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MDEA_TETA溶液中CO_2的解吸动力学研究

OIL AND GAS TREATMENT AND PROCESSING 油气处理与加工

MDEA

-TETA溶液中

CO2的解吸动力学研究

徐 莉1 贾 庆2 侯凯湖1

(1.河北工业大学绿色化工研究所 2.大庆油田工程有限公司)

摘 要 从工程应用出发,采用动态法测定了三个配比的N-甲基二乙醇胺+三乙烯四胺混合溶液的CO2解吸速率。基于解吸机理和实验数据,建立了该溶液CO2解吸的简化动力学方程。方程的CO2解吸速率预测值与实验值的平均相对误差<10%,方程可用于工业上该类胺溶液再生过程的设计和优化操作。

关键词 MD EA TETA 解吸 动力学

DOI:10.3969/j.issn.1007-3426.2009.04.008

20世纪80年代,烷醇胺(M EA)净化技术过渡到甲基二乙醇胺(MD EA)净化技术,后者的良好选择性、稳定性和低能耗等优点使之成为天然气净化技术的一大进步[1]。目前,国内外已开发了多种活化(或称配方)MDEA溶液,有关研究表明,加入TETA可以显著改善MD EA水溶液吸收CO2性能。TETA-MDEA溶液在一定程度上克服了单纯MDEA溶液脱除CO2的不足,既保留了伯或仲胺的强脱CO2能力,同时又具有MDEA的低腐蚀和节能效果(高溶解、低降解、高酸气负荷和低反应热等优点),以其较高的吸收速率、较低的解吸能耗越来越受到人们的重视,成为脱除酸性气体的新研究方向。但目前尚未见到关于MD EA-TETA溶液C02解吸动力学的研究。本文采用动态法在常压、343K~373K温度范围内,测定了MD EA-TE2 TA溶液的CO2解吸速率,并基于理论分析和实验数据,建立了简化的CO2解吸动力学方程,以期为该类溶液的工业再生过程提供技术支持。

1实验部分

1.1实验装置图

采用250mL三口瓶作为吸收与解吸的反应器。在常压、30℃下进行CO2吸收实验。当CO2吸收负荷达最大时,停止通入CO2;然后调节油浴控制在一定温度下搅拌解吸,同时进行色谱在线分析。当出口气体中不含CO2时,停止解吸

1.2实验试剂

MDEA,分析纯(四川精细化工研究所);TE2 TA,分析纯(天津市光复精细化工研究所)。

2实验结果与讨论

混合胺富液动态法解吸CO2实验在解吸温度343.15K~373.15K、常压下进行。MDEA-TETA 混合胺溶液总体积100mL,总胺浓度3.0mol/L,其中活化剂TETA浓度分别为0.3mol/L、0.4 mol/L和0.6mol/L。实验分别考察了解吸温度、再生次数、溶液组成及吸收负荷对此三个浓度配比溶液CO2解吸速率的影响。为节省篇幅,这里仅给

892

石油与天然气化工 CHE MICA L E NGI NEERI NG OF OI L&G AS 2009 

出部分具有代表性的实验结果并加以讨论。2.1再生次数对CO 2解吸速率的影响

在解吸温度一定时,溶液的再生次数对其CO 2

解吸速率的影响见图2、图3。从图中可见,再生次数对CO 2解吸速率的影响很小,基本可忽略不计,这表明再生过程对溶液的性质影响很小。此外,随着吸收负荷的减小,CO 2解吸的推动力亦随之减小,故其解吸速率也逐渐减小

2.2解吸温度对CO 2解吸速率的影响

图4、图5的结果给出了温度对CO 2解吸速率的影响。可以看出,随着解吸温度增高,

混合胺溶液

的CO 2解吸速率增加。混合胺溶液的CO 2解吸为吸热反应,解吸温度升高应有利于解吸过程的进行

2.3溶液组成对解吸速率的影响

溶液组成对CO 2解吸速率的影响见图6、图7。由图可以看出,在相同吸收负荷下,对应于不同活化剂浓度溶液的CO 2解吸速率差别较小,其中活化剂浓度0.4mol/L 溶液的解吸速率略为高一些

3解吸动力学方程

3.1解吸机理

被吸收的气体溶质与吸收剂分开的操作称为解吸。该过程在工业上称为再生,往往与吸收过程相

9

92 第38卷 第4期 MD EA -TETA 溶液中CO 2的解吸动力学研究

结合,且互为逆反应,目的在于获得被吸收的气体,并使吸收剂与溶质分开,使吸收剂重新循环使用。

MDEA (CH 3-N (C H 2CH 2O H )2)用R 3N 表

示,TETA (N H 2-C 2H 4-N H -C 2H 4-N H -C 2H 4-N H 2)用RN H 2表示。MDEA 是一种叔胺,

其氮原子为三耦合的,不像伯胺与仲胺易与CO 2生成稳定的胺基甲酸盐,而仅生成亚稳态的碳酸氢盐

[2]

。在高温的解吸条件下,极易水解

:

TETA 含2个伯胺氮原子,2个仲胺氮原子,伯

胺、仲胺易与

CO 2反应生成稳定的胺基甲酸盐。

有关研究发现[3],CO 2与混合胺水溶液反应可作虚拟一级反应处理。反应(1)分两步进行,发生在液膜中的反应(2)为对整个解吸过程起控制作用的反应步骤,反应(3)是在液流主体中进行趋于平衡的中和反应,即水解反应的逆反应。

Astarita 和Savage 指出,化学吸收速率的理论

可以直接运用于化学解吸过程,基于双膜理论可得CO 2解吸过程速率表达式为[4]:

N C O 2=βK L (P 3

C O 2-P CO 2)

(5)β=

M =

D C O 2?K C O 2

K 2

L

(6)N C O 2=

D C O 2?K C O 2(P 3

C O 2-P C O 2)

(7)K C O 2=k 0exp (-E/R T )(8)

P 3

C O 2=

1

2a αC O 2

αC O 2(y

3

-1)-a +[a +αC O 2(1-y 3)]2+4ay 3

αC O 2

(9)

P C O 2=f C O 2?W 2/(f CO 2?W 2+W 1)?0.101325

(10)

3.2CO 2解吸动力学方程的参数估值

基于CO 2解吸的实验数据,得到K C O 2与1/T 之间的关系见图8,采用最小二乘法得到不同活化

剂浓度的混合胺溶液的二级反应速率常数为:

K C O 2=A exp (B/T )

A =-1.08E -3+5.35E -3C TETA -5.82E -3C 2TETA

B =-34217.78+134193.4

C TETA -146700C 2TETA

表1 二级反应速率常数

C TETA K CO 2

表观活化能

Ea ,J /mol

0.3K C O 2=4.64×10-6exp (-7162/R T )71620.4K

C

O 2=1.32×10

-4

exp (-6513/R T )

65130.6

K C O 2=3.75×10-6exp (-4012/R T )

4012

3.3解吸动力学方程预测精度分析

CO 2解吸速率实验值与模型预测值的对比结

果见图9,二者的相对偏差见表2。

表2 CO 2解吸速率的相对平均偏差

C TETA ,mol/L 解吸温度T ,K

343.15353.15363.15373.15

CO 2解吸速率实验

值与模型预测值的相对平均偏差,%

0.3

6.54 4.918.17

7.410.47.65 6.2 5.527.870.6

2.31

5.6

2.57

9.81

由图9看出,三种配比混合胺溶液CO 2解吸速率实验值与模型值很好地分布在Y =X 直线上或两侧。表2为不同温度三种配比下CO 2解吸速率实

03石油与天然气化工

CHE MICA L E NGI NEERI NG OF OI L &G AS 2009 

验值与模型预测值的相对平均偏差。由表2可知,与实验值比较,CO2解吸速率模型预测值的相对平均偏差均<10%。可见,建立的解吸速率模型有较好的预测能力,可以满足工程设计的需要。

4结论

(1)M EDEA-TETA溶液的CO2解吸实验结果表明:CO2解吸速率随温度的增加而增加、随吸收负荷的减小而减小;溶液的再生次数对CO2解吸速率影响很小;在所考察的溶液组成范围内,溶液组成的变化对CO2解吸速率影响亦不明显。

(2)基于双膜理论,建立了MDEA-TETA混合胺溶液CO2解吸的速率关联式。根据实验数据,确定了混合胺溶液解吸CO2速率常数K CO

2

与温度的关系式,所得到的CO2解吸动力学模型的预测值与实验值的相对平均偏差小于10%,满足工业解吸装置设计及优化操作的需要。

符号说明

N C O

2—CO2解吸速率,kmol/(s?m2);β—化学

解吸增大因子;M—化学解吸无因次准数;K L—液

相反应速率常数;D C O

2

—CO2扩散系数,m2/s;

K C O

2

—反应速率常数,kmol2/(m6?s?M Pa2);

K0—反应速率系数;P C O

2

3—CO

2平衡状态分压,

M Pa;P C O

2

—气相中CO2分压,M Pa;а和α—模型参

数[5];T—绝对温度,K;y—吸收负荷,mol CO2/mol

Am;Am—胺。

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作者简介

徐 莉:硕士研究生(河北工业大学绿色化工研究所),主要从

事化学工艺方面的研究。地址:(300130)天津市红桥区光荣道8号

河北工业大学东院467信箱。电话:022-********,138********,

xuli2006a@https://www.sodocs.net/doc/3d16315927.html,。

收稿日期:2008-10-15;编辑:杨 兰

(上接第293页)

(2)负载量60%是催化剂最大负载量阈值,催化剂在达到负载量为40%后催化活性变化不大,选择40%负载量催化剂可以达到异戊醇最佳转化率及酯化反应最高选择性。

(3)催化剂具有较强催化活性,色谱分析表明异戊醇转化率65%,丙酸异戊酯选择性可达100%。催化剂具有能克服一般浸渍型催化剂容易溶脱的缺点,催化剂循环使用6次活性没有明显降低。

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作者简介

王 伟:男,1982年生。硕士生,主要从事碳四组分催化水合的研究。

收稿日期:2008-12-11;收修改稿:2009-03-11;编辑:康 莉

103

 第38卷 第4期 MD EA-TETA溶液中CO2的解吸动力学研究

Hu Hong(Nanjing College of Chemical Technology,Jiangsu Nanjing210048).C H EM I CA L EN GI N E ER I N G O F O IL &GA S,V OL.38,N O.4,p p288~290,2009(I S S N1007-3426,I N C H I N ES E)

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K eyw ords:mercaptan,Co PcS,MgO,Al2O3, CH3O H,C2H5O H,H2O

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Wang Wei,Sun Linbing,Liu Dinghua,et al(State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology,Nanjing210009).

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Abstract:A series of immobilized heteropolyacid cata2 lysts were prepared by means of sol-gel technology.Cata2 lytic activities were investigated via synthesis of isoamyl pro2 pionate.FT-IR spectra,X-ray diff raction and physical adsorption of nitrogen were employed to character the cata2 lysts.The experiments indicated that with the loading a2 mount increasing,the catalytic activity improved till the loading of the catalysts near the maximum crop load.HP2 Mo/SiO2showed the high catalytic activity during the esteri2 fication reaction.Conversion of isoamyl alcohol and selectivi2 ty of isoamyl propionate are65%and100%respectively.

K eyw ords:immobilized catalysts,heteropolyacid,sol -gel,esterification,isoamyl propionate

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Wang Qiuju1,Lei Yufei2(https://www.sodocs.net/doc/3d16315927.html, PC Dalian L N G Project Manager Dept.;2.PetroChina Engineering Co.,Dalian Company).C H EM I CA L EN GI N E ER I N G O F O IL& GA S,V OL.38,N O.4,p p294~297,2009(I S S N1007-3426,I N C H I N ES E)

Abstract:L N G cold energy application has a great potential in China.In this paper,L N G cold energy applica2 tion on air separation is emphatically explicated,and the con2 ception of L N G cold energy and its mathematic model is also explained.Adopting cold energy application technology may save energy during the establishment period of L N G receiv2 ing station,at the same time,the pollution come of sea wa2 ter drainage is also decreased.L N G cold energy application is a clean and energy-saving technology that can generate considerable economic and social benefits.

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Kinetic Study on C arbon Dioxide Desorption from the Mixed MDEA-TETA Aqueous Solution Xu Li1,Jia Qing2,Hou Kaihu1(1.Institute of Green Chemical Technology,Hebei University of Technology, Tianjin300130; 2.Daqing Oilfield Engineering Co Ltd, Heilongjiang Daqing,163712).C H EM I CA L EN GI N E ER2 I N G O F O IL&GA S,V OL.38,N O.4,p p298~301,2009 (I S S N1007-3426,I N C H I N ES E)

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2 C H EM I CA L EN GI N E ER I N G O F O IL&GA S A ug.2009,V ol.38,N o.4

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