Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
  • C07C209/82—Purification; Separation; Stabilisation; Use of additives
  • C07C209/86—Separation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
  • C07C209/82—Purification; Separation; Stabilisation; Use of additives
  • C07C209/84—Purification

Definitions

• the present invention relates to a hexamethylenediamine purification process.
• It relates more particularly to a process for purifying hexamethylenediamine by separation of tetrahydroazepine, or more generally imines present in hexamethylenediamine.
• Hexamethylenediamine is a major chemical intermediate used especially as a monomer for the manufacture of polymers such as polyamides or as an intermediate for the synthesis of isocyanate compounds.
• Hexamethylenediamine is obtained by hydrogenation of adiponitrile in the presence of catalysts comprising metal elements such as nickel, cobalt, iron, rhodium or ruthenium.
• THA tetrahydroazepine
• This compound must be separated from hexamethylenediamine because it can cause staining or branching in polyamides such as PA66 obtained with hexamethylenediamine containing tetrahydroazepine.
• US Pat. No. 5,192,399 describes a process for the distillation of a mixture of hexamethylenediamine (HMD) and aminocapronitrile (ACN) comprising THA.
• HMD hexamethylenediamine
• ACN aminocapronitrile
• This mixture is distilled in a distillation column in the presence of a solution of a basic compound.
• Aminocapronitrile and hexamethylenediamine are collected at the top of the column whereas the oligomers containing THA or heavy compounds are recovered in the bottom fraction of the column.
• the use of a basic compound generates saline effluents that can not be rejected without treatment.
• One of the aims of the present invention is to provide a simple process for separating hexamethylenediamine and tetrahydroazepine with a recovery of HMD containing a very low concentration of THA and a loss of minimized HMD.
• the invention provides a process for purifying hexamethylenediamine by separation of tetrahydroazepine distilling in a distillation column, the mixture containing hexamethylenediamine and tetrahydroazepine.
• the invention is characterized in that the residence time of the hexamethylenediamine in the column is between one minute and twenty minutes, preferably between one minute and fifteen minutes.
• residence time in a distillation column means the ratio between the volume of liquid retained in the column and the flow of liquid flowing inside the column.
• the part of the distillation column to be considered for the calculation of the residence time is the portion of the internal of the column above the feed point of the hexamethylenediamine to be purified.
• the residence time in the bottom of the column, in the boiler and in the condenser of the column are not to be taken into account.
• the residence time in the internals contained in the part of the column below the feed point of hexamethylenediamine is not to be taken into account.
• the term "distillation column" used in the present text corresponds to the internal part present in the part of the column situated above the feeding point of hexamethylenediamine. .
• internal content in a distillation column means the elements or devices arranged in the column to promote and achieve the liquid / vapor exchange.
• interns mention may be made of structured or non-structured packings, bell-plate trays, flap trays or the like.
• the internals constituted by structured packing are preferred in the process of the invention.
• the volume of liquid retained in the column is a function of the type of internal, column, dimensions and operating conditions (gas flow and liquid in the column).
• the volume of liquid is calculated from the packing volume and the retention rate of the packing (liquid volume per unit packing volume).
• the packing volume is, according to the invention, the volume contained in the portion of the column located above the feed point of hexamethylenediamine.
• the retention rate of a type of packing is indicated by the manufacturer or supplier of the packing and is a construction feature of this material and the operating conditions of the distillation.
• the volume of liquid retained corresponds to the volume of liquid present on each plate multiplied by the number of actual trays.
• the method is implemented in distillation columns comprising between 10 and 50 theoretical plates, preferably between 15 and 35. This number of plates corresponds to the part of the column located above the feed point of hexamethylene diamine.
• the method of the invention can be implemented in any type of distillation columns to obtain residence times as described above.
• distillation columns of the invention are those having a low pressure drop.
• suitable distillation columns are structured packing columns, thin-film distillation columns.
• the process is carried out in distillation columns operating at an operating pressure at the top of the column of between 10 and 300 mbar.
• the bottom temperature of the column is advantageously between 120 ° C. and 170 ° C.
• the mixture to be distilled is preferably fed at an intermediate plateau of the column, the purified hexamethylenediamine recovered as an overhead fraction or as an intermediate fraction at a level close to the column head comprises, according to the process of the invention, less than 8 mol of THA per million of mol of HMD, advantageously less than 4 mol of THA per million mol of HMD.
• the concentration of THA or reducible impurities with a mercury electrode in hexamethylenediamine is determined by pulsed polarography assay. These impurities exhibit a polarographic reduction wave at a voltage of -1.55 V / Ag-AgCl +/- 0.05V and are expressed in mmol of isobutanal per tonne of HMD (mmol iB / t) or in mol of THA per million moles of HMD (mpM).
• the distillation is carried out with a head pressure of 300 mbar, a column temperature of 160 ° C and an HMD feed rate of 2.5 kg / h (3.3 l / h).
• the liquid flow rate of the column is determined by calculation with the modeling tools conventionally used for the calculation of distillation columns (ASPEN ® software). The calculation shows that this flow rate is close to the feed rate in the case of the present example.
• the residence time of hexamethylenediamine is 3 minutes.
• the hexamethylenediamine collected at the top of the column contains 2.3 mol of THA per million mol of HMD.
• Test 1 is repeated except that the packing used is an outcry packing with a retention rate of 5% and a packing volume of 7 liters.
• the number of theoretical plates is 20.
• the residence time of HMD is 6 minutes.
• the hexamethylene diamine recovered at the top of the column contains 2.9 mol of THA per million mol of HMD.
• Example 1 is repeated.
• the packing volume is 3.6 I and the number of theoretical plates is 20.
• the residence time of HMD in the column is 4 minutes.
• the hexamethylenediamine collected at the top of the column contains 3.9 mol of THA per million mol of HMD.
• a plate distillation column is used to purify hexamethylenediamine containing 120 mol of THA per million moles of HMD.
• diameter 50 mm comprising 30 actual trays with a retention of 12 ml per tray.
• This column has a theoretical number of plates equal to 17.
• the feed hexamethylenediamine is located below the lower plate of the column.
• the distillation is carried out with a head pressure of 260 mbar, a column temperature of 160 ° C and an HMD feed rate of 0.5 kg / h (0.66 l / h).
• the liquid flow rate of the column is determined by calculation with the modeling tools conventionally used for the calculation of the distillation columns. The calculation shows that it is close to the feed rate in the case of the present example.
• the residence time of hexamethylenediamine is 33 minutes.
• Hexamethylenediamine collected at the top of the column contains 16.4 mol of THA per million mol of HMD.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Polyamides (AREA)

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• 2007
  • 2007-10-11 FR FR0707134A patent/FR2922207B1/fr active Active
• 2008
  • 2008-10-03 BR BRPI0816604-8A patent/BRPI0816604B1/pt active IP Right Grant
  • 2008-10-03 US US12/682,301 patent/US8436212B2/en active Active
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