Environmental Catalysis - ACS Publications - American Chemical

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Chapter 28

Deep Oxidation of Chlorinated Hydrocarbons 1

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Russell S. Drago , S. C . Petrosius , G . C . Grunewald , and William H . Brendley, J r . 2

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Department of Chemistry, University of Florida, Gainesville, F L 32611 R o h m and Haas Company, Spring House, PA 19477

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Catalysts comprising metal oxides dispersed in Ambersorb carbonaceous adsorbents are shown to be effective in the decomposition of halogenated hydrocarbons by air at and below 250° C. A wide range of chlorinated hydrocarbons are converted selectively to CO , CO and HCl. Surprisingly the Ambersorb adsorbent supports exhibited significant activity in the absence of metal oxide species. Trends in reactivity with catalyst variation suggest that the carbonaceous adsorbent pore content and acidity are determining factors in the catalytic activity. Kinetic studies of methylene chloride decomposition over undoped Ambersorb adsorbent show a first order dependence on C H C l concentration and an activation energy of 11.0 kcal/mol. Further examination of the catalytic decomposition process suggests that a source of hydrogen, either as a component of the chlorinated hydrocarbon or as an added reagent, is necessary to regenerate the catalyst. Water not only served this function but also was found not to saturate the active site for adsorption. 2

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H a l o g e n a t e d h y d r o c a r b o n s h a v e enjoyed w i d e s p r e a d acceptance as s o l v e n t s i n the c h e m i c a l i n d u s t r y because o f their relative inertness i n c h e m i c a l processes a n d their a b i l i t y to d i s s o l v e m a n y o r g a n i c c o m p o u n d s . H o w e v e r , the t o x i c i t y a n d carcinogenic properties of h a l o g e n a t e d o r g a n i c s h a v e r a i s e d i n d u s t r y awareness of the n e e d for p r o p e r d i s p o s a l of these h a z a r d o u s m a t e r i a l s (1). I n d e e d , p u b l i c awareness has l e d to m o r e stringent e m i s s i o n r e g u l a t i o n s b y the federal, state, a n d l o c a l g o v e r n m e n t agencies. P r e s e n t l y , air s t r i p p i n g a n d i n c i n e r a t i o n are the p r e f e r r e d m e t h o d o f d i s p o s a l b u t temperatures e x c e e d i n g 1000 Κ are r e q u i r e d to o b t a i n c o m p l e t e d e c o m p o s i t i o n (2,3). H i g h l y toxic materials s u c h as d i o x i n are often f o r m e d as b y p r o d u c t s . W i t h l o w concentration of c o n t a m i n a n t i n the gas phase, the process becomes e x c e e d i n g l y inefficient as the entire v o l u m e o f gas m u s t b e h e a t e d to the c o m b u s t i o n temperature. Incinerator fuel costs alone m a y r e a c h 4 0 % o f the total o p e r a t i n g costs (4). Consequently, development of

0097-6156/94/0552-0340$08.00/0 © 1994 American Chemical Society Armor; Environmental Catalysis ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

Downloaded by CORNELL UNIV on October 26, 2016 | http://pubs.acs.org Publication Date: February 23, 1994 | doi: 10.1021/bk-1994-0552.ch028

28. DRAGO ET AL.

Deep Oxidation of Chlorinated

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Hydrocarbons

l o w - t e m p e r a t u r e processes for h a l o g e n a t e d waste d i s p o s a l c a n offer significant i m p r o v e m e n t o v e r present methods. S p i v e y (5) presents a n exhaustive r e v i e w (to 1987) o f l o w - t e m p e r a t u r e o x i d a t i v e d e c o m p o s i t i o n catalysts for a p p l i c a t i o n i n e n v i r o n m e n t a l r e m e d i a t i o n . T h e majority of the catalysts c a n be p u t i n t o t w o categories: t r a n s i t i o n m e t a l o x i d e s (either u n s u p p o r t e d or a d s o r b e d onto a n i n o r g a n i c o x i d e support) a n d s u p p o r t e d n o b l e metals. T h e n o b l e m e t a l catalysts ( P d , P t , R h , R u ) are p o o r choices for o x i d a t i o n of h a l o g e n a t e d h y d r o c a r b o n s because o f their h i g h expense a n d their p r o p e n s i t y to p o i s o n i n g b y the C I 2 a n d H C 1 p r o d u c e d i n the reaction (6,7). A n u m b e r of patents h a v e b e e n i s s u e d for d e s t r u c t i o n of h a l o g e n a t e d h y d r o c a r b o n s w i t h m e t a l o x i d e catalysts (8) b u t o p t i m u m temperatures for these systems are u s u a l l y > 3 0 0 ° C a n d the h a l o g e n a t e d h y d r o c a r b o n concentration t y p i c a l l y i s l i m i t e d to less t h a n 10,000 p p m . T h i s s t u d y investigates A m b e r s o r b carbonaceous adsorbents as catalyst for the catalytic c o m b u s t i o n o f h a l o g e n a t e d h y d r o c a r b o n s at l o w temperatures (