Study on the solubility between diesel and ABE (Acetone

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Biofuels and Biomass

Study on the solubility between diesel and ABE (Acetone–Butanol–Ethanol) with or without water Chao Jin, Zhenlong Geng, Xiyuan Zhang, Mengxing Ma, Jing Ji, Gang Wang, Chunfeng Guan, and Haifeng Liu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b02150 • Publication Date (Web): 03 Sep 2019 Downloaded from pubs.acs.org on September 3, 2019

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Study on the solubility between diesel and ABE (Acetone–Butanol–Ethanol) with or without water

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Chao Jina b, Zhenlong Genga, Xiyuan Zhanga, Mengxing Maa, Jing Jia, Gang Wanga, Chunfeng Guana*,

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Haifeng Liuc*

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School of Environmental Science and Engineering, Tianjin University, 300072 Tianjin, China Tianjin Key Lab of Biomass/Wastes Utilization, Tianjin University, 300072 Tianjin, China

b

State Key Laboratory of Engines, Tianjin University, 300072 Tianjin, China

c

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*Corresponding author: Chunfeng Guan, Tel./Fax: +86-22-87402200, E-mail: [email protected];

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Haifeng Liu, Tel: +86-22-27406842ext.8011; Fax: +86-22-27383362; E-mail: [email protected].

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Abstract: Acetone-Butanol-Ethanol (ABE) is an intermediate product in the microbial fermentation

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process for producing bio-butanol. ABE not only retains the advantages of oxygen-containing fuels, but

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also reduces the cost of single-component fuel recovery during fermentation process. In this study, ABE

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fuels of different component volumetric ratios (A:B:E of 1:1:1; 3:6:1; 6:3:1) were mixed with diesel to

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investigate the mutual solubility of blends with and without water. Meanwhile, the effects of ABE single

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component on the mutual solubility of ABE and diesel with and without water systems were further

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studied. The blending ratio of ABE in the blends changed from 10% to 90% in volume with an increment

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of 10%. Four environmental temperatures (0, 20, 40 and 60 °C) were adopted to investigate the influence

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of temperature on the mutual solubility. Results show that both ABE and diesel fuel is inter-soluble and

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can keep single-phase transparency, which is important reference value for ABE to be mixed with diesel

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fuel and used for the achievability of diesel engines. Among of all different volumetric ratios in ABE fuels,

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the concentration of water added into diesel and ABE blend increases gradually with the increasing of the

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circumstance temperature from 0 °C to 60 °C. Meanwhile, ABE (3:6:1) is well balanced to maintain

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mutual miscibility with water and diesel compared to ABE (1:1:1) and ABE (6:3:1). The reason is the

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amount of n-butanol contained in ABE has a great influence on the water retention capacity. Thus, ABE

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(3:6:1), which is produced by microbial fermentation processes (no dehydration and no surfactant added)

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should be a good substitute for diesel fuel.

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Keywords: Acetone–Butanol–Ethanol (ABE), mutual solubility, diesel fuel, water solubility.

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1. Introduction

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Due to the scarcity of fossil energy in recent years, the development of clean and sustainable energy

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sources are the imperious demands for energy safety and energy diversity, and thus renewable fuels have

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obtained great attention.1-3 Among of renewable fuels, oxygen-containing fuels can be burned more

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completely and thus has lower pollutant emissions. A large number of studies have been carried out to

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investigate the effect of oxygenated fuel on the combustion and emissions in diesel engines.4-10 The

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investigated oxygenated fuels include methanol, ethanol, propanol, butanol, pentanol, esters, ethers and so

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on.11-15 Among various oxygenated compounds, butanol has been recognized as a potential next-generation

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bio-fuel due to its superior fuel properties.16,17

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Compared to ethanol, butanol has the advantages of the higher cetane number and calorific value, the

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greater miscibility with diesel and the lower vapor pressure.18 Because of its hydrophobicity, it is easy to

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transport through pipelines, which results in a lower tendency to separate from diesel or gasoline when

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mixed with water.19 Furthermore, it has been reported that the use of butanol mixed with diesel

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significantly reduced soot emissions, while reduced or slightly increased the emissions of nitrogen oxide

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(NOx), carbon monoxide (CO) and hydrocarbons (HCs) under various operating conditions.11,20,21 However,

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one of the key issue is that the relatively high production costs of butanol makes it hard to be used in


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modern engines, which has become the topic of many other studies to reach lower costs on butanol

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production.22-33

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Acetone–butanol–ethanol (ABE) fermentation has an long history that goes all the way back to in

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1860s.18 Figure 1 shows a partial scheme for the production of butanol by ABE fermentation.20 The

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biosynthesis of acetone, butanol and ethanol has the same metabolic pathway from glucose to acetyl

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coenzyme A (acetyl-CoA), but then branched to different pathways to produce acetone, butanol and

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ethanol with volume percentages of roughly 22-33%, 62-74% and 1-6%, respectively.35

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Recently, ABE, as an intermediate product in the production of bio-butanol, can be used as an substitute

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fuel because it has the potential to remove the consumption of various production costs.13,36 If ABE can be

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used directly with fossil energy, it will save the cost of the separation process for each single component.

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Alternatively, if water-containing ABE can be used with fossil energy, it will also save on the cost of water

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removal during ABE production. Meanwhile, ABE can be mixed with diesel or gasoline and used in

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engines, fossil energy consumption and pollutant emissions can also be reduced. Zhou et al.18 have studied

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the combustion properties of the mixture of diesel and ABE in a constant volume chamber and found that

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diesel with 20% ABE has higher combustion efficiency than pure diesel. A typical ratio of acetone, butanol

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and ethanol during the formation process of ABE fermentation is 3:6:1, but this is adjustable to some

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extent. With the continuous development of molecular biology and related technical means, genetic

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engineering has been used to genetically modify bacterial strains, directly change or optimize the genetic

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traits of the strain to provide excellent high-yield strains for industrial production.37 With the development

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and progress of ABE fermentation technology, the volume percentages of butanol, ethanol and acetone

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during ABE fermentation can be precisely controlled according to changes in bio-fuel demand.38,39 Chang


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et al.2 have studied the combustion characteristics of diesel and ABE (A:B:E of 5:4:1), the results showed

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that the mixture of ABE and diesel containing 0.5 vol.% water not only improved the braking thermal

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efficiency, but also reduced the emission of pollutants, and made a good evaluation of water-bearing ABE.

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Diesel fuel has a large consumption in the world, if ABE can be blended with diesel and used in diesel

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engines, the conventional petroleum consumption and CO2 emissions will be reduced. However, little

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research has been conducted systematically to study the inter-solubility between diesel fuel and ABE with

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different component volume ratios. Meantime, ethanol has strong tendency to water absorption. Therefore,

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it is also very important to study the maximum water storage capacity when ABE blends with diesel fuel.

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Furthermore, the study on the inter-solubility between ABE and diesel fuel is of great economic

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importance for the corresponding optimization of the production process. If ABE can be used with diesel

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directly, it will save the cost of the separation process for each single component. Also, the energy of the

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ABE production process can be saved if the blends of ABE and diesel can contain part of water. Moreover,

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ABE is more hygroscopic than diesel. Thus, the hybrid system on ABE and diesel may absorb moisture

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from circumstance humidity during transportation and storage when the storage tank is not fully sealed.

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Then, the phase separation will occur due to excessive moisture in the blend. To avoid this problem, it is of

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great importance to study the water holding capacity of the blends of ABE and diesel. Therefore, the

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current research has important reference on seeking suitable bio-fermentation alternative fuels and the

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storage and transportation of future blending fuels, as well as reducing the fuel recovery cost of individual

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components in the fermentation process.

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Based on the above points, it is quite significant to research the solubility of ABE and diesel with or

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without water for energy saving. In this research, the volumetric ratio of acetone, n-butanol and ethanol in


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ABE changed to 1:1:1, 3:6:1 and 6:3:1. For the mixture of diesel-ABE, the concentration of diesel and

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ABE ranged from vol.10% to vol.90% and the increment was 10 vol%, then a little water was added into

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the blends of diesel-ABE by using a high-precision pipette each time. The study was conducted at four

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temperatures of 0, 20, 40, and 60 °C. Under all conditions, the solubility of diesel and ABE with or without

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water has been observed and the effect of single component in ABE on the mutual solubility has also been

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studied.

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2. Materials and methods

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In the paper, regular diesel produced by Sinopec Co., Ltd. was selected for use as experimental diesel.

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The water content of tested diesel is less than 0.02% in volume and the ash content is less than 0.1% in

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weight, and thus its influence on the solubility performance can be ignored. Analytical pure ethanol

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(content greater than 99.8%), n-butanol (content greater than 99.5%) and acetone (content greater than

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99.5%) were purchased from Jiangtian Chemical Co., Ltd. For ABE solution, there were three variations in

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the volume ratio of acetone, n-butanol and ethanol in ABE, including 1:1:1, 3:6:1 and 6:3:1 and named as

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ABE (1:1:1), ABE (3:6:1) and ABE (6:3:1), respectively. These mixtures of ABE were prepared with a 10,

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000 rpm blender. For the ratio of 3:6:1, it is the most common fermentation products for ABE.30,40 To better

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understand the effect of reducing n-butanol and increasing acetone, the ratio of 1:1:1 is used. From the

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study of ABE (6:3:1), it can be seen that ABE (6:3:1) has great potential to improve combustion

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efficiency.34,53 Above is the main reason why we choose these three ratios for ABE. The performance of

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individual fuels can be seen from Table 1.

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A ternary phase diagram was used to describe the phase behavior of a three-component system on

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diesel-ABE-water in this paper. The phase boundary was determined by the water titration method. In


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general, water-containing emulsions can be classified according to its appearance stability as follows:

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single-phase transparency > single-phase crystallization > two-phase crystallization > two-phase

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transparent.2 Stable single-phase transparent liquid fuels are needed in this research and future applications.

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For ABE–diesel blends, the concentrations of ABE ranged from 10% to 90% in volume with an increment

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of 10%. The beginning volume of ABE–diesel mixture was set to 3 mL and taken in a centrifugal tube.

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Then, a high-precision pipette with an accuracy of 0.1 μL was used to add a small amount of water. In

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order to quickly achieve a mixing system of the water-ABE-diesel three-component system, an oscillating

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scroll blender with revolutions per minute of 5000 was adopted. The free water droplets happened or the

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single-phase transparent blends became a turbid liquid at the temperature of the experiment, which meant

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that the phase separation occurred. At this point, the water content was set to the maximum water content

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in the system.

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To investigate the influence of temperature on the blend system, four ambient temperatures were

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selected, including 0, 20, 40, and 60 °C. The experimental temperatures were controlled by a

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water-blocking electrothermal incubator with an accuracy of 0.1 °C. To ensure the accuracy of the

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experiment, the result was the average values on three repeated tests. It should be noted that the results

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have been placed for a long time (7 days) and then confirmed by observing the final state of all the

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mixtures.

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The hydrophilic lipophilic balance (HLB) value is an important parameter of surfactant selection in the

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emulsification process.41 Generally speaking, the larger HLB value is, the stronger the hydrophilicity will

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be. The smaller the HLB value is, the stronger the lipophilicity will be. The HLB values of the ABE

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systems with different constituent volume ratios were further calculated in this study. The hydrophilicity of


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the hydrophilic group and the lipophilicity of the lipophilic group currently have two relatively simple

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representation methods, one is the Davis method and the other is the Griffin method. In this paper, the

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Davis method is used to calculate the HLB value of ABE single phase.55 The formula is as follows:

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HLBD=7+∑H-∑L

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where the subscript D represents the Davis method, and H represents the HLB value of each hydrophilic

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group, and L represents the HLB value of each lipophilic group. In the mixture, due to the HLB value of the nonionic surfactant has an additive property. The following formula can be used to calculate the HLB value after mixing two or more surfactants56:

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HLBAB = (HLBA × WA + HLBB × WB)/(WA + WB)

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where WA and WB express the amounts of surfactants A and B, respectively, HLBA and HLBB are the

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HLB values of A and B, respectively, and HLBAB is the HLB value of mixed surfactants.

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As can be seen from Fig. 2(a), in the absence of water, the blend of ABE and diesel in any proportion is

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a stable single-phase liquid which is homogeneous and transparent. When the water content exceeds the

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maximum water storage capacity, the stable homogeneous solution is destroyed. The initial phenomenon

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can be seen from Fig. 2(b) that the free water appears in the bottom of the liquid. It can be seen from Fig.

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2(c) that a turbid liquid appears when water is continuously added. In this paper, when the free water

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droplet happens or the single-phase transparent blend becomes a turbid liquid, it is considered as a

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separation point at this time. To let the results more visible and clearer, this study used an optical

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microscope to observe the micro-structure of Fig. 2(a) and the result of micro-structure is shown in Fig.

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3(a). It can be seen that the red area is a stable single-phase liquid of water-ABE-diesel system, and the

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gray area is the glass slide. The water droplet at the bottom of test tube as shown in Fig. 2(b) was aspirated


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by a high-precision pipette and then placed under a microscope to observe the micro-structure as shown in

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Fig. 3(b). It can be seen that the white bubbles are water droplets and the red area is single-phase

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transparent liquid. Considering the phase separation of between diesel and ABE may occur during

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transport, so it is necessary to make sure that the permissible water concentration in the blends of ABE and

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diesel to avoid phase separation during transport and utilization. In addition, as can be seen from Fig. 2(c),

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when excessive water is added, the mixture of ABE and diesel will become a turbid liquid. Therefore, a

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surfactant will be needed to balance the mixture, which exceeds the study in the current paper. Therefore,

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the single-phase liquid is the key point of this study as shown in Fig. 2(a) and Fig. 3(a).

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3. Results and discussion

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3.1 Solubility analysis of ABE and diesel

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3.1.1 Miscibility of ABE and diesel

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To mimic the use of fossil fuels and ABE fermentation products, diesel was blended with ABE of

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different component volumetric ratios (A:B:E of 1:1:1; 3:6:1; 6:3:1) to investigate mutual solubility. The

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concentration of ABE in the blends were varied from 10% to 90% in volume with an increment of 10%

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and four ambient temperatures were tested including 0, 20, 40 and 60 °C. Results indicate that ABE

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mixture (A:B:E of 1:1:1; 3:6:1; 6:3:1) can be miscible with diesel at all tested temperatures mentioned

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above.

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Although ABE mixture has good solubility with diesel, the single component among ABE has different

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characteristics. In the current study, n-butanol is well miscible with diesel in any proportion at ambient

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temperatures of 0, 20, 40 and 60 °C. The result is also similar to previous studies that the binary system of

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n-butanol and diesel is stable in any proportion and phase separation does not occur. 42,43 Both acetone and


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diesel can also blend well in the current study and the phase separation between acetone and diesel can

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only be appeared at the ambient temperature of 0 °C.

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However, ethanol is quite different from n-butanol and acetone. Some studies have shown that ethanol

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does not mix well with diesel. Some previous study works, such as He et al.44, Hansen et al.45, Liu et al.46,

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have found that ethanol dose not mix well with diesel mainly caused by temperature, hydrocarbon

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composition of diesel and water content in the blend. Figure 4 presents the temperature of phase separation

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in the mixture of diesel/anhydrous-ethanol. As can be seen from Fig. 4, the solubility drops sharply when

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decreasing circumstance temperature, finally leading to phase separation of diesel/anhydrous-ethanol

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system. No matter how much ethanol is added, the mixture of diesel/anhydrous-ethanol is completely

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miscible when the ambient temperature is higher than 40 °C. This is due to the fact that the solubility of

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substances usually increases with the increase of temperature. The process of mutual dissolution of two

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substances is the process of destroying the original inter-molecular forces and reassembling them. This

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process often requires energy. Therefore, as the temperature rises, the thermal motion of the molecule

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increases, which is conducive to the dispersion and diffusion of the molecule.48 The dynamic interfacial

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tension is affected by the temperature, which means that increasing the temperature can curtailed the time

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it takes for the interfacial tension to achieve balance. Ye et al.47 have studied the influence of temperature

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on the interfacial tension between the gemini surfactant solution and base oil, it was found that the

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inter-facial tension between surfactant and oil solution was very sensitive to temperature and decreased

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with increasing temperature. Therefore, at a certain temperature, the two substances of ethanol and diesel

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can completely dissolve each other.

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At the same time, it indicates that the concentration of ethanol in the mixture can also affect the


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solubility. As the blending ratio of ethanol increases, the higher ambient temperatures are required to avoid

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phase separation. The temperature of phase separation reach the highest and is close to 40 °C when the

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volume fraction of ethanol is 50%. After that, the temperature of phase separation decreases as the volume

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fraction of ethanol increases further. When the content of ethanol is relatively low, ethanol is easily

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dispersed and attracted around diesel to form mutual solubility. Meantime, when the ethanol content is

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relatively high, diesel is more easily dispersed and attracted around ethanol to form mutual solubility. In

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Fig. 4, the curve of ethanol volume from 0% to 50% can be regarded as the solubility curve of ethanol in

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diesel, which indicates that the solubility of ethanol in diesel increases with the increase of temperature.

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While, the curve of ethanol volume from 50% to 90% can be regarded as the solubility curve of diesel in

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ethanol, which indicates that the solubility of diesel in ethanol increases with the increase of temperature.

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When the ratio of ethanol to diesel is equal, the internal molecular attraction of ethanol and diesel is very

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strong, and the ability to disperse and dissolve each other is weak. It needs more energy, that is, higher

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temperature to help them dissolve each other, so the inflection point in Fig. 4 appears.

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In addition, the composition of diesel is also an important effect factor on the solubility between diesel

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and ethanol.57 In general, since aromatic hydrocarbons have a solubility factor and polarity closer to that of

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ethanol than other alkanes, the miscibility of aromatic hydrocarbons with ethanol is better than that of

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alkanes. Therefore, if the aromatic content in diesel fuel is high, the phase separation temperature with

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ethanol is lower. At the same time, the compatibility of ethanol and diesel is also significantly affected by

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the content of the light component in diesel. The density of light components is closer to that of ethanol,

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and it is easier to dissolve with each other. Therefore, if there are more light components in diesel, the

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solubility of ethanol can be increased and the phase separation temperature of ethanol-diesel is lower.


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Therefore, the effect of diesel composition on the solubility of ethanol and diesel is the result of the

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interaction of aromatics and light components. The proportion of specific inflection points and the required

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temperature are also closely dependent on the component of diesel fuel.

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3.1.2 Effect of n-butanol and acetone on the mutual solubility of ABE and diesel

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To explore the influence of n-butanol and acetone in ABE system on the miscibility of ABE and diesel,

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both acetone and n-butanol have been tested as a surfactant separately in diesel/anhydrous-ethanol system

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at 20 °C and 40 °C. Figure 5 presents the effect of acetone and n-butanol on the miscibility of ethanol and

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diesel. It can be seen that both anhydrous-ethanol and diesel can be kept stable on one-phase with the

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surfactant of acetone or n-butanol. As the ambient temperature rises, the addition of surfactant (acetone or

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n-butanol) decreases significantly. When the temperature is raised from 20 °C to 40 °C, the addition of

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n-butanol reduces 95.6% and the addition of acetone reduces 97.1%. This should be attributed that ethanol

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is more readily soluble in the oil system at higher temperatures.54 In addition, the thermal motion will be

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more intense with the increase of temperature, which facilitates the dispersion and diffusion of the

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molecules.46 Thus, the higher ambient temperature leads to alcohols being closer to oil and more miscible

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with diesel and lower addition of n-butanol or acetone is needed. At the same time, Figure 5 also shows

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that the blending ratio of ethanol in the mixture has influence on the solubility. As the ratio of anhydrous

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ethanol increases, more n-butanol is used to keep stable of the ternary system of ethanol, diesel and

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n-butanol. When the volume fraction of ethanol reaches 50%, the required amount of n-butanol reaches its

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peak value. After that, as the ratio of ethanol is further increased, the amount of n-butanol required is

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decreased. The amount of acetone is also changed as similar to that of n-butanol. Therefore, it can be found

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that when the volumetric ratio of diesel and ethanol is 1:1, the solubility of the system is the worst and the


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most amount of the surfactant is needed at a specific ambient temperature.

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Figure 6 presents the effect of acetone and n-butanol on phase stability at 20 °C. To let the results more

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visible and clearer, the ternary phase diagram was adopted to describe the phase behavior in this figure. It

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can be founded that the one-phase region of ternary system with n-butanol is larger than that of acetone at

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20 °C, which demonstrates that n-butanol has better solubilizing ability than acetone in ABE system. This

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may benefit from the high carbon content of n-butanol, which results in its non-polar alkyl group being

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better linked to diesel and the OH group being linked to ethanol. The carbon number of acetone is lower,

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and the mutual solubility with diesel is worse than that of n-butanol.

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3.2 Water solubility of ABE and diesel system

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3.2.1 Water solubility of ABE compound and diesel

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The water dissolving capacity of this system is studied in this part. To investigate the influence of

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temperature on phase stability, four different experimental temperatures at 0, 20, 40 and 60 °C were chosen

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for this research. Three different component volumetric ratios of ABE (3:6:1; 1:1:1; 6:3:1) were selected in

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the system of ABE-water-diesel to study the water capacity. Figure 7 presents the effect of three volumetric

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ratios on phase stability at different temperatures. It can be seen that, as the circumstance temperature

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increases from 0 °C to 60 °C, the amount of water added into diesel and ABE blends increases gradually.

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For example, among different volumetric ratios of ABE fuels, the allowable water amount for ABE (1:1:1)

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and diesel blends increases about 31.8 ％, as the circumstance temperature is raised from 0 °C to 20 °C.

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Accordingly, the allowable water concentration for ABE (1:1:1) and diesel blends increases about 31.8％

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and 28.3 ％ , as the circumstance temperature is raised from 20 °C to 40 °C and from 40 °C to 60 °C,

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respectively. The blending ratio of water in ABE (3:6:1) and ABE (6:3:1) also increases in the same trend.


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Thus, it can be prove that the high circumstance temperature is beneficial to the proper settlement of

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unstable phases of the mixture.

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To study the effect of different component volumetric ratios in ABE on phase stability, diesel was

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blended with ABE fuels of different component volumetric ratios (A:B:E of 1:1:1; 3:6:1; 6:3:1) and the

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water allowable ability were tested. Figure 8 presents the solubility of three mixtures of ABE, water and

258

diesel at 0, 20, 40 and 60 °C. It can be seen from the ternary phase diagram that each line represents the

259

phase boundary of the single-phase isotropic region from the an-isotropic region. The point above the line

260

is an-isotropic situation, and any point below the line is single-phase soluble area. It can be found that the

261

allowable water concentration increases in the system with the ABE content increases. Meanwhile, the

262

allowable water concentration of ABE (3:6:1) system is higher than that of ABE (1:1:1) and ABE (6:3:1)

263

system. As shown in Figure 8(a), the maximum water storage capacity in the ternary system including

264

ABE (3:6:1) is 6.0% when the circumstance temperature is 0 °C, while that of ABE (1:1:1) and ABE (6:3:1)

265

is 4.3% and 3.3%, respectively. Fig. 8 (b) & (c) show that the maximum water storage capacity of ABE

266

(3:6:1) system is 42% and 82%, 68% and 106% higher than that of ABE (1:1:1) and ABE (6:3:1) systems

267

respectively when the ambient temperature is 20°C and 40 °C. With the temperature increasing, the water

268

allowable ability of ABE (3:6:1) are more outstanding. Fig. 8 (d) shows that the maximum water storage

269

capacity of ABE (3:6:1) in the ternary system is 1.69 times and 2.29 times compare to the system including

270

ABE (1:1:1) and ABE (6:3:1) at 60 °C, respectively. The area of the soluble liquid phase was calculated

271

from the grey area of the three-phase diagram using the mathematical integration method in the "Origin"

272

software. The results are shown in Table 2, the numerical value represents the area of the soluble liquid

273

phase and the unit of the area value is arbitrary units (A.U.). It can be observed that the soluble liquid area


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

274

of diesel-ABE (3:6:1)-water system is larger than that of ABE (1:1:1)- and ABE (6:3:1)-diesel-water

275

system at 0, 20, 40 and 60 °C. That is to say, the water retention ability of in the system of ABE (3:6:1) and

276

diesel is the largest.

277

In general, the HLB value is an important parameter for surfactant selection during emulsification and

278

can be used to reflect the hydrophilic-lipophilic tendency of the surfactant.49 The HLB value of single

279

component and the mixed HLB value of ABE have been calculated in this section as shown in Table 3. The

280

HLB value of ABE (3:6:1) is lower than that of ABE (1:1:1) and ABE (6:3:1) and the ternary system with

281

ABE (3:6:1) as the surfactant has better water allowable ability than that of other system including ABE

282

(1:1:1) and ABE (6:3:1), respectively. Compare to ABE (3:6:1), although ABE (6:3:1) of acetone content

283

of 60% has good mutual solubility to water in chemical properties, this system with ABE (6:3:1) as

284

surfactant has less water solubility in three-component system. For example, the maximum allowable

285

water content of ABE (6:3:1) ternary system decreases from 8.5% to 4.7% when the temperature is 20 °C,

286

compare with ABE (3:6:1). The HLB value of ABE (3:6:1) is 8.85, while the HLB value of ABE (6:3:1) is

287

10.61. According to the rule of “the larger HLB value is, the stronger the hydrophilicity will be”, the

288

hydrophilicity of ABE (6:3:1) is greater than ABE (3:6:1). However, in the water solubility experiments of

289

ABE and diesel systems, ABE (3:6:1) has the largest allowable water content in the ternary system is

290

because the surfactant can reduce interfacial tension due to its directional arrangement on oil-water

291

interface, so its hydrophilic and lipophilic abilities should be properly balanced. If the hydrophilic or

292

lipophilic ability is too large, the surfactant will be completely dissolved in the water or oil phase, and

293

rarely exist in the interface, so it is difficult to reduce the interfacial tension, resulting in the stratification

294

or turbidity of single-phase liquid. As surfactants, ABE (3:6:1) has more balanced hydrophilic and


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lipophilic capacities than that of ABE (6:3:1), while ABE (6:3:1) is very hydrophilic and easily attracted by

296

a small amount of water and completely dissolved in water, resulting in stratification or turbidity of the

297

water-ABE(6:3:1)-oil ternary system. So, ABE (3:6:1) can better maintain the mutual solubility of water

298

and diesel oil and has the maximum allowable water content in ternary system. Similar results have been

299

obtained by Scharnagl et al.43 and they have found that higher polarity and the smaller alcohol molecular

300

size increased the affinity between water and alcohols, but decreased the affinity with oil. Compared with

301

ABE (1:1:1), ABE (6:3:1) has excellent mixing with water due to its higher acetone content, probably

302

because the polarity of acetone is 5.1,58 which is the biggest of the three different components of ABE.

303

However, ABE (6:3:1) has the least water storage capacity in the ternary system. That is to say, ABE (3:6:1)

304

is well balanced to maintain mutual miscibility with water and diesel. This conclusion is constructive to the

305

use of ABE (3:6:1) mixed with diesel or as a surfactant additive for water-containing ABE/diesel system.

306

This is the first time that ABE with these three different component volumetric ratios has been found to

307

have different amphiphiles in the ternary fuel system.

308

Figure 9 presents the schematic diagram of the polarity between ABE/diesel/water. It is well known that

309

water is almost immiscible with diesel and completely stratified at any temperature due to the large

310

difference in polarity, as shown in Fig. 9(a). As ABE is added into the mixture of water/diesel, ABE acts as

311

a surfactant and forms micelles with a non-polar moiety (alkyl groups) and a polar moiety (OH groups),

312

the schematic diagram is shown in Fig. 9(b). The non-polar alkyl group can be linked to the “molecule” of

313

diesel, the OH group is highly attractive to water molecule. The water and diesel are attracted to the

314

liquid/liquid interfacial film through ABE, and finally the single-phase transparent liquid is obtained.

315

Therefore, the more water added, the more ABE needed. When the amount of added water exceeds the


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

316

critical micelle concentration of ABE, the attraction between the hydrophilic portion of ABE and water is

317

greater than the attraction between the hydrophobic portion of ABE and diesel, which brings ABE closer to

318

water. When the added water exceeds the critical micelle concentration of ABE, ABE will attract water to

319

form water-in-oil as shown in Fig. 9(c). When the amount of water exceeds a lot compare to the critical

320

micelle concentration of ABE, since the hydrophobic portion of ABE has less affinity with water, the

321

hydrophobic portions of ABE attract each other to form an association, this association is called a micelle

322

as shown in Fig. 9(d). The micelle has various shapes such as a spherical shape, a layered shape, and a rod

323

shape, this is the process of phase separation.

324

3.2.2 Water solubility of ABE single component and diesel

325

In order to study the capability of single component/diesel blends to hold water, a high-precision pipette

326

was used to gradually drip water into the mixture until three-component system was no longer a stable

327

one-phase transparent liquid. Figure 10 presents the effect of temperature on the solubility of different

328

one-component systems. Firstly, with the increase of circumstance temperature, the amount of water added

329

to the three single components increases significantly. Secondly, acetone and ethanol have been layered

330

with diesel at some temperatures and no additional water can be added, while n-butanol and diesel are well

331

mixed at the experimental temperature. Thirdly, with the content of acetone, n-butanol and ethanol

332

increases, it can also be seen that the water storage capacity increases, while n-butanol has the largest

333

maximum water storage capacity in the ternary system. This benefits from its high carbon content and its

334

polarity is lower than that of acetone and ethanol. According to the HLB value, the value of n-butanol is

335

also the smallest compared to acetone and ethanol, and thus n-butanol is more lipophilic. This conclusion

336

is constructive that ABE (3:6:1) containing 60% n-butanol has the largest maximum water storage capacity


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Energy & Fuels

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in the ternary system. That is to say, n-butanol promotes the mutual solubility and has a great influence on

338

the water retention capacity in ABE system.

339

Figure 11 presents the water capacity of n-butanol at normal temperature. It can be seen that as the

340

volume of n-butanol increases, the water content of n-butanol remains about 20% of its own volume.

341

However, the current study have found that acetone and ethanol can be miscible with water at any ratio.

342

Therefore, the water solubility of n-butnaol is weaker than that of acetone and ethanol n-butanol and the

343

system of n-butanol/water will be layered easily. In fact, due to the influence of polarity, ethanol has the

344

strongest hydrophilic ability compare to acetone and n-butanol, which ultimately leads to the water content

345

of ethanol/diesel/water system is very low. For n-butanol, although its water solubility is not so good, the

346

system of n-butanol/diesel/water is constituted a relatively stable system. In other words, n-butanol is well

347

balanced to maintain mutual miscibility with water and diesel. Therefore, the system of

348

n-butanol/diesel/water and ABE (3:6:1)/diesel/water has the best water retention capacity.

349

4. Conclusion

350 351

In order to evaluate the solubility between diesel and ABE (Acetone–Butanol–Ethanol) with or without water, a series of experiments have been conducted. The main results are summarized as follows.

352

(1) At four different experimental temperatures (0, 20, 40 and 60 °C), ABE mixture (A:B:E of 1:1:1;

353

3:6:1; 6:3:1) is well miscible with diesel in any blending ratios. However, the single component among

354

ABE has different characteristics. N-butanol is well miscible with diesel in any proportion. Both acetone

355

and diesel can also blend well in the current study and the phase separation between acetone and diesel can

356

only be appeared at the ambient temperature of 0 °C. Ethanol does not mix well with diesel, and it is more

357

affected by temperature. When acetone and n-butanol are used in the dissolution of ethanol and diesel, it is


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

358

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found that n-butanol has better solubilizing ability than acetone.

359

(2) The allowable water concentration increases in the system with the ABE content increases and the

360

maximum allowable water content of the ABE (3:6:1) ternary system is the highest at four tested

361

temperatures, followed by ABE (1:1:1), ABE (6:3:1) is the worst. That is to say, ABE (3:6:1) containing

362

60% n-butanol has the largest water storage capacity in the ternary system. Meanwhile, in the water

363

solubility experiment of ABE single component and diesel, compared to acetone and ethanol, n-butanol

364

has the best water retention capacity. Although its water solubility is not so good, n-butanol can

365

maintain the stability of diesel and water. In a word, n-butanol promotes the mutual solubility and has a

366

great influence on the water retention capacity in ABE system.

well

367

(3) Based on the current study, it can be concluded that ABE (3:6:1) should be a well substitute for

368

diesel fuel. Since ABE (3:6:1) has the highest allowable water content compared to ABE (1:1:1) and ABE

369

(6:3:1), therefore, single-phase stability can be well maintained in the process of mutual solubility with

370

diesel, even if a small amount of water is present in the fuel during transportation and utilization.

371

Acknowledgement

372

The authors would like to acknowledge the financial supports provided by the National Natural Science

373

Foundation of China (Grant No. 51922076, 31300329).

374

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solutions of Extractum Taraxaci e radix cum herba aqu. siccum in light of selected values of general

514

Hildebrand-Scatchard-Fedors theory of solubility. Herba Polonica, 2016, 62(4): 49-65.

515

(56) Xu C, An C, Li H, et al. Effect of HLB numbers of surfactant on the rheological properties of

516

HMX-BASED energetic ink. International Journal of Energetic Materials and Chemical Propulsion,

517

2016, 15(5):397-411.

518

(57) Gerdes K R, Suppes G J. Miscibility of ethanol in diesel fuels. Industrial & Engineering

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Chemistry Research, 2001, 40(3): 949-956.

520

(58) Hemwimol S, Pavasant P, Shotipruk A. Ultrasound-assisted extraction of anthraquinones from

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roots of Morinda citrifolia. Ultrasonics Sonochemistry, 2006, 13(6): 543-548.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

522

Figure & Table Captions

523

Fig. 1 Fermentation pathways employed by Clostridium acetobutylicum.

524

Fig. 2 Physical appearance of ABE-diesel-water ternary phase system.

525

Fig. 3 The observation of micro-structure of ABE-diesel-water.

526

Fig. 4 The temperature of phase separation of the anhydrous ethanol/diesel mixture.

527

Fig. 5 Effect of acetone and n-butanol on the miscibility of ethanol and diesel.

528

Fig. 6 Effect of acetone and n-butanol on phase stability at 20 °C. (The gray area is a mutually soluble

529

area.)

530

Fig. 7 Effect of three volumetric ratios on phase stability at different temperatures.

531

Fig. 8 Effect of four temperatures on phase stability at different volumetric ratios.

532

Fig. 9 The schematic diagram of polarity between ABE/diesel/water.

533

Fig. 10 Effect of ABE single component on phase stability at different temperatures.

534

Fig. 11 Water capacity of n-butanol at normal temperature.

535

Table 1 Fuel properties.

536

Table 2 The area value of the soluble liquid phase in ABE and diesel mixture (The unit of the area is

537

arbitrary unit).

538

Table 3 The HLB value of the ABE single component and the mixed HLB value of the ABE.


Page 26 of 40

Page 27 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

539

540 541

Fig. 1 Fermentation pathways employed by Clostridium acetobutylicum.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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542 543

(a) single phase liquid

544

Fig. 2 Physical appearance of ABE-diesel-water ternary phase system.

(b) water droplets in blends


(c) turbid liquid

Page 29 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

545 546

(a) magnification of single phase liquid with 100 X

547 548 549

(b) magnification of water droplets in blends with 100 X Fig. 3 The observation of micro-structure of ABE-diesel-water.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

550 551

Fig. 4 The temperature of phase separation of the anhydrous ethanol/diesel mixture.


Page 30 of 40

Page 31 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

552 553

(a) effect of acetone on the miscibility of ethanol and diesel

554 555 556

(b) effect of n-butanol on the miscibility of ethanol and diesel Fig. 5 Effect of acetone and n-butanol on the miscibility of ethanol and diesel.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

557 558

(a) effect of acetone on phase stability at 20 °C.

559 560

(b) effect of n-butanol on phase stability at 20 °C.

561 562

Fig. 6 Effect of acetone and n-butanol on phase stability at 20 °C. (The gray area is a mutually soluble area)


Page 32 of 40

Page 33 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

563 564

(a) the blending ratio in ABE at 1:1:1

565 566

(b) the blending ratio in ABE at 3:6:1

567 568

(c) the blending ratio in ABE at 6:3:1

569

Fig. 7 Effect of three volumetric ratios on phase stability at different temperatures


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

570

571 572

(a) Ambient temperature at 0℃

573 574

(b) Ambient temperature at 20℃

575 576

(c) Ambient temperature at 40℃

577 578 579

(d) Ambient temperature at 60℃ Fig. 8 Effect of four temperatures on phase stability at different volumetric ratios.


Page 34 of 40

Page 35 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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580

581 582

Fig. 9 The schematic diagram of polarity between ABE/diesel/water.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

583

584

585 586

Fig. 10 Effect of ABE single component on phase stability at different temperatures.


Page 36 of 40

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587

Energy & Fuels

Fig. 11 Water capacity of n-butanol at normal temperature.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

588

589 590

Page 38 of 40

Table 1 Fuel properties. Properties

Diesel

N-butanol

Ethanol

Acetone

Molecular formula

C12–C25

C4H9OH

C2H5OH

C3H6O

Density at 288 K (g/mL)

0.833

0.813

0.795

0.791

Cetane number

52.6

25

8

-

Lower heating value (MJ/kg)

42.6

33.1

26.8

29.6

Oxygen content (wt%)

-

21.6

34.8

27.6

Stoichiometric ratio

14.3

11.21

9.02

9.54

Auto-ignition temperature (K)

503

658

707

833

Boiling point (K)

-

390.8

351.5

329.2

Flammability limits (vol.%)

0.6–5.6

1.4–11.2

4.3–19

2.6–12.8

Viscosity at 413 K (mm2/s)

1.9–4.1

2.63

1.08

0.35

Saturation pressure at 311 K (kPa)

0.3

2.27

13.8

53.4

Latent heat at 298 K (kJ/kg)

270

582

904

518

Note: Properties of diesel are from the tested results based on ASTM D975; properties of acetone are from;50,

ethanol and butanol are from;51, 52

591


51

properties of

Page 39 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

592

Table 2 The area value of the soluble liquid phase in ABE and diesel mixture (The unit of the area is

593

arbitrary unit). ABE(1:1:1)

ABE(3:6:1)

ABE(6:3:1)

0℃

104.57

188.63

89.88

20℃

137.78

254.27

103.81

40℃

181.61

304.98

149.40

60℃

232.94

387.89

188.19


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

594

Page 40 of 40

Table 3 The HLB value of the ABE single component and the mixed HLB value of the ABE. Chemical

Acetone

N-butanol

Ethanol

ABE(1:1:1)

ABE(3:6:1)

ABE(6:3:1)

HLB value

12.85

7.00

7.95

9.27

8.85

10.61


Study on the solubility between diesel and ABE (Acetone

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