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Improved Processes to Remove Naphthenic Acids
Project Number

This work will use an integrated computational and experimental approach (for both kinetics and catalyst synthesis) to: 1) obtain a fundamental mechanistic understanding of the catalytic decarboxylation of model naphthenic acids and 2) develop an inorganic solid filter that is specific to extracting carboxylic acids from dilute solutions under rapid flow conditions.


California Institute of Technology
Pasadena, CA


Naphthenic acids, which are unfunctionalized aliphatic, alicylic, and aromatic carboxylic acids, cause enormous refinery problems due to their corrosivity toward mild steel. Naphthenic acids are unique components of most crude oils and are especially prevalent in heavy and biodegraded oils. They have a higher rate of chemical activity than other components of crude oil. Their reactivity translates to metal corrosion in refineries and processing plants. In the upstream phases of oil production and transportation to refineries, naphthenic acids can react with other materials to form sludge and gum, thus plugging pipelines and operating machinery.


Gaining a fundamental understanding of effective mechanisms of removing naphthenic acid compounds from heavy crude oil will significantly help the U.S. petroleum industry in improving refinery processing of heavy crude oils possessing high contents of naphthenic acid. 

Accomplishments (most recent listed first)

Project Summary
The project accomplishments included these developments:

  • More-oxidative metal oxide catalysts were developed that were effective in catalytic decarboxylation of model acid compounds. Ag2O shows excellent decarboxylation activity for naphthoic acid at 300° C; acid conversion reached 93.9%. A laboratory-scale flow reaction line was developed for continuous evaluation of catalytic activity. Kinetics were studied using IR adsorption, Total Acid Number, and oil viscosity.
  • The kinetic measurements were performed on two catalysts, which were typical of the effective catalysts that were developed. The two catalysts were effective for the removal of naphthenic acids for up to more than 10 hours. Treatment capacities could reach 95 grams per gram of catalyst.
  • Several clay minerals were selected for the adsorption of naphthenic acids. Sepiolite and montmorillonite demonstrate higher adsorptive capacities in comparison with other clays.
  • Theoretical studies of the decarboxylation mechanism suggest that:
    • The radical pathway will be predominant when transition metals such as Cu (II), Mn (III) are involved. These cation species are able to generate an internal electron-transfer due to the closed shell (from Cu (II), -3d9 to Cu (I), -3d10 electronic configurations) and half-closed shell (from Mn (III) -3d4 to Mn (II) -3d5 electronic configurations).
    • The concerted pathways could be a rationalized mechanism when base metals are involved. In the concerted pathway, the nucleuphilic attack on the ß-carbon is important as the initiative step.
    • The hydroxyl group on the metal surface could assist in C-C bond breaking. This result seems to suggest that a basic condition is essential for the initial base-acid reaction, an acidic condition would be important for the further decarboxylation reaction.

Tasks to be performed in this project include:

  • Task 1, which covers development of a low-temperature decarboxylation catalyst, including new catalyst design; determination of kinetics and the reaction mechanism of decarboxylation reactions under a specific catalyst system; ascertainment of reaction mechanisms and kinetic parameters (activation energies); and synthesis of new catalysts to remove naphthenic acids from crude oil via low-temperature decarboxylation.
  • Task 2, which calls for researchers to perform decarboxylation reaction study by time-resolved multiple cold trap analyzer that including establishing and validating a theoretical first-principles understanding of decarboxylation reactions; collect data on adsorption energy on various materials, heat capacity, enthalpy, and entropy terms; study the reaction pathways of catalyzed decarboxylation reactions; correlate results with critical catalyst properties; develop more-detailed complex models of the mechanism and rates for processes leading to decarboxylation; quantify the changes of products with temperature catalyst, pressure changes, and carboxylic acid feed compositional changes; optimize catalyst design and process conditions for decarboxylation; and characterize the catalyst before and after decarboxylation synthesis via x-ray techniques
  • Task 3, which entails performing computational modeling of carboxylic acid decarboxylation, including calculating the thermodynamic properties of various key intermediates in decarboxylation reactions; determining pathways and rate parameters for each reaction that plays an important role in decarboxylation; and developing simplified reaction models, including rates and pathways that can be used to fit the experimental data with a limited number of variables
  • Task 4, in which researchers model efforts to model naphthenic acid adsorption on solid phase that includes developing an improved Force Field (based on the MS-Q FF formalism) as the basis for the study of naphthenic acid-filter ligand interactions.
  • Task 5, which calls for project participants to perform naphthenic acid adsorption measurement on different solid surfaces, which includes validating modeling results of the calculated relative affinity of acid to adsorb on common solids such as polymer resins and clays; equilibrating a solution of known starting naphthenic acid concentration with a known mass of solid surface; calculating the amount of acid adsorbed onto the solid surfaces; determining which solid phase will provide best selective adsorption features for future potential filtration application; and running coreflood tests (flow oil through a solid packing) to measure naphthenic acid retention in dynamic conditions.
  • Task 6, in which researchers develop and optimize a process for efficiently removing naphthenic acids from crude oil, based on the experimental and the computational results, including evaluating the overall process and economic calculations and making recommendations toward a new naphthenic removal process.

Project Results

Two types of decarboxylation catalysts were developed. Catalyst A promotes catalytic decarboxylation, acid-base neutralization, and C-C cracking to some degree. Catalyst B shows excellent decarboxylation activity for the naphthoic acid model compound-acid conversion reached 93.9%.

Current Status

The project is nearing completion.

Project Start
Project End
DOE Contribution


Performer Contribution

$199,892 (20% of total)

Contact Information

NETL - Kathy Stirling ( or 918-699-2044)
California Institute of Technology - William Goddard ( or 626-395-2731)