Preparation of a Water-Based Lubricant from Lignocellulosic

Lubricant properties such as kinematic viscosity, pour, cloud, and flash points, ... (19) In our previous study, LA was used to prepare lubricant base...
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Preparation of a Water-Based Lubricant from Lignocellulosic Biomass and Its Tribological Properties Hairui Ji, Xu Zhang,* and Tianwei Tan National Energy R&D Center for Biorefinery College of Life Science and Technology, Beijing University of Chemical Technology, Beijing 100029, P. R. China S Supporting Information *

ABSTRACT: Lignocellulosic biomass is considered as a major feedstock to produce value-added renewable chemicals. In this study, a new water-based lubricant was prepared using biomassderived levulinic acid (LA) and polyols such as ethylene glycol and glycerol. The products were separated by rotary film molecular distillation and characterized by 1H NMR and mass spectrometry. Lubricant properties such as kinematic viscosity, pour, cloud, and flash points, copper strip corrosion, and volatility at 120 °C were evaluated according to standard ASTM methods. Furthermore, the hydrolytic stability and tribological properties of the products were tested for water-based lubricants. The results indicated that glycerol ester of levulinic acid (LAGLE) exhibited superior lubricant properties, strong resistance to hydrolytic degradation, and excellent antiwear performance, implying that the biomass-derived LAGLE was a potential water-based lubricant.

1. INTRODUCTION Lubricants have played an increasingly important role in industries, automobiles, aviation machinery, helicopter transmissions, etc., by performing critical functions such as reducing friction, removing wear particles, increasing efficiency, minimizing energy losses, etc.1 Many manufacturing operations, such as metal-cutting and forming operations, oil extraction, and turning, milling, and drilling processes, require not only proper lubrication but also an adequate cooling performance.2 The water-based lubricants are regarded as the perfect candidate compared with conventional oil and grease lubricants, being ecofriendly, saving oil resources, and having high fluidity and superb thermal conductivity.3 Water with poor lubricity is unsuitable as a good lubricant. In order to improve its lubricating properties, the development of water-miscible oils and additives is a necessary and promising domain.4 So far, various water-based lubricant additives such as polyalkylene glycol ester,5 TiO2 nanoadditive,6 imidazoline borates,7 fullerene−styrenesulfonic acid copolymer,8 monolayer graphene oxide sheets,9 and lanthanum fluoride nanoparticles10 have been proposed. According to reported works, these additives noticeably improved the lubricating and cooling properties of the base fluids. Their applications were, nevertheless, restrained because of the properties of nonrenewability and nonbiodegradability posing a constant threat to ecology and groundwater reserves, with a large proportion of these lubricants being released into the environment.11 The exploration of green water-based lubricants is hence essential to preserving the environment. Sulek et al. reported that © XXXX American Chemical Society

biodegradable alkyl polyglucosides were used as lubricity additives to formulate multicomponent aqueous solutions for water-based lubricants.12 Emulsions of vegetable oils were prepared using ionic and nonionic surfactants for metal working fluids.13 It is reported that low-cost glycerol (GL) aqueous solutions with good biocompatibility and low-temperature properties have been applied in multiple fields as a better green lubricant.14−16 However, the aqueous solutions were not able to form an effective fluid film between friction surfaces when the water content was above 20%, which led to a high and unstable friction coefficient. Therefore, it is essential to develop a novel water-based lubricant with the characteristics of sustainability and biodegradability derived from renewable resources. Among various renewable resources, lignocellulosic biomass, composed of three major components (cellulose, hemicellulose, and lignin), is considered to be a promising and abundant material. Cellulose can be hydrolyzed to glucose and subsequently converted to 5-hydroxymethylfurfural (HMF) as the intermediate product. Further conversion of HMF generates levulinic acid (LA).17 LA, a five-carbon molecule with carboxylic acid and ketone functionalities, is regarded as one of the 12 most promising molecules derived from biomass.18 The existence of two functional groups provides Received: Revised: Accepted: Published: A

April 21, 2017 June 12, 2017 June 19, 2017 June 19, 2017 DOI: 10.1021/acs.iecr.7b01665 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research LA with excellent reactivity. Meanwhile, a larger lignocellulosic biomass allocation value (more than 40%) was obtained for LA production to maximize an economic objective function as opposed to ethanol, which has a low biomass allocation because of its significantly low price.19 In our previous study, LA was used to prepare lubricant base stocks by esterification with polyols such as neopentyl glycol, trimethylolpropane (TMP), and pentaerythritol.20 Among these three polyol ester products, TMP-tri-LA ester was used as the base stock for the production of lubricant with high performance because of its superior lubricant properties and excellent antiwear performance. Whereas this kind of ester was insoluble in polar solvents such as water, the excellent water solubility of LA with high polarity21 is beneficial to preparing water-based biolubricant. The synthesis of a water-soluble lubricant with sustainability and good biodegradability from lignocellulosic biomass would therefore be a promising development trend. In this study, the preparation of a water-based lubricant employing LA derived from lignocellulosic biomass and polyols such as ethylene glycol and GL was reported. Furthermore, the physicochemical properties, hydrolytic stability, and potential tribological performance of both products as a water-based lubricant were investigated. A possible mechanism for the antifriction performance was also tentatively discussed.

Figure 1. Schematic routes for the preparation of LAEGE (A) and LAGLE (B). collect the target product. The final 75.26 g of the LAEGE product (72.60 wt % of the residue above) with a purity of 98.78% was obtained during a second distillation at 125 °C and a vacuum of 0.008 mbar. 2.3.2. Preparation for Glycerol Ester of Levulinic Acid (LAGLE). The preparation of LAGLE was according to Figure 1B and performed as described in a previous publication.20 A mixture of 150 g of crude LA, 30 g of GL (LA:GL, about 4:1 molar ratio), and 1.80 g of sulfuric acid (98 wt %) was added into an electrically heated reactor. The reaction was conducted at 95 °C for 2 h with a vacuum of 200 mmHg for removal of the formed water. At the end of the reaction, the reactor was cooled with tap water. The reaction mixture (141.76 g) was refined by rotary film molecular distillation (VTA GmbH and Co. KG, Niederwinkling, Germany). After removal of 40.02 g of distillate (29.64 wt %) including sulfuric acid and excess LA at 140 °C and a vacuum of 1 mbar, 97.93 g of residue (69.08%, w %) was subsequently refined to collect the target product. The final 71.59 g of LAGLE (73.11 wt % of the residue above) with a purity of 94.16% was obtained during a second distillation at 225 °C and a vacuum of 0.009 mbar. 2.4. Viscosity. The viscosities of the product at 40 and 100 °C were measured by a constant-temperature viscosity bath (Dalian Wuzhou Petroleum Equipment Co., Ltd.) in accordance with ASTM D445. 2.5. Pour Point. The pour points of both products were determined using an automatic pour-point tester (Dalian Wuzhou Petroleum Equipment Co., Ltd.) according to ASTM D97 with 3 °C increments. 2.6. Flash Point. The flash points of both products were determined using a flash point tester (Dalian Wuzhou Petroleum Equipment Co., Ltd.) as per ASTM D93. 2.7. Cloud Point. The cloud-point measurements of both products were carried out in a cloud-point apparatus (Dalian Wuzhou Petroleum Equipment Co., Ltd.) as per ASTM D2500. 2.8. Copper Strip Corrosion. Determination of the corrosiveness of both products was investigated using a copper strip corrosion tester (Dalian Zhilin Technology Co., Ltd.) in accordance with the ASTM D 130 method. The tarnish level was obtained by a comparison with Copper Strip Corrosion Standards. 2.9. Volatility Determination. The volatilities of both products were determined according to ASTM D2878 in a volatility determinator (Dalian Wuzhou Petroleum Equipment Co., Ltd.). 2.10. Thermogravimetric Analysis (TGA). TGA was carried out on a PerkinElmer thermogravimetric differential thermal analyzer to detain the decomposition pattern of the product. The sample was heated in air at a heating rate of 10 °C/min to 600 °C. 2.11. Hydrolytic Stability Assessment. The hydrolytic stability assessment was determined according to ASTM D2619 (Beverage Bottle Method). After hydrolysis, aqueous solutions were directly used for measuring the change in the total acid number (TAN) without separation of the water layers and oil. 2.12. High-Frequency Reciprocating Rig (HFRR) Configuration. The HFRR wear tests of aqueous solutions consisting of 20%, 50%, 75%, and 100% water-soluble esters in water (volume basis) were

2. MATERIALS AND METHODS 2.1. Chemicals. Ethylene glycol (EG) and glycerol (GL) were purchased from Beijing Chemical Works (Beijing, China). Crude levulinic acid (LA) used in this work was prepared from hybrid poplar in our laboratory. Hybrid poplar (41.72% cellulose, 16.15% hemicellulose, and 21.08% lignin) was pretreated using a 1.12 mol/L toluenesulfonic acid (p-TsOH) solution at 125 °C for 1 h to remove hemicellulose. The residual solid was subsequently washed to neutral pH for further enzymatic saccharification. Enzymatic hydrolysis was carried out at 200 rpm and 50 °C on a shaking-bed incubator with 25 FPU/g of glucan CTec 2. Further conversion of a glucose solution in the presence of a 6.5% HCl catalyst at a temperature of 180 °C for 1 h generates a LA solution. Crude LA was collected after removing water and HCl catalyst in the liquid by rotary evaporation. Hydrochloric acid with a purity of 36.5%, sulfuric acid (98 wt %), and p-TsOH were supplied by the Tianjin Fuchen Chemical Corp. (Tianjin, China). All of the solvents with analytical grade were provided by Tianjin Fuchen Chemical Corp. (Tianjin, China) and used directly without purification. Liquid-state cellulase (100 FPU/mL) was supplied by Novozymes, Beijing, China. 2.2. Analysis. A Bruker AR X 400 spectrometer (400, 200 MHz) and a VG Auto Spec-M (Manchester, U.K.) were used to analyze the structure and molecular weight of the ester product, respectively. The purity of the product was determined by a GC-2010 gas chromatograph (Shimadzu, Nagoya Japan) according to a previous publication,20 equipped with a DB-1ht capillary column (J&W Scientific, Folsom, CA) and a flame ionization detector. The chromatogram was run at 350 °C of oven, injection, and detection temperature using N2 as the carrier gas and H2 as the flaming gas. 2.3. Synthesis Methods. 2.3.1. Preparation for Ethylene Glycol Ester of Levulinic Acid (LAEGE). The preparation of LAEGE was according to Figure 1A and performed as described in a previous publication.20 A mixture of 150 g of crude LA, 26 g of EG (LA:EG, about 3:1 molar ratio), and 1.76 g of sulfuric acid (98 wt %) was added into an electrically heated reactor. The reaction was conducted at 95 °C for 2 h with a vacuum of 200 mmHg for the removal of formed water. At the end of the reaction, the reactor was cooled with tap water. The reaction mixture (134.52 g) was refined in a rotary film molecular distillation (VTA GmbH and Co. KG, Niederwinkling, Germany). After removal of 29.66 g of distillate (22.05 wt %) including sulfuric acid and excessive LA at 140 °C and a vacuum of 1 mbar, 103.67 g of residue (77.07 wt %) was subsequently refined to B

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Industrial & Engineering Chemistry Research performed according to ASTM D6079. The testing plate (15 mm × 15 mm) was fixed in a 10 mL oil groove, a weighed cast-iron pin cylinder (6 mm length) was driven by electromagnetic oscillators in a back and forth movement at 50 Hz and 200 g of loading for 75 min, and the sliding scale was maintained at 2 mm.

The pour point of a lubricant characterized its performance and potential application. LAEGE and LAGLE exhibited lower pour points (−33 and −17 °C, respectively) than a commercial vegetable cutting fluid (−12 °C).22 Low pour point suggested that the molecular configurations of both products were more effective at disrupting molecule packing and they were conducive to use in cold climates. The flash point is defined as the minimum temperature at which a mixture of lubricant vapor and air can be ignited. Generally, the higher flash point the lubricant has, the less fire hazard that exists. Table 1 also showed the flash points of both products. LAEGE and LAGLE exhibited excellent thermal stability with comparable flash points of 202 and 205 °C, respectively, compared with a commercial vegetable cutting fluid (205 °C) and a mineral cutting fluid (175 °C).22 Such high flash points suggested that both products could be regarded as potential water-based lubricants with high performance.24 The cloud point of a lubricant is a good indicator of its lowtemperature fluidity. LAGLE had a cloud point of −8 °C, while LAEGE with fewer branches exhibited a much lower-temperature performance with a cloud point of −21 °C. These results were in agreement with a previous study about LA-based polyol ester;20 the molecular configuration created a steric barrier around the individual molecule and inhibited crystallization, resulting in a low cloud point.25 A copper corrosion measurement was also carried out in order to assess the corrosiveness of the product on metals. Corrosion was triggered easily by the presence of moisture and oxygen in polyol ester products. The severity of the determination on metals for products was judged based on the color of the copper strip according to Copper Strip Corrosion Standards (ASTM D130). 1a was the lowest class and indicated a slight tarnish on metal materials. The results in Table 1 indicate that the corrosion class for both LAEGE and LAGLE is 1a (slight tarnish), which is the same as that of commercial vegetable and mineral cutting fluids.22 Thus, both products had a low corrosion effect on metals. The volatility of the lubricant can reflect its potential loss and impacts the environment. Some specifications about the volatility of the lubricants had previously been enacted by industrial organizations in Europe and the U.S.26 In this study, LAEGE and LAGLE exhibited very low volatility with only 0.02% and 0.01% weight loss at 120 °C, respectively. This low volatility meets the requirement of water-based lubricants. TGA assesses the thermal stability of materials. In the past years, it has been used to measure the oxidation stability of lubricants.28,29 A high onset temperature (Tonset) would suggest a high oxidation stability of the lubricant. TGA of both products was tested, with the results as shown in Figure 2 and analytical results listed in Table 2. As can be seen, LAGLE possessed a better thermal stability than LAEGE. Tonset of LAGLE was 186 °C compared with 174 °C of LAEGE. Besides, a 20% weight loss was observed for LAEGE at 209 °C and LAGLE at 265 °C. Both products exhibited superior oxidation stability compared with a commercially available water-based lubricant from Petronas, which had lost 20% of its mass through degradation/evaporation at 200 °C.27 The weight loss of LAEGE and LAGLE reached 97% at 276 and 512 °C, respectively. There was no further weight loss with increasing temperature. Both products were, however, slightly susceptible to undergoing autoxidation reactions.

3. RESULTS AND DISCUSSION 3.1. Characterization and Lubricant Properties of LAEGE and LAGLE. The purities of the LAEGE and LAGLE products were up to 98.78% and 94.16% after separation and gas chromatography analysis, respectively. Their structures were characterized by an electrospray ionization mass spectrometry (ESI-MS; Figure S1) spectral study and a 1H NMR technique (Figure S2). For LAEGE. 1H NMR (CDCl3): δ 2.19 [s, 6H, 2 × (−CH3)], 2.61 [s, 4H, 2 × (−COCH2−)], 2.75 [s, 4H, 2 × (−CH2CO−)], 4.27 [s, 4H, 2 × (−OCH2−)]. ESI-MS: m/z 259.12 ([M + H]+). For LAGLE. 1H NMR (CDCl3): δ 2.19 [s, 9H, 3 × (−CH3)], 2.61 [s, 6H, 3 × (−COCH2−)], 2.75 [s, 6H, 3 × (−CH2CO−)], 4.10−4.31 [s, 4H, 2 × (−OCH2−)], 5.24 [s, 1H, 1 × (−COH−)]. ESI-MS: m/z 387.16 ([M + H]+). The molecular weights of the LAEGE and LAGLE products correspond fairly well with those of the molecular ions: 259.12 for [M + H]+ in Figure S1A and 387.16 for [M + H]+ in Figure S1B. The results for 1H NMR presented in Figure S2 are in agreement with their target structures. These results indicate that both kinds of water-based lubricant products were prepared successfully. The physicochemical properties for the two products such as the viscosity at 40 and 100 °C, pour, flash, and cloud points, copper strip corrosion, and volatility at 120 °C were investigated (Table 1). Table 1. Comparison of the Physicochemical Properties between LA Esters and Commercial Water-Based Lubricants (Metal-Cutting Fluids)22 property viscosity at 40 °C(mm /s) viscosity at 100 °C(mm2/s) pour point (°C) flash point (°C) cloud point (°C) copper strip corrosion volatility at 120 °C (%) 2

LAEGE

LAGLE

CVCFa

CMCFa

12.28 2.77 −33 202 −21 1a 0.02

73.02 7.31 −17 205 −8 1a 0.01

85 N/R −12 205 N/R 1a N/R

29 N/R N/R 175 N/R 1a N/R

CVCF: commercial vegetable cutting fluid. CMCF: commercial mineral cutting fluid. N/R: not reported in the literature. a

The relationship between the viscosity and temperature for a lubricant can be demonstrated by its kinematic viscosity, a key indicator that can directly determine the lubricant’s area of application. As shown in Table 1, LAGLE exhibited a higher viscosity at 40 °C (73.02 mm2/s) than LAEGE did (12.28 mm2/s). A similar trend was observed for the viscosity at 100 °C, with the values varying from 7.31 mm2/s (LAGLE) to 2.77 mm2/s (LAEGE). This was attributed to an increase of the present acyl functionalities.23 This result was in agreement with our previous work revealing the relationship between the viscosity and number of branches in esters.20 Especially, LAGLE showed a viscosity at 40 °C (73.02 mm2/s) similar to that of a commercial vegetable cutting fluid (85 mm2/s).22 C

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than those of LAEGE solutions, and this was attributed to the high molecular weight of LAGLE, which possessed a structure similar to those of the GL analogues.30 Also, LAGLE, with more branches, was more resistant to hydrolytic degradation compared with LAEGE because of more steric hindrance.25 3.3. Tribological Properties of LAEGE and LAGLE. 3.3.1. Coefficient of Friction (COF). The aqueous solutions consisting of 20%, 50%, 75%, and 100% water-soluble esters in water (v/v) were used for further measurement of the COF. Figure 3 showed the COF plotted against the sliding time of

Figure 2. TGA curves of LAEGE and LAGLE.

Table 2. Comparison of the Thermal Stabilities of LA Esters and a Commercial Water-Based Lubricant from Petronas27 product

Tonset (°C)

20 wt % loss (°C)

97 wt % loss (°C)

LAEGE LAGLE CLPa

174 186 N/R

209 265 200

276 512 300

a

CPL: commercial water-based lubricants from Petronas. N/R: not reported in the literature. Figure 3. Friction coefficients of aqueous solutions differing in water content.

3.2. Evaluation of the Hydrolytic Stability. The aqueous solutions consisting of 20%, 50%, 75%, and 100% water-soluble esters in water (v/v) were tested and analyzed for their hydrolytic stability. The test results are summarized in Table 3.

various samples. Obviously, ID water without any ester product kept a constantly high COF (0.57 on average) within the operation time. The COF diminished with increasing mass concentration. In particular, slight fluctuations of the COF of about 75% and 100% LAGLE samples were observed, which indicated that a stable fluid film could be formed between friction surfaces when the water content was lower than 25% in the aqueous solution. For the 100% LAGLE sample, the value of the COF, which was 0.09 on average, was lower than that of the 75% LAGLE sample (0.11 on average). The possible reason was that the kinematic viscosity of the aqueous solution decreased with the addition of water, and the film thickness formed by the fluid decreased. Shi et al. reported that there was a linear relationship between the film thickness and kinematic viscosity of a fluid at a certain rotation speed.15 A LAGLE aqueous solution with a water content higher than 25% showed a remarkable fluctuation of the COF. The low concentration of LAGLE in aqueous solution could not generate an effective fluid film between friction surfaces, which led to more solid-tosolid contact during the test and the COF increased obviously as a result. A similar phenomenon was reported by Shi et al., who used GL aqueous solutions as water-based lubricants.15 It can also be summarized from Figure 3 that the COFs of LAEGE solutions were not able to reach a steady state within the operation time. This indicated that an unstable fluid film formed in LAEGE aqueous solutions. It is explicitly found that LAGLE as a water-based lubricant exhibited better lubricating properties than LAEGE. 3.3.2. Wear Scar Diameter (WSD). The frictional wear of aqueous solutions consisting of 20%, 50%, 75%, and 100% water-soluble esters in water (v/v) were studied using a HFRR. The microscopic images of wear scars generated on the surfaces of tested samples are shown in Figure 4, and the results of the WSD are given in Figure 5. It had a similar trend with the COF.

Table 3. Comparison of the Hydrolytic Stability for Aqueous Solutions Differing in Water Content tested sample 100% LAEGE 50% LAEGE 20% LAEGE 100% LAGLE 75% LAGLE 50% LAGLE 20% LAGLE

initial TAN (mg of KOH/ g)

final TAN (mg of KOH/g)

copper strip weight loss (mg/cm2)

appearance of copper strips

0.18 ± 0.01

1.41 ± 0.06

0.96

1a

0.31 ± 0.02

3.94 ± 0.19

1.91

3b

0.39 ± 0.05

4.15 ± 0.11

2.64

3b

0.87 ± 0.09

1.35 ± 0.08

0.02

1a

0.91 ± 0.07

1.77 ± 0.06

0.26

1b

0.79 ± 0.11

2.02 ± 0.12

0.34

1b

0.93 ± 0.07

1.95 ± 0.17

0.41

1b

There was a significant increase in the final TAN, varying from 1.41 ± 0.06 mg of KOH/g (100% LAEGE) to 4.15 ± 0.11 mg of KOH/g (20% LAEGE) with an increase of the water content, suggesting that the amount of water had a significant influence on the hydrolytic stability of LAEGE. Evaluation of the copper strip weight loss (from 0.96 to 2.64 mg/cm2) and appearance (from 1a to 3b) clearly showed that the corrosion of the copper strip depended largely on the hydrophilic acidic substances. Compared with LAEGE, LAGLE showed a higher resistance to hydrolytic degradation. The variations observed in the final TAN (from 1.35 ± 0.08 to 2.02 ± 0.12 mg of KOH/ g), copper strip weight loss (from 0.02 to 41 mg/cm2), and appearance (from 1a to 1b) for LAGLE were significantly lower D

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Figure 4. Microscopic images of wear scars of aqueous solutions differing in water content.

polyol esters are well-known for providing good lubricity because of their polar structure at the end of the molecular chain.32−34 The second possible mechanism for lubrication was a synergistic effect of water and polyol ester molecules, eventually forming a low-viscosity water-containing nanofilm. This water nanofilm in the hydrogen-bonding network system was stable at ambient temperature.35 According to the mechanism for the reduction of polyhydric alcohols proposed by Matta et al.,35 superlow friction could also be associated with a nanometer-thick film containing substrate and water. This behavior was suggested by Raviv and Klein, who showed that the bound water molecules retained a shear fluidity characteristic of the bulk liquid, even when compressed to films of nanometer thickness.36 Lee and Spencer assumed that an aqueous lubrication film of poly(ethylene glycol) exhibited an extended conformation of brushes into the bulk water due to strong brush−water interactions, such as a “water-like film” that can significantly reduce the friction between two moving surfaces.37 We assume that superlow friction was related to the presence of a water-containing nanometer-thick tribofilm existing in the contact area. Comparatively, LAGLE exhibited a superior lubricity performance and excellent antiwear properties, which favors the use of this kind of polyol ester as a potential water-based lubricant.

Figure 5. WSDs of aqueous solutions differing in water content.

In general, the WSD diminished with increasing concentrations of the esters in aqueous solution. There was a significant reduction in the WSD for 75% (315 μm) and 100% (336 μm) LAGLE compared with other samples, which was in agreement with analysis of the COF. Then a stable fluid film could be formed between the friction surfaces, and friction was obviously reduced as a result. The highest value of the WSD (528 μm) was generated for the 20% LAGLE solution. The 20% LAEGE solution generated a larger WSD (526 μm) than ID water (433.5 μm) for corrosion by acid from the degradation of ester, which is in agreement with the result in Table 3 (4.15 ± 0.11 mg of KOH/g of the final TAN for evaluation of the hydrolytic stability). As a comparison, WSDs of 200−350 and 200−400 μm were observed for nonaqueous ester products from palm and palm kernel (E. guineensis) oils in previous publications, respectively.31 LAGLE solutions as water-based lubricants exhibited competitive antiwear properties. A possible mechanism for the antifriction performance was that long-chain polar molecules enhanced the molecular adsorption on the surface of the metal, and an effective fluid monolayer film was formed between friction surfaces when the appropriate amount of water existed in aqueous solutions, which led to a low and stable friction coefficient. Basically,

4. CONCLUSIONS In this study, a new water-based lubricant was prepared using biomass-derived LA and polyols such as EG and GL. The products were distilled out by rotary film molecular distillation and characterized using 1H NMR and MS techniques. The lubricant properties, hydrolytic stability, and tribological performance of the products were comprehensively evaluated. Of both products, LAGLE exhibited superior lubricant properties, strong resistance to hydrolytic degradation, and excellent antiwear properties. LAGLE can be regarded as a potential water-based lubricant stock. Our work provided a potential applied foreground for the preparation of sustainable water-based lubricants with strong hydrolytic stability and excellent antiwear performance from a renewable lignocellulosic biomass resource. E

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b01665. MS and 1H NMR spectra of LAEGE and LAGLE (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Phone: (+86)10 64448962. E-mail: [email protected]. cn. ORCID

Xu Zhang: 0000-0002-8214-0474 Tianwei Tan: 0000-0002-9471-8202 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are thankful for support from the National Key Research and Development Program of China (Grant 2017YFB0306800) and 111 Project (Grant B13005).

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REFERENCES

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DOI: 10.1021/acs.iecr.7b01665 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX