Synthesis and performance evaluation of polymeric surfactant from rice husk and polyethylene glycol for the enhanced oil recovery process published by Ural Federal University eISSN 2411-1414; chimicatechnoacta.ru ARTICLE 2022, vol. 9(4), No. 20229406 DOI: 10.15826/chimtech.2022.9.4.06 1 of 9 Synthesis and performance evaluation of polymeric surfactant from rice husk and polyethylene glycol for the enhanced oil recovery process Slamet Priyanto, Ronny W. Sudrajat, Suherman Suherman * , Bambang Pramudono, Teguh Riyanto , Desty D. Setianingrum, Alfin A. Pratama Department of Chemical Engineering, Universitas Diponegoro, Semarang 50275, Indonesia * Corresponding author: suherman.mz@che.undip.ac.id This paper belongs to a Regular Issue. © 2022, the Authors. This article is published in open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract A tertiary recovery technique is needed to recover the remained oil in the oil field after primary and secondary recoveries, which can only recover approximately 30–50% of the total oil. This study investigated the synthesized polymeric surfactants from rice husk and polyeth- ylene glycol (PEG) for the enhanced oil recovery (EOR) process as a tertiary recovery technique. The rice husk was used as sodium ligno- sulfonate (SLS) surfactant production feedstock. SLS-PEG polymer surfactant from rice husk has not been widely studied, especially for the EOR process. This study has comprehensively investigated the ef- fect of PEG concentration on the polymeric surfactant properties. The surfactants were characterized using Fourier transform-Infrared (FT- IR) analysis. Several other tests were also conducted, including sur- factant compatibility, viscosity, thermal stability, interfacial tension (IFT), and phase behavior. It was found that the PEG introduction to the SLS surfactant could increase the hydrophilic property of the pol- ymeric surfactant due to the presence of the C−O−C group. In addition, the IFT value decreased with the increase in the PEG concentration due to the increase in the hydrophilic property. However, the IFT value decreased when the PEG concentration was too high. The lowest IFT value was obtained at the SLS to PEG ratio of 1:0.8. It produced the highest increase in the additional recovered oil after brine flooding. The results showed that the rice husk, which is agricultural waste, could be utilized as a feedstock for the surfactant production. Keywords polymeric surfactant rice husk sodium lignosulfonate polyethylene glycol enhanced oil recovery Received: 01.07.22 Revised: 08.07.22 Accepted: 08.07.22 Available online: 12.07.22 1. Introduction With the increase in the human population energy con- sumption tends to increase. In addition, the main resource supplying the energy demand in the world is fossil-based fuel. Therefore, exploitation of oil fields is going to in- crease. However, the primary recovery can only recover ap- proximately 10% of the total oil and the secondary recovery can give an additional 20–40% [1]. It means that around 50–70% of the original oil remains in the oil field after both primary and secondary recoveries. Therefore, a tertiary re- covery technique is required to retrieve the oil left in the oil field. One of the methods that can be used is the enhanced oil recovery (EOR) process, including thermal, chemical, gas flooding, and microbial EOR [2]. These methods can- not be applied to the same reservoir because of the differ- ent processes and the different characteristics of the ex- tracted oil. However, due to the low-cost process, one of the most developed EOR processes is the chemical injec- tion or CEOR [2, 3]. The injected chemical is a surfactant which can reduce the interfacial tension (IFT). IFT is the tendency of a liquid to possess a minimum free surface when it is in contact with another immiscible liquid [4]. Therefore, the primary requirement for the surfactant in the EOR process is the lowest IFT [5]. The surfactant in- jected into the oil reservoir will reduce the IFT of the oil - water, which will then reduce the capillary pressure so that the oil left after the water-flooding process can be taken up. http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2022.9.4.06 mailto:suherman.mz@che.undip.ac.id http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0002-3055-0295 https://orcid.org/0000-0002-3553-4219 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2022.9.4.06&domain=pdf&date_stamp=2022-7-12 Chimica Techno Acta 2022, vol. 9(4), No. 20229406 ARTICLE 2 of 9 An ionic surfactant such as sodium lignosulfonate (SLS) is the most developed lignin-based surfactant which can be applied for the EOR process. SLS molecule has the hydropho- bic and hydrophilic parts, which are associated with the aro- matic skeleton and sulfonate group, respectively [6]. Pramudono and co-workers [3, 7–9] have intensively devel- oped SLS surfactants for the EOR process from biomass- based lignin. Priyanto et al. [9] synthesized SLS from black liquor for the EOR process. They reported that the SLS sur- factant could decrease the IFT value of oil and water up to 0.0254 dyne/cm at an SLS concentration of 0.5%wt in a brine solution of 3000 ppm. Previously, Priyanto et al. [10] have also studied the hydrodynamic of the EOR process using the SLS surfactant from black liquor. Even though the SLS surfactant has a high performance to reduce the IFT value of oil-water, some disadvantages, such as intolerance to a high brine solution, easy adsorbance by the stone during the EOR process, and high sensitivity to divalent ions, make SLS less appropriate for the EOR process [3, 11]. Therefore, some modifications should be done to improve the characteristics and performance of the SLS surfactant. Modifications of the SLS surfactant can be conducted through the addition of a nonionic polymeric surfactant, such as polyethylene glycol (PEG). Nonionic surfactants are much more tolerant of high salinity [12]. In addition, the main ad- vantage of a polymeric surfactant is that, in addition to the IFT reduction, it also increases the viscosity of the solution, which is very important for enhanced sweep efficiency in enhanced oil recovery [13]. However, if the viscosity of the surfactant is too high, it can block the reservoir; conversely, if the viscosity of the surfactant is too low, mobility is not appropriate [14]. Yin and Zhao [15] have studied the effect of viscosity and in- terfacial tension on oil recovery in the heterogeneous reser- voir and determined the main controlling factors of the poly- mer-surfactant (SP) flooding. They reported that a higher pol- ymer concentration could increase the surfactant viscosity. To the best of our knowledge, research on synthesizing SLS-PEG polymer surfactants from rice husk has not been per- formed and published. The research that has been done is to produce SLS surfactant from rice husk [16]. Referring to this fact, it was necessary to conduct a study on the synthesis of the SLS-PEG polymer surfactant. Some characterization tests were carried out to determine the character of the polymer surfactant obtained and a core flooding test to determine the amount of the recovered oil using the SLS-PEG polymeric sur- factant. The effect of PEG concentration in the polymeric sur- factant on surfactant characteristics was also comprehen- sively studied. This study discovered the potential of rice husk, which is a waste, as a feedstock for the low-price and high- performance surfactants production for the EOR process. 2. Materials and Methods 2.1. Materials The sodium lignosulfonate surfactant was synthesized from rice husk which was obtained from Purwokerto, Central Java, Indonesia. The other raw material of the polymeric surfactant was polyethylene glycol with a molecular weight of 400 (PEG-400). The other chemicals which were used in this study were brine, hydrogen peroxide (H2O2), sodium bisulfite (NaHSO3) (Merck), sodium hydroxide (NaOH) (Merck), sulfuric acid (H2SO4) (Mallinckrodt), methanol, ammonium persulfate, and demineralized water which was obtained from the Integrated Laboratory of Universitas Diponegoro, Semarang, Central Java. In order to assess the performance of the surfactant in the EOR process, Kawengan oil from STEM AKAMIGAS Cepu, Indonesia, was used as the raw oil. 2.2. Lignin isolation from rice husk The isolation process of lignin from rice husk followed the method by Ma’ruf et al. [17], who isolated lignin from rice husk using alkaline hydrogen peroxide solution. About 20 g of dried rice husk (dried at 50 °C for 6 h) was immersed in 120 ml of demineralized water, which contained 1% H2O2 (volume/weight ratio of 1:6). The pH of the suspen- sion was maintained at 10.5 using NaOH solution with a concentration of 2 M. Furthermore, the suspension was heated to 100 °C and stirred (250 rpm) for 2 h. The sus- pension was then filtered and the obtained lignin was dried at 45 °C for 24 h. 2.3. Synthesis of sodium lignosulfonate and polymeric surfactant The SLS surfactant synthesis followed the Priyanto et al. method [18]. Approximately 3 g of lignin obtained from Sec- tion 2.2 was immersed in 90 ml of demineralized water. So- dium bisulfite (1 ml) was then added to the mixture. The pH was adjusted to 8.3 using NaOH 1 M. The sulfonation pro- cess was conducted for 2 h at 80 °C. After the sulfonation process, the mixture was then evaporated at 100 °C to ob- tain a black sludge. The sludge was filtered using a Büchner funnel which was equipped with a vacuum pump. The ob- tained SLS surfactant was then used to synthesize SLS-PEG polymeric surfactants. The SLS-PEG polymeric surfactants were synthesized using the SLS surfactant, PEG and ammonium persulfate, following the method by Priyanto et al. [3]. The SLS to PEG ratios were 1:0.5, 1:0.8, and 1:1. Afterwards, the synthe- sized polymeric surfactants were denoted as SLS-0.5PEG, SLS-0.8PEG, and SLS-1.0PEG, respectively. SLS was dis- solved in 80 ml of demineralized water, PEG was dissolved in 10 ml of demineralized water, and ammonium persulfate was dissolved in 10 ml of demineralized water. The SLS and PEG solutions were put into a three-neck flask and heated to a temperature of 70 °C with a stirring speed of 300 rpm. After the temperature was reached, the ammonium persul- fate solution was then put in a three-neck flask to react with the polymeric surfactant. The reaction was carried out for 2 h. The product of this reaction was extracted using ace- tone and then put into the oven for 12 h before characteri- zation tests. Chimica Techno Acta 2022, vol. 9(4), No. 20229406 ARTICLE 3 of 9 2.4. Characterization methods The obtained surfactants were characterized using Fourier transform-Infrared (FT-IR) analysis to determine their functional groups. FT-IR spectra were scanned using a Per- kin-Elmer Infrared spectrophotometer in the wavenumber range of 4000–400 cm−1. The other characterization tests were also conducted, including surfactant compatibility, viscosity, thermal stability, IFT, and phase behavior, before using the surfactants in the EOR process performance test. Prior to the characterization with the previously mentioned tests, the surfactant, with 0.1%wt concentration, was dis- solved in 5000 ppm of brine solution. The compatibility test was conducted for 28 days. In addition, the thermal stabil- ity test was also conducted for the same period of time at 70 °C, which is the reservoir temperature. The density of the polymeric surfactant was periodically measured. The viscosity test was conducted using the Ostwald viscometer. The IFT measurement was conducted using the Spinning Drop Interfacial Tensiometer at 70 °C [10]. The phase be- havior test was carried out in a tube test which consists of oil and brine solution (injection water) consisting of 0.1 wt.% of surfactants. The volumetric ratio of oil and brine solution was 1:1. The mixture was then shaken and heated to the reservoir temperature (70 °C) for 28 days. 2.5. Core flooding test The core flooding test was undertaken according to the pre- vious study [10] using the experimental rig as shown in Fig- ure 1. This test requires rock, brine solution, oil, and 0.1%wt polymeric surfactant. This study uses Kawengan oil, a heavy crude oil with a density of 0.96 g/cm3, as the oil for the EOR process. The brine solution was in a concentration of 5000 ppm. Filters are placed at both ends of the core holder to pre- vent rocks from clogging the pipe from the core holder. The size of the silica sandstone was 100 mesh with a 150-mesh filter. The performance tests were carried out at 70 °C. 3. Results and Discussion 3.1. Fourier Transform Infrared Spectroscopy analysis of surfactants The synthesized surfactants from rice husk and PEG were characterized using FT-IR analysis. This analysis was conducted to investigate the functional groups in the synthesized polymeric surfactants. The infrared spectra were recorded at a wavenumber of 4000–400 cm−1. Fig- ure 2 shows the infrared spectra of the synthesized sur- factants. As shown in Figure 2, the broad intense peak between 3600–3200 cm−1 was found in all surfactants. This peak corresponds to the hydroxy group stretches [3]. The hy- droxy group stretches could be found in the form of intra- molecular and intermolecular hydrogen bonds of O−H, which appear at a wave number of ~3550 cm−1 and ~3400 cm−1, respectively [19]. The peak at ~2925 cm−1 is attributed to the stretching vibration of methyl (−CH3). The peak at ~2850 cm−1 corresponds to the C−H stretching of methylene (−CH2−). The peak at ~2850 cm−1 seems to in- crease as the PEG concentration increases. It is because the PEG has more methylene groups than SLS. Therefore, the addition of PEG could increase the methylene group in the synthesized polymeric surfactants. In the SLS surfactant, the sulfonate group can be found at wavenumbers of ~1180 cm−1, ~1137 cm−1, ~1042 cm−1, and ~644 cm−1, which are assigned to the symmetric stretch vibration of O=S=O, asymmetric stretch vibration of O=S=O, S−O stretch, and S−O band, respectively [17, 20, 21]. In addition, the aromatic ring from the SLS surfactant molecules can also be detected using the FT-IR analysis. The C=C vibration of an aromatic ring is found at a wavenumber of ~1608 cm−1. In addition, the C−H stretch from an aro- matic ring is found at ~1512 cm−1 [21, 22]. Figure 1 Scematic diagram of the experimental rig for the EOR process. 1. Compressor 5. Oil 9. Heater 13. Thermometer 2. Temperature indicator 6. Brine 10. Input cone 14. Core 3. Heating indicator 7. Output valve 11. Manometer 15. Output 4. Surfactant 8. Air valve 12. Oven 16. Measuring cup Chimica Techno Acta 2022, vol. 9(4), No. 20229406 ARTICLE 4 of 9 Figure 2 FTIR analysis of SLS (a), SLS-0.5PEG (b), SLS-0.8PEG (c) and SLS-1.0PEG (d). (a) (b) (c) (d) Chimica Techno Acta 2022, vol. 9(4), No. 20229406 ARTICLE 5 of 9 After the PEG introduction, some new peaks are found in the synthesized polymeric surfactants. The scissoring vi- bration of two O−H from water molecules appears at a wavenumber of ~1632 cm−1, followed by a peak at ~1350 cm−1, which is assigned to the in-plane O−H deformation. The ether group of PEG is found, which is pointed by the appearance of intense peaks at ~1210 cm−1 and ~1100 cm−1. These peaks correspond to the asymmetric and symmetric stretching vibration of C−O−C, respectively [21]. The new peak at ~950 cm−1 is assigned to the C−C skeletal stretching vibration [23] or C−H deformation [24]. 3.2. Compatibility test of surfactants The compatibility test was conducted to investigate the be- havior of the surfactant in the brine solution and whether it can be dissolved or not. In this study, 0.1 wt.% of surfac- tant was dissolved in a 5000 ppm brine solution. A good surfactant will be dissolved in the brine solution. Dasilva et al. [7] reported that a surfactant is compatible or good if it can be completely mixed with the brine solution without any precipitates. Therefore, a completely dissolved surfac- tant in the brine solution is desired because the suspension is not allowed. During the EOR process, a suspended sur- factant should be because it can clog the pore of the rock during the EOR process when it is injected [3, 25]. In this study, the compatibility test was conducted for 28 days. Fig- ure 3 shows the appearance of the surfactant in the brine solution on day-0 and day-28. As can be seen, no precipita- tion was observed during the compatibility test even on day-28. It verifies that the polymeric surfactant of SLS from rice husk and PEG is highly soluble in the brine solution. It is speculated that the high solubility of the surfactant is caused by the presence of ether group (C−O−C) in the PEG structure and the hydrophilic nature of the SLS surfactant. The interaction between the ether group with water mole- cules allows the surfactant to be dissolved in the brine solu- tion. It was reported that the water molecules could bind with oxygen in the ether group through the hydrogen bond- ing interaction [3, 26]. In addition, the hydrophilic nature of SLS also affects the solubility of surfactants in the brine solu- tion. The SLS surfactant has a short chain molecular structure, allowing SLS to be easily dissolved in the brine solution [27]. Figure 3 Surfactant appearance on day-0 and day-28 during the compatibility test. Table 1 Viscosity, density, and IFT value of the polymeric surfactants. Polymeric Surfactant Viscosity (centipoise) Density (g/cm3) IFT (dyne/cm) SLS 0.835 0.992 1.012 SLS-0.5PEG 0.839 0.993 0.427 SLS-0.8PEG 0.841 0.995 0.386 SLS-1.0PEG 0.854 0.998 0.622 On the other hand, SLS has negative charges on its hy- drophilic part. It is known that the hydrophilic part of SLS surfactant consists of the sulfonate structure (−SO3−) and its salt (NaSO3) [28, 29]. The presence of the negative charges in the hydrophilic part makes SLS an anionic sur- factant which is water-soluble [25]. Therefore, the pres- ence of ether group (C−O−C) from PEG and negative charges from SLS makes the polymeric surfactant more sol- uble. 3.3. Viscosity test of surfactants The viscosity of the surfactant is one of the important param- eters in the EOR process. It was reported that a high surfac- tant viscosity is needed in the EOR process. Surfactants with high viscosity can enhance or increase oil recovery due to their ability to reduce oil-water mobility [14, 15]. Even though a viscous surfactant can enhance or increase the oil recovery in the EOR process, it may block the pore of rock [3]. Therefore, the viscosity of the surfactant should be con- trolled. The viscosity of the surfactants is presented in Table 1. As can be seen in Table 1, the viscosity of the SLS sur- factant is 0.835 centipoise. Furthermore, it can be observed that the viscosity of the surfactant increases after the addi- tion of PEG. It is also shown that the viscosity of the surfac- tant linearly increases with the PEG amount in the poly- meric surfactant. Therefore, it is reasonable to conclude that the viscosity of the surfactant can be increased and controlled by controlling the PEG concentration (ratio of SLS to PEG) in the polymeric surfactant. The increase in the viscosity of the polymeric surfactant after PEG addition can be caused by the fact that PEG is a viscous material. Therefore, the addition of PEG will indeed increase the viscosity of the polymeric surfactant. This find- ing is in accordance with some previous reports [3, 8]. Pri- yanto et al. [3] and Sudrajat et al. [8] reported that the vis- cosity of the SLS surfactant, which was synthesized from black liquor, can be increased by the addition of PEG. In ad- dition, Alli et al. [30] also reported that the viscosity of the injecting brine could be increased by adding PEG as a poly- mer. 3.4. Thermal stability test of surfactants The thermal stability test was conducted for 28 days at 70 °C. The temperature of 70 °C was chosen because it is the temperature of the reservoir. This test was conducted to investigate the effect of heat on the surfactant stability. The desired surfactant is a stable surfactant without any agglomerate being formed. As reported, sulfonate-type sur- factants tend to create agglomerate or precipitate at high S L S -1 .0 P E G S L S -0 .8 P E G S L S -0 .5 P E G S L S -1 .0 P E G S L S -0 .8 P E G S L S -0 .5 P E G day-0 day-28 Chimica Techno Acta 2022, vol. 9(4), No. 20229406 ARTICLE 6 of 9 temperatures because they are sensitive to divalent ions [11]. Density is the observed parameter during this thermal stability test. The change in the surfactants' density is pre- sented in Figure 4. As can be seen in Figure 4, the density of 0.1 wt.% sur- factants in 5000 ppm brine at all PEG concentrations was stable. After 28 days of observation, the density of all sur- factants is relatively unchanged. It can be concluded that the synthesized from rice husk polymeric surfactant is sta- ble in the brine solution. As expected, this thermal stability test found no precipitates or agglomerates in the surfactant solution. It confirms that this polymeric surfactant is stable at 70 °C. Moreover, it shows that rice husk can be utilized as a raw material for the stable polymeric surfactant pro- duction. As was explained before, the synthesized polymeric sur- factants are stable at 70 °C as the densities of the surfac- tants are constant during the test and as no precipitates or agglomerates were found. It is possibly caused by the fact that the surfactants have a high solubility. This solubility comes from the ether group of PEG (C−O−C) and the nega- tive charges in the SLS surfactant in the form of sulfonate structure (−SO3−) and its salt (NaSO3). It was reported that interaction between water molecules and oxygen of ether group in PEG could be separated at a high temperature through the dehydration process [26]. However, polymeric nonionic surfactants have a high solubility due to their high hydrophilic property [3, 26]. Therefore, the synthesized surfactants from rice husk and PEG have high stability in the brine solution. Figure 4 Density of surfactant in brine solution during the stability test for 28 days. 3.5. Interfacial tension (IFT) test of surfactants The interfacial tension (IFT) of the fluids indicates the mis- cibility of the two fluids. Moghadasi et al. [31] explained that the IFT determines the mixing potential between two fluids. The lower the IFT value, the higher the possibility of two fluids being mixed. In the EOR process, the addition of surfactants to the injected brine or water is to reduce the IFT value between water and oil and/or to alter wettability; therefore, the amount of the recovered oil from the reser- voirs will be increased [32]. Thus, the desired surfactant is the one that can reduce the IFT value as strongly as possi- ble. The IFT values as a function of the surfactant are pre- sented in Table 1. As shown in Table 1, the IFT value of the SLS surfactant from rice husk is 1.012 dyne/cm. This value shows the high- est value as compared to the other surfactants. Interest- ingly, the IFT value can be reduced after the addition of PEG. As can be seen, the IFT value decreases as the increase in PEG concentration. PEG is known as a polymeric surfac- tant. Bustamante-Rendón et al. [33] reported that the com- bination of ionic and nonionic surfactants has a good per- formance in decreasing the IFT value between oil and wa- ter. In addition, PEG is highly hydrophilic due to the pres- ence of ether groups that can bind with water molecules through hydrogen bonding [34, 35]. Therefore, the addition of PEG to SLS increases the hydrophilicity of the surfactant. As a result, the IFT value is reduced. Priyanto et al. [9] ex- plained that the IFT value could be reduced by increasing the hydrophilicity of surfactants. 3.6. Phase behaviour test of surfactants The phase behavior test was conducted to investigate the for- mation of microemulsions of brine and oil in the presence of polymeric surfactants. The test was carried out in a tube test which consists of oil and brine solution (injection water) con- sisting 0.1 wt.% of surfactants. The volumetric ratio of the oil and brine solution is 1:1. The mixture was then shaken and held at the reservoir temperature (70 °C) for 28 days. The minimum requirement of microemulsion type for the EOR process is Winsor Type I, which can also be mentioned as Winsor Type II(−) [36, 37]. As reported by Zulkifli et al. [11], Winsor Type III microemulsion type is the best micro- emulsion for EOR process, followed by Winsor Type I and Winsor Type II. Therefore, the desired surfactant is the one that can produce Winsor Type III microemulsion or at least Winsor Type I. Figure 5 shows the appearance of the for- mation of microemulsion by surfactants. Figure 5 The appearance of phase behavior test of polymeric sur- factants at day-28 (a) and illustration of Winsor Type I or II(−) microemulsion (b). 0 7 14 21 28 0.992 0.993 0.994 0.995 0.996 0.997 0.998 0.999 1.000 D e n s it y ( g / c m 3 ) Time (day) SLS-1.0PEG SLS-0.8PEG SLS-0.5PEG Chimica Techno Acta 2022, vol. 9(4), No. 20229406 ARTICLE 7 of 9 As shown in Figure 5, all surfactants produce micro- emulsions of Winsor Type I or lower-phase microemulsion (Winsor Type II(−)). It means that the surfactants tend to create oil-in-water microemulsion (o/w microemulsion). This type of microemulsion is formed by the presence of hy- drophilic or water-based surfactants [3, 38]. It is true since SLS was reported as a water-based surfactant [27]. It makes sense since the SLS surfactant contains negative charges in the form of sulfonate structures (−SO3−) in the hydrophilic part. In addition, the introduction of PEG to the SLS surfac- tant increases the surfactant’s hydrophilicity. The increase of the surfactant’s hydrophilicity is caused by the presence of the C−O−C group that can inter- act with water molecules. The interaction of water mole- cules with the C−O−C group occurs through hydrogen bonding [3, 26]. This fact is confirmed through the FT-IR analysis, which shows that the concentration of the C−O−C groups of the surfactants has increased after PEG addition. Therefore, the hydrophilicity of the surfactants increases [39, 40]. Being more focused on the microemulsion formation as the effect of PEG concentration, it is shown that the SLS- 0.8PEG has the darkest microemulsion, followed by SLS- 0.5PEG and SLS-1.0PEG. It means that the amount of oil that dissolved in the brine phase by SLS-0.8PEG is higher. It can be explained by the fact that the SLS-0.8PEG surfac- tant produces the lowest IFT value, followed by SLS- 0.5PEG and SLS-1.0PEG. As been explained, the lower the IFT value, the higher the possibility of two fluids being mixed [31]. Therefore, the SLS-0.8PEG is expected to give the highest yield in the enhanced oil recovery process. 3.7. Performance test of surfactants for EOR process The performance test of surfactants was conducted through the EOR process using the experimental rig, as shown in Figure 1 and described above. As can be seen in Figure 6, the brine injection with a concentration of 5000 ppm can recover the oil at around ~82% to ~84%. In addition, the injection of the surfactant can enhance oil recovery. As shown in Figure 6, the amount of the recovered oil can be increased by the surfactant injection. The injection of the surfactant increases the total recov- ered oil by about ~10% to ~12%. In addition, the increase in the total recovered oil percentage is affected by the PEG concentration in the SLS surfactant. The total recovered oil amount increases by 11.52% from 83.94% to 95.46% by us- ing the SLS-0.5PEG surfactant (SLS to PEG ratio of 1:0.5), increases by 12.22% from 84.72% to 96.94% by using the SLS-0.8PEG surfactant (SLS to PEG ratio of 1:0.8), and in- creases by 10% from 81.43% to 91.43% by using the SLS- 1.0PEG surfactant (SLS to PEG ratio of 1:1.0). It shows that the PEG as a polymeric surfactant affects the oil recovery process. Babu et al. [13] reported that the polymeric surfac- tant could increase the surfactant viscosity and reduce the IFT, which are very important to enhance the sweep effi- ciency in the EOR process. Figure 6 EOR performance of surfactants. As shown in Figure 6, the increase in the total recovered oil percentage after the surfactant injection is affected by the PEG concentration in the surfactant. The increase in the total recovered oil amount increases as the PEG concentra- tion increases. The total recovered oil percentage increases from 11.52% to 12.22% by increasing the SLS to PEG ratio from 1:0.5 to 1.08. However, a further increase in PEG con- centration or SLS to PEG ratio to 1:1.0 reduces the increase in the total recovered oil amount by 10%. It is caused by the fact that the SLS-1.0PEG has the highest IFT value as com- pared to SLS-0.5PEG and SLS-0.8PEG. Therefore, the less oil is recovered with the latter. It shows that the ratio of 1:0.8 (SLS-0.8PEG surfactant) gives the highest increase in the total recovered oil yield by 12.22%. This increase is caused by the fact that SLS-0.8PEG has the lowest value of IFT (Table 1). Surfactants can reduce the interface tension between oil and brine solution so that more oil is recovered. Bera et al. [41] reported that the re- sidual oil in the core could be emulsified if the IFT value is low enough. Since the SLS-0.8PEG has the lowest IFT value, it is reasonable that SLS-0.8PEG gives the highest increase in the total recovered oil amount. 4. Conclusions A polymeric surfactant from rice husk and PEG was success- fully synthesized. The PEG introduction to the SLS surfac- tant could increase the hydrophilic property of the poly- meric surfactant. The increase in the hydrophilic property was due to the presence of the C−O−C group. The increase in the hydrophilic property positively affected the surfac- tant because it could reduce the IFT value. It was found that the IFT value decreased with the increase in the PEG con- centration. However, the IFT value decreased when the PEG concentration was too high. The lowest IFT value (0.386 dyne/cm) was obtained by the SLS-0.8PEG surfactant (SLS to PEG ratio of 1:0.8), which produced the highest (12.22%) increase in the addi- tional recovered oil after brine flooding. The results showed 0 1 2 3 4 5 6 0 10 20 30 40 50 60 70 80 90 100 O il R e c o v e r y ( % ) Pore Volume SLS-1.0PEG SLS-0.8PEG SLS-0.5PEG surfactant injection 10% 12.22% 11.52% brine injection Chimica Techno Acta 2022, vol. 9(4), No. 20229406 ARTICLE 8 of 9 that the rice husk, which is agricultural waste, could be uti- lized as a feedstock for the surfactant production. Supplementary materials No supplementary materials are available. Funding This work was supported by the Ministry of Education and Culture, Indonesia through the research project of Penelitian Disertasi Doktor (grant no. 258- 43/UN7.6.1/PP/2020), https://www.kemdikbud.go.id/. Acknowledgments The authors would like to acknowledge Integrated Labora- tory Universitas Diponegoro for providing the instrumental analysis. Author contributions Conceptualization: S.P., S.S., B.P. Data curation: R.W.S Formal Analysis: S.S., B.P., T.R. Funding acquisition: S.S. Investigation: D.D.S., A.A.P. Methodology: S.P., R.W.S., S.S., B.P. Project administration: S.S. Resources: S.P., R.W.S. Software: S.P. Supervision: S.S. Validation: S.P., S.S., B.P. Visualization: T.R. Writing – original draft: T.R., D.D.S., A.A.P Writing – review & editing: S.S., B.P., T.R. Conflict of interest The authors declare no conflict of interest. Additional information Authors IDs: S. Priyanto, Scopus ID 6507005325; R.W. Sudrajat, Scopus ID 57213605660; S. Suherman, Scopus ID 57194070495; B. 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