COLD OXIDATION IN GASEOUS PHASE

Abstract: A vapour and gaseous effluent purification process wherein the gaseous flow is made to proceed between metal plates (1) subjected to oscillating electrical high voltages and then over a porous siliceous mass (2) having adsorbed therein an oxidation catalyst active at room temperature.

Description: COLD OXIDATION IN GASEOUS PHASE In a large number of industrial processes one can observe the emission towards the atmosphere of gaseous flows containing organic solvents from painting, spraying, drying processes, furnaces and so on. The conditioning technologies available nowadays to solve this problem, since the regulations enforced by the various regional authorities state particularly low limits, may be summarized in two families: - Adosorption on activated carbon : It has the following drawbacks: it is impossible to find commercial activated carbons adapted to systematically adsorb different types of solvents present in the same flow; - possible desorpt- ion of a solvent already fixed in a flow which does not include it; - difficulty in regenerating said carbons with the resulting problem of their disposal as "toxic wastes"; - in case said carbons get saturated with intrinsic flammable solvents and problems for the/ safety of the plant itself. - Thermal after-burning: The drawbacks experienced are the following: - it is necessary to raise the temperat¬ ure of the flow by an outside fuel addition with particularly high associated operation costs; possible formation of positively toxic chemical compounds within the flow, caused by high temperatures. Taking the above into account, the Applicant has provid¬ ed a new treatment suited to remove the above draw¬ backs, with the purpose of reaching the following benefits: - low operating costs measured in terms of the energy needed to destroy the solvents (by oxidation) . The oxidation takes place at ambient temperature (approximately 20°C); - approximately uniform effective¬ ness in the oxidation of both aromatic and aliphatic organic compounds; - nc production of solid toxic wastes; no generation of gaseous positively toxic compounds, or more toxic than the substances to be destroyed. The gaseous matter carrying the organic solvents to be destroyed enters, at a temperature ranging from 18°C to 40°C, the processing unit, shown schematically in the attached Figure 1, which substantially comprises two stages : - First stage, or ionizing stage: this portion substant- ially comprises metal plates 1 lying parallel to the flow and spaced apart from each other in such a way as to maximize the corona discharge generation. The plates are subjected to high voltages ranging from 15000 to 30000 V and from 500 tc 1500 Hz in frequency, provided by a high voltage generator 3 in order to enhance the ionizing effect on the gaseous flow. The spacing between the plates is such as to get the highest possible electrical field intensity allowable for the gaseos flow subject to treatment. The plate length is related to the flow velocity, in that it determines the effective processing time. The electronic apparatus is provided with all the automatic controls and safety features necessary to make the plant operation safe and reliable. - Second stage, or catalytic stage: the solvents carried by the gaseous substance undergo a first destructive treatment, while proceeding through the ionizing stage, for about 50% of the upstream contents. Free radicals are formed, in particular, which are able to develop their reactivity while contacting catalyst 2 comprised of oxides of metals of Group VIII, such as for instance Fe, Ni, Cr, V, and so on, whereby oxidation of the remaining portion takes place. The final result of this operation, if it were pushed to the extreme, would be the degradation of the solvents with production of carbon dioxide and steam. Since the cost of a plant increases exponentially versus the required efficiency, the system will be set up, with the objective of satisfying the limitations of the presently enforced law regulations, in such a way that there will still be traces of the solvent in the effluent. The results obtained by means of this equipment have been proved through laboratory research, where gas- chromatograms of the effluent were produced, in the original conditions and after processing through the system described herein. The laboratory tests were per¬ formed on a gaseous effluent containing xylene, toluene, butylacetate, butyl alcohol, methylisobutvlketone (MIBK) , methylethylketone (MEK) , ethylacetate , hexane. Tests were carried out at room temperature (about 20°C) , and the effluent processing time was approximately 1 sec (difference between inlet-outlet of the purifying unit) for a volume flowrate of 7 1/min. The used gas-chromatograph included a C20M column 6 meters long, with the following operating conditions: starting isotherm: 12 minutes at 100°C; gradient: 5°C mir final isotherm: 160°C r T. ,he cιh_romatograms s,hown i.n F_.i.gures2/ aarned r3el.ative to the effluent before and after the oxidation treatment of this invention. Before the Treatment (see Figure 2) The concentrations are listed in the following Table. PEAK NO . TIME AREA CONCENTRAT . Hexane 1 5. 1 13 16423 5 - 6459 Ethylacetate 2 15.507 6735 2.3154 Methylethylketone 3 16.948 9418 3.2378 Methylisobutylketone 4 22.738 41716 14.341 Butyl Alcohol 5 24.808 67515 23.2101 Butylacetate 6 25.513 34325 1 1 .8001 Toluene 7 28.72 41240 14. 1773 Xylenes 8 30.46 73514 25.2724 Aft er the Treatment ( see Figure 3 ) . Hexane 1 5.092 15041 34.6862 Ethylacetate 2 15.232 2977 6.8658 Methylethylketone 3 16.682 2718 6.2675 Methylisobutylketone 4 22.522 1463 3.3732 Butyl Alcohol 5 24.607 7200 16.6042 Butylacetate 6 25.317 4270 9.8472 Toluene 7 28.548 5232 12.0663 Xylenes 8 30.292 3614 8.3343 As it can be seen when comparing the height of the peaks and the extent of the related areas before and after the treatment , the quantities c organic components still present at the outlet are drast ically reduced compared to the starting ones . For the tests that were performed the following reduct- ions were obtained: Xylenes: - 95%; Toluene: - 83%; Butylacetate: - 87%; Butyl Alcohol: - 89%; MIBK: - 96%; MEK: - 70%; Ethylacetate: - 55%.

Claims: CLAIMS 1. An oxidation treatment for gaseous effluents carrying gaseous organic compounds, characterized in that the effluent is made to flow, at temperatures rang¬ ing from 10°C to 40°C, between metal plates (1) parallel to the flow direction, subjected to electrical alternate voltages ranging from 15000 to 30000 V, at a frequency ranging from 500 to 1500 Hz, and the resulting gas is then supported made to flow over/catalysts (2) comprising oxides of the metals of Group VIII of the Periodic Table of the Elements . 2. The oxidation treatment of Claim 1, characterized in that said gaseous organic compounds are comprised in the group including hexane, butyl alcohol, ethylacetate, butylacetate, methylethylketone, methylisobutylketone, toluene and xylenes. 3. The oxidation treatment of Claim 1 or 2 , charact¬ erized in that said oxides of the metals of Group VIII are Fe, Ni, Cr, and V oxides.

Inventors: BARDELLI ERNESTO, CASSINERIO ERALDO, BARDELLI, ERNESTO, CASSINERIO, ERALDO
Applicants: HRS ENG SRL, H.R.S. ENGINEERING S.R.L.
Application year: 1990
Main classification: B01D53
IPC codes: B01D53, B01J19