Hydrogen Rich Syngas Production through Synergistic Methane

Subscriber access provided by Nottingham Trent University

Article

Hydrogen Rich Syngas Production through Synergistic Methane Activated Catalytic Biomass Gasification Amoolya Dattatraya Lalsare, Yuxin Wang, Qingyuan Li, Ali Sivri, Roman Vukmanovich, Cosmin Emil Dumitrescu, and Jianli Hu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b02663 • Publication Date (Web): 04 Sep 2019 Downloaded from pubs.acs.org on September 4, 2019

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 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 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.

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 31 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

ACS Sustainable Chemistry & Engineering

Hydrogen Rich Syngas Production through Synergistic Methane Activated Catalytic Biomass Gasification Amoolya Lalsarea, Yuxin Wanga, Qingyuan Lia, Ali Sivrib, Roman J. Vukmanovicha, Cosmin E. Dumitrescub, Jianli Hua* Department of Chemical and Biomedical engineering, b Department of Mechanical and Aerospace Engineering, 395 Evansdale Dr., Morgantown, West Virginia, US 26505 a

West Virginia University, Morgantown, WV *Corresponding Author Email: [email protected]

1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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

Abstract The abundance of natural gas and biomass in the U.S. was the motivation to investigate the effect of adding methane to catalytic non-oxidative high-temperature biomass gasification. The catalyst used in this study was Fe-Mo / ZSM-5. Methane concentration varied from 5 vol. % to 15 vol. % and the reaction was performed at 850oC and 950oC. While biomass gasification without methane on the same catalysts produced ~60 mole% methane in the total gas yield, methane addition had a strong effect on the biomass gasification, with more than 80 mole% hydrogen in the product gas. This indicates that the reverse Steam Methane Reformation (SMR) reaction is favored in the absence of additional methane in the gas feed as the formation of H2 and CO shifts the equilibrium to the left. Results showed that 5 mole% of additional methane in the feed gas allowed for steam methane reforming due to formation of steam adsorbates from oxygen in the functional groups of aromatic lignin being liberated on the oxophilic transition metals like Mo and Fe. This oxygen was then available for the SMR reaction with methane to form H2, CO, and CO2. This study was not a detailed catalytic activity evaluation but exploratory research to ascertain the synergy presented in the co-gasification of biomass and natural gas.

Keywords: biomass gasification, co-gasification of biomass and methane, FeMo/ZSM-5 catalyst


Page 2 of 31

Page 3 of 31 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


Introduction Per-capita energy demand increased sharply over the last century, which caused irreversible changes in the weather patterns across the globe1. Climate change, which has long been perceived as a futuristic phenomenon is already producing adverse climatic changes around the globe. The average annual temperature of the planet has already risen by 1.5 oC and the current efforts in reducing emissions are focused on curbing this temperature rise to 2oC.2,3. At the current rate of emissions, the planet may see record temperature rise of 2oC by 2050. According to the Intergovernmental Panel on Climate Change (IPCC), the carbon dioxide (CO2) concentration in Earth’s atmosphere has crossed the unprecedented mark of 400 ppm.4 The world community is diligently working towards moving to cleaner, green, and sustainable energy sources like solar, wind, and biomass to meet the energy needs especially in power and transportation sectors.5 Biomass has been a major source of energy for humankind since the discovery of fire in the prehistoric era and was the predominant source of fuel for heating and cooking applications until fossil fuels like petroleum, coal, and natural gas were successfully harnessed in the 19th century. Fossil-fuel-based technologies enabled the human population to increase sharply from less than 1 billion before the 18th century to more than 7 billion by 2020 in a span of just three centuries. Fossil fuels account for nearly 80% of the world energy needs and the shift to renewable energy sources is not an easy task, owing to the high costs and unreliability of energy sources like solar and wind. Biomass, which accounts for 10 – 14% of the global energy supply, can replace fossil fuels as a reliable, sustainable, and green source of energy, contingent on the development of technologies that can harness its energy in clean, efficient, and economical (i.e., cost-effective) means.6 Even today biomass accounts for most of the energy utilized in the remotest, underdeveloped, and developing regions globally. Biomass is available in different forms such as agricultural and forestry waste, animal waste, biological materials by-products, wood, and municipal waste. These sources of biomass have vastly different moisture content and elemental compositions, thus making it difficult to develop cost-effective technology which utilizes most types of biomass.7,8 Although woody biomass such as dry firewood is used in combustion for heating and power generation,9 the energy efficiency is low and air emission control becomes an issue. In contrast, both heat and power generation requirements using gasification can be met in an efficient, effective, and clean way.10 Energy utilization by converting solid feedstock to high heating value syngas is one of the cleanest ways to harness renewable energy source from woody biomass. Biomass fast pyrolysis and gasification holds good potential for the production of hydrocarbon fuels and value-added chemicals.11,12 Pyrolysis has been extensively researched and applied for producing bio-fuels for direct use in transportation and related applications.13–21 However, the decomposition of the highly aromatic lignin structure in the lignocellulosic biomass leads to formation of bio-oil at temperatures below 700oC.22–24 Bio-oil is high in oxygen content and has limited direct application as fuel owing to high acidity, poor resistance to extreme weather conditions, and instability.11,25 These limitations are the result of the highly-oxygenated aromatic structure of biomass. The thermochemical conversion of biomass to energy and fuels have been extensively studied for the past few decades.26,27 Biomass decomposes rapidly between 400°C to 600oC giving devolatilization components like carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), bio-oil, aerosols, and bio-char.9,11,12,22 3 ACS Paragon Plus Environment


There have been numerous efforts to upgrade the yields from biomass to value added chemicals such as benzene, toluene, ethylbenzene, and xylene (BTEX), and produce hydrogen-rich syngas28,29. In-situ tar cracking, hydrodeoxygenation (HDO), and rearrangement to form ketonic intermediates leading to alkanes are typical reaction steps necessary for conversion of biomass to valuable chemicals.28,30,31 Transition metals on catalytic surfaces like zeolite (HZSM-5), SiO2, γAl2O3 have been studied to initiate biomass upgradation reactions like dehydration, rearrangement, decarboxylation, decarbonylation, and hydrodeoxygenation.7,28,32 However, the complexity of reaction chemistry, the requirement of high pressure hydrogen, and the rapid catalyst deactivation due to coke deposition and poisoning increases the cost of the process, rendering it economically unviable. Methane-promoted catalytic biomass gasification can achieve in-situ tar reformation and cracking, thus producing high syngas yields with an enhanced H2:CO ratio, suitable for chemical synthesis via a conventional Fischer Tropsch (FT) synthesis process. Air – steam catalytic and non-catalytic gasification was reported on Ni/CeO2/Al2O3 with catalyst loading of 20 – 40% in a fluidized bed reactor at 725oC, 825oC, and 900oC.33 Nishikawa et al reported that, at 900oC, highcatalyst-to-biomass loading of 40% was effective in tar cracking and high-purity hydrogen production.33 Ni nanoparticles on MCM-41 supports were utilized for biomass gasification to enhance hydrogen production.34,35 Use of a suitable catalyst for biomass gasification increased the H2:CO ratio in syngas from 1.15/2.15 to 1.87/4.45.36,37 Fe – Ni / CeO-Al2O3 and noble metals like Pt, Pd, Rh were synthesized and used for biomass steam gasification which showed that Fe promoted catalysts produce higher gas yields.33 Coconut-shell gasification was performed with steam on Pt, Fe, and Co promoted catalysts and it was reported that the use of Fe promoted catalysts increased hydrogen and carbon monoxide composition by improving the water gas shift reaction.38 Catalytic Fast Pyrolysis (CFP) on inexpensive Mo-Ag / ZSM-5 catalysts with methane a single reactor system operated at atmospheric pressure reported that the catalyst deactivation rate decreased with increasing H/Ceff ratio. This ratio can be increased by fast pyrolysis / gasification of biomass with a hydrogen-rich source like methane. H/Ceff ratio of biomass is about 0.3, which is not suitable for producing hydrogenrich syngas for production of value-added chemicals. Methane that comes from an inexpensive and abundant source like natural gas has a very high H / Ceff ratio of 4.39 In recent years there have been efforts to utilize methane and biomass in a single reactor but mainly for the purpose of fast pyrolysis. In one of the recent studies, pine saw dust biomass was impregnated by Ni and gasified with steam at 600oC to produce H2 rich syngas with maximum H2 yield of 60% in the outlet gas. Steam was replaced by methane to perform catalytic methane decomposition (CMD) for 10 hours at 850oC on Ni/carbon catalyst to further increase H2. About 90% methane conversion was reported with the process.35 The present study focuses on non-oxidative catalytic gasification in a single stage using co-feed of methane (5 - 15 mole%) with biomass. Although renewable energy sources have started contributing significantly to power generation in the US. Having said that, renewable energy sources like solar and wind face severe limitations to be considered as mainstream source for power generation. Thus natural gas biomass synergy is of key importance given the power and energy requirements of the US in coming decades. With the abundance of natural gas in the U.S and especially the Appalachian region, efficient and costeffective utilization of natural gas for fuels and conversion to valuable chemicals along with biomass offers great potential for meeting U.S energy needs in the near future. Methane is a major 4 ACS Paragon Plus Environment

Page 4 of 31

Page 5 of 31 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


constituent in natural gas (> 80 mole%), which makes it an inexpensive source of hydrogen for tar reforming in the biomass pyrolysis and gasification process. Methane can be activated with the use of synthetic transition metal catalysts like Ni, Fe, Co.33,40 This study chose Fe – Mo / ZSM-5 for the co-gasification of methane and biomass at 750 – 950oC in a fixed-bed reactor system. In general, zeolites such as ZSM-5 with acidic function can be utilized to crack large molecules such as biomass. Adding metals to zeolite creates bifunctional properties facilitating dehydrogenation and hydrogen transfer41–43. Fe on ZSM-5 was shown to assist methane decomposition with less energy intensive cleavage of the C-H bond.39,40,44 Fe impregnated ZSM-5 catalyst has been subjected to high temperature methane decomposition to produce hydrogen and carbon nanotubes (CNT). Fe-Mo / ZSM-5 catalyst has also been utilized for methane and ethane dehydroaromatization studies. Iron active sites supported on ZSM-5 have been shown to cause 3-dimentional coke deposition on the catalyst in the form of carbon nanotubes. Coke characterization on the iron based catalyst showed that crystalline coke formation is pronounced than amorphous coke. Amorphous coke deposition on the catalyst leads to blocking of active metal sites thus causing catalyst deactivation. Crystalline coke deposition in the form of CNTs’ delays Fe-Mo / ZSM-5 catalyst deactivation40. Iron is known to be conducive for high temperature methane activation and atomic molybdenum impregnated on ZSM-5 is highly oxophilic (oxygen binding affinity). Oxophilicity of Mo on ZSM-5 is key for hydrodeoxygenation and steam methane reforming in the methane activated biomass gasification reaction system. This is was the primary reason authors selected Fe-Mo/ZSM-5 catalyst. It is postulated that intermediate hydrogen species participate in cracking the oxygenated aromatic structure of lignocellulose biomass by hydrodeoxygenation (HDO), decarbonylation, and decarboxylation reactions. Fe and FeOx active sites are directly responsible for high temperature water gas shift (HT-WGS) and steam methane reforming (SMR) reactions41,45–47. Although there is little evidence that acid sites on ZSM-5 directly facilitate WGS and SMR reactions, acidity of the ZSM-5 support affects the conversion of CO (in WGS) and CH4 (in SMR). Meanwhile, Bronsted and some Lewis acidic sites on ZSM-5 are known to be effective in conversion of highly oxygenated lignin to value-added chemicals like BTEX31,34,48,49. This study investigated the possible synergy between cogasification of hardwood biomass and methane. Iron (Fe) and Molybdenum (Mo) were used as promoters on ZSM-5 zeolite as they are inexpensive and provide active sites for C-H bond activation and converting lignin oxygen, thus minimizing tar. Catalyst preparation method, type of biomass and its elemental composition, type of reactors used, product analysis technique are described in the experimental section. Biomass gasification in TGA, biomass gasification tests in fixed bed without methane, methane-biomass gasification tests, coke formation, synergistic effect of methane addition on H2:CO ratio have been discussed in detail in the results and discussion section.



Page 6 of 31

Experimental section Catalyst Preparation The catalyst (Zeolyst, Inc.) was NH4 – ZSM-5 zeolite with a silica/alumina (SAR) of 23. Ammonium molybdate (VI) tetrahydrate and iron (III) nitrate nonahydrate were purchased from Acros Organics. The zeolite catalyst was first calcined at 500oC in air for 3 h to convert NH4 – ZSM-5 to H – ZSM-5. The conventional incipient wetness technique was used to prepare MoFe/ZSM-5. After drying the catalysts at 105oC to remove the water overnight, the dry powder catalyst sample was further calcined in air at 550oC for 4 h. The chemical composition of the synthesized catalysts are shown in Table 1. Elemental composition of hardwood biomass subjected to all experimental tests presented in the manuscript is shown in Table 2. Table 1 Mo-Fe/ZSM-5 metal loading of Mo and Fe on ZSM-5 catalyst synthesized by wet incipient method Catalyst FeMo1 FeMo2

Mo 4 wt.% 4 wt. %

Fe 0.5 wt.% 1.5 wt.%

Table 2 Elemental composition, moisture, and ash wt.% of hardwood biomass used in the study (performed by National Research Center for Coal and Energy) Carbon (C) Hardwood 45.25 biomass Reaction Conditions

Hydrogen (H) 4.65

Oxygen (O) 49.2

Moisture 7.16

Ash 0.32

Catalytic hardwood-pellet biomass gasification was performed in a downdraft fixed bed reactor (12.7 mm diameter, 915 mm long) stainless steel (316SS) reactor tube (Charleston Valve and Fitting Co.). In a typical experimental test, 0.75 g of Mo-Fe/ZSM-5 catalyst was premixed with 1 g lignocellulose hardwood-pellet biomass. Biomass was ground and screened to a mean particle diameter of 432 microns. This particle size was selected to maintain consistency with the 432 micron particles used for a bench-scale continuous-bubbling fluidized-bed setup that is currently being tested under different parametric conditions of temperature, gasifying agent, feed/bed material ratio, and with a premixed catalyst. Reactor bed temperature was measured using a Ktype thermocouple (OmegaTM). Prior to loading into the reactor, the catalyst was subjected to reduction with 10 vol. % hydrogen (H2) with nitrogen (N2) at 600oC for 3 h. Catalyst and biomass were mechanically mixed in a ratio of 0.75:1 respectively. Nitrogen total flow of 300sccm was maintained when the temperature was raised from room temperature to 100oC. After moisture and air removal from the reactor, constant flow of 300sccm with desired methane concentration was maintained until the reactor pressure reached 50 psig. Fixed bed temperature ramp from 100oC to the reaction temperature was initiated while reactor valves were shut until the temperature ramp up was complete with a ramp rate of 20oC min-1. This method was adopted for replication of continuous feeding of biomass in a fluidized bed or moving bed reactor at the reaction temperature.


Page 7 of 31 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


It was observed through elemental composition analysis of hardwood lignocellulosic biomass that oxygen accounts of 49 wt.% of the biomass on dry basis. Therefore, for hydrogen rich syngas production, external source of oxygen is not required for the typical biomass. With use of external oxygen as gasifying agent like CO2 or H2O, it was observed that when >5 vol.% carbon dioxide was added along with 5 vol.% methane in the catalyst-biomass system, high concentration of CO and CO2 was observed in the product gas. However, 1%CO2 – 5%CH4 with biomass on FeMo/ZSM-5 and Fe-Mo/CNF(carbon nanofiber) catalysts produced H2:CO ratio = 2. CO2 thermal activation occurs in neighborhood of atomic hydrogen (from methane, biomass) on the catalyst active sites. This finding is being published as an independent study. Moreover, external steam addition would lead to direct steam methane reforming thus hindering the possible synergy between natural gas and biomass. Preliminary biomass gasification studies were also performed using a Thermogravimetric analyzer (TGA) instrument (TA Instruments – Waters LLC, model SDT 650). The product line from this instrument was connected to a mass spectrometer (Quantachrome) as described in the following section. Reaction conditions in the TGA were similar to the ones in the fixed-bed reactor. The reaction was performed at several temperatures ranging from 750oC to 950oC. Helium (He) was used as the carrier gas for these tests. Continuous product composition analysis was performed by the mass spectrometer connected downstream. Sample size for a typical test varied from 20 mg for biomass without catalyst to 70 mg for biomass – ZSM-5. Product analysis Product gases collected in sampling bags (SKC) from the fixed bed reactor tests were analyzed by a four-column gas chromatograph (Inficon Fusion micro-GC). The four columns consisted of a molecular sieve with a 3-m long PLOT U pre-column, an 8-m long RT – PLOT U with a 1-m long PLOT Q pre-column, an 8-m long aluminum column, and a 20-m long RTX – 1. The four columns allowed for calibrated (ppm level) detection of hydrogen, methane, carbon monoxide, carbon dioxide (complete syngas profile), ethylene, ethane, acetylene, water, nitrogen, and ammonia. All gases used for calibration were ultra-high purity (UHP) grade (AirGas).



Results and Discussion Conventional biomass gasification and devolatilization studies in TGA The TGA-MS performed the initial biomass gasification screening tests to identify temperature range for hydrogen and carbon monoxide evolution. Figure 1 shows the concentration profile versus time of the four major syngas components obtained from the TGA-mass spectrometry studies. For devolatilization and gasification at 650oC, only 7% H2 yield was obtained. CO, CO2 made up most of the gas yield obtained at temperatures less than 300oC with methane evolving beyond 300oC possibly indicating thermal cracking of the array of oxygenated aromatic rings in the lignin structure of biomass.

H2

CO

CO2

CH4

100% 9%

9%

14%

15% 26%

Normalized Conc.

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 8 of 31

80%

39% 54%

34% 42%

30%

6%

60% 79% 40% 67%

61% 20%

58% 46%

49%

55%

7%

0%

12, 255 14, 295 16, 335 18, 375 20, 420 25, 515 33, 646

Time, Temperature (min, oC)

Figure 1 Biomass gasification (hardwood pellet; heating rate of 20oC/min, then 30 min at 650oC; 100 sccm He flow) It is interesting to note that as methane started appearing in the gas products, carbon dioxide yield began to fall and only 6% carbon dioxide remained at 515oC. This suggested that the reverse SMR reaction dominated between 335oC to 515oC, where all the hydrogen that was bonded to saturated / unsaturated carbon in biomass reacted with the CO2 from devolatilization and thermal cracking forming CO. Higher CO concentrations were detected at higher temperatures as char oxidation reaction kicks in. Hydrogen started to appear as a predominant species in the normalized concentrations obtained from the mass spectrometry ionization signals only after a threshold temperature of about 650oC. Figure 2 and Figure 3 show that between 650oC to 950oC hydrogen and carbon monoxide constituted most of the gas yield. This indicated that at a lower temperature and without an oxidative atmosphere like steam or air, devolatilization and bio-char formation occurred between 200oC to 600oC50–52 In the TGA tests, the biomass sample size was too small (~20 mg) to trace any tar formation53. In the alumina crucible used for the tests only ash residue was observed with the end weight of the tared crucible around ~0.5 mg. The isothermal reaction time at the test temperatures was sufficient to completely gasify bio-char. Char gasification reactions were observed at higher temperatures, evident by the high H2:CO and CO/CO2 ratios at temperatures beyond 650°C/700oC (Table 3). Surprisingly, no methane formation was observed at 8 ACS Paragon Plus Environment

Page 9 of 31

char gasification temperatures (650 - 950oC) possibly indicating Boudouard reaction (Equation 1), which converted carbon to CO due to its highly endothermic nature:9 C + CO2 ⇌ 2CO ΔHo298 = 172 kJ mol-1……………………………………………… (Eq1) Similarly, a sharp increase in H2 and improvement in H2 / CO ratio may also be due to continuous heat being supplied driving the endothermic gasification reactions forward. Between 650-950oC, methane was not observed in the product probably because of reforming with water or CO2, which is evidenced by the increase in CO and H2 concentration shown in Figure 3. CH4 + H2 O ⇌ CO + H2 (Steam reforming) ΔHo298K = 206 kJ mol-1………………..(Eq 2) CH4 + CO2 ⇌ 2CO + H2 (Dry reforming) ΔHo298K = 247 kJ mol-1……................. (Eq 3)

H2 100%

8%

CO

CO2 6% 5%

9% 18%

Normalized Conc.

CH4 3% 4%

2%

27% 26% 32%

80%

33% 39% 53%

32% 14%

9%

52%

38%

69%

60%

40% 52% 49% 20%

59%

62%

61% 66% 51%

48%

40%

31%

50, 847

45, 843

40, 748

37, 688

35, 648

25, 449

20, 348

18, 302

30, 548

3%

0% 15, 248

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


Time, Temperature (min, oC)

Figure 2 Biomass gasification (hardwood pellet; heating rate of 20oC/min, then 30 min at 850oC; 100 sccm He flow) Typically, methane decomposition occurs at temperatures higher than 1000oC in the absence of a catalyst. Due to the presence of mineral materials in biomass, the methane decomposition reaction cannot be ruled out here. The proportion of tar in dry woody biomass ranges between 5 – 12 mg/g (0.5 - 1.2 wt.% on a dry basis) of dry biomass. 10 With only 20 mg of biomass in the TGA tests, possibility of traceable tar formation is very low.34,54–56 Endothermic equilibrium reactions in the regime of char gasification and homogeneous volatile reactions may have pronounced effects on the H2:CO and CO/CO2 ratios.57



Table 3 H2:CO and CO:CO2 ratios of TGA biomass gasification tests observed at temperatures between 750 - 950oC Temperature (oC) 750 850 950

H2 / CO 1.87 1.1 1.1

H2 100% 9%

Normalized Conc.

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 10 of 31

6%

CO / CO2 16.2 N/A 23

CO

CO2

13% 23%

23%

14%

10%

CH4 5% 7%

80%

3%

39% 50%

36%

1%

49%

47%

60% 86% 40% 63% 44%

20%

0%

67%

59%

52%

50% 41%

4% 10, 200 15, 300 20, 400 25, 500 30, 600 35, 700 40, 800 45, 900

Time (min)

Figure 3 Biomass gasification (hardwood pellet; heating rate of 20oC/min, then 30 min at 950oC; 100 sccm He flow) Figure 4 illustrates a TGA test where biomass was mixed with ZSM-5 and gasified under identical reaction conditions as used in the previous TGA tests. It was observed that the H2:CO ratio improved significantly at 750 – 800oC. The presence of ZSM-5 may have enabled cracking reactions at higher temperatures. Notably, a high concentration of methane was observed between 450oC to 550oC, indicating hydrogenation of higher aromatics and some aliphatic chains forming CH4 almost as much as CO at ~400oC. More CO and H2 was observed as temperature in the reactor increased. This indicated that the presence of a catalyst like zeolite helped to improve the syngas quality with in-situ tar reformation and cracking. The fixed-bed reactor biomass and methanebiomass gasification had a significantly different reaction environment, heat flux, and heat flux direction than the TGA sample crucible. Fixed bed reactor operated as a downdraft gasifier, whereas gas flow was horizontal in the case of TGA58. The interaction between catalyst active sites, char, and gaseous products was different in the case of the fixed bed reactor as compared to the TGA. Having said this, TGA provided a better study of the evolution and profile of possible gasification reactions occurring in a real reactor like the fixed-bed studies presented in following sections. 10 ACS Paragon Plus Environment

Page 11 of 31

H2 100%

8%

CO 10%

15% 31%

Normalized Conc.

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


80%

36%

28% 21%

18%

CH4

3% 8%

2% 6%

1% 4%

29%

33%

40%

60%

59%

2% 4%

10%

34% 60%

CO2

45%

45%

40% 58% 20%

0%

56%

48%

42%

54%

49%

36% 4% 17, 291 20, 351 24, 452 30, 551 35, 651 40, 751 42, 790 45, 850 50, 942 o

Time, Temperature (min, C)

Figure 4 Biomass gasification on ZSM-5 (hardwood pellet; heating rate of 20oC/min, then 30 min at 950oC; 100 sccm He flow)

Biomass catalytic gasification in the absence of methane in a fixed-bed reactor Figure 5 shows that in the absence of methane, biomass gasification yields in a fixed-bed reactor were (on average) 55 mole% and 58 mole% methane for the reaction at 850oC and 950oC, respectively. A H2:CO ratio between 0.5 and 1.0 was obtained, which was roughly in the range of the conventional non-catalytic gasification. However, with almost 55 - 60% methane in the gas yield, and a very low CO2 yield of 2 – 13 %, the results suggested that the reverse steam methane reformation (SMR) (Equation 2) was dominant at high temperature as both of these reactions were endothermic. Reverse SMR leading to conversion of hydrogen and carbon monoxide into methane could be due to the presence of acidic active sites on Fe and Mo metals59. In the case of biomass gasification on ZSM-5, the methane was 29 mole%, which is more than 3 times of the one seen in typical non-catalytic biomass gasification. The high methane yield in the product was attributed to the thermal cracking of the aromatic array of biomass. Moreover, in the absence of an acidic oxophilic transition metal like Fe or Mo, the oxygenated carbon in the biomass was converted to CO, CO2, and H2 which reacted on the surface. Also, without additional methane in the gas feed, the surface was deficient in methane, which favored the formation of methane and water vapor as the adsorbed CO and H2 underwent reverse SMR at high temperature. The results suggest a synergy between methane and biomass, which shifted the SMR equilibrium to right and forms hydrogen rich syngas. Detailed discussion on the results of methane – biomass gasification studies are discussed in the next section. Without external methane feed, typical gasification reactions only yield about 1:1 H2:CO ratio as is the molar ratio of biomass. Biomass and natural gas both being abundant and largely untapped sources of clean and efficient energy can help meet more than 80% of the total energy needs in the US by 2030. Utilization of natural 11 ACS Paragon Plus Environment


gas with development of new processes will also help revive the Appalachian economy especially that of West Virginia which strategically lies in the Marcellus shale gas basin60. Thus the synergy between biomass and methane has been explored in the following sections.

70% 60%

Normalized Conc.

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 12 of 31

H2 CO CO2 CH4

55% 54%

50% 44% 40% 30%

25%

19%

20% 10%

24%

24%

16%

16% 11% 5%

6%

0%

950 ZSM-5

850 FeMo1

950 FeMo1

Temperature (oC), Catalyst

Figure 5. Biomass gasification in the absence of methane operated in a fixed bed reactor ZSM-5 support and Mo-Fe/ZSM-5 at temperature: 850oC, 950oC

Coke formation and H2 from CH4 decomposition When using 0.5% and 1.5% Fe promoted Mo/ZSM-5 surface, coke formation was observed during co-feeding of biomass and methane. However, in the absence of methane, biomass gasification, coking was not observed on either catalyst. This indicates that some of the methane in the gas feed is decomposed at high temperatures to form coke and produce hydrogen (H2) due to the presence of Fe active sites on ZSM-5. Stoichiometric amount of hydrogen formed from methane decomposition was accounted for based on coke formed from methane decomposition.61 The calculation for hydrogen obtained from biomass-methane synergy was calculated in mole% as follows: H2(prod) = H2(total) – H2(coke) …………………………………………………………………….(Eq 4) H2:CO ratios obtained for various concentrations of methane and reaction temperatures were calculated after accounting for hydrogen obtained possibly from methane decomposition. Very little or no tar was recovered from the gas-liquid separator at the bottom of the vertical tubular reactor. However, small concentrations of ethane, ethylene, and acetylene were seen in the product analysis on the micro-GC.


Page 13 of 31 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


Gas yield, tar formation, and char deposition on catalyst Overall carbon balance for the methane activated biomass gasification was performed using inert gas and methane moles before the temperature ramp and molar volume occupied by the gas inside the tubular fixed bed reactor based on reaction temperature and pressure. All of the biomass carbon was recovered using TGA studies of spent catalyst for coke and char characterization. Amount of condensed tar was estimated using hexane solvent wash of the reactor tube and condenser. Mole% and yield of individual products was calculated based on gas moles obtained in the product. However, authors chose to present mole% and product yield based on syngas moles as it would be more accurate to do so in this case. This is because there was coke deposition on the catalyst as presented in the manuscript and hydrogen from methane decomposition was not considered as hydrogen produced from methane-biomass synergy. To be consistent with the objective of this work which is to show natural gas – biomass synergy, mole% and yield was calculated on product gas mole basis. To be fair, if one was to calculate mole% on basis of starting moles of biomass, the mole% of all the species would be less by about 10% to 20% depending on the gas, tar, and char yield. Yield (mole%) = number of moles of species / total product gas moles……………………..(Eq 5) It was also observed that normalized product gas composition and mole% calculated from yield of individual species based on gas moles were similar and thus were used interchangeably in discussing the results.It was observed that all the experimental tests produced greater than or equal to 80 mole% product gas. Tar mole% ranged between 10 to 15% while char was only about 2 to 8 mole%. Product gas yield from methane activated biomass gasification can be termed as biomass conversion obtained through the reaction. Gas yield, tar, and char composition of the biomass carbon balance is presented in Figure 6. It was observed that product gas yield was 88 mole% for reaction at 950oC and 84 mole% for reaction at 850oC. It was observed that gas yield substantially increased from 37.5 mole% at 750oC (not shown here) to 84 mole% at 850oC and further to 88 mole% at 950oC. However, gas yield decreased slightly from 84 mole% to 80 mole% at 850oC when gas feed methane concentration was increased from 5 to 15 vol.%. Similar trend was also observed at 950oC as gas yield decreased from 88 mole% to 82 mole% when methane concentration was increased from 5 to 15 vol.%. Marginal increase in char yield from 3 mole% to 8 mole% at 850oC and 2 mole% to 7 mole% at 950oC was also observed when methane concentration was increased from 5 to 15 vol.%. This could be explained based on the catalyst deactivation phenomenon possibly occurring due to high methane coverage on Fe and Mo active sites leading to paucity of sites available for methane-biomass reaction. Moreover, without methane in gas feed, biomass conversion was much higher on the FeMo1 catalyst (87.5% at 850oC and 90% at 950oC) compared to methane activated biomass gasification tests. However, >80 mole% product gas yield is an indication that low methane concentration leads to high methane and biomass conversion due to Fe and Mo being conducive to methane activation and biomass hydrodeoxygenation. Gas yield, char, and tar components in biomass gasification without methane and methane activated biomass gasification on FeMo1 catalyst in Table 4 and Figure 6.



Table 4 Co-Gasification of Biomass and methane gasification over Fe-Mo/ZSM-5; measured amount of coke on catalyst and gas yield for no-methane biomass gasification

Parameters Gas Yield Biomassno methane (mole%) Coking FeMo1 (mg, % CH4) Coking FeMo2 (mg, %CH4)

850oC 87.5

950oC 90.1

75.6, 5 135, 10 246, 15 51.5, 5 169.2, 10 267.3, 15

68.2, 5 136, 10 204.5, 15 NA

Gas Yield 100 12.5

9.9

3 13

5

Tar 8

15

12

80

80

Char 2 10

5

7

11

11

84

82

80

Yield (mole%)

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 14 of 31

60

40

87.5

90.1

84

850, 0

950, 0

850, 5

88

20

0 850, 10 850, 15

950, 5

950, 10 950, 15

Temperature (oC), CH4 (vol.%)

Figure 6: Gas, tar, and char yield obtained in biomass gasification without methane and methane activated synergistic catalytic biomass gasification at temperature: 850oC, 950oC and CH4 gas feed concentration: 0, 5, 10, 15 vol.%

As described in Table 4, coking on the catalyst was between 10 - 30 wt.% of the original weight of catalyst after reduction. Under identical conditions, biomass gasification in the absence of methane in the gas feed yielded almost no recoverable coke on the FeMo1 catalyst. No weight loss was seen in the catalyst before and after calcination. It can be concluded that coke deposition on both FeMo1 and FeMo2 catalysts was due to methane decomposition when 5 - 15% was used in the gas feed. The amount of coke from each test using methane is shown in Table 4. No considerable coke formation on the catalyst was observed for biomass gasification without methane, indicating that the aromatic components of lignin with branched functional groups like carbonyl carbon (C=O), hydroxyl carbon (C-OH) undergo surface reactions by latching onto the ZSM-5 acidic sites. Most of the oxygen from the biomass possibly reacted on the surface with the 14 ACS Paragon Plus Environment

Page 15 of 31 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


available hydrogen to undergo reverse SMR without external methane (Equation 2). The quantifications of moles of hydrogen, carbon monoxide, carbon dioxide, and methane were provided in Table S1 in supporting information.

Synergistic methane activated biomass gasification Synergistic gasification of hardwood biomass with methane was studied in the fixed-bed reactor on FeMo1 and FeMo2 catalysts for methane concentration ranging from 5 - 15 mole%. Figure 7 and Figure 8 shows the concentration of typical syngas components obtained from methane activated biomass gasification. Hydrogen was the dominant species in the product gas with hydrogen to carbon monoxide (H2:CO) ratio as high as 7.5 when reaction was performed at 950oC under 5% CH4 concentration in the gas feed along with 95% carrier gas N2. As the methane concentration is further increased to 10% and 15%, the H2:CO ratio dropped sharply at 950oC to 3.8 and 3.7 respectively. The same reaction when performed at 850oC for 5%, 10%, and 15% CH4 in the feed, H2:CO drops steadily from 6 to 4.2. In the absence of a catalyst, typical hardwood biomass gasification produced a H2:CO ratio of 0.3 to 0.5. This sharp increase in hydrogen by adding methane was an interesting aspect of this study, which likely shows the synergy between methane and biomass at high temperatures on a catalyst surface. The same gasification reaction when performed under identical conditions on the same catalyst without methane in the gas feed showed contrasting results. As high as 70 mole% methane was seen in the product gas with hydrogen yield averaging at 17% at 850oC and 950oC. CO, CO2 yield averaged at 19% and 11% respectively for 850oC as seen in Figure 5. At 950oC, CO yield increased to 25% and CO2 decreased to 4%. However, average methane yield was more than 50% of the total moles obtained in the product gas at both 850°C and 950oC. Hydrogen mole% in biomass that was used for the study is almost equal to the mole% of carbon (ref. Figure 5). Biomass gasification typically yields H2:CO less than or close to 1.54 The synergy between methane and biomass reacting together on an active catalyst like FeMo/ZSM-5 was apparent from the multifold increase in the hydrogen yield. The presence of methane in the gas feed suggested an equilibrium shift in some of the typical gasification reactions with steam methane reforming possibly occurring on the active sites of Mo and Fe. Both molybdenum (Mo) and iron (Fe) are known to be moderately oxophilic that is they have a higher binding affinity to oxygen as compared to metals like Zn, Ni, and Cu but lower oxygen binding affinity as compared to Ti, V, and Sc amongst the transition state or d-block metals. Mo is slightly more oxophilic than Fe (0.6 and 0.4) thus having the capability to activate C-OH, C=O type of bonds abundantly present in the complex array of aromatics in lignin component of the hardwood biomass.62 Hydrodeoxygenation (HDO) reactions studied on PdZn surfaces have shown that Zn being an oxophilic metal latches the oxygen present in the functional groups thus activating C-OH bonds.62



100%

H2 CO CO2 CH4

84% 76%

Normalized Conc.

81% 80%

60%

40%

20%

5% CH4

3%3%

1%1%

1%1%

H2:CO = 6

18%

17%

14%

0%

10% CH4

H2:CO = 5.0

15% CH4

H2:CO = 4.2

Figure 7 Methane activated biomass gasification at 850oC and for methane concentration of 5 mole%, 10 mole%, and 15 mole% using FeMo1 catalyst

100%

H2 CO CO2 CH4

77%

80%

80%

Normalized Conc.

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 16 of 31

74%

60%

40% 21% 20%

20% 11% 5%5%

2%4%

1%1%

0% 5% CH4

10% CH4

H2:CO: 7.4

H2:CO: 3.7

15% CH4

H2:CO: 3.7

Figure 8 Methane activated biomass gasification at 950oC and for methane concentration of 5 mole%, 10 mole%, and 15 mole% using FeMo1 catalyst

Figure 9 shows a representative structure of aromatic and furfural chains and -OH functional groups in lignin. The loosely-bonded oxygen and hydroxyl groups on the surface potentially react with the hydrogen obtained from devolatilization gases of biomass to produce H2O adsorbates on the active sites of Mo and Fe. Methane in the feed reacts with the H2O adsorbates on the surface sites undergoing high-temperature steam methane reforming to produce hydrogen and carbon 16 ACS Paragon Plus Environment

Page 17 of 31 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


monoxide. H2O adosrbates would evolve by selective adsorption of ligno-cellulosic oxygenates like alcohols, phenols, furfurals, ethers, and acids. High temperature thermal cracking of lignoceullosic components to single chain phenols, furfurals, and alcohols allows for passage through microporous ZSM-5 channels and selective adsorption of iron and molybdenum active sites in the ZSM-5 framework. The presence of Fe and Mo on acidic ZSM-5 in metallic form helps shift the SMR reaction forward thus producing more H2 and CO. Reverse SMR is one of the main reactions grouped in biomass gasification reaction chemistry. Although reverse SMR is a highly exothermic reaction with ΔHrxn, 298K of -206 kJ mol-1, in the presence of methane as a gas feed, reaction equilibrium seems to shift to the right to form hydrogen and carbon monoxide. This likely scenario explains the more than 85% yield of hydrogen in the gas feed with a very high H2:CO ratio of 7.5 in one of the cases. The effect of temperature and methane concentration on biomass gasification was compared at 750oC, 850oC and 950oC in the presence of 5 mole% CH4 concentration. As seen in Figure10, methane activated biomass gasification reaction produces H2:CO ratio of 1.18 which is higher than that obtained from fixed bed biomass gasification but not suitable for hydrogen rich syngas production. Product gas composition obtained from methane activated biomass gasification reaction at 850oC and 950oC with 10 vol.% CH4 in gas feed on FeMo1 catalyst is shown in Figure 11. As shown in Figure 10, H2:CO ratio drops sharply when the methane concentration is increased to 10 mole% at 950oC whereas the decrease in H2:CO ratio is not as steep at 850oC. Decrease in H2:CO from 7.4 at 950oC to 3.7 when methane concentration was increased from 5 vol.% to 15 vol.% is possibly due to partial catalyst deactivation and reaction kinetics. Fe – Mo / ZSM-5 catalyst has a tendency to form carbon nanotube formation due to carbon deposition. It appears from H2:CO trend that optimum methane concentration in the gas feed gives hydrogen rich syngas. When excess methane is available in the reaction atmosphere, high temperature methane decomposition leads to coke deposition on the catalyst. However, it is important to note that the catalyst subjected to higher methane concentrations is not completely deactivated since the H2:CO ranges from 3.7 to 5 for 10-15 vol.% CH4 at 850oC and 950oC. Without catalyst and methane in the gas feed, H2:CO ratio reached a maximum of 0.9 which is typical for the given biomass gasification. Another possibility behind decrease in H2:CO is adverse effect of high gas feed methane concentrations on other hydrogen producing reactions like water gas shift. This may be possibly due to gradual increase in Fe:O ratio at the wustite-Fe interface when the temperature increases from 700oC to 950oC, leading to the loss of active sites on the surface and consequently leading to decrease in hydrogen production and a slight increase in carbon monoxide production 63 .



Figure 9 Representation of the type of C - O bonds in lignin. Note that R represents similar type of aromatic structure in the rest of proposed description of lignin molecule64

100%

Normalized Conc.

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

H2 CO CO2 CH4

84% 80%

80%

60%

40% 29% 24% 20%

21%

18%

14% 11% 5% 5% 1% 1%

0% 750 H2:CO = 1.18

850 Temperature (oC) H2:CO = 5.9

950 H2:CO = 7.45

Figure 10 Effect of Temperature on biomass gasification on MoFe1 catalyst in the presence of 5 vol.% methane at 750oC, 850oC, and 950oC


Page 18 of 31

Page 19 of 31

100%

81%

H2 CO CO2 CH4

77%

80%

Normalized Conc.

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


60%

40% 21% 20%

0%

17%

1% 1% 850

H2:CO = 5

1% 1%

Temperature (oC)

950

H2:CO = 3.8

Figure 11 Effect of Temperature on biomass gasification on MoFe1 catalyst in the presence of 5 vol.% methane at 750oC, 850oC, and 950oC

Standard deviation and 95% confidence interval for biomass gasification without methane and methane activated biomass gasification are shown in Table 5. Table 5: Statistical analysis for product composition of syngas components for reaction temperatures 850oC, 950oC without CH4 and CH4 concentration 5 to 15 vol.% Test Conditions

Syngas species H2 CO CO2 CH4

Average Standard Deviation 16.47 0.11 18.63 4.64 10.81 2.51 54.09 7.26

Confidence Interval ±0.15 ±6.43 ±3.48 ±10.06

950oC, No CH4

H2 CO CO2 CH4

16.35 23.78 4.60 55.27

1.26 8.11 3.29 11.93

±1.43 ±9.17 ±3.73 ±13.50

850oC, 5% CH4

H2 CO CO2 CH4

72.64 12.29 0.90 0.81

15.33 2.96 0.32 0.29

±21.2 ±4.1 ±0.45 ±0.4

850oC, 10% CH4

H2 CO CO2 CH4

81.58 16.42 1.05 0.94

0.78 0.44 0.61 0.55

±0.88 ±0.49 ±0.69 ±0.62

850oC, No CH4



Page 20 of 31

850oC, 15% CH4

H2 CO CO2 CH4

68.26 16.14 2.77 2.49

13.28 0.79 0.29 0.26

±18.41 ±1.10 ±0.40 ±0.36

950oC, 5% CH4

H2 CO CO2 CH4

74.90 10.04 4.73 4.26

13.98 1.94 3.86 3.48

±19.37 ±2.69 ±5.35 ±4.82

950oC, 10% CH

H2 CO CO2 CH4

63.30 16.83 0.82 0.74

20.41 6.64 0.61 0.55

±28.29 ±9.21 ±0.85 ±0.76

950oC, 15% CH

H2 CO CO2 CH4

70.84 18.93 2.13 3.83

1.57 1.45 3.01 0.00

±2.18 ±2.00 ±4.17 0


Page 21 of 31 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


Proposed reaction mechanism of synergistic methane – biomass gasification The following elementary reaction pathways are proposed to illustrate the interaction of methane with water molecules produced from biomass over the catalyst surface. Reactant molecules are associatively adsorbed on a single metal site (Fe or Mo) for simplification 65–69. The Langmuir – Hinshelwood adsorption mechanism is considered in our analysis (Table 6) (‘*’ represents an active site): Table 6: Proposed reaction pathway for synergistic methane – biomass gasification k6

(Eq 6) – methane adsorption on the active site

CH4(g) + * ⇌ CH4* k-6

k7

[R – C – OH] (g) + * ⇌ [R – C – O*H] k-7

k7

H2(g) + * ⇌ 2H* k-7

k9

[R – C – O*H] + H* ⇌ [R – C+ – O-*H2] k-9 k10 [R – C+ – O-*H2] ⇌ R’ + H2O* k-10 k11 CH4* + H2O* → CHO* + 2H2(g) + H* k12

CHO* + * ⇌ CO* + H* k-12

k13

[R – C – O*H] + H* ⇌ [R – C+ – O-*H2] k-13

k14

CO* + H2O* → CO2* + H2* k15

CO* ⇌ CO(g) + *

k-15 k16 CO2* ⇌ CO2(g) + * k-16 k17 2H* ⇌ H2(g) + * k-17 k18 H2* ⇌ H2(g) + * k-18

(Eq 7) – selective adsorption of functional group oxygen atom of the lignocellulosic biomass on Fe or Mo (Eq 8) – Gas phase hydrogen dissociation on catalyst surface (Eq 9) – Coordination of adsorbed oxygen with H2 present in the gas phase (Eq 10) – H2O molecule breaks off from the phenolic carbon and forms steam adsorbate (Eq 11) – First Equation of methane reforming with steam adsorbate from step 4 (Eq 12) – Intermediate CHO* converting to CO* and H* adsorbates (Eq 13) – Further phenolic oxygens coordinate with H* atom adsorbate and follows similar kinetics as Step 3 to Step 6 (Eq 14)– Water gas shift reaction (Eq 15) – CO* desorption (Eq 16) – CO2* desorption (Eq 17) – H* atom adsorbates combine to form gas phase H2 (Eq 18) – H2* desorption



Note that [R – C – OH] is the type of bond that is present in the lignin component of hardwood biomass. C – OH bonds are possibly activated on either Fe / Mo active sites which interacts with the surface and methane as described in the equations above. Based on the discussion of the experimental results of methane – biomass gasification, the common aspect for all methane concentrations and iron loadings was a high H2:CO ratio, 1 - 5 mole% CO2, CH4 yield 50 – 90% less than conventional biomass gasification, and high hydrogen mole% in the gas yield. This pathway can explain the major distinction between biomass gasification, methane dissociation, methane SMR, and synergistic methane – biomass gasification. Based on the experimental data, the following assumptions can be made for the above mechanistic model. Rate constant k18 >> k-18, which implies that desorption of H2 in gaseous form from the surface is fast step. On the contrary, based on the product composition, it could be argued that the rate constant k-16 >> k16 and rate constant k-15>>k15, implying that both CO2 and CO are highly stable on the surface, respectively. This could be due to the oxygen in CO and CO2 binding strongly with oxophilic Fe / Mo metals on the surface. This could also be the reason behind the 50-90% less yield obtained for CO and CO2. Equation 17 shows two surface hydrogen atoms forming H2*. Desorption of the surface H2 appears to be relatively easy if the assumption for Equation 17 was true. Among the fast, non-equilibrium reactions Equations 11 and 14, the rate of formation of CHO*, H2, and surface adsorbed H* must be higher than that of CO2* and H2* formation (k11>>k14), as apparent from the very low CO2 yield. Experimental studies indicate that water gas shift (WGS) does not contribute significantly to the gas yield apparent from low CO2 yield in the gas phase. Surface adsorbed atomic hydrogen (H*) is possibly in the neighborhood with other H* adsorbates, thus combining to form more hydrogen (H2) in the gas phase. Based on high hydrogen yield in the gas phase, it can be said that k17>>k-17. The remaining Equations 6, 9, 10, 12, and 14 could be competent in being the rate limiting steps. However, among these five equations, reactions from Equations 9 and 13 could be the rate limiting steps depending on the stability and binding energy of [R – C+ - O-*H] on the given surface. The mechanistic pathway proposed above for unique SMR reaction explains the high H2 yield (> 80 mole%) in the product gas.

Comparison of catalytic and non-catalytic biomass gasification Figure 12 and 13 compares the product composition and H2:CO ratios for hardwood biomass gasification without catalyst and external methane, biomass gasification on ZSM-5 catalytic support without methane, and methane activated biomass gasification with 5 vol.% and 10 vol.% CH4 on FeMo1 and FeMo2 catalysts. Biomass only gasification was performed non-catalytically and on ZSM-5. On FeMo1 and FeMo2 catalysts, biomass-methane experiments were performed with methane concentration 5% and 10%. The H2:CO ratio on ZSM-5 more than doubled compared to a typical non-catalytic test. This indicated that the presence of acid sites on ZSM-5 along with Fe active sites provide favorable atmosphere for water gas shift and SMR reactions. This is evident from the decrease in methane concentration and increase in carbon dioxide formation. The addition of Fe and Mo to ZSM-5 leads to the synergistic interaction between methane and biomass to produce hydrogen rich syngas. H2:CO increases significantly when methane-biomass gasification was performed on FeMo1 and FeMo2 catalyst. With 5% CH4 in gas feed, an H2:CO ratio of ~7 was obtained on FeMo1 which increased further to 10 on the FeMo2 catalyst. With 10% CH4 in the feed, H2:CO ratio is lower than that for 5% CH4, 5 for FeMo1 and ~8 for FeMo2 catalyst 22 ACS Paragon Plus Environment

Page 22 of 31

Page 23 of 31

respectively. Lower H2:CO ratios observed for higher methane concentrations is possibly due to rapid catalyst deactivation due to coke deposition and high temperature. The comparison of catalytic and non-catalytic biomass and methane activated biomass gasification was in tune with the proposed reaction mechanism in Table 6.

100%

H2 CO CO2 CH4

80%

Normalized Conc.

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


60%

89% 84%

55% 44%

40% 24% 25% 20%

19%

14% 13% 12%

9% 6% 1%1%

1% 1%

0% No catalyst / No CH4 ZSM-5 / No CH4

H2:CO = 0.35

H2:CO = 0.57

FeMo1 / 5% CH4

FeMo2 / 5% CH4

H2:CO = 6

H2:CO = 10

Figure 12 Hardwood biomass gasification without catalyst and external methane, biomass gasification on ZSM-5 catalytic support without methane, and methane activated biomass gasification with 5 vol.% CH4 on FeMo1 and FeMo2 catalysts.



100%

85%

H2 CO CO2 CH4

80%

Normalized Conc.

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 24 of 31

81%

55%

60%

44% 40% 24% 25% 19%

20%

17%

13% 12% 6%

1%1%

0% No catalyst / No CH4 ZSM-5 / No CH4

H2:CO = 0.35

H2:CO = 0.57

FeMo1 / 10% CH4

H2:CO = 5

11% 2% 2% FeMo2 / 10% CH4

H2:CO = 7.6

Figure 13 Hardwood biomass gasification without catalyst and external methane, biomass gasification on ZSM-5 catalytic support without methane, and methane activated biomass gasification with 10 vol.% CH4 on FeMo1 and FeMo2 catalysts.

Conclusions Co-gasification of methane-biomass was conducted on 0.5% Fe – 4% Mo / ZSM-5 and 1.5%Fe4%Mo/ZSM-5 catalysts. The results showed a synergy between additional methane and biomass that produced hydrogen-rich syngas with more than 80% hydrogen in the gas yield. The high hydrogen production on the Fe-Mo based catalyst was probably due to the oxophilic nature of both iron (Fe) and Molybdenum (Mo), which converted the oxygen in the various functional groups of lignin to steam that in turn reacted with the available methane to form more hydrogen. Catalyst surface and active sites on the metals were also favorable to the high-temperature water gas shift reaction (WGSR), as suggested by the multifold increase in the H2:CO ratio. However, the H2:CO ratio dropped by more than 50% when the methane concentration increased from 5 – 15 vol.%, possibly due to partial catalyst deactivation and adverse reaction kinetics. The synergistic biomassmethane non-oxidative gasification provided a good motivation for the catalytic conversion of biomass to fuels with natural gas utilization. The synergistic relationship between methane and hardwood biomass will be investigated in detail using transition metals like Ni and Ru along with DFT calculations for getting information of the reaction intermediates, activation barriers, transition state pathway, and high selectivity towards hydrogen.

Conflict of Interest This work was funded by the Department of Energy, National Energy Technology Laboratory, an agency of the United States Government, through a support contract with Leidos Research Support Team (LRST). Neither the United States Government nor any agency thereof, nor any of their 24 ACS Paragon Plus Environment

Page 25 of 31 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


employees, nor LRTS, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Acknowledgements Authors are pleased to acknowledge U.S Department of Energy and National Energy Technology Laboratory, Morgantown along with Leidos Research Support Team for the continuous support and cooperation for the specific work and broadly for the NETL Gasifier Support Stand Project (Project #: 10024037).

Supporting Information Moles of gas species (Table S1), Scanning Electron Microscopy (SEM) characterization of spent FeMo1 catalyst (Figures S1-S3)

References (1)

International Energy Agency’s webpage on World Energy Statistical Outlook, 2018, URL: https://www.iea.org/weo2018/

(2)

Intergovernmental panel on climate change – report 2018.

(3)

Hansen, J.; Ruedy, R.; Sato, M.; Lo, K. Global surface temperature change, Reviews of geophysics 2010, 48, 1–29.

(4)

Lindsey, R.; Dlugokencky, E. Climate change – atmospheric carbon dioxide, Climate.gov 2019, 8431, 1–5.

(5)

Renewables 2018, Intergovernmental Energy Agency - report 2018.

(6)

Annual Energy Outlook, U.S. Energy Information Agency administration - report 2016.

(7)

Fantini, M. Biomass Availability , Potential and Characteristics., Biorefineries, 2017, 2, 2152.

(8)

Molino A.; Larocca V.; Chianese S.; Musmarra D.; Biofuels Production by Biomass Gasification: A Review, energies 2018, 11,811, 1–31.

(9)

Qian, K.; Kumar, A.; Patil, K.; Bellmer, D.; Wang, D.; Yuan, W.; Huhnke, R. L. Effects of Biomass Feedstocks and Gasification Conditions on the Physiochemical Properties of Char. 25 ACS Paragon Plus Environment


energies 2013, 6, 3972–3986. (10)

Uzi, A.; Shen, Y.; Kawi, S.; Levy, A.; Wang, C. Permittivity and chemical characterization of woody biomass during pyrolysis and gasification. Chem. Eng. J. 2019, 355, 255–268.

(11)

Fatih Demirbas, M.; Balat, M. Biomass pyrolysis for liquid fuels and chemicals: A review. J. Sci. Ind. Res. 2007, 66, 797-804

(12)

Kumar, A.; Jones, D. D.; Hanna, M. A. Thermochemical Biomass Gasification: A Review of the Current Status of the Technology, energies 2009, 2, 556–581.

(13)

Czernik, S.; Bridgwater, A. V., Overview of Applications of Biomass Fast Pyrolysis Oil, Energy and Fuels 2004, 18 (2), 590–598.

(14)

Wang, D.; Czernik, S.; Chornet, E. Production of Hydrogen from Biomass by Catalytic Steam Reforming of Fast Pyrolysis Oils. Energy and Fuels 1998, 12(1), 19–24.

(15)

Bridgwater, A. V. Review of fast pyrolysis of biomass and product upgrading. Biomass and Bioenergy 2012, 38, 68–94.

(16)

Chen, N. Y.; Walsh, D. E.; Koenig, L. R., Fluidized-Bed Upgrading of Wood Pyrolysis Liquids and Related Compounds In: Pyrolysis Oils from Biomass, ACS Symposium Series 1988, 277–289.

(17)

Gayubo, A. G.; Aguayo, A. T.; Atutxa, A.; Aguado, R.; Bilbao, J. Transformation of Oxygenate Components of Biomass Pyrolysis Oil on a HZSM-5 Zeolite. I. Alcohols and Phenols, Ind. Eng. Chem. Res. 2004, 43, 2610-2618

(18)

Czernik, S.; Bridgwater, A. V., Overview of Applications of Biomass Fast Pyrolysis Oil, Energy and Fuels 2004, 18 (2), 590–598.

(19)

Sharma, R. K.; Bakhshi, N. N. Catalytic Upgrading of Pyrolysis Oil, Energy and Fuels 1993, 7, 306 - 314

(20)

Carlson, T. R.; Vispute, T. P.; Huber, G. W. Green Gasoline by Catalytic Fast Pyrolysis of Solid Biomass Derived Compounds, ChemSusChem 2008, 1, 397 - 400.

(21)

French, R.; Czernik, S. Catalytic pyrolysis of biomass for biofuels production, Fuel Process. Technol. 2010, 91, 25 - 32.

(22)

Mohan, D.; Pittman, C. U.; Steele, P. H. Pyrolysis of Wood/Biomass for Bio-oil: A Critical Review Dinesh. Energy and Fuels 2006, 20, 848–889.

(23)

Huber, G. W.; Corma, A. Angewandte Chemie - International Edition. Synergies between Bio- and Oil Refineries for the Production of Fuels from Biomass, 2007, 46, 7184 - 7201. 26 ACS Paragon Plus Environment

Page 26 of 31

Page 27 of 31 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


(24)

Wright, M. M.; Brown, R. C.; Boateng, A. A. Distributed processing of biomass to bio-oil for subsequent production of Fischer-Tropsch liquids, Biofuels, Bioprod. Biorefining 2008, 2, 229 - 238.

(25)

Mettler, M. S.; Vlachos, G.; Dauenhauer, P. J. Top ten fundamental challenges of biomass pyrolysis for biofuels, Energy and Environmental Science 2012, 5, 7797–7809.

(26)

Evans R.J.; Milne, T.A. Chemistry of Tar Formation and Maturation in the Thermochemical Conversion of Biomass In. Bridgwater A.V., Boocock D.G.B. (eds) Developments in Thermochemical Biomass Conversion. Springer, Dordrecht, 1997.

(27)

Demirbaş, A. Yields of oil products from thermochemical biomass conversion processes, Energy Convers. Manag. 1998, 39(7), 685–690.

(28)

Gallezot, P.; Pinel, C. Conversion of Biomass into Chemicals over Metal Catalysts, Chemical reviews 2014, 114, 1827-1870.

(29)

Mullen, C. A.; Boateng, A. A.; Dadson, R. B.; Hashem, F. M. Biological Mineral Range Effects on Biomass Conversion to Aromatic Hydrocarbons via Catalytic Fast Pyrolysis over HZSM-5, Energy and Fuels 2014, 28, 7014–7024.

(30)

Xie, Y.; Su, Y.; Wang, P.; Zhang, S.; Xiong, Y. In-situ catalytic conversion of tar from biomass gasification over carbon nanofibers- supported Fe-Ni bimetallic catalysts, Fuel Process. Technol. 2018, 182, 77–87.

(31)

Wang, A.; Song, H. Maximizing the production of aromatic hydrocarbons from lignin conversion by coupling methane activation, Bioresour. Technol. 2018, 268 (July), 505–513.

(32)

Balagurumurthy, B.; Singh, R.; Bhaskar, T. Catalysts for Thermochemical Conversion of Biomass In: Recent Advances in Thermo-Chemical Conversion of Biomass; Elsevier Inc. 2015; 109–132.

(33)

Nishikawa, J.; Nakamura, K.; Asadullah, M.; Miyazawa, T.; Kunimori, K.; Tomishige, K. Catalytic performance of Ni/CeO2/Al2O3 modified with noble metals in steam gasification of biomass, Catal. Today 2008, 131, 146 - 155.

(34)

Ye, M.; Tao, Y.; Jin, F.; Ling, H.; Wu, C.; Williams, P. T. Enhancing hydrogen production from the pyrolysis-gasification of biomass by size-confined Ni catalysts on acidic MCM41 supports, Catal. Today 2018, 307, 154–161.

(35)

Zhang, J.; Li, X.; Xie, W.; Hao, Q.; Chen, H.; Ma, X. Handy synthesis of robust Ni/carbon catalysts for methane decomposition by selective gasification of pine sawdust, Int. J. 27 ACS Paragon Plus Environment


Hydrogen Energy 2018, 43, 19414 - 19419. (36)

Shahbaz, M.; Inayat, A.; Onoja, D.; Ammar, M. The influence of catalysts in biomass steam gasification and catalytic potential of coal bottom ash in biomass steam gasification: A review, Renewable and sustainable energy reviews 2017, 73, 468–476.

(37)

Sutton, D.; Kelleher, B.; Ross, J. R. H. Review of literature on catalysts for biomass gasification, Fuel processing technology 2001, 73, 155-173.

(38)

Chaiprasert, P.; Vitidsant, T. Effects of promoters on biomass gasification using nickel/dolomite catalyst, Korean J. Chem. Eng. 2009, 26, 1545–1549.

(39)

Kumar, A; Yang, Z; Apblett, A. W. Synergistic co-pyrolysis of biomass and methane for hydrobarbon fuels and chemicals production, Int. patent numberWO 2016/196517 Al 2016.

(40)

Robinson, B.; Bai, X.; Samanta, A.; Abdelsayed, V.; Shekhawat, D.; Hu, J. Stability of Feand Zn-Promoted Mo/ZSM-5 Catalysts for Ethane Dehydroaromatization in Cyclic Operation Mode. Energy & Fuels 2018, 32, 7810–7819.

(41)

Galvita, V.; Sundmacher, K. Hydrogen production from methane by steam reforming in a periodically operated two-layer catalytic reactor, Appl. Catal. A Gen. 2005, 289, 121 - 127

(42)

Blasco, T.; Corma, A.; Martínez-Triguero, J. Hydrothermal stabilization ofZSM-5 catalyticcracking additives by phosphorus addition, J. Catal. 2006, 237, 267 - 277

(43)

Ogura, M.; Shinomiya, S. Y.; Tateno, J.; Nara, Y.; Nomura, M.; Kikuchi, E.; Matsukata, M. Alkali-treatment technique — new method for modification of structural and acid-catalytic properties of ZSM-5 zeolites, Appl. Catal. A Gen. 2001, 219, 33 - 43.

(44)

Kutteri, D. A.; Wang, I.; Samanta, A.; Li, L.; Hu, J. Methane decomposition to tip and base grown carbon nanotubes and COx-free H2 over mono- and bimetallic 3d transition metal catalysts. Catal. Sci. Technol. 2018, 8, 858–869.

(45)

Zhang, L.; Wang, X.; Millet, J. M. M.; Matter, P. H.; Ozkan, U. S. Investigation of highly active Fe-Al-Cu catalysts for water-gas shift reaction, Appl. Catal. A Gen. 2008, 351, 1-8.

(46)

Wang, X.; Gorte, R. J. The effect of Fe and other promoters on the activity of Pd/ceria for the water-gas shift reaction. Appl. Catal. A Gen. 2003, 247, 157 - 162.

(47)

Andreeva, D.; Tabakova, T.; Idakiev, V.; Christov, P.; Giovanoli, R. Au/α-Fe2O3 catalyst for water±gas shift reaction prepared by deposition±precipitation, Appl. Catal. A Gen. 1998, 169, 9 - 14.

(48)

Wang, A.; Austin, D.; Qian, H.; Zeng, H.; Song, H. Catalytic Valorization of Furfural under 28 ACS Paragon Plus Environment

Page 28 of 31

Page 29 of 31 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


Methane Environment, ACS Sustain. Chem. Eng. 2018, 6, 8891–8903. (49)

Pineda, D. I. Modeling Biomass Gasification Surface Reactions: The Effect of Hydrogen Inhibition, thesis Univ. of Cali. 2014.

(50)

Biagini, E.; Lippi, F.; Petarca, L.; Tognotti, L. Devolatilization rate of biomasses and coalbiomass blends: an experimental investigation, Fuel 2002, 81, 1041–1050.

(51)

Albadri, S.; Jiang, Y.; Wagland, S. Reduce toxic emissions of As, Cr, and Cu phases during woody biomass gasification: A thermodynamic equilibrium study, International scientific journal of environmental science (conference paper) 2018.

(52)

Nikoo, M. B.; Mahinpey, N. Simulation of biomass gasification in fluidized bed reactor using ASPEN PLUS, Biomass and bioenergy 2008, 32, 1245–1254.

(53)

Gebhard, S.C.; Wang, D; Overend, R. P., Paisley M.A. Catalytic Conditioning of synthesis gas produced by biomass gasification. Biomass and bioenergy 1994, 7, 307–313.

(54)

Zhou, B.; Dichiara, A.; Zhang, Y.; Zhang, Q.; Zhou, J. Tar formation and evolution during biomass gasification: An experimental and theoretical study. Fuel 2018, 234, 944–953.

(55)

Rakesh, N.; Dasappa, S. A critical assessment of tar generated during biomass gasification - Formation, evaluation, issues and mitigation strategies. Renew. Sustain. Energy Rev. 2018, 91, 1045–1064.

(56)

Ferrin, P.; Simonetti, D.; Kandoi, S.; Kunkes, E.; Dumesic, J. A.; Nørskov, J. K.; Mavrikakis. Modeling Ethanol Decomposition on Transition Metals: A Combined Application of Scaling and Brønsted-Evans-Polanyi Relations. J.A.C.S articles 2009, 20, 5809–5815.

(57)

Lucia, M.; Rios, V.; González, A. M.; Eduardo, E.; Lora, S.; Agustin, O. Reduction of tar generated during biomass gasification: A review. Biomass and Bioenergy 2018, 108, 345– 370.

(58)

Pérez, J. F.; Melgar, A.; Benjumea, P. N. Effect of operating and design parameters on the gasification/combustion process of waste biomass in fixed bed downdraft reactors: An experimental study. Fuel 2012, 96, 487–496.

(59)

Li, Y.; Wang, Y.; Zhang, X.; Mi, Z. Thermodynamic analysis of autothermal steam and CO2 reforming of methane. Int. J. Hydrogen Energy 2008, 33(10), 2507–2514.

(60)

Kargbo, D. M.; Wilhelm, R. G.; Campbell, D. J. Natural Gas Plays in the Marcellus Shale: Challenges and Potential Opportunities. Environ. Sci. Technol., 2010, 44 (15), 5679–5684. 29 ACS Paragon Plus Environment


(61)

Page 30 of 31

Wang, D.; Lunsford, J. H.; Rosynek, M. P. Characterization of a Mo/ZSM-5 Catalyst for the Conversion of Methane to Benzene. J. Catal. 1997, 169, 347–358.

(62)

Kepp, K. P. A Quantitative Scale of Oxophilicity and Thiophilicity, Inorganic chem. 2016, 55, 9461-9470.

(63)

Chen, R. Y.; Yuen, W. Y. D. Review of the High-Temperature Oxidation of Iron and Carbon Steels in Air or Oxygen. Oxidation of metals 2003, 59, 433-467.

(64)

Structure of lignocellulosic biomass, Springer Briefs Green Chemistry for Sustainability 2016.

(65)

Arcotumapathy V.; Alenazey F.S.; Al-Otaibi R.L.; Vo D-V.N.; Alotaibi F.M.; Adesoji A. Mechanistic investigation of methane steam reforming over Ce-promoted Ni/SBA-15 catalyst. Appl. Petrochemical Res. 2015, 5, 393–404.

(66)

Hou, K.; Hughes, R. The kinetics of methane steam reforming over a Ni/α-Al2O catalyst. Chem. Eng. J. 2001, 82, 311–328.

(67)

Froment, G. F. Production of synthesis gas by steam- and CO2-reforming of natural gas J. Mol. Catal. A Chem. 2000, 163, 147–156.

(68)

Maier, L.; Schädel, B.; Delgado, K. H.; Tischer, S.; Deutschmann, O. Methane Over Nickel: Development of a Multi-Step Surface Reaction Mechanism. Top. Catal. 2011, 54, 845– 858.

(69)

Maestri, M.; Vlachos, D. G.; Beretta, A.; Groppi, G.; Tronconi, E. Steam and dry reforming of methane on Rh: Microkinetic analysis and hierarchy of kinetic models 2008, 259, 211–222.


J. Catal.

Page 31 of 31 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


Figure: TOC Graphic

Synopsis: Novel biomass – flare gas synergistic co-processing to produce hydrogen rich syngas on FeMo/ZSM-5 to prevent flaring of natural gas and utilize sustainable energy source such as biomass

--END--


Hydrogen Rich Syngas Production through Synergistic Methane

Recommend Documents