Rare earth zeolite Y and the preparation process thereof

Details Rare earth zeolite Y and the preparation process thereof Rare earth zeolite Y and the preparation process thereof

2002-04-26

2004-09-07

Sample, David (Department: 1755)

Chemistry of inorganic compounds

Zeolite

Isomorphic metal substitution

C423SDIG002, C502S079000, C502S085000

Reexamination Certificate

active

06787123

ABSTRACT:

The present invention relates to a rare earth zeolite Y and the preparation process thereof
Catalytically cracked gasoline is a major component of the vehicle gasoline. Now, catalytically cracked gasoline in China accounts for about 70% of the vehicle gasoline. In recent years, as more and more attention of the whole society is paid to the environmental protection, it becomes more and more urgent to produce the low olefin, low sulfur, high quality clean catalytically cracked gasoline. However, the heavier feedstock for catalytic cracking has put forward higher requirements for the catalytic cracking catalyst, which should not only have higher activity, better selectivity and higher hydrogen transfer activity, but also have higher hydrothermal stability.
As the major component of the catalytic cracking catalyst, zeolite Y has gone through the following developing stages:
NaY is inactive for catalytic reactions, and only after being changed into HY by exchanging Na
−
with NH
4
+
, it possesses a pretty high activity. In 1960's, zeolites have already been used in oil refining. The stability of zeolites is always an important problem which should be taken into consideration in the catalyst preparation, and especially in catalytic cracking. Zeolites must possess good hydrothermal stability.
U.S. Pat. No. 3,384,572, and U.S. Pat. No. 3,506,440 indicate that HY prepared by exchanging Na
+
in zeolite with NH
4
+
has a pretty high activity but poor structure stability, which will lose its crystallinity in dry air at a temperature higher than 500° C., and its structure will be destroyed even when placed in air at room temperature. Rare earth exchanged HY (abbreviated as REHY) prepared by further partly replacing NH
4
+
with rare earth ions based on HY has very high activity, and has also overcome the shortcoming of poor thermal stability of HY With the further development of catalytic cracking of heavy oil, although REHY and REY prepared by hybrid exchanging with rare earth ions and NH
4
+
have high hydrogen transfer activity and cracking activity, it also has the problems that its initial unit cell contracts difficultly and that it can not be stable under high hydrothermal conditions, which exhibits as easy to produce coke and deactivate in the catalytic cracking unit.
U.S. Pat. No. 3,293,192 and C. V. M C Darid and P. K. Maher, in “Zeolite stability and ultrastable zeolite” (Zeolite Chemistry and Catalysis, Acs Monograph 171, Washington D.C., 1976, 285-231) described a procedure that NaY is exchanged with NH
4
+
in an aqueous solution and then the exchanged zeolite is calcined in steam at a temperature of 600° C. to 825° C., which can be carried out repeatedly. After such a treatment of multiple exchanging and calcining, the unit cells of the zeolite contract and achieve ultrastableness. Thus the ultrastable zeolite Y (abbreviated as USY) prepared by the hydrothermal process is obtained. Such kind of zeolite was widely used in 1990's, which is characterized in the less unit cell contraction, good thermal and hydrothermal stability, low hydrogen transfer activity and good coke selectivity, but also has the disadvantage of the limited activity and needs to improve its activity by exchanging with a solution of rare earth. USY has a rather high silica to alumina ratio and less cation sites in its framework, meanwhile partial crystal strcture collapsed and pluged the pores during ultrastabilization, which results in the small ion exchange capacity of the USY. Generally, the content of RE
2
O
3
in the rare earth exchanged USY (abbreviated as REUSY) is up to 3-4 wt %, and a considerable amount of RE
2
O
3
is absorbed at the outside of zeolite crystal.
In summary, although REY and REHY have high contents of rare earth, namely 10-20 wt % of RE
2
O
3
in REY and 6-14 wt % of RE
2
O
3
in REHY, and have higher activity and hydrogen transfer activity, the unit cell can not further contract. The unit cell constant &agr;
0
is generally between 2.468-2.470 nm, the hydrothermal stability is relative poor, and the differential thermal collapsed temperature thereof is 900-980° C. On the contrary, USY has a better unit cell contraction, namely &agr;
0
=2.445-2.450 nm, a good hydrothermal stability, and the differential thermal collapsed temperature is higher than 1000° C., but it contains very little rare earth because it is very difficult for the rare earth cations to enter into the lattice of the crystal. Besides, the unit cells of the above two types of zeolites contract in a large extent after aging, and the equilibrium unit cell constant is only 2.425-2.428 nm; therefore the hydrogen transfer activity is low and it is hard to meet the requirement of the new cracking catalyst, e.g. the selective hydrogen transfer activity.
Presently, a mixture of rare earth exchanged ultrastable zeolite Y, i.e. rare earth-containing ultrastable zeolite Y (the content of RE
2
O
3
in REUSY is usually about 3 wt %), moderate rare earth content zeolite REHY (the content of RE
2
O
3
is usually 6-14 wt %) and high rare earth content zeolite REY (the content of RE
2
O
3
is usually 10-20 wt %) are combined and mixed in different ratios when a cracking catalyst is prepared. Although the activity of the catalyst is improved, due to the poor hydrothermal stability of REHY and REY per se, the thermal and hydrothermal stability of the catalyst become poor; therefore the catalyst easily deactivates in operation, which is reflected by the low activity of equilibrium catalyst and the poor coke selectivity. However, the amount of REUSY is increased from the conventional 30-35% to 40% or even 45%, there is no doubt that the production cost will be greatly raised.
It is an object of the present invention to provide a zeolite Y which simultaneously has high intracrystalline rare earth content, smaller initial unit cell constant, good thermal and hydrothermal stability, and can be directly used to prepare cracking catalysts. It is till another object to provide a process for preparing such a zeolite Y.
The content of the intracrystalline rare earth of the zeolite Y according to the present invention on the basis of RE
2
O
3
is 4-15 wt %, the unit cell constant thereof is 2.450-2.458 nm, and the differential thermal collapsed temperature thereof is 1000-1056° C.
The content of the intracrystalline rare earth of the zeolite Y according to the present invention on the basis of RE
2
O
3
is preferably 6-12 wt %, and the unit cell constant thereof is preferably 2.452-2.456 nm. Such a zeolite has a higher framework silica to alumina ratio, which is 8.3-8.8, and a sodium oxide content less than 1.0 wt %, preferably 0.5 wt %.
The present invention also provides a process for preparing such a zeolite Y, which comprises: drying rare earth-containing zeolite Y as raw material so that the water content thereof is lower than 10 wt %, introducing gaseous silicon tetrachloride carried by dry air in a zeolite Y to silicon tetrachloride weight ratio of 1:0.1-0.9 and reacting at a temperature ranging from 150° C. to 600° C. for 10 min-6 b, then purging with dry air for 5 min-2 h, and washing with de-cationized water to remove the residual soluble by-products such as Na
−
, Cl
−
, Al
3+
and the is like in the zeolite.
In the provided process, said rare earth-containing zeolite Y can be either commercial products of REY and REHY, or the product derived from NaY by rare earth exchanging.
Generally, the content of the rare earth in said commercial product of REHY on the basis of RE
2
O
3
is 6-14 wt %, and the content of Na
2
O is hither than 2 wt %; the content of the rare earth in said commercial product of REY on the basis of RE
2
O
3
is 10-20 wt %, and the content of Na
2
O is higher than 4 wt %.
In the preparation process of zeolite Y, said procedure of the rare earth exchanging NaY is that NaY having a silica to alumina ratio higher than 3.5 is exchanged with an aqueous solution of rare earth chloride in a weight ratio of NaY:RECl
3
:H
2
O=1:0.1-0.25:5-15 under

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