1000 2000 3000 4000 5000 6000 0.2 0.4 0.6 0.8 1.0 Surface pressure(mN/m) Mma(A 2 ) NaCl 1000 ppm NaCl 2000 ppm NaCl 3000 ppm Relaxation Experiment at different salt concentration Napthenic Acid 1000 ppm in Toluene Volume spread 20ul, Barrier speed 10mm/min 20 40 60 80 100 0.2 0.4 0.6 0.8 1.0 Normalize Surface pressure Time(min) pH 4 pH6 pH7 pH9 pH12 Relaxation Isotherm at different pH 20 40 60 80 100 120 0 5 10 15 20 Surface pressure(mN/m) Mma(A 2 ) pH4 pH9 Slope comparision at different pH Napthenic acid 1000 ppm in Toluene Volume spread 20ul, Barrier speed - 10 mm/min The measurements on LB were done using the KSV NIMA Langmuir Trough. The sample is first dissolved in toluene and then spread over the surface of water & allowed toluene to evaporate. Repeated compression- decompression studies were then carried out to get the excess pressure vs area/molecule plots. Monolayers of Napthenic Acids, one of the surface active components of crude oil, were prepared using Langmuir Blodgett technique. Commercially available Poly- Disperse Naphthenic acids (Acros Chemicals) were used for Surface Pressure-Mean Molecular Area Isotherm experiments. Effect of pH, nature and concentration of electrolyte concentrations on the film properties were investigated. It is found that Naphthenic acids form stable film at air/water interface. The pH of the bulk phase and concentration of salt has significant effect on the film properties. The surface pressure isotherms indicate the changes in film behaviour as pH is varied from 4, 9 and 12. The surface pressure-area isotherm deviates distinctly from high to low mean molecular area as the pH of sub phase changes from 4 to 12. The film on a bulk phase at pH 4 consists basically of protonated naphthenic acid however when the pH is higher deprotonation of proton occurred (forming sodium naphthenate) hence causing solubilisation of sodium salt of naphthenic acid into water resulting in decline of surface pressure. Hysteresis pattern in compression-relaxation cycles were observed for almost 10 cycles. Further, The interaction of different metal salt with Napthenic acid at different pH will be evaluated by using surface potential measurements. Study of Langmuir Blodgett Monolayers of Napthenic Acids at Air/Water Interface: Effect of pH and Salt on Film Behaviour Manu Vashishtha 1 , Laksh Agarwal 1 , Abusaif Khan 2 , Rochish Thaokar 1 and Vinay A. Juvekar 1 1 Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai – 400 076, India. 2 Department of Chemical Engineering, Institute of Chemical Technology, Mumbai MATERIALS USED RESULTS AND DISCUSSIONS ABSTRACT Napthenic Acid METHOD Effect of pH on Film Elasticity Many molecules in the crude are acidic, which ionize at the o/w interface, lower IFT and stabilize the interface •The acids are: simple alkyl carboxylic acids, alkyl benzene carboxylic acids (benzoic acids), naphthenic acids and metal salts, fused aromatic ring acids, e.g. napthoic acids •Above should be acidic stabilization •Can form calcium soaps and stabilize emulsions • Tetra acids with carbon number 80 are the ARN acids 1,2,3,4 butane tetra carboxylic acid Langmuir-Blodgett Trough At pH 4 Carboxylic group remains protonated At pH 9 Partial Deprotonation occurs At pH 12 Complete Deprotonation occurs Langmuir–Blodgett Trough is a laboratory apparatus that is used to compress monolayers of molecules on the surface of a given sub phase (usually water) and measures surface phenomena due to this compression. It can also be used to deposit single or multiple monolayers on a solid substrate. Typical LB measurements gives us information about the following: •Packing(Mean molecular Area) •Elasticity(Steepness of the curve) •Hysteresis(Molecular Interaction) •Relaxation(Stability of the films) •Poly-Disperse Naphthenic Acids (Acros Chemicals) •Toulene (Sigma) •Sodium Hydroxide (Merck) •Chloroform (Merck) •De-Ionized Water (Mili Q) •Buffer Capsules (Merck) 20 40 60 80 100 120 5 10 15 20 Surafce pressure(mN/m) Mma(A 2 ) Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 Typical Langmuir Blodgett Experiment 20 40 60 80 100 120 0 10 20 Surface pressure(mN/m) Mma(A 2 ) pH4 pH9 pH12 Effect of pH Napthenic Acid 1000ppm in Toluene Volume spread 20ul, barrier speed 10mm/min pH 4 No Dissociation pH 9 Partial Dissociation pH 12 Complete Dissociation 20 40 60 80 100 120 0 10 20 Surface pressure(mN/m) Mma(A 2 ) pH4 pH9 pH12 Hysteresis study Napthenic Acid 1000ppm in Toluene Volume spread 20ul, barrier speed 10mm/min Slope = 0.346 Slope = 0.96 Slow Hysteresis at pH 4 - Entanglement Fast Hysteresis at pH 9 - Charge Repulsion No Hysteresis at pH 12 - Completely Soluble 20 40 60 80 100 120 2 4 6 8 10 12 14 16 18 20 Surface pressure(mN/m) Mma(A 2 ) NaCl 1000 ppm NaCl 2000 ppm NaCl 3000 ppm Salt Effect at pH 6 Napthenic acid 1000 ppm in Toluene Volume spread 20ul, Barrier Speed 10mm/min NO Effect since No Ionization at Interface Effect of pH Hysteresis Isotherm Effect of Salt Study of Relaxation Curves Study suggests that pH has influence on the film properties of Napthenic Acid at Air /Water Interface. At pH 9 partial deprotonation causes formation of negatively charged carboxylate ions, which produce more steeper rise in Surface Pressure Isotherm at pH 4. Higher value of slope at pH 9 indicates the formation of rigid films due to charge interactions. This study indicates that pH has influence on molecular interaction among Napthenic Acid molecules at Air/Water Interface. At pH 4 molecules are unionized and show large Hysteresis pattern because of slow relaxation of Napthenic Acid molecules held together by Vander-Wall/Hydrophobic interactions. However partial deprotonation of Napthenic Acid molecules at pH 9 causes repulsion between negatively charged carboxylate ions resulting in faster rate relaxation and less area Hysteresis. At pH 12 Napthenic Acid molecules are completely deprotonated making them soluble in water resulting in decrease in Surface Pressure and hence no Hysteresis is observed. Effect of NaCl concentration on the surface properties of Napthenic Acid were studied results in all three concentration range found to be similar. References Future Scope Conclusion • Surface morphology of Napthenic Acid film using Brewster Angle Microscopy(BAM) • Effect of CaCl2 concentration(Monovalent cation vs Divalent cation) • Visco-Elastic properties(G’ & G’’) of Napthenic Acid films using Oscillation Barrier Technique at Air/Water Interface • Dipping Experiments of Napthenic Acid monolayer for contact angle measurement • Atomic Force Microscopy of deposited Napthenic Acid films • Alkalinity of the aqueous phase has significant influence on the film properties of surface active molecule(Napthenic Acid) present in crude oil • Low pH (pH 4) causes viscous behavior in the films • Moderate alkalinity (pH 9) induces elasticity in the films • High alkalinity (pH 12) cause complete solubalization of Napthenic Acid in the form of Metal Napthenates. • Fastest Relaxation at pH 9 indicates the rearrangement of molecules at interface • Song Gao, Kevin Moran, Zhenghe Xu and Jacob Masliyah J. Phys. Chem. B, 2010, 114 (23), pp 7710–7718. • Ramesh Varadaraj and Cornelius Brons Energy Fuels, 2007, 21 (1), pp 199–204. • Øystein Brandal , Ann ‐ Mari D. Hanneseth , Pål V. Hemmingsen , Johan Sjöblom , Sunghwan Kim , Ryan P. Rodgers & Alan G. Marshall Journal of Dispersion Science and Technology, 27:295–305, 2006. This study indicates that pH has influence on stability of the films of Napthenic Acid at Air/Water Interface. At pH 9 faster relaxation of Napthenic Acid molecules is observed due to re-orientation of molecules at Air/Water Interface High concentrations of salt (NaCl 3000 ppm) allow Napthenic Acid molecules to stay at Air/Water Interface Time(s) Normalized Surface Pressure(mN/m)