Method for preparing rare-earth ultra-steady Y molecular sieve

Abstract

The invention relates to a method for preparing a rare-earth ultrastable Y molecular sieve, which comprises the following steps: preparing a reaction mixture according to a total feeding molar ratio of 2.5-4 of Na2O / Al2O3, 7-11 of SiO2 / Al2O3, and 15-25 of H2O / SiO2, using inorganic acid to adjust pH of the material within a range of 12.5-13.6, then preparing an NaY molecular sieve as a matrix having a cell constant less than or equal to 2.466nm through hydrothermal crystallization, combining the material with ammonium salt and roasting the mixture once or many times to remove Na until NaO2 is less than 1 wt%, introducing steam with air speed of 0.3-1.5 / h during the Na removal and roasting step to allow the cell constant of the molecular sieve to shrink to 2.455 to 2.462nm, and carrying out surface coating modification of the molecular sieve in a stirring mill on the basis that the feeding ratio of the molecular sieve by dry basis to the phosphoric acid rare-earth and / or carbonic acid rare-earth is between 1:0.01-0.05 and the ratio of the molecular sieve to grinding medium is between 1:3-7 to obtain the rare-earth ultrastable Y molecular sieve with higher crystal integrity, wherein the prepared rare-earth ultrastable Y molecular sieve has better capability of resisting heavy metal vanadium pollution and better coke selectivity under regenerative condition of harsh water vapor.

Description

technical field [0001] The invention relates to a preparation method of a rare-earth ultra-stable Y molecular sieve, specifically a rare-earth ultra-stable Y molecular sieve with better resistance to heavy metal vanadium pollution, low coke selectivity and high crystal integrity. Background of the invention [0002] Y-type molecular sieve is the main active component of catalytic cracking catalyst and one of the most used molecular sieves. With the increasing weight of raw oil and the pursuit of better economic benefits, the current catalytic cracking unit generally increases the amount of residual oil. In order to reduce the amount of coke and meet the harsh regeneration conditions, the active components of the cracking catalyst used Ultrastable Y molecular sieves are widely used. [0003] Due to the different preparation methods, the resulting product is also called differently. The product obtained by the hydrothermal method is often referred to as ultra-stable Y (USY), ...

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Problems solved by technology

[0013] In summary, although there are many methods for preparing ultra-stable Y molecular sieves and catalysts with anti-vanadium functions in the prior art, a common feature in the disclosed prior art for preparing ultra-stable Y molecular sieves is that the crystallinity of the parent NaY molecular sieve is not controlled. In this way, the molecular sieve must be treated with hydrothermal or acid in a wider range to obtain the desired unit cell constant or skeleton silicon-aluminum ratio. During the treatment, the crystal integrity of the molecular sieve is seriously damaged, thus affecting the activity of the molecular sieve. , in order to maintain activity and anti-vanadium pollution, it can only be compensated by exchanging a large number of rare earths or depositing rare earth oxides and increasing the amount of molecular sieve in the catalyst. When the catalyst prepared by molecular sieve is used in the catalytic cracking unit, the coke selectivity becomes poor, and the dry gas increases accordingly

Increasing the amount of molecular sieve in the catalyst will increase the difficulty and cost of catalyst preparation. In fact, when the amount of molecular sieve is large, its wear resistance will be seriously reduced

[0014] In addition, the exchanged or deposited rare earths are not ideal for the anti-metal pollution of the molecular sieve. The vanadium species deposited on the surface of the molecular sieve decomposes in an oxidizing atmosphere to form oxygen-containing vanadium ions, which are further reacted during the high-temperature hydrothermal process of catalyst regeneration to form Vanadic acid with strong acid properties accelerates the destruction of the molecular sieve skeleton structure, resulting in a decrease in cracking reactivity

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