DE19650682A1 - Recovery of aircraft deicing agents - Google Patents

Abstract

A method for recovering de-icing agent comprises chemical and mechanical treatment of the de-icing agent effluent and then purifying the glycols present in the vapour phase in an adsorber in at least one distillation step.

Description

The invention relates to a method for the recovery of Deicing agents, in particular based on glycol.

Large amounts of glycol-containing are used for aircraft de-icing Deicing agents used up. The waste water contaminated with glycol prepares large amounts Processing problems.

The wastewater after aircraft de-icing contains:

• - glycols,
• anionic and / or nonionic surfactants,
• Inhibitors,
• Thickeners to increase the viscosity,
• - Salt and solid contaminants from the environment.

The wastewater treatment in municipal wastewater treatment plants leads to high ones COD values for acute lack of oxygen. This often has the failure of the Wastewater treatment plant. For this reason, are for biological Waste water treatment of aircraft deicing agents separate sewage treatment plants and correspondingly high investments are necessary.

There is a recovery of the glycols from the de-icing waste water more ecological and economical than decomposition in the organic process.

The processing of aircraft de-icing agents involves two tasks:

• 1. recovery of the glycols with a high degree of purity,
• 2. Separation of the aqueous phase with COD values that can be introduced.

The glycols used in the manufacture of aircraft deicing compositions are high Purity requirements. In a simple distillation as in the  Process for the recovery of glycols from the polycondensation and Polymerization processes (PN EP 0 609 931 A1 940 810; PN EP 0 592 053 A1 940 413; PN EP 9 402 084 A1 940 627) can the organic Impurities, especially surfactants, cannot be separated.

When recovering the antifreeze (PN EP 0 706 416 A1 960 417; PN EP WO 9 901 213 A1 990 112) or in the preparation of technical liquids containing glycol (PN EP 0 679 624 A1 951 102) don't have to be that high compared to the De-icing agent recovery, tenside-glycol separation limits reached will.

In the case of distillation of the glycols from the deicing agents, Especially from the aircraft deicing agents, surfactants become relative stripped with the glycol vapor in large quantities.

By adding organic agents before distillation such as Amidosulfonic acid (PN WO 9 501 213 A1 950 112 and PN 43 21 846), Methanol (PN WO 9 116 289 A1 911 031) or organic solvents (PN 44 13 419; PN 44 41 371) becomes the necessary glycol-surfactant separation limit not reached.

Use of ion exchangers after distillation Surfactant discharge as in (PN 31 18 915; PN WO 9 426 684 A1 941 124) leads to the separation of only the ionic surfactants. The nonionic, the often the major proportion of surfactants in the deicing agents, are not dosed by the ion exchange resins.

The problem of separating the nonionic surfactants is also in the Process PN EP 0 637 620 A2 950 208 with process combination Ultrafiltration, ion exchangers and distillation are not solved because of that Surfactants are largely ultrafiltratable.

The invention was based on the object of developing a method for recycling the de-icing agents and water treatment with guaranteed COD values. In the process according to the invention (Scheme 1), a small amount of lime milk (Ca (OH) ₂ ) is added to the wastewater to bind the anionic surfactants ( 1 ). The Ca ions form a solid, poorly soluble compound with ionic surfactants, which are not volatile at the distillation temperatures. The pH value is thus set in the slightly alkaline range.

After that, in particular mechanical impurities and undissolved connections are filtered off in the filtration device ( 2 ). The pretreated wastewater is then fed to the first distillation stage ( 3 ). The majority of the water is evaporated in the first distillation stage (either without or with heat recovery). The water distillate from the first distillation stage is freed from the stripped organic substances (surfactants and inhibitors) in the activated carbon adsorber ( 4 ) and can be introduced with the COD value granted.

In the bottom of the first distillation stage, glycols with a low water content and impurities such as salts, surfactants, inhibitors, thickeners, possibly solids, are concentrated. The bottom product from the first stage is fed to a second distillation stage ( 5 ) for separating the glycols from the impurities. Below the glycol distillation temperatures, salts, calcium-bound anionic surfactants remain in the sump and are thus separated from the distilled glycols.

The organic impurities stripped with the glycols (in particular predominantly nonionic surfactants) are removed from the glycol vapor phase in the adsorber ( 6 ). The pressure / temperature ratio in the adsorber ( 6 ) achieves selective adsorption of the organic impurities. The glycols do not load the activated carbon. Adsorption from the liquid phase, such as in the recovery of ethylene glycol (PN WO 9 426 684 A1 941124), is not possible in the case of the reprocessing of aircraft de-icing agents because propyl and higher glycols have been proven to support the activated carbon and the adsorption of the organic ones Prevent contamination.

The process combination according to the invention is characterized by chemical Pretreatment, distillation in at least two stages and subsequent Purification of the glycol vapors in the activated carbon adsorption, regardless of the Design or composition of the deicing agents and the pollution from the environment a high degree of purity recovered glycols reached.  

Reference list

1

Lime milk metering

2nd

Filtration

1

1st distillation stage

4th

A-carbon adsorber for wastewater treatment

5

2nd distillation stage

6

A-carbon adsorber for glycol cleaning
W1, W2, W3 heat exchanger.

Claims (1)

Process for the recovery of deicing agents, characterized in that after the chemical and mechanical wastewater treatment of the deicing agents, the glycols are cleaned in the vapor phase in at least one second distillation stage in the adsorber.