Fuel Processing Technology (v.91, #4)

Selective synthesis of mixed alcohols from syngas over catalyst Fe2O3/Al2O3 in slurry reactor by Xiaobing Zhang; Zhong Li; Qihai Guo; Huayan Zheng; Kechang Xie (379-382).
The Fe2O3/Al2O3 catalyst was studied to selectively synthesize mixed alcohols from syngas in a continuously stirred slurry reactor with the oxygenated solvent Polyethylene Glycol-400 (PEG-400). The selectivity of mixed alcohols in the products reached as high as 95 wt.% and the C2+ alcohols (mainly ethanol) was more than 40 wt.% in the total alcohol products at the reaction conditions of 250 °C, 3.0 MPa, H2/CO = 2 and space velocity = 360 ml/gcat h. The hydrogen temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) measurements of the catalyst confirmed that the FeO phase was responsible for the high selectivity to mixed alcohols in the process. And the oxygenated solvent PEG-400 was also necessary for the selective synthesis of mixed alcohols in the reaction system.
Keywords: Mixed alcohol synthesis; Syngas; Fe2O3/Al2O3; Slurry reactor;

Study of induction period over K2CO3/MoS2 catalyst for higher alcohols synthesis by Haicheng Xiao; Debao Li; Wenhuai Li; Yuhan Sun (383-387).
The K2CO3/MoS2 catalyst for higher alcohols synthesis with synthesis gas as feedstock was prepared. The catalyst was characterized by TPR, in-situ XPS, XRD and SEM. Effects of pretreatment with H2, CO or synthesis gas on activity and selectivity of the catalyst were investigated. Results showed that there was a remarkable induction period about 180 h at the initial reaction stage for the un-treated catalyst. The catalytic performances for alcohols synthesis changed notably during the induction period. The induction period was confirmed to be resulted primarily from the sulfur losing and K element dispersion on the surface of ADM catalysts. Pretreatment of the catalyst could remarkably shorten the time of induction period as well as promote the catalytic activity. Furthermore, the higher alcohols (C2  + OH) content in the liquid products were enhanced after the catalyst pretreated by CO or synthesis gas which could be ascribed to the increasing of Mo4+ content on the surface of the catalyst.
Keywords: MoS2; ADM; Induction period; Higher alcohols synthesis; Pretreatment;

Gasoline-range hydrocarbon synthesis over Co/SiO2/HZSM-5 catalyst with CO2-containing syngas by Yu-ping Li; Tie-jun Wang; Chuang-zhi Wu; Hai-bin Li; Xin-xin Qin; Noritatsu Tsubaki (388-393).
Selective synthesis of gasoline-range hydrocarbons (C5-C12) was investigated in a fixed-bed micro reactor using two series of CO2-containing syngas with various mole CO2/(CO + CO2) and H2/(CO + CO2) ratios, where Fischer-Tropsch synthesis(FTS) and in situ hydrocracking/hydroisomerization were performed over bifunctional Co/SiO2/HZSM-5 catalyst. CO2 was converted at 0.15-0.55 of CO2/(CO + CO2) ratio under H2-rich condition (H2/(CO + CO2) = 2.0), highest conversion of 20.3% at 0.42. Further increasing CO2 content decreased CO2 conversion and quite amount of CO2 acted as diluting component. For the syngas with low H2 content or H2/(CO + CO2) ratio(< 1.85, H2/CO = 2.0), the competitive adsorption of CO, H2 and CO2 resulted in low CO, CO2 and total carbon conversion, which was 57.9%, 12.7% and 31.4% respectively at 0.74 of H2/(CO + CO2) ratio(H2/CO/CO2/N2  = 40.8/20.4/34.8/4). FTS results indicated that high H2 content and proper H2/(CO + CO2) ratio were favorable for the conversion of CO2-containing syngas. More than 45% selectivity to gasoline-range hydrocarbons including isoparaffins was obtained under the two series of syngas. It was also tested that the catalytic activity of Co/SiO2/HZSM-5 kept stable under CO2-containing syngas(< 7.5%). And the quick catalytic deactivation under high CO2 containing syngas(H2/CO/CO2/N2  = 45.3/23.2/27.1/3.06) was due to carbon deposition and pore blockage by heavy hydrocarbon, tested by thermal gravimetry, N2 physisorption and scanning electron microscopy(SEM).
Keywords: Fischer–Tropsch synthesis; Gasoline-range hydrocarbon; CO2-containing syngas; Co/SiO2/HZSM-5;

SiO2 was modified by various organic groups before the impregnation of cobalt precursor. These modified supports and the corresponding catalysts were characterized by BET, 29Si CP MAS NMR, XRD, Raman, XPS and H2-TPR. These characterizations clearly show the changes of morphology as well as reducibility of the catalysts. The organic modification of SiO2 remarkably influences the reducibility and catalytic properties of Co catalysts. Co catalyst supported on (CH3)3-modified SiO2 exhibits high activity and C5 + hydrocarbon selectivity. However, COOH-, NH2-, and NH2(CH2)2NH-modified SiO2 distinctly suppress the catalytic activity of Co catalysts.
Keywords: Fischer–Tropsch synthesis; Organic modification; Cobalt catalysts;

ZSM-5 supported iron catalysts for Fischer–Tropsch production of light olefin by Suk-Hwan Kang; Jong Wook Bae; Kwang-Jae Woo; P.S. Sai Prasad; Ki-Won Jun (399-403).
Fischer–Tropsch Synthesis (FTS) for olefin production from syngas was studied on Fe–Cu–K catalysts supported on ZSM-5 with three different Si/Al ratios. The catalysts were prepared by slurry-impregnation method of metallic components, and were characterized by BET surface area, XRD, hydrogen TPR and ammonia TPD. Fe–Cu–K/ZSM-5 catalyst with a low Si/Al ratio (25) is found to be superior to the other catalysts in terms of better C2–C4 selectivity in the FTS products and higher olefin/(olefin + paraffin) ratio in C2–C4 because of the facile formation of iron carbide during FTS reaction and also due to a larger number of weak acidic sites that are present in these catalysts.
Keywords: Fischer–Tropsch Synthesis; Fe-based catalyst; ZSM-5; Olefin;

Influences of minerals transformation on the reactivity of high temperature char gasification by Jin Bai; Wen Li; Chun-zhu Li; Zongqing Bai; Baoqing Li (404-409).
Two Chinese coals were used in this study and coal chars were prepared at different temperatures. High temperature gasification of coal chars with CO2 was investigated in a bench scale fixed-bed reactor and the transformations of minerals from these two coals were also studied from 1100 to 1500 °C. Mineral matters produced at different temperature and ash generated after gasification were collected and analyzed by XRD and FTIR. It was found that the iron oxides were only catalytic mineral matters existing at high temperature. And gasification behaviors above ash melting temperature were different for different mineral composition, especially the content and form of iron oxide, which not only accelerates the gasification reaction, but also reduces the influence caused by melting minerals.
Keywords: High temperature; Mineral transformation; Char gasification;

Cross-linking reactions (CLR) of oxygen groups during liquefaction of lignite were quantitatively studied by a new model system. Chinese Yitai lignite (YT) was first oxidized by nitric acid at 70 °C and about 98% of the oxidized sample could be dissolved in tetrahydrofuran (THF) at room temperature. Then benzyl alcohol, PhCH2OH (BA), as a model compound was added into the oxidized coal, also acted as solvent in the subsequent liquefaction. Temperature-programmed reactions (TPR) at liquefaction conditions under hydrogen atmosphere were performed to evaluate the CLR by quantitative analysis of THF-insoluble solid products (THFI) after reaction. Extensive CLR were observed even under high pressure of H2 at 200–400 °C, and more than 51.7% and 81.2% of the THFS fraction was converted into the THFI at 300 °C with tetralin (TET) and BA as solvent, respectively. The THFI fraction was almost solely caused by the CLR, which makes it possible to quantitatively study the CLR by analyzing the amount of the cross-linked solid products (CSP). The pyrolysis behaviours of CSP and oxidized coal were examined by TG. Other model compounds containing oxygen-functional groups (alcohol, phenol, carboxyl, carbonyl and ether groups) can also be used in this model system to study CLR of oxygen groups in low-rank coals.
Keywords: Oxidized coal; Cross-linking reaction; Liquefaction; New model system;

Effect of surfactant on structure and performance of catalysts for DME synthesis in slurry bed by Jinchuan Fan; Chaoqiu Chen; Jie Zhao; Wei Huang; Kechang Xie (414-418).
The Cu–Zn–Al slurry catalysts prepared via modified sol–emulsion–gel method by adding different water-soluble surfactants were studied for CO hydrogenation to produce dimethyl ether (DME) in slurry bed reactor. The results indicated that the catalyst adding Tween80 or PEG600 had higher activity than the catalyst with the PVP additive. All the catalysts had good stability. X-ray diffraction (XRD) results showed that Cu and Cu2O existed in the pre-reduced Cu–Zn–Al catalysts, while ZnO did not appear. Nitrogen adsorption studies showed that the catalyst prepared with the additives of PEG600 or Tween80 was mesoporous structure with higher specific surface area compared with the one prepared with the additive of PVP. X-ray photoelectron spectroscopy (XPS) results indicated that the Cu/Zn ratio on the surface of all catalysts increased after subject to reduction and reaction. The morphology and size of the catalyst particles could be adjusted by adding water-soluble surfactants.
Keywords: Sol–emulsion–gel; Cu–Zn–Al catalyst; DME;

Integrated coal pyrolysis with CO2 reforming of methane over Ni/MgO catalyst for improving tar yield by Jiahe Liu; Haoquan Hu; Lijun Jin; Pengfei Wang; Shengwei Zhu (419-423).
A new process to integrate coal pyrolysis with CO2 reforming of methane over Ni/MgO catalyst was put forward for improving tar yield. And several Chinese coals were used to confirm the validity of the process. The experiments were performed in an atmospheric fixed-bed reactor containing upper catalyst layer and lower coal layer to investigate the effect of pyrolysis temperature, coal properties, Ni loading and reduction temperature of Ni/MgO catalysts on tar, water and char yields and CH4 conversion at fixed conditions of 400 ml/min CH4 flow rate, 1:1 CH4/CO2 ratio, 30 min holding time. The results indicated that higher tar yield can be obtained in the pyrolysis of all four coals investigated when coal pyrolysis was integrated with CO2 reforming of methane. For PS coal, the tar, water and char yield is 33.5, 25.8 and 69.5 wt.%, respectively and the CH4 conversion is 16.8%, at the pyrolysis temperature of 750 °C over 10 wt.% Ni/MgO catalyst reduced at 850 °C. The tar yield is 1.6 and 1.8 times as that in coal pyrolysis under H2 and N2, respectively.
Keywords: Coal pyrolysis; CO2 reforming of methane; Tar yield; Ni/MgO catalyst;

Experimental study of improved two step synthesis for DME production by Yingying Zhu; Shurong Wang; Xiaolan Ge; Qian Liu; Zhongyang Luo; Kefa Cen (424-429).
Dimethyl ether (DME) has received growing attention due to its potential use as a multi-purpose fuel. A new technical route of improved two step synthesis is proposed for DME production, which is composed of methanol synthesis and methanol dehydration in a fixed-bed reactor. The influences of the operating conditions including reaction pressure, temperature, H2/CO mole ratio in the syngas and space velocity on CO conversion, selectivity and yield of DME are investigated. CO conversion and DME yield both increase monotonically with the pressure increase. The optimal reaction temperatures for the synthesis and dehydration of methanol are different. CO conversion increases at first and keeps constant when the H2/CO mole ratio is above 2. DME yield increases obviously and then decreases gradually with the space velocity increase. The optimal conditions are obtained to maximize the CO conversion and DME selectivity. The reaction temperatures of the top and bottom stage are in the range of 270–280 °C and 235–245 °C, respectively. The optimal ratio of H2/CO is above 2, and the space velocity is in the range of 1000–1300 h− 1.
Keywords: Dimethyl ether; Improved two step; Synthesis; Catalyst stability;

Study on the structure and pyrolysis characteristics of Chinese western coals by Junhong Wang; Juan Du; Liping Chang; Kechang Xie (430-433).
The structure and pyrolysis characteristics of three inertinite-rich Chinese western coals were researched and compared with one relative vitrinite-rich Chinese middle coal by means of XRD, TG–DTG and fixed-bed reactor. The results show that the atomic ratio O/C, aromaticity factor, even ring condensation number and ring condensation index increase and atomic ratio H/C decreases with increasing inertinite content in coal; inertinite contains more aromatic ring structure than that of vitrinite; the crystallite structure order of coal char increases slightly with increasing heat treatment temperature. The higher inertinite content in coal is, the lower pyrolysis reactivity of coal is at lower temperature, and yet they have obvious second pyrolysis reactivity in higher temperature. The pyrolysis reaction in primarily devolatilisation phase that comes mainly from the decomposition of containing hydrogen function groups and the secondary devolatilisation at high temperature is mainly the decomposition of stable containing oxygen function groups in coal matrix with higher inertinite.
Keywords: Structure; Pyrolysis characteristic; Coal; Inertinite-rich;

Performance of a slurry bubble column reactor for Fischer–Tropsch synthesis: Determination of optimum condition by Kwang-Jae Woo; Suk-Hwan Kang; Seung-Moon Kim; Jong-Wook Bae; Ki-Won Jun (434-439).
The CO conversion and selectivity to C1 + and C11 + wax products over Co/Al2O3 as well as Ru/Co/Al2O3 Fischer–Tropsch (F–T)catalysts were investigated by varying reaction temperature (210–250 °C), system pressure (1.0–3.0 MPa), GHSV (1000–6000 L/kg/h), superficial gas velocity (1.7–13.6 cm/s) and slurry concentration (9.09–26.67 wt.%) in a slurry bubble column reactor (0.05 m diameter × 1.5 m height) to determine the optimum operating conditions. Squalane or paraffin wax was used as initial liquid media. The overall CO conversion increased with increasing reaction temperature, system pressure and catalyst concentration. However, the local maximum CO conversion was exhibited at GHSV of 1500–2000 L/kg/h and superficial gas velocity of 3.4–5.0 cm/s. The CO conversion in the case of Ru/Co/Al2O3 was much higher and stable than that in the case of Co/Al2O3. The selectivity to C11 + wax products increased slightly with increasing GHSV; on the other hand, it decreased with increasing reaction temperature, system pressure, and solid concentration in a slurry bubble column reactor. It could be concluded that the optimum operating conditions based on the yield of hydrocarbons and wax products were; U G  = 6.8–10 cm/s, Cs = 15 wt.%, T  = 220–230 °C, P  = 2.0 MPa in a slurry bubble column reactor for F–T synthesis.
Keywords: Fischer–Tropsch synthesis; SBCR; Co/Al2O3; Ru/Co/Al2O3;