Welcome to the Clausthal Centre for Material Technology > Research > Projects (concluded) > Innovative accumulation procedure for solvent recovery in flexo-packaging printing (Neuartiges Aufkonzentrationsverfahren zur Lösemittelrückgewinnung im Flexoverpackungsdruck, NALF)

Innovative accumulation procedure for solvent recovery in flexo-packaging printing (Neuartiges Aufkonzentrationsverfahren zur Lösemittelrückgewinnung im Flexoverpackungsdruck, NALF)

(Kopie 3)

Project Leader: Prof. O. Carlowitz (Dr.Eng)

Funding period: 03/2015 – 09/2017
Funding body: DBU

Objective and motivation for the project
In order to guarantee the best possible image depth and brilliance, and thus a high standard of quality, nowadays it is primarily organic solvents (mainly ethyl acetate and ethanol) that are used in flexo-packaging printing. These vaporise after the ink is applied and are fed to a downstream treatment plant as waste gas (waste air), together with aspirated ambient air. From solvent mass flow rates of one tonne per hour, it now proves economically viable to remove the organic substances adsorbtively from the waste air, to desorb it with steam and condense it. Following complex processing – determined by the high total discharge – reuse is then possible. When below a solvent mass flow of 1 t/h the use of regenerative, thermal post-combustion planes is currently considered state of the are, whereby the solvents are oxidised to form mainly carbon dioxide and water, and are as such detoxified.

The objective of this project is to develop a recovery procedure for solvent mass flows of less than 1 t/h (mass flow range 0.2…0.8 t/h, which on the one hand is economically interesting for the operation of flexo-packaging printing and on the other hand significantly reduces the overall carbon dioxide emissions. Here the fact that the manufacture of on kilogram if ethyl acetate, for example, produces just 2.9 kg CO2 plus around 2 kg CO2 during oxidation in a regenerative thermal post-combustion pland, must be considered, meaning that in the case of the recovery of the solvent a considerable reduction in carbon dioxide emissions can be expected.

The innovative accumulation procedure, which is to be developed for the relatively high loads of waste air with solvents in flexo-packaging printing, and thus far is not considered to be state of the art, is based on the scrubbing of the waste air using high boilers (Genosorb 1843) and desorption
•    either to 130 °C using inert gas at ambient pressure or
•    at lower temperature and under a vacuum,
so that the high temperatures of > 200 °C required in the case of an adsorption procedure (using zeoliths or active carbons) for inert gas desorption (without steam!) can be avoided and increased acetic acid formation (from ethyl acetate) is, if applicable, also largely avoided under the influence of catalytic effects caused by the adsorption. The subsequent condensation is designed as a three-stage process: It is initially cooled to 50°C and Genosorb is separated off and fed back into the desorption. Then, during the adsorption, entrained water (origin: ambient air) with low solvent content at temperatures above the freezing point of water is separated. Finally, condensation takes place, primarily of the organic solvents with an as yet very low water content, at minus temperatures. The reconditioning of the water-rich fraction is planned by means of distillation, with subsequent membrane drying - the primarily solvent-containing fraction requires only membrane drying. The recovered solvent should then be used for the viscosity adjustment of the printing dyes.

Representation of the work steps and applied methods
The challenge of the project lies in the relatively complex system technology of the overall procedure, the experimental validation of which is supplemented in terms of plant engineering with a testing facility created within the scope of an ongoing R&D project (Objective: development of an efficient washing stage with a high-performance demister), will have a transportable design and will undergo technical testing in bypass mode within a flexo-packaging company, in order to deduce meaningful findings with regard to the planning of real-world applications.

With regard to the methods, the standard analytics (temperature, FID, particle measurement technology) are examined in order to evaluate the deposition performance of the new module. Further quality analyses are planned on the recovered (GC-analyses).

The NALF project is a DBU-funded prject, with third-party funding from AWS Group AG, Clausthaler Umwelttechnik-Institut GmbH, Ilgen Laboratory and Arwed Löseke Papierverarbeitung und Druckerei GmbH.


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