Formation of Polychlorinated Dibenzofurans by Chlorination and de Novo Reactions with FeC13 in Petroleum Refining Processes Adrian Beard,? Krlshnat P. Naikwadl, and Francis W. Karasek'
Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 The formation of polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs) in catalytic reforming, a petroleum refining process, was studied using a laboratory apparatus. Conditions in the catalyst regeneration step in catalytic reforming were simulated, and the reactions of precursor compounds for the formation of PCDFs and PCDDs were studied. No PCDFsIPCDDs were produced by the reforming catalyst and potential precursors under any conditions studied. During treatment of the coked catalyst, dibenzofuran (DBF) was found in the flue gases. Chlorination experiments with flue gas concentrates and standard solutions in the presence of FeC13 and HC1 or Cln in the temperature range of 220-540 "C indicated that DBF can be chlorinated to PCDFs. A precursor mixture of l,l,l-trichloroethane (TCE) and CCl, in hexane also produced PCDFs by de nouo formation. Introduction PCDFs and PCDDs were first detected in internal process effluents from Canadian petroleum refineries in 1989 (I). PCDFs were found in the concentration range of emissions from municipal waste incinerators, one of the major sources of PCDDs and PCDFs, whereas the concentrations of PCDDs were 1-2 orders of magnitude lower. In the catalytic reforming process, coke accumulates on the catalyst surface. The coked catalyst is regenerated at temperatures of 380-525 "C by burning off the coke in a controlled oxygen atmosphere followed by reactivation of the catalyst by the addition of chlorinated compounds such as CCld, l,l,l-trichloroethane, and HC1. Catalytic reforming is a major source for the aromatic and highoctane aliphatic constituents of unleaded gasoline. The U.S. reforming capacity amounts to 625 000 m3/d, which is about half of the total world capacity of 1 390 000 m3/d (2). Although PCDFs and PCDDs were found in the catalyst regeneration effluents ( I ) ,it was not known which step or conditions in the process were contributing to the formation of PCDFs and PCDDs. To investigate the mechanism of PCDD/F formation in this process, a series of experiments with a benchtop flow tube apparatus were undertaken. We have reported that 13C-labeledpentachlorophenol (PCP) as a precursor did t Present address: Institut fur Umwelt-und Sicherheitstechnik, Osterfelder Strasse 65, W-4200 Oberhausen, Germany.
0013-936X/93/0927-1505$04.00/0
0 1993 American Chemical Soclety
not form PCDDs on the coked catalyst in contrast to municipal waste incinerator fly ash (3). Added octachlorodibenzo-p-dioxin was destroyed on the catalyst at temperatures above 300 "C. In this paper, we describe the search for PCDDs, PCDFs, and their possible precursors in samples from the catalytic reforming process and reactions carried out in a flow tube reactor with precursor candidates. A possible pathway for the formation of PCDFs was found; however, the formation of PCDDs could not be explained by our experimental results. Experimental Section Safety Requirements. Due to the toxic nature of the compounds involved, all the described experiments were carried out in fume hoods under proper precautions, i.e., wearing laboratory coats, gloves, and safety glasses. Extraction of Catalysts. Samples of 20-50 g of fresh, coked, and regenerated catalysts from catalytic reforming plants of a major petroleum refining industry (PRI) were extracted with 300 mL of toluene by Soxhlet for 48 h. The extracts were reduced in volume by rotary evaporation, transferred into vials, and further concentrated under a gentle stream of high-purity nitrogen. Twenty-gram samples of coked reforming catalysts were also thermally extracted by heating them to 485 "C for 2 h under a stream of 30 mL/min of high-purity nitrogen. Catalyst Burns. To simulate the conditions of the catalyst regeneration in catalytic reforming, catalyst burns were carried out. Samples of 2-80 g of coked reforming catalyst were placed in a Pyrex tube (20 mm i.d. X 480 mm length) and held in place by two glass wool plugs. A chromel-alumel thermocouple (type K) with a quartz sheath was placed inside the catalyst bed for temperature control. The pyrex tube was inserted into a Mellen oven (Webster, NH; horizontal heated zone, 32 mm i.d. X 150 mm length). The initial set temperature of 480 "C in the catalyst bed increased to a maximum of 530 "C during the burn due to the exothermic reactions. The carrier gas was air. After the column (Pyrex tube), the carrier gas passed through an ice-cooled impinger containing 50 mL of hexane. One burn experiment was carried out in a large scale apparatus with two 500-g portions of coked Pt catalyst. The initial temperature of the bed was 425 "C. A mixture of nitrogen and air was used to limit the temperature Envlron. Scl. Technol., Vol. 27, No. 8, 1993
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Table I. Summary of Diknzofuran Quantitations. sample catalyst no. 7% C
thermocouple
syringe pum with precursor sorution
A
5.6
B
1.3
Teflon coated septum
c quartz column
D
1.0 5.0
twe
DBF gof ng nglgof nglg catalyst found catalyst of C
cokedcatalyst 16.1 burnt catalyst 15.3 flue gas 15.3 cokedcatalyst 2.0 burnt catalyst 2.0 flue gas 2.0 B3 burnt catalyst 2.0 Ngthermalextract 2.0 B3 impinger, air 2.0 fluegas 81.9 cokedeatalyst 21.6 burnt catalyst 29.8 flue gas 1000.0 N~therrnalextract 22.5
