SCALEUP OF ALUMINUM PHOSPHATE CATALYST FOR PILOT PLANT LPDMEtm RUN Page: 4 of 36
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2. Laboratory Background
This section summarizes the information obtained during the laboratory effort to devise a
scaleable process. It contains an overview of the laboratory preparation and details of the
importance of some of the scaleup variables.
The aluminum phosphate is prepared by precipitation resulting from the addition of base to a
solution containing A13+ and PO43-. The precipitate is washed, dried and calcined. A number of
synthesis variables were tested and optimized in the laboratory. These variables include
" Aluminum-to-phosphorus ratio
" Aluminum precursor
" Concentration of solutions
" Addition order for precipitation
" Final pH during precipitation
" Duration of precipitate aging step
" Choice of wash solution
" Number of washes
" Method of filtration
" Calcination temperature
" Duration of calcination
The factors that had a large effect on catalyst performance are discussed in the following
paragraphs.
2.1. Al/P
An Al/P (aluminum-to-phosphorus ratio) of 1.6 was chosen. At lower Al/P we always observed
lower activity, and at higher Al/P we obtained mixed results for deactivation behavior. In some
cases the methanol catalyst deactivated faster than baseline, but in one case of high Al/P,
excellent activity and methanol catalyst stability were observed. We do not understand what
chemical/structural factors controlled these performance properties. We made the target an Al/P
of 1.6 since this ratio gave consistently acceptable performance.
2.2 Mixing
The quality of mixing during the precipitation affects catalyst performance. The precipitation
begins at a pH near 1.0 and ends at a target pH of 9.0. The pH follows a typical titration curve,
rising rapidly with incremental base addition around pH 7. The precipitate begins to dissolve
rapidly above pH 9, due to the amphoteric nature of aluminum. Most of the material precipitates
between pH 3 and 6. The pH history of the precipitation step could affect the composition or
structure of the final material, since part of the product is precipitated in a highly acidic
environment; another part is precipitated near neutral pH. Furthermore, the distribution of pH in
the precipitation vessel and the pH history depend on rates of addition and local mixing
efficiency within the vessel. Therefore, it seems reasonable that variations between preparations
might arise from the sensitivity of the precipitation process to pH2
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Wang, Andrew W. SCALEUP OF ALUMINUM PHOSPHATE CATALYST FOR PILOT PLANT LPDMEtm RUN, report, May 15, 2002; Pittsburgh, Pennsylvania. (https://digital.library.unt.edu/ark:/67531/metadc741896/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.