Cu-Zeolite Adsorbent Nixes Nitrogen in Diesel

Nanoporous materials (NPMs)materials featuring accessible, molecular-size pores - have many environmental applications, such as the adsorption of metals, organic chemicals and other pollutants from gaseous or aqueous waste streams. Zeolites, a mature category of NPMs, captured 48% of the market share for NPMs in 2002 and are expected to grow 3.4%/yr from $740 million in 2002 to $875 million by 2007, according to the Freedonia Group (Cleveland. OH; www.freedoniagroup.com), Zeolites have carved out significant niches in petroleum for the removal of organonitrogen compounds from liquid fuels in order to lower NO^sub x^ emissions upon fuel combustion.

This process, known as hydrodenitrogenation (HDN) is typically performed simultaneously with desulfurization by reacting the fuel with H^sub 2^ at 20-100 atm and 300-380�C using a CoMo/Al^sub 2^O^sub 3^ or NiMo/Al^sub 2^O^sub 3^ catalyst. While successful at removing heterocycles (where N^sub 2^ is bound in rings, such as in pyridine and pyrrole), HDN fails to remove non-heterocycles (e.g., N^sub 2^ is contained in linear molecules, such as anilines and aliphatic amines) due to stearic interference.

Univ. of Michigan (Ann Arbor; www.umich.edu) chemical engineering professor Ralph Yang and PhD student Arturo Hernandez-Maldonado have developed a regenerable copperzeolite (CuY) sorbent that works at room temperature and atmospheric pressure in a fixed-bed adsorber to reduce the overall N^sub 2^ content of diesel from 83 ppm to under 0.1 ppm.

Their patent-pending technology was demonstrated in a bed containing 1-2 g CuY, with a diesel fuel feed rate of 0.5 cm^sup 3^/min and a capacity of 43 cm^sup 3^ diesel per g sorbent (or 3 mg N^sub 2^ per g sorbent). Effluent (or eluent) is collected until saturation is reached and is analyzed using a gas Chromatograph (GC) equipped with a chemiluminescent N^sub 2^ detector.

The adsorbent is prepared by ion exchange of NaY zeolite (Si/A1 = 2.43) with Cu^sup 2+^ followed by reduction to form CuY. Molecular orbital (MO) theory calculations were used to determine the type and location of the cation that should be placed on the surface of the zeolite to bond the organonitrogen molecules most strongly. "We found that nitrogen bonds to the adsorbent by p complexation, during which electrons are donated from the p orbital of, say, a pyrrole ring to the vacant s orbital of metals (a process known as s donation), and simultaneously from the d orbitals of the metals to the p* orbital of pyrrole. "As a result of p complexation, organonitrogen adsorbs on CuY in a flat, face-down manner, eliminating the steric hindrance that inhibits its activity during HDN," says Yang. CuY is regenerated by treatment with air at 350�C (to burn off organonitrogen) followed by auto-reduction (of Cu^sup 2+^).