NL1003594C2 - Distillation and drying process for spent solvents. - Google Patents

Description

Distillation and drying work for finished solvents

The present invention relates to a combined distillation and drying process for spent solvents, which makes it possible to separate the solvents present in a process step from the solids and resinous products present.

In Germany, approximately 100,000 tons of finished solvents are obtained annually, for example as rinse thinners in 10 paint companies, as degreasing solutions in galvanizing companies, as cleaning solutions in the chemical industry, etc. Depending on the process from which these solvents originate, the composition is of course different, but the these are essentially in the range of from about 60 DEG-180 DEG C. normal boiling organic liquids, which are mixed with up to 20¾ water and about 2-20% inorganic and / or organic solids or resinous or tar-like products.

Such spent solvents have previously been worked up by separating the solvents by distillation until the bottom phase has concentrated to a solids content of about 30-50%. A further distillation would lead to an irremovable, adhered and sintered material. The consequence would be damage to the distillation equipment and the shutdown of the process. The still substantial amount of solvent-containing residue is then either processed by incineration or mixed with a bulky solid, for example sawdust, coal waste, clay powder, plastic foam powders, etc., to form a solid, crumbly mass, which can be further dried and finally deposited, burned or used as an additive for the manufacture of plastic sheets (see DE 4,327,037, 4,125,909, DE 3,506,358. DE 3,924,312). In this process it is a problem that in order to be sufficiently liquid, the bottom phase has to be removed from the distillation device at relatively high temperatures, with solvents posing a considerable danger (fire hazard, odor nuisance, danger to the health). On the other hand, in order to convert this liquid mixture into a solid, processable state, a relatively large amount of additives, usually at least 30, preferably more than 50, 1 0 0 35 94 2 of the amount, must be added so that the mass of the residue thereby increases significantly. Furthermore, removing from the distillation devices, mixing with the additives and optionally transferring them to a further drying device is of course a labor-intensive and expensive process.

It was therefore the task to develop a process in which the distillation and drying of spent solvents can be carried out in an installation with the smallest possible amount of additives.

Surprisingly, this statement is fulfilled by the features of the main claim and supported by the features of the subclaims.

With the process according to the invention a virtually quantitative yield of solvent can be obtained, at the same time avoiding the formation of "crack" products by the mild distillation. The process is carried out in an apparatus without interruption at the transition from the distillation phase to the drying phase and results in an almost solvent-free, powdery or. granulated residue, which can be removed from the distillation apparatus without problems.

According to the invention, the spent solvents to be cleaned for distillation are mixed with a surfactant additive, which remains in the plant throughout the distillation and drying process. As the additive, a polyurethane foam powder with a bulk density between 20 and 150 kg / m3 is used, the amount of additive being 5 ~ 20 wt% of the solids and resinous products present in the spent solvent.

The solvents are distilled off at a temperature of 40-100 ° C, preferably 40-70 ° C, with a correspondingly low vacuum of maximum 0.5 bar being applied for solvents with a higher boiling point. In order to drive off the residual solvents still present in the forming residue phase, the temperature of the material is raised to 100 ° C towards the end of the distillation and the vacuum is increased to 0.01 -0.1 bar increased.

The yield of reusable solvents in this combined distillation drying process is up to 95% by weight of the original solvents and thus is 20% higher than in conventional processes.

The distillation residue is obtained as a granulate or as a flow-phase powder and can be used directly in the further processing of the material without further post-treatment.

Since no "tacky" phase is passed through in the distillation and drying process, because the tacky substances, for example lacquer binders and the like, are deposited in and on the added polyurethane granules during the distillation process, the process according to the The invention uses very simple distillation devices, for example distillation flasks with a simple stirring device for thermal mixing, which considerably reduces the use of equipment. Of course, other more complicated devices known to a person skilled in the art are also suitable.

The very volatile solvents with a boiling point of up to about 120 ° C are essentially under normal pressure or. distilled off under a vacuum of up to 500 mbar and a material temperature of * 10-100 ° C, preferably * 40-70 ° C. After a temperature increase at 100 ° C and optionally a reduction of the vacuum to 100 resp. The solvent residues are also distilled off at 50 mbar. According to the invention, the temperature of the material is maintained until no more distillate passes.

The loose, crumbly distillation residue has a maximum residual solvent content of 5%. usually 1-3%. Since the total amount of solvent is not condensed by the applied vacuum, the solvent yield is usually in the order of 93-95%

If solvent mixtures are present, they can either be collected fractionally during the distillation and separated, or fine-separated in a subsequent distillation to recover the pure solvents. If solvent mixtures are obtained from a special process step, they can usually be recycled to this process step, so that a fine separation is unnecessary.

It as crumbly resp. powdered distillation residue obtained in this form can simply be dumped, burned or used as a filler in a known manner. Because of its structure, this residue is of course also excellently suitable for extracting individual components with chemical reagents, if necessary, and thus returning them to the production process.

The polyurethane used is an inexpensive waste product, which can be prepared by grinding from residues of the polyurethane foam preparation. As far as this makes sense with regard to the products to be used, other materials, such as lime, inorganic oils, inorganic additives, etc. can of course also be used in the process.

The invention is further illustrated in the following examples, without being limited thereto.

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Example I: Combined distillation and drying of a used wax thinner from the lacquer industry

The laundry thinner with the composition: 88 wt.% Organic solvents 7 wt.% Organic binders 5 wt.% Inorganic pigments and fillers is first mixed with 1.2 wt.% Polyurethane powder (50 kg / m3) and vacuum-dried in the distillation apparatus.

The low boiling solvents with a boiling point up to 100 ° C are distilled off under a vacuum of maximum 500 mbar and a temperature of the material of 40-70 ° C. After a temperature increase to 100 ° C, the residual solvent content is distilled off. This temperature of the material is maintained until no more distillate passes.

The loose crumbly distillation residue (dry residue) is removed after the vacuum is broken. This residue still contains a residual solvent content of 4.5% by weight. The solvent yield is 93% by weight, based on the total amount of solvent.

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Claims (3)

A method of distilling and drying finished solvents with the addition of an additive for reducing the tackiness of the distillation residues, while simultaneously recovering the pure solvents and a granulated or powdered residue, characterized in that the spent solvents before distillation are mixed with 5 “20% by weight of a polyurethane foam powder with a density of 20-150 kg / m3, based on the solids content of the solvents, and that most of the solvents at a temperature of the material of ^ 0-100 ° C and under a pressure of 0.5-1 bar are distilled off and the residue at a temperature of 80-100 ° C and under a pressure of 0.05 ~ 0.5 bar is further dried. 15 Process according to claim 1, characterized in that the distillation is carried out at a temperature of 40 ~ 70 ° C and the drying at a temperature of 100 ° C. 3. Process according to either of Claims 1 and 2, characterized in that the distilled solvents are subjected to fractional distillation. Method according to any one of claims 1 and 2, characterized. 25 that the distillation residue is reused. A method according to any one of claims 1 to characterized. that the spent solvent has a composition of: 60-95 wt% organic solvents, 0-20 wt% water, 5-10% by weight of organic solids, resins and tar-like products and 0-10% by weight of inorganic pigments and fillers. 1003594