Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
  • C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
  • B01D61/04—Feed pretreatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/58—Multistep processes
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
  • C02F1/444—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
  • B01D61/025—Reverse osmosis; Hyperfiltration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/14—Ultrafiltration; Microfiltration
  • B01D61/145—Ultrafiltration
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
  • C02F1/448—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by pervaporation
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/14—Paint wastes

Definitions

• the present invention relates- bo- a method of obtaining a solvent-containing concentrate from used rinising liquids from the paint processing industry.
• the initial rinsing liquids which are used to rinse and clean the paint supply in painting units as a consequence of colour changeover, change of coating material, cleaning, maintenance, etc. contain organic solvents in an amount of 10-50% by weight in deionized water. In the course of the cleaning process the paint supply apparatuses are flushed with deionized water.
• Used rinsing liquids which are obtained in painting processes in the automotive industry when waterborne paint systems are used, therefore have in general a solids content of 4 - 15% by weight and a proportion of low molecular mass organic solvents of up to 15% by weight, the remainder being deionized water, based on the overall mass of the rinsing liquid.
• the concepts known and employed to date for the treatment of used rinsing liquid include incineration, distillation and direct introduction of the rinsing liquid into the circuit water of spray booths for the painting process. Because of the high water content of the rinsing liquid, the energy consumption entailed by the first two concepts set out above is very high. In addition, the emissions of environmental pollutants are unacceptably high in the case of incineration and of introduction into the circuit water, and additional costs and hazards arise from the transportation of the rinsing liquid from its site of formation to the site of disposal, which is generally necessary for incineration and distillation. In the case of incineration and of introduction into the circuit water, moreover, valuable substances, such as organic solvents and deionized water, are lost.
• EP-A-0 675 080 discloses a method of concentrating the overspray produced by wet washing-out in spray booths by means of a multistage membrane filtration.
• the booth water/overspray mixture to be concentrated is initially concentrated in an ultrafiltration stage by separating it into a retentate and a permeate, which contains low molecular mass constituents.
• the ultrafiltration permeate is supplied together with a nanofiltration permeate to a reverse osmosis stage.
• the retentate of the reverse osmosis and the retentate of the ultrafiltration are supplied to a nanofiltration stage, where separation takes place into a retentate and a permeate.
• the retentate of the nano- filtration corresponds substantially to the aqueous paint employed and can therefore be used for this purpose directly or as a constituent of a paint composition.
• the permeate of the reverse osmosis can be recycled into the booth water circuit.
• the object on which the present invention is based is therefore to provide a cost-effective treatment method for solvent-containing rinsing liquids which makes it possible, in particular, to use both the solvents and the process water again.
• This object is achieved by a method of obtaining a solvent-containig concentrate from used rinising process liquids from the paint processing industry, comprising solids fractions, organic solvents and water, by:
• the ultrafiltration of the present invention is a membrane separation process which is carried out with membranes having a cutoff point of from 200 to 500,000 Da, preferably from 1000 to 250,000 Da.
• the pressure difference between entry and exit of the module in the ultrafiltration of the invention is 0.5 - 5 bar, preferably below 1 bar. With this mode of operation it is possible to achieve a permeate flow of from 10 to 80 l/m 2 h, preferably from 15 to 50 l/m 2 h. In this con- text, the permeate flow of the ultrafiltration depends not only on this pressure difference but also, in particular, on the feed temperature.
• the transmembrane pressure difference in the ultrafiltration of the invention is between 1 - 5 bar.
• membrane modules are suitable for the ultrafiltration unit employed in the method of the invention, such as cushion modules, plate modules, spiral modules, tubular modules, capillary modules, multi-channel modules or hollow- fibre modules.
• the membranes can be made of polysulphone, polyacrylo- nitrile, polyolefins such as polypropylene or polyethylene, Teflon, porous carbon, ceramic (such as e.g.
• modules which have been found to be particularly suitable for the ultrafiltration stage of the invention are multi-channel modules or tubular modules with alumina, silicon carbide, polyvinylidene fluoride and polyacrylonitrile membranes.
• a process liquid from the paint processing industry can be separated into a concentrate and into a permeate which essentially contains only constituents having a molecular weight of less than 1000 Da, preferably less than 200 Da.
• the membrane used for the ultrafil- tration stage has a large pore size, corresponding to a cutoff point of 250,000 - 500,000 Da, and is doped with charge carriers, preferably positive charge carriers.
• a membrane of this kind achieves both a very sharp separation and a very high permeate flow at low differential pressures, between the entry and exit of the module, of less than 1 bar.
• both the permeate flow and the separation performance are greater at low differential pressures, between entry and exit of the module, of less than 1 bar, than at higher pressures, so that particularly effective separation at especially favourable cost is possible with such a membrane.
• the ultrafiltration can also be practised in a plurality of stages.
• the reverse osmosis of the invention is likewise a membrane separation method, using membranes which retain at least 95% by weight, preferably at least 98% by weight and, more preferably, at least 99% by weight of sodium chloride.
• the transmembrane pressure difference is normally between 15 and 100 bar, preferably between 20 and 60 bar and, more preferably, between 20 and 50 bar. In this case a permeate flow of from 3 to 30 l/m 2 h is achieved.
• Customary membrane modules are suitable for the reverse osmosis, such as spiral modules, tubular modules, capillary modules and hollow-fibre modules.
• membrane materials particular care should be taken to ensure that the membranes are resistant to the organic solvents, especially aprotic organic solvents, which become concentrated in the retentate of the reverse osmosis.
• suitable materials are those described above in connection with the ultrafiltration.
• Polyamide membranes have been found to be particularly suitable.
• a permeate which is essentially free of organic solvents is essentially free of organic solvents.
• "essentially free” means a concentration of organic solvents in the reverse osmosis permeate of less than 0.2% by weight based on the overall mass of the permeate, preferably of less than 0.1% by weight, more preferably of less than 0.05% by weight and, most preferably, of less than 0.01% by weight.
• the separation can be improved further, if required, by a multistage reverse osmosis method.
• pervaporation stage a diffusion-controlled membrane separation technique in which a vapour mixture which becomes established above a mixture of liquids is separated as a result of the differing permeability of an appropriate membrane. Continual pumped removal of the vapour on the gas side of the membrane produces a concentration gradient which maintains the diffusion. Pervaporation is particularly suitable for concentrat- ing further the retentate of the reverse osmosis.
• the method of the invention is particularly suitable for treating used rinsing liquids which are obtained when cleaning and rinsing the paint supply of painting units in the automotive industry.
• This relates in particular to painting units which process waterborne paint systems.
• Rinsing liquids which have been found suitable for such painting units comprise, in addition to deionized water, one or more solvents selected from isobutanol, n-butanol, n-propanol, iso- propanol, ethylene glycol monobutyl ether, butyldigly- col and N-methylpyrrolidone .
• the used rinsing liquids obtained in such operations generally have a solids content of 4 - 15% by weight, a proportion of low molecular mass organic solvents of up to 15% by weight, the remainder being deionized water, based on the overall mass of the rins- ing liquid.
• the solids fraction is composed essentially of the components of the particular paints used. These components comprise pigments and binders in the range between 2000 and 250,000 Da, and low molecular mass constituents, especially crosslinking agents, which may have a molecular weight of less than 2000 Da.
• the organic solvents originate mainly from the rinsing liquid and to a small extent from the particular paint system used, or are elimination products of the paint system. The principle of the method of the invention is illustrated in Figure 1.
• the used rinsing liquid 1 is collected in a tank (not shown) and then passed into an ultrafiltration stage 2 for reprocessing.
• the ultrafiltration stage the high molecular mass constituents of the rinsing liquid are concentrated in the retentate 3 to a solids content of preferably at least 50% by weight.
• the retentate 3 of the ultrafiltration is then supplied for re-use 4 - for example, for direct use as paint constituents.
• the permeate 5 from the ultrafiltration stage 2 is essentially free from constituents of relatively high molecular mass, with a molecular weight of more than 1000 Da, preferably more than 2000 Da, and contains organic solvents and water.
• This permeate 5 is supplied to a reverse osmosis stage 6 in which the organic solvents in the retentate 7 are concentrated to a concentration of at least 25% by weight, preferably at least 50% by weight, and are supplied for separate use 8 - for example, as initial rinsing liquid.
• the permeate 9 of the reverse osmosis 6 is essentially pure water and can, for example, be recycled into the rinsing process or else employed for other applications where deionized water is required.
• a used rinsing liquid having the composition stated in Table 1 was passed from a reservoir, at a reservoir temperature of 20°C, through an ultrafiltration stage for concentration.
• a tubular module with a ceramic membrane having a cutoff point of 100,000 daltons was employed in the ultrafiltration stage.
• the rinsing liquid entered the module on the feed side at 3 m 3 /h, the pressure upstream of the module being 2.3 bar and the pressure downstream of the module being 2.0 bar.
• Ultrafiltration was conducted to a solids content of 50% by weight in the concentrate. The composi- tion of the permeate and of the retentate of the ultrafiltration was determined analytically and is shown in Table 1.
• the permeate of this ultrafiltration was then supplied to a reverse osmosis stage.
• a spiral module with a polyamide membrane having a sodium chloride retention of not more than 99.2% was used in the reverse osmosis stage.
• the ultrafiltration permeate entered on the feed side at 0.75 m 3 /h, the transmembrane pressure difference being 41 bar.
• the reverse osmosis was conducted up to a solvent concentration of 25% in the concentrate.
• the composition of the concentrate and of the permeate of the reverse osmosis was determined analytically and is reproduced in Table 1.

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• Engineering & Computer Science (AREA)
• Water Supply & Treatment (AREA)
• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Hydrology & Water Resources (AREA)
• Environmental & Geological Engineering (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Nanotechnology (AREA)
• Separation Using Semi-Permeable Membranes (AREA)

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• 1997
  • 1997-07-17 EP EP97112200A patent/EP0891950A1/de not_active Withdrawn
• 1998
  • 1998-07-16 WO PCT/EP1998/004422 patent/WO1999003786A1/en not_active Application Discontinuation
  • 1998-07-16 AU AU85425/98A patent/AU8542598A/en not_active Abandoned
  • 1998-07-16 EP EP98936427A patent/EP1001911A1/de not_active Withdrawn

Non-Patent Citations (1)

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