Síntesis De Zeolita ZSM-5 Utilizando Diatomita Como Precursor; Su Aplicación en El Proceso De Metanol a Hidrocarburos (Mth)

Abstract

Zeolite H-ZSM-5 is widely applied in the petrochemical industry, such as the synthetic process of methanol to hydrocarbons (methanol to hydrocarbons MTH). ZSM-5 zeolite is currently obtained through reagents and expensive processes, being available only a few cheaper alternative routes. In the present investigation, zeolite H-ZSM-5 was obtained from natural diatomite, then characterized, and finally tested in the synthetic MTH process. The natural diatomite was treated with sulfuric acid to perform hydrothermal synthesis with tetrapropyl ammonium hydroxide (TPA-OH). As a result, the H-ZSM-5 zeolite obtained had a Si / Al molar ratio of 23, it exhibited high thermal stability and showed Lowry-Brönsted and Lewis acid sites. The application of this zeolite in the MTH reaction showed a methanol conversion of 88%. The products were: dimethyl ether (DME) in 40%, olefins (mostly ethylene and propylene) in 40% and others in 20%. The reaction conditions were: 300 ° C, 1.2L metanol /g cat h at atmospheric pressure (0.65 bar). The selectivity of the products can be modified in such a way that DME can be

The effect of the acid pre-treatment temperature of natural diatomaceous earth on the Si/Al ratio of ZSM-5 zeolite

“…Figure 5 shows the experimental NH 3 -TPD profiles for each zeolite. The profiles have a typical form of ZSM-5 zeolite from NH 3 -TPD-experiments [23], [24]. Four deconvoluted signals were assigned from the NH 3 -TPD profile for the ZSM-5 zeolite with Si/Al=12.6.…”

“…And the fourth signal has a maximum temperature around 850 °C. The first signal can be attributed to physically desorbed NH 3 , where the NH 3 comes from NH 4 + nNH 3 species adsorbed on the zeolite surface [23], [25]. The second signal is partially attributed to physically desorbed NH 3 and to interactions between NH 3 and weak Lewis acid sites [23], [26].…”

“…The first signal can be attributed to physically desorbed NH 3 , where the NH 3 comes from NH 4 + nNH 3 species adsorbed on the zeolite surface [23], [25]. The second signal is partially attributed to physically desorbed NH 3 and to interactions between NH 3 and weak Lewis acid sites [23], [26]. Lewis acid sites are generated by the presence of cations in the crystalline structure for charge compensation [26], [27].…”

“…Lewis acid sites are generated by the presence of cations in the crystalline structure for charge compensation [26], [27]. The third signal is due to strong Brönsted acid sites (BAS) [23]. Finally, the fourth signal is due to strong Lewis acid sites (LAS) [28].…”

“…These cations could come from undesired species, such as metallic species (weak Lewis acid sites) or by way of ion exchange. The studied zeolites were in a protonated form (H-ZSM-5), so the final aluminum concentration will determinate the BAS concentration [23].…”