Movable or removable closures
Patent
1996-06-10
1998-09-15
Clardy, S. Mark
Movable or removable closures
202200, B01D 300, C07C20900
Patent
active
058081593
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/DE 95/00595 filed May 3, 1995.
DESCRIPTION
Amines are used in numerous processes as reaction partners, solvents and catalysts. Examples are the production of quaternary ammonium compounds and the catalytic hardening of polyolisocycanate-binder systems (e.g. cold box process for hardening core sand in foundries).
Because of the offensive smell and the low toxicity threshold of the amines an aftertreatment of the exhaust air is necessary at those processes in order to dispose the amines safely or to recover them.
A common gas purifying process is the thermal post-combustion, where the amines are burnt. In the post-combustions it is possible by a complex reaction procedure and the addition of ammonia to control the nitrogen oxide emission. In small plants with discontinuous production as for example the cold box core producing plants in foundries this process is generally not to be controlled effectively. In any case it's also a disadvantage that a valuable chemical substance is burnt which is additionally present in an unfavourably high dilution for combustion.
Another very common process is the chemical absorption of the amines contained in the exhaust air into mineral acids. As absorbers there are used e.g. spraying absorbers or packed columns with reverse flow procedure. In a 15-40% sulphuric acid amine charges in the range of 10-30% are reached in practice depending on the amine and acid concentrations. It is essential to work in a pH-range below pH 3 to avoid amine emissions. The advantage of this process is that the amines are concentrated in the acid simply and safely with regard to process technology and that gaseous emissions can be avoided.
Instead of sulphuric acid also other acids e.g. phosphoric acids can be used. The cheap sulphuric acid is, however, preferred.
By the absorption the problem of disposal has been transferred from the exhaust air primarily to the acid charged with amine. The problem resulting from that is the disposal or usage of the saturated scrub liquors. In practice the following ways of disposal for the exhausted absorber liquid are gone:
1. Dilution with the sewage after neutralisation and decomposition of the amines in a biological sewage treatment plant.
Therewith the amines are lost without using them. The high salt freight means a contribution to salting up the lakes and rivers and in the case of the usual application of sulphuric acid as absorption liquid means a significant source of corrosion for drains made of concrete. Apart from that after the necessary neutralisation of the sewage a part of the amines escapes as gaseous emission.
2. Combustion of the amine sulphate solutions in cracking ovens.
Here the amines are burnt and the sulphates are turned into sulphur oxides. In plants especially designed for this purpose the sulphur dioxide can be utilised e.g. for the production of sulphuric acid. This process is complex and means a loss of the amines which are valuable chemicals.
3. Recovering amines from the scrub liquors.
In the patent specification DE 31 04 343 Al (Arasin) an amine recycling process is described which is based on phosphoric acid as absorption liquid. The charged amine phosphate solution is neutralised in the recycling plant with calcium oxide or calcium hydroxide. By stirring and warming up until max. 105.degree. C. the amines are set free in a stirring boiler and subsequently condensed and distilled. For dehydrating the amine/water-azeotropes molecular sieves are suggested.
The patent specification also deals with the reprocessing of the residue consisting of a suspension of calcium hydroxide and calcium phosphate remaining in the stirring boiler. It is neutralised with phosphoric acid. Then you let the solid deposit and you filter the sludge deposited. Previous experience has shown that the watery solution on top is not completely deaminated; this is the reason why the reuse of this solution is described in the deamination stage.
For drying the--as the solution on top--also still amine-containing filter cake wel
REFERENCES:
patent: 3741272 (1973-06-01), Ullrich et al.
patent: 4472246 (1984-09-01), Stamerjohn et al.
patent: 4919911 (1990-04-01), Shirota et al.
Badio Barbara
Clardy S. Mark
TRG Technologie Und Recyclingservice GmbH
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