Oil recovery from refinery oily sludge via ultrasound and freeze/thaw

Characterization and treatment of oily sludge: A systematic review

Oily sludge is a prevalent hazardous waste generated in the petroleum industry, and effectively treating it remains a key challenge for the petroleum and petrochemical sectors. This paper provides an introduction to the origin, properties, and hazards of oil sludge while summarizing various treatment methods focused on reduction, recycling, and harmlessness. These methods include combustion, stabilization/solidification, oxidation and biodegradation techniques, solvent extraction, centrifugation, surfactant-enhanced oil recovery processes as well as freezing-thawing procedures. Additionally discussed are pyrolysis, microwave radiation applications along with electrokinetic method utilization for oily sludge treatment. Furthermore explored are ultrasonic radiation techniques and froth flotation approaches. These technologies have been thoroughly examined through discussions that analyze their process principles while considering influencing factors as well as advantages and disadvantages associated with each method. Based on the characteristics of oily sludge properties and treatment requirements, a selection methodology for choosing appropriate oily sludge treatment technology is proposed in this study. The development direction of processing technology has also been explored to provide guidance aimed at improving efficiency by optimizing existing processing technologies. The paper presents a comprehensive treatment method for oily sludge, ensuring that all the parameters meet the standard requirements.

Molecular Dynamics Study on the Effect of Polyacrylamide on Electric Field Demulsification of Oil-in-Water Emulsion

The effect of the water-soluble polymer (partially hydrolyzed polyacrylamide, HPAM) in produced water on the demulsification process of the electric field was studied by molecular dynamics simulations. By comparing the coalescence process of oil droplets in the electric field environment with or without HPAM, we find that HPAM in the water phase can promote the coalescence of nearly oil droplets but hinder the deformation and migration of oil droplets. By analyzing the radial distribution function and interaction energy between molecules, we conclude that the existence of HPAM molecules can reduce the hydrophilicity of other molecules through their strong interaction with water, and sodium ions (Na+) have strong interaction with bound water in the process of breaking away from HPAM, thus leading the movement of water molecules. At the same time, the influence of HPAM molecules located between the two oil droplets on the demulsification process was also studied. The HPAM molecules and sodium ions located between the two oil droplets also affected the coalescence process of oil droplets under an electric field by interacting with water.

Advances in ultrasonic treatment of oily sludge: mechanisms, industrial applications, and integration with combined treatment technologies

In the petroleum sector, the generation of oily sludge is an unavoidable byproduct, necessitating the development of efficient treatment strategies for both economic gain and the mitigation of negative environmental impacts. The intricate composition of oily sludge poses a formidable challenge, as existing treatment methodologies frequently fall short of achieving baseline disposal criteria. The processes of demulsification and dehydration are integral to diminishing the oil content and reclaiming valuable crude oil, thereby playing a critical role in the management of oily sludge. Among the myriad of treatment solutions, ultrasonic technology has emerged as a particularly effective physical method, celebrated for its diverse applications and lack of resultant secondary pollution. This comprehensive review delves into the underlying mechanisms and recent progress in the ultrasonic treatment of oily sludge, with a specific focus on its industrial implementations within China. Both isolated ultrasonic treatment and its combination with other technological approaches have proven successful in addressing oily sludge challenges. The adoption of industrial-scale systems that amalgamate ultrasound with multi-technological processes has shown marked enhancements in treatment efficacy. The fusion of ultrasonic technology with other cutting-edge methods holds considerable potential across a spectrum of applications. To fulfill the goals of resource recovery, reduction, and neutralization in oily sludge management, the industrial adoption and adept application of a variety of treatment technologies are imperative.

Recent advances of ultrasound applications in the oil and gas industry

In the last two decades, ultrasound (US) technologies research has increasingly earned attention for applications in the oil and gas industry. Numerous laboratory and field research have proven ultrasonics as an efficient, sustainable and cost-effective technology for improving well productivity. This paper pursues the elaboration of a comprehensive review of the most recent research related to ultrasonic technologies for applications in the oil and gas industry. Statistical analysis of different functional categories and classification of the research publications were performed. Considering the research reviewed, there is a huge gap between numerical and field studies in comparison with the numerous laboratory studies, deeming it necessary to increase efforts on developing mathematical and numerical models and field-testing cases of the ultrasonic effect. A comprehensive review of the ultrasonic waves' mechanisms of action for enhanced oil recovery (EOR) and emulsification/demulsification was conducted. Despite the lack of consensus regarding the mechanisms, cavitation and thermal effects on wellbore fluid and formation rock have been widely accepted as two of the most influencing mechanisms. A compilation of the state-of-the-art research of numerical, laboratory and field studies in the last two decades was assembled. Most authors agreed that ultrasonics is a highly efficient method for EOR and emulsion treatment if the optimal conditions are identified and achieved. The development of screening criteria for the application of ultrasonic waves was recommended, as this technique and the same parameters should not be utilized for all reservoir types. Treatment with ultrasound waves has shown improvement of oil recovery efficiency rates of over 90% and viscosity reduction values over 80%. The most efficient results were observed when in combination with another conventional EOR method, where ultrasound boosts recovery efficiency. Potential new applications related to rock mechanics and additional research topics were also recommended.

Petroleum sludge formation and its treatment methodologies: a review

Different petroleum operations produce huge amount of oil sludge annually. For instance, US EPA estimates the annual sludge production of each US refinery of 30,000 tons, while the average oily sludge produced from petrochemical industries in China is estimated about 3 million tons per year. In the last year, our center could recover about 30,206 barrels of raw oil from 32,786 barrels of tank bottom sludge (TBS) for different petroleum companies. This sludge causes huge economic losses besides its negative environmental impacts. The accumulation of sludge in the tanks results in reducing the tanks' capacity for storing liquid crude, accelerating the corrosion of the tanks, delay in the production schedule, and disturbing the whole production operation. There are diverse treatment methodologies such as solvent treatment, addition of certain chemicals, and centrifuging. Of course, the environmental regulations and the overall cost limitations are very important in deciding the preferred applicable method(s). Although several works handled the problem of sludge deposition and treatment from different aspects, we intend to introduce a different work. First, composition, formation, types, and properties of TBS were reviewed. Then, environmental and economic problems caused by TBS were revised. At last, different methodologies applied for treatment of oily TBS to recover oil and safe disposal of hazardous remains were investigated focusing on the most straightforward and environmentally friendly protocols. It is expected that this review attracts the experts in petroleum chemistry, and other relevant fields and provides a comprehensive understanding of current sludge control and treatment research.

Simulation and Experimental Study of Solid-Liquid Extraction of Coal Tar Residue Based on Different Extractants

Coal tar residue (CTR) is recognized as a hazardous industrial waste with a high carbon content and coal tar consisting mainly of toxic polycyclic aromatic hydrocarbons (PAHs). The coal tar in CTR can be deeply processed into high-value-added fuels and chemicals. Effective separation of coal tar and residue in CTR is a high-value-added utilization method for it. In this paper, ethyl acetate, ethanol, and n-hexane were chosen as extractants to study the extraction process of coal tar from CTR, considering the mass transfer in the liquid phase outside the CTR particles and the diffusion inside the CTR particles, and a mathematical model of the solid-liquid extraction process of CTR was established based on Fick's second law. First, the mass-transfer coefficients (kf) and effective diffusion coefficients (De) of ethyl acetate, ethanol, and n-hexane in solid-liquid extraction at 35 °C were determined to be 1.54 × 10-5 and 4.99 × 10-10 m2·s-1, 1.14 × 10-5 and 3.57 × 10-10 m2·s-1, and 1.01 × 10-5 and 3.48 × 10-10 m2·s-1, respectively. Furthermore, the simulated values obtained by the model also maintained a high degree of agreement with the experimental results, which indicates the high accuracy prediction of the model. Finally, the model was used to investigate the effects of the solvent-solid ratio, temperature, and stirring speed on the extraction rates with the three extractants. According to the analysis with gas chromatography-mass spectrometry (GC-MS), among the three solvents, n-hexane extracted the highest content of aliphatic hydrocarbons (ALHs), ethyl acetate extracted the highest content of oxygenated compounds (OCs), and ethanol extracted the highest content of aromatic hydrocarbons (ARHs). The model and experimental data can be used to provide accurate predictions for industrial utilization of CTR.

Optical Tweezers-Based Measurements of Colloidal Forces between Asphaltene Thin Films: Effect of Ultrasonication

Oil production and processing often involve the treatment of water-in-oil emulsions stabilized by asphaltenes. The asphaltenes adsorb irreversibly at the water-oil interface and, by self-association at the interface, form a viscoelastic film that stabilizes the emulsions mechanically and sterically. Hydrophobic forces associated with these films may also contribute to the emulsion stability. A key step in treating these emulsions is to weaken the asphaltene film at the interface, and one way to do so is with ultrasonic treatment. The effect of ultrasonic waves on the interactions between asphaltene films was investigated at a silica-water interface using optical tweezers. Silica microparticles were aged in asphaltene solutions to form asphaltene coatings on their surfaces. The particles were dispersed in water, and interparticle force measurements were performed with optical tweezers to capture the steric force and hydrophobic force contributions. The asphaltene coating thickness and hydrophobic coefficient (a factor resembling the strength of the hydrophobic interaction) were obtained from fitting these forces. The effect of ultrasonication on the thickness of the asphaltene films on the surfaces of the particles was investigated. No change in the hydrophobic coefficient was observed upon changing the interfacial asphaltene concentration. The asphaltene film thickness increased with the concentration of the asphaltene solution and aging time. After treatment of the dispersion with ultrasonic waves for different durations (between 5 and 40 min), a significant reduction in the coating thickness was observed. This reduction was confirmed by thermogravimetric analysis (TGA) measurements. It is hypothesized that cavitation at the interface removed part of the surface layer of asphaltenes from the coated particles. Based on these findings, we proved that a low-power ultrasound field can effectively break asphaltene-stabilized water-in-oil emulsions.

Ultrasonication-flotation-advanced oxidation tertiary treatment of oil-based drilling cuttings

The treatment of oil-based drilling cuttings (OBDCs) with high oil content is difficult. In this study, a tertiary treatment of ultrasonication-flotation-advanced oxidation for treating OBDCs with a high oil content of 20.10 wt% was proposed for the first time. All stages of the treatment processes were optimised. The recommended parameters for ultrasonication at room temperature were a mass ratio of OBDCs to the degreaser of 1:8, an ultrasonication power of 600 W and treatment time of 30 min. After the ultrasonication treatment, the oil content of the OBDCs decreased from 20.10 wt% to 5.00 wt%. Flotation was performed at room temperature with a mass ratio of OBDCs to the degreaser of 1:10, a stirring speed of 400 rpm, an aeration head aperture of 3 μm and airflow rate of 400 mL/min under N2 injection for 60 min. After the flotation treatment, the oil content of the OBDCs decreased from 5.00 wt% to 2.01 wt%. Advanced oxidation was performed at room temperature with a mass ratio of OBDCs to water of 1:10, 3.57 wt% sodium persulphate in water, 4.17 wt% ferrous sulphate heptahydrate in water and ultrasonication power of 1000 W for 100 min. Following the advanced oxidation treatment, the oil content of the OBDCs decreased from 2.01 wt% to 0.58 wt%. The results of this study provide a new method and idea for treating OBDCs with high oil content.

New insight into desorption behavior and mechanism of oil from aged oil-contaminated soil in microemulsion

The intractable nature of oil-contaminated soil (OS) constitutes the chief limiting factor for its remediation. Herein, the aging effect (i.e., oil-soil interactions and pore-scale effect) was investigated by analyzing the properties of aged OS and further demonstrated by investigating the desorption behavior of the oil from the OS. XPS was performed to detect the chemical environment of N, O, and Al, indicating the coordination adsorption of carbonyl groups (oil) on the soil surface. Alterations in the functional groups of the OS were detected using FT-IR, indicating that the oil-soil interactions were enhanced via wind-thermal aging. SEM and BET were used to analyze the structural morphology and pore-scale of the OS. The analysis revealed that aging promoted the development of the pore-scale effect in the OS. Moreover, the desorption behavior of oil molecules from the aged OS was investigated via desorption thermodynamics and kinetics. The desorption mechanism of the OS was elucidated via intraparticle diffusion kinetics. The desorption process of oil molecules underwent three stages: film diffusion, intraparticle diffusion, and surface desorption. Owing to the aging effect, the latter two stages constituted the major steps for controlling oil desorption. This mechanism provided theoretical guidance to apply microemulsion elution for remedying industrial OS.

Deep dewatering of refinery oily sludge by Fenton oxidation and its potential influence on the upgrading of oil phase

Highly efficient dewatering is essential to the reduction and reclamation disposal of oily sludge, which is a waste from the extraction, transportation, and refining of crude oil. How to effectively break the water/oil emulsion is a paramount challenge for dewatering of oily sludge. In this work, a Fenton oxidation approach was adopted for the dewatering of oily sludge. The results show that the oxidizing free radicals originated from Fenton agent effectively tailored the native petroleum hydrocarbon compounds into smaller organic molecules, hence destructing the colloidal structure of oily sludge and decreasing the viscosity as well. Meanwhile, the zeta potential of oily sludge was increased, implying the decrease of repulsive electrostatic force to realize easy coalescence of water droplets. Thus, the steric and electrostatic barriers which restrained the coalescence of dispersed water droplets in water/oil emulsion were removed. With these advantages, the Fenton oxidation approach derived the significant decrease of water content, in which 0.294 kg water was removed from per kilogram oily sludge under the optimal operation condition (i.e., pH value of 3, solid-liquid ratio of 1:10, Fe²⁺ concentration of 0.4 g/L and H₂O₂/Fe²⁺ ratio of 10:1, and reaction temperature of 50 °C). In addition, the quality of oil phase was upgraded after Fenton oxidation treatment accompanying with the degradation of native organic substances in oily sludge, and the heating value of oily sludge was increased from 8680 to 9260 kJ·kg^-1, which would facilitate to the subsequent thermal conversion like pyrolysis or incineration. Such results demonstrate that the Fenton oxidation approach is efficient for the dewatering as well as the upgrading of oily sludge.

Highly Efficient Treatment of Oily Sludge by a Novel High-Speed Stirring Method at Room Temperature

Oily sludge is one of the main hazardous wastes which seriously endangers the ecological environment and human health. In this paper, in order to effectively treat oily sludge, a novel high-speed stirring (HSS) method was proposed to clean oily sludge, and the main parameters affecting the residual oil rate of oily sludge were studied experimentally. Firstly, the cleaning time and stirring speed were optimized in the one-stage HSS cleaning, and then the optimal cleaning time of two-stage HSS cleaning was determined by the response surface method. The results suggested that the oil can be efficiently separated by high-speed stirring at room temperature, and that the two-stage cleaning with a circular-hole outlet (Rotor-C) followed by a vertical hole-outlet (Rotor-V) presented the best effect. The optimal stirring speed was 6000 r/min, and the optimal cleaning times of the two-stage cleaning were 7 min and 8 min, respectively. After cleaning, the residual oil rate of the treated oily sludge was 1.65%, and the removal rate of the petroleum hydrocarbons was 84.3%.

Trend in Research on Characterization, Environmental Impacts and Treatment of Oily Sludge: A Systematic Review

Oily sludge is a hazardous material generated from the petroleum industry that has attracted increasing research interest. Although several review articles have dealt with specific subtopics focusing on the treatment of oily sludge based on selected references, no attempt has been made to demonstrate the research trend of oily sludge comprehensively and quantitatively. This study conducted a systematic review to analyze and evaluate all oily sludge-related journal articles retrieved from the Web of Science database. The results show that an increase in oily sludge-related research did not take place until recent years and the distribution of the researchers is geographically out of balance. Most oily sludge-related articles focused on treatment for harmfulness reduction or valorization with limited coverage of formation, characterization, and environmental impact assessment of oily sludge. Pyrolytic treatment has attracted increasing research attention in recent years. So far, the research findings have been largely based on laboratory-scale experiments with insufficient consideration of the cost-effectiveness of the proposed treatment methods. Although many methods have been proposed, few alone could satisfactorily achieve cost-effective treatment goals. To enable sustainable management of oily sludge on a global scale, efforts need to be made to fund more research projects, especially in the major oil-producing countries. Pilot-scale experiments using readily available and affordable materials should be encouraged for practical purposes. This will allow a sensible cost-benefit analysis of a proposed method/procedure for oily sludge treatment. To improve the treatment performance, combined methods are more desirable. To inform the smart selection of methods for the treatment of different oily sludge types, it is suggested to develop universally accepted evaluation systems for characterization and environmental risk of oily sludge.

Enhancing low-temperature thermal remediation of petroleum sludge by solvent deasphalting

Thermal treatment is a promising technique for treating petroleum sludge (PS). However, asphaltenes as a recalcitrant fraction of PS induce strong bounding between petroleum and minerals, and therefore lead to the need for high temperature and hence high energy consumption in thermal treatment of PS. In this study, a novel method combining a deasphalting pretreatment of PS with low-temperature thermal desorption (LTTD) was developed. The efficiency of deasphalting was found to be positively correlated to the ability of n-alkanes and asphaltene dispersants in dispersing asphaltenes. In treating six different kinds of PS, the residual oil contents were all below 2.5% after the deasphalting alone. Compared with direct thermal desorption at 600 °C for 1 h, dodecyl benzene sulfonic acid (DBSA)-assisted heptane deasphalting made thermal desorption at 350 °C for 1 h sufficient to treat these APS. The residual oil content of sludge after LTTD is lower than 0.45%. FT-IR, Raman spectra and XPS analysis confirmed that the carbon residue in APS after LTTD is primarily graphite state, which is extremely stable and does not migrate to the surrounding environment as compared with the crude oil in the APS. Hence, solvent deasphalting results in effective treatment of PS by LTTD, while the solvent can be recycled by distillation and crude oil recovered as value-added petroleum resource. The LTTD represents therefore a novel green strategy for treating PS and resource utilization.

Effect of the Anode Structure on the Performance of Oily Sludge Sediment Microbial Fuel Cells

The anode is considered to be a key factor to improve the single-chamber bioelectrochemical system's efficiency to degrade oily sludge in sediment while generating electricity. There are few studies on the effect of the anode structure on the performance of oily sludge MFCs systematically. In this paper, an oily sludge bioelectrical system was constructed using carbon felt and carbon plate as anode materials, adjusting the anode material arrangement as transverse and longitudinal, and using different anode materials from single to sextuple anodes. The results of this study showed that the rate of degradation of oily sludge was greater with carbon felt (17.04%) than with the carbon plate (13.11%), with transverse (23.61%) than with the longitudinal (19.82%) arrangement of anodes, and with sextuple anodes (33.72%) than with a single anode (25.26%) in the sediment microbial fuel cells (SMFCs). A similar trend was observed when the voltage, power density, and electromotive force (EMF) of SMFCs were estimated between the carbon felt and carbon plate, transverse and longitudinal arrangements, single and sextuple anodes. It is concluded that the proper adjustment of anode arrangements, using carbon felt as an anode material, and increasing the number of anodes to six may accelerate the rate of degradation of oily sludge in oily sludge sediment microbial fuel cells (SMFCs). Furthermore, the electricity generation performance was also improved.

Analysis of Pyrolysis Characteristics of Oily Sludge in Different Regions and Environmental Risk Assessment of Heavy Metals in Pyrolysis Residue

As a resource treatment method, pyrolysis realizes the recovery of oil and immobilization of heavy metals in oily sludge (OS). The results showed that the composition of OS had little effect on the trend of the whole pyrolysis process, but it had different effects on the mass loss and maximum weight loss rate at each pyrolysis stage. SEM-EDS results showed that the pyrolysis residue had a porous internal structure, which was similar to that of activated carbon. The elements S, Ca, O, Fe, Al, and Si were embedded in the carbon skeleton. After OS pyrolysis, the oil content of the solid residue was far less than 2%, which met the pollution control requirements for comprehensive utilization specified in China's oil and gas industry standard. At the same time, the ratio of exchangeable fraction decreased and the ratio of residual fraction increased after OS pyrolysis. The potential ecological hazard coefficient (E _r) of Cd in OS2, OS2-500, and OS2-600 was greater than 40, which were strong and medium hazards. The E _r values of OS2-700 and other metals were far lower than 40, which were low hazards. With the increase of pyrolysis temperature, the comprehensive ecological hazard index (RI) of heavy metals in the residue gradually decreased and the RI value of OS2-700 decreased to 28.01. Therefore, the pyrolysis residue had an internal porous structure and controllable environmental risk. It could be used as an adsorption material for heavy metals to realize the comprehensive utilization of OS.

Petroleum sludge treatment and disposal techniques: a review

Petroleum sludge is a solid emulsified waste and contaminant commonly produced in the petroleum industry. In the recent past, there has been increased business growth in the oil sector, resulting in increased volumes of oily sludge characterized by high viscosity and toxicity. Therefore, sludge treatment before discarding is extremely necessary. This review seeks to highlight various conventional and evolving approaches in the treatment, recovery, and disposal of petroleum sludge and assess their suitability under various conditions.

A review of application and development of combustion technology for oil sludge

Oil sludge is a typical hazardous waste in the petrochemical and electric power industry. It has complex components and special properties, and has serious hazards to humans, plants, water, and soil. Therefore, how to realize the effective disposal of oil sludge has become an urgent issue to be solved worldwide. Among the existing oil sludge treatment approaches, combustion has been considered to be a promising technology to realize the large-scale industrial application. In the present work, the characteristics of oil sludge were described in detail. The application and development of oil sludge combustion technology were critically summarized and discussed, including factors affecting combustion, drying process, combustion characteristics, synergistic treatment technology, and formation and control of secondary pollution. Besides, the development of combustion equipment, and integrated thermal treatment technology for oil sludge were prospected. This work can be used for guiding the industrial disposal of oil sludge.

The Formation, Stabilization and Separation of Oil–Water Emulsions: A Review

Oil–water emulsions are widely generated in industries, which may facilitate some processes (e.g., transportation of heavy oil, storage of milk, synthesis of chemicals or materials, etc.) or lead to serious upgrading or environmental issues (e.g., pipeline plugging, corrosions to equipment, water pollution, soil pollution, etc.). Herein, the sources, classification, formation, stabilization, and separation of oil–water emulsions are systematically summarized. The roles of different interfacially active materials–especially the fine particles–in stabilizing the emulsions have been discussed. The advanced development of micro force measurement technologies for oil–water emulsion investigation has also been presented. To provide insights for future industrial application, the separation of oil–water emulsions by different methods are summarized, as well as the introduction of some industrial equipment and advanced combined processes. The gaps between some demulsification processes and industrial applications are also touched upon. Finally, the development perspectives of oil–water treatment technology are discussed for the purpose of achieving high-efficiency, energy-saving, and multi-functional treatment. We hope this review could bring forward the challenges and opportunities for future research in the fields of petroleum production, coal production, iron making, and environmental protection, etc.

Bacterial diversity and competitors for degradation of hazardous oil refining waste under selective pressures of temperature and oxygen

Oil refining waste (ORW) contains complex, hazardous, and refractory components, causing more severe long-term environmental pollution than petroleum. Here, ORW was used to simulate the accelerated domestication of bacteria from oily sludges and polymer-flooding wastewater, and the effects of key factors, oxygen and temperature, on the ORW degradation were evaluated. Bacterial communities acclimated respectively in 30/60 °C, aerobic/anaerobic conditions showed differentiated degradation rates of ORW, ranging from 5% to 34%. High-throughput amplicon sequencing and ORW component analysis revealed significant correlation between bacterial diversity/biomass and degradation efficiency/substrate preference. Under mesophilic and oxygen-rich condition, the high biomass and abundant biodiversity with diverse genes and pathways for petroleum hydrocarbons degradation, effectively promoted the rapid and multi-component degradation of ORW. While under harsh conditions, a few dominant genera still contributed to ORW degradation, although the biodiversity was severely restricted. The typical dominant facultative anaerobes Bacillus (up to 99.8% abundance anaerobically) and Geobacillus (up to 99.9% abundance aerobically and anaerobically) showed oxygen-independent sustainable degradation ability and broad-spectrum of temperature adaptability, making them promising and competitive bioremediation candidates for future application. Our findings provide important strategies for practical bioremediation of varied environments polluted by hazardous ORW.

Novel conditioner for efficient dewaterability and modification of oily sludge with high water content

The oily sludge with high water content (OS) was dewatered, modified, and converted into solid fuel by a novel chemical conditioner (OSO-101). The effect of OSO-101 dosage on the dewaterability of OS was studied, showing that OSO-101 dosage of 15% (wt.) could achieve the best dewaterability efficiency of OS (98.18%). Meanwhile, compared with some conventional conditioners, OSO-101 developed by our team was more effective in improving OS dewaterability efficiency. And OSO-101 may have free radical reaction, polar reaction, and redox reaction with petroleum hydrocarbons in OS, thereby polymerizing and forming condensed solid structures. The calorific value change of OS after conditioning, heavy metal content, and dioxin content of fly ash leached from incinerated product were measured for resource analysis and environmental assessment. Results showed that the resultant OS fuel blocks had extremely low content of heavy metals, dioxins, and other toxic and hazardous substances leached from fly ash. And this process did not require secondary treatment and fully met environmental protection emission standards. Additionally, OSO-101 had certain economic rationality and could effectively recover the calorific value contained in OS. This research is expected to provide new insights for efficient dewaterability and modification of OS, as well as subsequent resource utilization and harmless treatment, bringing potential environmental and economic benefits.

Application of a Fenton process for the pretreatment of an iron-containing oily sludge: A sustainable management for refinery wastes

The feasibility of a Fenton-type process for the pretreatment of an oily refinery sludge has been explored taking advantage of the iron contained in the own sludge. This process reduces the content of total petroleum hydrocarbons (TPHs) accompanied by an increase in the total organic carbon concentration in the liquid phase. The effect of the temperature and the hydrogen peroxide loading was thoroughly studied in this work being the oxidant concentration the most critical parameter. Under 60 °C and 90 g/L of initial hydrogen peroxide concentration, the Total Organic Carbon (TOC) of the liquid phase was increased up values of 1336 mg/L and with a remarkable contribution of acetic acid as final oxidized compound (396 mgC/L). Additionally, nitrogen and phosphorous compounds were also dissolved in the aqueous phase achieving values of 250 mg/L and 7 mg/L for total Kjeldahl nitrogen and total phosphorous, respectively. Respirometry assays of the aqueous phase after the Fenton pretreatment have evidenced an increase of biodegradability up to 49% which makes this phase suitable for further biological processing in the refinery scheme. The reduction of the content of TPHs (61%) of the oily sludge, has also improved the settleability of the treated effluent (reducing the capillary suction time (CST) in ca. 88%).

Characterization of heavy metals and oil components in the products of oily sludge after hydrothermal treatment

In this study, the method combining hydrothermal treatment (HT) and in-situ mechanical compression (MC) is used to treat oily sludge. The possible transfer and reaction pathways of different oil components during the process of HT&MC were investigated. In addition, the leaching toxicity, distribution, and risk of heavy metals in oily sludge treated in different temperatures and residence times were evaluated. The results revealed that siloxane and heavy oil components are left in the solid residue, and the light oils and oils with hydrophilic groups are transferred to hydrothermal fluids. The content of Cd, Cr, Pb, and Zn in form of F4 (residual) in the solid residue obtained at a hydrothermal temperature of 240 °C and residence time of 60 min increased by 7.37%, 1.21%, 3.06%, and 9.97%. This reduced the biological availability and environmental risk of heavy metals in the treated oily sludge. Meanwhile, the result of FT-IR illustrated an increase in hydroxyl groups of alcohols, phenols and organic acids, which have a beneficial effect on the adsorption of heavy metals and other pollutants. All results indicated that HT&MC might be a suitable pretreatment method for the stabilization of heavy metals in oily sludge.

Enhanced Separation of Oil and Solids in Oily Sludge by Froth Flotation at Normal Temperature

Oily sludge (OS) contains a large number of hazardous materials, and froth flotation can achieve oil recovery and non-hazardous disposal of OS simultaneously. The influence of flotation parameters on OS treatment and the flotation mechanism were studied. OS samples were taken from Shengli Oilfield in May 2017 (OSS) and May 2020 (OST), respectively. Results showed that Na2SiO3 was the suitable flotation reagent treating OSS and OST, which could reduce the viscosity between oil and solids. Increasing flotation time, impeller speed and the ratio of liquid to OS could enhance the pulp shear effect, facilitate the formation of bubble and reduce pulp viscosity, respectively. Under the optimized parameters, the oil content of OST residue could be reduced to 1.2%, and that of OSS could be reduced to 0.6% because of OSS with low heavy oil components and wide solid particle size distribution. Orthogonal experimental results showed that the impeller speed was the most significant factor of all parameters for OSS and OST, and it could produce shear force to decrease the intensity of C-H bonds and destabilize the OS. The oil content of residue could be reduced effectively in the temperature range of 24–45 °C under the action of high impeller speed.

Petroleum oil and products recovery from oily sludge: Characterization and analysis of pyrolysis products

Oily sludge (OS) has attracted special interest because of its hazardous nature and high potential as an energy resource. This study investigated the oil recovery from OS by thermal cracking and catalytic pyrolysis. The oil yield increased when the temperature exceeded 450 °C and reached a maximum (76.84 wt%) at 750 °C. Catalysts significantly improved the quality of oil produced during catalytic pyrolysis. Aromatic hydrocarbons were dominant (10.01-52.69%) in pyrolysis oil (PO) from OS catalytic pyrolysis, and the catalysts significantly reduced the presence of oxygen heterocycles. In addition, KOH and CaO reduced the I_D (D-band peak intensity)/I_G (G-band peak intensity) of OS char (OC) and increased the degree of graphitization. Owing to its higher iodine adsorption value and methylene blue (MB) adsorption value, OC exhibits potential as an adsorbent. The environmental assessment and potential applications of OC, along with possible reaction mechanisms and kinetic characteristics, are also discussed.

Mechanism and Characteristics of Oil Recovery from Oily Sludge by Sodium Lignosulfonate Treatment

The separation of oil components from oily sludge is an important component of soil remediation and energy recovery. Therefore, establishing a green and efficient separation technology is of great significance. In this study, oily sludge was separated using sodium lignosulfonate (SL) treatment. The effects of temperature, SL concentration, rotate speed, time, and pH on the oil removal rate were studied. The optimal conditions were as follows: temperature, 30 °C; SL concentration, 2.0 g·L-1; rotate speed, 200 rpm; time, 60 min; and pH 11. The maximum oil removal rate was 83.21%. The physicochemical properties of oily sludge were analyzed. The soil was looser, and the contact angle (55°) of the soil surface was reduced. Alkanes, aldehydes, ketones, carbonic acids, benzene rings, and alicyclic ethers were removed. The result shows that the SL treatment removed a wider range of petroleum hydrocarbon and had a stronger oil removal capacity. It provides a new method for the green and efficient separation of oily sludge.

A review of the interfacial stability mechanism of aging oily sludge: Heavy components, inorganic particles, and their synergism

Oily sludge is widely produced in the processes of petroleum exploitation, storage, transportation, and refining, and becomes more stable during aging. The interfacial stability of aging oily sludge hinders the recovery and disposal of oil resources. This review summarizes the interfacial film stability of aging oily sludge, which occurs through the formation of viscoelastic and rigid bilayer interfacial films between heavy components (asphaltenes and resins) and inorganic particles. The bilayer interfacial films enhance interfacial film strength and hinder the aggregation of droplets, contributing to the formation of a stable and high-viscosity oil-water-solid three-phase mixture. Recent demulsification technologies for reducing the stability of interfacial films have been classified as follows: removing heavy components, changing asphaltene aggregate structure, and reducing inorganic particle content. More efficient demulsification technologies are expected to be developed by deeply analyzing the microstructure and interfacial properties of asphaltenes and resins, as well as comprehensively studying the complex interactions among various components. This review constructs a bridge between the stability mechanism and the corresponding destabilization methods, which would promote future studies in aging oily sludge treatment.

The sludge-based adsorbent from oily sludge and sawdust: preparation and optimization

Sludge-based adsorbent (S-AB) converted by oily sludge can make full use of the precious resource. In this paper, oily sludge and discarded sawdust are used to prepare adsorbent through chemical activation. The adsorbent prepared is used to adsorb raw petroleum. Firstly, the most reasonable chemical activator ZnCl₂ is ascertained through parallel comparative experiments. The characterization results of N₂-adsorption are consistent with adsorption experiment results, which shows that higher mesopore surface area and volume are benefitted by the adsorption process. Secondly, the optimization of preparation technology is investigated through orthogonal experiments after parallel comparative experiments. The adsorption capacity of S-AB-ZnCl₂ is stronger when the preparation conditions are as follows: an activation temperature of 550°C, an activation time of 3.5 h, a solid-liquid ratio of 1:1.5, a sludge-sawdust ratio of 1:0.5 and the heating rate of 15°C/min. The maximum quantity adsorbed Q₀ = 434.78 mg/g, calculated through the Langmuir adsorption isothermal models, of S-AB-ZnCl₂ prepared under optimized condition is higher than that before optimization. In addition, the most reasonable kinetics fits were of the second-order model.

Comprehensive characterization of an oily sludge from a petrol refinery: A step forward for its valorization within the circular economy strategy

Refinery treatment plants produce large quantities of oily sludge during the petroleum refining processes. The hazardousness associated with the disposal of these wastes, make necessary the development of innovative technologies to handle it adequately, linked to the concepts of circular economy and environmental sustainability. This work provides for the first time a methodology for the deep characterization of this kind of wastes and consequently new insights regarding its valorization. A review of works dealing with the characterization of this type of wastes has been addressed evidencing the complexity and variability of these effluents. The oily sludge under study contains a high concentration of Chemical Oxygen Demand of 196 g COD/L, a Total Kjeldahl Nitrogen of 2.8 g TKN/kg, a phosphorous content as PO₄^3- of 7 g/kg, as well as a great presence of heavy metals in a different range of concentrations. This sludge is composed of three different phases: oily, aqueous and solid. The oily and the solid phases present high percentages of carbon content (84 and 26%, respectively), related to the presence of alkanes ranged from n-C₉ to n-C₄₄. Therefore, it could be possible their valorization by the synthesis of catalyst and/or adsorbents. A dark fermentation process could be also proposed for the oily phase to obtain H₂ as an alternative energy source. Finally, the aqueous phase contains low carbon and nutrients concentration. A previous thermal pre-treatment applied to the oily sludge might increase nutrient and organic loading in the aqueous phase due to solid destruction, making this aqueous effluent suitable for a further conventional biological treatment.

A critical review on energy recovery and non-hazardous disposal of oily sludge from petroleum industry by pyrolysis

This review systematically reports the pyrolysis of oily sludge (OS) from petroleum industry in regards to its dual features of the energy recovery potential and the environmental risks. The petroleum hydrocarbons are the nonbiodegradable fractions in OS that possess hazardous properties, i.e. ignitability and toxicity. Besides, complicated hazardous elements (i.e. N, S and Cl) and heavy metals inherently existing in OS further aggravate the environmental risks. However, the high oil content and heating value of OS contribute to its huge energy resource potential. Considering the energy demand and the environmental pressure, the ultimate purposes of the OS management are to enhance the oil recovery efficiency to minimize the oil content as well as to stabilize the hazardous elements and heavy metals into the solid residue. Among various OS management technologies, pyrolysis is the most suitable approach to reach both targets. In this review paper, the pyrolysis principle, the kinetics and the product distribution in three-phases are discussed firstly. Then the effects of operating parameters of the pyrolysis process on the quality and the application potential of the three-phase products, as well as the hazardous element distribution are discussed. To further solve the dominant concerns, such as the oil content in the solid residue, the pyrolytic oil quality and the migration of hazardous elements and heavy metals, the potentials of the catalytic pyrolysis and the co-pyrolysis with additives are also summarized. Also, the typical pyrolysis reactors are then presented. From the perspective of the energy efficiency and the non-hazardous disposal, the integrated technology combining the pyrolysis and the combustion for the OS management is recommended. Finally, the remaining challenges of OS pyrolysis encountered in the research and the industrial application are discussed and the related outlooks are itemized.

Ecotoxicity of oil sludges and residuals from their washing with surfactants: soil dehydrogenase and ryegrass germination tests

Oil sludge washing (OSW) with surfactants and co-solvents is used to recover the oil, and this process leaves some residuals (sediments and surfactant solution). Currently, there are no data on the ecotoxicological effects of these OSW residuals from different sludges. This study evaluated the toxicity of OSW residuals from washing four types of oil sludges with five surfactants (Triton X-100 and X-114, Tween 80, sodium dodecyl sulphate (SDS) and rhamnolipid) and a co-solvent (cyclohexane). The toxicity of the residuals was evaluated with the impact on the soil microbial dehydrogenase activity (DHA) and ryegrass (Lolium perenne) seed germination. There was a high DHA detected directly in the sludges and all OSW residual combinations, but this activity could not be attributed to the DHA itself but to some chemical interferences. The DHA was then tested in the soils amended with the OSW residuals to simulate a bioremediation scenario. There were no chemical interferences in this case. In general, the INTF concentrations were significantly higher at low concentrations, 1 and 5% (p < 0.01). There were no significant differences in the DHA at high concentrations of OSW residuals (10, 25 and 50%) which implied that the concentration of the contaminants is not directly proportional to the levels of ecotoxicity. Unexpectedly, the INTF values of the 10, 25 and 50% rhamnolipid-OSW residuals were significantly lower than the Triton X-100 residuals. The ryegrass germination rates were higher than 70% with no apparent phytotoxicity symptoms in the seedlings. Particularly, there was a highly significant negative effect of the residuals on the germination rates at high concentrations (p < 0.01). Given that the extractable petroleum hydrocarbon (EPH) concentrations in the OSW residual-amended soils in both DHA and germination tests were very low (13-21 ppm), other co-contaminants could be contributing to the toxicity. These findings implied that biotreatment techniques can be applied to treat the OSW residuals if necessary.

Enhanced production of mono-rhamnolipid in Pseudomonas aeruginosa and application potential in agriculture and petroleum industry

Differences in the rhamnolipid structures must result in its different activities, thus affecting its application effect. The rhlC gene in Pseudomonas aeruginosa SG was knocked out to construct strain P. aeruginosa SGΔrhlC. Rhamnolipid production was enhanced by 23.3% through knocking out rhlC gene. P. aeruginosa SGΔrhlC produced 14.22 g/L of rhamnolipid using glycerol and nitrate. Five kinds of mono-rhamnolipid but no di-rhamnolipid were produced by strain SGΔrhlC. The main rhamnolipid homologues were Rha-C₁₀-C₁₀, Rha-C₁₀-C_12:1 and Rha-C₁₀-C₁₂. Mono-rhamnolipid exhibited better antimicrobial activity to Escherichia coli, Staphylococcus aureus, Aspergillus niger and Penicillium chrysogenum. Rhamnolipid produced from strain SGΔrhlC showed greater emulsifying activity to crude oil with EI₂₄ of 84.73%. Rhamnolipid produced from strain SGΔrhlC efficiently washed oily sludge at 35 °C. High-producing strain P. aeruginosa SGΔrhlC and its produced mono-rhamnolipid are more promising in agriculture and petroleum industry. This study is a step forward to the tailor-made biosynthesis and application of rhamnolipid.

Hydrothermal treatment combined with in-situ mechanical compression for floated oily sludge dewatering

Due to the high moisture content of the oily sludge, the conventional use of oily sludge treatment presents poor feasibility in industrial applications. Hence, finding an efficient and energy-saving technology is still an urgent need for the dewatering of oily sludge. In this paper, an innovative method combining hydrothermal treatment (HT) and in-situ mechanical compression (MC) for dewatering of floated oily sludge (FOS) was proposed. Series of experiments on HT&MC were conducted to verify the method. 77-96 wt% of water can directly be separated from FOS by the HT&MC treatment under the temperature of 120-240 °C and residence times of 10-60 min. The bound water content in raw and HT&MT treated FOS were measured by employing the differential scanning calorimetry (DSC) to evaluate the dewatering ability. The result of DSC illustrates the freezing peaks shifted from -11.1 °C to -21.2 °C as the diameter of water droplets reduced. Meanwhile, the comprehensive characterization analysis of products, including chemical oxygen demand (COD), NH4⁺-N, and gas chromatograph (GC) were conducted. All results indicated that HT&MC is advisable for dewatering of oily sludge.

Emission characteristics of nitrogen and sulfur containing pollutants during the pyrolysis of oily sludge with and without catalysis

The oily sludge is a category of hazardous solid waste generated in petrochemical industries. Pyrolysis is an efficient approach for sustainable treating the oily sludge with limited environmental impacts, but the pollutant emission during the pyrolysis process is still a big challenge. Herein, the emission characteristics of nitrogen (N) and sulfur (S) containing pollutants during the oily sludge pyrolysis with and without catalysis was illuminated via a TG-FTIR-MS system (ThermoGravimetric-Fourier Transform InfaRed-Mass Spectroscopy). The FeMg layer double hydroxide (FeMg LDH) was employed as a catalyst for pyrolysis. The emission characteristics of six inorganic N-/S-containing pollutants, as well as ten organic N- and nine S-containing pollutants were analyzed. The results indicate that the FeMg LDH could efficiently suppress the emission of N-/S-containing pollutants. The amide and heterocyclic-N species were identified as primary resources of N-containing pollutants emission. The aliphatic- and disulfides-S were the main contributions to the S-pollutants emission. Comprehensive analysis of pollutants emission characteristics for oily sludge pyrolysis could provide a better understanding for sustainable managements of the hazardous solid wastes.

A review of the application of different treatment processes for oily sludge

Oily sludge contains high concentrations of total petroleum hydrocarbons and heavy metals, which seriously impact the environment and human health. How to dispose of and use the oily sludge has attracted an increasing amount of attention. This study introduces harmless and resource-based oily sludge treatment technologies. It summarizes the technologies from various aspects, such as the process principle, influencing factors, advantages, and disadvantages, and analyzes and summarizes the status quo of the development of the technologies. In comparison, the direction of processing technology development is discussed to provide reference for processing technology improvements, optimization, and efficiency improvements.

Recent advances in applications of power ultrasound for petroleum industry

Power ultrasound, as an emerging green technology has received increasing attention of the petroleum industry. The physical and chemical effects of the periodic oscillation and implosion of acoustic cavitation bubbles can be employed to perform a variety of functions. Herein, the mechanisms and effects of acoustic cavitation are presented. In addition, the applications of power ultrasound in the petroleum industry are discussed in detail, including enhanced oil recovery, oil sand extraction, demulsification, viscosity reduction, oily wastewater treatment and oily sludge treatment. From the perspective of industrial background, key issue and resolution mechanism, current applications and future development of power ultrasound are discussed. In addition, the effects of acoustic parameters on treatment efficiency, such as frequency, acoustic intensity and treatment time are analyzed. Finally, the challenges and outlook for industrial application of power ultrasound are discussed.

Research on mechanism and characteristics of oil recovery from oily sludge in ultrasonic fields

The acoustic parameters and operating conditions that determine efficiency of oil recovery from oily sludge are studied. Based on this, the mechanism of ultrasonic disintegration of oily sludge is analyzed. The results show that lower frequency ultrasound results in larger and more energetic cavitation bubbles that are more effective in the desorption of oil from solid particles. Moreover, acoustic intensity and treatment time that correspond to maximal oil recovery are found. Increasing the ratio of water to sludge and pH can reduce the slurry viscosity and facilitate the formation of HSiO₃^-, respectively, which improves the oil recovery efficiency. Moreover, Triton X-100 has better oil solubilizing effects than SDBS. After ultrasonic treatment, small amounts of asphaltenes are more stable on solid particles than other components. The heteroatoms such as S, N, and O in asphaltenes form hydrogen bonds with hydroxyl groups on the surface of the particles, impeding the desorption of oil. Mechanical effects such as shock waves and micro jets due to acoustic cavitation can break the hydrogen bonds between asphaltenes and solid particles, thereby facilitating oil recovery from oily sludge.

Insight into essential channel effect of pore structures and hydrogen bonds on the solvent extraction of oily sludge

In this study, solvent extraction experiments were conducted to investigate the channel effect of pore structures and hydrogen bonds by analyzing the desorption behavior of oil components. The highest oil recovery efficiency was 87.9 % under optimum conditions. Pore structure of oily sludge was analyzed by N₂ adsorption-desorption analysis and scanning electron microscope (SEM) measurements. Mesopores of sludge inhibited the desorption of oil molecules by analyzing the pore width and cumulative pore volume of residual sludge in desorption process. In addition, saturates and aromatics were easily extracted from sludge, while the desorption rate and desorption efficiency of oily sludge were limited by resins and asphaltenes respectively through component analysis and kinetic analysis. Furthermore, channel effect of pore structures and hydrogen bonds was investigated in the desorption process of oily sludge, which also provided a guidance to selectively extract light components from oily sludge with high efficiency in industry processing.

Application of biosurfactant surfactin as a pH-switchable biodemulsifier for efficient oil recovery from waste crude oil

Efficient oil separation is the most desirable, but still challenging solution for the waste crude oil problem. This study developed biosurfactant surfactin as a novel pH-switchable biodemulsifier for efficient oil separation. As found, surfactin demulsification achieved a quite well oil separation ratio of over 95% on model emulsions after 20 min at 50 °C. The validity of this demulsification process should be mainly based on the readily lost stabilization ability of surfactin in emulsions triggered by acid addition. Then, surfactin (0.2 g/L) treatment with the aid of ethanol (2%) to improve its distribution could recover over 95% of oil from waste crude oil. After treated by surfactin, the separated oil phase contains tiny water (less than 0.5%) and thus can be reused for resource recycling to reach a compromised balance between satisfying the strict environmental regulations and decreasing the high treatment costs. Hence, in consideration of high demulsification efficiency, environmental-friendly properties and cost-efficiency, surfactin has a great potential for industrial applications for oil recovery from waste crude oil which is a severe problem presents in most of the petroleum-related factories.