Synthesis of petroleum sulfonate via gas-phase sulfonation in rotating packed bed: Process optimization and interfacial tension-composition relationship
Graphical abstract
Introduction
At present, oil consumption accounts for the largest proportion of energy consumption in the world [1]. Most oil fields have reached maturity and begun to adopt the enhanced oil recovery (EOR) technologies, which play an increasing important role in the recovery process [2,3]. The EOR technologies include thermal method, miscible method and chemical method [4]. Among these, the method of surfactant flooding, which belongs to chemical method, is one of the most effective methods in the EOR process. Previous researchers have found that the indigenous surfactants prepared by the reactive component of crude oil could effectively reduce the oil–aqueous interfacial tension (IFT) [5,6]. Petroleum sulfonate (PS), a kind of anionic surfactant, has been widely used in EOR process due to its similar composition to crude oil and the ultra-low oil-aqueous IFT (10−3 mN/m orders of magnitude) [7].
Generally, PS was synthesized by sulfonating high-boiling petroleum fractions with sulfonating agents, such as sulfuric acid, oleum, and sulfur trioxide (SO3) so on [8]. Among these, gaseous SO3 has been widely used in the different sulfonation processes like alkylbenzenes sulfonation [9], primary alcohols sulfonation [10], and fatty acid methyl esters sulfonation [11] due to its low-cost and easy to prepare. In addition, using the gaseous SO3 as the sulfonating agent is less dangerous owing to its low concentration and without the transportation and storage. Therefore, the gaseous SO3 was adopted as the sulfonating agent to prepared the PS in this study.
The sulfonation process using gaseous SO3 as the sulfonating agent is a gas-liquid two-phase reaction process, which belongs to diffusion-controlled instantaneous reaction with strongly exothermic effect [12]. The sulfonation reaction process is mainly controlled by the gas film resistance and the reaction rate can be written as:where -rA is the overall reaction rate; kAg is the mass transfer coefficient in gas phase. Therefore, the gas-liquid mass transfer and heat- transfer of the sulfonation process requires to be intensified to achieve the high reaction rate, sulfonate yield as well as to avoid over-sulfonation. Furthermore, the viscosity of the system increases sharply as the reaction proceeds, which would impede the reaction process. Therefore, it is essential to solve these problem to obtain a desired yield of PS. However, the conventional sulfonation reactors mainly include stirred tank reactors (STR) and falling-film reactors (FFR) [13], [14], [15], [16]. In the STR, the liquid feedstock is added into the bottom of the reactor, into which gaseous SO3 diluted with air is flowed to react. Especially for the high viscosity systems, the STR exists relatively poor micromixing and gas-liquid mass transfer performance, and cannot achieve homogeneous distribution of reactant, easily leading to the increase of by-products and poor product quality. In the FFR, the liquid feedstock flows down in a film form along the tube wall and contacts gaseous SO3 diluted with air in cocurrent flow. As the liquid and SO3 flow along the tube, SO3 is absorbed on the surface of the liquid film and then reacts to form the sulfonate product. The viscosity of the reaction system increases sharply with the increase of conversion. As a result, the liquid film thickness increased to reduce the fluidity of reactants and gas-liquid mass transfer performance, leading to the occurrence of oversulfonation and coking. Therefore, a reactor with short residence time and good mass and heat transfer performance is desirable for the gas-liquid sulfonation process.
Rotating packed bed (RPB), which is a typical process intensification device, has been widely used to enhance the micromixing and mass transfer process [17]. The basic principle of RPB is to create a centrifugal field in which liquids are split into tiny liquid elements including liquid droplets, threads and thin films, resulting in a significant increase in gas-liquid contact area, micromixing and mass transfer efficiency [18]. Previous researches have reported that RPB has been used for the gas-liquid reaction system, such as sulfur dioxide, hydrogen sulfide and nitrogen oxide absorption [19,20]. Therefore, RPB can be adopted as a sulfonating reactor for petroleum fractions sulfonation to improve the reaction rate and sulfonate yield.
In this work, PS was synthesized via gas-phase SO3 sulfonation in the RPB. The effects of various operating conditions including reaction temperature (T), SO3/distillate oil molar ratio (η), SO3 volume concentration (ζ), distillate oil feeding rate (Q), rotation speed (N) and ageing time (t) on the content of active matter were investigated to obtain the optimal operating conditions. Also, the relationship between IFT at the oil-aqueous interface and the composition of PS was studied. In addition, the similarity of PS samples of different batches was evaluated by calculating the correlation coefficient.
Section snippets
Materials
The distillate oil was obtained from the Daqing Oil-field with a broad boiling range from 277.4 to 625 °C (Fig. 1), an average molecular weight of 360 and a kinematic viscosity of 16 Pa▪s in the temperature of 20 °C. It comprised 63.8% saturates, 31.6% aromatics and 4.6% resins. Other reagents such as pentane, isopropanol (IPA), sodium hydroxide (NaOH), sodium carbonate (Na2CO3) and sodium chloride (NaCl) were of analytically grade purchased from Aladdin Industrial (Shanghai).
Synthesis and separation of PS
PS was synthesized
Effect of reaction temperature (T)
Fig. 5 shows the effect of the T on the contents of active matter and unsulfonated oil at Q of 60 mL/min, N of 1800 rpm, ζ of 3.0 v%, η of 1.1, t of 60 min. The content of active matter increased from 32.1% to 42.5% while that of unsulfonated oil decreased from 54.7% to 43.8% with an increase of the T from 30 °C to 60 °C. Moreover, the content of active matter slightly decreased and that of unsulfonated oil increased with further increase in the T from 60 °C to 80 °C. The viscosity of the
Conclusions
In this work, PS with a high active matter was synthesized by gas-phase SO3 sulfonation in RPB. The effects of various operating conditions including reaction temperature (T), SO3/distillate oil molar ratio (η), SO3 volume concentration (ζ), distillate oil feeding rate (Q), rotation speed (N) and ageing time (t) on the content of active matter were investigated. The content of active matter can reach up to 42.5% at the optimal conditions of T = 60 °C, η=1.1, ζ = 3.0 v%, Q = 60 mL/min, N =1800
Novelty statement
This work first adopted the rotating paced bed (RPB) in the gas-phase SO3 sulfonation of distillate oil to prepare petroleum sulfonate (PS). Through process optimization, the content of active matter in the prepared PS reach up to 42.5% under the optimized operating conditions, which was 4.5% higher than that obtained in falling-film reactor (FFR) in industry. And the oil-aqueous interfacial tension (IFT) of the prepared PS could reach an ultra-low value of 1.41 × 10−3 mN/m. In addition, the
CRediT authorship contribution statement
Xiaoke Ma: Conceptualization, Methodology, Writing – original draft. Bing Liu: . Kun Dong: . Yong Yuan: . Guang-Wen Chu: . Hai-Kui Zou: . Bao-Chang Sun: Supervision, Resources, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was financially supported by the National Key R&D Program of China (No. 2016YFB0301500).
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