From natural zeolite to synthetic zeolite（2）
In recent years, a large number of natural zeolite resources have been discovered all over the world. Therefore, the utilization of natural zeolite has attracted extensive attention, and considerable research has been carried out, and great progress has been made. So far, natural zeolite has been used in the drying and separation of some gases and liquids, the treatment of softened sewage in hard water, and the improvement of soil. There are also selected or processed natural zeolites in industry as catalysts and catalyst carrier.
Since the founding of the People's Republic of China, my country has
carried out a series of exploration work on zeolite resources, according to
incomplete statistics. my country has found a large number of mordenite and
clinoptilolite resources, in addition to a variety of products such as
analcite, helium zeolite, and sodium zeolite. With the deepening of people's
understanding of natural zeolite, its application range is getting wider and
wider. Since natural zeolite cannot meet the large-scale needs of industry, it
has become an urgent requirement in production practice to replace natural
zeolite with synthetic zeolite. Synthetic Research. In fact, the synthesis of
zeolite was first carried out at the end of the 19th century. Since the natural
zeolite was initially found to exist in the deep underground volcanic rock
pores, it was inferred that the zeolite was formed under high temperature and
high pressure conditions. Therefore, the initial work of synthesizing zeolite
was carried out in the environment where zeolite was formed in geology, that
is, high temperature hydrothermal synthesis technology was adopted.
Later, a large number of natural zeolites
were found in sedimentary rocks. Since most of these zeolite deposits are
located near the surface, it is believed that they can be formed under not too
high temperature and pressure. Therefore, people have carried out bold
experiments, using low-temperature hydrothermal synthesis technology (reaction
temperature is 25~150 ° C, usually 100 ° C) to carry out zeolite synthesis
research, starting from the 1940s, the synthesis of zeolite has been carried
out in a few years. The first batch of low-silica zeolites were produced. The
application of low-temperature hydrothermal synthesis technology provided
favorable conditions for large-scale industrial production. By the end of 1954,
A-type molecular sieves and X-type molecular sieves began industrial
production. Then a number of companies in the United States, such as Linde,
Union Carbide Corporation, UCC, Mobil, and Exxon, simulated the types and formation
conditions of natural zeolite, and continuously researched and developed a
series of low-silicon-aluminum ratio and medium-silicon-aluminum ratio
(silicon-aluminum ratio). Synthetic zeolite molecular sieves with aluminum
ratio = 2.5), such as Na-Y type zeolite, large pore mordenite, L type zeolite,
erionite
Stone, chabazite, clinoptilolite, etc. And
it has been widely used in the adsorption separation and purification of gas,
many catalytic processes in petroleum refining and petrochemical industry, and
in ion exchange and other fields.
In 1959, my country successfully synthesized A-type molecular sieve
and X-type molecular sieve. Then Y-type molecular sieve and mordenite were
synthesized, and they were quickly put into industrial production. With the
continuous development of production, the application range of zeolite
molecular sieve is getting wider and wider. In the 1950s, zeolite molecular
sieves were mainly used for drying, separation and purification of gases. Since
the 1960s, they have been widely used as catalysts and catalyst carriers for
petroleum processing. Recently, zeolite molecular sieve has become the most
important adsorption separation and catalytic material in petroleum refining
and petrochemical industry, coal chemical industry and a large number of fine
chemicals.
Although synthetic zeolite has many advantages over natural zeolite
(such as higher purity, better pore size uniformity, ion exchange performance,
etc.) and has a wide range of applications, because many natural zeolite deposits
are located near the surface, they are easy to be mined and crushed. It can be
used after simple steps such as screening, so its price is far lower than that
of synthetic zeolite. Therefore, in the case of large demand and low quality
requirements, natural zeolite is more suitable, especially in agriculture,
light industry, environmental protection, etc., the application of natural
zeolite still has great development prospects.
