Process for the synthesis, with multiple seeding, of zeolite crystals having a controlled particle size

Process for preparing zeolite crystals having a multimodal particle size distribution, and the sizes of which are between 0.02 μm and 20 μm, said process comprising at least the following steps:

• a) preparing a synthesis gel by mixing at least one source of silica, at least one source of alumina and optionally, at least one aqueous alkali or alkaline-earth metal hydroxide solution,
• b) feeding a tubular reactor with said synthesis gel,
• c) first introduction of one or more seeding agents into the tubular reactor or upstream of the tubular reactor,
• d) second introduction of one or more, identical or different, seeding agents into the tubular reactor,
• e) carrying out the crystallization reaction, in the tubular reactor, of the synthesis gel in the presence of the seeding agent(s), forming the reaction medium,
• f) filtering the reaction medium in order to recover crystals produced.