# Diffusion-Reaction - PowerPoint PPT Presentation

1 / 28

Diffusion-Reaction. Acid Base Reactions. k 1. RCOOH RCOO - + H +. k -1. Naproxen. Naproxen Physical Properties. Solubility of free acid [HA] o =1.37x10 -4 M Mw=230.36 [HA] o = 315.6 gm/L. =0.315 mg/ml pKa= 4.57

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Diffusion-Reaction

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

## Diffusion-Reaction

k1

RCOOH RCOO- + H+

k-1

### Naproxen Physical Properties

• Solubility of free acid [HA]o=1.37x10-4M

• Mw=230.36

• [HA]o = 315.6 gm/L. =0.315 mg/ml

• pKa= 4.57

• How long does it take a small particle ~ 0.1mm in radius to dissolve (in acid)?

Cs

SS

C=0

h

A-

Cs

H+

C=0

HA

h

### Assumptions

• Stagnant fluid vi=0

• Steady State dC/dt = 0

• One dimensional

k1

RCOOH RCOO- + H+

k-1

HAtot

Htot

### Resulting Equations

Interface BC’s

HA=HA0= solubility

KA = H+ A -/HA

dH+ /dx=dA - /dx=0 (can not penetrate boundary)

Solid

Bulk:

HA=0

A - = 0

H +=H + bulk

x

0

h

### Solve these equations: Key assumptions

• Equilibrium rate constants are fast relative to diffusion

• Equal diffusivities

• Equal film thickness

### Conclusion

• Ionization at the interface accelerated dissolution…due to added species (A-)

• The effect can be orders of magnitude.

pH=pKa +2 ~ 102 increase in rate

k1

A

B

k-1

(A)

K=[E]/[A}

(E)

### Reversible Reaction: (Not include ionization at this time)

Membrane Phase;

k1,m

,k-1,m

Km

Aqueous phase

k1,a

,k-1,a

Ka

Partition Coefficients

PCA

PCE

Equilibrium constant differs in two phases: Ka>Km

### Let’s do one Phase (Olander reference)

Material A diffuses into film m’ and can react to form E in film