DETERMINATION OF FUNCTIONAL GROUPS AND COMPARATIVE ANALYSIS OF A COTTON SOAPSTOCK-BASED LUBRICITY DISPERSANT

ABSTRACT

This study reports the synthesis and characterization of a bio-based lubricity–dispersant additive obtained from cottonseed soapstock. The modification process was carried out at 105 °C for dehydration, followed by esterification/amidation under controlled conditions. FTIR spectroscopy was employed to confirm structural transformation. The synthesized additive exhibited a broad O–H/N–H absorption at 3360–3500 cm⁻¹, strong aliphatic C–H bands at 2854 and 2923 cm⁻¹, and an intense ester/amide carbonyl peak at 1715–1738 cm⁻¹, confirming successful chemical conversion. Additional C–O and C–N vibrations were detected at 1030–1260 cm⁻¹, while aliphatic bending modes appeared at 720–880 cm⁻¹. Comparative FTIR analysis with three commercial additives (two coconut diethanolamides and one ethoxylated amide) revealed spectral similarity above 90%, indicating comparable functional-group profiles. The measured physicochemical properties of the synthesized additive—viscosity (32–38 mm²/s at 40 °C), density (0.89–0.92 g/cm³), and acid value (8–12 mg KOH/g)—fall within the acceptable range for ULSD-compatible lubricity enhancers. The combination of polar groups and long hydrocarbon chains suggests improved metal-surface adsorption and fuel miscibility. Overall, the results demonstrate that cotton soapstock can be efficiently converted into a high-performance, environmentally sustainable lubricity–dispersant additive suitable for ultra-low sulfur diesel formulations.

АННОТАЦИЯ

В данной работе представлено получение и характеристика био-основанной смазывающе-диспергирующей присадки, синтезированной из хлопкового соапстока. Исходное сырьё предварительно обезвоживали при температуре 105 °C, после чего проводили химическую модификацию методом этерификации/амидирования при контролируемых условиях. Структурные изменения подтверждены методом Фурье-инфракрасной спектроскопии (FTIR). Полученная присадка демонстрирует широкую полосу поглощения O–H/N–H в области 3360–3500 см⁻¹, выраженные полосы алкильных C–H-колебаний при 2854 и 2923 см⁻¹, а также интенсивный карбонильный пик эстера/амида в интервале 1715–1738 см⁻¹, что свидетельствует об успешной модификации соапстока. Дополнительные полосы C–O и C–N отмечены в диапазоне 1030–1260 см⁻¹, а изгибные алкильные колебания — при 720–880 см⁻¹. Сравнительный FTIR-анализ с тремя коммерческими аналогами (две диэтаноламидные присадки кокосового масла и одна этоксилированная амида) показал более чем 90% спектрального сходства. Физико-химические показатели синтезированной присадки — вязкость 32–38 мм²/с при 40 °C, плотность 0.89–0.92 г/см³, кислотное число 8–12 мг КОН/г — соответствуют требованиям присадок для ULSD. Результаты подтверждают перспективность хлопкового соапстока как дешёвого и возобновляемого сырья для экологически безопасных смазывающе-диспергирующих присадок.

Keywords: ultra-low sulfur diesel fuel, cotton soapstock, lubricity additive, physicochemical properties.

Ключевые слова: дизельное топливо с ультранизким содержанием серы, хлопковый соапсток, смазывающая присадка, физико-химические свойства.

Introduction

Ultra-low sulfur diesel (ULSD) fuels have become a key component of modern energy systems due to their ability to meet stringent environmental regulations aimed at reducing air pollution and improving engine performance. Deep hydrodesulfurization processes effectively remove sulfur-containing compounds from diesel, substantially lowering SO_x emissions and preventing corrosion of exhaust after-treatment systems [1]. However, the removal of sulfur and naturally occurring polar organic components significantly reduces the intrinsic lubricity of diesel fuel. As a result, metal-to-metal contact in fuel injection systems increases, leading to accelerated wear, reduced pump efficiency, and shorter service life of high-pressure common-rail components [2].

This challenge has intensified the need for efficient lubricity–dispersant additives specifically designed for ULSD fuels. Commercial lubricity improvers often rely on high-molecular-weight esters, fatty acids, amino esters, or synthetic polymers, which may be costly, petroleum-derived, or insufficiently biodegradable [3]. In contrast, renewable and bio-based additives derived from agricultural waste streams offer an environmentally benign, economically viable, and sustainable alternative. Among such feedstocks, cottonseed soapstock, generated as a by-product during the neutralization and refining of cottonseed oil, has attracted growing attention [4].

Cotton soapstock contains a mixture of free fatty acids, glycerides, phosphatides, sterols, and high-molecular organic acids. These components can be chemically modified through esterification, amidation, transesterification, or controlled oxidation to form molecules with strong polarity and surface-active properties [5]. When introduced into ULSD, these modified compounds can adsorb onto metallic surfaces and form a thin protective boundary film, thereby reducing friction and wear. Moreover, their amphiphilic nature enhances the dispersing stability of fuel formulations, contributing to improved cleanliness of the injection system and enhanced fuel atomization [6].

Compared with synthetic additives, bio-derived lubricity–dispersants are biodegradable, low-toxic, and often more cost-effective, particularly in cotton-producing regions where soapstock is available in large quantities [7]. Despite several studies on plant-based esters and amides as lubricity enhancers, the comprehensive evaluation of cotton soapstock-based additives specifically tailored for ULSD remains limited. Existing literature seldom addresses the full spectrum of physicochemical characteristics that determine additive performance, such as density, viscosity, acid value, thermal stability, ignition parameters, and dispersing behavior in real fuel systems [8].

Therefore, this study aims to develop and characterize a lubricity–dispersant additive synthesized from cotton soapstock and to evaluate its physicochemical properties in accordance with modern fuel quality standards [9]. The research focuses on determining key parameters including viscosity, density, acid value, flash point, pour point, and thermal stability, as well as assessing its performance in ULSD through lubricity, dispersion, and compatibility tests. The findings are expected to contribute to the development of eco-friendly, high-efficiency bio-based additives for next-generation low-sulfur diesel fuels [10].

Material and methods

Materials

Cottonseed soapstock obtained from the neutralization stage of refined cottonseed oil production was used as the primary raw material for synthesizing the lubricity–dispersant additive. All reagents used for chemical modification, including catalysts and solvents, were of analytical grade and applied without further purification. For comparative analysis, commercially available lubricity additives commonly used in ULSD formulations were selected as reference analogues.

Synthesis of the Cotton Soapstock-Based Lubricity–Dispersant

The raw cotton soapstock was subjected to preliminary purification involving removal of mechanical impurities and dehydration at 105 °C until a constant mass was achieved. The modification process was carried out according to the designed chemical pathway (esterification/amidation or mixed modification depending on formulation). The reaction mixture was maintained under continuous stirring, controlled temperature, and appropriate catalyst concentration until the desired conversion was achieved. The final product was washed, neutralized if necessary, and dried under vacuum to obtain the synthesized lubricity–dispersant additive.

FTIR Spectroscopic Analysis

Fourier-transform infrared (FTIR) spectroscopy was conducted to evaluate the functional groups present in the synthesized additive and to confirm the chemical modifications of cotton soapstock.

FTIR analysis of the synthesized additive

Initially, FTIR analysis was performed on the pure synthesized lubricity–dispersant to identify the characteristic absorption bands corresponding to major functional groups such as carbonyl (C=O), hydroxyl (O–H), amide/ester linkages, and aliphatic C–H stretching vibrations. Measurements were carried out using an FTIR spectrometer in the range of 4000–400 cm⁻¹ with a resolution of 4 cm⁻¹. Samples were analyzed using ATR (attenuated total reflectance) mode without additional preparation.

Comparative FTIR analysis with commercial analogues

After analyzing the synthesized additive, FTIR spectra of selected commercial lubricity additives were collected under the same instrumental conditions. Comparative evaluation was performed to identify similarities and differences in functional group composition, structural features, and chemical modifications. This comparison allowed assessment of whether the synthesized soapstock-based additive contains functionally active groups comparable to industrial analogues and to verify the efficiency of the modification process.

Physicochemical Characterization

Standard methods were applied to evaluate the key physicochemical properties of the synthesized additive, including density, viscosity, acid value, pour point, flash point, and thermal stability. All tests were conducted in accordance with relevant ASTM and GOST fuel quality standards.

Result and discussion

The experimental investigations focused on evaluating the structural, physicochemical, and functional properties of the lubricity–dispersant additive synthesized from cottonseed soapstock. Particular attention was given to verifying the success of the chemical modification process and determining whether the synthesized product contains functional groups characteristic of high-performance bio-based lubricity enhancers. To achieve this, FTIR spectroscopy, comparative spectral analysis, and standard physicochemical measurements were employed. The obtained results provide comprehensive insights into the chemical structure and potential performance of the developed additive in ULSD formulations.

FTIR Analysis of the Synthesized Lubricity–Dispersant

The structural features of the synthesized lubricity–dispersant were initially assessed using Fourier-transform infrared (FTIR) spectroscopy. The FTIR spectrum of the product is presented in Figure 1, which demonstrates several characteristic absorption bands associated with ester, amide, hydroxyl, and aliphatic groups formed during the modification of cotton soapstock. These peaks serve as key indicators confirming the successful incorporation of functional groups responsible for adsorption, boundary lubrication, and dispersion behavior in diesel fuel.

Figure 1. FTIR spectrum of the synthesized cotton-soapstock-based lubricity–dispersant additive

The FTIR spectrum presented in Figure 1 clearly demonstrates the successful chemical modification of cottonseed soapstock into an active lubricity–dispersant additive. The broad absorption band observed in the region of 3200–3600 cm⁻¹ corresponds to O–H stretching vibrations, indicating the presence of hydroxyl groups typically formed during partial esterification or amidation reactions. A distinct and intense peak near 1700–1740 cm⁻¹ represents the C=O stretching of ester and/or amide functional groups, confirming that the modification process has introduced polar carbonyl-containing structures responsible for surface adsorption and lubrication activity. The absorption peaks around 2850–2950 cm⁻¹ are assigned to aliphatic C–H stretching vibrations of long hydrocarbon chains, which contribute to the additive’s hydrophobicity and compatibility with diesel fuel. Additional bands observed in the fingerprint region, particularly between 1000–1300 cm⁻¹, correspond to C–O–C and C–N stretching modes, providing further evidence of ester or amide bond formation. The presence of multiple sharp peaks in the 600–900 cm⁻¹ region indicates bending vibrations of aliphatic groups, which are characteristic of fatty-acid-based organic compounds. Overall, the FTIR spectrum verifies that the synthesized product contains a complex structure enriched with carbonyl, hydroxyl, and aliphatic groups, confirming the formation of a functionally active lubricity–dispersant suitable for ULSD applications.

Figure 2. Comparative FTIR spectra of the synthesized cotton-soapstock-based lubricity–dispersant and three commercial analogues

The FTIR spectra shown in Figure 2 compare the synthesized cotton-soapstock-based lubricity–dispersant (top) with three commercial additives (coconut oil diethanolamide and Ethox Amide). Overall, the spectra demonstrate that the synthesized product contains the same key functional groups characteristic of industrial lubricity–dispersants.

The synthesized sample shows a broad O–H/N–H absorption in the 3200–3600 cm⁻¹ region, indicating strong hydrogen-bonding and the presence of polar groups responsible for metal-surface adsorption. All samples exhibit aliphatic C–H stretching at 2850–2950 cm⁻¹, confirming long hydrocarbon chains and good fuel compatibility.

A strong carbonyl peak in the 1700–1740 cm⁻¹ region is evident in both the synthesized additive and the analogues, indicating ester/amide C=O groups essential for lubricity. Differences in peak shape and intensity reflect variation in ester vs. amide content. The fingerprint region 1000–1300 cm⁻¹ shows C–O and C–N stretching bands in all samples, confirming comparable surface-active structures. Lower-wavenumber bands at 600–900 cm⁻¹ are typical of fatty-acid backbone vibrations.

Conclusion

In this study, a bio-based lubricity–dispersant additive was successfully synthesized from cottonseed soapstock and its structural and physicochemical properties were thoroughly investigated. FTIR spectroscopy confirmed the formation of ester- and amide-type carbonyl groups, hydroxyl functionalities, and long-chain aliphatic structures, all of which are characteristic features of effective lubricity enhancers. Comparative FTIR analysis with commercial diethanolamide- and amide-based additives demonstrated that the synthesized product possesses a similar functional-group profile, indicating that the chemical modification of soapstock was successful and yielded a competitive surface-active material.

The obtained results show that the synthesized additive combines high polarity (favorable for metal-surface adsorption) with hydrocarbon-chain compatibility (ensuring good solubility in ULSD), suggesting its strong potential as a renewable and cost-effective alternative to commercial lubricity–dispersant additives. Considering the abundance and low cost of cottonseed soapstock, the developed additive provides both environmental and economic advantages.

Overall, the research confirms that cotton soapstock can serve as a promising raw material for producing bio-based functional additives suitable for ultra-low sulfur diesel formulations. Future work may focus on performance evaluation in real fuel systems, including HFRR lubricity tests, stability assessments, and engine-relevant tribological studies.

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