There are two different principles for the synthesis of aluminum-rich zeolites in industrial processes: Manufacturing of highly pure crystalline zeolite powders from a synthesis gel and Conversion of natural minerals into zeolite matter. Usually, in the industrial production of zeolite A, X, and NaY, the sodium form is manufactured except the zeolite LSX synthesis [ 36 ]. Therefore, different raw materials as silicon source such as silicic acid, colloidal silica, sodium silicate, or silica gel [ 37 ] are used.
Possible alumina sources are alumina trihydrate, sodium aluminate, activated alumina, gamma alumina. Sodium may be obtained from sodium hydroxide which controls simultaneously the pH value [ 37 ].
A convenient way to prepare such a reactant mixture is to pour under more or less intensive stirring an aqueous solution containing the aluminum source and sodium hydroxide into an aqueous solution containing the silica source. After crystallization, the zeolite suspension is filtered at temperatures between room temperature and reaction temperature [ 37 ], for example, in a filter press [ 38 ] or a centrifuge [ 39 , 40 ] or a vacuum belt filter [ 40 ].
The zeolite crystals are washed directly on the filter device till a pH value between 9 and 12 [ 37 ] is achieved. If desired, the zeolite powder in its virgin sodium form can be ion exchanged or otherwise modified. For example, the filter cake can be suspended in a suitable salt solution and stirred at a suitable temperature. Alternatively, the exchange step is done in a column [ 41 ] or directly on the filter press [ 42 ] with a suitable salt solution at a suitable temperature.
After the ion-exchange procedure is completed, the zeolite is washed as described above. Afterwards, the filter cake is dried in a direct or indirect heated thermal treatment process, as, for example, spray drying, spin flash drying, or long gap mill drying [ 40 , 43 ]. The dried zeolite powder is processed in the following steps. The mother liquor from the filtration step can usually at least to a certain extent be reused in the following zeolite synthesis batch [ 37 , 44 ].
The manufacturing of zeolites by conversion of minerals is not really a commonly used process. In several papers which deal with the synthesis of zeolite A, X, and NaY from minerals, kaolin or metakaolin is used as aluminum source [ 45 — 47 ].
A disadvantage of such procedures is the presence of impurities in the applied minerals [ 45 ], but some advantages simple treatment of the mother liquor and a nearly waste-free production support the application of that synthesis method especially in the case of zeolite NaY [ 46 ]. The properties of zeolite molecular sieves can be influenced by the properties of the starting zeolite powder.
For instance, the hydrothermal stability or desorption characteristics of FAU vary with the chemical composition, especially the aluminum content [ 48 ]. The particle size, particle size distribution, and the surface characteristics of single zeolite crystals affect the adsorption properties as well as the mechanical stability of zeolite molecular sieves.
By varying the synthesis gel composition, time, or temperature or by adding additives to the synthesis gel, the mentioned properties of the zeolite powder can be changed [ 49 , 50 ]. Depending on the intended applications, the particle size distribution is adjusted. Binder-containing zeolite molecular sieves In dynamic adsorption processes, where the adsorbent has to be regenerated frequently, the fluid dynamics e.
Because pure zeolite powder does not exhibit binding properties, an appropriate binder needs to be applied to form the above-mentioned macroscopic particles. Figure 2 shows the main principles for the manufacturing of conventional binder-containing zeolite molecular sieves bulk material. The zeolite component is the main component of the pre-mixture and can be applied as dried zeolite powder occasionally as filtercake. Usually, the zeolite component is modified as described above, e.
Besides the zeolite component a binder material is put into the pre-mixture. Mineral binders such as bentonite, attapulgite, or kaolin are common [ 53 , 54 ] as well as synthetic binders such as alumina, silica [ 54 , 55 ], or a mixture thereof [ 56 ].
The type of binder material to be applied depends on the shaping procedure and on the final application of the zeolite molecular sieve. Bentonite montmorillonite for example is commonly used for extrusion [ 57 , 58 ], attapulgite for beading [ 59 ].
It should be noted that natural mineral binders may contain impurities e. If necessary, additives such as shaping aids e. Such mainly organic compounds are burnt out in subsequent thermal treatment steps. In order to create a defined secondary pore system see below thermally or chemically, removable spacers e.
Figure 2. Scheme of the principle manufacturing procedures for binder-containing zeolite molecular sieve shapes bulk material. After the mainly dry mixing of all aforementioned materials in the pre-mixture usually a certain amount of water is added in order to adjust the viscosity and plasticity of the mixture for the related shaping process that can be agglomeration granulation [ 59 ], spray granulation [ 61 ], or extrusion [ 62 ].
After the shaping process, the molecular sieve has to be dried and activated in a thermal step, for example, in a rotary kiln [ 63 ] or belt calciner [ 64 ] to remove the water and other adsorbed compounds. The applied temperature is often higher than required for the zeolite activation, since the binder system needs such higher temperatures for setting. Due to the limited hydrothermal stability [ 67 — 69 , 95 ] of hydrophilic zeolites, the activation step has to be carried out carefully.
To avoid partial zeolite destruction during the activation step, the released water needs to be removed from the shape as fast as possible in order to avoid the appearance of hydrothermal conditions.
The higher the temperature and higher the moisture concentration directly at the zeolite centers the higher the probability for partial zeolite destruction [ 70 ]. Depending on the particular conditions, a residual water content of less than one percent can be reached.
During the cooling step as well as during the storage of the activated material, the presence of humidity or other adsorptive components should be avoided to prevent undesired adsorption on the material. Chemistry of Materials , 28 14 , The Journal of Physical Chemistry C , 28 , Lesch, and Michael Tsapatsis. Chemistry of Materials , 28 12 , Nils E. Zimmermann and Maciej Haranczyk. Luis A. Villaescusa and Miguel A.
Chemistry of Materials , 28 9 , John R. Di Iorio and Rajamani Gounder. Chemistry of Materials , 28 7 , Manoj B. Chemical Reviews , 6 , Chemistry of Materials , 28 6 , Mohammad Navaid Khan, Scott M. Auerbach, and Peter A. The Journal of Physical Chemistry C , 50 , Journal of the American Chemical Society , 45 , Inorganic Chemistry , 54 18 , Journal of the American Chemical Society , 30 , The Journal of Physical Chemistry C , 23 , Inorganic Chemistry , 54 8 , The Journal of Physical Chemistry C , 6 , Journal of the American Chemical Society , 3 , Aruni Gankanda and Vicki H.
Lee, Dongxia Liu, and Baoxia Mi. Sarika Goel, Stacey I. Zones, and Enrique Iglesia. Journal of the American Chemical Society , 43 , Chemistry of Materials , 26 15 , Paula M. Cantos and Christopher L. Inorganic Chemistry , 53 7 ,
Of these partides Chemistry of Materials , 28 9 , Besides the mentioned examples, the use of zeolite molecular sieves in automotive applications such as drying of brake air in rail vehicles, trucks, or busses is also a well-known application. The reaction product is a coherent mass of substantially homogeneous amorphous composition and is the precursor of the desired synthetic crystalline zeolite. Lee, Dongxia Liu, and Baoxia Mi.
Sarika Goel, Stacey I. In addition, die process of diis invention creates the potential for the development of novel molecular sieves. As mentioned earlier, the use of adsorption inert binder material reduces the adsorption capacity zeolite molecular sieves by approximately the percentage of binder in the shape see Table 1.
It also affects the interior pores by filling or collapsing pores thereby reducing the particle's pore volume.
Zeolite powder with different particle sizes Within the manufacturing of synthetic zeolite molecular sieves, the synthesis of the related zeolite powder is first step. Because dust may cause problems in a running adsorption process e. Google Scholar Thus successful crystallization sometimes can be suspected if a very dense, easily settling solid phase is observed in the crystallization vessel when the crystallization is terminated.
Mixtures of two or more templating agents can either produce mixtures of the desired molecular sieve or the more strongly directing templating species may control the course of the reaction with die odier templating spedes serving primarily to establish the pH conditions of the reaction gel. This invention relates to the hydrotiiermal treatment of nutrients used in the manufacture of molecular sieves where at least one of the nutrients possesses geometric frame- works that contains one or more of macro and meso porosity the "framework porosity" within it. Whalley, S. Meier, W.
Nagy, J. Maesen, Th. Ward eds.
Robson, H. Chemistry of Materials , 30 16 , Derouane and W. Van Erp, W.
White eds. Den Ouden, C. The process of daim 9 wherein the molecular sieve structure is a zeolite. Occelli and H. Engelhardt, G.
They found that the product has comparable catalytic properties to samples prepared by previous methods. Lee, Dongxia Liu, and Baoxia Mi. Then, this solution was added to a highly reactive fumed silica and stirred widi a spatula for about 15 minutes.