Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
  • B01D17/06—Separation of liquids from each other by electricity

Definitions

• the invention relates to a method for segregating a dispersion having a continuous organic phase and a disperse aqueous phase from a caprolactam production process.
• caprolactam is prepared from cyclohexanoxime after a Beckmann-rearrangement in the presence of sulphuric acid or oleum. The rearrangement-mixture is then neutralised with ammonia whereby ammonium sulphate is formed. Subsequently caprolactam is extracted from water with an organic solvent, for example benzene. In the resulting organic phase also a disperse aqueous water phase is present. This aqueous phase comprises besides caprolactam also ammonium sulphate. The presence of ammonium sulphate is disadvantageous in the subsequent processing and puryfying of caprolactam. Removing the disperse aqueous phase as much as possible is therefore highly desired.
• US patent 3,528,907 describes the possibility of separation of water dispersed in a hydrocarbon, for example crude oil, from said oil by the use of an electric field.
• this patent also teaches that the voltage of the applied electric field must definitely not exceed 1000 volts per inch, or 400 volts per cm, because this would cause a short-circuit between the electrodes.
• a disadvantage of this method is that, in particular, a dispersion containing at most only about 5 wt.% aqueous phase of the combined total liquid phases cannot be readily separated from the organic phase.
• European patent application No. 51463 describes settling of liquid emulsions by means of electrostatic coalescence. This process however requires the presence of high volumes of conducting liquid (the aqueous phase), for example 50%. Especially insulated electrodes are needed because otherwise short-circuiting would occur.
• German patent application No. 3,709,456 and European patent application 438790 both describe separation of liquid membrane systems where the aqueous phase is the continuous phase.
• dispersions exhibit a continuous particle size distribution.
• Dispersions can be subdivided into primary and secondary dispersions.
• primary dispersions the particles forming the disperse phase have an average particle size > 0.1 mm.
• secondary dispersions however, the particles forming the disperse phase have an average particle size of only « 0.1 mm. Segregating these latter dispersions by means of settling tanks takes an unacceptably long time, however, for industrial applications. To shorten this segregation time it is therefore possible and advantageous to employ electrostatic coalescence according to this invention.
• This invention has as its primary object the provision of a method whereby a dispersion from a caprolactam production process, in particular a dispersion containing at most only about 5 wt. of aqueous phase, can be segregated very efficiently.
• This object is achieved by applying electrostatic coalescence at an electric field of at least 500 volts per centimetre and a frequency of at least 5 Hz.
• Electric fields with a (peak) strength of at least 1000 volts per cm, preferably at least 3000 volts per cm, more preferably at least 5000 volts per cm and especially at least 10,000 volts per cm can also be advantageously used, and by so doing the segregation results achieved become increasingly better.
• Fig. 1 illustrates in schematic form one type of apparatus which may be used in the practice of this invention.
• Fig. 2 illustrates in schematic form another type of apparatus which may be used in the practice of this invention.
• the shape of the vessel or container in which the electrostatic coalescence can take place is less important.
• the vessel may be cylindrical, square, rectangular, etc.
• the electrostatic coalescence technique of this invention can be conducted either continuously or batchwise. When continuous application of electrostatic coalescence is carried out, however, care should be taken regarding the internal surface configuration of the vessel or the container, to ensure that laminar flow is established; the length/diameter ratio may be significant in this context. In particular, turbulent flow should be avoided, since this turbulence adversely affects segregation or, as the case may be, segregation time requirements. Electrodes which can be used may be made from various materials, e.g. conductive glass, metal etc. The shape of the electrodes employed is not essential to the invention. Examples include rod-shaped or plate- shaped electrodes. The electrodes may be either insulated or noninsulated. The use of noninsulated electrodes may make suggest an advantageous cost difference for the procurement. On the grounds of safety and/or energy consumption, however, one may alternatively opt for insulated electrodes.
• the temperature at which segregation with the aid of electrostatic coalescence can take place is not really essential to the invention and may preferably be at room temperature. While, in general higher temperatures favor a more rapid achievement of the phase segregation, it is generally necessary to guard against the temperature rising too high, such that the dispersion to be segregated starts to boil or lead to generation of a gas, thereby inducing turbulence and resulting reformation of the dispersion.
• organic phase refers to one or more organic compounds composed of carbon and hydrogen, for example linear and cyclic hydrocarbons, and which may also contain other atoms such as oxygen, sulphur, nitrogen, halogens etc. Examples of such compounds include benzene, toluene, cyclohexane, heptane, dimethyl sulphoxide, chloroform, tr ichlorethane, etc.
• the aqueous phase may also contain other compounds, for example salts or even organic compounds dissolved in the aqueous phase.
• the aqueous phase may even contain up to 60 wt.% of organic compound(s), for example caprolactam. Nonetheless, in the context of this invention, the "aqueous phase" is considered to be aqueous provided that its water content is at least 20 wt.%.
• the aqueous phase may also contain water soluble salts, for example between 0.1 and 5 wt.% ammonium sulphate.
• the now segregated aqueous disperse phase can be separated from the organic continuous phase by means which will be apparent to those skilled in the art, for example by drawing off the aqueous layer, by decantation, and the like. It is possible to recycle the separated aqueous phase into the caprolactam production process.
• the preparation of caprolactam involves various preparation steps in which such dispersions are formed. These then generally require an effective liquid/liquid separation technique. Examples at various process steps include the cyclohexane oxidation, the preparation of hydroxylammonium salts, the top and bottom streams from extraction columns.
• Examples An Ultra-Torrax7 T50 mixer was used to disperse water having caprolactam dissolved therein (50 wt.) in benzene as the organic phase with 2 wt. of water phase dispersant based on the total mixture, at 5000 revolutions per minute (rpm) over a period of 5 minutes. Within 1 minute, this dispersion was introduced into an electrostatic coalescer, the frequency and the voltage being subsequently set. The examples employed alternating current in each case and were carried out at room temperature.
• the coalescer used in Examples I-III is schematically illustrated in Figure 1, where 1 is an insulated glass electrode, 2 is a glass jacket containing 3 sulphuric acid as the outer electrode and 4 is the voltage source with frequency controller. The gap between electrodes 1 and 3 was 1.5 cm.
• a coalescer as employed in Examples IV and V is depicted in Figure 2, where 10 is a thermostatted vessel within which a glass vessel 20, (100:30:100 mm) has been placed which is sealed by means of a cover 30 through which two noninsulated stainless steel electrodes 40 have been positioned. The gap between the electrodes was 1.5 cm. After various intervals, samples of the dispersion were taken and analysed.
• Examples I-III were carried out as described above, the frequency was 50 Hz, the electric field was sinusoidal. The voltage was varied and is shown in Table I, together with the corresponding separation results.
• Example ??? A sample of the dispersion of Example ??? was introduced into a cylindrical vessel allowed to settle with no application of electrical coalescence. After 1 minute, only 6% of aqueous layer had separated, after 5 minutes this amounted to 9% and after 10 minutes only to 12%.

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• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Water Treatment By Electricity Or Magnetism (AREA)
• Processes Of Treating Macromolecular Substances (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Electrostatic Separation (AREA)
• Colloid Chemistry (AREA)
• Other In-Based Heterocyclic Compounds (AREA)
• Polyesters Or Polycarbonates (AREA)
• Developing Agents For Electrophotography (AREA)

Priority Applications (8)

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Publications (1)

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Citations (5)

• 1996
  • 1996-07-15 NL NL1003591A patent/NL1003591C2/nl not_active IP Right Cessation
• 1997
  • 1997-07-08 EA EA199900105A patent/EA199900105A1/ru unknown
  • 1997-07-08 CN CN97197802A patent/CN1230131A/zh active Pending
  • 1997-07-08 AU AU33615/97A patent/AU3361597A/en not_active Abandoned
  • 1997-07-08 CZ CZ99138A patent/CZ13899A3/cs unknown
  • 1997-07-08 SK SK50-99A patent/SK5099A3/sk unknown
  • 1997-07-08 JP JP10505871A patent/JP2000514352A/ja active Pending
  • 1997-07-08 CA CA002260248A patent/CA2260248A1/en not_active Abandoned
  • 1997-07-08 EP EP97929593A patent/EP0920349A1/en not_active Withdrawn
  • 1997-07-08 GE GEAP19974636A patent/GEP20002017B/en unknown
  • 1997-07-08 PL PL97331170A patent/PL331170A1/xx unknown
  • 1997-07-08 WO PCT/NL1997/000396 patent/WO1998002225A1/en not_active Application Discontinuation
  • 1997-07-09 CO CO97038166A patent/CO4790158A1/es unknown
  • 1997-07-15 ID IDP972450A patent/ID18566A/id unknown
  • 1997-08-01 TW TW086111028A patent/TW374083B/zh active
• 1999
  • 1999-01-14 KR KR1019997000241A patent/KR20000023771A/ko not_active Application Discontinuation
  • 1999-01-15 BG BG103086A patent/BG103086A/xx unknown

Patent Citations (5)

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