CN113429198A - 一种应用于固定床甲烷化学链水蒸气重整的整体式载氧体及其制备方法 - Google Patents

一种应用于固定床甲烷化学链水蒸气重整的整体式载氧体及其制备方法 Download PDF

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CN113429198A
CN113429198A CN202110853975.9A CN202110853975A CN113429198A CN 113429198 A CN113429198 A CN 113429198A CN 202110853975 A CN202110853975 A CN 202110853975A CN 113429198 A CN113429198 A CN 113429198A
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肖艳
尹相雷
闫景春
沈来宏
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Abstract

本发明涉及一种应用于固定床甲烷化学链水蒸气重整的整体式载氧体的制备方法。所述整体式载氧体具有分层结构,表面层为钙钛矿型的LaFe0.3Mn0.7O3+δ,其质量占比为10~15 wt.%;内部为CeO2‑Fe2O3‑Al2O3泡沫陶瓷,CeO2:Fe2O3:Al2O3质量比为2~9:4~18:1。本发明通过直接发泡法与造孔剂法相结合,得到高孔隙率CeO2‑Fe2O3‑Al2O3开孔泡沫陶瓷,随后采用柠檬酸络合浸渍法将LaFe0.3Mn0.7O3+δ负载于泡沫陶瓷表面,得到整体式载氧体。所制整体式载氧体耦合了钙钛矿型LaFe0.3Mn0.7O3+δ良好的重整性能、CeO2快速氧迁移能力与Fe2O3/Fe3O4的经济性和载氧能力,载氧体循环稳定性高、抗积碳能力强、合成气选择性好,适用于甲烷化学链水蒸气重整过程。本发明制备工艺相对简单,条件容易控制,具有高比表面积、高活性组分分散度的特点。

Description

一种应用于固定床甲烷化学链水蒸气重整的整体式载氧体及 其制备方法
技术领域
本发明涉及甲烷化学链水蒸气重整技术领域,特别是涉及一种应用于固定床反应器的整体式载氧体的制备方法。
背景技术
甲烷是天然气和非常规天然气的主要成分,有着丰富的储量,甲烷重整制备合成气是一种高效、低能耗的甲烷利用途径,重整产物(CO、H2合成气)通过费托合成可进一步转化为化工产品和液体燃料。目前工业甲烷重整主要采用甲烷水蒸气重整技术,即
CH4 + H2O → CO + 3H2
该技术生成的合成气中H2/CO摩尔比值接近3,而下游合成气应用中常用比例为2,重整所得合成气产物在应用中需要进一步分离,增大了转化成本。
化学链甲烷水蒸气重整(CL-SMR)是一种新型的甲烷重整技术,在重整过程中可以实现H2原位分离,产出合适配比的合成气和高纯度氢气。CL-SMR通常采用具有氧化还原能力的金属氧化物作为载氧体,将甲烷水蒸气重整过程分为甲烷重整和水蒸气制氢两步:
(1)甲烷重整阶段:CH4 + MexOy → CO + 2H2 + Mex-1Oy
(2)制氢阶段:H2O + Mex-1Oy → MexOy + H2
CL-SMR系统需要载氧体在两个反应阶段之间循环,在甲烷重整阶段,载氧体被甲烷还原,在制氢阶段,载氧体被水蒸气氧化再生。化学链技术常采用串行流化床反应器实现载氧体的传递和反应阶段切换,循环过程中载氧体颗粒碰撞、摩擦会导致载氧体表面活性组分磨损、使用寿命降低,影响系统稳定运行。采用固定床反应器,通过气体切换实现载氧体还原-氧化过程交替进行,可降低对载氧体机械强度的要求、减少载氧体物理损失,且固定床反应器结构更简单、能量消耗更少,高压运行时可与下游产物利用工艺相耦合。将整体式载氧体应用于固定床反应器,可使反应区孔隙分布均匀、床层压降小,具有良好的应用前景。
载氧体性能是影响CL-SMR运行效果的重要因素,合适的载氧体需具备良好的热稳定性、循环再生性、载氧能力、反应活性、合成气选择性以及抗积碳能力。具有钙钛矿结构(ABO3)的复合金属氧化物在高温下有着很强的稳定性、反应活性和氧传递能力,通过A、B位离子的掺杂可使晶体结构产生更多缺陷,达到改变其反应活性和离子迁徙能力的目的,具有作为CL-SMR系统载氧体的潜力。Mn是一种多价态过渡金属,在钙钛矿结构常以Mn2+、Mn3+、Mn4+价态存在,表面高浓度阴离子空位使LaMnO3+δ具有良好的还原活性,受限于结构内氧传递能力,LaMnO3+δ在重整时反应速率和甲烷转化率较低。目前公开了一种使用Cu对LaMnO3+δ进行A/B位掺杂改性的方法(DOI: 10.1016/j.fuproc.2021.106744),实验显示掺杂后载氧体在重整阶段的合成气选择性、甲烷转化率均有显著提升,但载氧体的循环性能较差。此外,还公开了使用LaMn1-xFexO3+δ作为CL-SMR载氧体的方法,Fe元素掺杂削弱了结构中Mn-O键强度、增加了Mn4+占比,载氧体可利用选择性晶格氧增多,提高了载氧体中氧空位形成、氧迁移能力与反应活性,但过多的Fe元素(x= 0.5、0.7,DOI:10.1007/s11814-016-0329-6)掺杂会导致重整阶段甲烷裂解、积碳现象严重,合成气H2比例上升,掺杂太少(x= 0.1,DOI:10.1016/j.ces.2020.116085)则重整性能改善效果较差,总之还需进一步研究合适的掺杂的比例。
作为一种理想的载氧体,钙钛矿型氧化物较其他简单金属氧化物物料和制备成本更高,制约了CL-SMR技术的经济性。中国专利CN112295566A公开了一种应用于CL-SMR的具有分层结构的Fe3O4-MeOx@La0.5Ce0.5FeO3载氧体粉末,其中Fe3O4起到了提高载氧体携氧能力与分散表面活性组分的作用,通过表面层La0.5Ce0.5FeO3和内部Fe3O4协同作用,载氧体具有高携氧量和良好的反应活性、合成气选择性;但受限于Fe3O4晶格氧迁移速率,重整过程中载氧体表面可能被深度还原至Fe0(DOI: 10.1016/j.ces.2020.115707),导致钙钛矿结构破坏、催化甲烷裂解产生析碳,使重整阶段H2/CO摩尔比升高、制氢阶段H2纯度下降。Ce是地球上储量最多的稀土元素,CeO2具有特殊的晶体结构、键合性能和可变氧化态,稳定的半开放萤石晶体结构中Ce4+和Ce3+可快速转化,实现氧空位快速形成、转移和消除,常用作金属基催化剂载体,将其应用于整体式载氧体中可得到良好的供氧/储氧效果。
发明内容
针对现有化学链甲烷水蒸气重整载氧体面临的反应活性较低、机械强度较低、抗积碳性较差等问题,本发明提供了一种应用于固定床甲烷化学链水蒸气重整的整体式载氧体及其制备方法,所制整体式载氧体耦合了LaFe0.3Mn0.7O3+δ的高选择性、高反应活性与CeO2、Fe2O3的经济性、供氧/储氧特性,所制整体式载氧体循环稳定性好、重整性能良好。
本发明采用的技术方案如下:
第一方面,本发明提供的整体式载氧体为一种具有分层结构、由泡沫陶瓷负载活性组分的复合金属氧化物,由LaFe0.3Mn0.7O3+δ、CeO2、Fe2O3和Al2O3组成。
进一步的,所述整体式载氧体表面层为钙钛矿型LaFe0.3Mn0.7O3+δ,内部为CeO2-Fe2O3-Al2O3泡沫陶瓷。
进一步的,所述整体式载氧体各组分质量分数为:LaFe0.3Mn0.7O3+δ= 10~15wt.%,CeO2- Fe2O3-Al2O3= 85~90wt.%;其中,CeO2:Fe2O3质量比为1:2,MexOy(Me=Ce、Fe):Al2O3质量比为9~19:0~1。
第二方面,本发明提供所述整体式载氧体的制备方法,首先,结合直接发泡法与造孔剂法,制备出高孔隙率CeO2-Fe2O3-Al2O3开孔泡沫陶瓷;随后采用柠檬酸络合浸渍法将LaFe0.3Mn0.7O3+δ负载于泡沫陶瓷表面,得到整体式载氧体。具体制备流程包括以下步骤:
步骤1泡沫陶瓷浆料配制:将CeO2、Fe2O3与Al2O3粉末加入去离子水中,使用球磨充分研磨至粒径<0.1μm,得到浆料a,取部分浆料a加入表面活性剂十二烷基硫酸钠和造孔剂二氧化硅空心微球,并使用氨水或稀盐酸调节混合物pH至弱酸性,得到浆料b。
步骤2浆料发泡与成型:以2000r/min搅拌浆料b,得到均匀稳定的泡沫浆料,将泡沫浆料倒入模具中,经干燥、煅烧处理,随炉冷却后得到CeO2-Fe2O3-Al2O3开孔泡沫陶瓷。
步骤3表面层原液配制:按LaFe0.3Mn0.7O3+δ分子式称取化学当量的硝酸镧和硝酸铁颗粒、量取硝酸锰溶液溶于去离子水中得到金属盐溶液a,配制适量柠檬酸溶液,将柠檬酸溶液和乙二醇逐滴加入溶液a中并伴随搅拌,得到溶液b,使用氨水调节pH至弱酸性,水浴搅拌蒸发溶液b得到高浓度溶液作为LaFe0.3Mn0.7O3+δ原液。
步骤4原液浸渍:将步骤2所制CeO2-Fe2O3-Al2O3泡沫陶瓷完全浸没于步骤3所制原液中,浸渍一定时间后缓慢取出,随后进行干燥、焙烧处理,重复浸渍、干燥和焙烧直负载质量比至设定值。
步骤5煅烧成型:将步骤5所制样品放置于马弗炉中进行煅烧处理,随炉冷却后得到应用于化学链甲烷水蒸气重整的整体式载氧体CeO2-Fe2O3-Al2O3@LaFe0.3Mn0.7O3+δ
进一步的,步骤1所述浆料b中CeO2、Fe2O3与Al2O3总含量为30~50wt.%,表面活性剂含量为0.03~0.15wt.%,造孔剂含量为10~15wt.%,造孔剂粒径为为30~70μm。
进一步的,步骤2所述泡沫浆料在室温下干燥,随后以2~3℃/min升温速率匀速升温至1400~1500℃,并恒温煅烧2~4h。
进一步的,步骤3所述溶液b内金属阳离子:柠檬酸:乙二醇摩尔比 = 1 : 1.5~2 :1.5~2,金属阳离子浓度0.1~0.15mol/L,水浴搅拌温度为60~80℃,搅拌蒸发后溶液b中金属阳离子浓度达到0.5~1mol/L。
进一步的,步骤4所述浸渍时间为0.5~1h,在110~120℃下干燥4~6h,在400℃下焙烧2~4h。
进一步的,步骤5所述煅烧升温速率10℃/min,由室温升至800~900℃并恒温煅烧2~4h。
第三方面,本发明提供所述整体式载氧体应用于固定床甲烷化学链水蒸气重整的方法。
通过整体式载氧体所在反应区甲烷-水蒸气气氛的切换,使载氧体进行还原-氧化循环反应,实现在水蒸气和甲烷互不接触的条件下利用载氧体传递晶格氧,制备得到高品质合成气和高纯度氢气。受水蒸气氧化性限制,制氢阶段载氧体内部Fe元素难以被氧化至Fe2O3,以Fe3O4或其他无定形状态存在。
与现有技术相比,本发明取得的有益效果为:
(1)LaFe0.3Mn0.7O3+δ具有良好的合成气选择性、反应活性以及循环稳定性,本发明所制整体式载氧体使用钙钛矿型LaFe0.3Mn0.7O3+δ作为载氧体表面层覆盖于泡沫金属表面,表面活性组分分散性好,反应过程中与反应气体充分接触。
(2)本发明所制整体式载氧体内部活性组分为CeO2和Fe2O3,其来源广泛、经济性好,具有良好的供氧/储氧能力,在反应过程中几乎不与反应气体直接接触,重整阶段为表面层提供选择性晶格氧,制氢阶段存储表面吸附的氧元素。其中,CeO2具有快速氧迁移能力,及时为表面层提供晶格氧,避免了长时间运行过程中表面层金属深度还原,载氧体抗积碳能力强、合成气H2/CO比例稳定。
(3)本发明所制整体式载氧体比表面积大,为开孔结构,具备一定的机械强度和抗压能力,适用于固定床甲烷化学链水蒸气重整。
(4)本发明所述整体式载氧体制备工艺相对较简单,条件易控制、重复性好。
附图说明
图1为本发明整体式载氧体的制备流程图;
图2为新鲜钙钛矿型LaFexMn1-xO3+δ(x=0,0.1,0.2,0.3)载氧体在CL-SMR实验中还原阶段出口气体流量;
图3为钙钛矿型LaFe0.3Mn0.7O3+δ载氧体还原后、循环1次以及循环20次的XRD图谱;
图4为为实施例1在CL-SMR实验10次循环中甲烷转化率、CO选择性、产物H2/CO摩尔比以及积碳量。
具体实施方式
对比例1:
以柠檬酸作为络合剂采用溶胶-凝胶法制备了钙钛矿型LaFexMn1-xO3+δ(x=0,0.1,0.2,0.3)载氧体进行CL-SMR实验。实验反应温度850℃,载氧体均匀铺设于布风板上,质量为2g。重整阶段甲烷流量为15ml/min,反应时间20min;还原阶段水蒸气流量为0.1g/min,反应时间30min;每次切换反应阶段前使用N2吹扫20min。
(1)图2为新鲜钙钛矿型LaFexMn1-xO3+δ(x=0,0.1,0.2,0.3)载氧体在甲烷重整阶段出口气体流量。实验过程中各载氧体都具有稳定的重整效果,几乎没有甲烷裂解现象发生,x=0.3时甲烷转化率最高。
(2)图3为钙钛矿型LaFe0.3Mn0.7O3+δ载氧体还原后(20min)、循环1次以及循环20次的XRD图谱,可以看出LaFe0.3Mn0.7O3+δ结构稳定,循环再生性能良好。
实施例1:
(1)载氧体制备方法
步骤1泡沫陶瓷浆料配制:将质量比为8 : 18 : 1的CeO2、Fe2O3与Al2O3粉末加入去离子水中,使用球磨充分研磨至粒径<0.1μm,得到浆料a。取部分浆料a配制得到含CeO2、Fe2O3与Al2O3总量40wt.%、表面活性剂十二烷基硫酸钠含量0.1wt.%、造孔剂二氧化硅空心微球含量15wt.%的混合浆料b,调节浆料b的pH至弱酸性。
步骤2浆料发泡与成型:以2000r/min搅拌浆料b,得到均匀稳定的泡沫浆料,将泡沫浆料倒入模具中,在室温下干燥得到干坯,随后置于马弗炉中随后以2~3℃/min升温速率匀速升温至1500℃并恒温煅烧2h,随炉冷却后得到CeO2-Fe2O3-Al2O3开孔泡沫陶瓷。
步骤3表面层原液配制:按La3+:Mn2+:Fe3+离子摩尔比10:7:3配制化学当量的硝酸盐溶液a,溶液a中金属阳离子浓度0.1mol/L。按金属阳离子:柠檬酸:乙二醇摩尔比1:2:2配制柠檬酸溶液、量取乙二醇,将柠檬酸溶液和乙二醇逐滴加入溶液a中并伴随搅拌,得到溶液b,使用氨水调节溶液b的pH至弱酸性,以80℃水浴搅拌蒸发至溶液中金属阳离子浓度至1mol/L,作为LaFe0.3Mn0.7O3+δ原液。
步骤4原液浸渍:将步骤2所制CeO2-Fe2O3-Al2O3泡沫陶瓷完全浸没于步骤3所制原液中,浸渍1h后缓慢取出,随后在120℃下干燥6h,并在400℃下焙烧2h,重复浸渍、干燥和焙烧至负载量达到10wt.%。
步骤5煅烧成型:将步骤4所制样品放置于马弗炉中以升温速率10℃/min由室温升至850℃,并恒温煅烧4h,随炉冷却后得到整体式载氧体CeO2-Fe2O3-Al2O3@LaFe0.3Mn0.7O3+δ
(2)反应性能评价方法
将所得整体式载氧体在固定床上进行气化实验,实验在固定床进行,反应温度恒定在850℃、常压。整体式载氧体固定于反应区中央,质量为2g。(a)还原阶段:通入流量为100ml/min的N2/10vol.%CH4混合气20min;(b)使用80ml/minN2吹扫至管路中不再含有CH4;(c)氧化阶段:通入流量为0.1g/min的水蒸气和80ml/min的N2至出口气体中不再含有H2和CO;(d)使用1L/minN2吹扫至管路中无水蒸气。上述(a)~(d)为一个完整的循环,出口气体经干燥后由气体分析仪实时检测。
图4为10次循环中实验的甲烷转化率、CO选择性、产物H2/CO摩尔比以及积碳量。实验结果显示,在10次循环实验中载氧体表现出良好的循环反应性能和稳定性;还原阶段甲烷的平均转化率为84%,第二次循环后CO的选择性平均值为91%,H2/CO平均值为2.16;氧化阶段均未检测到CO,表明载氧体表面积碳量极少。
实施例2:
按实施例1的制备方法制备整体式载氧体,区别仅在于步骤4的负载量为15%。
按实施例1的反应性能评价方法对载氧体性能进行实验分析。实验结果显示在10次循环实验中载氧体表现出良好的循环反应性能;还原阶段甲烷的平均转化率为79%,第二次循环后CO的选择性平均为92%,H2/CO平均为2.12;氧化阶段均未检测到CO,表明载氧体表面积碳量极少。
对比例2:
按实施例1的制备方法制备整体式载氧体,区别仅在于步骤3的原液中阳离子摩尔比为La3+:Mn2+ =1:1。
按实施例1的反应性能评价方法对载氧体性能进行实验分析,结果显示在5次循环实验中,还原阶段甲烷的平均转化率为66%,载氧体反应活性较低。
以上显示和描述了本发明的基本原理、主要特征和本发明的优点。本行业的技术人员应该了解,本发明不受上述实施例的限制,上述实施例和说明书中描述的只是说明本发明的原理,在不脱离本发明精神和范围的前提下,本发明还会有各种变化和改进,这些变化和改进都落入要求保护的本发明范围内。本发明要求保护范围由所附的权利要求书及其等效物界定。

Claims (9)

1.一种应用于甲烷化学链水蒸气重整的整体式载氧体,其特征在于,所述整体式载氧体由钙钛矿型LaFe0.3Mn0.7O3+δ、CeO2、Fe2O3和Al2O3组成。
2.根据权利要求1所述一种应用于甲烷化学链水蒸气重整的整体式载氧体,其特征在于,所述整体式载氧体具有分层结构,表面层为钙钛矿型LaFe0.3Mn0.7O3+δ,表面层负载量为10~15wt.%,内部为CeO2-Fe2O3-Al2O3泡沫陶瓷,其中,CeO2:Fe2O3质量比为1:2,MexOy(Me=Ce、Fe):Al2O3质量比为9~19:0~1。
3.制备权利要求1所述的应用于甲烷化学链水蒸气重整的整体式载氧体的方法,其特征在于,通过直接发泡法与造孔剂法相结合,得到高孔隙率CeO2-Fe2O3-Al2O3开孔泡沫陶瓷,随后采用柠檬酸络合浸渍法将LaFe0.3Mn0.7O3+δ负载于泡沫陶瓷表面,得到整体式载氧体;该方法具体分为以下步骤进行:
步骤1泡沫陶瓷浆料配制:将CeO2、Fe2O3与Al2O3粉末加入去离子水中,使用球磨充分研磨至粒径<0.1μm,得到浆料a,取部分浆料a加入表面活性剂十二烷基硫酸钠和造孔剂二氧化硅空心微球,并使用氨水或稀盐酸调节混合物pH至弱酸性,得到浆料b;
步骤2浆料发泡与成型:搅拌浆料b,得到均匀稳定的泡沫浆料,将泡沫浆料倒入模具中,经干燥、煅烧处理,随炉冷却后得到CeO2-Fe2O3-Al2O3开孔泡沫陶瓷;
步骤3表面层原液配制:按LaFe0.3Mn0.7O3+δ分子式称取化学当量的硝酸镧和硝酸铁颗粒、量取硝酸锰溶液溶于去离子水中得到金属盐溶液a,配制适量柠檬酸溶液,将柠檬酸溶液和乙二醇逐滴加入溶液a中并伴随搅拌,得到溶液b,使用氨水调节pH至弱酸性,水浴搅拌蒸发溶液b得到高浓度溶液作为LaFe0.3Mn0.7O3+δ原液;
步骤4原液浸渍:将步骤2所制CeO2-Fe2O3-Al2O3泡沫陶瓷完全浸没于步骤3所制原液中,浸渍一定时间后缓慢取出,随后进行干燥、焙烧处理,重复浸渍、干燥和焙烧直负载质量比至设定值;
步骤5煅烧成型:将步骤5所制样品放置于马弗炉中进行煅烧处理,随炉冷却后得到应用于化学链甲烷水蒸气重整的整体式载氧体CeO2-Fe2O3-Al2O3@LaFe0.3Mn0.7O3+δ
4.根据权利要求3所述制备应用于甲烷化学链水蒸气重整的整体式载氧体的方法,其特征在于,步骤1所述浆料b中CeO2、Fe2O3与Al2O3总含量为30~50wt.%,表面活性剂含量为0.03~0.15wt.%,造孔剂含量为10~15wt.%,造孔剂粒径为为30~70μm。
5.根据权利要求3所述制备应用于甲烷化学链水蒸气重整的整体式载氧体的方法,其特征在于,步骤2所述泡沫浆料在室温下干燥,随后以2~3℃/min升温速率匀速升温至1400~1500℃,并恒温煅烧2~4h。
6.根据权利要求3所述制备应用于甲烷化学链水蒸气重整的整体式载氧体的方法,其特征在于,步骤3所述溶液b内金属阳离子:柠檬酸:乙二醇摩尔比 = 1 : 1.5~2 : 1.5~2,金属阳离子浓度0.1~0.15mol/L,水浴搅拌温度为60~80℃,搅拌蒸发后溶液b中金属阳离子浓度达到0.5~1mol/L。
7.根据权利要求3所述制备应用于甲烷化学链水蒸气重整的整体式载氧体的方法,其特征在于,步骤4所述浸渍时间为0.5~1h,在110~120℃下干燥4~6h,在400℃下焙烧2~4h。
8.根据权利要求3所述制备应用于甲烷化学链水蒸气重整的整体式载氧体的方法,其特征在于,步骤5所述煅烧升温速率10℃/min,由室温升至800~900℃并恒温煅烧2~4h。
9.权利要求1所述整体式载氧体在固定床甲烷化学链水蒸气重整方面的应用,其特征在于,通过整体式载氧体所在反应区甲烷-水蒸气气氛的切换,使载氧体进行还原-氧化循环反应,实现在水蒸气和甲烷互不接触的条件下利用载氧体传递晶格氧,制备得到合成气和氢气。
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CN114931952A (zh) * 2022-04-11 2022-08-23 华东理工大学 内热式甲烷蒸汽重整制氢泡沫整体式催化剂的制备方法
CN114931952B (zh) * 2022-04-11 2023-11-10 华东理工大学 内热式甲烷蒸汽重整制氢泡沫整体式催化剂的制备方法
CN114917916A (zh) * 2022-05-30 2022-08-19 昆明理工大学 一种高储氧量和高稳定性载氧体及其制备方法

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