Surface and Interface Chemistry Adsorbents with technological impact: zeolites and activated carbon Valentim M. B. Nunes Engineering Unit of IPT 2014

Throughout the course were explored classical areas of chemistry of surfaces and Interfaces, with some detail (in some cases) and comprehensiveness. zeolitesactivated carbon In this lesson, we will deepen a subject discussed earlier, solid surfaces, focusing the study on two kinds of materials with large industrial application: zeolites and activated carbon.

Drying, purification and separation of gases and hydrocarbons zeolites adsorbents Ionic Exchangers Catalysts in refining processes heterogeneous catalysis

The origin of the term zeolite was due to the chemist and mineralogist Axel Fredrik Cronstedt and derives from the Greek words "zein" (boil) and "lithos" (stone). From 1954 synthetic zeolites began to be used as molecular sieves in industrial processes of separation and purification of gases The most important use (heterogeneous Catalysis) began in 1962 – catalytic cracking.

General formula: M z [(AlO 2 ) x (SiO 2 ) y ].wH 2 O A zeolite is a crystalline aluminosilicate (mineral or synthetic) with micro porous structure and well defined cavities occupied by ions and molecules of H 2 O with freedom of movement for exchange with other ions and reversible dehydration.

Structure Zeolites have a three-dimensional structure with a porosity of regular dimensions comparable to those of organic molecules, and with pore openings ranging from about 3 to 10 Å. They contain SiO 4 and AlO 4 units linked by oxygen. The zeolite of type A contains equal amounts of silicon and aluminum. The pores are formed by rings of 4, 6 and 8 oxygen atoms, being the largest pore dimension equal to 4.1 Å

Synthesis (example)

Industrial applications: adsorption Molecular Sieves. Capillary condensation as a result of small dimensions of surface, increasing the adsorbed concentration. Selectivity adsorption due to existence of charges (Polar molecules) Example: gas drying!

Industrial application : ionic exchangers Application in great expansion, is the use of zeolites as adjuncts in household detergents, for removal of cations, such as calcium and magnesium, to reduce the water hardness. Ammonia removal from municipal sewage

Industrial application: catalysis Selectivity of molecules by geometric motifs, and kinetic effects related to diffusion. High specific area or BET area. Example: Catalytic Cracking to obtain petrol with C5 ~ C6 with high octane index.

In petrochemical processing, zeolites are used as catalysts for Fluid Catalytic Cracking (FCC process), a process which transforms long- chain alkanes (heavy oil) into shorter ones (petrol), to enhance the octane number of the petrol by producing branched species.

Activated carbon is a material with high porosity. With the use of nitrogen adsorption techniques at 77 K, it can be verified that it contains essentially micro pores. Activated carbon has the ability to selectively collect gases, liquids or impurities inside the pores, showing a great ability for clarification, deodorizing and purification of liquids or gases (wastewater treatment).

Activated carbon Water treatment: purification of public supply water Industrial water recycling: removal of substances present in the water, as for example, naphthalene's, benzene, phenol, benzene and sulfonates. Food industry: adsorption of molecules that cause taste, color or undesirable odor. Drug detox treatment

Activated carbon is characterized by the high specific area (m 2 /g); 600 to 1600 m 2 /g, withe typical values in the range of 900 m 2 /g. However, the activity of coal is associated to internal pores and fissures: specific surface has little influence on the total capacity of the activated carbon.

Activated carbon (AC) filters have been used in home water purification systems primarily to remove taste and odor

Adsorption isotherms