Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen; Reversible storage of hydrogen
  • C01B3/50—Separation of hydrogen or hydrogen-containing gases from gaseous mixtures, e.g. purification
  • C01B3/501—Separation of hydrogen or hydrogen-containing gases from gaseous mixtures, e.g. purification by diffusion
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2311/00—Details relating to membrane separation process operations and control
  • B01D2311/14—Pressure control
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
  • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
  • C01B2203/0465—Composition of the impurity
  • C01B2203/048—Composition of the impurity the impurity being an organic compound

Definitions

• the present invention relates to a method of treating a gas containing hydrogen and other components, such as hydrocarbons, membranewise to separate hydrogen.
• Membrane permeation processes consist in separating the constituents of a gaseous mixture by contacting said mixture with a membrane.
• the membrane selectively permeates the constituents of the gas mixture through its wall.
• the separation of hydrogen (said “fast” gas) from other gaseous species (so-called “slow” gases) is carried out thanks to the pressure difference between the gaseous mixture with treat and permeate the membrane: this pressure difference acts as a driving force for permeation.
• the gaseous mixture to be treated contains hydrocarbons, especially C 4+ , or other condensable compounds
• these constituents are concentrated in the waste gas, or retentate, during permeation.
• the dew point of the retentate can then be very close to, or even greater than, the operating temperature of the membrane, hence a risk of condensation of these constituents on the fibers of the membrane and premature deterioration of the performance of these fibers.
• This risk is directly related to the excessive amount of hydrogen recovered in the permeate gas (or permeate).
• the recovery of hydrogen in the permeate should be regulated to prevent condensation of the retentate in the membrane.
• Membrane permeation process control systems have thus been developed.
• a first control system either the pressure of the gas to be treated or the pressure of the permeate is controlled as a function of the variation of the gas flow rate to be treated.
• the flow rate of the gas to be treated decreases, the recovery of hydrogen increases and must then be controlled by means of an increase in the pressure of the permeate or by reducing the pressure of the gas to be treated.
• the pressure of the permeate is controlled so as to maintain a set point corresponding to the ratio of the flow rate of the retentate to the flow rate of the gas to be treated (Qr / Q).
• the object of the present invention is therefore to propose a method for controlling a hydrogen-selective membrane permeation of a gas containing hydrogen and compounds capable of condensing in the membrane, said gas having a variable concentration in hydrogen.
• the object of the present invention is to propose a method for controlling a hydrogen-selective membrane permeation of a gas containing hydrogen and compounds capable of condensing in the membrane, said gas having a variable concentration of hydrogen. , so as to avoid the risk of condensation in the membrane.
• the object of the present invention is to propose a method for controlling a hydrogen-selective membrane permeation of a gas containing hydrogen and compounds capable of condensing in the membrane, said gas having a variable concentration of hydrogen. , so as to avoid the risk of condensation in the membrane while optimizing the hydrogen recovery.
• the invention relates to a method for treating a gas comprising at least hydrogen and at least one other compound by means of a hydrogen permeable separation membrane, in which the gas to be treated is contacted with the membrane to produce a hydrogen-enriched permeate and a hydrogen depleted retentate, and wherein the differential pressure across the membrane is adjusted so that the ratio R of formula:
• Qr represents the flow rate of the retentate
• Q represents the flow rate of the gas to be treated
• F H2 represents a characteristic quantity of the hydrogen concentration of the gas to be treated
• n is a strictly positive or negative decimal number, is greater than or equal to the value of the ratio R min at which at least one compound present in the retentate condenses.
• the invention therefore relates to a method for treating a gas comprising hydrogen and other compounds, said treatment consisting in putting the gas in contact with a hydrogen permeable separation membrane.
• Compounds other than hydrogen are compounds that can condense in the retentate of the membrane: they can especially be hydrocarbons or water.
• the gas to be treated by the membrane may be, for example, a wet synthesis gas.
• the process is controlled by adjusting the differential pressure across the membrane, i.e. adjusting the difference between the pressure of the gas to be treated upstream of the membrane and the pressure of the permeate downstream of the membrane. In practice, this differential pressure across the membrane can be adjusted by controlling the permeate pressure, preferably by means of a valve placed on the permeate line downstream of the membrane.
• the adjustment of the differential pressure across the membrane is performed as a function of the value of the ratio R defined from the flow rates of the retentate (Qr) and the gas to be treated (Q) and a characteristic quantity.
• the hydrogen concentration of the gas to be treated F H2
• F H2 can be chosen from the hydrogen concentration of the gas to be treated or the molar density of the gas to be treated.
• the exponent n of the ratio formula R depends on the nature and the surface of the membrane, the nature of the gas to be treated and the expected cases of walking, fixed by the upstream process.
• the exponent n can be positive or negative depending on the nature of the magnitude F H2 .
• the value of the exponent n is set by following the following steps: a - determination of the maximum temperature T Ma ⁇ of the dew point of the retentate that can be used in the membrane , b - for different types of gas to be treated having flow rates Q and a characteristic quantity of the hydrogen concentration F H2 different, determination of the flow rate of the retentate Qr optimal to maximize the differential pressure across the membrane while maintaining the temperature of dew of the retentate T less than T Ma ⁇ , c - search for the value n making it possible to correlate the dew point temperature T with the values of R for the different types of gas studied in step b.
• correlate is meant to establish a relationship between R and the dew point temperature T so that they vary with each other. In practice, it can be faster to give n integer values to find the correlation. However, in order to have a refined value of the exponent n, it is preferable to give it decimal values.
• the differential pressure across the membrane is adjusted so that the ratio R is greater than or equal to the value of the ratio R min to which at least one compound present in the retentate condenses.
• the value of R min corresponds to the operating point of the membrane below which at least one compound present in the retentate condenses.
• the value of R min is set from the correlation established between R min and T (step c).
• the differential pressure across the membrane is adjusted so that the ratio R is equal to the value of the ratio R min .
• the process according to the invention is particularly suitable for treating a gas comprising hydrocarbons having a carbon number greater than 4.
• ratio R in the process according to the invention makes it possible to automatically adapt the operating conditions to the different gases to be treated, firstly to prevent the risks of condensation in the membrane, and secondly to maintain the recovery of hydrogen at its optimum value.
• maintaining the ratio R at its set point R min maintains the recovery in hydrogen while maintaining the margin of safety on the condensation of the retentate.
• the gas to be treated comes from a refinery hydrotreating purge and contains hydrogen and hydrocarbons in more or less variable contents depending on the operations of the upstream units, with variable flow rates.
• Table 1 gives different compositions that the gas to be treated may present during the implementation of the permeation process. According to the prior art, if the selective hydrogen permeation process adapted to the treatment of case 1 and 2 with the gas of case 3, a condensation of the retentate is observed in the membrane.
• n in the formula of the ratio R necessary for the control of the permeation process is determined which avoid the condensation of the retentate in the membrane while maximizing the recovery of hydrogen.
• the membrane operating at 90 ° C. the dew point of the retentate must not exceed 80 ° C. (T max ) (step a).
• T max 80 ° C.
• the differential pressure is varied across the membrane by adjusting the pressure of the permeate, so as to maximize the recovery of hydrogen while preventing the retentate dew point temperature from reaching 80 ° C. (step b).
• the conditions optimal operating conditions (dew point below 80 0 C and maximized hydrogen recovery) are identified in Table 2.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Combustion & Propulsion (AREA)
• Inorganic Chemistry (AREA)
• Analytical Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Hydrogen, Water And Hydrids (AREA)

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• 2006
  • 2006-03-01 FR FR0650707A patent/FR2898065B1/fr not_active Expired - Fee Related
• 2007
  • 2007-02-09 US US12/281,225 patent/US20100229721A1/en not_active Abandoned
  • 2007-02-09 EP EP07731593A patent/EP1993690A2/de not_active Withdrawn
  • 2007-02-09 JP JP2008556823A patent/JP2009528159A/ja active Pending
  • 2007-02-09 WO PCT/FR2007/050768 patent/WO2007099242A2/fr not_active Ceased
  • 2007-02-09 CN CNA2007800072807A patent/CN101394909A/zh active Pending

Non-Patent Citations (1)

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