Technique and apparatus for recycling volatile organic compounds of coating printing

Abstract

The present invention discloses an integrated new technique and apparatus for recycling volatile organic compounds of coating printing. The new technique collects a mixed gas of volatile organic compounds produced in the process of coating and drying of a coating machine with a volatiles collecting hood of coating machine, compresses and lead the mixed gas of volatile organic compounds into a condensation system for condensation; the obtained condensate enters a gas-liquid separator to obtain a coating solvent with high concentration; non-condensable lean gas enters a membrane separation and enrichment system to obtain a mixed gas of high concentration organic compounds after membrane separation and enrichment with a complete set of membrane assembly, and then returns to front of the condensation system to repeat the integrated technique. The separation membrane as claimed in the present invention has an extremely high permselectivity for volatile organic compounds of coating printing and can quickly enrich the volatile organic compounds. Recycling rate of volatile organic compounds of the apparatus may reach 90%, and the content of organic compounds in the tail gas emission after treatment is no more than 1 g/m.sup.3. This integrated new technique largely reduces the production cost of coating printing industry and at the same time protects the atmospheric environment.

Claims

1. A method for recycling volatile organic compounds of coating printing industry, comprising following steps: (1) collecting a mixed gas of volatile organic compounds comprising hydrocarbons, alcohols, esters, ethers and nitriles produced in a printing process of the coating machine, which evaporates at least 85% of coating liquids it consumes, with a collecting hood of coating machine, precooling the mixed gas to 0° C. and compressing and leading the mixed gas into a condensation system for condensation at −30˜−50 to obtain a condensate; and (2) leading the condensate obtained in the above step into a gas-liquid separator to obtain a liquid of coating solvent with high concentration after an enrichment process, of which a measurement is taken, and a non-condensable gas; and leading the non-condensable gas into a membrane separation using a PDMS composite membrane and enrichment system to obtain a mixed gas of organic compounds which is sent back to the compressor through a vacuum pump for recycling.

2. The method as claimed in claim 1, wherein in Step 2, after measurement, the coating solvent with high concentration enters a solvent preparation area of an appointed workshop section for recycling uses according to the measurement.

3. The method technique as claimed in claim 1, wherein in Step 2, the absolute pressure of the vacuum pump on the permeation side during operation of the complete set of membrane assembly is 10˜40 kPa.

4. The method technique as claimed in claim 1, wherein the PDMS composite membrane is an organophilic composite membrane where modified polydimethyl siloxane is coated on and crosslinked with an inorganic ceramic tubular membrane or a PVDF matrix membrane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of the apparatus for recycling volatile organic compounds of coating printing.

(2) Wherein, 1. volatiles collecting hood of coating machine; 2. vacuum pump; 3. compressor; 4. condenser; 5. gas-liquid separator; 6. buffer tank; 7. collecting tank; 8. liquid pump; 9. complete set of membrane assembly; 10. tail gas sampling outlet; 11. gas inlet detector; 12. emergency vent; 13. tail gas vent.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

(3) FIG. 1 indicates the apparatus for recycling volatile organic compounds of coating printing. The apparatus consists of a volatiles collecting hood of coating machine 1, a compressor 3, a condenser 4 and a gas-liquid separator 5 connected and positioned successively; the bottom of the gas-liquid separator 5 is connected to a liquid storage device, and the top of the gas-liquid separator 5 is connected to a complete set of membrane assembly 9.

(4) The complete set of membrane assembly 9 adopts an organic permselective membrane. The organic permselective membrane in the present invention includes PDMS composite membrane, organic compound membrane, molecular sieve membrane, and mixed matrix membrane adulterated with inorganic substances, wherein, the PDMS composite membrane is an organophilic composite membrane where modified polydimethyl siloxane is coated on and crosslinked with an inorganic ceramic tubular membrane or a PVDF matrix membrane. The organic permselective membrane adopted by the present invention has an existing structure, against which the present invention does not state any restriction. Technicians in this field can select an organic permselective membrane that can efficiently realize corresponding functions to carry out the technical scheme of the present invention according to the actual production technique. Furthermore, a gas inlet detector 11 and an emergency vent 12 for detecting gas and discharged gas in emergency respectively are arranged between the volatiles collecting hood of coating machine 1 and the compressor 3. The liquid storage device consists of a buffer tank 6 and a collecting tank 7 connected successively. The collecting tank 7 may be further connected to a liquid pump 8.

(5) Further, the complete set of membrane assembly 9 is provided with a tail gas sampling outlet 10, a tail gas detecting device 10 and a tail gas vent 13. A vacuum pump 2 is arranged between the complete set of membrane assembly 9 and the compressor 3. The vacuum pump 2 can pump the mixed gas of organic compounds enriched in the complete set of membrane to the compressor for recycling.

(6) When the present apparatus operates, the volatiles collecting hood of coating machine 1 feeds organic compounds produced in the process of coating printing and air into the compressor 3 through a header, and then into a condensation system after pressurized by the compressor 3; the condenser 4 is used for cooling of the cold box to condense the volatile organic compounds with a high boiling point; then the gas-liquid separator 5 is used for collecting liquid organic compound solvent, which is led to the buffer tank 6 and finally to the collecting tank 7; when a large amount of organic compound solvent is collected, the liquid pump 8 is used for pumping it the preparation area; at the same time, the saturated organic compound gas with a low boiling point above the gas-liquid separator 5 enters the complete set of membrane assembly 9; then the complete set of membrane assembly 9 enriches the organic compound gas through the vacuum pump 2 on the downstream side; after enrichment, the organic compound gas is recycled again before entering the compressor 3; meanwhile, the concentration of organic compounds on the retentate side of the membrane reaches the standard for discharge.

(7) The volatile organic compounds produced in the process of coating printing is taken as the raw material (butanone for 31.6 wt %, ethyl acetate for 31.7 wt %, n-propyl acetate for 31.7 wt % and methyl ether for 5 wt %). The volatilization amount of organic compound is 40 kg/h (which means 40 kg organic compounds are volatilized per hour). The volatile organic compounds are driven out by the blower with an outlet gas flow of 5,000 m.sup.3/h and then enter the “condensation+membrane” apparatus in the present invention for recycling through the volatiles collecting hood of coating machine.

Embodiment 1

(8) Set the condensing temperature to be −30° C.; Adopt organic permselective membrane (PDMS tubular membrane); set the absolute pressure of the vacuum pump to be 10 kPa. The result of experiment is as below:

(9) TABLE-US-00001 Temper- Ethyl N-propyl Methyl ature Pressure Butanone acetate acetate ether Air ° C. kPa g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 Gas inlet 100 Atmospheric 2.54 2.54 2.54 0.40 1160 pressure Condenser −30 Atmospheric 1.27 1.29 0.54 0.30 1200 pressure Permeate gas 30  10 5.43 5.29 1.98 1.06 400 Discharged 30 120 0.23 0.29 0.18 0.11 1400 gas

(10) Set the condensing temperature to be −40° C.; Adopt organic permselective membrane (PDMS tubular membrane); set the absolute pressure of the vacuum pump to be 10 kPa. The result of experiment is as below:

(11) TABLE-US-00002 Temper- Ethyl N-propyl Methyl ature Pressure Butanone acetate acetate ether Air ° C. kPa g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 Gas inlet 100 Atmospheric 2.54 2.54 2.54 0.40 1160 pressure Condenser −40 Atmospheric 1.26 1.27 0.53 0.30 1182 pressure Permeate gas 30  10 5.42 5.19 1.97 1.06 380 Discharged 30 120 0.22 0.29 0.17 0.11 1383 gas

(12) Set the condensing temperature to be −50° C.; Adopt organic permselective membrane (PDMS tubular membrane); set the absolute pressure of the vacuum pump on the permeation side to be 10 kPa. The result of experiment is as below:

(13) TABLE-US-00003 Temper- Ethyl N-propyl Methyl ature Pressure Butanone acetate acetate ether Air ° C. kPa g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 Gas inlet 100 Atmospheric 2.54 2.54 2.54 0.40 1160 pressure Condenser −50 Atmospheric 1.26 1.27 0.52 0.30 1200 pressure Permeate gas 30  10 5.42 5.19 1.96 1.06 380 Discharged 30 120 0.22 0.29 0.16 0.11 1405 gas

(14) Seen from the above three experiments, the recycle of volatile organic compounds increases as the condensing temperature decreases, but not obviously, which means a vapor-liquid equilibrium is achieved at −30˜−50° C., so the preferred condensing temperature is −30˜−50° C.

Embodiment 2

(15) Set the condensing temperature to be −30° C.; Adopt organic permselective membrane (PDMS tubular membrane); set the absolute pressure of the vacuum pump on the permeation side to be 20 kPa. The result of experiment is as below:

(16) TABLE-US-00004 Temper- Ethyl N-propyl Methyl ature Pressure Butanone acetate acetate ether Air ° C. kPa g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 Gas inlet 100 Atmospheric 2.54 2.54 2.54 0.40 1160 pressure Condenser −30 Atmospheric 1.27 1.29 0.54 0.30 1200 pressure Permeate gas 30  20 5.35 5.21 1.9 1.06 500 Discharged 30 120 0.25 0.31 0.20 0.11 1375 gas

(17) Set the condensing temperature to be −30° C.; Adopt organic permselective membrane (PDMS tubular membrane); set the absolute pressure of the vacuum pump on the permeation side to be 40 kPa. The result of experiment is as below:

(18) TABLE-US-00005 Temper- Ethyl N-propyl Methyl ature Pressure Butanone acetate acetate ether Air ° C. kPa g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 Gas inlet 100 Atmospheric 2.54 2.54 2.54 0.40 1160 pressure Condenser −30 Atmospheric 1.27 1.29 0.54 0.30 1200 pressure Permeate gas 30  40 5.27 5.17 1.70 1.02 520 Discharged 30 120 0.27 0.32 0.25 0.12 1370 gas

(19) Seen from the above two experiments, under a certain condensing temperature, the recycling rate of volatile organic compounds is relatively high when the vacuum pressure on the permeation side is 10 KPa-40 KPa.

Embodiment 3

(20) Set the condensing temperature to be −30° C.; Adopt organic permselective membrane (PDMS coiled type composite membrane); set the absolute pressure of the vacuum pump on the permeation side to be 20 kPa. The result of experiment is as below:

(21) TABLE-US-00006 Temper- Ethyl N-propyl Methyl ature Pressure Butanone acetate acetate ether Air ° C. kPa g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 Gas inlet 100 Atmospheric 2.54 2.54 2.54 0.40 1160 pressure Condenser −30 Atmospheric 1.27 1.29 0.54 0.30 1200 pressure Permeate gas 30  20 5.34 5.22 2.00 1.06 510 Discharged 30 120 0.25 0.28 0.18 0.11 1373 gas

Embodiment 4

(22) Set the condensing temperature to be −30° C.; Adopt organic permselective membrane (PDMS organic membrane); set the absolute pressure of the vacuum pump on the permeation side to be 20 kPa. The result of experiment is as below:

(23) TABLE-US-00007 Temper- Ethyl N-propyl Methyl ature Pressure Butanone acetate acetate ether Air ° C. kPa g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 Gas inlet 100 Atmospheric 2.54 2.54 2.54 0.40 1160 pressure Condenser −30 Atmospheric 1.27 1.29 0.54 0.30 1200 pressure Permeate gas 30  20 5.33 5.23 2.02 1.02 490 Discharged 30 120 0.24 0.30 0.17 0.12 1378 gas

Embodiment 5

(24) Set the condensing temperature to be −30° C.; Adopt organic permselective membrane (PDMS mixed matrix membrane); set the absolute pressure of the vacuum pump on the permeation side to be 20 kPa. The result of experiment is as below:

(25) TABLE-US-00008 Temper- Ethyl N-propyl Methyl ature Pressure Butanone acetate acetate ether Air ° C. kPa g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 g/m.sup.3 Gas inlet 100 Atmospheric 2.54 2.54 2.54 0.40 1160 pressure Condenser −30 Atmospheric 1.27 1.29 0.54 0.30 1200 pressure Permeate gas 30  20 5.51 5.33 2.10 1.04 512 Discharged 30 120 0.21 0.28 0.15 0.11 1372 gas

(26) Seen from Embodiments 1-5 and data analysis, when the condensing temperature is set to be −30˜−50° C., the organic permselective membrane is adopted, and the absolute pressure of the vacuum pump on the permeation side is set to be 10-40 KPa, recycling rate of the technique may reach 90%, and the content of organic compounds in tail gas emission is no more than 1 g/m.sup.3 according to experiments and on-line chromatographic analysis.

(27) The schemes in the above embodiments may be further combined or replaced, and the above embodiments only relates to description of preferred embodiments of the present invention rather than restriction of concept and scope of the present invention. Various changes and improvements of the technical schemes of the present invention made by technicians in this field are within the scope of protection of the present invention provided that such changes and improvements are within the design concept of the present invention.