1、Gas Processors Association 6526 E 60th Street Tulsa, OK 74145 TP 29 HYDROCARBON / WATER and HYDROCARBON / AQUEOUS AMINES MUTUAL SOLUBILITIES August 2003 FOREWORD At the 2001 Laurence Reid Gas Conditioning Conference, Mr. Jim Critchfield of Huntsman Corporation presented the paper titled “Solubility
2、 of Hydrocarbons in Aqueous Solutions of Gas Treating Amines” summarizing some data taken from previous literature, plus a considerable amount of new data taken for Huntsman by DB Robinson Research, Ltd. (now Oilphase-DBR) and The University of Calgary. There are a total of 84 new data points for th
3、e following systems. Most (70) are VLE but there are a few (14) LLE points. Propane in multiple strengths of DGA, MDEA, DIPA, DEA, MEA solutions Propylene in multiple strengths of DGA, MDEA, DIPA, DEA, MEA solutions Butane in multiple strengths of DGA, MDEA, DIPA, DEA, MEA solutions 1-Butene in mult
4、iple strengths of DGA, MDEA, DIPA, DEA, MEA solutions n-Pentane in multiple strengths of DGA, MDEA, DIPA, DEA solutions Ethane in a DGA solution Ethylene in multiple strengths of DGA solution Benzene in multiple strengths of DGA, MDEA, DIPA, DEA, MEA solutions Toluene in 4.5 M DGA, MDEA, DIPA, DEA,
5、MEA solutions P-Xylene in 4.5 M DGA, MDEA, DIPA solutions Huntsmans paper and conference presentation included several figures that summarize the data in a very clear and usable format. By permission from Huntsman, these documents are provided in Sections II and III, respectively, of this TP. The ra
6、w data is concisely formatted in pdf format and available as a 2-page table in Section IV of this TP. GPA wishes to offer special thanks to Mr. Critchfield and Huntsman Corporation for this excellent work in assimilating the previous data and collecting this new data into a composite data base, for
7、interpreting the data, and for presenting it in such a clear and usable format for the industry. Their willingness to share this valuable data and information with the GPA and the gas processing industry is commendable and appreciated. DISCLAIMER GPA publications necessarily address problems of a ge
8、neral nature and may be used by anyone desiring to do so. Every effort has been made by GPA to assure accuracy and reliability of the information contained in its publications. With respect to particular circumstances, local, state, and federal laws and regulations should be reviewed. It is not the
9、intent of GPA to assume the duties of employers, manufacturers, or suppliers to warn and properly train employees, or others exposed, concerning health and safety risks or precautions. GPA makes no representation, warranty, or guarantee in connection with this publication and hereby expressly discla
10、ims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict, or for any infringement of letters of patent regarding apparatus, equipment, or method so covered. “Copyright 20
11、03 by Gas Processors Association. All rights reserved. No part of this report may be reproduced without the written consent of the Gas Processors Association” TABLE OF CONTENTS I. Introduction II. 2001 Laurence Reid Gas Conditioning Conference Published Paper III. 2001 Laurence Reid Gas Conditioning
12、 Conference Presentation IV. Raw Data Developed for from Huntsman Corporation I. INTRODUCTION Accurate data on the solubility of various hydrocarbons in amines are necessary for process simulation, design, and minimum cost operation of amine treating plants. Solubility of hydrocarbons in amine solut
13、ions may be a factor in the selection of amine type. Most of the available public information on hydrocarbon solubility is limited to methane and ethane. Data for solubility of propane and heavier paraffins and aromatic compounds are lacking for most amine solutions. Taken as a whole, much of the av
14、ailable fundamental data seem contradictory. In order to help the industry to more accurately represent hydrocarbon solubility in the various products, Huntsman Corporation commissioned DB Robinson Research, Ltd. (now Oilphase - DBR) to measure hydrocarbon solubility in MEA, DEA, DGA Agent, MDEA and
15、 DIPA solutions. The project generated results for the mid-range hydrocarbons (paraffins and olefins) and for benzene, toluene and p-xylene. Analysis and presentation of the information includes data from various sources for the solubility of the hydrocarbons in water. II. 2000 LAURENCE REID GAS CON
16、DITIONING CONFERENCE Published Paper “SOLUBILITY OF HYDROCARBONS IN AQUEOUS SOLUTIONS OF GAS TREATING AMINES” SOLUBILITY OF HYDROCARBONS 1N AQUEOUS SOLUTIONS OF GAS TREATING AMINES Jim Critchfield and Pat Holub Huntsman Corporation Heng-Joo Ng DB Robinson Research Ltd. Alan E. Mather and Fang-Yuan J
17、ou University of Alberta Tom Bacon Consultant When scrubbing acid gases from hydrocarbons there is often concern about solubility of hydrocarbons in the aqueous amine solution, and about the resulting amount of hydrocarbons in the produced acid gas. Absorbed hydrocarbons will partially flash if the
18、pressure is reduced in a three-phase vessel, and the remaining hydrocarbons will strip into the acid gas. Excessive absorption of hydrocarbons may result in emission of hydrocarbon to the environment or increased cost and poorer operation of a sulfur plant. Accurate data on the solubility of various
19、 hydrocarbons in amines are necessary for process simulation, design and minimum cost operation of amine treating plants. Solubility of hydrocarbons in amine solutions may be a factor in the selection of amine type in a grass-roots design or in the expansion of an existing plant. Yet most of the ava
20、ilable public information on hydrocarbon solubility is limited to the lightest hydrocarbons (mainly methane and ethane). Data for solubility of propane and heavier paraffins are lacking for most amine solutions. Amine solutions are commonly used to scrub acid gases from olefin-containing streams in
21、refineries. Even though olefins are more soluble in water than are paraffins, very few data are available for the solubility of olefins in amine solutions. Similarly, the absorption of aromatics is of interest in amine plants, yet few data are currently available for the solubility of aromatics in a
22、mine solutions. In order to help the industry to more accurately represent hydrocarbon solubility in the various products, Huntsman commissioned DB Robinson Research, Ltd., to measure hydrocarbon solubility in MEA, DEA, DGA Agent, l MDEA and DIPA solutions. The DGA and Diglycolamine are registered t
23、rademarks of the Huntsman Corporation project generated results for the mid-range hydrocarbons (paraffins and olefins) and for benzene, toluene and p-xylene. Direct comparisons of hydrocarbon solubility between amine solutions are presented at equal molarity. Introduction Aqueous solutions of alkano
24、lamines are commonly used to remove CO2, H2S, and COS from gas and liquid hydrocarbon streams. “Alkanolamines“ are chemicals that have three functional parts. Alkanolamines contain at least one nitrogen atom. The nitrogen atom is the chemically active portion of the molecule - it is the site where a
25、cid gases react. An alkanolamine has at least one alcohol (hydroxyl) group. The alcohol group improves the miscibility with water. It also modifies the base strength of the amine so that the gas treating solution will have the proper balance between good affinity for acid gases and ease of regenerat
26、ion. The alcohol group helps lower the vapor pressure of the amine, and that minimizes vapor losses. All alkanolamines have at least one alkane (hydrocarbon) arm that separates the amine and the hydroxyl group. Separation by two or more carbon atoms provides chemical stability. Amines may be primary
27、 (1), secondary (2), or tertiary (3) depending on the number of alkane arms attached to the nitrogen. The number, size, and type of alkane groups attached to the nitrogen determine the different physical and chemical properties of common gas treating alkanolamines. Comparing Solutions of Different A
28、mines Because the various gas treating amines have different chemical and physical properties, it can be difficult to establish a meaningful basis of comparison. Some (DIPA, TEA, MDEA) are capable of partial selectivity towards HzS in the presence of CO2. Others (MEA, DEA, DGA Agent) react readily w
29、ith both CO2 and H2S. The base strength of the amines differs by more than one magnitude. The amines mentioned in this work include l, 2, and 3 amines that vary in molecular weight by more than a factor of two. Units for amine strength In commercial application of the products, amine solutions are t
30、ypically discussed in terms of weight percent strength. This is a useful measure to apply when considering like solutions: for instance, when monitoring the solvent concentration in a given plant. However, weight percent strength does not allow direct comparison between different amines that have un
31、equal molecular weights. If they have different molecular weights, equal weight percent solutions of two different amines can have very different capacities towards H2S. In the absorption of H2S, one mole of H2S reacts with one mole of amine, regardless of how much the mole of amine weighs. What mat
32、ters is the potency of the solvent - how many moles are contained in a given volume of solvent. Molarity (M) is a measure of the potency of the solvent - the number of moles of amine per liter of solution. Figure 1 shows the effect of molecular weight on amine molarity when amines are compared at eq
33、ual weight percent strength. In applications that contain mostly H2S and in applications where selective treating towards H2S is not the requirement, molarity correlates better with capacity than does weight percent. Use of equal molarity as a basis of comparison removes the bias introduced by unequ
34、al Figure 1: Molarity of the amines at equal weight percent strength Amine mole weights vary from 149 to 61 00ooo so 30%wt Amine solution = ? Molar .= 1 mole weights when comparisons are made of dissimilar amines. For example, a 30%wt solution of MEA (-5M) contains much more amine than a 30%wt solut
35、ion of MDEA (2.5M). In this work, molarity is used as a common basis of comparison between solutions of different amines. It should be noted that some of the data presented in this work are for amine solutions that are more concentrated than is typically recommended in commercial application. The da
36、ta presented in this work are intended to demonstrate the solubility of hydrocarbons in amine solutions and are not intended to suggest recommended amine strength for industrial application. Units for Henrys constants and for gas solubility Henrys Law defines a solubility relationship when the parti
37、al pressure of a sparingly- soluble compound is much lower than the compounds vapor pressure. Hemys Law is a specific case of the general fugacity relationship: Fugacity in gas phase = fugacity in liquid phase Simplifying assumptions allow the general relationship to be expressed as YiP = Hi Xi Wher
38、e Hi* is a constant of proportionality (Henrys Constant) in units of pressure over mole fraction Xi P yi is the moles of solute per mole of solution (mole fraction) is the system pressure is the mole fraction of compound in the gas phase As written in the above equation, Henrys constant is a measure
39、 of the insolubility of a material - the larger the Henrys constant, the lower the solubility. Typically Henrys constants are written in units of Pressure / mole fraction. These are useful units for correlating a single hydrocarbon-solvent system, or for comparing different solutes at in a single so
40、lvent system. However, when comparisons between solvent systems are intended, the use of mole fraction can create bias in the comparison. Because the mole weights of the gas treating amines can be so different, solutions of different amines can contain very different concentrations of water. This me
41、ans that solutions of different amines of the same molarity may have very different total molar volumes. For example, compare one liter of 3 M MEA and of 3 M TEA: TABLE I. Amine Molar %wt -In 1 Liter of amine solution- g g mole mole total amine water amine water moles MEA 3 18.3 183 817 3 45.4 48.4
42、TEA 3 44.7 447 553 3 30.7 33.7 The density in this comparison is assumed to be the same (1.0 g/ml) for simplicity. Because there is so much less water in the TEA solution, the TEA solution contains fewer total moles in a liter. The difference in molar volume becomes larger as the amine strength incr
43、eases and the concentration of water in solution decreases. When Henrys constant (or any other measure of gas solubility) is expressed on the basis of mole fraction, the total number of moles of solution matters. In contrast, if gas solubility or Henrys constant is expressed as the amount of gas dis
44、solved per volume of solution, very unlike solutions can be compared on a common basis. Henrys constants can be defined with concentration, as in: yiP = Hi Ci Where Hi cd P yi is a constant of proportionality (Henrys Constant) in units of pressure over concentration is the concentration of solute in
45、 a volume of solution, e.g., scf/gallon is the system pressure is the mole fraction of compound in the gas phase It is practical to consider the amount of gas dissolved per volume of solvent circulated, since the volume of solvent circulated is an important operating variable in gas treating applica
46、tions. In this work, when comparisons are made of solubility in different solvents, solubility is expressed in units of standard cubic foot dissolved per gallon of solution. How solubility changes with partial pressure The straight-line behavior described by the Henrys constant represents the solubi
47、lity relationship so long as limiting assumptions apply. In practical terms, the important assumptions are that The vapor phase is fairly ideal the temperature is much below the critical temperature of the solvent (T Terit) the partial pressure (YiP) is much lower than Psat, the vapor pressure of li
48、quid compound at the given temperature (YiP Psat) the presence of the solute doesnt change the properties of the solution As the partial pressure of a solute increases, the amount of that compound in solution increases. This remains the case up to the point that the compound condenses. After the com
49、pound condenses, increased pressure no longer has as much effect on the amount of hydrocarbon in solution. That behavior is illustrated in the data of Carroll et al. (1992) for propane lOOO solubility in 3M MDEA and in water (Figure 2). At . low partial pressure, the amount of propane in loo dissolved is proportional to *, the partial pressure. At higher pressures propane condenses and the . solubility of liquid propane 10 is comparatively constant. Figure 2: Solubility of Gas and Liquid Propan
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