Study on Steam Reforming of Tar in Hot Coke Oven Gas for Hydrogen

Subscriber access provided by The University of Montana

Article

Study on steam reforming of tar in hot coke oven gas for hydrogen production Huaqing Xie, Jianrong Zhang, Qingbo Yu, Zongliang Zuo, Jialin Liu, and Qin Qin Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b02551 • Publication Date (Web): 12 Feb 2016 Downloaded from http://pubs.acs.org on February 16, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Study on steam reforming of tar in hot coke oven gas for hydrogen production Huaqing Xie, Jianrong Zhang, Qingbo Yu*, Zongliang Zuo, Jialin Liu, Qin Qin School of Materials and Metallurgy, Northeastern University, No. 11, Lane 3, WenHua Road, HePing District, Shenyang, 110819, Liaoning, P.R. China. Abstract: Thermodynamic analysis and experiments of the steam reforming process of 1-methylnaphthalene as tar model compound from COG were performed in this paper. In the thermodynamic analysis, as temperature and S/C ratio rose, the hydrogen yield firstly increased and then flattened out, yet with the compound completely converted and almost no coke deposition formed. In the experiments using Ni/Mg catalyst with Ca12Al14O33 as carrier, with the increases of temperature and S/C ratio and the decrease of GC1HSV, the reforming result for hydrogen production became better gradually. After the temperature and S/C ratio increased to 800 oC and 12:1 respectively and GC1HSV decreased to 145 h-1, the hydrogen yield and carbon conversion could reach over 90% and 97%, respectively, even very close to the thermodynamic values. Additionally, the catalytic stability and the resistance to coke formation of the used catalyst got also improved in such conditions.

Keywords: Steam reforming; Tar; 1-methylnaphthalene; Coke oven gas; Ca12Al14O33

1. INTRODUCTION As the main co-product of coke-making process, coke oven gas (COG) mainly containing hydrogen and methane, and thus was as one of the prospective candidates for hydrogen production and syngas production [1~3]. For China as the largest COG producer in the world, over 186 billion Nm3 COG was produced per year [4, 5]. However, only 20% COG is utilized as fuel, and the most is discharged directly into the atmosphere, causing serious environmental pollution and considerable energy waste [6]. What’s more, COG emitted from coking chamber, normally called hot COG with the temperature 700~900 oC, is a complex mixture, containing C2H4, C2H6, C3H6 and tar components (like benzene and naphthalene) 1

ACS Paragon Plus Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

aside from H2, CH4, CO and CO2, and the tar components accounting for about 30% of the total hot COG mass, will become a kind of viscous liquid below about 500 oC, more likely causing equipment blockage [7-9]. Ammonia solution spraying is one of the most common methods used to remove the tar from COG. Although tar can be removed efficiently, the temperature of COG was cooled to less than 100 oC, causing huge amounts of high-quality COG sensible heat loss, and due to part of tar dissolved in water, substantial energy waste was loss, leading to serious secondary pollution [10, 11]. So, developing new technologies to convert COG into more energy-valued products or to recover COG more efficiently is urgent and significant for enhancing the energy efficiency of the coking enterprises and the steel industry. Currently, hydrogen is mainly produced from fossil fuels containing nature gas, naphtha and coal via steam reforming, gasification, etc. But due to the depletion of fossil fuels and the deterioration of the environment resulting from its utilization process, increasing attention is being paid to the development of renewable energy or industrial by-products for hydrogen production [12]. The main method which has been applied in the industry to produce hydrogen from COG is pressure swing adsorption (SPA), via which the purified COG is separated to obtain high-purity hydrogen [4]. However, this method only collects the original hydrogen from COG, with other components in COG (such as CO, CH4, tar and other hydrocarbons) yet not rationally used (normally as fuel to be combusted or directly emitted). At present, COG has been being highly investigated via some chemical methods (such as partial oxidation, catalytic reforming of CO2 or steam), in order to convert tar and other hydrocarbon components in COG to light fuel gases or rich-H2 syngas and meanwhile to increase the syngas volume, by using the sensible heat and chemical energy in hot COG [1-5, 9,11,13-17]. Due to the complex components of real tar, toluene, benzene, naphthalene and 1-methylnaphthalene were normally selected as tar model compounds, and the researchers mainly studied their conversions to light fuel gases via hydrocracking reactions or steam reforming at lower steam/carbon (S/C) molar ratio [9, 11, 16, 17]. For hydrogen production or hydrogen amplification in COG, some reports used methane (the mole fraction of which amounts to 24~28 % in COG) or purified COG (tar-free) via steam reforming or partial oxidation reforming [4, 13-15]. For the COG containing tar, partial oxidation was studied 2


Page 2 of 26

Page 3 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

widely. Cheng et al. [18] investigated hydrogen production from simulated hot COG with toluene as model tar compound by partial oxidation, and found that the amount of H2 in the outlet gas was about 2 times more than that of original H2 in the inlet gas. Onozaki and Norinaga et al. [19-21] studied the partial oxidation steam of hot COG directly from coke oven, and found that most tar was effectively converted to hydrogen and CO. However, the method had an unavoidable drawback, which was the high cost of supplying pure oxygen [13]. On the other hand, the method of the steam reforming with higher S/C ratio was an attractive technique for tar removal and has been widely investigated for hydrogen or H2-rich syngas production in the past few years [22-24]. What’s more, there generally is surplus steam or substantial energy waste to produce steam in the coking enterprises and the steel industry, although hot COG contains only 10~15 vol% steam and the S/C ratio is low. So, the steam reforming of tar from COG for hydrogen production is studied in this paper. Catalyst has a very important role on the steam reforming of tar, and various catalysts have been tested for catalytic steam reforming of tar or its model compounds, including natural minerals (dolomite and olivine) [25, 26], synthetic catalysts (Ni-based ones [1, 8, 11, 15-17, 22, 23, 27] and noble metal-based ones [28, 29]). Among them, Ni-based catalysts with Al2O3 as carrier were widely studied because of the high catalytic activity for tar cracking and their low cost [15-17, 27]. But, common Ni-based catalysts were easily deactivated because of carbon deposition and sintering or loss of active Ni component at high temperature, and thus the catalysts were often modified by adding assistant metals or changing carrier. As assistant metal, Mg was commonly added and was reported to be able to improve the steam adsorption capability and the Ni dispersion [30-32]. Besides Al2O3 carrier, mayenite (Ca12Al14O33) with high oxygen restored property had been investigated as the carrier of the reforming catalyst in some literatures in the past few years [33, 34]. Li et al. [33] developed a Ni/Ca12Al14O33 catalyst for the steam reforming of toluene as biomass tar model compound, and found that the catalyst had excellent carbon formation resistance and sulfur-tolerant ability, attributed to the “free” oxygen in the special structure of mayenite. But Vagia et al. [34] found that nickel metal surface area and dispersion were lower for their prepared Ni/Ca12Al14O33 catalyst and nickel inserted in the bulk of Ca12Al14O33 was more difficult to reduce, thus causing the low activity of the catalyst in reforming process. Herein, 3


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

in this paper, a Ni-based catalyst supported Ca12Al14O33 was prepared with the modification by adding Mg metal, in order to obtain a catalyst with superior resistance to carbon poisoning and excellent catalytic reforming activity for hydrogen production in the steam reforming process of tar from hot COG. In this work, the thermodynamic analysis of the tar steam reforming process was firstly performed, to support reference function towards the reforming experiments. Then, using prepared Ni/Mg catalyst with Ca12Al14O33 as carrier, the experiments of tar steam reforming were performed, and the effects of temperature, S/C ratio and space velocity were investigated, with the comparison of the thermodynamic results. Finally, the characterization of the used catalysts was discussed.

2. EXPERIMENTAL 2.1. Model compound of tar Considering the extremely complex compositions of tar with hundreds of organic compounds, the tar was simplified as 1-methylnaphthalene (C11H10), mainly because it can decompose into naphthalene, benzene and so on under high temperature, and such a reaction process much approaches the conversion process of the real tar in hot COG [9, 35]. In the steam reforming process of 1-methylnaphthalene, the key chemical reactions involved were shown in Table 1. Table 1 Key chemical reactions involved in the steam reforming process of 1-methylnaphthalene

2.2. Catalyst In this work, the Ni/Mg catalyst supported on Ca12Al14O33 carrier was prepared and applied. First, the employed carrier, Ca12Al14O33, was prepared with the high-temperature roasting method [34]. Analytical pure CaCO3 and Al2O3 were mixed well with their molar ratio of 12:7, and then were calcined at 1350 oC for 4 h to ensure the solid state reaction between each other thorough for the formation of Ca12Al14O33 phase. The formed particles were ground into the size ≤300 µm, used for catalyst preparation. The wet impregnation method was applied with Ni(NO3)2·6H2O and Mg(NO3)2·6H2O as the precursors of Ni and Mg 4


Page 4 of 26

Page 5 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

metals, respectively. The aqueous solution of Mg precursor was firstly mixed with the support particles, then dried over night at 110 oC, afterwards calcined at 800 oC for 4 h. Then, the obtained particles were impregnated in the aqueous solution of Ni precursor, and the above procedures were repeated. Finally, the samples were cooled to room temperature, and ground into 300~600µm. The nominal metal composition of the final catalyst was 10 wt. % for Ni and 5 wt. % for Mg. Fig. 1 XRD patterns of the Ca12Al14O33 carrier (a) and the Ni/Mg catalyst (b).

The phase compositions of the carrier and catalyst were determined by X-ray diffraction (XRD, Shimadzu, XRD-7000) using Cu Kα radiation operated at 30 kV and 40 mA, and the results were shown in Fig. 1. For the Ca12Al14O33 carrier, the main phase was Ca12Al14O33, although the phases of CaO (decomposed from CaCO3) and Al2O3 were determined, likely due to the non-sufficient contact between both of the raw materials. For the Ni/Mg catalyst, the addition of Ni and Mg metals didn’t damage the structure of Ca12Al14O33, and both the metal existed mainly in the form of NiO and MgO, with their solid solution such as MgNiO2. The carbon deposited on the catalysts after experiment was detected with a thermogravimetric analyzer (Netzsch STA409C). About 10 mg of the used catalyst was loaded into a corundum crucible, and then the thermogravimetric temperature-programmed oxidation (TG-TPO) experiment was performed with a 50 mL/min air flow at a heating rate of 10 oC/min from room temperature to 1200 oC. Additionally, the morphologies of the catalysts were examined by scanning electron microscopy (SEM) using a Hitachi SU-8010 microscope. 2.3. Apparatus Fig. 2 shows a schematic illustration of the experiment apparatus. The experiments were conducted in a fixed-bed reactor made of stainless steel, heated by an electric furnace. 20 mL catalysts were mixed with the same-size quartz sand in the same volume, and then were placed in the middle of the steel tube. The Al2O3 balls with the size of 1~2mm were packed with the packing height of 5cm on the top of the catalyst bed, to preheat the feedstock. The tar model compound and water were pumped into the reactor drop by drop through two peristaltic pumps. The product gas from the reactor was in sequence cooled, dried and finally 5


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 26

detected by gas meter and gas analyzer. Prior to the catalytic steam reforming experiments, the catalysts were reduced under a 10 mol% H2/N2 stream for 2 h at 800 oC. Fig. 2 The schematic illustrations of experiment apparatus.

2.4. Data analysis From Eq. (10) and (19), there is 27mol H2 produced theoretically per mol C11H10 completely reacting to CO2 and H2 (i.e. the produced CO via Eq. (10) with C11H10 completely reacting then reacted completely via Eq. (19)). But in the real steam reforming process, besides the above reactions, some side reactions also took place, such as thermal cracking reaction, hydrodealkylation reaction and so on (seen in Table 1). So, the hydrogen yield (Eq. (22)), as an important evaluation index for the tar steam reforming process, was studied in the present work, and was defined as the mole ratio of H2 obtained in the final products to H2 obtained theoretically when complete reforming of C11H10 to CO2 and H2 occurs via Eq. (10) and (19): H 2 yield(%) =

Moles of H 2 obtained in final products ×100 27 moles of C11H10 in the feed

(22)

Because the main compositions of final gaseous products via C11H10 steam reforming reactions were H2, CO, CH4 and CO2, the four compositions were considered to constitute the whole dry gaseous products in the present work. So, the carbon conversion (Eq. (23)) was defined as the ratio of the sum mole of CO, CH4, CO2 in the final products to the mole of carbon in the feed. Higher carbon conversion means the fewer carbonaceous materials deposited in the reactor and other hydrocarbons (CxHy) produced. Carbon conversion (%) =

Total moles of CO, CO 2 and CH 4 in the final products ×100 (23) 11 moles of C11H10 in the feed

In this paper, besides temperature and S/C ratio, the effect of space velocity was also studied. The methane-equivalent gas hourly space velocity (GC1HSV) was used, and it was defined as the volume of the feed, stated in the terms of methane equivalents, processed by a unit volume of the catalyst in 1 h [36].

3. RESULTS AND DISCUSSION 6


Page 7 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

3.1. Thermodynamic analysis Before the experiments, the thermodynamic analysis of the C11H10 steam reforming process was performed via the Gibb’s free energy minimization method with the thermodynamic software of HSC Chemistry 6.0, stating at isothermal condition with heat loss ignored and regardless of the kinetics. Fig. 3 Effect of temperature and S/C ratio on the hydrogen yield and concentration in the steam reforming process of C11H10 with thermodynamic analysis.

The yield and concentration of H2 as functions of temperature under different S/C ratios were shown in Fig. 3. As the temperature rose, the hydrogen yield and concentration firstly increased and then flattened out, and the hydrogen yield even decreased in higher temperature zone. The above result was attributed to that the increase of temperature was favorable to accelerate the endothermic steam reforming reactions (Eq. (9~13)) and the water gas shift (WGS) reaction (Eq. (19)) was thermodynamically favoured in low temperature zone, resulting in the rapid increase of the hydrogen yield below 500~600 oC, while in higher temperature zone the hydrocarbons (such as 1-methylnaphthalene, naphthalene, benzene) have reacted completely and the exothermic WGS reaction was yet inhibited, resulting in the stabilization or mild decline of H2 production. As the S/C ratio rose, the steam reforming reactions (Eq. (9~13)) and WGS reaction (Eq. (19)) were accelerated more according to Le Chatelier’s principle, and thus, the hydrogen yield and concentration gradually increased, and the corresponding temperatures of their maximum values removed forward to lower temperatures. However, after the S/C ratio increased to a certain value, the increase amplitudes of hydrogen yield and concentration were gradually decreased, with just a slight increase at the S/C ratio above 8, and especially for the hydrogen concentration in high temperature zone, it almost had no change after the S/C ratio reached 8 and was stable at around 69%, indicating increasing blindly steam amount is economically inadvisable for hydrogen production. Almost all of carbon in the feed via the steam reforming process was converted to the three following materials, CO, CO2 and CH4, under the temperature zone above 300 oC and the S/C ratio range above 4. The carbon distribution in the reforming products (the proportion 7


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

of the carbon in the products to the total carbon in the feed) was shown in Fig. 4. In lowe temperature zone, there was almost no CO produced, mainly attributed to WGS reaction, via which CO produced in the reforming process reacted subsequently. It also can account for the increase of CO2. Then in high temperature zone, WGS reaction was inhibited, causing CO increase with the temperature, with the increase almost in the parallel to the decrease of CO2. For CH4, it showed a monotonous decease with the increase of temperate till it vanished, mainly because the steam reforming reaction of CH4 (MSR, Eq. (13)) was accelerated and the exothermic reactions of CH4 formation (Eq. (1~6, 17, 18)) were inhibited. As the S/C ratio rose, due to the steam reforming reactions (Eq. (9~13)) and WGS reaction (Eq. (19)) accelerated, the amounts of CH4 and CO decreased and the amount of CO2 increased, with the increase of H2. According to Fig. 3 and Fig. 4, the main gas was CO2 besides H2 in the gaseous products, so to obtain higher-concentration H2 from tar or hot COG, the technology of situ CO2 sorption-enhanced steam reforming may be feasible, which has been applied in bio-oil steam reforming process for hydrogen production with over 90% hydrogen yield and concentration [21, 37-39]. Fig. 4 Effect of temperature and S/C ratio on the carbon distribution in the steam reforming process of C11H10 with thermodynamic analysis.

Note that there was no coke deposition found in the thermodynamic result, attributed to the heterogeneous composition of deposited coke. Solid carbon can generally be represented into three different structures, such as graphite, nanotubes and amorphous carbon. Because there was only the thermodynamic property of graphite in the used thermodynamic databases and the thermodynamic descriptions of the other two structures were very complex, only graphite was used for representing coke deposition in the steam reforming process in the present work. Additionally, graphite was found to be dominated at lower temperature and lower S/C ratio. Diaz Alvarado et al. [40] found in the ethanol steam reforming process, the carbon deposits were formed with graphite dominated for below 400 oC and the Steam/Ethanol ratio below 4, with the other carbon structures prevailed at higher temperature yet still under lower Steam/Ethanol ratio. All of the above finally caused no coke deposition formation in the present thermodynamic results. Based on the thermodynamic analysis, the experimental study of the steam reforming 8


Page 8 of 26

Page 9 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

process of tar model compound was performed in the following.

3.2. Effect of S/C ratio Fig. 5 Hydrogen yield as a function of the reaction time at different S/C ratios at 750 oC and the GC1HSV=145 h-1.

Since the delivery of the feed into the reactor was not continuous, subjected to the working principle of peristaltic pump (i.e. the droplets were fed into the reactor every 3~5 s), the hydrogen yield showed a fluctuation with the reaction time, as shown in Fig. 5. From Fig. 5, the hydrogen yields (instantaneous) at the three S/C ratios (8:1, 10:1, 12:1) were almost equivalent at the initial stage. As time went on, overall, the hydrogen yield at the S/C ratio of 12:1 still kept stable, just with a slight decline. However, for the other two lower S/C ratios, the hydrogen yields decreased more obviously, especially at the S/C ratio of 8:1. In order to analyze conveniently, the average values of the evaluation indexes in the time range between 15 min and 50 min were discussed in the following (before 15min, the reaction system almost didn’t achieve stability). Taking average hydrogen yield as an example, it was defined as the mole ratio of H2 in all the practical products to H2 obtained theoretically when complete reforming of all C11H10 in the feed to CO2 and H2 occurs in the whole tested time range. Fig. 6 Average yields and concentrations of the gaseous products at different S/C ratios at 750 oC and the GC1HSV=145 h-1: (a) for yields and (b) for concentrations.

Fig. 6 (a) & (b) show the average yields and concentrations of the gaseous products at different S/C ratios, respectively. From Fig. 6 (a), as the S/C ratio rose, both of the experimental hydrogen yield and carbon conversion increased, with the increase amplitude gradually decreased, showing the similar trend with the thermodynamic hydrogen yield, attributed to the steam reforming reactions (Eq. (9~13)) and WGS reaction (Eq. (19)) accelerated. However, the experimental hydrogen yield and carbon conversion were obviously lower than the thermodynamic values, likely attributed to the reaction dynamic effect and the catalyst activity. For carbon conversion, it even didn’t reach 70% at the S/C ratio of 8:1, indicating carbon deposition formed easily at such a low S/C ratio. In spite of the difference between the experimental and thermodynamic yields, both of their hydrogen concentrations were almost equal at different S/C ratio, with the other experimental 9


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

component concentrations little changed under the S/C ratios from 8:1 to 12:1 (seen in Fig. 6 (b)). But the experimental CO concentration was obviously higher than the thermodynamic one, to some extent implying the WGS reaction was one of the main restrictive links in the steam reforming process of tar to produce hydrogen.

3.3. Effect of temperature Fig. 7 Hydrogen yield as a function of the reaction time at different temperatures at the S/C ratio=12:1 and the GC1HSV=145 h-1.

Fig. 7 shows the instantaneous hydrogen yield as a function of reaction time at different temperatures. From Fig. 7, although the hydrogen yields at the different temperatures were almost equivalent at the initial stage, as time went on, the three hydrogen yields showed different developments: at the low temperatures (650 oC and 750 oC), the hydrogen yields obviously decreased, especially at 650 oC, while at 850 oC, the hydrogen yield overall had no change, even when the reaction time extended to over 60 min, indicating higher temperature (in this paper) were favorable to the catalytic steam reforming reaction of tar model compound for hydrogen production. Fig. 8 Average yields and concentrations of the gaseous products at different temperatures at the S/C ratio=12:1 and the GC1HSV=145 h-1: (a) for yields and (b) for concentrations.

Fig. 8 (a) & (b) show the average yields and concentrations of the gaseous products at different temperatures, respectively. From Fig. 8 (a), as the temperature rose, the hydrogen yield and carbon conversion gradually increased, and then flattened out after the temperature reached 800 oC. And, over 800 oC, the hydrogen yield and carbon conversion can reach over 90% and 97%, respectively, which were obviously higher than those at other temperatures and S/C ratios, indicating that in such conditions the steam reforming process was developed fully and there was just rare carbon deposition or other hydrocarbons (CxHy) produced. However, the trend of the experimental hydrogen yield with temperature was totally opposite to the thermodynamic one. On the one hand, as mentioned in the above, the WGS reaction, as one of the main restrictive links in the tar steam reforming process, was an exothermic reaction, thus causing the decrease of hydrogen over a certain temperature (about 550 oC for the S/C ratio=12:1) in the thermodynamic analysis regardless of the dynamics. On the other 10


Page 10 of 26

Page 11 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

hand, in the real experiment, mass and heat transfer in the reactor and the used catalyst activity can affect the steam reforming reaction course. For one thing, below 700 oC, the experimental hydrogen yield and carbon conversion were obviously lower than the thermodynamic ones, to some extent implying that the used catalyst had a lower activity on the steam reforming reactions at such low temperatures and much of tar compound was involved in the thermal cracking reaction (Eq. (1)), carbon formation reactions (Eq. (7 & 8)) and so on, thus causing the hydrogen concentrations higher than those in thermodynamic result (seen in Fig. 8 (b)). As the temperature rose, the catalyst activity was improved, resulting in more tar compound involved in the steam reforming reactions (Eq. (10)). For another thing, the hysteresis of heat transfer for the feed in the reactor likely caused the higher hydrogen yield obtained at higher temperature where the value from the thermodynamic analysis was lower than those at lower temperatures, and thus, an interesting thing appeared that the experimental hydrogen yield was slightly higher than the thermodynamic one at 850 oC.

3.3. Effect of GC1HSV According to the definition of GC1HSV, the lower the GC1HSV was, the less the amount of the feed conveyed through the catalyst bed per unit time, meaning the residence time of the feed in the catalyst bed was longer and the heating rate of the feed was faster, i.e. the feed temperature was faster to the approach the reactor temperature. Fig. 9 (a) & (b) show the average yields and concentrations of the gaseous products at different GC1HSVs, respectively. From Fig. 9 (a), as the GC1HSV decreased, the hydrogen yield and carbon conversion increased gradually, mainly because the prolongation of residence time made more reactants and intermediate products involved in the correlative chemical reactions shown in Table 1, before they were taken away from the catalyst bed. But, when the GC1HSV was lower than 145 h-1, although the residence time was prolonged more, the feed was heated very fast to approach the reactor temperature (850 oC), at which the WGS reaction was inhibited, so the hydrogen yield and carbon conversion at the GC1HSV of 102 h-1 did not continue to rise, but almost held the same level with that at the GC1HSV of 145 h-1. The reasonability of the above explanation can be confirmed from the increase of CO concentration and the decrease of CO2 11


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

concentration (shown in Fig. 9 (b)). Additionally, when the GC1HSV decreases below a certain value, one of main restriction factors for accelerating the steam reforming process further to produce hydrogen likely will be the catalytic activity of the used catalyst. Fig.9 Average yields and concentrations of the gaseous products at different GC1HSVs at 850 oC and the S/C ratio=12:1: (a) for yields and (b) for concentrations.

3.4. Characterization of used catalysts SEM images of the used catalysts under different reaction conditions were shown in Fig. 10. Carbon deposited on the used catalyst was found, especially at low temperature and low S/C ratio (Fig. 10 (a) and (b)). But when the reaction temperature was over 750 oC and the S/C ratio reached 12:1, there was almost no carbon deposition from their SEM images. Additionally, the XRD patterns of the used catalysts under the above same four conditions were shown in Fig. 11. Compared to the fresh catalyst shown in Fig.1 (before H2 activation), nickel element in the used catalysts essentially existed in the form of elemental Ni, and the diffraction peaks of deposited carbon were also found on the XRD patterns of the used catalysts. At low temperature and S/C ratio, the diffraction peaks of carbon deposition were remarkable, but as the temperature and S/C ratio rose, the peaks were significantly decreased, and at 850 oC and S/C ratio of 12:1, the peaks became very weak. Fig. 10 SEM images of the catalysts after reforming reactions with the conditions: (a) at 650 oC and S/C ratio of 12:1, (b) at 750 oC and S/C ratio of 8:1, (c) at 750 oC and S/C ratio of 12:1, and (d) at 850 oC and S/C ratio of 12:1. Fig. 11 XRD patterns of the used catalysts under different reforming conditions. Fig. 12 TG-TPO result of the used catalysts under different reforming conditions.

Then, the amount of carbon deposition on the catalyst used in the different reaction conditions was investigated by TG-TPO method as well as the theoretical calculation. The result of TG-TPO was showed in Fig. 12. As the temperature in the TG experiment rose, each sample exhibited a weight loss overall with two slight weight augments in the process. The diversifications of the sample weights can be attributed to the removal of deposited carbon and the augment of oxygen element including the oxidation of Ni metal and the increase of free O2- in mayenite, i.e. the amount of carbon deposited on the catalyst was the sum of the 12


Page 12 of 26

Page 13 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

weight loss of TG-TPO and the weight change caused by the oxygen increase. Then, we assumed that, for the used catalyst, before the TG-TPO experiment all Ni metal existed in the form of elemental nickel and all mayenite lose free oxygen mainly in consideration of initial hydrogen activation and reducing atmosphere produced in the reforming process, and after the TG-TPO experiment all the elemental nickel was replaced by Ni2O3 and all the mayenite contained free oxygen given that the sample was fully oxidized. Therefore, the theoretical maximum weight change caused by the above two kinds of oxidation can be calculated according to the initial catalyst composition, and then the maximum amount of carbon deposited on the catalysts can also be obtained. From Table 2, just a small amount of carbon deposition was formed, and especially at 850 oC and S/C ratio of 12:1, the amount was obviously lower than the values in the literatures [9, 18]. And, the change of carbon deposition with the temperature and S/C ratio was consistent with the result of Fig. 10 and Fig. 11. Additionally, from Table 2, the amount of carbon deposit at low temperature and S/C ratio was far lower than the carbon loss, and as the temperature and S/C ratio rose, the two values were gradually approaching. The result meant that considerable amount of carbon-containing material produced in the reforming process couldn’t be further converted into small-molecule gases at such low temperature and S/C ratio, but was taken away from the reactor and then purified in the cooling system. Table 2 The maximum amount of carbon deposited on the used catalysts.

4. CONCLUSIONS In this paper, the steam reforming process of 1-methylnaphthalene as tar model compound from COG for hydrogen production was performed via thermodynamic analysis and experiments. In the thermodynamic analysis, the hydrogen yield firstly increased and then flattened out with the increases of temperature and S/C ratio, due to the exothermic WGS reaction which was considered as one of the main restrictive links in the steam reforming process of tar to produce hydrogen; the compound can be completely converted and almost no coke deposition formed, different from the real experimental results, due to the drawback of the thermodynamic property of deposited coke in the used thermodynamic databases. In 13


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

the steam reforming experiments, Ni/Mg catalyst with Ca12Al14O33 as carrier was prepared and employed. With the increases of temperature and S/C ratio and the decrease of GC1HSV, the catalytic activity and stability of the catalyst were improved gradually and the thermal hysteresis was weakened gradually, and thus, the tar reforming result for hydrogen production became better gradually. After the temperature, S/C ratio increased to 800 oC and 12:1 respectively and GC1HSV decreased to 145 h-1, the hydrogen yield and carbon conversion could reach over 90% and 97%, respectively, even very close to the thermodynamic values. Additionally, under the above conditions, the Ni/Mg catalyst with Ca12Al14O33 as carrier showed an excellent resistance to coke formation.

AUTHOR INFORMATION *Corresponding Author: Telephone/Fax: +86-024-83672216. E-mail: [email protected] (Q.B. Yu), [email protected] (H.Q. Xie) Mailing address: P.O, Box345, Northeastern University, No11, Lane 3, Wenhua Road, Heping District, Shenyang, Liaoning, P. R. China.

ACKNOWLEDGMENTS This research was financially supported by the National Natural Science Foundation of China (No. 51576035), the National Key Technology R&D Program of China (No. 2013BAA03B03), and the National Science Foundation for Post-doctoral Scientists of China (No. 2015M571322), and the Post-doctoral Scientific Research Foundation of Northeastern University (No. 20150309).

REFERENCES (1) Koo K. Y.; Lee J. H.; Jung U. H.; Kim S. H.; Yoon W. L. Combined H2O and CO2 reforming of coke oven gas over Ca-promoted Ni/MgAl2O4 catalyst for direct reduced iron production. Fuel 2015, 153: 303-309. (2) Bermúdez J. M.; Ferrera-Lorenzo N.; Luque S.; Arenillas A.; Menéndez J. A. New process for producing methanol from coke oven gas by means of CO2 reforming. Comparison with conventional process. Fuel Processing Technology 2013, 115: 215-221. (3) Tao W.; Cheng H. W.; Yao W. L.; Lu X. G.; Zhu Q. H.; Li G. S.; Zhou Z. F. Syngas 14


Page 14 of 26

Page 15 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

production by CO2 reforming of coke oven gas over Ni/La2O3–ZrO2 catalysts. International

Journal of Hydrogen Energy 2014, 39: 18650-18658. (4) Cheng H. W.; Yao W. L.; Lu X. G.; Zhou Z. F.; Li C. H.; Liu J. Z. Structural stability and oxygen permeability of BaCo0.7Fe0.2M0.1O3 − δ (M = Ta, Nb, Zr) ceramic membranes for producing hydrogen from coke oven gas. Fuel Processing Technology 2015, 131: 36-44. (5) Qin Z. F.; Ren J.; Miao M. Q.; Li Z.; Lin J. Y.; Xie K. C. The catalytic methanation of coke oven gas over Ni-Ce/Al2O3catalysts prepared by microwave heating: Effect of amorphous NiO formation. Applied Catalysis B: Environmental 2015, 164: 18-30. (6) Razzaq R.; Li C. S.; Zhang S. J. Coke oven gas: Availability, properties, purification, and utilization in China. Fuel 2013, 113: 287-299. (7) Kirton J.; Crisp T. The analysis of organic oven emissions in coke. Fuel 1991, 70: 1383-1389. (8) Quitete C. P. B.; Bittencourt R. C. P.; Souza M. M. V. M. Steam reforming of tar using toluene as a model compound with nickel catalysts supported on hexaaluminates. Applied

Catalysis A: General 2014, 478: 234-240. (9) Yang J.; Wang X. G.; Li L.; Shen K.; Lu X. G.; Ding W. Z. Catalytic conversion of tar from hot coke oven gas using 1-methylnaphthalene as a tar model compound. Applied

Catalysis B: Environmental 2010, 96: 232-237. (10) Kohl A. L.; Nielsen R. B. Gas purification; Gulf Professional publishing: Texas, 1997. (11) Yue B. H.; Wang X. G.; Ai X. P.; Yang J.; Li L.; Lu X. G.; Ding W. Z. Catalytic reforming of model tar compounds from hot coke oven gas with low steam/carbon ratio over Ni/MgO–Al2O3 catalysts. Fuel Processing Technology 2010, 91(9): 1098-1104. (12) Wang S. R.; Zhang F.; Cai Q. J.; Li X. B.; Zhu L. J.; Wang Q.; Luo Z. Y. Catalytic steam reforming of bio-oil model compounds for hydrogen production over coal ash supported Ni catalyst. International Journal of Hydrogen Energy 2014, 39: 2018. (13) Zhang Y. W.; Li Q.; Shen P. J.; Liu Y.; Yang Z. B.; Ding W. Z.; Lu X. G. Hydrogen amplification of coke oven gas by reforming of methane in a ceramic membrane reactor.

International Journal of Hydrogen Energy 2008, 33(13): 3311-3319.

15


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(14) Zhang Y. W.; Liu J.; Ding W. Z.; Lu X. G. Performance of an oxygen-permeable membrane reactor for partial oxidation of methane in coke oven gas to syngas. Fuel 2011, 90: 324-330. (15) Yang Z. B.; Zhang Y. Y.; Ding W. Z.; Zhang Y. W.; Shen P. J.; Zhou Y. D.; Liu Y.; Huang S. Q.; Lu X. G. Hydrogen production from coke oven gas over LiNi/γ-Al2O3 catalyst modified by rare earth metal oxide in a membrane reactor. Journal of Nature Gas Chemistry

2009, 18(4): 407-414. (16) Yue B. H.; Kong L. H.; Wang X. G.; Lu X. G.; Ding W. Z. Catalytic conversion of tar components from hot coke oven gas over Ni/MgAl(O) catalyst. Chinese Journal of Catalysis

2010, 31: 218-224. (17) Ai X. P.; Yue B. H.; Wang X. G.; Yang J.; Lu X. G.; Ding W. Z. Catalytic conversion of tar components in hot coke oven gas over Ni/MgO-Al2O3 catalystS. Acta Physico-Chimica

Sinica 2009, 25:1517-1522. (18) Cheng H. W.; Zhang Y. W.; Lu X. G.; Ding W. Z.; Li Q. Hydrogen production from simulated hot coke oven gas by using oxygen-permeable ceramics. Energy & Fuels 2009, 23: 414-421. (19) Onozaki M.; Watanabe K.; Hashimoto T.; Saegusa H.; Katayama Y. Hydrogen production by the partial oxidation and steam reforming of tar from hot coke oven gas. Fuel

2006, 85 (2): 143-149. (20) Norinaga K.; Yatabe H.; Matsuoka M.; Hayashi J.-i. Application of an existing detailed chemical kinetic model to a practical system of hot coke oven gas reforming by noncatalytic partial oxidation. Industrial & Engineering Chemistry Research 2010, 45(6): 1911-1917. (21) Appari S.; Tanaka R.; Li C.; Kudo S.; Hayashi J.-i.; Janardhanan V. M.; Watanabe H.; Norinaga K. Predicting the temperature and reactant concentration profiles of reacting flow in the partial oxidation of hot coke oven gas using detailed chemistry and a one-dimensional flow model. Chemical Engineering Journal 2015, 266: 82-90. (22) Li C. S.; Hirabayashi D.; Suzuki K. Development of new nickel based catalyst for biomass tar steam reforming producing H2-rich syngas. Fuel Processing Technology 2009,

90(6): 790-796. 16


Page 16 of 26

Page 17 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(23) Li C. S.; Hirabayashi D.; Suzuki K. Steam reforming of biomass tar producing H2-rich gases over Ni/MgOx/CaO1-x catalyst. Bioresource Technology 2010, 101(S1): 97-100. (24) Yoon S. Y.; Choi Y. C.; Lee J. G. Hydrogen production from biomass tar by catalytic steam reforming. Energy Conversion and Management 2010, 51(1): 42-47. (25) Simell P. A.; Hirvensalo E. K.; Smolander V. T.; Krause A. O. I. Steam reforming of gasification gas tar over dolomite with benzene as a model compound. Industrial &

Engineering Chemistry Research 1999, 38: 1250-1257. (26) Kuhn J. N.; Zhao Z.; Felix L. G.; Slimane R. B.; Choi C. W.; Ozkkan U. S. Olivine catalysts for methane- and tar-steam reforming. Applied Catalysis B: Environmental 2008,

81: 14-26. (27) Xie H. Q.; Yu Q. B.; Yao X.; Duan W. J.; Zuo Z. L.; Qin Q. Hydrogen production via steam reforming of bio-oil model compounds over supported nickel catalysts. Journal of

Energy Chemistry 2015, 24: 299-308. (28) Colby J. L.; Wang T.; Schmidt L. D. Steam Reforming of Benzene As a model for biomass-derived syngas tars over Rh-based catalysts. Energy & Fuels 2010, 24 (2): 1341-1346. (29) Polychronopoulou K.; Costa C. N.; Efstathiou A. M. The steam reforming of phenol reaction over supported-Rh catalysts. Applied Catalysis A: General 2004, 272 (1-2): 37-52. (30) Iriondo A.; Barrio V. L.; Cambra J. F.; Arias P. L.; Guemez M. B.; Navarro R. M.; Sanchez-Sanchez M. C.; Fierro J. L. G. Hydrogen production of glycerol over nickel catalysts supported on Al2O3 modified by Mg, Zr, Ce or La. Top Catal 2008, 49: 46-58. (31) Zhang N. W.; Huang C. J.; Kuang F. P.; Gao X. X.; Weng W. Z.; Wan H. L. Effect of a Mg Promoter on the Structure and Catalytic Performance of a Co/Mg/HZSM-5 Catalyst for the Partial Oxidation of Methane to Syngas. Acta Physico-Chimica Sinica 2008, 24(12): 2165-2171. (32) Nakamura K.; Miyazawa T.; Sakurai T.; Miyao T.; Naito S.; Begum N.; Kunimori K.; Tomishige K. Promoting effect of MgO addition to Pt/Ni/CeO2/Al2O3 in the steam gasification of biomass. Applied Catalysis B-Environmental 2009, 86 (1-2): 36-44.

17


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(33) Li C. S.; Hirabayashi D.; Suzuki K. A crucial role of O2− and O22− on mayenite structure for biomass tar steam reforming over Ni/Ca12Al14O33. Applied Catalysis B: Environmental

2009, 88(3-4): 351-360. (34) Vagia E. C.; Lemonidou A. A. Hydrogen production via steam reforming of bio-oil components over calcium aluminate supported nickel and noble metal catalysts. Applied

Catalysis A: General 2008, 351(3-4): 111-121. (35) Yang J.; Wang X. G.; Li L.; Shen K.; Lu X. G.; Ding W. Z. Catalytic conversion of tar 1-Methylanaohthalene as tar model compoound from hot coke oven gas over Ni/MgO/Al2O3 catalysts. Chemical Journal of Chinese Uiversities 2010, 31: 1841-1847. (36) Marquevich M.; Czenik S.; Chornet E.; Montane D. Hydrogen from biomass: Steam reforming of model compounds of fast-pyrolysis oil. Energy and Fuels 1999,

13(6):1160-1166. (37) Xie H. Q.; Yu Q. B.; Wen M. Q.; Duan W. J.; Yao X.; Qin Q.; Zuo Z. L. Hydrogen production from steam reforming of simulated bio-oil over Ce–Ni/Co catalyst with in continuous CO2 capture. International Journal of Hydrogen Energy 2015, 40(3): 1420-1428. (38) Xie H. Q.; Yu Q. B.; Wang K.; Shi X. B.; Li X. H. Thermodynamic analysis of hydrogen production from model compounds of bio-oil through steam reforming. Environmental

Progress & Sustainable Energy 2014, 33(3): 1008-1016. (39) Xie H. Q.; Yu Q. B.; Duan W. J.; Yao X.; Li X. H.; Qin Q. Selection of CO2 sorbent used in bio-oil steam reforming process for hydrogen production. Environmental Progress &

Sustainable Energy 2015, 34(4): 1208-1214. (40) Alvarado F. D.; Gracia F. Steam reforming of ethanol for hydrogen production: Thermodynamic analysis including different carbon deposits representation. Chemical

Engineering Journal 2010, 165: 649-657.

18


Page 18 of 26

Page 19 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

TABLE LIST: Table 1 Key chemical reactions involved in the steam reforming process of 1-methylnaphthalene.

Table 2 The maximum amount of carbon deposited on the used catalysts.

FIGURE LIST: Fig. 1 XRD patterns of the Ca12Al14O33 carrier (a) and the Ni/Mg catalyst (b). Fig. 2 The schematic illustrations of experiment apparatus. Fig. 3 Effect of temperature and S/C ratio on the hydrogen yield and concentration in the steam reforming process of C11H10 with thermodynamic analysis. Fig. 4 Effect of temperature and S/C ratio on the carbon distribution in the steam reforming process of C11H10 with thermodynamic analysis. Fig. 5 Hydrogen yield as a function of the reaction time at different S/C ratios at 750 oC and the GC1HSV=145 h-1. Fig. 6 Average yields and concentrations of the gaseous products at different S/C ratios at 750 oC and the GC1HSV=145 h-1: (a) for yields and (b) for concentrations. Fig. 7 Hydrogen yield as a function of the reaction time at different temperatures at the S/C ratio=12:1 and the GC1HSV=145 h-1. Fig. 8 Average yields and concentrations of the gaseous products at different temperatures at the S/C ratio=12:1 and the GC1HSV=145 h-1: (a) for yields and (b) for concentrations. Fig. 9 Average yields and concentrations of the gaseous products at different GC1HSVs at 850 oC and the S/C ratio=12:1: (a) for yields and (b) for concentrations. Fig. 10 SEM images of the catalysts after reforming reactions with the conditions: (a) at 650 oC and S/C ratio of 12:1, (b) at 750 oC and S/C ratio of 8:1, (c) at 750 oC and S/C ratio of 12:1, and (d) at 850 o

C and S/C ratio of 12:1.

Fig. 11 XRD patterns of the used catalysts under different reforming conditions. Fig. 12 TG-TPO result of the used catalysts under different reforming conditions.

19


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 26

Table Table 1 Key chemical reactions involved in the steam reforming process of 1-methylnaphthalene ΔHθ800°C (kJ/mol)

No.

-

(1)

-53.89

(2)

CxHy+(4x-y)H2→xCH4

-

(3)

C11H10+17H2→11CH4

-1075.82

(4)

C10H8+16H2→10CH4

-1021.93

(5)

C6H6+9H2→6CH4

-599.71

(6)

CxHy→xC+y/2H2

-

(7)

C11H10→11C+5H2

-91.88

(8)

CxHy+xH2O→xCO+(x+y/2)H2

-

(9)

C11H10+11H2O→11CO+16H2

1401.54

(10)

C10H8+4H2O→C6H6+4CO+5H2

478.64

(11)

C6H6+6H2O→6CO+9H2

751.58

(12)

CH4+H2O→CO+3H2

225.22

(13)

C11H10+11CO2→22CO+5H2

1776.82

(14)

C10H8+4CO2→C6H6+8CO+H2

615.10

(15)

C6H6+6CO2→12CO+3H2

956.28

(16)

CO+3H2↔CH4+H2O

-225.22

(17)

C+ 2H2↔CH4

-89.45

(18)

Water gas shift

CO+H2O↔H2+CO2

-34.12

(19)

Water gas

C+H2O↔CO+H2

135.77

(20)

Boudouard

C+CO2↔2CO

169.88

(21)

Reaction

Equation

Thermal cracking

nC11H10→mCxHy+oH2+pCO+qCH4+rCO2+sC

Hydrodealkylation

C11H10+H2→C10H8 +CH4

Hydrocracking

Carbon formation

Steam reforming

Dry reforming

Methanation

20


Page 21 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 2 The maximum amount of carbon deposited on the used catalysts. Reforming conditions

Amount of carbon deposit

Carbon loss*

12:1

≤6.21%

38.14%

8:1

≤5.53%

30.99%

750

12:1

≤4.95%

7.24%

850

12:1

≤4.75%

2.86%

Temperature

S/C

650 750

*Carbon loss is the carbon percentage except carbon conversion with carbon balance in the reforming experiment.

21


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 26

Figure

Fig. 1 XRD patterns of the Ca12Al14O33 carrier (a) and the Ni/Mg catalyst (b).

Tar

N2 Hydrogen generator

Peristaltic pump Electric furnace

Flow meter

Water

Feeding system Detecting system

Cooling system

Exhaust

Drier Gas meter Gas analyzer Computer

Fig. 2 The schematic illustrations of experiment apparatus.

Fig. 3 Effect of temperature and S/C ratio on the hydrogen yield and concentration in the steam reforming process of C11H10 with thermodynamic analysis.

22


Page 23 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Fig. 4 Effect of temperature and S/C ratio on the carbon distribution in the steam reforming process of C11H10 with thermodynamic analysis.

Fig. 5 Hydrogen yield as a function of the reaction time at different S/C ratios at 750 oC and the GC1HSV=145 h-1.

Fig. 6 Average yields and concentrations of the gaseous products at different S/C ratios at 750 oC and the GC1HSV=145 h-1: (a) for yields and (b) for concentrations

23


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 7 Hydrogen yield as a function of the reaction time at different temperatures at the S/C ratio=12:1 and the GC1HSV=145 h-1.

Fig. 8 Average yields and concentrations of the gaseous products at different temperatures at the S/C ratio=12:1 and the GC1HSV=145 h-1: (a) for yields and (b) for concentrations.

Fig. 9 Average yields and concentrations of the gaseous products at different GC1HSVs at 850 oC and the S/C ratio=12:1: (a) for yields and (b) for concentrations. 24


Page 24 of 26

Page 25 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Fig. 10 SEM images of the catalysts after reforming reactions with the conditions: (a) at 650 oC and S/C ratio of 12:1, (b) at 750 oC and S/C ratio of 8:1, (c) at 750 oC and S/C ratio of 12:1, and (d) at 850 oC and S/C ratio of 12:1.

Fig. 11 XRD patterns of the used catalysts under different reforming conditions.

25


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 12 TG-TPO result of the used catalysts under different reforming conditions.

26


Page 26 of 26

Study on Steam Reforming of Tar in Hot Coke Oven Gas for Hydrogen

Recommend Documents