Correlation of Catalytic Efficiency of Faujasites in the Alkylation of Isobutane by Butenes and their IR Spectral Characteristics

Abstract

Three HLaCaNaX samples with approximately the same cation content but differing in their IR spectral characteristics were synthesized under different conditions. Testing these samples in the alkylation of isobutane by butenes showed that the catalyst displaying IR bands at 3540 and 3610 cm -1 have the greatest efficiency.The acidity of zeolite catalysts is the determining factor in activity in carbonium ion processes [1,2]. The alkylation of isobutane by butenes yielding 2,2,4-, 2,2,3-, 2,3,4-, and 2,3,3-trimethylpentanes (TMP), which are high-octane gasoline components, holds considerable practical and theoretical interest [3,4]. The replacement of presently used but outdated and ecologically dangerous alkylation techniques with concentrated sulfuric acid and hydrogen fluoride by modern heterogenous catalytic technologies is an important current problem [5]. In this regard, greatest interest is found in faujasite zeolite catalysts. As a rule, polycation-decationized forms of zeolite type-Y are preferred among such faujasites [6]. However, a significant difference in relative efficiency between types X and Y has not been found.Nevertheless, HLaCaNaY and HLaCaNaX zeolites have nonidentical IR spectra in the OH bond stretching region (3500-3800 cm -1 ). Thus, for example, while the HLaCaNaY samples absorb at 3540 and 3650 cm -1 (depending on the preparation conditions and their cationic occupancy, these bands may shift in the range of 10-15 cm -1 [7]), an additional band is found at 3610 cm -1 in the IR spectrum of HLaCaNaX [8,9].The band at 3650 cm -1 , which disappears after chemisorption of, for example, pyridine, is related to acid hydroxyls in large cavities, while the band at 3540 cm -1 , which remains in the spectrum, is related hydroxyls at sites inaccessible for pyridine molecules [7]. The band at 3610 cm -1 has not yet been assigned.Hence, it was of interest to synthesize HLaCaNaX samples differing in the IR bands at 3550, 3610, and 3650 cm -1 and study these samples as alkylation catalysts. EXPERIMENTALThree portions of synthetic zeolite NaX (provided by Sorbent, Nizhnii Novgorod, Russia, SiO 2 /AlO 2 = 2.3) were subjected to ion exchange modification to give acid forms of HLaCaNaX with optimal cation composition [10]. The ion exchange sequence was the same for all the samples. The procedure entailed exhaustive exchange of starting calcium by 192 0040-5760/05/4103-0192

Obtaining glucose-based 5-hydroxymethylfurfural on large-pore zeolites

“…Two polycationic samples were synthesized based on the faujasite-type zeolite. In their synthesis, the following sequence of exchanges was used: first calcium was introduced (four exchanges), followed by lanthanum (two exchanges), and, in the end, ammonium (one exchange) [21].…”