Aqueous methods for titanating a chromium/silica catalyst with an alkali metal
Methods for making titanated silica supports, titanated chromium/silica pre-catalysts, and activated titanated chromium/silica catalysts are disclosed in which hydrogen peroxide and an alkali metal precursor are used during catalyst preparation. Resulting titanated chromium/silica pre-catalysts often contain silica, 0.1 to 5 wt. % chromium, 0.1 to 10 wt. % titanium, and less than or equal to 4 wt. % carbon, and further contain an alkali metal or zinc at a molar ratio of alkali metal:titanium or zinc:titanium from 0.02:1 to 3:1 and/or at an amount in a range from 0.01 to 2 mmol of alkali metal or zinc per gram of the silica. High melt index potential activated titanated chromium/silica catalysts can be used to polymerize olefins to produce, for example, ethylene based homopolymers and copolymers having HLMI values of greater than 30 g/10 min.
1 . A process for preparing a titanated silica support, the process comprising:
(i) contacting water, a peroxide compound, and a titanium precursor to form a first mixture;
(ii) contacting a silica with the first mixture under conditions sufficient for titanium to adsorb onto the silica and form a second mixture;
(iii) isolating a solid fraction from the second mixture and washing the solid fraction; wherein:
isolating the solid fraction comprises filtering and/or centrifuging; and
washing the solid fraction comprises contacting the solid fraction with a wash solution containing water; and
(iv) drying the solid fraction to form the titanated silica support.
2 . The process of claim 1 , wherein:
step (i) comprises contacting water, hydrogen peroxide, a sodium precursor, a nitrogen-containing compound, and the titanium precursor to form the first mixture; and
the second mixture is subjected to a reaction temperature in a range from 40 to 100° C. before isolating the solid fraction.
3 . The process of claim 2 , wherein:
the silica is a preformed silica.
4 . The process of claim 1 , wherein:
step (i) comprises contacting water, hydrogen peroxide, a sodium precursor, and the titanium precursor to form the first mixture; and
the second mixture is subjected to a reaction temperature in a range from 40 to 100° C. before isolating the solid fraction.
5 . The process of claim 4 , wherein:
the silica is a preformed silica.
6 . The process of claim 1 , wherein the process further comprises a step of adjusting a pH of the first mixture to within a range from 3 to 12, prior to contacting the silica with the first mixture.
7 . A process for preparing a titanated chromium/silica pre-catalyst, the process comprising:
performing the process for preparing a titanated silica support of claim 1 ; and
contacting a chromium precursor with the first mixture or the second mixture in any step prior to the step of isolating the solid fraction from the second mixture.
8 . A process for preparing a titanated chromium/silica catalyst, the process comprising:
performing the process for preparing a titanated chromium/silica pre-catalyst of claim 7 ; and
activating the titanated chromium/silica pre-catalyst to form the titanated chromium/silica catalyst.
9 . A process for preparing a titanated chromium/silica pre-catalyst, the process comprising:
performing the process for preparing a titanated silica support of claim 1 ; and
contacting a chromium precursor with the solid fraction after isolating the solid fraction from the second mixture.
10 . A process for preparing a titanated chromium/silica catalyst, the process comprising:
performing the process for preparing the titanated chromium/silica pre-catalyst of claim 9 ; and
activating the titanated chromium/silica pre-catalyst to form the titanated chromium/silica catalyst.
11 . A process for preparing a titanated chromium/silica pre-catalyst, the process comprising:
performing the process for preparing a titanated silica support of claim 1 , except instead of contacting the silica with the first mixture, contacting a chromium/silica pre-catalyst with the first mixture.
12 . The process of claim 1 , wherein
a weight ratio of titanium of the titanium precursor to the water (Ti:H 2 O) is in a range from 0.0001:1 to 0.02:1; and
a weight ratio of the silica to the water (silica:H 2 O) is in a range from 0.001:1 to 1:1.
13 . The process of claim 12 , wherein the silica is a preformed silica.
14 . The process of claim 12 , wherein the silica is a silica hydrogel.
15 . The process of claim 12 , wherein a molar ratio of the peroxide compound to the titanium precursor is in a range from 0.5:1 to 100:1.
16 . The process of claim 1 , wherein drying comprises spray drying or flash drying.
17 . The process of claim 1 , wherein a sodium precursor is added in step (ii) after the silica is contacted with the first mixture.
18 . The process of claim 17 , wherein a molar ratio of the sodium precursor to the titanium precursor is in a range from 0.1:1 to 300:1.
19 . The process of claim 18 , wherein the silica is a preformed silica.
20 . The process of claim 18 , wherein the silica is a silica hydrogel.