US3695002A - Process for production of pure ethylene - Google Patents

Process for production of pure ethylene Download PDF

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US3695002A
US3695002A US68672A US3695002DA US3695002A US 3695002 A US3695002 A US 3695002A US 68672 A US68672 A US 68672A US 3695002D A US3695002D A US 3695002DA US 3695002 A US3695002 A US 3695002A
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boiling
acetylene
solvent
boiling solvent
process according
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Friedrich Rottmayr
Hans Reimann
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Linde GmbH
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Linde GmbH
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C7/00—Purification; Separation; Use of additives
    • C07C7/005—Processes comprising at least two steps in series
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C7/00—Purification; Separation; Use of additives
    • C07C7/11—Purification; Separation; Use of additives by absorption, i.e. purification or separation of gaseous hydrocarbons with the aid of liquids

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  • This invention relates to a process for obtaining acetylene-free ethylene from a mixture of C -hydrocarbons by selective absorption of the acetylene and separation of the ethane by rectification.
  • the gaseous mixtures produced during the cracking of hydrocarbons contain acetylene in amounts, depending on the type of the starting material and the selection of the cracking method, which can range from about 0.1 to percent and higher. In cracking processes which produce primarily ethylene and higher olefins, cracking temperatures of between about 750 and 900 C. are employed.
  • the thus-obtained gaseous mixtures contain about 25-40 percent of ethylene and, in addition thereto, acetylene in amounts of from a few tenths of one percent up to about 2 percent.
  • These gaseous mixtures are normally compressed, afier removing therefrom the content of heavy oil and cracked gasoline components, and cooled countercurrently to cold fractionation products.
  • the C;,- and higher hydrocarbons are liquefied in a first separating stage; the C hydrocarbons in the remaining gaseous phase are separated in the liquid phase in a second separating stage operated at a lower temperature, the lower boiling components, such as methane, hydrogen, and nitrogen, being fed therefrom to further processing stages; and, a third separating stage, the ethylene in the condensed C,- hydrocarbons is then obtained in the pure form.
  • Ethylene intended for the production of polyethylene in particular, must be as completely free of acetylene as possible.
  • acetylene from ethylene is accomplished according to the process of German Pat. No. 953,700, by scrubbing the acetylene from the C -mixture with a solvent which selectively absorbs acetylene, especially acetone, at or closely above the liquefaction temperature of the C -mixture.
  • a solvent which selectively absorbs acetylene, especially acetone, at or closely above the liquefaction temperature of the C -mixture.
  • the separation of the ethane by rectification can be conducted either prior to or after this process step.
  • the higher-boiling solvents When the acetylene is absorbed at a relatively low pressure, the higher-boiling solvents have been employed, dimethylformamide being generally preferred. See Chemical Engineering Progress, Vol. 56, No. 1, January 1960, p. 54, right-hand column, and p. 55, left-hand column.
  • the low-boiling solvents appeared to be more suitable when operating with high pressures and low temperatures, primarily because they generally also have low melting points, so that there is no danger of solid deposits.
  • the amount of scrubbing solvent entrained by the scrubbed gas is low. In such low temperature processes, the high vapor pressure of the solvent thus does not represent a significant disadvantage.
  • the low-boiling solvents can be regenerated with low energy requirements and are thermally stable at their boiling temperature.
  • Dimethylformamide has been employed for scrubbing out acetylene from a C mixture at an elevated pressure. See, for example, U.S. Pat. No. 2,805,733, according to which the absorption of the acetylene takes place at 27 atmospheres and -l2 C.
  • Solvents which are set forth as being equally suitable for the same purpose are acetone and methyl ethyl ketone, the acetals thereof, the acetals of aliphatic aldehydes or aliphatic ethers, especially those exhibiting, in addition to the ether oxygen atom, a hydrophilic group.
  • such compounds are, for example, the glycol monoalkyl ethers with their free hydroxy group.
  • Carboxylic acid esters containing a further hydrophilic group either in the acid residue or in the alcohol residue, e.g., lactic acid esters or the glycol monoesters of lower carboxylic acids, can be employed as well as acid amides, alkylated urea compounds, bis-dialkylamides of dicarboxylic acids, lactarns, and lactones.
  • the present invention is based on the discovery that the selectivity of the conventional acetylene solvents, i.e., the ratio of the solubility coefficient A (Nm of dissolved gas per ton of solvent and per atmosphere of partial pressure) of the acetylene to that of ethylene or ethane, decreases with increasing pressure to a very different degree, depending on the particular solvent. It was found that the high-boiling polar aprotic solvents exhibit, in addition to a high selectivity at low pressures, only a minor decrease in selectivity with increasing pressure.
  • aprotic solvent means a solvent having no I-I-atom capable of forming a hydrogen bridge, in contrast to proton-active solvents, e.g., water, alcohols, and carboxylic acids.
  • the characteristic value for the selectivity is the ratio of the solubility coefficients (C H )t (CJL).
  • C H solubility coefficients
  • CJL solubility coefficients
  • FIGS. 1 and 2 are graphs showing the effect of pres sure on the selectivity of several solvents at C. and -20 C. respectively;
  • FIG. 3 is a graph showing the effect of methanol on the melting point of N-methyl-pyrrolidone.
  • FIGS. 4 and 5 are schematic representations of apparatus which can be employed to practice the process of this invention.
  • the quotient (F, F,)/( F l is plotted in FIGS. 1 and 2 as a measure of the decrease in selectivity against the total pressure P (in case of p C l-I, p C,I-I l 100).
  • F is the ratio of A (C l-I A (C l-I at the total pressure of l atmosphere absolute, and F,, is the same ratio at x atmospheres absolute.
  • the quotient indicates the difference with respect to the initial selectivity in multiples of the initial selectivity reduced by I.
  • the quotient becomes 1.
  • the quotient at 0 C., and in FIG. 2, the quotient at C. is given.
  • the process of this invention is conducted at pressures of more than 5 atmospheres absolute, preferably about 8-40 atmospheres absolute, e.g., about 15-35 atmospheres absolute.
  • pressures within this range can be employed at different stages of the process.
  • the selective absorption can be conducted at any temperature conventionally employed in low temperature, high pressure ethylene purification processes, e.g., between 55 C at 8 ata and 0 C at 40 ata, preferably between -50 C at 10 ata and 30 C at 20 ata.
  • the polar aprotic solvents employed in the process of this invention have a boiling point, at atmospheric pressure, of above C.
  • Preferred are those having a boiling point of at least C., especially those having a boiling point above C.
  • these solvents must have a melting point above the absorption temperature employed in the process. Those having a melting point below 0 C., especially those having a melting point below 50 C., are preferred.
  • a wide variety of solvents can be employed, so long as they are polar, aprotic and have a boiling point, at atmospheric pressure, of above 120 C.
  • Classes of compounds which fall within this class are tertiary amines, especially the N-lower-alkyl-heterocyclic amines, e.g., of the pyrrolidine, piperidine, homopiperidine, morpholine and thiomorpholine series; N,N-dialkyltertiary amides and N-alkyl-heterocyclic amides, e.g., of lower-fatty acids and phosphoric acid; dialkyl sulfoxides; dialkyl sulfones; loctones, especially of lower-fatty acids.
  • the solvents employed in the present invention have the disadvantage that the melting point of those solvents which have the highest selectivity have the highest melting points. Thus, the scrubbing temperature cannot be lowered to the optimum extent. For this reason, in a preferred embodiment of this invention, the absorption is conducted with a mixture of the highboiling polar aprotic solvent and a low-boiling solvent.
  • the low-boiling solvent is preferably one which lessens the selectivity of the high-boiling solvent to an only minor degree.
  • acetone, methanol and low-boiling esters or ethers are especially preferred. As shown in FIG. 3, the temperature at which solids are deposited from pure N-methylpyrrolidone is reduced from 24 to 40 C. by the addition of by weight of methanol. In so doing, selectivity is reduced only by about 10 percent.
  • the feature of conducting the process with a mixture of a high-boiling solvent and a low-boiling solvent offers a further advantage in the regeneration of the solvent.
  • stripping vapor In order to drive off the dissolved components from the spent solvent, stripping vapor must be produced, i.e., solvent must be evaporated. if the absorption liquid consists of such a mixture, the stripping vapor can be produced at the boiling temperature of this mixture, i.e., the sump temperature of the regenerating column is lower then the boiling point of the high-boiling component.
  • the rising solvent vapor is condensed as reflux and the thus-liberated acetylene escapes via the head.
  • the regenerated solvent mixture is withdrawn from the sump of the column and recycled to the absorption stage.
  • the sump of the column is maintained at the boiling temperature of the mixture so that the regenerated absorption solvent retains its composition.
  • a solvent which is not entirely stable at its boiling point and which decomposes under the constant effect of higher temperatures and would otherwise cause decomposition products to enter into the acetylene and, particularly, into the ethylene which has been freed of acetylene in the absorption column and is discharged as product.
  • Another aspect of the process of this invention resides in admixing a low-boiling solvent with the acetylene-laden, high-boiling solvent immediately prior to or during the regeneration thereof, vaporizing the low-boiling solvent therefrom in the sump of the regenerating column to a residue, condensing the vaporized low-boiling solvent at the head of the regenerating column, and then again admixing the condensed low-boiling solvent with the high-boiling solvent to be regenerated.
  • the amount of the low-boiling solvent remaining in the sump liquid during the regeneration is regulated so that the boiling temperature of the solvent mixture does not exceed the temperature at which the high-boiling solvent is thermally stable.
  • Another embodiment of the invention resides in conducting the selective absorption with a mixture of two polar aprotic solvents boiling at above 120 C.
  • Examples are mixtures of N-methylpyrrolidone with 'y-butyrolactone or dimethylformamide.
  • the eutectic of the N-methylpyrrolidone 'y-butyrolactone system is approximately 65 percent by weight of 'y-butyrolactone and -65 C.
  • the eutectic of the N-methylpyrrolidone dimethyl-formamide system is about percent by weight of dimethylformamide and -7l C.
  • the high-boiling solvent mixture can also be regenerated by stripping with a foreign gas, e.g., ethane, methane or nitrogen.
  • a foreign gas e.g., ethane, methane or nitrogen.
  • Another embodiment of the invention resides in that the absorption is conducted with an absorbent saturated with ethylene, preferably liquid ethylene. During the absorption step proper, it is then only necessary to remove the heat of solution of the acetylene.
  • ethylene preferably liquid ethylene.
  • the use of liquid ethylene offers the additional advantage that because only a minor amount of mixing heat occurs as heat of reaction during the saturation of the solvent, the heat of solution of the acetylene is compensated for by vaporization of part of the dissolved ethylene.
  • ethane When ethane is also present in the ethyleneacetylene mixture, it is preferably separated by rectification from the ethylene obtained after the selective absorption of acetylene therefrom.
  • the above sequence of steps can be reversed, i.e., the ethane can first be separated by rectification from the mixture with ethylene and acetylene, and the acetylene subsequently absorbed therefrom.
  • the C and higher hydrocarbons are separated from a crude ethylene fraction consisting of 40 percent by volume of hydrogen and methane, 1 percent by volume of acetylene, 49 percent by volume of ethylene and ethane, and 10 percent by volume of C and higher hydrocarbons, by conventional means, not shown, by compressing the mixture to 35 atmospheres absolute and cooling countercurrently to separate the C and higher hydrocarbons.
  • a second separation stage likewise not shown, the hydrogen and part of the methane are separated by conventional means.
  • the c -hydrocarbon fraction containing acetylene, ethylene, ethane, and methane pass through conduit 1 into methane column 2 in which the hydrocarbon mixture is rectified at a pressure of about 35 atmospheres absolute.
  • a condensate is collected in the sump of column 2 which consists of acetylene, ethylene and ethane, along with perhaps traces of c -hydrocarbons and other impurities, e.g., sulfur compounds or carbon dioxide.
  • the acetylene concentration of this condensate has increased to about 2 percent by volume due to the separation of the higher boiling components and those boiling lower than the C -hydrocarbons.
  • the sump product is completely evaporated in evaporator 4 and passes at or slightly above its condensation temperature, i.e., depending on the ratio of the concentration of ethylene ethane, between 8 C. and about +5 C., at a pressure of 35 atmospheres absolute.
  • the evaporated sump product passes through conduit 5 into the lower section of scrubbing column 6.
  • the scrubbing agent employed is N-methylpyrrolidone to which percent by weight of methanol has been added.
  • the solid deposit point of this mixture is about -40" C. Therefore, it can still be utilized as the scrubbing agent when a lower pressure is employed in the scrubbing stage. For example, when the scrubbing column is operated, at atmospheres, the condensation temperature of the C -mixture is lowered to about 35 to 28 C.
  • the scrubbing agent after having been precooled to approximately the temperature of the C -mixture to be scrubbed, is introduced via conduit 7 into column 6 several plates below the gas outlet thereof where it mixes with the mixture of ethylene and ethane condensed at coil 8 as reflux liquid.
  • the only heat of reaction in this procedure is the minor amount of mixing heat.
  • the scrubbing agent thus saturated with liquid etyhlene and ethane, absorbs the acetylene and other impurities, such as propylene and organic sulfur compounds, from the rising c mixture, the heat of solution of the acetylene being compensated by the evaporation of the dissolved ethylene.
  • a propylene cycle is provided.
  • the propylene is compressed in compressor 13, cooled first in water cooler 14 and then in the countercurrent heat exchanger 15 by heat exchange with cold propylene and ethylene, and then liquefied by heating evaporator 16 of column 10 and finally in countercurrent heat exchanger 17 by further heat exchange with cold propylene and ethylene.
  • One portion is expanded via valve 18 into condenser 19 of column 10, and the other portion is expanded via valve 33 into condenser 8 of column 6, where the propylene evaporates under the condensation of reflux liquid.
  • the cold gaseous propylene is then warmed as set forth above and recycled to the compressor.
  • the scrubbing agent leaves scrubbing column 6 via conduit 20 and is warmed in heat exchanger 21.
  • the thus-liberated ethylene is recycled into column 6 via conduit 22.
  • the scrubbing agent is now introduced, via expansion valve 23, into regenerating column 24, which is operated at a pres sure slightly above atmospheric pressure.
  • the sump of the column is maintained by evaporator 25 at the boiling temperature of the mixture of N-methylpyrrolidone with 10 of methanol, i.e., about 117 C.
  • the thusproduced methanol vapors strip the acetylene and the still-dissolved ethylene and ethane from the descending scrubbing agent.
  • the methanol vapor is cooled and condensed in water cooler 26 and in low-temperature cooler 27 and recycled into the column via separator 28.
  • the exhaust gas which consists of 50-90 percent by volume of acetylene and the remainder ethylene and ethane, leaves the plant via conduit 29.
  • the regenerated scrubbing agent is withdrawn from the sump of column 24 and is introduced, via pump 30, heat exchanger 21 and conduit 7, again into column 6.
  • the process according to H0. 5 differs from the above-described embodiment in that N-methylpyrrolidone is employed as the scrubbing agent with an only minor content of methanol, which does not influence selectivity, and the methanol required for the production of the necessary stripping vapor is added thereto immediately prior to the regeneration step.
  • the methanol evaporates to a content of about 2 percent by weight, which for all practical purposes does not lessen the selectivity of the absorbent at all, and simultaneously entrains the acetylene, ethylene, and ethane from the N-methylpyrrolidone solution.
  • the mixture of methanol vapor and the C hydrocarbons escaping overhead is first conducted through water cooler 26 and then through low-temperature cooler 27.
  • the thus-condensed methanol is collected in separator 28, to be recycled into the N- methylpyrrolidone solution to be regenerated.
  • the acetylene-containing waste gas is withdrawn via conduit 29.
  • the regenerated N-methylpyrrolidone, with the low methanol content, is drawn by pump 30 through heat exchanger 31 and water cooler 32, further cooled in countercurrent heat exchanger 21, and then recycled to scrubbing column 6 via conduit 7.
  • a process for the production of acetylene-free ethylene from a mixture of c -hydrocarbons by selective absorption of the acetylene therefrom and separation of the ethane therefrom by rectification which comprises selectively absorbing the acetylene at a pressure of more than atmospheres absolute with a highboiling polar aprotic solvent boiling above 120C, and regenerating the resultant loaded high-boiling solvent by stripping the acetylene therefrom, and conducting the selective absorption at or slightly above the liquefaction temperature of the C mixture,
  • the improvement comprising admixing a low-boiling solvent with the resultant loaded high-boiling aprotic polar solvent immediately prior to or during the regeneration thereof, evaporating the lowboiling solvent therefrom in a solvent regenerating zone, condensing the low-boiling solvent, and then admixing the condensed low-boiling solvent with further loaded high-boiling solvent prior to the regeneration thereof.
  • a process for the production of acetylene-free ethylene from a mixture of C hydrocarbons by selective absorption of the acetylene therefrom and separation of the ethane therefrom by rectification which comprises absorbing the acetylene with a high-boiling solvent composed of hexamethylphosphoric acid triamide saturated with ethylene, the selective absorption being conducted at 8-40 atmospheres absolute and at or slightly above the liquefaction temperature of the C,-mixture, and regenerating resultant loaded high boiling solvent in a solvent regenerating zone maintained below the boiling point of the high-boiling solvent by the presence of a low-boiling solvent therein.
  • a high-boiling solvent composed of hexamethylphosphoric acid triamide saturated with ethylene

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  • Engineering & Computer Science (AREA)
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US68672A 1969-09-02 1970-09-01 Process for production of pure ethylene Expired - Lifetime US3695002A (en)

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DE19691944505 DE1944505A1 (de) 1969-09-02 1969-09-02 Verfahren zum Gewinnen von Reinaethylen

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BE (1) BE755590A (xx)
DE (1) DE1944505A1 (xx)
FR (1) FR2060862A5 (xx)
NL (1) NL167671B (xx)
SU (1) SU459885A3 (xx)
ZA (1) ZA706015B (xx)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4655798A (en) * 1984-04-13 1987-04-07 Ec Erdolchemie Gmbh Process for removing acetylene from a C2 -stream
US4863493A (en) * 1987-08-07 1989-09-05 Nichigo Acetylene Kabushiki Kaisha High purity acetylene gas
US5520724A (en) * 1992-05-27 1996-05-28 Linde Aktiengesellschaft Process for the recovery of low molecular weight C2+ hydrocarbons from a cracking gas
CN1034226C (zh) * 1991-08-23 1997-03-12 林德股份公司 从粗煤气混合物中吸收乙炔的方法和吸收塔
CN1034225C (zh) * 1991-08-23 1997-03-12 林德股份公司 从粗煤气混合物中吸收乙炔的方法和吸收塔
US9714204B1 (en) * 2016-07-28 2017-07-25 Chevron Phillips Chemical Company Lp Process for purifying ethylene produced from a methanol-to-olefins facility

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1516082A (fr) * 1967-01-06 1968-03-08 Quenot & Cie Sarl Procédé de freinage d'un ruban métallique d'instrument de mesures linéaires et instrument de mesures linéaires comportant application de ce procédé
FR1550436A (xx) * 1967-11-10 1968-12-20

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2849514A (en) * 1955-04-21 1958-08-26 Standard Oil Co Extraction of hydrocarbon mixtures with hydroxy sulfones
US3002586A (en) * 1960-02-19 1961-10-03 Dow Chemical Co Inhibiting thermal degradation of phosphoryl tri-dimethyl amide
US3272885A (en) * 1962-10-01 1966-09-13 Phillips Petroleum Co Separation of ethylene from acetylene
US3530199A (en) * 1967-06-22 1970-09-22 Stone & Webster Eng Corp Ethylene production process

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2849514A (en) * 1955-04-21 1958-08-26 Standard Oil Co Extraction of hydrocarbon mixtures with hydroxy sulfones
US3002586A (en) * 1960-02-19 1961-10-03 Dow Chemical Co Inhibiting thermal degradation of phosphoryl tri-dimethyl amide
US3272885A (en) * 1962-10-01 1966-09-13 Phillips Petroleum Co Separation of ethylene from acetylene
US3530199A (en) * 1967-06-22 1970-09-22 Stone & Webster Eng Corp Ethylene production process

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4655798A (en) * 1984-04-13 1987-04-07 Ec Erdolchemie Gmbh Process for removing acetylene from a C2 -stream
US4863493A (en) * 1987-08-07 1989-09-05 Nichigo Acetylene Kabushiki Kaisha High purity acetylene gas
CN1034226C (zh) * 1991-08-23 1997-03-12 林德股份公司 从粗煤气混合物中吸收乙炔的方法和吸收塔
CN1034225C (zh) * 1991-08-23 1997-03-12 林德股份公司 从粗煤气混合物中吸收乙炔的方法和吸收塔
US5520724A (en) * 1992-05-27 1996-05-28 Linde Aktiengesellschaft Process for the recovery of low molecular weight C2+ hydrocarbons from a cracking gas
US9714204B1 (en) * 2016-07-28 2017-07-25 Chevron Phillips Chemical Company Lp Process for purifying ethylene produced from a methanol-to-olefins facility

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AU1949970A (en) 1972-03-09
FR2060862A5 (xx) 1971-06-18
BE755590A (fr) 1971-02-15
DE1944505A1 (de) 1972-02-10
SU459885A3 (ru) 1975-02-05
ZA706015B (en) 1971-04-28
NL7012983A (xx) 1971-03-04
NL167671B (nl) 1981-08-17

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