originally present in the silicate.  The gelation temperature is desirably 26 DEG  to 60 DEG  C. The gel particles are preferably dispersed during gelation.  A suitable colloidal magnesium complex may be prepared by rapidly adding magnesia to a solution of a magnesium salt, e.g. magnesium sulphate, with continual agitation, at under 60 DEG  C., adding sufficient water to prevent solidification. The dispersion should have a pH of about 8.8 or lower.  After ageing for about an hour at below 65 DEG  C. with continuous agitation the dispersion and the unwashed alkaline silica gel are mixed, free sodium and sulphate ions combining to form soluble sodium sulphate which can be washed away in a filtration step, freeing the catalyst from undesirable sodium ions.  The filtered complex is then reslurried in an aqueous solution which either contains free Mg + + ions, e.g. MgSO4, or yields them from the complex, e.g. sulphuric acid or ammonium sulphate.  The pH at this stage is preferably below 8.6.  The complex is then aged for a short period at 60 DEG  to 65 DEG  C. to produce a catalyst having a compacted density of 0.40 to 0.88 gm./cm3.  This period is preferably 2 to 3 hours, giving a density of 0.48 to 0.53, but may be 3 to 4 1/2 hours, giving a density up to 0.59, or over 4 1/2 hours, giving a density over 0.59. after ageing the slurry is filtered without cooling and the filter cake reslurried in water to which a solution of a fluorine compound is added, e.g. HF, H2SiF6, (NH4)2SiF6, NH4F, and NH4HF2.  The slurry is then dried, e.g. spray dried; Na + and SO4- ions removed by washing, e.g. with ammonium sulphate, or base exchange, e.g. with magnesium sulphate, redried and, optionally, activated.  The process can be used to produce catalysts consisting essentially of 65 to 80% silica, 20 to 30% magnesia and 0.5 to 5% fluorine with a surface area of at least 150 m. 2/g. and an activity of at least 25 D + L after 3 hours treatment at 843 DEG  C., particularly such catalysts where the fluorine is insoluble combined fluorine, the attrition index less then 30% and the compacted density 0.44 to 0.67 g./cm.3 which are further characterized by a pore volume of 0.4 to 1 ml./g. and a pore diameter of 35 to 100   after 3 hours thermal treatment at 677 DEG C. and a pore value of at least 0.25 ml./g. after 3 hours at 843 DEG C.  Specification 721,326, [Group V], is referred to.