A biodegradable pour point depressant from coconut oil for flow assurance of Indian waxy crude oil, a process for the preparation thereof and the use thereof in flow assurance of Indian waxy crude oil

Abstract

The present invention relates to a pour point depressant from Cocos nucifera for flow assurance of Indian waxy crude oil. The bio-based pour point depressants as well as viscosity reducer is synthesised from coconut oil (CPGL) to assure the flow of Indian waxy crude oil. These raw materials used for synthesis are easily available and inexpensive. The eco-friendly PPD, CPGL is biodegradable within 21 days of experiment, and non-toxic to the aquatic organisms. Fig. 2

Specification

Description:FIELD OF THE INVENTION:
This invention relates to a biodegradable pour point depressant for flow assurance of Indian waxy crude oil, a process for the preparation thereof and the use thereof in flow assurance of Indian waxy crude oil.

This invention further relates to a novel biodegradable pour point depressant (PPD) synthesized from Cocos nucifera in flow assurance of Indian waxy crude oil. The bio-based pour point depressants as well as viscosity reducer is synthesised from coconut oil (CPGL) to assure the flow of Indian waxy crude oil. These raw materials used for synthesis are easily available and inexpensive. The eco-friendly PPD, CPGL is biodegradable within 21 days of experiment, and non-toxic to the aquatic organisms. Moreover, CPGL shows a better performance with a very small dosage (600 ppm) compared to commercial PPD. So, CPGL is a sustainable, affordable, biodegradable, safe, and environmentally friendly PPD that can be substituted for commercial ones.

BACKGROUND OF THE INVENTION:
Wax deposition in crude oil during production from reservoirs and transportation through offshore or onshore pipelines is a significant flow assurance challenge in the petroleum industry, especially under low-temperature conditions (Huang et al., 2015. Wax Deposition. CRC Press. https://doi.org/10.1201/b18482; Radulescu et al., 2012. Tailored Polymer Additives for Wax (Paraffin) Crystal Control.; Sarica and Panacharoensawad, 2012. Review of paraffin deposition research under multiphase flow conditions, in: Energy and Fuels. pp. 3968-3978. https://doi.org/10.1021/ef300164q). Ensuring of the continuous flow of crude oil from GGS/CTF to its destination or refineries is crucial. When the temperature of crude oil drops below the wax appearance temperature (WAT), wax particles become less soluble and settle on the pipeline walls (Sharma et al., 2022. Experimental investigation into the development and evaluation of ionic liquid and its graphene oxide nanocomposite as novel pour point depressants for waxy crude oil. J Pet Sci Eng 208. https://doi.org/10.1016/j.petrol.2021.109691). The Subsequent wax deposition leads to a three-dimensional network structure, which ultimately develops a gel like structure in crude oil. As a result, the flow properties such as pour point, viscosities, and yield stresses are increased (Singh et al., 1999. Prediction of the wax content of the incipient wax-oil gel in a pipeline: An application of the controlled-stress rheometer. J Rheol (N Y N Y) 43, 1437-1459. https://doi.org/10.1122/1.551054; Yang et al., 2015. Polymeric Wax Inhibitors and Pour Point Depressants for Waxy Crude Oils: A Critical Review. J Dispers Sci Technol 36, 213-225. https://doi.org/10.1080/01932691.2014.901917). Moreover, continuous wax deposition causes a reduction in the inner diameter of pipelines. Therefore, the flowability of crude oil is restricted and causes a complete blockage of pipelines when temperature considerably decreased (Hoffmann and Amundsen, 2013. Influence of wax inhibitor on fluid and deposit properties. J Pet Sci Eng 107, 12-17. https://doi.org/10.1016/j.petrol.2013.04.009). Sometimes, these phenomena lead to a complete shutdown of the well (Coto et al., 2014). The annual economic impact of wax deposition is more than two billion USD worldwide, and each blocking incident costs nearly USD 40 million (Sousa et al., 2022. On the economic impact of wax deposition on the oil and gas industry. Energy Conversion and Management: X 16. https://doi.org/10.1016/j.ecmx.2022.100291). Recent studies showed that almost 85% of the world's oil is facing wax formation and depositional problems (Thota and Onyeanuna, 2016. MITIGATION OF WAX IN OIL PIPELINES Spatial Seasonal Variations in the Groundwater Chemistry in Ogbia Urban and Peri-urban Areas, Southern Nigeria Using ArcGIS View project Chukwuemeka Onyeanuna Politecnico di Torino MITIGATION OF WAX IN OIL PIPELINES, International Journal of Engineering Research and Reviews.). Petroleum industries used to invest a lot of money and valuable time to reawaken the flow (Van Engelen et al., 1979. Study On Flow Improvers For Transportation Of Bombay High Crude Oil Through Submarine Pipeline, in: Offshore Technology Conference. Offshore Technology Conference. https://doi.org/10.4043/3518-MS). Several techniques are frequently used to reduce or remove wax deposition in the oil industry for smooth oil production and transportation, including mechanical, thermal, electrical, and chemical methods, etc (Aiyejina et al., 2011; Hilbert and Esso, 2010).

Pour point depressants (PPDs) or wax inhibitors are the most recommended wax mitigation alternatives since they require less maintenance and operational costs. These PPDs improve the flowability of crude oil by lowering its pour point, reducing the amount of wax deposited, and altering the morphology of wax crystals (Alves et al., 2023). Commercial PPDs that are mainly used to cope with this wax deposition problem are polymeric additives that belong to one of three classes: EVA copolymers, copolymers of maleic anhydride, or copolymers of polyacrylamide (Chi et al., 2017; Gholami et al., 2019; Ghosh and Das, 2014; Yang et al., 2015). However, the impact of these commercial PPDs on operating costs is significant and they can also pose environmental risks in case of a spill because they are non-biodegradable and toxic. This has increased the focus on investigating natural alternatives as more sustainable options with less environmental impact while maintaining or enhancing performance.
PPDs synthesized from several vegetable oils such as sunflower oil, olive oil, canola oil, palm oil, coconut oil, soybean oil, etc. are becoming more and more popular as eco-friendly and cost-effective alternatives of commercial PPDs (Akinyemi et al., 2016; Azeem et al., 2020; Banerjee et al., 2015; Chen et al., 2011). The interaction between the hydrophobic chains of free fatty acids or triglycerides present in vegetable oil and the waxes prevents the wax formation while the polar carboxylic groups of fatty acid inhibit wax precipitation by stopping the agglomeration of wax crystal through steric hindrance (Akinyemi et al., 2016).
(Ragunathan et al., 2020) studied the influence of palm oil on the pour point reduction of crude oil, and it was reported that almost 18℃ pour point was decreased after the addition of 1wt.% palm oil. (Modi and Nagar, 2024) have synthesized a series of terpolymers from Helianthus oil, styrene, and fatty ester from erucic acid. By varying the amounts of the additives from 500 ppm to 1000 ppm, it was possible to reduce the pour point of crude oil by 3 to 12 °C using those terpolymers. (Akinyemi et al., 2016) investigated the effect of castor seed oil, rubber seed oil, and jatropha seed oil on Nigerian crude oil regarding pour point and viscosity reduction. The pour point was decreased by 17°C after dosing with jatropha seed oil and castor seed oil at 0.3% concentration. (Fadairo et al., 2019) synthesized biodiesel from rubber seed oil, and castor seed oil to enhance the flow of crude oil within 0.1 to 0.5 % concentrations. Biodiesel synthesized from castor oil showed the better performance on pour point and viscosity reduction.
Previous investigations revealed that fatty ester synthesized from coconut oil has significant performance on reduction of viscosity as well as pour point of crude oil. (Pal and Naiya, 2022b) developed coconut oil ethyl ester and treated it with Indian crude oil in several dosages. The maximum lowering of the pour point was observed by 12°C at 1000 ppm concentrations. Coconut oil contains 40 % of lauric acid, and the aliphatic chain of lauric acid interacts with the wax molecules to hinder their agglomeration. It is reported that polyethylene glycol esters are utilized as pour point depressants in waxy petroleum oil or middle distillate oil due to the dispersing abilities of polyethylene glycol (PEG) (Khidr et al., 2015). (Eke et al., 2021) evaluated the effectivity of the ester derivative of polyethylene glycol 400 and liquid extracted from cashew nut shell on Chenor crude oil. The pour point was decreased by 12°C at 1000 ppm dosage. However, different types of PPDs are available, but still research on the synthesis of new PPDs and modifying the existing ones are essential. This is because the PPDs usually behave differently in different crude oils, even when they are taken from the same region (García et al., 1998).

The pour point of crude oil can effectively be lowered by commercial PPDs that have previously been developed, but they are costly and required in larger dosages. Further, these are hazardous, toxic to the environment and not biodegradable.
Therefore, the need exists, to address these problems and to provide a novel green PPD having good pour point reducing efficiency and other rheological property lowering capacity. In addition to this, the PPD should be biodegradable, nontoxic, ecofriendly, biodegradable, nontoxic and economically favourable and should show better performance than commercial PPD.

OBJECTS OF THE INVENTION:
It is therefore an object of this invention to propose a pour point depressant for flow assurance of Indian waxy crude oil, a process for the preparation thereof and the use thereof to overcome wax deposition issue in the petroleum industry.

It is a further object of this invention to propose a pour point depressant for flow assurance of Indian waxy crude oil, which is environment friendly.

Yet another object of this invention is to propose a pour point depressant for flow assurance of Indian waxy crude oil, which is sustainable and more effective than some of the commercial pour point depressants.

A further object of this invention is to propose a pour point depressant for flow assurance of Indian waxy crude oil, which is cost-effective and has superior performance compared to the common commercial PPDs.

These and other objects and advantages of the invention will be apparent from the ensuing description when read in conjunction with the accompanying drawings.


BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

Figure 1: Reaction scheme of Coconut oil polyethylene glycol ester (CPGL).
Figure 2: Flow chart of synthesis of Coconut oil Polyethylene glycol ester (CPGL).

Figure 3: (a) FTIR Spectra of CPGL; (b) FTIR spectra of CPPD
Figure 4: 1H NMR spectra of CPGL.
Figure 5: Analysis of particle sizes of PPDs (a) Differential light scattering measurement of CPGL; (b) Differential light scattering of CPPD.
Figure 6: Percentage mortality of the test true shrimp vs. PPD concentration for LC50 determination
Figure 7: Effect on viscosity of crude oil (CO), after addition of 600 ppm CPGL, and 600 ppm CPPD (a) at temperature 30°C; (b) at temperature 35°C; (c) at temperature 40°C.
Figure 8: Figure 8. Microscopic images of wax crystals in (a) pure crude oil (CO); (b) crude oil with 600 ppm CPGL (CO+600 CPGL); (c) crude oil with 600 ppm CPPD (CO+ 600 CPPD).
Figure 9: Microscopic images of phase analysis of CO with PPD: (a) pure crude oil; (b) crude oil
With 600 ppm CPGL; (c) crude oil with 600 ppm CPPD.

Figure 10: Wax appearance temperature (WAT) determination of (a) CO (0 ppm); (b) CO
with CPGL (600 ppm); CO with CPPD (600 ppm)

Figure 11: Schematic mechanism of interaction of PPD with wax crystal

SUMMARY OF THE INVENTION:
According to this invention is provided a pour point depressant from Cocos nucifera for flow assurance of Indian waxy crude oil. The bio-based pour point depressants as well as viscosity reducer is synthesised from coconut oil (CPGL) to assure the flow of Indian waxy crude oil. These raw materials used for synthesis are easily available and inexpensive. The eco-friendly PPD, CPGL is biodegradable within 21 days of experiment, and non-toxic to the aquatic organisms. Moreover, CPGL shows a better performance with a very small dosage (600 ppm) compared to commercial PPD. So, CPGL is a sustainable, affordable, biodegradable, safe, and environmentally friendly PPD that can be substituted for commercial ones. This invention further relates to a process for the preparation of a pour point depressant from Cocos nucifera for flow assurance of Indian waxy crude oil


DETAILED DESCRIPTION OF THE INVENTION:
According to this invention is provided a biodegradable pour point depressant Coconut oil polyethylene glycol ester (CPGL), for flow assurance of Indian waxy crude oil.

According to this invention is further provided a process for the preparation of the pour point depressant Coconut oil polyethylene glycol ester (CPGL), which comprises the steps of subjecting coconut oil to hydrolysis to obtain free fatty acid, followed an esterification reaction with an equimolar amount of the fatty acid and polyethylene glycol (PEG) (1:1).
Still further, the invention provides the use of the pour point depressant (CPGL) in flow assurance of Indian waxy crude oil.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without some of these specific details.
Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the spirit and scope of the invention.
As used in the description herein and throughout the claims that follow, the meaning of "a," "an," and "the" includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of "in" includes "in" and "on" unless the context clearly dictates otherwise.
In the application, where an element or component is said to be selected from a list of recited elements or components, it should be understood that the element or component can be any one of the recited elements or components, or the element or component can be selected from a group consisting of two or more of the recited elements or components. Further, it should be understood that elements and/or features of a composition or a method described herein can be combined in a variety of ways without departing from the spirit and scope of the present teachings, whether explicit or implicit herein.
The use of the terms "include," "includes", "including," "have," "has," or "having" should be generally understood as open-ended and non-limiting unless specifically stated otherwise.
Throughout the application, where compositions are described as having, including, or comprising specific components, or where processes are described as having, including, or comprising specific process steps, it is contemplated that compositions of the present teachings can also consist essentially of, or consist of, the recited components, and that the processes of the present teachings can also consist essentially of, or consist of, the recited process steps.
In interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms "comprises" and "comprising" should be interpreted as referring to elements, components, or steps in a non- exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.
It will be understood by those skilled in the art with respect to any chemical group containing one or more substituents that such groups are not intended to introduce any substitution or substitution patterns that are sterically impractical and/or physically non-feasible.
Where a range of values is provided, it is to be understood that each intervening value, including the limiting values, to the tenth of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the described subject matter.
The technical expressions as used herein are standard expressions which will be apparent to a person skilled in the art as being a part of standard terminology.
It is to be understood that, for a clear understanding, the description of the present invention has been simplified to illustrate the relevant elements only. For the sake of clarity, other details that may be well known are omitted.
The expressions as used herein are standard expressions which will be apparent to a person skilled in the art as being a part of standard terminology. However, in order to lend further clarity to the description, some of the expressions are defined hereinbelow.

Wax deposition: The formation of paraffin or wax crystals and their accumulation on the inner wall pipelines is a complex and costly issue during the production and transportation of crude oils. The dissolved wax crystals started to separate from crude oil when the temperature of crude oil dropped below the wax appearance temperature (WAT). The wax molecules start to associate or agglomerate, eventually forming a three-dimensional network structure with continuous lowering of temperature. Due to the successive deposition of wax, the rheological properties of the crude oil change, changing the behaviour of crude oil from Newtonian to non-Newtonian. Therefore, the flowability of crude oil decreases, leading to blockages of pipelines. This phenomenon is more severe in deep sea water, colder environments, or regions where the temperature is around 5°C or less.
Several established mechanisms are there to explain the wax deposition phenomenon, Molecular diffusion mechanisms is widely accepted one. Small wax crystals precipitated when the temperature of crude oil flowing in pipelines is lower than its WAT. An equilibrium is maintained between the liquid oil and those solid wax/asphaltenes crystals. As the temperature lowers, the wax coming out from the bulk phase and the amount of these crystals that can remain dissolved in the liquid oil will decrease. The temperatures at the pipeline walls are lower than those at the centres when the crude oil flows. Therefore, a temperature gradient along the wall creates a wax concentration gradient. This causes the wax crystals to move towards the pipeline walls through molecular diffusion, leading to deposition, and ultimately severe blockages over time.
Pour Point: The maximum temperature below which a fluid loses its capacity to flow is known as the pour point.
Pour Point Depressants (PPDs): Polymeric additives that are used to reduce the pour point of crude oil, making it easier for transportation known as pour point depressants or PPDs. PPDs consist of a hydrophilic polar part of ester, amide, or other functional group bonded to an alkyl chain (hydrophobic part). The crystallization process of wax molecules is hindered due to the capability of wax molecules to co-precipitate with these wax molecules and the polar groups provide steric hindrance, which inhibits further wax crystals growth and aggregation. This minimizes the pour point of crude oil and thereby also stops deposits in pipes.
Synthesis Process: The term "synthesized" refers to the act of combining or modifying simpler chemical components or substances to produce a new material. This process involves the chemical reaction of two or more chemical compounds or components to produce a more complex material with distinctive properties.
WAT: Wax Appearance Temperature
PPD: Pour Point Depressants
CPGL: Coconut oil polyethylene glycol ester
COM PPD: Commercial PPD
In accordance with this invention the novel pour point depressant is (PPD) synthesized from Cocos nucifera. The synthesised Coconut oil polyethylene glycol ester (CPGL) is non-toxic, biodegradable PPD utilizing a fatty ester derived from abundantly available coconut oil and polyethylene glycol (CPGL). This non-ionic surfactant was prepared by hydrolysis of coconut oil followed by esterification with PEG. CPGL features a long aliphatic chain of lauric acid and polar functional groups such as ester and hydroxyl. This hydrophobic aliphatic chain resembles wax crystals, which are co-crystallized with them and help to prevent further aggregations. The polar groups reduce the three-dimensional wax network by creating steric hindrance. CPGL is a fatty ester derived from a mixture of fatty acids found in coconut oil such as caprylic acid (8%), myristic acid (14%), capric acid (8%), and lauric acid (49%). The presence of other fatty acids and PEG 1000 also helps to reduce the pour point of crude oil effectively by 12°C with a minimal dosage of 600 ppm.
Moreover, the BOD and toxicity test of CPGL were performed to establish its eco-friendly nature. The synthesized PPD may be used as a cost-effective and eco-friendly alternative to commercial PPDs for the transportation of crude oil from GGS/CTF to the refinery. Special treatment will not be required to feed this PPD-treated crude oil for refining as it is biodegradable. Figure 1 illustrates the synthetic procedure of CPGL.
The performance of CPGL has been assessed on waxy crude oil in terms of viscosity and pour point and compared with commercial PPD (CPPD), which has a similar functional group. Optimal dosage of 600 ppm of CPGL reduced pour point of the crude oil from 35°C to 23°C, whereas the reduction is only 6°C when treated with 600 ppm CPPD. Viscosity was significantly reduced by around 36% at 30°C when treated with 600 ppm CPGL which is responsible for substantial reduction in pumping power requirements. Additionally, optimal dosage (600 ppm) of CPGL resulted in a 73% decrease in wax deposition. The alteration in wax crystal morphology was studied using a cross-polarized microscope. The percentage of wax crystals present in crude oil (in the studied area in the microscope) dropped from 28.45 % to 14.70 % after the addition of 600 ppm CPGL, as determined by phase analysis software. XRD analysis confirmed a significant decrease in the grain size of CPGL-treated wax. So, the synthesized PPD, (CPGL) established superior performance in reducing the pour point, viscosity, and wax deposition compared to the commercial PPD. Furthermore, the BOD and toxicity tests confirmed the ecological friendliness of CPGL. So, the synthesised CPGL can be used as an alternative low cost, biodegradable and efficient material for transportation of waxy crude oil.

In accordance with this invention, the process for the preparation of the pour point depressant comprisinges the steps of subjecting coconut oil to hydrolysis by adding an alkali solution,
maintaining the mixture at around 50 to 60°C for about 2 to 4 hours to obtain the free fatty acid,
subjecting the same to esterification reaction, by dissolving the fatty acid and polyethylene glycol (PEG) in a first solvent and allowing them to react at a temperature in the range of 130 to 150℃ using a catalyst,
separating out the water generated followed by distilling off the solvent on completion of reaction to obtain the product,
adding a second solvent to the product, followed by neutralisation with saturated sodium chloride (NaCl) solution to get free product from the unreacted fatty acid and catalyst,
separating the organic layer, washing till the impurities are removed to obtain the fatty ester, CPGL

For a clearer understanding of the invention, the process will be described in greater detail hereinbelow. Coconut oil is placed in a round-bottom flask, to which 10% NaOH solution is added. The mixture is maintained at around 50 to 60°C for about 2 to 4 hours. Thereafter, distilled water is added in small parts with continuous stirring for 1 to 2 hours to achieve an almost clear solution. The mixture is then cooled to room temperature and an acid solution is added in portions with continuous stirring for about 2 to 4 hours. After the reaction is complete, the oil phase is separated from the aqueous layer. The remaining salt present in the oil phase is removed by washing and the resulting product is then vacuum-dried at 40 to 50°C for about 24 hours. Lauric acid was found to be the major fatty acid in hydrolysed coconut oil (Ajogun and Chibor, 2024).
An esterification reaction is performed using an equimolar amount of fatty acid obtained from the above procedure and PEG (1:1). The reactants are dissolved in a first solvent and allowed to react at 130 to 150℃ using a catalyst PTSA, until complete water is separated to avoid the formation of diester. After evaporation of the solvent, the product is washed with toluene for removal of impurities. A second solvent is added, followed by the addition of sodium chloride solution to eliminate the unreacted fatty acid and PTSA. The solvent layer is separated using a separating funnel and evaporated. Finally, the obtained fatty ester, CPGL, is dried under vacuum at 40 to 50°C for 40 to 50 hours. The flow chart of the synthesis and reaction mechanism is presented in Figure 2.



In accordance this invention, the polyethylene glycol is selected from polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, and polyethylene glycol 2000, preferably polyethylene glycol 1000.

In accordance this invention, the first solvent used in the esterification reaction is selected from xylene and toluene.
In accordance this invention, the second solvent is selected from ethyl alcohol, propanol, butanol, and 2-isopropanol.
In accordance this invention, the catalyst is p-toluenesulphonic acid (PTSA).
The invention will now be explained in greater details with the help of the following non- limiting examples. However, such examples are merely for the purpose of explaining the invention and are not to be construed as limiting the scope of the invention.

EXAMPLES:
Synthesis of pour point depressant and its characterization
Pour Point Depressant CPGL was synthesized from coconut oil (Cocos nucifera). Initially, the coconut oil was hydrolysed to obtain free fatty acid. Approximately 10 g of coconut oil was placed in a 250 ml round-bottom flask, to which 30 ml of 10% NaOH solution was added. The mixture was maintained at 50°C in an oil bath for 2.5 hours. 50 ml of distilled water was added in small parts with continuous stirring for 1.5 hours to achieve an almost clear solution. mixture was then cooled to room temperature. Subsequently, 30 ml of 30% HCl solution was added in six portions with continuous stirring for 3 hours. After the reaction was complete, the oil phase was separated from the aqueous layer using a separating funnel. The remaining salt present in the oil phase was removed by washing it several times with distilled water. The resulting product was then vacuum-dried at 50°C for 24 hours. Lauric acid was found to be the major fatty acid in hydrolysed coconut oil.
An esterification reaction was performed using an equimolar amount of fatty acid obtained from the above procedure and PEG-1000 (1:1). The reactants were dissolved in xylene (100 ml) and allowed to react at 138℃ using PTSA, 0.2 wt. % of reactant as a catalyst in a Dean-Stark apparatus until complete water was separated to avoid the formation of diester. After evaporation of the solvent, the product was washed with toluene for removal of impurities. About 50 ml isopropanol was added, followed by the addition of sodium chloride solution to eliminate the unreacted fatty acid and PTSA. The isopropanol layer was separated using a separating funnel and evaporated. Finally, the obtained fatty ester, CPGL, was dried under vacuum at 50°C for 48 hours.

Figure 3 (a) and 3(b) presents the FTIR spectra of CPGL and CPPD, respectively. A broad stretch at 3448 cm-1 indicates the hydroxyl group (-OH) present in polyethylene glycol. The strong absorption peaks at 2925 cm-1 and 2855 cm-1 are attributed to the asymmetric and symmetric stretching of the repetitive methylene (CH2) groups in the alkyl chain of ester. The formation of ester (-COOR) was confirmed by the appearance of a strong carbonyl (C=O) stretching at 1739 cm-1 (Dhandhi et al., 2023). This is further supported by the presence of two C-O-C stretching vibrations of ester at 1249 cm-1 and 1104 cm-1. The medium absorption band at 1454 cm-1 is due to the bending vibration of the methylene (CH2) group in the alkyl chain.
In the case of CPPD, FTIR spectrum analysis revealed a broad stretching at 3444 cm-1, indicating the presence of hydroxyl (-OH) groups. The C-H stretching vibrations at 2932 cm-1, 2854 cm-1, and 1463 cm-1 correspond to methyl and methylene groups. The stretch at 1614 cm-1 is associated with the -C=C of alkene groups, confirming the presence of unsaturated hydrocarbons in CPPD, this vibration was not found in CPGL. Vibrations at 1729 cm-1, and 1170 cm-1 indicate the presence of ester (-COOR) functional groups.
The structure of synthesized pour point depressant CPGL was confirmed using 1H NMR spectroscopy. The 1H NMR spectra of CPGL are shown in Figure 4. In 1H NMR spectra, the signal at δ= 0.78 ppm indicates the methyl proton of fatty ester, 1.18 ppm, and 1.51 ppm correspond to the repetitive methylene groups of esters. The remaining groups of the moiety which were appeared in the signal at δ= 2.22 ppm, 3.55 ppm, and 4.11 ppm represent the -CH2, -O-CH2-CH2-O- and -CH2-O- groups, respectively (Dhandhi et al., 2023).
Particle size distribution of CPGL and CPPD are shown in Figure 5a and Figure 5b respectively. In the case of CPGL, the hydrodynamic diameter was found 379.38 nm whereas for CPPD it was 2006.24 nm. As the hydrodynamic diameter of CPGL is much smaller than the CPPD, the particles of CPGL are more diffusive in crude oil than CPPD particles (Pal and Naiya, 2022a). Therefore, the molecules of CPGL can interact with the wax particles in a better way than that of CPPD. It was also confirmed by the polydispersity index value. The polydispersity index of CPGL is 37% and for CPPD, it is 40%. From this investigation, it is concluded that, as the particles of CPGL are smaller in size than particles of CPPD, so, it has greater efficiency in terms of reducing pour point, viscosity, and wax deposition.
CHNS analysis determines the chemical composition of the synthesized bio additive CPGL and CPPD. It was observed that the total carbon and hydrogen content of CPGL is 56.725 and 9.626% respectively. Nitrogen and sulphur are present in very small quantities. 0.005% nitrogen and 0.078% sulphur are present as heteroatom. From the CHNS data, it is confirmed that a monoester of polyethylene glycol is formed in the esterification step. The CPPD contains 73.041 % carbon, 9.743% hydrogen, 1.5424% nitrogen, and 0.115 % sulphur. The higher carbon content of CPPD indicates the presence of long-chain hydrocarbon or aromatic compounds in its structure.
Biodegradability test:
A standard biochemical oxygen demand (BOD) test was performed to measure the biodegradability of synthesized pour point depressant CPGL. In this experiment, the amount of dissolved oxygen consumed by microorganisms present in water due to their biological activity was measured (Emadian et al., 2017; Tosin et al., 2012). For each sample, the experiment was carried out three times, and the mean was calculated. Following the Winkler titration method, the BOD of the sample was evaluated by measuring the dissolved oxygen (DO) after 0, 7, 14, and 21 days. A similar procedure was applied to a blank sample. Equation 1 and Equation 2 were used to calculate the experimental BOD and biodegradation.
BOD (mg/L) = (D1 - D2) - (D3 - D4) (1)
Where, D1 represents the DO (mg/L) of diluted sample after 0 days, D2 the DO (mg/L) of diluted sample after 7, 14, and 21 days, D3 is the DO (mg/L) of the blank sample after 0 days, and D4 is the DO (mg/L) of the blank sample after 7, 14, and 21 days.
Biodegradation (%) = (Experimental BOD)/(Theoritical BOD) ×100 (2)
BOD from experiments were 1.6 mg/L and 3.4 mg/L after 7 and 14 days respectively whereas the theoretical value of BOD i.e., the value obtained from the molecular formula was 3.93 mg/L. After substituting the values in Equation 2, biodegradation was calculated. The experimental findings revealed that the synthesized pour point depressant CPGL is degraded by 41% after seven days, 87% after 14 days, and eventually fully degraded after 21 days at 20°C. As per the OECD standards, a test substance is readily biodegradable if its degradation rate equals 60% of its theoretical value. So, the CPGL is biodegradable and is not harmful to the environment.
Toxicity test:
The toxicity of the CPGL has been assigned by following the standard OECD 203. To conduct this experiment, shrimps (Pandalus borealis) were collected from the local market of Dhanbad, India. Before starting the experiment, the shrimps were accustomed to the artificial environment created in the laboratory (Gautam and Guria, 2020). Lethal concentration (LC50) i.e., the concentration at which 50% of the test species will die was calculated after 96 hours of experiment. To detect the toxicity (toxic or non-toxic) of CPGL, the percentage of mortalities for test shrimps was plotted against PPD concentration over a 96‐hour survival period to determine the LC50. From the graph, it has been observed that the LC50 value of CPGL is 2500 ppm. According to the guidance of OECD 203, the toxicity of chemicals has been classified based on the LC50 value. The non-ionic surfactants are considered toxic if the LC50 falls in the ranges of 1 to 10 ppm (Sutormin et al., 2023). So, from the toxicity experiment, it is to be concluded that our developed PPD is nontoxic and causes no harmful effects on the environment. Figure 6 depict plot to determine LC50 value.
Measurement of pour point:
In a thermostatic water bath, crude oil was heated to 60°C, and the PPDs were added in certain concentrations (200 ppm to 1000 ppm) with homogeneous mixing. The pour point of untreated and treated crude oil with PPDs were measured using the ASTM D5853-17a (2017) procedure.
The impact of PPDs on the pour point was studied in varying dosages ranging from 200 to 1000 ppm and the result is mentioned in Table 1. The observations demonstrated that up to a specific dosage, the addition of both CPGL and CPPD consistently reduced the pour point of crude oil. However, CPGL perform much better than CPPD to assure flow of crude oil. Treatment with 600 ppm, the optimum dosage of CPGL, depressed the pour point from 35°C to 23°C. Whereas the addition of CPPD decreased the pour point by 6°C only at the same dosage. The efficiency of PPD depends on the molecular weight, number of carbon atoms, or chain length of PPD as well as wax molecule. The major fatty acid found in hydrolysed coconut oil is lauric acid, a saturated fatty acid of carbon number C12. This aliphatic hydrophobic chain is similar to paraffin wax crystals and co-crystallizes with them, inhibiting wax growth and preventing wax agglomeration (Alves et al., 2023). The aliphatic chain of CPGL is more resembles with structure of wax molecules than the commercial one, as a result it showed an encouraging performance than CPPD. The dosage of additive is a critical factor, it has been observed that the pour point decreased regular way during increased dosage from 200 ppm to 600 ppm, but beyond this dosage, adverse effect observed and pour point started to increase. After certain critical concentration which is 600 ppm in this case, the active PPD molecules co-crystallize inside themselves in addition to adhering to wax crystals. As a result, the amount of active PPD molecules to interact with wax considerably decreased, causing the mixture pour point to increase rather than decrease (Machado and Lucas, 2001).The effectivity of PPD was most noticeable at lower dosages (200 to 600 ppm). Within this range, the adsorption or co-crystallization of PPD molecules with wax particles was more effective, leading to significant lowering of the pour point.
Table 1 Effect of CPGL and CPPD on Pour Point of CO
Pour Point (℃)
Sample CO+ CPGL CO + CPPD
CO 35 35
CO + 200 ppm PPD 32 35
CO + 400 ppm PPD 26 29
CO + 600 ppm PPD 23 29
CO + 800 ppm PPD 26 32
CO + 1000 ppm PPD 29 32

7.3. Wax deposition studies with Cold Finger Apparatus:
The percentage reduction of wax deposition in crude oil was assessed before and after adding CPGL and CPPPD using a Cold Finger Apparatus. The basic parts of the equipment are a water bath to control the uniform heat distribution during the experiment, and six 100 ml screw cap glass bottles, in which six cylindrical hollow fingers made up of stainless steel are immersed. A chiller is connected to the flow of cold water through the wall of the finger. Supervisory control and data acquisition software (SCADA) are used to control the temperature of the finger and the water bath. The experiment was conducted with and without PPDs in several concentrations (200 to 1000 ppm). Around 50 ml of crude oil was taken into the glass bottles along with a magnetic stirrer for homogeneous mixing and placed in the hot water bath. A temperature gradient was maintained between the hot water bath and the cold finger, so that wax can deposit on the wall of the cold finger. The duration of the experiment was conducted for both two hours and four hours. Calculation of deposited wax was done according to Equation 3.
WDW = WDTW - BTW (3)
where, WDW represents the weight of deposited wax in grams, BTW stands for the weight of dry tissue paper, and WDTW denotes the weight of tissue paper after wax deposition in grams, respectively.
The percentages of reduction of wax deposition were reported in Table 2 and Table 3. The experiment was conducted by varying the time interval for 2 hours and 4 hours with different dosages of PPDs. It was seen that deposited wax on the surface of the cold finger decreased gradually up to the 600-ppm concentration of CPGL. A similar observation was found in the case of CPPD but its efficiency was much lower than CPGL. A significant reduction in wax deposition was observed when crude oil was treated with a 600 ppm dosage of CPGL. At higher dosages, deposition again started to increase instead of being decreased. The reduction in wax deposition was 0.2530 g to 0.0889 g after 2 hours of experiment. Therefore, almost 64% of wax deposition was decreased due to the mixing of 600 ppm CPGL. Similarly, after 4 hours of studies, almost 73 % of wax deposition decreased for 600 ppm CPGL-treated crude oil. For crude oil treated with 600 ppm CPPD, the decrease in percentages of deposited wax was 34% and 54% after 2 hours and 4 hours of experiment, respectively. The best result was observed when crude oil was treated with a 600 ppm dosage of CPGL. This effect can be attributed to the PPD molecules acting as coating material over the wax molecules, thereby inhibiting the development of a three-dimensional network of wax particles (Chi et al., 2017; Pal and Naiya, 2022a; Ragunathan et al., 2020). This is due to the dispersion of wax molecules, which prevents further attachment of wax molecules. So, from this study, it is inferred that clogging of pipelines is prevented after the addition of 600 ppm dosage of CPGL which helps to enhance the flowability of crude oil. As stated earlier, after a certain concentration, the PPD molecules self-agglomerated instead of co-crystallization with wax particles. When the dosage of additives exceeds 600 ppm, substantial improvement on wax deposition mass reduction was not observed. After reaching a critical concentration, the co-crystallization of paraffins with the PPD molecules reached a saturation, therefore it shows a reverse effect.
After cold finger test, remaining wax content (wax present in crude oil) was determined before and after addition of PPDs. It was observed that after 4 hours of studies, the remaining wax content of pure crude oil was 6.06%, i.e., maximum waxes were deposited on the finger. The remaining wax content of bottles having crude oil mixed with 600 ppm CPGL and CPPD are 7.03 and 6.83% respectively. Therefore, wax particles deposited on the surface of fingers are very less in quantity after dosing with CPGL
Table 2 Effect of treatment of CPGL and CPPD on weight of the precipitated wax at 2 hours of experiment

Weight of deposited wax (g)
Sample CO + CPGL % reduction in wax deposition CO + CPPD % reduction in wax deposition
CO
CO + 200 ppm PPD 0.2530
0.1645 -
34.18 0.2530
0.1952 -
22.84
CO + 400 ppm PPD 0.1229 51.42 0.1857 26.60
CO + 600 ppm PPD 0.0889 64.86 0.1665 34.18
CO + 800 ppm PPD 0.1521 39.88 0.1895 25.09
CO + 1000 ppm PPD
0.1844 27.11 0.2020 20.15


Table 3 Effect of treatment of CPGL and CPPD on the weight of the precipitated wax at 4 hours of experiment

Weight of deposited wax (g)
Sample CO + CPGL % reduction in wax deposition CO + CPPD % reduction in wax deposition
CO
CO + 200 ppm PPD 0.5660
0.3539 -
37.47 0.5660
0.3885 -
31.36
CO + 400 ppm PPD 0.2475 56.27 0.2725 51.85
CO + 600 ppm PPD 0.1495 73.58 0.2600 54.06
CO + 800 ppm PPD 0.3285 41.96 0.3895 31.18
CO + 1000 ppm PPD 0.4075 28.00 0.4644 17.98

7.4. Viscosity study:
The effect of addition of PD on viscosity was studied under different temperature. Temperature has also significance effect on viscosity of crude oil. The effectiveness of bio additive with crude oil was determined by measuring viscosity at temperature ranges from 30℃ to 40℃ at varying shear rates of 10 to 1000 s-1 in an Anton Paar (MCR 302e, Austria) air-bearing rheometer. Temperature ranges are selected from 30°C to 40℃ to study the change of viscosity at the pour point, below and above the pour point. A set of crude oil samples was prepared by addition with the optimum dosage of CPGL and CPPD, and a homogeneous mixture was prepared. The degree of viscosity reduction (%DVR) was measured with temperature according to the following Equation 4.
% DVR= (μ_CO-μ_(CO+PPD))/μ_CO ×100 (4)
where, μCO, and μCO +PPD are the viscosity of untreated waxy crude oil and waxy crude oil treated with PPD respectively.
The combined effect of temperature and PPD synthesized from coconut oil, CPGL, and CPPD on the viscosity of waxy crude oil was investigated at three different temperatures 30°C, 35°C and 40℃ as shown in Figure 7 (a, b and c) and reported in Table 4. The gradual decrease in viscosity was observed with increasing shear rate, and rise in temperature. From the viscosity vs shear rate plot (Figure 7), at 145 s-1 shear rate, the initial viscosity of virgin crude oil was 608.39 mPa.s, which reduced to 391.77 mPa.s and 510.86 mPa.s after dosing of 600 ppm CPGL, and CPPD at 30°C temperature. Therefore, the reduction of viscosity is 35.60% and 16.03% at 30°C with CPGL and CPPD respectively. When the temperature increased from 30°C to 40°C, at 145 s-1 shear rate the viscosity of untreated crude oil decreased by 90.69%. The viscosity of 600 ppm CPGL and CPPD added crude oil decreased by 95.47% and 91.58 %, respectively, at the same temperature. The combination effect of temperature and PPDs together reduced the viscosity when the temperature increased from 30℃ to 40℃. The effectiveness of our synthesized pour point depressant CPGL is more than the commercial one in the reduction of viscosity. Therefore, it is concluded that our synthesized pour point depressant CPGL has higher effectiveness in terms of viscosity reduction. So, it can be used as an alternative to the heating method. The crude oil behaves like a non-Newtonian fluid at low temperatures and low shear rates, but as the temperature and shear rate increase, it behaves like a Newtonian fluid, with wax particles diffusing into the oil. As a result, the viscosity of crude oil decreases naturally. The addition of PPD accelerates the reduction. When crude oil is dosage with CPGL fatty ester, the alkyl chain of fatty ester is co-crystallized with wax particles of crude oil and coated over them. So, another wax particle will not be able to come closer to the previous wax molecules due to steric hindrance of ester groups. A gel-breaking phenomenon was observed after addition of PPDs, which prevents the formation of a three-dimensional network of wax crystals and enhances the flow. Besides, the presence of asphaltene and resin in crude oil triggers to increase the viscosity of crude oil. The deposition of asphaltene along with wax is another factor. The polar part of the fatty ester, the ethylene oxide group, interacts with asphaltene and resin and helps to reduce the viscosity of crude oil (Sutormin et al., 2023).

Table 4 Effect of addition of CPGL and CPPD over a temperature range of 30-40℃ at 145 s-1
At shear rate 145 s-1
30℃ 35℃ 40℃
Sample Viscosity (mPa.s) %DVR Viscosity (mPa.s) %DVR Viscosity (mPa.s) %DVR
CO 608.39 - 154.25 74.64 56.63 90.69
CO + 600 ppm CPGL 391.77 35.60 82.67 86.41 27.52 95.47
CO + 600 ppm CPPD 510.86 16.03 119.26 80.39 51.22 91.58

7.5. Microscopic study:
The morphology of wax crystals with and without PPDs was investigated through an Olympus cross-polarized microscope (BX53M) equipped with Stream Basic software. The crude oil was initially heated to 60℃ and then a very small drop was placed above the glass slide. Samples covered with a glass slip were initially heated to 60℃ and then allowed to cool at 0.5℃/min. The microimages were taken at 30℃. The microscopic images of pure crude oil and PPD dosage crude oil at their optimum concentrations of 600 ppm are shown in Figure 8. Saturate present in crude oil was precipitated as wax crystal at lower temperatures and agglomerated to form a three-dimensional network as time elapsed. This leads to a higher viscosity of crude oil. The micrograph showed a notable change in the arrangement of wax crystals after treating crude oil with CPGL. The aggregation or association of wax crystals was decreased, and effective crystal size was reduced, gradually loose, and dispersed in crude oil. The dispersion or separation of wax crystals was predominant at the optimum concentration of CPGL i.e., 600 ppm (Figure 8). As stated previously, the wax crystals were co-crystallized or adsorbed onto the chain of PPD, and the polar ester group provided a steric hindrance. So, the tendency of a wax crystal to overlap with another wax crystal is reduced, and they remain dispersed. This phenomenon is corroborated by the pour point data. The micrographs of CPPD-treated crude oil showed a similar type of observation, but wax molecules are not dispersed properly, and the size of wax crystals is also larger than that of the CPGL-treated crude oil. Therefore, our synthesized PPD has better performance in reducing pour point, wax deposition thickness, and viscosity which is strongly confirmed by the microscopic study.
7.6. Phase analysis of crude oil:
The changes in wax percentages after the interaction of PPD molecules with wax particles were observed in a polarized optical microscope using phase analysis software at a constant temperature, 30°C during cooling at 0.5°C/ min. Figure 9 presents the microscopic images of phase analysis of crude oil treated with and without PPDs. Two phases are observed in the microscopic images of crude oil. The first one is black (crude oil, indicated in red), and the second one is a shining white crystal (paraffin or wax, indicating green). The percentages of these two phases are calculated by phase analysis software and mentioned in Table 5. Initially, the percentage for virgin crude oil, represented by the fraction of the black (red) region is 69.71%, and the shining white (green) region is 28.45%, indicating the aggregation of paraffin or waxes widely. But when bio-additives are mixed with crude oil, the percentage of the black region is increased, and the shining white region, i.e., the wax fraction, is gradually decreased. After dosing 600 ppm CPGL and CPPD in crude oil, the percentages of black regions became 85.22% and 78.29%, respectively. So, CPGL shows greater efficiency in modifying wax crystals than CPPD. Therefore, it is inferred that, after the addition of PPDs, a substantial amount of wax is diffused into the crude oil. Therefore, waxes will be in dissolved form rather than agglomerated form. As a result, the space occupied by crude oil (black region) became greater in the case of PPD treated crude oil compared to virgin crude oil.
Table 5 Phase analysis of crude oil with PPDs
Sample Black (Crude oil)
% White (Wax)
%
CO 69.71 28.45
CO+600 CPGL 85.22 14.70
CO+600 CPPGD 78.29 17.48


7.7. Determination of Wax Appearance Temperature (WAT):
The WAT was measured for crude oil with and without PPDs (Ruwoldt et al., 2020). Using a cross-polarized microscopic equipped with a temperature controller, a microscopic studies was done to determine the WAT. Crude oil samples were heated to 60°C and then placed on a glass slide to ensure that the wax particles were completely dissolved and distributed evenly. Following that, samples were allowed to cool at a rate of 0.5°C per minute to determine the temperature at which wax crystals began to reappear. The observations are depicted in Figure 10. The wax crystallization process was investigated for both untreated and PPD-treated oil at their optimum dosage of 600 ppm. When waxes are present in an untreated oil sample, they first emerge as big, white, circular droplets at a temperature of roughly 60.2°C. Over time, they agglomerate to create a network structure of wax crystals, as seen in Figure 10. As a result, 55.4°C might be thought of as the wax appearance temperature, or WAT, for untreated crude oil. However, the formation of wax crystals in treated crude oil containing 600 ppm CPGL begins at 48.2°C, which is nearly 7.2°C lower than that of untreated crude oil. In the case of CPPD-treated crude oil, the WAT was determined as 52.7°C. As previously mentioned, the addition of PPD inhibited the process of wax crystallization by interacting with the hydrophilic polar ethylene oxide of PEG and ester group and their hydrophobic alkyl chain. Furthermore, the loss of tiny wax crystals made the micrographs clearer, and maximum wax crystals were solubilised in crude oil. These observations agreed with the earlier conclusions.
The present invention presents the synthesis of bio-based pour point depressants as well as viscosity reducer from coconut oil (CPGL) to assure the flow of Indian waxy crude oil. These raw materials used for synthesis are easily available and inexpensive. The major problems associated with the mostly used synthesized and commercial PPDs are that these are expensive and non-biodegradable, and their toxicity disrupts the ecological balance of aquatic systems. To overcome these problems, an eco-friendly PPD, CPGL has been synthesized which is biodegradable within 21 days of experiment, and non-toxic to the aquatic organisms. Moreover, CPGL shows a better performance with a very small dosage (600 ppm) compared to commercial PPD. So, CPGL is a sustainable, affordable, biodegradable, safe, and environmentally friendly PPD that can be substituted for commercial ones.
The main objective of the invention is the use of CPGL as PPD, which is produced by hydrolysis of coconut oil followed by esterification with Polyethylene glycol (PEG) using PTSA as a catalyst.
There are no environmental impacts with the synthesised bio additive CPGL. The major fatty acid present in coconut oil is lauric acid which is used in the food industry because of its lubricating qualities. The additive CPGL has undergone testing to determine its biodegradability and toxicity, and the results demonstrate that it is both environmentally benign and quickly biodegradable.
The pour point of Indian waxy crude oil was decreased from 35°C to 23°C after treatment with 600 ppm concentrations i.e., 12°C reduction in pour point was observed. A comparative study was also performed with CPPD which was able to reduce the pour point by 6°C at similar concentrations.
CPGL can improve the flowability of crude oil by lowering the viscosity of crude oil substantially, e.g., addition of 600 ppm dosage at 30°C reduce viscosity by 36%. The reduction in viscosity reduces the need of heating of crude for assurance of flow of crude.
The pour point, viscosity, wax deposition, and morphological examination of wax for both untreated and crude oil treated with PPD were measured in order to establish the efficacy of CPGL as a pour point depressant.
A phase analysis study using phase analysis software (fitted with a microscope) provides quantitative measurements of wax and crude oil to support all of these previous investigations. This is a unique method in this field, calculating the proportion of wax in crude oil before and after the addition of PPD. Along with ensuring environmental safety, this CPGL can meet the petroleum industry's present need for wax inhibitors. , Claims::
1. A pour point depressant for flow assurance of Indian waxy crude oil, prepared from coconut oil (Cocos nucifera) and polyethylene glycol (PEG).

2. The pour point depressant as claimed in claim 1, wherein the the polyethylene glycol is selected from polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, polyethylene glycol 2000, preferably polyethylene glycol 1000.

3. The pour point depressant as claimed in claim 1, which can, at a dosage of 600 ppm reduces the pour point by 12°C, the viscosity by 36% at 30°C (shear rate of 145 s-1) and reduces the percentage of wax crystals present in crude oil (in the studied area in the microscope) from 28.45 % to 14.70 %, as determined by phase analysis.

4. A process for the preparation of the pour point depressant as claimed in claim 1, comprising the steps of subjecting coconut oil to hydrolysis by adding an alkali solution,
maintaining the mixture at around 50 to 60°C for about 2 to 4 hours to obtain the free fatty acid,
subjecting the same to esterification reaction, by dissolving the fatty acid and polyethylene glycol (PEG) in a first solvent and allowing them to react at a temperature in the range of 130 to 150℃ using a catalyst,
separating out the water generated followed by distilling off the solvent on completion of reaction to obtain the product,
adding a second solvent to the product, followed by neutralisation with saturated sodium chloride (NaCl) solution to get free product from the unreacted fatty acid and catalyst,
separating the organic layer, washing till the impurities are removed to obtain the fatty ester, CPGL

4. The process as claimed in claim 4, wherein the esterification reaction is effected with an equimolar quantity of the fatty acid and polyethylene glycol (PEG) (1:1).

5. The process as claimed in claim 4, wherein the first solvent used in the esterification reaction is selected from xylene and toluene.

6. The process as claimed in claim 4, wherein the second solvent is selected from ethyl alcohol, propanol, butanol, and 2-propanol.

7. The process as claimed in claim 4, wherein the catalyst is p-toluenesulphonic acid.

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