Lignosulfonate adsorbent from Camellia oleifera shells removes basic nitrogen compounds from oils with high selectivity

Basic nitrogen compounds in hydrogenation feedstock oils are among the most stubborn poisons of refining catalysts. These molecules, which include quinoline and related heterocycles, bind strongly to the active sites of hydrotreating catalysts and suppress the reactions that upgrade inferior oils into cleaner fuels. Refineries typically control their content below 10 μg g⁻¹ before feeding by extracting the oil with acidic aqueous solutions or polar solvents, but those approaches can introduce byproducts and cause equipment corrosion. A new study published in the Journal of Materials Science offers an alternative: an adsorbent prepared from Camellia oleifera shell-derived lignosulfonic acid that captures basic nitrogen compounds from oil phases with high efficiency and selectivity, while turning a renewable biomass waste stream into a high-value material for petroleum refining.

The research team, led by Mengru Shang and Yepeng Xiao of Shaoguan University together with colleagues at Guangdong University of Petrochemical Technology, prepared the lignosulfonate-based adsorbent specifically for denitrogenation in oil phases. The choice of feedstock is significant. Camellia oleifera, the oil-tea plant cultivated widely in southern China for edible oil, generates large quantities of shells as processing waste. Previous work has shown that Camellia oleifera shell carbon can serve as a renewable bio-adsorbent for removing hexavalent chromium and methylene blue from aqueous solution, and walnut shell biochars have been used to capture quinoline from wastewater. The new study extends this biomass platform into the petroleum refining context, where the adsorbent must perform in an oil matrix rather than water.

The headline result is striking. In model hydrogenation feedstock oil, using quinoline as the model basic nitrogen compound at a concentration of 85 μg g⁻¹ and a temperature of 35 °C, the adsorbent achieved a removal efficiency of 97.01 percent after 120 minutes of adsorption. That performance brings the quinoline content well below the 10 μg g⁻¹ threshold that refineries demand before feeding hydrogenation units. The kinetics of the process followed a pseudo-second-order model, which indicates that the rate-limiting step is the chemical interaction between the quinoline molecules and the adsorbent surface rather than diffusion of the adsorbate through the bulk liquid.

Equilibrium data fit the Langmuir isotherm model, suggesting that adsorption occurs as monolayer coverage on a surface with a finite number of equivalent binding sites. Thermodynamic analysis confirmed the process as spontaneous and endothermic chemisorption. The endothermic character is technically meaningful: it implies that modest heating enhances uptake, and it distinguishes the mechanism from simple physical adsorption, where uptake typically decreases with temperature. Together, the kinetic, isotherm, and thermodynamic evidence points to a chemisorption process in which the Brønsted acidic sites of the lignosulfonic acid framework interact with the basic nitrogen centers of quinoline, an acid-base pairing consistent with the broader literature on Brønsted acid-Lewis base interactions used to separate phenolic and nitrogenous compounds from oil mixtures.

Selectivity is where the adsorbent proves its practical worth. In experiments with real hydrogenation feedstock oil, the non-basic nitrogen compound content remained unchanged before and after adsorption, while the basic nitrogen compounds were decreased by 86.72 percent. In other words, the material targets the specific class of molecules that poison hydrogenation catalysts while leaving the rest of the oil matrix untouched. This discrimination matters because indiscriminate adsorbents that strip desirable components from the oil would degrade feedstock quality. The result also suggests that the acid-base chemistry underlying the capture is specific enough to operate in the complex chemical environment of a real refinery stream, not only in simplified model oils.

Reusability is another critical criterion for any industrial adsorbent, and the lignosulfonate material passed the test. After five reuse cycles, the study found no significant decline in adsorption performance. This durability addresses a common weakness of biomass-derived adsorbents, which can lose capacity as pores foul or surface sites saturate. Combined with the low cost of the shell waste feedstock and the simplicity of the preparation route, the cycling data support the argument that the material could be economically viable at scale, in line with the green and low-cost separation technologies, such as deep eutectic solvents and piperazine-based ionic liquids, now being explored for extractive denitrogenation of fuel oils.

The broader context is the green energy transition in petroleum refining. Basic nitrogen compounds are not only catalyst poisons; they also complicate hydrodesulfurization and hydrodenitrogenation reactions in heavy oil upgrading, and refractory basic and neutral nitrogen compounds evolve in complex ways during residue hydrotreating. Catalyst particle structure optimization and phosphorus-doped Y zeolites with increased mesopore and Lewis acidity have been pursued to improve hydrodenitrogenation efficiency, but these catalytic strategies operate downstream and consume hydrogen. Adsorptive denitrogenation, by contrast, removes the poisons before the hydrogenation step, protecting catalysts and potentially extending their life. Commercial materials, including clays and modified activated carbons, have been investigated for nitrogen compound adsorption from diesel oil, and mesoporous and iron-functionalized walnut shell-activated carbons have been tested for quinoline removal from liquid fuels, establishing adsorption as a credible unit operation for fuel cleanup.

What distinguishes the new work is the combination of feedstock, mechanism, and application. Lignosulfonate, a sulfonated lignin byproduct of the pulping industry, has previously been used in adsorbents for heavy metal removal, including cadmium, lead, and copper ions from wastewater, and in composite hydrogels for dye adsorption. Sodium lignosulfonate-chitosan composites and lignin/cellulose hydrogels have shown promise for pollutant capture in aqueous systems. The new study redirects this well-characterized biopolymer chemistry toward oil-phase denitrogenation, where the sulfonic acid groups provide the Brønsted acidity needed to bind basic nitrogen heterocycles. The approach also promotes high-value utilization of renewable feedstocks, converting Camellia oleifera shell waste into a functional material rather than a disposal problem.

The implications reach beyond petroleum. Nitrogenous compounds also plague bio-oils from algae and microalgae pyrolysis, where nitrogen evolution in heavy components complicates upgrading, and catalytic pyrolysis strategies aim to produce bio-oil with low oxygenated and nitrogenous compounds. An adsorbent that selectively captures basic nitrogen compounds in oil phases could serve the emerging biofuel sector as well, where inferior oils contaminated with nitrogen require treatment before catalytic conversion. The authors describe the study as providing a novel strategy for the preparation of biomass-based adsorbents and opening a new pathway for the efficient treatment of nitrogen-contaminated inferior oils, a framing that positions the material at the intersection of biomass valorization and fuel refining.

For refineries weighing their options, the technical case is concrete: 97.01 percent removal of quinoline from model oil in 120 minutes at 35 °C, 86.72 percent removal of basic nitrogen compounds from real hydrogenation feedstock oil with no change in non-basic nitrogen content, pseudo-second-order kinetics and Langmuir monolayer adsorption confirming chemisorption, and stable performance across five reuse cycles. The material avoids the byproducts and equipment corrosion associated with acidic aqueous extraction and polar solvent extraction, and it draws on an abundant agricultural waste stream. As the industry seeks green technologies for preparing clean fuels that conciliate desulfurization and denitrogenation, a shell-derived lignosulfonate adsorbent that selectively strips the very compounds that poison hydrogenation catalysts offers a technically grounded step toward nitrogen-controlled feedstocks without corrosive chemistry.

Subject of Research: Materials Science

Article Title: Preparation of lignosulfonate adsorbent and its highly efficient selective adsorption for basic nitrogen compounds

Article References: Shang, M., Xiao, Y., Ren, Q., Cheng, L., & Zhang, L. (2026). Preparation of lignosulfonate adsorbent and its highly efficient selective adsorption for basic nitrogen compounds. Journal of Materials Science, 61(42), 33334-33349. https://doi.org/10.1007/s10853-026-13402-7

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13402-7

Keywords: lignosulfonate, adsorption, basic nitrogen compounds, biomass, Camellia oleifera shell, quinoline, hydrogenation feedstock, petroleum refining, green energy transition, Journal of Materials Science, Preparation, adsorbent