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Title: Chloromethane to olefins over H-SAPO-34: Probing the hydrocarbon pool mechanism

Abstract

In this paper, by means of in situ FTIR and ex situ 13C NMR studies, the initial periods of the chloromethane-to-olefins (CTO) reaction over SAPO-34 were probed in order to investigate the activation period of the reaction and to elucidate the formation of the catalyst active site. A methylated benzene species has been observed to form during the initial activation period of the reaction, and a direct positive correlation was constructed between the formation of this species and the catalytic activity. The data thus indicate that these methylated benzene species contribute to the formation of active sites within SAPO-34 for the CTO reaction. This is the first known report identifying a direct semi-quantitative correlation between the catalyst activity and growth of a methylated benzene active species, during the activation period of the chloromethane to olefins reaction. Finally, the findings here in correspond well to those reported for the methanol to olefins reaction, suggesting that a similar ‘hydrocarbon pool’ mechanism may be responsible for the formation of light olefins in CTO chemistry as well.

Authors:
 [1];  [1];  [1];  [1];  [2];  [3];  [4]
  1. SABIC Technology Center, Sugar Land, TX (United States)
  2. Columbia Univ., New York, NY (United States). Dept. of Chemical Engineering
  3. Brookhaven National Lab. (BNL), Upton, NY (United States). Chemistry Dept.
  4. Columbia Univ., New York, NY (United States). Dept. of Chemical Engineering; Brookhaven National Lab. (BNL), Upton, NY (United States). Chemistry Dept.
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States); SABIC Technology Center, Sugar Land, TX (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1341680
Report Number(s):
BNL-113408-2017-JA
Journal ID: ISSN 0926-860X; R&D Project: CO035; KC0302010
Grant/Contract Number:
SC0012704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Applied Catalysis. A, General
Additional Journal Information:
Journal Volume: 527; Journal ID: ISSN 0926-860X
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; SAPO-34; Hydrocarbon pool; Chloromethane; Induction period; 13C NMR

Citation Formats

Fickel, Dustin W., Sabnis, Kaiwalya D., Li, Luanyi, Kulkarni, Neeta, Winter, Lea R., Yan, Binhang, and Chen, Jingguang G.. Chloromethane to olefins over H-SAPO-34: Probing the hydrocarbon pool mechanism. United States: N. p., 2016. Web. doi:10.1016/j.apcata.2016.09.004.
Fickel, Dustin W., Sabnis, Kaiwalya D., Li, Luanyi, Kulkarni, Neeta, Winter, Lea R., Yan, Binhang, & Chen, Jingguang G.. Chloromethane to olefins over H-SAPO-34: Probing the hydrocarbon pool mechanism. United States. doi:10.1016/j.apcata.2016.09.004.
Fickel, Dustin W., Sabnis, Kaiwalya D., Li, Luanyi, Kulkarni, Neeta, Winter, Lea R., Yan, Binhang, and Chen, Jingguang G.. 2016. "Chloromethane to olefins over H-SAPO-34: Probing the hydrocarbon pool mechanism". United States. doi:10.1016/j.apcata.2016.09.004. https://www.osti.gov/servlets/purl/1341680.
@article{osti_1341680,
title = {Chloromethane to olefins over H-SAPO-34: Probing the hydrocarbon pool mechanism},
author = {Fickel, Dustin W. and Sabnis, Kaiwalya D. and Li, Luanyi and Kulkarni, Neeta and Winter, Lea R. and Yan, Binhang and Chen, Jingguang G.},
abstractNote = {In this paper, by means of in situ FTIR and ex situ13C NMR studies, the initial periods of the chloromethane-to-olefins (CTO) reaction over SAPO-34 were probed in order to investigate the activation period of the reaction and to elucidate the formation of the catalyst active site. A methylated benzene species has been observed to form during the initial activation period of the reaction, and a direct positive correlation was constructed between the formation of this species and the catalytic activity. The data thus indicate that these methylated benzene species contribute to the formation of active sites within SAPO-34 for the CTO reaction. This is the first known report identifying a direct semi-quantitative correlation between the catalyst activity and growth of a methylated benzene active species, during the activation period of the chloromethane to olefins reaction. Finally, the findings here in correspond well to those reported for the methanol to olefins reaction, suggesting that a similar ‘hydrocarbon pool’ mechanism may be responsible for the formation of light olefins in CTO chemistry as well.},
doi = {10.1016/j.apcata.2016.09.004},
journal = {Applied Catalysis. A, General},
number = ,
volume = 527,
place = {United States},
year = 2016,
month = 9
}

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  • {sup 13}C-Methanol and {sup 12}C-ethene (fed as ethanol) have been co-reacted over SAPO-34 in a flow system at 400{degrees}C using argon as a carrier (diluent) gas. The feed contained an equal number of {sup 13}C and {sup 12}C atoms. The products were analyzed by GC-MS, allowing the determination of the isotopic composition of the reactor effluent. The ethanol was immediately converted to ethene, so the reaction system was equivalent to a feed consisting of methanol/ethene/water. While the methanol was completely or almost completely converted to hydrocarbons, the larger part of the ethene emerged unreacted. The products propene and butenes weremore » mostly formed from methanol and contained a large excess of {sup 13}C atoms. The ethene effluent consisted mainly of all {sup 12}C or all {sup 13}C atoms, and only to a small extent of {sup 12}C-{sup 13}C molecules. The reaction system was followed from an initially very active catalyst until the catalyst was sufficiently deactivated that C{sub 1} was not completely converted to hydrocarbons. The tendency for ethene to emerge unreacted, and for all new hydrocarbons to be formed from methanol became more pronounced with progressing catalyst deactivation. The results show clearly that the higher hydrocarbons are, over this catalyst, not formed by successive methylations of ethene. A previously proposed {open_quotes}carbon pool{close_quotes} mechanism can explain the gross effects seen in the product and isotopic distribution. 15 refs., 6 figs., 4 tabs.« less
  • [{sup 13}C]Methanol and [{sup 12}C]propene (fed as isopropanol, which is immediately converted to propene) have been co-reacted over SAPO-34 in a flow system at 400{degrees}C using argon as a carrier gas. The feed was equimolar in {sup 13}C and {sup 12}C atoms. The products were analyzed by gas chromatography-mass spectrometry, allowing determination of the isotopic composition. While the methanol was completely or almost completely converted to hydrocarbons, the larger part of the propene emerged unreacted. The products ethen and butenes were mostly formed from methanol and contained a large excess of {sup 13}C atoms. The propene effluent consisted mainly ofmore » all- {sup 12}C or all-{sup 13}C molecules and, only to a small extent, isotopically mixed molecules. The tendency for propene to emerge unreacted and all new hydrocarbons to be formed from methanol became more pronounced with progressing catalyst deactivation. The results show that the higher hydrocarbons are, over this catalyst, not formed by successive methylations of bulk gas-phase propene. A previously proposed {open_quotes}carbon pool{close_quotes} mechanism can explain the gross effects seen in the product and isotopic distribution, but it is pointed out that the nonreactivity of propene in SAPO-34 may be caused by slow diffusion of propene in the pores. 16 refs., 5 figs., 4 tabs.« less
  • The catalytic conversion of methanol to lower olefins (MTO) is a way of converting natural gas and coal to chemicals via methanol. The effects of adsorption and diffusion of the reactants on methanol to olefins (MTO) and propene conversion over SAPO-34 have been studied in an oscillating microbalance reactor. The adsorption parameters of methanol and propene at reaction conditions (698 K) were determined by a pulse method, and the results were identical to the values obtained by extrapolation from low temperatures (323--398 K). Inverse uptake diffusion times were calculated form adsorption data at low temperatures, and these results were dependentmore » on the temperature and the adsorbed amount. The inverse steady-state diffusion times calculated form the inverse uptake diffusion times were independent of the temperature and the adsorbed amount. The influence of diffusion on the reaction rates was estimated on the basis of the inverse steady-state diffusion times, using the Weisz-Prater criterion. The methanol conversion over SAPO-34 was influenced by diffusion of the reactant, while the propene conversion was not. A kinetic study revealed that both the rate constant and the site coverage of propene were much lower than that of methanol at 698 K. The deactivation behavior during the MTO reaction over SAPO-34 was studied by measuring both the adsorbed amount of methanol and the conversion at different coke contents. Catalyst deactivation was proposed to be due to a decreasing number of sites available for adsorption at high coke contents and a lower diffusivity, hence a lower effectiveness factor due to coke deposition.« less
  • {sup 13}C solid-state MAS NMR was used to probe the chemistry of a number of species involved in the methanol-to-hydrocarbon process over H-SAPO-34 molecular sieve at both high (573 K) and low (473-563 K) temperature ranges and at very low conversion (<0.1%). Isobutane was the only hydrocarbon product observed at 473 and 573 K. Evidence for the operation of a stepwise methylation reaction via surface-bound species derives from, first, the treatment of several samples with different loadings of methanol at 523-563 K and, second, when either [{sup 13}C]methanol is coadsorbed with [{sup 12}C]ethene over the catalyst or [{sup 12}C]ethene ismore » reacted with pre-[{sup 13}C]methylated SAPO-34. The hydrocarbon products in these experiments were mainly isobutane and isopentane as well as methane, ethene, and propane. Based on these experimental findings, a number of mechanistic approaches concerning the very first stages of the reaction are discussed. 56 refs., 13 figs., 3 tabs.« less
  • For its unique position in the coal chemical industry, the methanol to olefin (MTO) reaction has been a hot topic in zeolite catalysis. Due to the complexities of catalyst structure and reaction networks, many questions such as how the olefin chain is built from methanol remain elusive. On the basis of periodic density functional theory calculations, this work establishes the first complete catalytic cycle for MTO reaction via hexamethylbenzene (HMB) trapped in HSAPO-34 zeolite based on the so-called side chain hydrocarbon pool mechanism. The cycle starts from the methylation of HMB that leads to heptamethylbenzenium ion (heptaMB{sup +}) intermediate. Thismore » is then followed by the growth of side chain via repeated deprotonation of benzenium ions and methylation of the exocyclic double bond. Ethene and propene can finally be released from the side ethyl and isopropyl groups of benzenium ions by deprotonation and subsequent protonation steps. We demonstrate that (i) HMB/HSAPO-34 only yields propene as the primary product based on the side chain hydrocarbon pool mechanism and (ii) an indirect proton-shift step mediated by water that is always available in the system is energetically more favorable than the traditionally regarded internal hydrogen-shift step. Finally, the implications of our results toward understanding the effect of acidity of zeolite on MTO activity are also discussed.« less