A Romero

AL Kustov

DL Trimm

E Kok

G Zhanga

H Zhang

J Engbæk

J Gao

J Kopyscinski

J Sehested

M Kimura

P Panagiotopoulou

PK Cheekatamarla

T Bligaard

V Frøseth

VM Lebarbier

Y Bang

Y Huang

Y Yu

Z Kowalczyk

Applied Petrochemical Research

Zhong He

Xiaolong Wang

Shiwang Gao

Tiancun Xiao

Crossref

ORIGINAL ARTICLEEffect of reaction variables on CO methanation process over NiO–La2O3–MgO/Al2O3 catalyst for coal to synthetic natural gasZhong He1 • Xiaolong Wang1 • Shiwang Gao1 • Tiancun Xiao1Received: 21 June 2015 / Accepted: 10 July 2015 / Published online: 29 July 2015 The Author(s) 2015. This article is published with open access at Springerlink.comAbstract Reaction variables for methanation processwere investigated using self-independently developedNiO–La2O3–MgO/Al2O3 catalyst in a big lab scale reactor.The effects of reaction parameters, such as temperature,pressure, H2/CO flow ratio and space velocity on theactivity of methanation catalyst were studied. 100 % COconversion and 95 % of selectivity of methane can beachieved at 400 C and 3 MPa with the feed ratio of H2/CO as 3.25:1 and space velocity of 12,000 h-1.The opti-mization reaction parameters were suggested on the basisof this work for the further development and commercial-ization of methanation catalyst.Keywords Methanation  Carbon monoxide  Syntheticnatural gas  CatalystIntroductionMethanation is one of the key techniques for the coal tosynthetic natural gas [1]. This technology requires catalystwith high activity and high stability due to the strongexothermicity of the methanation reaction. Currently,commercial methanation technology is being supplied byLurgi (LURGI), Johnson Matthey (DAVY) and Topsoe(TOPSØE). All of these processes are equipped with afixed-bed reactor [2–4]. Ni-based catalyst is often the mostpractical choice for methanation because of its relativelyhigh activity and low price. NiO/Al2O3 catalysts have beenintensively explored for the methanation of carbonmonoxide [5].A satisfactory methanation catalyst should be excellent,coking-resistant, and possess high thermal stability at hightemperature and pressure [6–8]. The target of this work isto develop a nickel-based catalyst. It is found that theaddition of lanthanum increased the catalyst stability [9].MgO was found to be an effective promoter to improveresistance to carbon deposition and to minimize Ni parti-cles’ sintering [10–12]. In this paper, we would like tostudy the effect of the reaction conditions on the NiO–La2O3–MgO/Al2O3 catalyst to investigate the effects ofreaction variables on the methanation. Moreover, theoperation parameters would be optimized for the furtherdevelopment and commercialization of methanationcatalyst.Experimental methodExperimental deviceAll the experiments were carried out with a high-temper-ature, high-pressure fixed-bed reactor system. The flowchart of the experimental apparatus is shown in Fig. 1. Thesystem is composed of three parts, which are gas mixersystem, reactor system and analysis system. The feed gas isdecompressed by the pressure-reducing valves of differentgas cylinders. The flow rate of feed gas is controlled by amass flowmeter. After mixing, proportional synthesis gas isintroduced into the high-pressure reactor. The tail gas fromthe reactor is cooled with 10 C cold water trap to convertit into gas and liquid phases. Then the outlet gas filtered bydryer is connected to an Agilent GC 7890B instrument foronline measurement. The liquid product collected from the& Tiancun Xiaoxiaotiancun@hnceri.com1 Huaneng Clean Energy Research Institute, Beijing 102209,China123Appl Petrochem Res (2015) 5:413–417DOI 10.1007/s13203-015-0127-9liquid collector was weighed and analyzed afterward.During the reaction, the content of all components wasanalyzed by GC 7890B, such as CO, CO2, H2, CH4, C2H6and C3H8 by TCD and FID detectors with proper columnseparation. Carbon monoxide conversion (CCO), methanespace–time yield (STYCH4) and selectivity to methane (Sm)were determined by following formulas:CCO ¼ VCO;in  VCO;outVCO;in 100 %CH2 ¼VH2;in  VH2;outVH2;in 100 %STYCH4 ¼VCH4;out  16  60mcat  22; 400 ðg  kg1cat  h1ÞSmCH4 ¼VCH4;outVCO;in  VCO;outmcat: Mass of the catalyst (g); Vi,in (ml/min) and Vi,out (ml/min) are the inlet and outlet volumetric flow rate of speciesi (i = CO, CH4), respectively.Catalyst preparationThe NiO–La2O3–MgO/Al2O3 catalyst precursor was pre-pared using coprecipitation method at constant pH. Aqu-eous solutions of the metal nitrates and the precipitatingagent (NaOH/Na2CO3) were simultaneously dripped intobeaker. The pH during precipitation in the stirred beakerwas maintained at a constant value 8. After finishing theaddition of the precipitation agent, the resultant slurry wasaged at 80 C for 12 h under constant stirring, followed byfiltration, washing and drying overnight at 120 C. Thecatalyst precursor was calcined in a muffle burner at450 C for 4 h. Graphite and cement were added in thecatalyst precursor for granulation and tableting, steam andcuring treatment. The resultant catalyst products have NiOcontent of 40 wt %, MgO content of 15 wt % and La2O3content of 5 wt %. It has relatively more meso-pores withaverage pore size of 9.5 nm. It was ground and meshed to425–850 lm particles for experiments.Catalyst evaluationThe catalyst sample was loaded into a pressurized fixed-bed reactor. Firstly, a gas stream consisting of H2:N2 withratio of 1:4 was used for NiO reduction for 4 h at tem-perature of 550 C. Then, the reactor was cooled to 200 Cat the end of the reduction. The pressure of the system wasslowly increased with nitrogen gas. The feed gas wasswitched into the reactor gradually to the required pressure.The activity of methanation catalyst was tested for reactiontemperature of 250–700 C, the reaction pressure of1–4 MPa, the flow ratio of the H2/CO as 2:1–4:1 and thespace velocity of 6000–48,000 h-1.Result and discussionReaction temperatureHolding the reactor pressure at 1 MPa, a space velocity of12,000 h-1 and H2/CO of flow rate of 3, the effect oftemperature on methanation reaction was investigated from250 to 700 C. The experiment results are shown in Fig. 2.With increase of temperature, carbon monoxide andhydrogen conversion rate, selectivity and space–time yieldof methane were firstly increased and then decreasedgradually. When the reactor temperature reached 400 C,the CO conversion and the H2 conversion reached thehighest value. This is due to the methanation reaction beingan exothermic reaction; lower temperature favors the COFig. 1 Flow chart of the experimental apparatusFig. 2 CO and H2 conversion, CH4 selectivity, and CH4 space–timeyield at different temperatures at 1 MPa, H2/CO = 3,SV = 12,000 h-1414 Appl Petrochem Res (2015) 5:413–417123conversion [13]. When the reaction temperature increased,the equilibrium constant of the reaction rate decreased,leading to a lower CO conversion. Moreover, the metha-nation reaction is a reversible reaction. Methanation reac-tion equilibrium moves in the reverse direction at highertemperature. All this would inhibit the conversion of CO athigh temperature [14].For methanation reaction, the basic requirements for thecatalyst are that it must maintain the activity at the tem-peratures during the normal operation, meanwhile, itshould be able to start up the reaction at the possible lowesttemperature so as to keep the inlet temperature as low aspossible. This would relieve the thermal effects of theentire reactor bed [15]. Under our experimental conditions,the optimal temperature range is between 350 and 450 C;methanation reached the desired CO conversion between350 and 450 C temperature range, which is consistentwith the thermodynamic prediction of methanation byprevious researchers [16, 17].Reaction pressureMaintaining a temperature of 350–450 C, a space velocityof 12,000 h-1, H2/CO ratio of flow rate of 3, the effect ofpressure on methane synthesis reaction was studied from 1to 4 MPa. The experiment results are shown in Figs. 3, 4and 5.Figures 3, 4 and 5 present the change of carbonmonoxide and hydrogen conversion, methane selectivityand STY at different temperatures and different pressures.When the temperature was 350 C, the conversion rate ofcarbon monoxide, hydrogen and methane increased grad-ually with the increase of pressure, while the selectivity ofmethane increased and then tended to be stable. The space–time yield of methane was gradually increased with theincrease of pressure as well. The carbon monoxide conversion rate remained at 100 % as the pressureincreased, when the temperature was 400–450 C. How-ever, the space–time yield of methane remained constantwhen the temperature was 400–450 C. According to thekinetics of the reaction, the number of moles of carbonmonoxide methanation reaction is reduced; increasing ofpressure is in favor of the reaction equilibrium because thereaction constant is shifted to the gas volume decreasingdirection [18, 19]. The experimental data showed that theconversion of carbon monoxide can be improved at a rel-atively low temperature with the increase of pressure.However, the increase of pressure has little effect on theconversion of carbon monoxide when temperature is higherthan 350 C. It indicated the high pressure was not nec-essary for methanation reaction pressure at high tempera-ture. When the pressure increases to a certain degree, thecatalyst activity is not affected. The optimal pressure mustbe determined when considering the load of industrialFig. 3 CO and H2 conversion, CH4 selectivity, and CH4 space–timeyield at different pressures at 350 C, H2/CO = 3, SV = 12,000 h-1Fig. 4 CO and H2 conversion, CH4 selectivity, and CH4 space–timeyield at different pressures at 400 C, H2/CO = 3, SV = 12,000 h-1Fig. 5 CO and H2 conversion, CH4 selectivity, and CH4 space–timeyield at different pressures at 450 C, H2/CO = 3, SV = 12,000 h-1Appl Petrochem Res (2015) 5:413–417 415123production and the thermodynamic effects of methanationreaction in the normal production process.H2/CO ratio of the syngasMaintaining a temperature of 400 C, 1 MPa pressure, theeffect of H2/CO ratio on methane synthesis reaction wasstudied at flow rate of 2:1, 2.5:1, 3:1, 3.25:1, 3.5:1, 3.75:1and 4:1. The experiment results are shown in Fig. 6.Figure 6 shows that the trends of methane selectivityand the space–time yield of carbon monoxide and hydro-gen change with the H2/CO ratio. However, the carbonmonoxide conversion rate tended to be stable at the H2/COratio of more than 3. The best theoretical molar ratio of themethane reaction is H2/CO flow ratio of 3:1, when the masstransfer process is not considered [20]. However, in orderto avoid carbon deposition on the surface of nickel catalyst,the practical reaction condition of H2/CO ratio is usuallyhigher than the stoichiometric ratio [21, 22]. The conver-sion rate of carbon monoxide and the space–time yield ofmethane were highest when the H2/CO ratio of the raw gaswas 3.25:1, which was suggested as most suitable for theprocess of methane conversion.Space velocityMaintaining a temperature of 400 C, 1 MPa pressure, H2/CO ratio of flow rate of 3.25:1, the effect of space velocityon methane synthesis reaction was studied at 6000, 12,000,18,000, 24,000 and 48,000 h-1 conditions. The experimentresults are shown in Fig. 7.Figure 7 shows that the conversion of carbon monoxideand hydrogen, selectivity and the space–time yield ofmethane are increased with the increase of space velocity.The methanation reaction activity was gradually decreasedwhen the velocity is higher than 12,000 h-1. Then, thespace–time yield of methane downward trend is moresignificant. This is because the contact time between thefeed gas and the catalyst surface becomes shorter at highspace velocity. The effective collision between reactantsand feed gas is reduced, and the conversion efficiency ofthe methanation reaction is reduced. Production at lowspace velocity is beneficial to improve single pass con-version of carbon monoxide in the actual production pro-cess, but productivity of the reactor will be very low.Single pass conversion rate was lower in high spacevelocity operating conditions. In order to improve the uti-lization efficiency of the feed gas, the feed gas needs manycycles, which will increase the operation cost. Thus, aproper space velocity needs to be selected to ensure that thecatalyst activity is optimal in the actual production. Ourexperimental results suggest that the space velocity of12,000 h-1 gives a balance of operation and productivity.ConclusionIn this study, the effects of the reaction variables such astemperature, pressure, H2/CO ratio of the feed and spacevelocity on the activity of methanation catalyst for COmethanation have been investigated. According to theexperimental results, the high pressure was not necessaryfor methanation reaction pressure at high temperature. Theoptimal pressure needs to be determined when consideringthe load of industrial production and the thermodynamiceffects of methanation reaction in the normal productionprocess. From our experimental, the optimal temperaturerange is between 350 and 500 C, the optimal H2/CO ratioFig. 6 CO and H2 conversion, CH4 selectivity, and CH4 space–timeyield at different H2/CO ratios at 400 C, 1 MPa, SV = 12,000 h-1Fig. 7 CO and H2 conversion, CH4 selectivity, and CH4 space–timeyield at different space velocities at 400 C, 1 MPa and H2/CO = 3.25416 Appl Petrochem Res (2015) 5:413–417123of the raw gas is 3.25:1 and the optimal space velocity is12,000 h-1. These parameters were suggested as mostsuitable for the process of syngas to methane conversion.Acknowledgments This work presented in this paper was fundedby China Huaneng Group (CERI/TY-14-HJK04). The authors wouldalso like to thank Professor Shuren Hao for providing constructiveadvice.Open Access This article is distributed under the terms of theCreative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricteduse, distribution, and reproduction in any medium, provided you giveappropriate credit to the original author(s) and the source, provide alink to the Creative Commons license, and indicate if changes weremade.References1. Kopyscinski J, Schildhauer TJ, Biollaz SMA (2010) Productionof synthetic natural gas (SNG) from coal and dry biomass—atechnology review from 1950 to 2009. Fuel 89:1763–17832. Kustov AL, Frey AM, Larsen KE et al (2007) CO methanationover supported bimetallic Ni–Fe catalysts: from computationalstudies towards catalyst optimization. Appl Catal A Gen320:98–1043. 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Effect of reaction variables on CO methanation process over NiO–La2O3–MgO/Al2O3 catalyst for coal to synthetic natural gas

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Effect of reaction variables on CO methanation process over NiO–La2O3–MgO/Al2O3 catalyst for coal to synthetic natural gas

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