Unveiling coke formation mechanism in MFI zeolites during methanol-to-hydrocarbons conversion

Lee, Songhyun,Choi, Minkee Elsevier 2019 Journal of catalysis Vol.375 No.-

<P><B>Abstract</B></P> <P>Coke formation over MFI zeolites of different crystallite sizes was rigorously investigated in methanol-to-hydrocarbon conversion (MTH). The key experimental idea was based on the fact that soft coke in the zeolite micropores (internal coke) could be selectively removed by thermal treatment under H<SUB>2</SUB>, while heavy coke at the zeolite external surface (external coke) remained intact. This enabled us to analyze the amount, composition, chemical nature, and deactivating effects of internal and external cokes, separately. As the mass transfer of hydrocarbons was retarded with increasing zeolite crystallite size, an aromatic-based catalytic cycle became dominant in MTH compared to an olefin-based cycle. Consequently, methylated benzene intermediates were accumulated within the zeolite micropores. These methylated benzenes could also act as coke precursors and polymerize to form internal coke within the micropores. Aromatic products that diffused out of zeolite micropores could also be condensed at the external surface of the zeolite crystallites. Once the carbon deposits were formed at the external zeolite surface, the external coke continued to grow even non-catalytically by the thermal reaction with the methylated benzenes. Different zeolite catalysts and reaction times affected only the relative amounts of internal and external cokes, but not their respective chemical natures. The internal coke appeared to have the H/C ratio of 1.26 and a density of 1.0 g cm<SUP>−3</SUP>, while the external coke had much lower H/C ratio (0.28) and higher density (1.5 g cm<SUP>−3</SUP>). We propose that internal coke is likely to have the polymeric structures of the methylated acenes (<I>i.e</I>., linearly fused aromatic rings such as benzene, naphthalene, and anthracene) connected via methylene bridges. On the other hand, the external coke is highly polyaromatic with many fused rings. In terms of catalyst deactivation, the internal coke proved to be much more detrimental than the external coke.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Formation mechanism, location, and nature of coke species in MFI zeolites were studied in MTH. </LI> <LI> Methylated benzenes accumulated within the zeolite micropore polymerize to form internal coke. </LI> <LI> External coke grow non-catalytically by the thermal reaction with the methylated benzenes. </LI> <LI> Different zeolites and reaction times affected the amounts of internal/external cokes, not their natures. </LI> <LI> In terms of catalyst lifetime, internal coke is much more detrimental than external coke. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Cooperative effects of zeolite mesoporosity and defect sites on the amount and location of coke formation and its consequence in deactivation

Lee, Kyungho,Lee, Songhyun,Jun, Youngsun,Choi, Minkee Academic Press 2017 Journal of catalysis Vol.347 No.-

<P><B>Abstract</B></P> <P>The cooperative effects of secondary mesoporosity and defects on the coke formation and deactivation of zeolite were investigated in <I>n</I>-pentane aromatization using model Ga/ZSM-5 catalysts. Mesoporosity was introduced to a commercial ZSM-5 by alkaline desilication, while the defects sites (<I>i.e.</I>, internal silanols) in zeolites were annealed by the treatment with ammoniumhexafluorosilicate. Aromatization after supporting Ga showed that the mesopore generation retarded catalyst deactivation via the suppression of internal coke formation while facilitating the external coke formation due to the enhanced diffusion of coke precursors <I>(e.g</I>., alkylaromatics) out of zeolite micropores. Internal coke can cause a more severe deactivation than external coke because the acid sites are mainly located in the zeolite micropores. However, the mesopore generation alone could not efficiently reduce the total amount of coke deposition (it mainly changed the location of coke). In contrast, the annealing of internal silanols could suppress the overall coke formation. This phenomenon could be explained by the fact that coke precursors are initially generated at the zeolite internal defects, and then deposited as coke at either the internal or the external surfaces of the zeolite depending on the relative kinetics of coke precursor diffusion and its polymerization. Consequently, the catalyst with mesoporosity and annealed internal silanols exhibited the slowest catalyst deactivation due to the suppression of both internal and external coke depositions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effects of zeolite mesopore and internal defects on coke formation were studied. </LI> <LI> Mesopore mainly changes the location of coke deposition, not its overall quantity. </LI> <LI> Mesopore induces external coke deposition which is less harmful than internal coke. </LI> <LI> Annealing defects suppress coke formation by inhibiting coke precursor formation. </LI> <LI> Generating mesopore while minimizing defect is effective for retarding deactivation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

열천칭과 유동층반응기에서 석탄과 Petroleum Coke의 수증기 가스화반응

지근호 ( Keun Ho Ji ),송병호 ( Byung Ho Song ) 한국화학공학회 2012 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.50 No.6

석탄 및 pet coke (petroleum coke)는 그 이용이 제한적이지만 공급이 풍부한 에너지원이므로, 가스화 공정에 적용하여 고급연료인 수소나 액체연료를 생산할 수 있다. 본 연구에서는 열천칭반응기와 실험실규모의 유동층반응기(내경 0.02 m, 높이 0.6 m)에서 갈탄, 무연탄, pet coke의 수증기 가스화 반응특성을 조사하였다. 가스화 온도 600~900˚C, 수증기 분압 0.15~0.95atm 및 수증기/연료 비의 조업변수가 가스화반응속도 및 생성가스의 발열량에 미치는 영향을 조사하였다. 기체-고체 반응모델로서 modified volumetric reaction model을 적용하여 가스화반응의 거동을 묘사하고 kinetic 인자들을 도출하였다. 가스화 반응온도가 높을수록 생성가스 중의 수소농도와 가스의 발열량은 증가하였다. 생성가스 발열량은 무연탄 > 갈탄 > pet coke의 순으로 높게 나타났는데, 반응온도 900˚C, 수증기분압 95%의 조건에서 10.0 > 6.9 > 5.7 MJ/m3로 각각 얻어졌다. 본 연구를 통하여 갈탄과 pet coke에 대해 가스화공정의 잠재적인 연료로서 의 가능성을 확인하였다. Lignite of low rank coal and petroleum coke of high sulfur content can be high potential energy sources for coal gasification process because of their plentiful supply. The steam gasification of lignite, anthracite, and pet coke has been carried out in both an atmospheric thermobalance reactor and a lab-scale fludized bed reactor (0.02 m i, d. × 0.6 m height). The effects of gasification temperature (600~900˚C) and partial pressure of steam (0.15~0.95atm) on the gasification rate and on the heating value of product gas have been investigated. The modified volumetric reaction model was applied to the experimental data to describe the behavior of carbon conversion, and to evaluate kinetic parameters of char gasification. The results shows that higher temperature bring more hydrogen in the product syngas, and thus increased gas heating value. The feed rate of steam is needed to be optimized because an excess steam input would lower the gasification temperature which results in a degradation of fuel quality. The rank of calorific value of the product gas was anthracite > lignite > pet coke. Their obtained calorific value at 900 oC with 95% steam feed were 10.0 > 6.9 > 5.7 MJ/m3. This study indicates that lignite and pet coke has a potential in fuel gas production.

Rapid evaluation of coke resistance in catalysts for methane reforming using low steam-to-carbon ratio

Jeon, Jiyoon,Nam, Seongju,Ko, Chang Hyun Elsevier 2018 CATALYSIS TODAY - Vol.309 No.-

<P><B>Abstract</B></P> <P>The formation and subsequent accumulation of coke is one of the major reasons for the catalyst deactivation in methane reforming reaction. Although the investigation of coke-resistant catalysts is closely related to their long-term stability of given catalysts, it takes a long time to quantitatively measure the amount of carbon deposition on catalysts under normal reaction operational conditions. To overcome this problem, we used the steam deficient reaction condition, i.e. a low steam-to-carbon ratio (S/C) of 0.5 to accelerate the carbon deposition on catalysts. In this condition, the base catalyst of 10wt.% Ni/alumina rapidly lost its catalytic activity, indicating fast coke deposition. However, adding proper additives, such as Ru among various precious metals (Ru, Rh, Pt, and Pd) and alkaline earth metals (Mg, Ca, Sr, and Ba) with the appropriate loading (5wt.%) effectively suppressed coke formation. The optimized catalyst composition is 0.5wt.% Ru/5wt.% Mg/10wt.% Ni/alumina, which displayed coke resistance in the long-term stability test of steam methane reforming and 40h test of dry reforming of methane. These experimental results indicate that the method developed in this study is useful for the rapid evaluation of given catalysts for their coke resistance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of steam-to-carbon ratio on coke formation during methane reforming studied. </LI> <LI> Coke formation measured within 5h using low steam-to-carbon ratio and high WHSV. </LI> <LI> Quick development of Ru-Mg catalysts with high coke resistance. </LI> <LI> Long-term stability for both steam and dry methane reforming demonstrated. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of crystallinity and particle size on coke-based anode for lithium ion batteries

Lee Seung Eun,김지홍,이영석,배병철,임지선 한국탄소학회 2021 Carbon Letters Vol.31 No.5

This study examined the efects of micro- (crystallinity) and macro (orientation)-crystalline properties of graphite on the initial efciency, discharge capacity, and rate performance of anodic materials. Needle coke and regular coke were selected as raw materials and pulverized to 2–25 μm to determine the efects of crystalline properties on particle shape after pulverization. Needle coke with outstanding crystallinity had high initial efciency, and smaller particles with larger specifc surface areas saw increased irreversible capacity due to the formation of SEI layers. Because of cavities existing between crystals, the poorer the crystalline properties were, the greater the capacity of the lithium ions increased. As such, regular coke had a 30 mAh/g higher discharge capacity than that of needle coke. Rate performance was more afected by particle size than by crystalline structure, and was the highest at a particle distribution of 10–15 μm.

The effect of additive chemicals on the viscosity of coal-petroleum coke-water slurry fuel for a gasification process

Sang Jun Yoon,Young-Chan Choi,이재구 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.5

As a preliminary study for the gasification of an anthracite and petroleum coke mixture, viscosity was measured at various temperatures (20-50℃), slurry concentrations (60-70 wt%) and additive amounts (0-0.8 wt%) by using an LV-II type viscometer. In addition, four types of different additives, sodium naphthalene sulfonate, poly(methyl methacrylate), polypropylene and a polypropylene glycol based additive, were applied to Korean anthracite, petroleum coke and mixtures of these materials, and the viscosity data were compared. Viscosity dependency values for coal, anthracite, bituminous and sub-bituminous coal, were compared, and it was found that a high content of moisture and particularly ash increases CWS viscosity. The four types of additives tested in this research can effectively diminish the viscosity of coal and especially petroleum coke-water slurry by more than 70% to 95%, respectively. Moreover, the sodium naphthalene sulfonate-based additive reduced the viscosity of coal and petroleum coke-water slurry best, especially at concentrations in excess of 65 wt%. Based on these results, highly loaded slurry created by mixing anthracite and petroleum coke with additives was achieved. Key words: Coal, Petroleum Coke, Slurry, Viscosity,

열분해유 유래 피치로부터 이방성 미세구조 코크스 제조 및 특성 평가

조종훈 ( Jong Hoon Cho ),김지홍 ( Ji Hong Kim ),이영석 ( Young-seak Lee ),임지선 ( Ji Sun Im ),강석창 ( Seok Chang Kang ) 한국공업화학회 2021 공업화학 Vol.32 No.6

본 연구에서는 열분해유 유래 피치 합성 및 합성 피치로부터 이방성 미세구조를 갖는 코크스를 제조하고 그 특성을 평가하였다. 열분해유는 주로 방향족 고리가 2~3개로 구성된 분자로 이루어져 있어, 400 °C 이상의 온도에서 흡열반응인 축합중합으로 피치가 제조되었다. 코크스 반응기는 피치를 유동화 시키는 전처리 반응기, 코킹화 열에너지를 가해주는 preheater 및 코크스의 미세구조를 유도하는 코크스 드럼으로 구성되었으며, preheater의 온도를 400~490 °C로 조절하여 제조된 피치로부터 코크스를 제조하고 편광현미경, XRD 및 Raman spectroscopy로 특성을 평가하였다. Preheater의 온도가 460 °C에서 제조된 코크스는 이방성 미세조직이 flow 형태로 나타났으며, 높은 결정성으로 전기전도성이 72.0 S/cm이였다. 그리고 전도성 탄소 재료인 Super-P보다 대략 2.2배 높은 전기전도성을 나타냈다. In this study, pitch was synthesized using pyrolysis fuel oil (PFO). Coke with mesophase microstructure was then prepared from the synthesized pitch and its properties were evaluated. Pitch was synthesized by poly-condensation reaction, which is an endothermic reaction at a temperature above 400 °C because the PFO was mainly composed of molecules with two to three aromatic rings. The Coke reactor was composed of the pretreatment reactor, preheater for applying heat energy, and coke drum for inducing microstructure of coke. Coke was prepared from synthesized pitch by controlling the temperature of the preheater to 400~490 °C, and properties were evaluated by polarization microscope, XRD and Raman spectroscopy. The coke prepared at a preheater temperature of 460 °C identified flow anisotropic microstructure, and the electrical conductivity was 72.0 S/cm due to high crystallinity. And the flow anisotropic coke showed approximately 2.2 times higher electrical conductivity than that of Super-P, a conductive carbon material.

Probability of Chain Growth in Coke Formation on Metals and on Supports during Catalytic Reforming over Pt, Pt-Sn and Pt-Sn-K Catalysts Mixed Physically with Al₂O₃

Srihiranpullop, Sunee,Praserthdam, Piyasan 한국화학공학회 2003 Korean Journal of Chemical Engineering Vol.20 No.6

The main goal of this contribution was to study the probability of chain growth of coke on metal sites and on support sites for hexane dehydrogenation. The coke structure of the catalysts examined by IR was found to have the aromatic structure. Soxhlet extraction coupled with GC-14B(DB1 column) analysis was mainly employed for coke composition analysis and determination of the probability of chain growth (alpha value). It was found that the soluble coke was mainly composed of C_(8)-C_(12) on both sites. Interestingly, the probabilities of chain growth on both sites were identical. However, the extracted coke on the metal site was more easily removable and had lower carbon numbers than that on the support site. Moreover, the addition of promoter, especially of K promoter, was sensitive to inhibit the probability of chain growth, resulting in the reduction of the amount of coke.

Controlling the acid-base properties of alumina for stable PtSn-based propane dehydrogenation catalysts

Jang, Eun Jeong,Lee, Jaekyoung,Jeong, Hu Young,Kwak, Ja Hun Elsevier 2019 Applied Catalysis A Vol.572 No.-

<P><B>Abstract</B></P> <P>The surface properties of catalyst supports are important in regulating the catalytic properties of heterogeneous catalysts. Herein, we studied the effect of acid-base properties of alumina on metal-support interaction and coke deposition, and investigated the stability of catalysts in propane dehydrogenation (PDH) using PtSn/Al<SUB>2</SUB>O<SUB>3</SUB>. We prepared γ-Al<SUB>2</SUB>O<SUB>3</SUB> (A750) from ammonium aluminum carbonate hydroxide (AACH) and compared it with a commercial sample (Sasol Puralox SBA-200; P200). We loaded 0.5 wt% Pt and 0.9 wt% Sn on alumina then conducted propane dehydrogenation at 590 °C (WHSV = 5.2 h<SUP>−1</SUP>). PtSn/A750 and PtSn/P200 showed compatible initial activity (conversion = ˜50%) and selectivity (> 95%). After 20 h of reaction, PtSn/A750 showed a slight decrease in activity (39.9%) while the activity of PtSn/P200 dropped significantly (28.4%). Spent catalysts showed different metal sintering behavior and coke deposition which are well known causes for catalyst deactivation. A high strength of Lewis acid sites in A750 (higher T<SUB>d</SUB> in ethanol TPD) prevented the sintering of metal by strong metal-support interaction. Also, the lower number of Lewis acid sites in A750 than that of P200 reduced deposited coke on the catalysts (PtSn/A750: 1.8 wt% and PtSn/P200: 8.6 wt%). Furthermore, diffuse reflectance infrared Fourier-transform spectroscopy after CO adsorption at -150 °C clearly demonstrated that coke deposition was initiated from Lewis acid sites on the alumina surface, but then aromatization occurs at these sites. These results suggested that strong metal-support interactions to hold metal particles and less residual Lewis acid sites after metal loading to reduce coke deposition are important factors for designing stable and coke-resistant PtSn on alumina catalysts. Furthermore, precise characterization and understanding of the acid-base properties of alumina will contribute in developing catalysts with high stability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Strong Lewis acid sites on alumina inhibit metal sintering during PDH. </LI> <LI> Excess Lewis acid sites increased coke deposition during PDH. </LI> <LI> Strong but less residual Lewis acid sites are important for control the deactivation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Preparation of needle coke from petroleum by-products

Humala Paulus Halim,Ji Sun Im,Chul Wee Lee 한국탄소학회 2013 Carbon Letters Vol.14 No.3

Needle coke is an important material for graphite electrodes. Delayed coking is used to produce needle coke. Producing good quality needle coke is not simple because it is a multi-parameter controlled process. Apart from that, it is important to understand the mechanism responsible for the delayed coking process, which involves mesophase formation and uniaxial rearrangement. Temperature and pressure need to be optimized for the different substances in every feedstock. Saturate hydrocarbon, aromatic, resin and asphaltene compounds are the main components in the delayed coking process for a low Coefficient Thermal Expansion value. In addition, heteroatoms, such as sulphur, oxygen, nitrogen and metal impurities, must be considered for a better graphitization process that prevents the puffing effect and produces better mesophase formation.