Ethylene To Propylene Research Articles

A low-temperature regenerable catalyst for stable and selective propylene production from ethylene using Ni and P-supported SSZ-13 zeolite

Due to the increasing demand for propylene, highly selective propylene production from ethylene using small pore zeolite has received significant attention. However, rapid catalyst deactivation due to coke deposition on the catalyst impedes effective propylene production in industry. Therefore, it is essential to develop a low-temperature regeneration ethylene-to-propylene (ETP) catalyst with stable catalytic activity. To achieve such a catalyst, various hydrocracking metal species and phosphorus-supported SSZ-13 were prepared and evaluated using a one-pass ETP and ETP-Regen test. The optimized catalyst NiO(1.0)-P(0.6)-SSZ-13 exhibited a constant, excellent propylene yield of over 70 wt% with 90 wt% of propylene selectivity over ETP reaction and consecutive ETP-Regen cycles. The unprecedented catalytic performance of NiO(1.0)-P(0.6)-SSZ-13 was ascribed to the synergistic effect of NiO and P components, where nickel is responsible for catalyst recovery through effective coke removal, while phosphorus plays an essential role in size-selective diffusion.

Microwave-assisted rapid synthesis of nanosized SSZ-13 zeolites for effective conversion of ethylene to propylene

SSZ-13 is an attractive zeolite with chabazite topology composed of small pores with 8-membered rings. In this work, we report a highly effective method to synthesize SSZ-13s with microwave (MW) heating. Compared with conventional electric (CE) heating, MW heating accelerates both the nucleation and crystal growth rates of the synthesis by 6 and 18 times, respectively. Importantly, MW-assisted rapid synthesis produces the SSZ-13 with the smallest particles (<50 nm). However, the CE-assisted synthesis produces large/inhomogeneous particles (size: 0.4–1 μm). The obtained SSZ-13s were employed in acid catalysis or ethylene-to-propylene (ETP) reactions. The record-small SSZ-13s were more efficient in the ETP reactions, with more stable ethylene conversion/propylene yield (at the same time on stream) and higher propylene selectivity (at the same ethylene conversion), than large SSZ-13s. Finally, the maximum propylene yield (62%) is competitive or better than any SSZ-13s obtained via direct synthesis from precursors like silica and alumina.

Enhanced catalytic activity of phosphorus-modified SSZ-13 zeolite in the ethylene-to-propylene reaction by controlling acidity and intracrystalline diffusivity

A highly selective means of producing propylene via the ethylene-to-propylene (ETP) reaction is required to manage the supply-demand balance of light olefins. To improve the catalytic activity of the ETP reaction, a phosphorus-modified SSZ-13 zeolite (P-SSZ-13) was prepared by introducing phosphorus to the SSZ-13 zeolite via a simple impregnation method. The P-SSZ-13 catalyst exhibited increased propylene selectivity and yield compared to the pristine catalyst. According to solid-state NMR spectroscopy and STEM-EDS observation, the phosphorus species were mainly located on the outer part of the crystal as a form of polyphosphate. To reveal the effect of the phosphorus loading on the enhancement of ETP reactivity, a series of surface-modified SSZ-13 catalysts were prepared and investigated. It was found that the polyphosphate species in the P-SSZ-13 catalyst not only weakened the acidity of the zeolite by bonding with the framework aluminum species but also reduced the diffusion out of the relatively large-sized hydrocarbon species by partially blocking the pore mouths. The change in the diffusivity of the hydrocarbons over the SSZ-13 catalysts also affected the ETP reactivity. The relationship between the amount of phosphorus and the ETP reactivity of the P-SSZ-13 catalysts could also be clearly demonstrated in terms of the change in both acidity and intracrystalline diffusivity. Moreover, 13C MAS NMR measurement with isotopic switch experiment confirmed the alkyl naphthalene-based hydrocarbon pool mechanism over the P-SSZ-13 for the ETP reaction.

Tungsten Oxide-Modified SSZ-13 Zeolite as an Efficient Catalyst for Ethylene-To-Propylene Reaction

Among the zeolitic catalysts for the ethylene-to-propylene (ETP) reaction, the SSZ-13 zeolite shows the highest catalytic activity based on both its suitable pore architecture and tunable acidity. In this study, in order to improve the propylene selectivity further, the surface of the SSZ-13 zeolite was modified with various amounts of tungsten oxide ranging from 1 wt% to 15 wt% via a simple incipient wetness impregnation method. The prepared catalysts were characterized with several analysis techniques, specifically, powder X-ray diffraction (PXRD), Raman spectroscopy, temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and N2 sorption, and their catalytic activities were investigated in a fixed-bed reactor system. The tungsten oxide-modified SSZ-13 catalysts demonstrated significantly improved propylene selectivity and yield compared to the parent H-SSZ-13 catalyst. For the tungsten oxide loading, 10 wt% loading showed the highest propylene yield of 64.9 wt%, which was 6.5 wt% higher than the pristine H-SSZ-13 catalyst. This can be related to not only the milder and decreased strong acid sites but also the diffusion restriction of bulky byproducts, as supported by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) observation.

Direct Transformation of Ethylene to Propylene by Cascade Catalytic Reactions under Very Mild Conditions

Converting ethylene to propylene (ETP) at low temperatures, without adding other hydrocarbons, is a great challenge today. In this study, we explored an ETP process based on cascade reactions, oper...

Conversion of Y into SSZ-13 zeolite, in the absence of extra silica, alumina and seed crystals, with N,N,N-dimethylethylcyclohexylammonium bromide, and application of the SSZ-13 zeolite in the propylene production from ethylene

SSZ-13 zeolite (CHA structure) with small pore or 8-membered ring has been widely studied in catalysis and adsorption. Even SSZ-13 might be very useful in such applications, the synthesis usually relies on expensive organic templates. In this study, SSZ-13 was obtained, with a relatively inexpensive template, N,N,N-dimethylethylcyclohexylammonium bromide, from conversion of Y zeolites with wide silica/alumina ratios (SARs), especially in the absence of any crystal seed, additional silica and alumina. The obtained SSZ-13 s have relatively wide SAR of 6.9–36.7; and phase-pure SSZ-13 s could also be obtained from mixture of Y zeolites. The obtained SSZ-13 s, in proton form, were applied in ethylene-to-propylene (ETP) reaction, and the SSZ-13 with suitable SAR (18.8) had not only high propylene yield but also stable propylene production compared with other SSZ-13 s, showing the possible application of the SSZ-13 in ETP reaction.

Synthesis of SSZ-13 zeolite in the presence of dimethylethylcyclohexyl ammonium ion and direct conversion of ethylene to propylene with the SSZ-13

The conversion of Y zeolites having wide silica/alumina ratio (SAR, 5.1–80) into SSZ-13s was carried out in the presence of N,N,N-dimethylethylcyclohexylammonium (DMCHA) ion, as an organic structure directing agent (OSDA). SSZ-13 zeolites could be obtained from siliceous Y zeolites; however, another phase, analcime (ANA) was obtained when aluminous Y zeolites (SAR: 5.1–12) were converted. Sodium silicate was used not only to successfully convert the aluminous Y zeolites into SSZ-13s but also to increase the SAR of the obtained SSZ-13 zeolites. The synthesis of SSZ-13 with DMCHA was possible in the absence of any seed, which is advantageous in the viewpoint of both the expense and convenience of the synthesis. Moreover, the synthesized SSZ-13s were utilized in the direct conversion of ethylene-to-propylene (ETP). Moderately siliceous SSZ-13s (SAR: 18–24) showed better performance in ETP than aluminous or siliceous SSZ-13s. DMCHA-derived SSZ-13 was also competitive or better in ETP than SSZ-13s prepared with other reported templates including N,N,N-trimethyl-1-adamantanamine hydroxide (TMAda-OH). For example, the maximum propylene yield in ETP over SSZ-13s (with similar SAR of 15–19) prepared with choline chloride, tetraethylammonium hydroxide (TEA-OH), TMAda-OH, and DMCHA-Br were 51, 61, 65 and 68%, respectively. Based on the syntheses and ETP reactions, DMCHA ion can be recommended as a versatile/inexpensive OSDA for the conversion of Y (with wide SARs) into SSZ-13 zeolites which can be effective in ETP reaction. However, further work is required to understand the reason of the competitiveness of the DMCHA-derived SSZ-13 and the effect of the SAR on the propylene yield in ETP.

Preparation of SSZ-13 zeolites from beta zeolite and their application in the conversion of ethylene to propylene

For the first time, beta zeolites (IZA code: BEA with 12-membered rings, having a wide range of SiO2/Al2O3) were converted into SSZ-13s (IZA code CHA, having 8-membered rings) in the presence of external silica source (here, Na2SiO3) and N,N,N-trimethyl-1-adamantanamine hydroxide as a structure directing agent. Na2SiO3 was essential for the successful conversion when the parent zeolite beta was Al-rich. The conversion of beta into SSZ-13 zeolite can be explained by the relative stabilities of beta and SSZ-13 zeolites, where pore size had more dominant role than the framework density. The obtained SSZ-13s were highly porous, had both weak and strong acidic sites and composed of tetrahedral aluminum. Finally, the synthesized SSZ-13s were applied in the direct conversion of ethylene-to-propylene (ETP) as a solid catalyst. The results showed that the SSZ-13s, converted from beta, were better or competitive in ETP (especially in the stable conversion of ethylene) against the SSZ-13 (synthesized by using tetraethylammonium hydroxide) that had showed very competitive performances earlier in ETP.

Conversion of ethylene into propylene with the siliceous SSZ-13 zeolite prepared without an organic structure-directing agent

The SSZ-13 zeolite was synthesized via seed-assisted method without an organic structure-directing agent (OSDA) from sodium silicate, sodium aluminate, and seed crystals using a wide range of silica/alumina ratios (SARs) in the precursor gels. The SAR of the SSZ-13 was quite high (10) when the SAR of the precursor gel was 40, which was the optimum ratio for high crystallinity. The zeolite was steamed at a high temperature to further increase the SAR via dealumination. The crystal structure of SSZ-13 was stable during steaming because of its high SAR, quite different from another SSZ-13 zeolite obtained from the conversion of zeolite Y in K+ ion in the absence of an OSDA. Steaming at 800 °C and further washing with acid led not only to an increase in the SAR up to 21, but also to a steady increase in porosity. However, the concentration of acid sites, especially strong ones, decreased steadily with increasing steaming time, and octahedral aluminum was removed successfully after adequate steaming. Both pristine and steamed SSZ-13 zeolites were applied to the ethylene-to-propylene (ETP) reaction. With increased steaming time, both the stability of the ethylene conversion and the maximum propylene yield increased. Compared to conventional SSZ-13 zeolites synthesized using expensive OSDAs, adequately steamed SSZ-13 zeolites were competitive for catalyzing the ETP. The exceptional performance of the SSZ-13 zeolite obtained in this study may be understood in terms of its adequate SAR and the decreased number of acid sites (especially strong acid sites), which might be active for hydrogen transfer and ethylene oligomerization. Therefore, it could be suggested that the SSZ-13 zeolite synthesized without an OSDA can be effective in the ETP reaction when steam-treated under suitable conditions.

Conversion of Y into SSZ-13 zeolite in the presence of tetraethylammonium hydroxide and ethylene-to-propylene reactions over SSZ-13 zeolites

The conversion of Y-zeolites having a wide silica/alumina ratio (SAR, 5.2–80) into other zeolites was attempted using tetraethylammonium hydroxide (TEA-OH) as an organic structure directing agent (SDA). Depending on the SARs of the Y-zeolites, different zeolite phases, either pure or mixed, were obtained from the same reaction precursors (TEA-OH, Y zeolite, etc.) and conditions. To investigate the obtained phase selectivity and phase transformation, the effects of the reaction temperature and times were evaluated. The phase selectivity or transformation could be explained using the framework density or pore size of zeolites. Zeolites Y having SARs of 12 and 30 were also applied to examine the effects of alkali metal ions (AMIs; Li+, Na+, K+, and Cs+) on the conversion. The results showed that AMIs also have a dominant influence on the phase of the obtained zeolite, and Na+ was the most effective for the production of the SSZ-13 zeolite. The protonated SSZ-13 zeolites (obtained from zeolite Y with an SAR of 12 or 30) were employed in the direct conversion of ethylene-to-propylene (ETP). The results showed that these SSZ–13s were better or competitive in ETP against SSZ–13s synthesized from various organic SDAs or SSZ–13s prepared under SDA-free conditions. Therefore, TEA-OH can be suggested as a competitive SDA to synthesize SSZ-13 zeolites, especially for ETP, from Y zeolites.

Controlling size and acidity of SAPO-34 catalyst for efficient ethylene to propylene transformation

Acidity- and size-controlled SAPO-34 zeolites were prepared via a hydrothermal method by controlling the type and ratio of the structure-directing agents (SDA) such as tetraethylammonium hydroxide (TEAOH) and/or morpholine (MP). The SAPO-34 catalysts were applied and tested for their ability to convert ethylene to propylene (ETP) directly. The propylene formation from ethylene showed a volcano-type trend with a crystal size of 0.3–13μm of the SAPO-34 zeolite by changing the ratio of TEAOH and MP. In addition, the propylene yield increased with an increase in the Si/(Si+P+Al) ratio from 0.042 to 0.105 and decreased at a Si/(Si+P+Al) ratio of 0.119. The results show that the proper size and acidity of the SAPO-34 catalyst with controlling the ratio of TEAOH and MP are required for an efficient ETP transformation process. The improved catalytic performance achieved while controlling the size and acidity may be related to number and strength of the active acid sites on the SAPO-34 zeolite.

Conversion of Y into SSZ-13 zeolites and ethylene-to-propylene reactions over the obtained SSZ-13 zeolites

Y zeolites having wide ranges of SiO2/Al2O3 ratios (silica/alumina ratios or SARs) were converted into SSZ-13 zeolites in the presence of N,N,N-trimethyl-1-adamantanamine iodide (TMAda-I) as a template. SSZ-13s with increased SARs could be obtained from Y zeolites having SARs of 5.1–80 and sodium silicate by both conventional electric (CE) and microwave (MW) heating. The syntheses conducted using MW and CE heating at 140°C were completed in 2h and 144h, respectively, because of accelerations by MW in both the nucleation and crystal growth stages. The obtained yields of SSZ-13 decreased as SARs of the starting Y zeolites increased, demonstrating the relatively easy conversion of aluminous Y into SSZ-13. The obtained SSZ-13s with wide SAR ranges (19–287) were applied as catalysts in the direct conversion of ethylene-to-propylene (ETP) to understand the effect of the SARs on the ETP performances, including the conversion of ethylene and propylene selectivity. The stability of ETP was highly dependent on the SAR of the SSZ-13 zeolites. SSZ-13s with excessively high or low SARs caused low ethylene conversion (from the beginning of the reaction) or rapid deactivation in the conversion, respectively. The propylene selectivity or yield (at a fixed ethylene conversion of 80%) generally increased with decreasing SARs (up to 19) of SSZ-13s under the studied conditions because of a steady increase in the selectivities for butenes and higher products with increasing SARs of SSZ-13s.