Vapor‐liquid equilibria for aqueous sulfuric acid

Abstract

Co f o r H2So4(g) . Constants in Equations P B. P a r t i a l Molal P r o p e r t i e s I)IV. Calculation of P a r t i a l P r e s s u r e s . t i a l p r e s s u r e s f r o m -50 t o 400" C at t h i r t y -s i x compositions between 10 and 100 weight-percent acid. A. T r i a l Calculations2 3 Tables and g r a p h s a r e provided which give the above p a r --1 - I, INTRODUCT'IOiuThe vapor phase over sulfuric acid solutions is composed of water and sulfuric acid, together with sulfur trioxide f r o m the d i ssociation of the acid:In principle, the distribution of these t h r e e components at various t e m p e r a t u r e s and a c i d concentrations can be d e t e r m i n e d by e i t h e r (a) experimental p a r t i a l -p r e s s u r e m e a s u r e m e n t s p a r t i a l p r e s s u r e s f r o m liquid-phase thermodynamic data. 4 E x p e r i m e n t a l difficulties notwithstanding, the total vapor p r e ss u r e of sulfuric a c i d , which i n m o s t c a s e s is due e n t i r e l y t o the p a r t i a l p r e s s u r e of H 0, was t h e subject of n u m e r o u s investigations between 2 1845 and 1923, Greenewalt, reviewed 19 s e p a r a t e v a p o r -p r e s s u r e d e t e r m i n a t i o n s . s u l t , b a s e d e s s e n t i a l l y on the m e a s u r e m e n t s of Burt' and of Daudt, is the accepted s t a n d a r d that a p p e a r s in todayo s r e f e r e n c e w o r k s . (1) pure-component data for two liquids and t h r e e g a s e s and G o ) , and (H;98' '"298 P -o r '298 ( 2 ) p a r t i a l m o l a l data for binary solutions (H298, Because of t h i s , no c o r r e c t i o n h a s been 11.. DERIVATION O F EQUATIONSA, P a r t i a l -P r e s s u r e Euuation F o r any component in a multicomponent m i x t u r e at equilibrium, the p a r t i a l molal f r e e energy of the vapor i s equal to the p a r t i a l molal f r e e e n e r g y of the liquid:(2) If the p r e s s u r e i s low enough s o that the vapor a c t s as a perfect gas, Equation (3b) holds at any t e m p e r a t u r e and composition. The p a r t i a l p r e s s u r e under consideration is given by the sum of two t e r m s : a pure-component t e r m , -AF"JR'L a function of. t e m p e r a t u r e only; and a n activity t e r m y In a , a function oi both t e m p e r a t u r e and composition.In o r d e r t o evaluate the p r e s s u r e y e a c h t e r m m u s t be r e l a t e d to its s t a n d a r d -s t a t e value.The pure-component term is evaluated as foPPows : This i n t e g r a t e s t o give----Any coefficient 01 ;abr;cript shown a s 298 i s actually computed a s 2 9 8 -1 5 ' K (25' C ) . I --The activity t e r m i s evaluated in a. s i m i l a r m a n n e r :wheres{ [98 298 298 Combining Eqs. (3b), (5), and, ( 7 ) , we obtainThe evaluation of G ( T ) m a y be m a d e by using heat-capacity 3 functions in a f o r m given in the l i t e r a t u r e . F o r the g a s , we haveThis gives, upon combining G 1 9 G2' and G3(T): m a y be determined as a function of t e m p e r a t u r e , a s follows.The equilibriu...

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“…However, as recommended in Hamill et al (1982), vapour pressures of H 2 SO 4 from the Ayers et al (1980) relationship are divided by 0.086 to obtain values close to the measurements of Gmitro and Vermeulen (1964). We account for the Kelvin effect, whereby the saturation vapour pressure of H 2 SO 4 over a curved surface is higher than the saturation vapour pressure over a flat surface.…”

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