Research Article
Ni/SiO2Catalyst Prepared with Nickel Nitrate
Precursor for Combination of CO2Reforming and
Partial Oxidation of Methane:Characterization and Deactivation Mechanism Investigation
Sufang He,1Lei Zhang,2Suyun He,2Liuye Mo,3
Xiaoming Zheng,3Hua Wang,1and Yongming Luo2
1Research Center for Analysis and Measurement,Kunming University of Science and Technology,Kunming650093,China
2Faculty of Environmental Science and Engineering,Kunming University of Science and Technology,Kunming650500,China
3Institute of Catalysis,Zhejiang University,Key Lab of Applied Chemistry of Zhejiang Province,Hangzhou310028,China
Correspondence should be addressed to Y ongming Luo;environcatalysis222@https://www.doczj.com/doc/ed5347558.html,
Received5August2014;Revised6January2015;Accepted6January2015
Academic Editor:Mohamed Bououdina
Copyright?2015Sufang He et al.This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use,distribution,and reproduction in any medium,provided the original work is properly cited.
The performance of Ni/SiO2catalyst in the process of combination of CO2reforming and partial oxidation of methane to produce syngas was studied.The Ni/SiO2catalysts were prepared by using incipient wetness impregnation method with nickel nitrate as a precursor and characterized by FT-IR,TG-DTA,UV-Raman,XRD,TEM,and H2-TPR.The metal nickel particles with the average size of37.5nm were highly dispersed over the catalyst,while the interaction between nickel particles and SiO2support is relatively weak.The weak NiO-SiO2interaction disappeared after repeating oxidation-reduction-oxidation in the fluidized bed reactor at 700°C,which resulted in the sintering of metal nickel particles.As a result,a rapid deactivation of the Ni/SiO2catalysts was observed in2.5h reaction on stream.
1.Introduction
The Ni-based catalyst has recently attracted considerable attention due to the plentiful resources of nickel,as well as its low cost and good catalytic performance comparable to those of noble metals for many catalytic reactions,such as hydrogenation of olefins and aromatics[1],methane reforming[2],and water-gas shift reaction[3].Therefore,Ni-based catalyst is believed to be the most appropriate catalyst applied in the industrial process[4–6].It is generally accepted that the catalytic performance of Ni-based catalyst is closely related to several parameters,including the properties of support,preparation method,and active phase precursor employed.
Support plays an important role in determining the performance of Ni-based catalyst.Generally,a support with high surface areas is very necessary since it is effective in increasing Ni dispersion and improving thermal stability, hence not only providing more catalytically active sites,but also decreasing the deactivation over time of the catalysts due to sintering and migration effects[7,8].For its good thermostability,availability,and relative high specific surface area,SiO2support was widely used for preparing Ni-based catalyst[9].In particular,spherical silica is successfully used as a catalyst support in fluidized bed reactor due to its high mechanical strength.
The method of catalyst preparation is another key param-eter which needs to be optimized because it will result in different structural and textural properties of Ni-based catalyst.Therefore,numerous methods,including precipi-tation,homogeneous deposition-precipitation,and sol-gel techniques,have been developed to enhance the performance of Ni-based catalyst[10–18].However,allthe above method-ologies mentioned are too complex or expensive to scale
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up in industry.The incipient wetness impregnation(IWI) is one of the most extensively used method[19–23]due to its simplicity in practical execution on both laboratory and industrial scales,in addition to its facility in controlling the loading amount of the active ingredient.
In addition,the choice of the precursor salt is also crucial since it determines whether the Ni-based catalyst will be prepared successfully or not.As an efficient precursor,two terms must be met:firstly,high solubility is desirable because the precursor concentration in the impregnation solution must be high[24];secondly,the ability to be decomposed during calcinations is prerequisite since the precursor must be fully transformed into oxide particles without leaving side species that may modify the properties of the support [24].As a result,owing to its commercial availability and low cost,as well as its high solubility in water and effortless decomposition at moderate temperatures,nickel nitrate is the precursor most often used in the preparation of Ni-based catalyst[23,24].
In this paper,Ni/SiO2catalyst was prepared by incipient wetness impregnation(IWI)with nickel nitrate as precursor and tested in the process of combination of CO2reforming and partial oxidation of methane(CRPOM)to produce syngas.TG-DTA,HR-TEM,IR,UV-Raman,XRD,and H2-TPR were employed to characterize the Ni/SiO2catalysts in detail to reveal the relationship between synthesis,properties, and catalytic performances as well as to investigate the causes of deactivation.
2.Experimental Section
2.1.Catalyst Preparation.The Ni/SiO2catalysts were pre-pared with IWI using nickel nitrate as precursor according to our previous works[21,22].The SiO2was commer-cially obtained(S BET=498.8m2/g,Nanjing Tianyi Inorganic Chemical Factory).Prior to use,the SiO2was pretreated with5%HNO3aqueous solution for48h and then washed with deionized water until the filtrate was neutrality.The size of SiO2was selected between60and80mesh.It was then impregnated with an aqueous solution of nickel nitrate. The obtained sample was dried overnight at100°C and subsequently calcined in air at700°C for4h.Unless otherwise stated,the loading of Ni was3wt%,and the calcination temperature was700°C.The Ni/SiO2catalyst was designated as3NiSN.
2.2.Catalytic Reaction.The catalytic reaction was performed in a fluidized-bed reactor that was comprised of a quartz tube (I.D.=20mm,H=750mm)under atmospheric pressure at700°C.Prior to reaction,2mL of catalyst was reduced at700°C for60min under a flow of pure hydrogen at atmospheric pressure with a flow rate of50mL/min.A reactant gas stream that consisted of CH4,CO2,and O2,with a molar ratio of1/0.4/0.3,was used with a gas hourly space velocity(GHSV)of9000h?1.The feed gas was controlled by mass flow controllers.The effluent gas cooled in an ice trap was analyzed with an online gas chromatograph that was equipped with a packed column(TDX-01)and a thermal conductivity detector.Under our reaction conditions,the oxygen in the feed gas was completely consumed in all cases.
2.3.Catalyst Characterization.FTIR spectra were measured using a Nicolet560spectrometer equipped with a MCT detector.The samples were tabletted to thin discs with KBr.
Thermogravimetric analysis(TGA)and differential ther-mal analysis(DTA)were performed on a PERKIN ELMER-TAC7/DX with a heating rate of10°C/min under oxygen (99.99%,20mL/min).The samples were pretreated with oxygen flow at383K for1h.
UV-Raman spectra were carried out with a Jobin Yvon LabRam-HR800instrument,using325.0nm Ar+laser radi-ation.The excitation laser was focused down into a round spot approximately2μm in diameter.The resolution was 4cm?1and1000scans were recorded for every spectrum.The catalysts were ground to particle diameters<150μm before analysis.
X-ray powder diffraction(XRD)patterns of samples were obtained with an automated power X-ray diffractometer (Rigku-D/max-2550/PC,Japan)equipped with a computer for data acquisition and analysis,using Cu Kαradiation, at40kV and300mA.The reduced samples were priorly reduced at700°C for1h and cooled to room temperature in hydrogen atmosphere,but the fresh samples were used directly after calcined in air at700°C for4h.All the samples were ground to fine powder in an agate mortar before XRD measurements.
Transmission electron microscopy(TEM)images were recorded on a Philips-FEI transmission electron microscope (Tecnai G2F30S-Twin,Netherlands),operating at300kV. Samples were mounted on a copper grid-supported carbon film by placing a few droplets of ultrasonically dispersed suspension of samples in ethanol on the grid,followed by drying at ambient conditions.
H2-temperature-programmed reduction(H2-TPR) experiments were performed in a fixed-bed reactor(I.D.= 4mm).50mg samples were used and reduced under a stream of5%H2/N2(20mL/min)from50°C to800°C with a ramp of7°C/min.Hydrogen consumption of the TPR was detected by a TCD and its signal was transmitted to a personal computer.
The experiments for reduction-oxidation cycle(redox) performance were performed as follows.The catalysts were pretreated with H2flow at700°C for1h and then were cooled down to room temperature and reoxidized in O2at different temperature for1h.The reoxidized samples were then performed by H2-TPR experiments as above.
3.Results and Discussion
3.1.Catalytic Activity Measurements.The catalytic perfor-mance of Ni/SiO2was shown in Figure1.A rapid deactivation was detected for the3NiSN,and the corresponding conver-sion of CH4(X CH4)decreased from～58%to～25%within 1.5h reaction on stream.In order to investigate the causes of deactivation,the3NiSN catalyst was characterized by TG-DTA,HR-TEM,IR,UV-Raman,XRD,and H2-TPR in detail.
Time on stream (h)
60555045403530252015
C o n v e r s i o n o f C H 4(%)
Figure 1:CH 4conversion versus time on 3NiSN catalyst for combination of CO 2reforming and partial oxidation of methane to produce syngas (reaction temperature:700°C,CH 4/CO 2/O 2=1/0.4/0.3,and GHSV =9000h ?1).
Wavenumber (nm)
Figure 2:FT-IR spectra of 3NiSN (dried at 100°C)and nickel nitrate (Ni(NO 3)2).
3.2.Catalyst Characterization Results
3.2.1.FT-IR Analysis.The FT-IR spectra of 3NiSN before cal-cination and Ni(NO 3)2precursor were illustrated in Figure 2.Two intense bands of Ni(NO 3)2centered at 1620cm ?1and 1376cm ?1were ascribed to asymmetric and symmetric vibra-tions of nitrate,respectively [25].After Ni(NO 3)2being impregnated on SiO 2,the position of the two bands of Ni(NO 3)2shifted to higher wavenumber about 1643cm ?1and
1385cm ?1,respectively.Similar to our previous study [23],this shift to higher wavenumber might be contributed to the interaction between nickel nitrate and support SiO 2.3.2.2.Thermal Analysis.In order to study the formation of NiO from precursor,thermal analysis of 3NiSN before calcination was carried out (shown in Figure 3).The extra water should be removed by holding the precursor under O 2at 110°C for 1h.The thermal oxidation degradation of the dried 3NiSN consisted of two main steps.The first weight loss (9.1wt%)at 110–240°C region in TG together with a differential peak at around 224°C in DTG curve was probably due to the dehydration of 3NiSN.The second large weight loss at region of 240–380°C (11.1wt%)in TG,accompanied with a small endothermic peak around 293°C in DTA,had been attributed to thermoxidative degradation of nickel nitrate.This decomposition step exhibited a differential peak around 277°C in DTG profile.Above 380°C,practically weight loss could not be observed any more.The TG-DTA curves confirmed the absolute volatility of water and nitrate and also the formation of NiO over catalysts around 380°C.The calcination of 3NiSN beyond 380°C would enhance the interaction between the NiO and SiO 2support,according to our earlier study [23].
3.2.3.UV-Raman Analysis.Further evidence for the for-mation of NiO might be drawn from UV-Raman spectra exhibited in Figure 3.Herein,the spectrum for NiO was included as a reference.As seen from Figure 4,the intense and sharp peak at 1139cm ?1,together with three weak peaks at 900,732,and 578cm ?1,was assigned to the Raman responses of NiO.Similar to NiO reference,the peaks of 3NiSN center at about 1135,900,726,and 580cm ?1were also attributed to NiO.Furthermore,compared with the reference of NiO,the four Raman peaks of NiO over 3NiSC appeared more intensive,thus suggesting that the NiO particles over 3NiSN catalyst were larger [23,26,27].
3.2.
4.XRD Analysis.XRD measurements were carried out to understand the crystalline structure of 3NiSN catalysts,and the results were presented in Figure
5.The XRD patterns of all samples exhibited a broad and large peak around 22°,which was attributed to amorphous silica of support.After calcination,the sample showed only the fcc-NiO phase,with typical reflections of the (111),(200),and (220)planes at 2θ=37°,43°,63°,respectively.After being reduced with H 2for 4h,the peaks assigned to NiO disappeared,and three other peaks around 44°,52°,and 76°for Ni (111),Ni (200),and Ni (220)planes were detected,thus inferring the successful transformation of NiO to metallic Ni after reduction with H 2.3.2.5.TEM Analysis.Further insight on the aggregation of Ni particles over the 3NiSN could be obtained by TEM analysis.Figures 6(a)and 6(b)exhibited the TEM images of 3NiSN after reduction and deactivation,respectively.The Ni particles over both catalysts were approximately spherical in shape.Highly dispersed Ni particles were detected for the Ni/SiO 2just after reduction.However,obvious glomeration
200
300400
500600700
Temperature (°
C)
T G +D T G
(a)
200300
400
500600700
Temperature (D T A
°
C)
(b)
Figure 3:(a)TG +DTG and (b)DTA thermogram of 3NiSN dried at 100°
C.
Raman shift (cm ?1
)
I n t e n s i t y (a .u .)
Figure 4:UV-Raman spectra of 3NiSN (calcined at 700°C for 4h)and NiO (as a reference).
of Ni particles was observed for the 3NiSN catalyst after deactivation.In order to make a profound analysis,the corresponding particle size distributions obtained from TEM were summarized in Figures 6(c)and 6(d)for 3NiSN after reduction and deactivation,respectively.The particle size values of reduced 3NiSN were distributed in a range of 16.1–84.0nm with the average size around 37.5nm.As for 3NiSN after deactivation,the mean size increased to 50.4
nm
2θ(deg)
Ni NiO
I n t e n s i t y (a .u .)
Figure 5:XRD patterns of 3NiSN before and after reduction in H 2for 4h.
with distributed range of 36.0–73.6nm.An evident particle aggregation was formed over 3NiSN catalyst,which was in accordance with the XRD result.
3.2.6.H 2-TPR Analysis.TPR is an efficient method to char-acterize the reducibility of supported nickel-based catalysts.
(a)
(b)
Particle diameter (nm)
0.25
0.200.15
0.10
0.05
0.00
R e l a t i v e p a r t i c l e n u m b e r (%)
(c)
0.20
0.15
0.10
0.05
0.00
R e l a t i v e p a r t i c l e n u m b e r (%
)
Particle diameter (nm)
(d)
Figure 6:TEM images of (a)reduced 3NiSN and (b)deactivated 3NiSN,and histogram of the particle size distribution obtained from sampling of nanoparticles from TEM data (c)for reduced 3NiSN and (d)for deactivated 3NiSN.
TPR profiles of 3NiSN catalysts were depicted in Figure 7.Two reduction peaks were observed for the fresh 3NiSN cata-lyst (just calcined)at 430°C and 450°C.The low-temperature peak might be contributed to the reduction of NiO which is negligible weak interaction with SiO 2.The high-temperature peak was caused by the reduction of nickel oxide which interacted weakly with SiO 2.Furthermore,ttthe reduction-oxidation cycle (redox)performance of a catalyst would strongly influence the catalytic activity for an oxidation involved reaction [28].Therefore,the redox performances of 3NiSN catalysts were investigated,and the corresponding experiment results were depicted in Figure 7.After being
reduced in H 2flow at 700°C for 1h,the 3NiSN catalysts were reoxidized in O 2at different temperatures and then tested with H 2-TPR.No clear reduction peak of NiO was detected for 3NiSN with reoxidized temperature below 300°C.As reoxidization temperature increased from 400to 700°C,the rereduction temperature increased from ～290to ～370°C;however,it was always less than the temperature needed to reduce the NiO of fresh 3NiSN.Distinctly,the weak NiO-SiO 2interaction over 3NiSN catalyst disappeared with repeat-ing oxidation-reduction-oxidation process.Studies from the previous work show that the strong interaction between NiO and support could suppress efficiently the sintering of
200
300
400500
600
Temperature (F
E
D C B A
°
C)
H 2c o n s u m p t i o n (a .u .)
Figure 7:The reduction-oxidation cycle (redox)performance of 3NiSN catalysts with different reoxidization temperature (A:300°C;B:400°C;C:500°C;D:600°C;E:700°C;F:fresh,just calcined).
metallic nickel [21–23].Therefore,the disappearance of NiO-SiO 2interaction would lead to the sintering of active nickel particles at high reaction temperature.
3.2.7.Effect of the Particle Size of Ni.It is generally accepted that the crystalline size of metallic nickel plays an important role in the catalytic performance for nickel-catalyzed reac-tions:smaller metallic Ni size helps to provide more active sites to reach the much better catalytic activity.Our previous works had also demonstrated this view [21,22].In order to investigate the particle size dependence of the catalytic reaction,the 3NiSN catalysts after different time (1.5h,2.0h,and 2.5h)reaction on stream were taken out to be estimated by XRD and calculated with the Scherrer equation (shown in Figure 8).For all the 3NiSN (even after deactivation),only Ni and amorphous SiO 2phase detected by XRD.No NiO phase was found,which meant no significant change in Ni phase was observed for 3NiSN even after deactivation.Noteworthily,the diffraction intensity of nickel crystalline increased with reaction time,which indicated the crystalline size of nickel on 3NiSN increased with reaction time.The crystalline size of nickel on 3NiSN as a function of reaction time was shown in Figure 9.The crystalline size of nickel was ～30.3nm,～32.6nm,～33.6nm,and ～3
4.6nm,for 3NiSN after 0h,1.5h,2h,and 2.5h reaction on stream,respectively.The change trend of Ni size was in conformance with the catalytic activity of 3NiSN in process of https://www.doczj.com/doc/ed5347558.html,bined with H 2-TPR results above,with the process of CRPOM proceeding,the NiO-SiO 2interaction over 3NiSN catalyst weakened down as it disappeared.At the same time,the crystalline size of nickel increased with the weakening of NiO-SiO 2interaction,finally leading to the sintering of active nickel particles over 3NiSN
catalyst.
2θ(deg)
Ni
I n t e n s i t y (a .u .)
Figure 8:The effect of reaction time on the XRD patterns of
3NiSN.
Reaction time (h)
35
34
33
32
31
30
C r y s t a l l i n e s i z e o f n i c k e l (n m )
Figure 9:Crystalline size of nickel as a function of reaction time.
By comprehensively analyzing the characterization results,important information could be concluded.On one hand,graphic carbon was not detected in the spent 3NiSN catalyst by XRD and TEM,suggesting that no carbon deposition was formed during the reaction.On the other hand,except for the characteristic XRD peak of metallic nickel,no other nickel species (such as NiO)was detected,indicating that the transformation of active metallic Ni was not the reason for deactivation of 3NiSN.Importantly,the weak interaction between Ni and support disappeared as
the reaction proceeding,resulting in sintering of active nickel particles.This was the reason that3NiSN catalyst showed a rapid deactivation in the CRPOM reaction.
4.Conclusions
In this work,Ni/SiO2catalysts were prepared with nickel nitrate precursor by IWI method and characterized by FT-IR,TG-DTA,UV-Raman,XRD,TEM,and H2-TPR.By being calcined around380°C,water and nitrate were volatilized absolutely to form NiO,which could be reduced into metallic Ni after being treated with H2at700°C.The active nickel particles(around37.5nm)of3NiSN catalyst were dispersed highly but weakly interacted with SiO2support.However, this weak interaction disappeared after repeating oxidation-reduction-oxidation in the fluidized bed reactor at700°C. Therefore,3NiSN catalyst suffered from obvious sintering of the active nickel particle.In light of these,a rapid deactivation of3NiSN was shown in the process of combination of CO2 reforming and partial oxidation of methane(CRPOM)to produce syngas.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper. Acknowledgments
The authors thank the financial supports of National Natural Foundation of China(nos.21003066,21367015,and51068010) and Zhejiang Province Key Science and Technology Innova-tion Team(2012R10014-03).
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doi:10.6043/j.issn.0438-0479.201811009 氨辅助浸渍法制备抗烧结Ni/SiO 2催化剂 及其甲烷二氧化碳重整反应的性能 万吉纯，朱孔涛，翁维正*，楚沙沙，郑燕萍，黄传敬，万惠霖 （厦门大学化学化工学院，固体表面物理化学国家重点实验室，醇醚酯化工清洁生产国家 工程实验室，福建 厦门 361005） 摘要：以硝酸镍为前驱盐，商品SiO 2为载体，采用氨水辅助浸渍法通过改变n (NH 3)/n (Ni)制备了系列Ni/SiO 2催化剂，并将其应用于甲烷二氧化碳重整（DRM ）制合成气反应，实验结果表明：在浸渍过程中加入氨水可显著改善Ni/SiO 2的DRM 反应活性、稳定性和抗积碳性。进一步的表征结果表明，随着氨水添加量的增加，催化剂活性相分散度提高，当n (NH 3)/n (Ni) ≥ 6 后，经800 ℃焙烧后催化剂上NiO 物种的平均粒径小于5 nm 。通过改变氨水，SiO 2，前驱盐的浸渍顺序发现只有用硝酸镍与一定浓度的氨水配成的混合溶液浸渍SiO 2才能获得具有良好分散度的Ni/SiO 2催化剂。氨水与Ni 形成镍氨络合物能够避免在浸渍过程中生成Ni(OH)2沉淀，进而有利于Ni 物种在SiO 2表面的均匀分散。氨水所形成的碱性环境还可使载体表面Si-O 物种部分溶解或“软化”，进而促进Ni 物种与载体表面Si-O 物种的相互作用，在后续的焙烧过程中生成与SiO 2具有较强相互作用的镍物种以及表面镍硅酸盐物种。这些物种具有良好的抗烧结性能，可防止Ni 物种在高温下团聚并在600 ℃以上通H 2还原后得到分散性良好且具有较强抗烧结性能的的金属Ni 颗粒。 关键词： Ni/SiO 2；氨水辅助浸渍；抗烧结；镍硅酸盐；甲烷二氧化碳重整 中图分类号：O 643.36+1 文献标志码： A 甲烷二氧化碳重整（DRM ）制合成气反应是利用甲烷和二氧化碳这两种重要的含碳资源的一个有效途径，对缓解能源危机，减轻温室气体排放等具有重要意义[1-2]。目前用于DRM 反应的催化剂主要有3类，其中，负载型贵金属催化剂虽然催化活性高，稳定性好但是价格昂贵[3-6]；金属硫化物或氧化物等虽然价格低廉但是常压下相比于Ni 基催化剂反应速率更慢且易于失活[7-8]，需要在高压下反应；负载型非贵金属催化剂，尤其是Ni 基催化剂价格便宜，催化活性高，但在反应条件下容易发生烧结和积碳，导致催化剂失活[9-10]。如果能够解决厦门大学学报（自然科学版）
吸附强化甲烷重整制氢中的几种吸附剂的比较分析 吸附强化甲烷重整制氢中的几种吸附剂的比较分析 摘要：本文采用有限元的模拟方法研究了几种常用的CO2吸附剂，比较四种CO2吸收剂的特点可以为实际应用提供参考依据，也为后续吸收剂的改性指出了方向。 关键词：吸附强化甲烷重整制氢 化石燃料燃烧所引发的CO2温室效应越来越引起人们的重视，氢由于其零污染、高能量密度的特性成为替代能源的首选。CO2吸附强化甲烷重整技术的中心思想是利用CO2吸附脱除打破化学平衡的原理，使反应过程与分离过程结合起来，这样催化剂上生成的CO2能够迅速脱除，从而打破化学平衡，使反应向着H2合成的方向反应。 一、吸附强化反应的数学模型 吸附强化甲烷重整过程中主要发生以下反应 二、温度对吸附剂的影响 影响吸收剂在甲烷重整制氢效率的主要因素有： CO2吸附速率吸附容量、CO2吸附饱和速率、CO2吸附容量。四种吸收剂的最大吸附容量计算显示，CaO的最大吸附容量最大，高于其他三种吸收剂。当反应体系产生越多的CO2，CO2吸收速率越大，则反应物向H2的转化率越高，这与前述的结论一致。 三、压力对吸附剂的影响 综上所述，对比分析反应温度和反应压力对甲烷重整制氢的影响，得出：（1）为了得到高的H2产出，Li4SiO4吸附剂更适合在较低反应温度、较低反应压力体系下运行；CaO吸附剂更适合在较高反应温度体系下运行。此时条件下两种吸附剂的CO2吸收速率快，能够迅速从反应系统吸附大量生成的CO2，使整个反应向有利于H2生成的方向进行；（2） Li2ZrO3吸附剂更适合在较高反应压力体系下运行，在高的反应压力下，有利于反应逆方向，但是高的压力能够提高吸附剂CO2吸收速率，特别是对Li2ZrO3吸附剂，与CO2生成速率相匹配，但还是压力不能过高，否则会促进反应的逆方向，不利于甲
CJR4/5 型甲烷二氧化碳测定器 使用说明书 上海高致精密仪器有限公司 警告： 1、维修时不得改变本安电路和与本安电路有关的元器件的电气参数﹑规格和 型号！ 2、不得随意与其它未经联检的设备连接！ 3、不得随意更改甲烷催化元器件生产厂家及型号、规格！ 4、报警仪要由专人维护使用，初次使用应完整阅读使用说明书！ 5、按规定的时间期限对报警仪进行零点、精度调节，如没有超差，可继续使 用！ 6、要定期清扫报警仪；对于煤尘比较大，空气比较潮湿地点使用的报警仪要 经常检查报警仪气室内的粉末冶金过滤罩，当积累较多粉尘时，应换上干净的粉末冶金过滤罩；并将换下器件拿到地面进行清洗，以便下次使用！
仪器使用注意事项 （1）本仪器防护等级IP54，可以使用于较为阴暗、潮湿、粉尘等场所，但应避免强外力的猛烈撞击和挤压。 （2）仪器充电应在地面安全区域。 （3）仪器检修时不得随意更改产品元器件的参数、规格及型号。 （4）仪器使用时必须佩带动物皮套。 （5）仪器更换的催化元件应符合AQ6202-2006 的要求。 保管和维修 （1）仪器应有专人保管，并建立登记制度，将使用情况一一记录在案。 （2）仪器长期不用，应放于通风干燥处储存。 （3）禁止随意拆卸仪器，维修工作应由经过专门培训的专业人员担任。 仪器可能出现的现象或故障及可能原因
前言：本说明书为北京卓安恒瑞科技有限公司生产的CJR4/5 型甲烷二氧化碳测定器（以下简称仪器）使用说明书。使用本仪器前请详细阅读本说明书。 1 防爆型式和型号及含义 1.1 测定器防爆型式为矿用本质安全兼隔爆型，防爆标志为“ExdibⅠ Mb”。 1.2 由国家检验机构统一归口编制型号： C J R 4 / 5 1.3 外形尺寸及重量二氧化碳测量范围：0~5.00% CO2 甲烷测量范围：0~4.00%CH4 测定对象：二氧化碳测定对象：甲烷产品类型代号：测定器 1.3.1 外形尺寸：113.5mm×60.7mm×30mm 1.3.2 重量： 220g 1.3.3 外壳材质：ABS 工程塑料。 2. 用途 CJR4/5 型甲烷二氧化碳测定器适用于煤矿井下、巷道等处连续监测环境中甲烷（瓦斯）和二氧化碳浓度。当甲烷浓度超限或二氧化碳浓度低于某一设定值时，能自动发出声、光报警。可供相关工作人员、管理人员、专业人员、流动工作人员、煤矿通防人员等随身携带使用，也可供上述场所固定使用。 仪器防爆型式为矿用本安兼隔爆型，防爆标志为ExibdI。在具有甲烷爆炸性危险的煤矿井下： a）温度：0～40℃；b）湿 度：≤98％(25℃)；c）大气 压力：80～116kPa；d）风 速：0～8m／s； e）贮存温度为-40～+60℃。 f）在具有爆炸性气体混合物的危险场所。 警示：当仪器使用环境条件超出上述使用条件时，可能会造成仪器误差增大。3. 测量原理 甲烷测量原理：甲烷可燃性气体检测采用热催化型高性能传感器组成惠斯顿电桥，测量臂由载体催 化元件（俗称黑元件）和纯载元件（俗称白元件）组成，辅助臂由金属膜电阻和电位器组成，稳压电路为电桥提供稳定的电压：在新鲜空气中桥路处于平衡状态，在被测气体中，甲烷在黑元件表面发生催化反映（无焰燃烧），使黑元件温度增高，电阻增大，桥路失去平衡，从而输出一个电位差，该电位差在一定范围内其大小与甲烷浓度成正比。此信号进入微处理器经过内部A/D 转换、数据处理、滤波之后直接驱动发光数码管显示出被测甲烷的浓度，并给出声光报警、电池检测等。
1 (一) 全球CO 2循环策略系统，包括第一步，用电解产生氢气；第二步，H 2 和 2 CO 2反应生成CH 4 和少量其他碳氢化合物；第三步，生成的CH 4 作为能源消耗又生 3 成了CO 2，如此循环往复。其中的核心环节就是利用太阳能发电和CO 2 催化加氢 4 甲烷化的反应。5 CO 2甲烷化反应是由法国化学家Paul Sabatier提出的，因此，该反应又叫做 6 Sabatier反应，反应过程是将按一定比例混合CO 2的和H 2 气通过装有催化剂的反 7 应器，在一定的温度和压力条件下CO 2和H 2 发生反应生成水和甲烷。化学反应方 8 程式如下。 9 CO2+4H2=CH4+2H2O 10 (二) CO 2加氢甲烷化机理： 11 1 不经过一氧化碳中间物的机理 12 13 2 包括一氧化碳中间物的机理 14 随着研究的深入，CO 2甲烷化反应机理被推定可能由下列2个途径组成：吸附 15 的H和气相的CO 2反应生成吸附态的CO，随后吸附态的CO直接加氢生成甲烷； 16 或吸附的H和吸附的CO 2反应生成吸附态的CO，随后吸附态的CO加氢生成中间 17 体如甲酸根、碳酸根等再进一步加氢生成甲烷。Prairie提出了CO 2加氢甲烷化 18
的反应机理： 19 20 式中，m，s，i分别表示金属上，载体上及未经确定吸附点上的吸附物种。 21 Schild 等提出了Ni/ZrO 2催化CO 2 加氢甲烷化的反应机理。CO 2 先在催化剂活 22 性中心上转化为吸附的甲酸根和碳酸根，然后再进一步加氢为甲烷。 23 Os簇合物催化剂上反应机理表示为： 24 25 其中*表示吸附二氧化碳的活性点，M表示Os上的吸附活性点，主要用于加氢。 26 Ni/ZrO2上的甲烷化机理可表示为： 27
Ni/TiO2催化甲烷水蒸气低温重整 摘要 负载镍的二氧化钛（Ni/TiO2）被用于甲烷水蒸气低温重整反应的研究。然而研究经常被报道，在传统高温条件下进行甲烷重整反应，二氧化钛负载金属的催化剂会失活，如此所示，它应该在一个温和的温度（400℃）下激活使用。Ni/TiO2在500℃，甚至在较低的甲烷和水蒸气输入比（1:1）条件下，能够保持稳定和高效的氢气产量。程序升温的研究表明，镍的存在和更有力的支撑交互作用是低温活化甲烷的关键，同时在水汽转换反应中，镍元素之间更弱的相互作用，使得其对氢气生成的生成做出贡献。这个检测报告进一步证实，当相同的反应进行时，镍负载在惰性氧化物（二氧化硅）表面时，即镍元素间的主要的金属负载影响会较弱。在500℃以及水和甲烷进料比为3:1的条件下，当输入SMR系统的蒸汽数量增加时，在Ni/TiO2催化剂作用下甲烷转化率增强，可以观察出甲烷转化率达到45%。根据水和甲烷进料的比例，在96小时内，负载镍的二氧化钛催化剂展现出稳定的转化率和产品的选择性。 1.简介 氢气是许多工业过程的关键原料同时高效的制氢技术在工业上具有重要作用。应该进一步加强水分解制氢体系的研究，它在技术方面仍然不太成熟，大大的阻碍了实现更大规模的发展。水碳重整，即通过水蒸气或者干气重是目前最有利的氢气生产途径。干气重整具有吸收二氧化碳的优点，但是易于引起碳污染，，除非能找到合适的催化剂。因此，传统的烃类蒸汽转化以甲烷蒸汽重整为主，在短期内，甲烷蒸汽转化仍然是最可行的工业制氢过程。 因为甲烷蒸汽重整反应是吸热反应，为了得到有效的转化率，甲烷蒸汽转化应该在800℃甚至更高温度下进行。为了增加氢气产量，这就经常伴随着下游的水汽转换过程。甲烷水蒸气重整反应需要的高温条件的能源消耗通常是通过焚烧天然气或者炼油厂的废料提供。为了获得可持续的制氢方式，利用可再生
CH4与CO2重整制合成气研究的研究报告 杨真一1 ，胡莹梦2，徐艳3 ，郑先坤4 （1：2009级化学工程与工艺四班，学号：0943084137 2：:2009级化学工程与工艺三班，学号：0943084141 3：2009级化学工程与工艺三班，学号：0943084136 4：2009级化学工程与工艺三班，学号：0943084008） 摘要：二氧化碳和甲烷既是温室气体的主要组成，又是丰富的碳资源。在石油资源日益匮乏以及环境问题日益严重的今天，二氧化碳的资源化利用已受到了广泛的关注，二氧化碳与甲烷重整制合成气的方法也越来越多，从传统的催化重整反应到现今受到更多研究的等离子体重整CH4-CO2技术，还有等离子体协同催化剂重整技术，都有大量的研究基础，本文就目前常用的几种甲烷-二氧化碳重整技术进行了调研研究并对热等离子体重整制合成气的实验方法进行了简要说明与探讨。 关键词：甲烷二氧化碳重整合成气 研究二氧化碳和甲烷的化学转化和利用对于降低甲烷使用量、消除温室气体等具有重大意义；而合成气又是合成众多化工产品以及环境友好型清洁能源的重要原料。以天然气和CO 2 为原料制备合成气，与其他方法相比较，在获得同量碳 值的合成气情况下，不仅可以减少天然气消耗量50%，还有利于减排CO 2 。目前利用二氧化碳和甲烷重整制备合成气的方法主要有三种：（1）利用催化剂催化重 整制合成气；（2）利用等离子体技术重整CH 4-CO 2 ；（3）前两种方法的综合利用。 一、催化重整反应 在催化剂的作用下，发生CH4与CO2重整的反应。而其使用的催化剂则为重点研究对象。 （1）活性组分第ⅤⅢ族过渡金属除Os 外均具有重整活性,其中贵金属催化剂
工艺与设备 化 工 设 计 通 讯 Technology and Equipment Chemical Engineering Design Communications ·56· 第45卷第9期 2019年9月 随着经济水平和科学技术不断的发展，我国的工业水平也得以不断的提高和强大。但是在工业生产的发展过程中，能源问题成为制约发展最为关键的因素。甲烷和二氧化碳作为两种主要的温室气体，它们的化学利用是一条非常好的节能减排途径，能够缓解当前日益严重的温室效应。1 甲烷二氧化碳催化重整制合成气的工艺技术 甲烷在实际化工过程中的利用主要可以分为两个部分。首先它可以直接转化：甲烷可以发生氧化反应，生产乙烯等一些重要的化工基本的原料。但是因为甲烷分子结构比较特殊，非常的稳定，所以它在发生氧化反应的过程中对反应的条件非常的苛刻，目前的技术手段下，没有办法大规模应用。第二种就是间接转化，可以将甲烷先转化成合成气，然后再转化成某种化工产品。生产过程中也可以通过一系列的反应来生产比较重要的化工产品。在目前的发展阶段中，完成规模化的生产甲烷制成合成气有三种办法：通过水蒸气来进行催化重整、进行甲烷的部分氧化、二氧化碳的重整。这三种模式在实际操作的过程中，最为基本的理论都是要提供一些还原性的物质。二氧化碳重整制成合成气的方法较其他两种方法相比具有一定的优点。首先通过这种方法制成的合成气具有较低的氢碳比，这样的比例可以使得在实际反应过程中直接作为合成的原料，这样就可以弥补在实际制成合成气过程中的一些不足。其次就是生产过程中使用了甲烷和二氧化碳这两种对地球温室效应影响大的气体，可以有效地改善人类的生存环境，提高人们生活的质量。还有就是甲烷和二氧化碳的催化重整，在实际反应过程中是具有较大反应热的可逆反应，所以它可以作为能源的储存介质。这样就可以使得甲烷和二氧化碳这样的惰性气体能够在一定程度上实现活化来进行相应的转变。近几年以来，人们对重整过程中催化剂的选择给予了高度的重视，并且在催化剂助剂、催化剂积碳行为以及催化反应理论等方面都取得了一系列的成果。 2 负载型技术催化剂 2.1 活性组分 活性组分见表1。 表1 活性组分 活性金属担载量% 反应温度K 1.Al 2O 3 Rh>Pd>Ru>Pt>Ir 1823Rh>Pd>Pt>>Ru 0.5~1823~973Ir>Rh>Pd>Ru 1 1 050Ni>Co>>Fe 9773~973Ni>Co>>Fe 10 1 023Ru>Rh 0.5873Ru>Rh 0.5 923~1 073 2.SiO 2 Ru>Rh>Ni>Pt>Pd 1973Ni>Ru>Rh>Pt>Pd>>Co 0.5 893 3.MgO Rh>Ru>Ir>Pt>Pd 0.5 1 073Ru>Rh>Ni>Pd>Pt 1973Ru>Rh~Ni>Ir>Pt>Pd 1823Ru>Rh>Pt>Pd 1 913 4.Eu 2O 3Ru>Ir 1~5 873~973 5.NaY Ni>Pd>Pt 2 873 在实际研究的过程中，甲烷二氧化碳重整制合成气的催化剂一般都会采用除锇外贵金属元素（钌、铑、铱、钯、铂）作为主要的活性组分，表1所示，其中钌、铑、铱催化性能较好，钯、铂次之。贵金属催化剂在甲烷氧化碳的重整反应中表现出了较高的活性，并且其选择性和抗积碳的性能也比非贵金属的性能要好。然而实际生产中，贵金属资源稀缺，价格昂贵，并且要考虑再回收问题，所以我国在实际研究的过程中，对 摘 要：近几年随着我国科学技术和经济水平的不断发展和提升，随之而来的环境问题也日益严峻，而二氧化碳则是重要的一环，为此我国政府以及相关工作部门加强了对甲烷和二氧化碳催化重整制合成气的研究力度。在甲烷和二氧化碳催化重整的相关技术取得阶段成果的同时，在反应时涉及的难点部分：催化剂的活性组分、载体的研究以及助剂的研究取得了突破，这体现出对工业发展质量和速度的高度肯定，但重整过程中仍然存在催化剂积碳失活等问题。主要对重整过程进行了综述，对重整过程需要的催化剂活性组分、载体以及催化剂积碳行为进行了介绍，并对制备方法进行了讨论。 关键词：甲烷；二氧化碳；催化重整；制合成气；研究进展；工艺技术中图分类号：O643.36；X51 文献标志码：A 文章编号：1003–6490（2019）09–0056–02 Research Progress and Technology of Catalytic Reforming of Methane with Carbon Dioxide to Synthetic Gas Chang Hui Abstract ：In recent years ，with the continuous development and improvement of science ，technology and economy in China ，the environmental problems are becoming more and more serious.Carbon dioxide is an important link.Therefore ，our government and relevant departments have strengthened the research on catalytic reforming of methane and carbon dioxide to syngas ，in methane and carbon dioxide.At the same time ，the related technologies of carbon dioxide catalytic reforming have achieved some achievements ，and the difficult parts involved in the reaction ：the research of active components ，carriers and promoters of catalysts have made breakthroughs ，which reflects the high affirmation of the quality and speed of industrial development ，but the deactivation of catalyst carbon deposition still exists in the process of reforming.And so on.In this paper ，the reforming process is reviewed.The active components ，supports and carbon deposition behavior of catalysts needed in the reforming process are introduced.The preparation methods are also discussed. Key words ：methane ；carbon dioxide ；catalytic reforming ；synthesis gas ；research progress ；process technology 甲烷二氧化碳催化重整制合成气的研究进展和工艺技术 常?卉 （山西潞安煤基合成油有限公司，山西长治?046000） 收稿日期：2019–07–04作者简介： 常卉（1989—），女，山西长治人，助理工程师，主要从 事化工工艺相关工作。
Research Article Ni/SiO2Catalyst Prepared with Nickel Nitrate Precursor for Combination of CO2Reforming and Partial Oxidation of Methane:Characterization and Deactivation Mechanism Investigation Sufang He,1Lei Zhang,2Suyun He,2Liuye Mo,3 Xiaoming Zheng,3Hua Wang,1and Yongming Luo2 1Research Center for Analysis and Measurement,Kunming University of Science and Technology,Kunming650093,China 2Faculty of Environmental Science and Engineering,Kunming University of Science and Technology,Kunming650500,China 3Institute of Catalysis,Zhejiang University,Key Lab of Applied Chemistry of Zhejiang Province,Hangzhou310028,China Correspondence should be addressed to Y ongming Luo;environcatalysis222@https://www.doczj.com/doc/ed5347558.html, Received5August2014;Revised6January2015;Accepted6January2015 Academic Editor:Mohamed Bououdina Copyright?2015Sufang He et al.This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use,distribution,and reproduction in any medium,provided the original work is properly cited. The performance of Ni/SiO2catalyst in the process of combination of CO2reforming and partial oxidation of methane to produce syngas was studied.The Ni/SiO2catalysts were prepared by using incipient wetness impregnation method with nickel nitrate as a precursor and characterized by FT-IR,TG-DTA,UV-Raman,XRD,TEM,and H2-TPR.The metal nickel particles with the average size of37.5nm were highly dispersed over the catalyst,while the interaction between nickel particles and SiO2support is relatively weak.The weak NiO-SiO2interaction disappeared after repeating oxidation-reduction-oxidation in the fluidized bed reactor at 700°C,which resulted in the sintering of metal nickel particles.As a result,a rapid deactivation of the Ni/SiO2catalysts was observed in2.5h reaction on stream. 1.Introduction The Ni-based catalyst has recently attracted considerable attention due to the plentiful resources of nickel,as well as its low cost and good catalytic performance comparable to those of noble metals for many catalytic reactions,such as hydrogenation of olefins and aromatics[1],methane reforming[2],and water-gas shift reaction[3].Therefore,Ni-based catalyst is believed to be the most appropriate catalyst applied in the industrial process[4–6].It is generally accepted that the catalytic performance of Ni-based catalyst is closely related to several parameters,including the properties of support,preparation method,and active phase precursor employed. Support plays an important role in determining the performance of Ni-based catalyst.Generally,a support with high surface areas is very necessary since it is effective in increasing Ni dispersion and improving thermal stability, hence not only providing more catalytically active sites,but also decreasing the deactivation over time of the catalysts due to sintering and migration effects[7,8].For its good thermostability,availability,and relative high specific surface area,SiO2support was widely used for preparing Ni-based catalyst[9].In particular,spherical silica is successfully used as a catalyst support in fluidized bed reactor due to its high mechanical strength. The method of catalyst preparation is another key param-eter which needs to be optimized because it will result in different structural and textural properties of Ni-based catalyst.Therefore,numerous methods,including precipi-tation,homogeneous deposition-precipitation,and sol-gel techniques,have been developed to enhance the performance of Ni-based catalyst[10–18].However,allthe above method-ologies mentioned are too complex or expensive to scale Hindawi Publishing Corporation Journal of Nanomaterials Volume 2015, Article ID 659402, 8 pages https://www.doczj.com/doc/ed5347558.html,/10.1155/2015/659402
甲烷化技术 甲烷化就是利用催化剂使一氧化碳和二氧化碳加氢转化为甲烷的方法，此法可以将碳氧化物降低到10ppm以下，但需要消耗氢气。 一、加氢反应 CO+3H2=CH4+H2O+206.16KJ CO2+4H2=CH4+2H2O+165.08KJ 此反应为强放热反应，有氧气存在时，氧气和氢气反应会生成水，在温度低于200℃，甲烷化催化剂中的镍会和CO反应生成羰基镍： Ni+4CO=Ni(CO)4 因此要避免低温下，CO和镍催化剂的接触，以免影响催化剂的活性。 甲烷化的反应平衡常数随温度增加而下降，作为净化脱除CO和CO2作用的甲烷化技术，反应温度一般在280～420℃之间，平衡常数值都很大，在400℃、2.53Mpa压力下，计算CO和CO 2 的平衡含量都在10－4ppm级。湖南安淳公司开发的甲烷化催化剂起活温度210℃，使用温度为220～430℃之间。 进口温度增加，催化剂用量减少，压降和功耗有较大的降低。这部分技术在国内已经非常成熟，而且应用多年。 目前，甲烷化技术已经用在大规模的合成气制天然气上，因此最大的问题是催化剂的耐温及强放热反应器的设计制作上。 二、甲烷化催化剂 甲烷化是甲烷蒸汽转化的逆反应，因此甲烷化反应的催化剂和蒸汽转化催化剂一样，都是以镍作为活性组分，但是甲烷化反应在温度更低的情况下进行，催化剂需要更高的活性。 为满足上述需要，甲烷化催化剂的镍含量更高，通常为15～35％（镍），有时还需要加入稀土元素作为促进剂，为了使催化剂能承受更高的温升，镍通常使用耐火材料作为载体，且都是以氧化镍的形态存在，催化剂可压片或做成球形，粒度在4～6mm之间。 催化剂的载体一般选用AI 2O 3 、MgO、TiO、SiO 2 等，一般通过浸渍或共沉淀
文章编号:042727104(2003)0320253204 Ξ甲烷部分氧化与甲烷二氧化碳重整耦合制 合成气Co 系催化剂研究 郑小明,莫流业,井强山,费金华,楼 辉 (浙江大学催化研究所,杭州 310028) 摘 要:研究了Co/γ2Al 2O 3,Co/α2Al 2O 3和Co/SiO 2催化剂上的甲烷部分氧化与甲烷二氧化碳重整制合成气反应,只有Co/α2Al 2O 3是有效的.证明Co 和载体的相互作用过强或过弱都不利与此耦合反应.Co 和α2Al 2O 3的作用正好合适.此外,Co 的担载量和催化剂稳定性关系很大,Co 量过低则在反应过程中会因Co 0→CoAl 2O 4而失活,Co 担载量过高则会导致严重结碳. 关键词:甲烷部分氧化;甲烷二氧化碳重整;耦合反应;Co 催化剂 中图分类号:O 64 文献标识码:A CO 2是全球最丰富的碳资源.由于消耗化石燃料而排放的CO 2日益增多,其增加程度远远超过了以光合作用为主的植物对环境CO 2的自净化能力.CO 2是一种温室气体,其含量增加必然会逐渐造成生态灾难,严重威胁人类的生存环境.因此,效法自然生态系统,实现CO 2的资源化转化是一项重要而迫切的工作,也是目前国际上资源化生态化领域的研究热点之一.甲烷二氧化碳重整反应是利用甲烷和二氧化碳这2种最为廉价且都具有“温室效应”的一碳化合物作为氢源和碳源转化为合成气,它不仅具有环境效益,在经济上也有吸引力,但该反应是一个强吸热反应,能耗太高.若将甲烷二氧化碳重整与甲烷部分氧化、甲烷水蒸汽重整反应耦合,利用甲烷氧化放出的热量支持吸热的甲烷二氧化碳(或水蒸汽)重整反应,只要控制甲烷、二氧化碳、氧的比例,就可实现CO 2的低能耗或零能耗转化.该工艺过程克服了甲烷部分氧化和甲烷二氧化碳重整反应的缺点,是一个绿色的原子经济反应. 1 实验部分 载体γ2Al 2O 3为贵州产TL 202型;α2Al 2O 3由γ2Al 2O 3经1200℃焙烧5h 而得(经XRD 确证为α2Al 2O 3).SiO 2为南京天一无机化工厂生产.除SiO 2为0.280～0.450mm 外,载体使用前均取0.450～0.900mm. 负载钴催化剂的制备采用等体积浸渍制备,即用一定量的载体和Co (NO 3)2?6H 2O 溶液等体积浸渍过夜后,经120℃干燥,最后在空气气氛中650℃焙烧5h. 催化剂的体相组成用X 2射线衍射(XRD )方法测定.实验在日本理学公司生产的Rigaku D/Max 2ⅢB 型X 2射线粉末衍射仪上进行,Cu K α 射线,管流为40mA ,管压45kV.钴晶粒度的测定采用X 2射线宽化法.H 22TPR 在AM I 2200催化剂表征系统上进行.在Ar 气流中于300℃处理30min ,温度降至50℃后通H 2/Ar (φ(H 2)=10%)混合气,流速为25mL/min ,升温速率为20℃/min ,升温至900℃. 催化剂活性评价在自建常压固定床流动反应装置上进行,采用内径4mm 的石英反应管.原料气CO 2、CH 4、O 2纯度均达到99.9%.原料气流量由北京建中机器厂生产的D07212A/ZM 型质量流量控制器Ξ收稿日期:2003202226 基金项目:浙江省自然科学基金重点资助项目(ZD9903) 作者简介:郑小明(1941— ),男,教授,博士生导师.第42卷 第3期2003年6月 复旦学报(自然科学版)Journal of Fudan University (Natural Science ) Vol.42No.3J un.2003
(一) 全球CO2循环策略系统，包括第一步，用电解产生氢气；第二步，H2和CO2反应生成CH4和少量其他碳氢化合物；第三步，生成的CH4作为能源消耗又生成了CO2，如此循环往复。其中的核心环节就是利用太阳能发电和CO2催化加氢甲烷化的反应。 CO2甲烷化反应是由法国化学家Paul Sabatier提出的，因此，该反应又叫做Sabatier反应，反应过程是将按一定比例混合CO2的和H2气通过装有催化剂的反应器，在一定的温度和压力条件下CO2和H2发生反应生成水和甲烷。化学反应方程式如下。 CO2+4H2=CH4+2H2O (二) CO2加氢甲烷化机理： 1 不经过一氧化碳中间物的机理 2 包括一氧化碳中间物的机理 随着研究的深入，CO2甲烷化反应机理被推定可能由下列2个途径组成：吸附的H和气相的CO2反应生成吸附态的CO，随后吸附态的CO直接加氢生成甲烷；或吸附的H和吸附的CO2反应生成吸附态的CO，随后吸附态的CO加氢生成中间体如甲酸根、碳酸根等再进一步加氢生成甲烷。Prairie提出了CO2加氢甲烷化的反应机理：
式中，m，s，i分别表示金属上，载体上及未经确定吸附点上的吸附物种。 Schild 等提出了Ni/ZrO2催化CO2加氢甲烷化的反应机理。CO2先在催化剂活性中心上转化为吸附的甲酸根和碳酸根，然后再进一步加氢为甲烷。 Os簇合物催化剂上反应机理表示为： 其中*表示吸附二氧化碳的活性点，M表示Os上的吸附活性点，主要用于加氢。Ni/ZrO2上的甲烷化机理可表示为： 二氧化碳先在催化剂表面转化为吸附的甲酸根和碳酸根，再进一步氢化为甲烷。图中虚线表示热力学可行但未被观察到。 由非晶态合金Pd25Zr71制得的催化剂也显示出与之相似的结果。如下图所示：
2019年第44卷 天然气化工—C1化学与化工开发应用 收稿日期:2018-09-27;基金项目:国家重点研发计划(2016YFA0202802);作者简介:刘俊义(1981-),男,工程师,从事化工、生产管理工作,Email:luanljy@https://www.doczj.com/doc/ed5347558.html, ;*通讯作者: 祝贺,Email:zhuh@https://www.doczj.com/doc/ed5347558.html, ;张军,Email:zhangj@https://www.doczj.com/doc/ed5347558.html, 。合成气是一种重要的碳一化工原料气,可以合成甲醇、甲酸甲酯、二甲醚、合成油等化工产品。以天然气为原料重整制备合成气,按照O 原子供应原料不同可分为:(1)水蒸气为氧原料的湿重整SMR ;(2)O 2为氧原料的甲烷部分氧化POM ;(3)CO 2为氧原料的干重整;(4)上述两种或三种物质为氧原料的耦合重整。 其中水蒸气重整SMR ,最早于1926年成功工业化,但所得合成气的n (H 2)/n (CO)高(约为3),该工艺过程能耗高、投资大、设备庞大、生产成本高、活性组分为Ni 的催化剂面临严重的积炭问题[1,2]。甲 烷部分氧化POM ,包括非催化部分氧化和催化部分氧化,非催化部分氧化为了获得甲烷的高转化率和最小的挥发分,要求温度控制在1573K 以上[3],不仅浪费资源并且对反应器材质的要求苛刻,催化部分氧化在催化床层中存在热点并且容易发生爆炸[4],因此难以得到广泛的工业应用。CO 2干重整,同时利用温室气体二氧化碳和甲烷作为原料,原料来源广泛,变废为宝,获得低n (H 2)/n (CO)的合成气, 引起学术界和产业界的广泛关注[5?7]。 CO 2干重整的重难点包括催化剂和高温条件 下热量供给等。制备高活性、高选择性、高稳定性、耐热性能好的催化剂是现阶段国内外研究的重点,已取得了很多有意义的结果[8]。许峥等[7]根据CO 2干重整可能包括的化学反应及热力学数据指出,重整反应CH 4+CO 2=2CO+2H 2是独立的吸热反应,高温对反应有利,且只有t >645℃才是热力学上可行的反应。甲烷部分氧化释放的高温热量用于满足干重整吸热的能量所需,实现甲烷二氧化碳自热重整(CO 2/CH 4/O 2重整),将是一个高效节能的方法,这也 是目前研究的热点[9]。 本项目组前期通过热力学Gibbs 自由能、计算 流体力学CFD 方法等对自热重整反应器进行了研究,并且在山西潞安进行了万方级的中试实验[10]。本文通过热力学方法对甲烷二氧化碳自热重整过程进行研究,分析其产物性质、转化率等主要特点,为原料选择、工艺条件、催化剂设计等提供帮助和指导。 1二氧化碳自热重整分析方法 甲烷二氧化碳自热重整主要反应有: (1)(2)(3)(4) 反应(1)为甲烷燃烧反应。反应(2)为CO 2?CH 4 重整反应,反应(3)为H 2O ?CH 4重整反应,水蒸气可为入口原料或过程产生,反应(2)和反应(3)均为可逆 甲烷二氧化碳自热重整工艺分析 刘俊义1,祝贺2*,张军2* (1.山西潞安矿业(集团)有限责任公司,山西 长治 046204; 2.中国科学院上海高等研究院低碳转化科学与工程重点实验室,上海 201203) 摘要:基于吉布斯自由能最小法,分析甲烷二氧化碳自热重整(CO 2/CH 4/O 2重整)工艺过程,可知:温度增加,合成气中甲烷 含量减少、二氧化碳转化率增加;压力增加,合成气中甲烷含量增加、二氧化碳转化率降低;碳碳比n (CO 2)/n (CH 4)增加,合成气中甲烷含量减少、二氧化碳转化率降低;温度、压力对氢碳比n (H 2)/n (CO)有影响,但n (CO 2)/n (CH 4)对n (H 2)/n (CO)影响更为显著;少量或适量水蒸气可以保护甲烷二氧化碳自热重整转化炉内关键设备、调节产物n (H 2)/n (CO)等。根据工业生产要求和特点,定 义出口合成气中甲烷的物质的量分数1%为临界条件,获得临界条件时n (CO 2)/n (CH 4)、重整平衡温度与压力、二氧化碳转化率以及n (H 2)/n (CO)等特性参数的关系图,指导工业生产的工艺过程和催化剂研究。 关键词:二氧化碳;甲烷含量;自热重整;干重整;合成气;临界条件 中图分类号:TE64;TQ01 文献标志码:A 文章编号:1001?9219(2019)03 ? 56
甲烷、CO2、氮气及乙烷等对煤的吸附作用的关系 Richard Sakurovs , Stuart Day, Steve Weir （澳大利亚纽卡斯尔2300号330号邮箱CSIRO能源技术） 摘要：将CO2封存在煤层中能够减少其大气中的排放量。如果封存CO2能提高煤层气产量，那么部分封存成本就可通过生产的煤层气得到补偿。这需要了解CO2和甲烷在高压条件下的吸附作用。为了阐明CO2、甲烷、乙烷及氮气之间的关系，对其在55°C、20MPa下的吸附作用对多组煤样进行了研究。运用修正后的Dubinin–Radushkevich模型对等温吸附曲线进行了拟合。煤体对不同气体的最大吸附量高度相关。气体对煤体的最大吸附量与其临界温度成正比关系。乙烷和氮气的最大吸附量尤为接近：从体积来看，所以煤样对乙烷的最大吸附量是氮气的两倍。随着碳含量增加，CO2和乙烷的最大吸附率呈线性减少的关系。尽管碳含量增加较少，甲烷/乙烷的吸附率也呈现减小的趋势，这表明低阶煤的较大吸附率并不是CO2特有的。吸收的热量随着镜质体反色率的增加而增加；这可能反映了高阶煤更高的极化度（这也决定了它们的反射率）。 关键词：煤；CO2吸附；甲烷吸附；煤层气产量增加 1.引言 因为煤层能够存储其重量为6-12%的CO2，所以可选择不可开采煤层封存CO2 [1]。通常，煤层中含有甲烷。如果将CO2封存在这样的煤层中，同时能提高煤层气产量，部分封存成本能通过生产的煤层气得到补偿[2]。 众所周知，尽管已知的摩尔吸附比例从2:1到10:1，但相比乙烷，煤能吸附更多的CO2。这种变化在一定程度上是因为这些比例值并不是在饱和压力状态下测定的，CO2的吸附能力比甲烷更强，这一比例特别是在低压状态下会提高。然而，更为根本的是这两种气体的最大吸附量，并没有进行大量的研究。 从基本的单层模型来看，因为煤的表面积和孔隙容积是不变的，所以气体的最大吸附体积大致相同。简单的储层也能到出相应的结论。最大吸附体积保持不变被称之为Gurvich准则。尽管有些孔隙只有体积较小的分子能够进入，而体积较大的分子无法进入，当煤接触到极易被吸附的气体，煤体会膨胀，这样会导致表面积和微孔体积改变，甲烷和CO2最大吸附量之间的差异太大，没有哪种假设能够对其进行解释。其他研究者表示，CO2和煤之间存在着特定的关系，但是甲烷和煤却不存在这种关系[2]。 Sakurovs等[8]发现，如果气体都能进入煤体结构，那么煤对气体的最大吸附量与气体的临界温度近似成正比关系。这就可以解释为何CO2的最大吸附量约为甲烷的2倍：CO2的临