REMOVAL OF CONTAMINANTS FROM CRACKING CATALYSTS BY ION EXCHANGE E. CONNOR, J R .
L. N. LEUM AND J. dtlantic Rejning Go., Philadelphia, Pa,
The effects of metals which accumulate on cracking catalysts have long been recognized as increasing the production of light gases and hydrocarbonaceous deposits a t the expense of desired products. The development of a procedure for removing these contaminants b y ion exchange is described, including the results of a detailed study of the variables of such treating as it affects decontamination and stability of the catalysts. This procedure is tied in with a continuous pilot unit cracking operation, and the resulting improvements in product distribution are shown.
THE
EFFECT of certain metals on changing the product distribution in catalytic cracking in the direction of producing more light gases and hydrocarbonaceous deposits on the catalyst has long been recognized. Mills ( 9 ) showed the detrimental effect of nickel: vanadium, and copper on the product distribution of synthetic and clay catalysts. Duffey and Hart (5) showed that contamination leads to decreased gasoline and a n increase in gas and “coke.” McIntosh (8) studied the effect of several metal oxides on activity and selectivity. Rothrock, Birkhimer, and Leum (70) and Connor and coworkers (3) published the results of a rather extensive laboratory investigation of the factors affecting the activityof contaminants. In a recent symposium, two reports (4, 7 ) were concerned with this specific problem. Many other investigations have also been carried out: and in many of thc above articles the economic significance has been pointed out and emphasized. Methods for overcoming 01’eliminating the detrimental effects of contaminants in catalytic cracking have been the subject of many patents. One approach is to remove the metals from the cracking stock. but this is usually rather impractical because of the large volume of liquid involved. -4more useful approach is to allow the metals to concentrate
Table I.
Equilibrium Catalyst Properties
Cracking Trst
41.7 49.1 2.19 .A1?03, wt. Na, wt. 7; Fe, wt. % Xi, wt c/I v, wt. e/;
:
40 D A Y S OF O P E R A T I O N
20
60
Grone,
Thermal Stability Surf. Area, Sq. Meters/ DfL, Gram Val. yc
Pore
Volume, Cc. /Gram
Before teqt
Original Ion exchanged at pH 3.5 Treated 2 hr. at 1700' F. Original Ion exchanged Treated 2 hr. at 1800' F. Original Ion exchanged
148
1
--
20 40 D A Y S OF O P E R A T I O N
Data from Fowle, Masologites, Grone, Katz (6)
and
level, so that these metals may be removed from the catalyst a t such a high p H that there are no detrimental effects to the silica-alumina catalyst. The silica-alumina itself, of course, has ion exchange properties. The strong acid ion exchange resin, however, can effectively compete with the silica-alumina for the metal ions, and so the active metals are transferred from the catalyst to the resin. Ion exchange does remove alumina from the catalyst to some extent. However, repeated treats at the proper p H level have not removed enough alumina to harm the steam stability of the catalyst. This alumina removal has been the subject of further work. 'r"ERM.a STABILITY. Besides steam stability, the effect on the thermal stability of the catalyst must also be considered. Some data on this property are shown in Table I V . Here, untreated and treated material are again compared, and the properties before thermal deactivation, after deactivating at 1700' F. for 2 hours, and after deactivating a t 1800" F. for 2 hours. are given. The activities, surface areas, and pore volumes all indicate that the treated material was more stable than the untreated material. One explanation of this effect is that the ion rxchange treatment appeared to increase the pore volume of the catalyst, and it is already known that thermal stability is improved by such an increase ( 7 ) . Also?
Table IV.
0
60
Figure 5. Analysis of catalyst during pilot plant trial
Figure 4. Product yields using decontaminated catalyst (corrected to 50% conversion) Data from Fowle, Masologiter, Katz (6)
1
BASE CASE MET-X
304
~
2 "a
---
0001
CASE
41 55
98 110
0.33 0.35
39 43
65 95
0.24 0.31
28 36
35 50
0.12 0.17
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
and
of course, the activity of the treated material was higher in itially than that of the untreated, and this increase appeared to be relatively stable to thermal deactivation. Treatment of Experimentally Contaminated Samples. The equilibrium catalyst studied contained minor amounts of nickel and vanadium, as well as iron and sodium, but because the concentrations of the former two metals were so low, it was not possible to be sure that their contaminating effects were being removed. To study them separately, a synthetically contaminated sample was prepared in the laboratory using metal naphthenates and the procedure of dripping the contaminated oil onto a fluid bed a t high temperature, as described (70). When 0.10 wt. 70 nickel was deposited on a 60 D+L (200gram test) steam-deactivated silica-alumina, which was equal to 35 D+L on a 40-gram test. and this contaminated materiai was tested using a 40-gram D f L test. the D+L activity was found to be 21 and the CPF 6.5. This material was then ion exclianged as described above at 212' F. for 4 hours at a p H of 2.7. I t then shoired a D + L of 35 and a CPF of 1.3. The nickel content after exchange was 0.03%. The removal of vanadium was found to be extremelv easy, much easier than iron. The removal of nickel and vanadium, as well as iron. by ion exchange from plant equilibrium catalysts and from catalysts used in reduced crude cracking to produce catalysts of 1.0 CPF has been the subject of further work. Effect on Product Distribution. The effect of decontamination by ion exchange on the product distribution in a continuous cracking operation has already been reported ( 6 ) . The results are summarized here only to tie in with the description of the method of decontamination. A full scale pilot plant program was run to demonstrate rhe change in product yield over a period of time with and without decontamination using an ion exchange resin. A sample of commercial equilibrium catalyst was used and run for an extended period of time using a fresh catalyst make-up rate of 0.31 lb. per barrel of gas oil feed. The catalyst was removed from the pilot plant unit. ion exchanged, and returned to the unit at the rate of 2.0 Ib. per barrel of gas oil feed,
equivalent to 11 /o per day of the pilot unit catalyst inventory. The gas oil used in this work was found by analysis to contain 2.5,
