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

Energy recoveries and heavy metal migration behaviors of different oily sludges treated by pyrolysis versus solvent extraction

The pyrolysis and trace element mitigation characteristics are investigated by contrast to solvent extraction for four oily sludges, including storage tank bottom sediment (OS-1), scum from a wastewater separator (OS-2), white-clay-adsorbed waste oil (OS-3), and settlings from wastewater treatment (OS-4). Slow pyrolysis at 700 °C generated a single oil phase for OS-1 and separate oil and aqueous phases for OS-2, OS-3 and OS-4. Up to 73.0-88.3 % of the total energy were recovered from OS-1, OS-2 and OS-3 in the oil phase with 19.9-77.1 % oil yield; however, the oil phase from OS-4 accounted for only 13.3 % of the total energy, while the aqueous product accounted for 68.0 % of the total energy. Quantification of 16 trace elements revealed that OS-2 and OS-4 had much higher contents of Cu/Zn/As/Se/Cd/Pb and Ni/Cu/Zn/Se/Cd contents than the average crustal abundances, respectively. Correlations between evaporation and extraction rates indicated that the mitigation behaviors of trace elements were related to their occurrence modes in different oily sludges. Except for Cd, As and Se, all other trace elements were enriched in the pyrolysis residues of the oily sludges. Ni in the pyrolysis residue of OS-4 posed a moderate potential ecological risk.

New insights into interaction between oil and solid during hydrothermal treatment of oily sludge

Hydrothermal treatment (HT) can effectively dehydrate and reduce oily sludge (OS) volume, but the resulting hydrothermal oily sludge (HOS) presents greater challenges for washing than the initial oily sludge (IOS). This study examines the effects of HT on OS by analyzing changes in water, oil, and solid. Results indicate that HT considerably decreases the water content in OS while increasing resin and asphaltenes contents. In addition, condensation, side-chain scission, and oxidation reactions occur during the HT process, resulting in coking, agglomeration, and an increase in oxygen-containing groups. This increase, further confirmed by X-ray photoelectron spectroscopy (XPS), enhances the interaction between oil and solids. Calcite, the most prevalent solid-phase component, may form a calcium bridge with the oxygen-containing groups. Moreover, HT reduces the solid particle size, thereby increasing the oil-solid contact area. Interestingly, the process of deasphalting diminishes the interaction between oil and solids, facilitating sludge washing. After washing, the residual oil content in HOS is reduced to less than 0.34%. This study elucidates why HOS is challenging to separate from oil and solids and introduces a novel method that combines dodecylbenzene sulfonic acid (DBSA)-assisted heptane deasphalting with conventional washing techniques. This method shows promise for applications in OS affected by weathering processes.

Role of municipal solid waste incineration fly ash components in co-pyrolysis of oily sludge: Pyrolysis products and catalytic mechanism

The co-pyrolysis of oily sludge (OS) and municipal solid waste incineration fly ash (IFA) is a promising strategy for sustainable waste management. This study delves into the distinct catalytic roles of individual IFA components during co-pyrolysis and assesses their impact on the inherent Fe species in OS, highlighting their contributions to overall catalytic activity. Notably, in comparison to IFA, CaCl2 and KCl significantly enhance pyrolysis oil upcycling, while IFA components collectively exhibit a positive catalytic effect on pyrolysis gas and coke production. Ca(OH)2 notably boosts H2 yield by 137.16 %. Alkali chlorides facilitate gaseous hydrocarbon formation and convert oxygen-containing compounds to CO and CO2 which are subsequently consumed and absorbed by CaO and Ca(OH)2. CaCl2 and KCl promote heavy compound decomposition and alkane aromatization, reducing coke formation and increasing light aromatic production. Conversely, NaCl increases alkane proportions. However, CaSO4 and CaCO3 hinder catalytic reactions, promoting carbon conversion to coke. Importantly, IFA compounds aid the dispersion of inherent Fe-based species from OS on char surface, enhancing in-situ catalytic pyrolysis. Additionally, the augmented H2 production accelerates the reduction of Fe-based species. The findings expand waste utilization possibilities and provide insights for co-processing solid wastes.

Chemical speciation and environmental risk assessment of heavy metals in ash from smouldering combustion of oily sludge

Smouldering combustion of oily sludge (OS) was carried out to learn the characteristics of heavy metals (HMs) in ash products. Ash collected from four different height layers of the column reactor was analysed for the chemical speciation and environmental risk of six HMs, including Cr, Ni, Cu, Zn, As, and Pb. The results showed that after smouldering combustion, only 21.3-32.2 % of the total HMs was remained in the ash products. The retention of HMs in ash was closely relevant to the carbonaceous destruction efficiency of OS. Smouldering combustion led to the decrease of HMs in acid-soluble/exchangeable fraction from 21.5-49.3 to 0.8-19.8% and oxidizable fraction from 22.6-49.6 to 5.3-21.3, and the increase of reducible fraction from 13.6-38.0 to 30.5-89.1% and residue fraction from 7.8-27.3 to 24.1-63.6%. Upward migration of HMs during smouldering was evidenced by their occurrence in the top clean sand layer, which was dominated in acid-soluble/exchangeable and reducible fractions, accounting for 89.7-99.1% in total. Toxicity extraction and environmental risk studies indicated that smouldering combustion would effectively reduce the toxicity and pollution risk of HMs; however, attention should be paid to the disposal of the top sand layer after smouldering operation due to its high pollution risk of HMs according to the evaluation of Risk assessment code.

Comparative study by microwave pyrolysis and conventional pyrolysis of pharmaceutical sludge: Resourceful disposal and antibiotic adsorption

Compared with conventional pyrolysis, microwave pyrolysis has superior heat transfer performance and promotes the decomposition of organic matter. The paper focuses on the harmless treatment and resource utilization of pharmaceutical sludge (PS) by microwave heating and conventional heating methods. The experimental results showed that the conventional pyrolysis gas is dominated by CO2, CO and H2. For microwave pyrolysis gas, the "microwave effect" promoted secondary cracking of volatile fractions and increases the content of CH4, CxHy, H2 and CO through condensation, aromatization, and dehydrogenation. Conventional pyrolysis oils contained the highest percentage of oxygenated compounds. However, high-temperature microwave radiation accelerated the cleavage of polar oxygenated molecular bonds and long-chain hydrocarbons, thereby increasing the aromatics content of pyrolysis oils. The solid residues obtained from microwave pyrolysis is highly graphitized and porous, with a surface area of 146.2 m2/g. Furthermore, the solid residue was rich in pyridine-N and pyrrole-N that could be utilized for adsorption and catalysis. The MA-600 removes up to 99% of tetracycline (TC) in 6 h. It was also found that the adsorption process of TC by the two pyrolysis residues was consistent with the proposed secondary and Freundlich models.

Aliphatic hydrocarbons in fin spines of adult sturgeon (Acipenser stellatus) and their relationship with potentially toxic elements in the northern and southern regions of the Caspian Sea

Currently, the pollution of the Caspian Sea by the oil industry is one of the highest problems in this area. Critically endangered species inhabit this sea, such as sturgeons, whose ecological value is incalculable. Thus, we aimed to evaluate the level of contamination of aliphatic hydrocarbons of petroleum and its relation with several toxic elements directly on sturgeons spines. A total of 40 adult starry sturgeons (Acipenser stellatus) were obtained within a repopulation programme in the northern and southern coastal waters of the Caspian Sea. The marginal pectoral fin was extracted from each fish to determine aliphatic hydrocarbons, arsenic, cadmium, mercury, nickel, lead, and vanadium. Subsequently, the sturgeons were released. Clearly, the presence of hydrocarbons was evidenced in all the sampled areas finding higher concentrations in the northern areas (N1 = 1.35 ± 0.4; N2 = 1.65 ± 0.46; N3 = 1.27 ± 0.40; S1 = 0.61 ± 0.22; S2 = 0.85 ± 0.43 mg/kg). Furthermore, to a greater or lesser extent, some toxic elements, mainly Hg and As, have been linked to aliphatic hydrocarbons.

Recent advances in organic waste pyrolysis and gasification in a CO2 environment to value-added products

The persistent combustion of fossil fuels has resulted in a widespread greenhouse effect attributable to the continual elevation of carbon dioxide (CO2) levels in the atmosphere. Recent research indicates that utilizing CO2 as a pyrolysis gasification medium diminishes CO2 emissions and concurrently augments the value of the resultant pyrolysis gasification products. This paper reviews recent advancements in the pyrolysis gasification of organic solid wastes under a CO2 atmosphere. Meanwhile, the mechanisms of CO2 influence in the pyrolysis and gasification processes were also discussed. In comparison to noble gases, CO2 exhibits reactivity with char at≥710 °C, resulting in additional mass loss of the sample. In addition, CO2 was able to increase the specific surface area and stability of biochar and reduce biooil toxicity by lowering the content of cyclic compounds in the biooil, while CO2 was able to react with GPRs with some volatile products (e.g., light hydrocarbons) to increase biogas yield. Finally, CO2 also prevents catalyst deactivation by reducing secondary coke formation. We also recommend directing future attention toward utilizing unpurified CO2 in pyrolysis and gasification. This review aims to expand the utilization of CO2 and advocate for applying pyrolysis gasification products.

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.

Assessment and comparison of thermochemical pathways for the rice residues valorization: pyrolysis and gasification

Lignocellulosic biomass conversion applying thermochemical routes has been postulated as an alternative for generating renewable energy. This research compares energy-driven biorefineries based on two thermochemical routes addressed to upgrade rice husk and rice straw produced in the Department of Sucre-Colombia. Initially, this research analyzes the physico-chemical and structural characterization of the rice residues. Four different scenarios were proposed to compare the energy-driven biorefineries based on fast pyrolysis and gasification considering technical, economic, and environmental metrics. These biorefineries were simulated using the Aspen Plus V.14.0 software. The novelty of this research is focused on the identification of the biorefinery with the best techno-economic, energetic, and environmental performance in the Colombian context. Economic and environmental analyses were done by using economic metrics and emissions. From an economic perspective, the stand-alone gasification process did not have a positive economic margin. In contrast, the fast pyrolysis process has the best economic performance since this process has a positive profit margin. Indeed, scenario 1 (fast pyrolysis of both rice residues) presented an economic margin of 13.75% and emissions of 2170.92 kgCO2eq/kg for 10 years. However, this scenario was not energetically the best, holding second place due to the feedstock requirements, compared to gasification. The biorefinery scenario 1 has the best performance.

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.

Enhancement of H2 and light oil production and CO2 emission mitigation during co-pyrolysis of oily sludge and incineration fly ash

The proper treatment and utilization of oily sludge (OS) and incineration fly ash (IFA) remains a significant challenge due to their hazardous nature. To attain effective recovery of petroleum hydrocarbons and synergistic disposal, this study investigated the co-pyrolysis of OS and IFA, resulting in successful energy recovery, CO2 mitigation, and heavy metal immobilization. Results revealed that the peak ratio of light oil to heavy oil fractions reached 179.42% with 20 wt% IFA addition, accompanied by the highest aromatic hydrocarbons selectivity of 30.72% and the lowest coke yield of 106.13 mg/g OS under the optimal temperature of 600 °C. In-depth analysis indicated that IFA inhibited the poly-condensation of macromolecular PAHs and promoted their cracking into light aromatic hydrocarbons. The addition of 50 wt% IFA significantly increased H2 yield (21.02 L/kg OS to 60.95 L/kg OS) and facilitated CO2 sequestration due to its higher content of Ca-bearing minerals. Moreover, high IFA ratios promoted the reduction of Fe species in OS to a low-valence state. Heavy metals in co-pyrolysis char were well immobilized into stable fractions with lower environmental risks. This work highlights the potential of co-pyrolysis as a viable approach for simultaneous disposal of multiple hazardous wastes and offers new insights for their utilization.

Sustainable Utilization of Surfactant-Free Microemulsion Regulated by CO2 for Treating Oily Wastes: A Interpretation of the Response Mechanism

Surfactant-free microemulsions (SFMEs) have been explored extensively to avoid the residual surfactant problem caused by traditional surfactant microemulsions. Many researchers focused on the SFMEs with tertiary amine, which exhibited the typical CO2 response behavior. In this study, the phase diagram of the SFMEs consisting of tripropylamine (TPA), ethanol, and water was readily prepared via the measurements of electrical conductivity. The CO2 response behavior of SFME was confirmed by determination of conductivity and measurement of the average diameter of SFME, which was mainly dependent on the protonation of TPA induced by the additional CO2. The transition of protonated TPA to a more hydrophilic nature from lipophilicity to hydrophilicity should be responsible for the variation of SFME average diameter. In addition, the SFMEs exhibited remarkable solubilizing capacity of crude oil, and three types of SFMEs achieved more than 80% oil removal rate in the washing process of oil sands. It was noted that both oil-in-water and bicontinuous SFMEs could be circularly utilized at least three times with a relatively high oil removal rate (%). Our work provided the insight perspective on the mechanism of SFMEs with a CO2 response behavior.

An experimental and thermodynamic equilibrium investigation of heavy metals transformation in supercritical water gasification of oily sludge

Supercritical water gasification (SCWG) is an advanced and highly efficient method for treating oily sludge. However, it is crucial to consider the transformation characteristics of heavy metals (HMs) during the SCWG process to prevent potential secondary pollution. This work studied the transformation and distribution characteristics of Cu, Cr and Zn after SCWG of oily sludge in a batch reactor at temperatures ranging from 550 to 700 °C. Additionally, thermodynamic equilibrium analysis was conducted to assess the distribution of HMs based on the minimization of Gibbs free energy. Experimental results indicated that higher temperatures led to the conversion of HMs into more stable forms, effectively immobilizing them within solid products. Furthermore, the addition of Na2CO3 enhanced this process and contributed to a reduction in HMs pollution in the effluent. Thermodynamic equilibrium results were consistent with our experimental data, indicating that the molar fraction of stable HMs forms followed the order: Cr > Cu > Zn. Besides, it is worth noting that Na2CO3 had a limited impact on the distribution of Cu and Cr. However, it played a significant role in inhibiting the formation of silicate Zn at lower temperatures, promoting the decomposition of ZnO*Al2O3 into unstable Zn. This may explain the higher presence of unstable Zn when Na2CO3 was introduced. In summary, this study offers valuable insights into the transformation characteristics of heavy metals and strategies for pollution control during SCWG of oily sludge.

Activation of peroxymonosulfate by biochar-supported Fe3O4 derived from oily sludge to enhance the oxidative degradation of tetracycline hydrochloride

Carbon materials used for catalysis in advanced oxidation processes tend to be obtained from cheap and readily available raw materials. We constructed a carbon material, OSC@Fe3O4, by loading Fe3O4 onto the pyrolyzed hazardous waste oily sludge. OSC@Fe3O4 was then used to activate peroxymonosulfate (PMS) for the removal of tetracycline hydrochloride (TTCH) from water. At 298 K, 0.2 g⋅L-1 of catalyst and 0.3 g⋅L-1 of PMS, the reaction rate constant of the OSC@I-2/PMS system reached 0.079 min-1, with a TTCH removal efficiency of 92.6%. The degradation efficiency of TTCH remained at 81% after five cycles. The specific surface area and pore volume of OSC@I-2 were 263.9 m2⋅g-1 and 0.42 cm3⋅g-1, respectively, which improved the porous structure of the carbon material and provided more active points, thus improving the catalytic performance. N and S were doped into the oily sludge carbon due to the presence of N- and S-containing compounds in the raw oily sludge. N and S doping led to more electron-rich sites with higher negative charges in OSC@I-2 and gave the oily sludge carbon a higher affinity to PMS, thereby promoting its ability to activate PMS. Sulfate radicals (SO4•‾) played a dominant role in the degradation of TTCH, with demethylation and the breaking of double bonds being a possible degradation pathway. A biotoxicity test showed that the microbial toxicity of the degradation intermediates was significantly reduced. This work provides a strategy for the application of PMS-based catalysts derived from waste carbon resources.

Kinetic analysis of slow pyrolysis of oily sludge at medium temperature (350 ℃-650 ℃) and the effects of heating rate on pyrolysis

ABSTRACTPyrolysis is an effective way for the harmless treatment of oily sludge. The composition, physicochemical properties, and pyrolysis of oily sludge were experimentally studied in the present study. The Starink and Coats-Redfern methods were used to analyze the pyrolysis kinetics of oily sludge. Pyrolysis of oily sludge is divided into four stages: water evaporation stage, light component evaporation stage, heavy component pyrolysis stage, and final pyrolysis stage. The light component evaporation and heavy component pyrolysis stages are the main stages of medium-temperature pyrolysis. The pyrolysis characteristic parameters under heating rates of 10, 20, 30, and 40 K/min were obtained, and the effects of heating rates on the pyrolysis characteristics of oily sludge were discussed. The results show that with the increase in heating rate, the temperature range of each stage expands, and the temperature of the pyrolysis peaks also increases, with an average increase of 14.88%. The activation energies of the main pyrolysis stages obtained by the Starink method and Coats-Redfern method are consistent. In the light component evaporation stage, the activation energies obtained by the two methods are 61.93kJ/mol and 68.6kJ/mol, while the activation energies are 294.88kJ/mol and 367kJ/mol in the heavy component pyrolysis stage. The pyrolysis mechanism functions are obtained, and the pyrolysis kinetic equations under 10, 20, 30, and 40 K/min were constructed and validated by comparison with the results of the calculated properties and experimental measurement. This study can provide a better insight into the heat and mass transfer processes of oily sludge in pyrolysis reactors for further development and optimization.

Actionable insights into hazard mitigation of typical 3D printing waste via pyrolysis

3D printing waste (3DPW) contains hazardous substances, such as photosensitizers and pigments, and may cause environmental pollution when improperly disposed of. Pyrolysis treatment can reduce hazards and turn waste into useful resources. This study coupled thermogravimetric (TG), TG-Fourier transform infrared spectroscopy-gas chromatography/mass spectrometry, and rapid pyrolysis gas chromatography/mass spectrometry analysis to evaluate the pyrolytic reaction mechanisms, products, and possible decomposition pathways of the three typical 3DPW of photosensitive resin waste (PRW), polyamide waste (PAW), and polycaprolactone waste (PCLW). The main degradation stages of the typical 3DPW occurred at 320-580 °C. The most appropriate reaction mechanisms of PRW, PAW and PCLW were D1, A1.2 and A1.5, respectively. The main pyrolysis processes were the decomposition of the complex organic polymers of PRW, the breaking of the NH-CH2 bond and dehydration of -CO-NH- of PAW, and the breaking and reorganization of the molecular chains of PCLW, mainly resulting in toluene (C7H8), undecylenitrile (C11H21N), tetrahydrofuran (C4H8O), respectively. Unlike the slow pyrolysis, the rapid pyrolysis produced volatiles consisting mainly of phenol, 4,4'-(1-methylethylidene)bis- (C15H16O2) for PRW; 1,10-dicyanodecane (C12H20N2) for PAW; and ɛ-caprolactone (C6H10O2) for PCLW. These pyrolysis products hold great potential for applications. The findings of the study offer actionable insights into the hazard reduction and resource recovery of 3D printing waste.

Synchronous stabilization of Pb, Zn, Cd, and As in lead smelting slag by industrial solid waste

In order to prevent heavy metal (HM) pollution from lead smelting slag (LSS) to the surrounding environment, this work investigated the feasibility, influencing factors, and mechanisms of using industrial solid waste such as fly ash (FA), oil sludge pyrolysis residue (PR), and steel slag (SS) as remediation amendments. The results demonstrated that the stabilization process was influenced by the material dosage, water content, and LSS particle size. Compared to single materials, the combination amendment PR2FA1 (with a mass ratio of PR to FA as 2:1) exhibited the best stabilization effect, simultaneously reducing the leaching concentrations of As, Zn, Cd, and Pb in LSS to 0.032, 0.034, 0.002, and 0.014 mg/L, respectively. The pH value of the leachate remained between 8 and 9, which met the requirements of surface water quality class IV (GB3838-2002). Through morphological analysis, microscopic characterization, and simulated solution adsorption experiments, it was determined that the stabilization process of HMs was controlled by various mechanisms, including electrostatic attraction, physical adsorption, ion exchange, and chemical precipitation. PR2FA1 had more active components, and its fine-porous structure provided more active sites, resulting in good stabilization performance for As, Zn, Cd, and Pb. Furthermore, cost analysis showed that PR2FA1, as an environmentally friendly material, could generate profits of 157.2 ¥/ton. In conclusion, the prepared PR2FA1 not only addressed the HMs pollution from lead smelting slag to the surrounding environment but also achieved the safe and resourceful disposal of hazardous waste-oil sludge. Its excellent performance in stabilizing HMs and cost-effectiveness suggested promising commercial applications.

A critical review on sustainable hazardous waste management strategies: a step towards a circular economy

Globally, industrialisation and urbanisation have led to the generation of hazardous waste (HW). Sustainable hazardous waste management (HWM) is the need of the hour for a safe, clean, and eco-friendly environment and public health. The prominent waste management strategies should be aligned with circular economic models considering the economy, environment, and efficiency. This review critically discusses HW generation and sustainable management with the strategies of prevention, reduction, recycling, waste-to-energy, advanced treatment technology, and proper disposal. In this regard, the major HW policies, legislations, and international conventions related to HWM are summarised. The global generation and composition of hazardous industrial, household, and e-waste are analysed, along with their environmental and health impacts. The paper critically discusses recently adapted management strategies, waste-to-energy conversion techniques, treatment technologies, and their suitability, advantages, and limitations. A roadmap for future research focused on the components of the circular economy model is proposed, and the waste management challenges are discussed. This review stems to give a holistic and broader picture of global waste generation (from many sources), its effects on public health and the environment, and the need for a sustainable HWM approach towards the circular economy. The in-depth analysis presented in this work will help build cost-effective and eco-sustainable HWM projects.

Hydrogen production from hazardous petroleum sludge gasification over nickel-loaded porous ZSM-5 and Al2O3 catalysts under air condition

In this study, the potential of petroleum sludge (PS) for hydrogen production via the gasification process was evaluated. For this purpose, nickel (Ni)-loaded ZSM-5 and γ-Al₂O₃ (Ni-ZS and Ni-Al) catalysts were prepared and employed for PS gasification in air condition. The effects of different supports, Ni loading content, and reaction temperatures on the production of hydrogen-rich syngas along with the stability and reusability of the best catalyst were investigated. Applying 5%Ni-ZS obtained more gas yield (68.09 wt%) and hydrogen selectivity (25.04 vol%) compared to those obtained by 5%Ni-Al mostly owing to weak metal-support interactions which led to the dominance of well-dispersed metallic Ni. At various Ni loading percentages, 10%Ni-ZS showed the highest catalytic efficiency, which increased both gas yield (70.92 wt%) and hydrogen selectivity (30.74 vol%). However, excessive Ni content (especially 20%) significantly reduced the gas yield and hydrogen selectivity because of limited accessibility of support's active sites, poor dispersion of Ni, and inappropriate acidity. Increasing the temperature promoted the gas yield and produced hydrogen, where the highest gas yield (73.18 wt%) and hydrogen selectivity (33.15 vol%) were obtained at 850 °C due to the endothermic nature of gasification reactions. The 10%Ni-ZS catalyst showed proper stability during three consecutive experiments at 850 °C. The spent catalyst was successfully regenerated without a significant reduction in activity or selectivity.

Efficient Treatment of Oily Sludge via Fast Microwave-Assisted Pyrolysis, Followed by Thermal Plasma Vitrification

Oily sludge, as a critical hazardous waste, requires appropriate treatment for resource recovery and harmfulness reduction. Here, fast microwave-assisted pyrolysis (MAP) of oily sludge was conducted for oil removal and fuel production. The results indicated the priority of the fast MAP compared with the MAP under premixing mode, with the oil content in solid residues after pyrolysis reaching below 0.2%. The effects of pyrolysis temperature and time on product distribution and compositions were examined. In addition, pyrolysis kinetics can be well described using the Kissinger-Akahira-Sunose (KAS) and the Flynn-Wall-Ozawa (FWO) methods, with the activation energy being 169.7-319.1 kJ/mol in the feedstock conversional fraction range of 0.2-0.7. Subsequently, the pyrolysis residues were further treated by thermal plasma vitrification to immobilize the existing heavy metals. The amorphous phase and the glassy matrix were formed in the molten slags, resulting in bonding and, hence, immobilization of heavy metals. Operating parameters, including working current and melting time, were optimized to reduce the leaching concentrations of heavy metals, as well as to decrease their volatilization during vitrification.

In-depth insight into the effects of intrinsic calcium compounds on the pyrolysis of hazardous petrochemical sludge

To understand the potential effects of intrinsic calcium compounds on sludge pyrolysis, the pyrolysis behavior of petrochemical sludge (PS), calcium carbonate blend PS (CaPS), and decalcified PS (DePS) were investigated using thermogravimetric analysis (TGA) and in-situ Fourier-transform infrared spectroscopy coupled with pyrolysis-gas chromatography and mass spectrometry (Py-GC/MS). The TGA results indicated that decalcification increased and decreased the energy barriers of PS decomposition in ranges 200-350 °C and 350-600 °C, respectively. In contrast, copyrolysis with CaCO₃ decreased the activation energy (E) of the pseudoreaction phase 2 (PH2) and altered the mechanism model. Meanwhile, during copyrolysis, char deposition and interaction hindered CaCO₃ decomposition. The two-dimensional correlation spectroscopy results, on the other hand, showed that the reaction priority of O-containing groups and CH- vibration of methyl groups were affected by both decalcification and CaCO₃ copyrolysis. The Py-GC/MS results indicated that the three sludges mainly released hydrocarbons, N-containing organics, alcohols, aldehydes, and acids. During pyrolysis, CaCO₃ also played a neutralization role, which reduced the release of pyrolytic acidic products. In addition, the increase of the pyrolysis temperature increased the hydrocarbon content. This research will guide the industrial application of sludge pyrolysis.

Biochar-Assisted Catalytic Pyrolysis of Oily Sludge to Attain Harmless Disposal and Residue Utilization for Soil Reclamation

Pyrolysis of oily sludge (OS) is a feasible technology to match the principle of reduction and recycling; however, it is difficult to confirm the feasible environmental destination and meet the corresponding requirements. Therefore, an integrated strategy of biochar-assisted catalytic pyrolysis (BCP) of OS and residue utilization for soil reclamation is investigated in this study. During the catalytic pyrolysis process, biochar as a catalyst intensifies the removal of recalcitrant petroleum hydrocarbons at the expense of liquid product yield. Concurrently, biochar as an adsorbent can inhibit the release of micromolecular gaseous pollutants (e.g. HCN, H₂S, and HCl) and stabilize heavy metals. Due to the assistance of biochar, pyrolysis reactions of OS are more likely to occur and require a lower temperature to achieve the same situation. During the soil reclamation process, the obtained residue as a soil amendment can not only provide a carbon source and mineral nutrients but can also improve the abundance and diversity of microbial communities. Thus, it facilitates the plant germination and the secondary removal of petroleum hydrocarbons. The integrated strategy of BCP of OS and residue utilization for soil reclamation is a promising management strategy, which is expected to realize the coordinated and benign disposal of more than one waste.

Self-circulation of oily spent hydrodesulphurization (HDS) catalyst by catalytic pyrolysis for high quality oil recovery

In this study, roasted spent HDS ash (sHDSc-A) was used for the first time to catalytically pyrolyze oily spent HDS catalysts (sHDSc) to improve the yield and quality of pyrolysis oil. The results showed that sHDSc-A promoted the decomposition of coke in oily sHDSc, resulting in the recovery of more oil and gas. Meanwhile, sHDSc-A significantly improved the quality of the pyrolysis oil. They inhibited the aromatization of alkanes to increase the saturation of the pyrolysis oil from 59.39% to 74.25% and the H/C radio from 1.62 to 1.72; promoted the decomposition of long-chain alkanes to increase the content of C11-C22 from 41.97% to 61.99%; enhanced the conversion of carboxylic acids to ketones led to the reduction of heteroatomic compounds such as N (56.10%-45.39%), S (66.95%-56.59%), and O (45.26%-26.70%) in the pyrolysis oil. The promotion of sHDSc-A in the pyrolysis process is attributed to the catalytic effect of the metal oxides in sHDSc-A. Among them, Al₂O₃ and Fe₂O₃ can promote decarboxylation of carboxylic acids and reduce O mobility, while MoO₃ and Fe₂O₃ play a significant role in reducing coke and increasing pyrolysis oil. NiO can also promote methane vapor reforming, and thus increase the production of H₂ in non-condensable gas. This study achieves self-circulation of oily sHDSc with a "waste-treatment-waste" strategy that presents the advantage of value-added energy recovery and waste reuse.

Pyrolytic kinetics, reaction mechanisms and gas emissions of waste automotive paint sludge via TG-FTIR and Py-GC/MS

The present study experimentally quantified the pyrolysis behaviors of waste solvent-based automotive paint sludge (OAPS) and water-based automotive paint sludge (WAPS) at four different heating rates using thermogravimetric-Fourier transform infrared (TG-FTIR) spectrometry and pyrolysis-gas chromatography-mass (Py-GC/MS) spectrometry analyses. Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods combined with the master-plots method were employed to investigate the pyrolysis kinetics and reaction mechanisms of waste automotive paint sludge. Three reaction stages and three reaction peaks in stage 2 were distinguished for both OAPS and WAPS degradation. The average activation energy (E_a) estimates for OAPS (FWO: 179.09 kJ/mol; KAS: 168.28 kJ/mol) were slightly higher than WAPS (FWO: 175.90 kJ/mol; KAS: 164.80 kJ/mol) according to FWO and KAS methods. The main pyrolysis reaction mechanisms of both OAPS and WAPS closely matched with the order-based model corresponding to 3rd and 2nd order random nucleation on an individual particle. The evolved gas species of CH₄, CO₂, phenols, NH₃, H₂O, and CO from OAPS and WAPS pyrolysis were identified by TG-FTIR. According to Py-GC/MS, hydrocarbons (47.2%) and O-components (42.7%) were relatively large after OAPS and WAPS pyrolysis, respectively. Melamine was the most abundant N-component product after pyrolysis of OAPS (5.8%) and WAPS (4.8%).

Environmental Risk Analysis Based on Characterization of Ground Oily Sludge

Oily sludge is recognized as hazardous waste. To reduce the potential danger and harmful factors of oily sludge, it is very important to analyze its environmental risk. In this paper, the characterization of oily sludge from Shengli Oilfield in China was tested experimentally, including the composition content, particle size, microscopic morphology, heavy metal content, organic composition, inorganic composition, and thermogravimetric analysis, which were used to analyze environmental risks. The results show that the oil content of oily sludge is as high as 10.3%, which will cause serious pollution. It is calculated that China can recover 772.5 million liters of oil and reduce 553.9 million kg of carbon emissions compared with incineration in one year, if the oily sludge can be managed effectively. The content of heavy metals such as Ba, Zn, Cr, As, Ni, Se, Be, and Hg in oily sludge exceeds the standard. It will restrain the self-healing ability of soil, pollute groundwater, and endanger animals and plants. The organic matter of oily sludge is concentrated in C₁₁ to C₂₉. It contains a large amount of benzene series and polycyclic benzene hydrocarbons, which can lead to cancer in the human body. Inorganic substances in oily sludge are mixed with some additives, which can not only reduce the toxicity of heavy metals, but also be used as building materials. The median particle size D₅₀ of oily sludge is 0.91 μm, and it spreads all over the narrow pores. Generally, it needs to be treated under high temperature conditions, which will cause secondary pollution to the environment. The research content of this paper provides a theoretical reference for the management of oily sludge.

Carbonaceous material prepared by pyrolysis of refinery oily sludge for removal of flotation collectors in wastewater

The carbonaceous material (CM) prepared by refinery oily sludge was proposed to remove flotation collectors, butyl xanthate (BX), and diethyldithiocarbamate (DDTC) in synthetic wastewater. The effects of the CM on removal efficiency, adsorption kinetics, and isotherms were experimentally carried out. The surface structure and composition of CM were characterized by BET isotherm, XRD, and SEM-EDS, and the concentration of BX and DDTC was tested by UV-VIS spectrometer. The adsorption behavior and removal mechanism were investigated by zeta potential, ToF-SIMS, FTIR, etc. The removal efficiencies of BX and DDTC were both more than 99%, and the maximum adsorption capacity peaked when the pH of the solution was neutral. The two collectors were heterogeneous adsorption on the surface of CM. BX, DDTC, and related metal compounds were found on the surface of carbonaceous material, confirming the existence of both physical and chemical adsorption, and physical adsorption accounted for the main mechanism. It is proved that BX and DDTC can be removed by carbonaceous material and realize the high-effective utilization of refinery oily sludge.

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.

Production of valuable chemicals through the catalytic pyrolysis of harmful oil sludge over metal-loaded HZSM-5 catalysts

This research studied the catalytic pyrolysis of oil sludge (OS) over metal-loaded HZSM-5 catalysts, an eco-friendly and cost-effective technology to produce value-added aromatics such as benzene, toluene, ethylbenzene, and xylene (BTEXs). In particular, it evaluated the respective effects of the experimental parameters: the type and amount of the metal loaded, the reaction temperature, and the OS/catalyst ratio, on the BTEXs yield sequentially to achieve optimum conditions. This evaluation showed that the highest yields of the BTEXs (6.61 wt%) and other aromatics were achieved when Ni was incorporated into the HZSM-5 (Ni/HZSM-5) followed by the corresponding yields of Ga/HZSM-5 and Fe/HZSM-5, due to a better distribution of Ni on the support surface and an enhanced acidity strength of this catalyst. Further, increase in Ni loading (up to 10 wt% Ni/HZSM-5) increased the BTEXs yield to 13.48 wt%. However, the excessive Ni loading (15 wt% Ni/HZSM-5) resulted in a reduced BTEXs yield due to the blockage of the zeolite channels. Next, an increase in the reaction temperature from 500 °C to 600 °C increased the yield of the BTEXs and other aromatics. However, a further increase in the reaction temperature to 650 °C decreased slightly their yield because of the stimulating secondary reactions at high temperatures. The increase of catalyst amount (OS/catalyst of 1/3) also maximized the BTEXs yield (30.50 wt%).

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.

Synergistic optimization of syngas quality and heavy metal immobilization during continuous microwave pyrolysis of sludge: Competitive relationships, reaction mechanisms, and energy efficiency assessment

To realize the efficient resource utilization of sewage sludge, this work explored the competitive relationship and reaction mechanisms between syngas quality optimization and heavy metals (HMs) immobilization. The results showed that continuous microwave pyrolysis (CMP) technology with an instantaneous temperature increase could shorten the pyrolysis time, and the biogas yield and syngas concentration reached 51.68 wt% and 83.6 vol%, respectively. Although a higher pyrolysis (750 °C) temperature could optimize the syngas quality, the HMs immobilization efficiency was reduced due to the deep pyrolysis of the biochar. The moderate pyrolysis temperature (650 °C) facilitated the rapid formation of biochar with abundant surface functional groups and pore structure, thus enhancing HMs immobilization. Furthermore, the HMs could also form more stable crystalline compounds with inorganic components (SiO₂, Al₂O₃, inorganic sulfur). By optimizing the process parameters, the risk factor of HMs in the sludge decreased from 117.36 to 62.5 while obtaining high-quality syngas. The energy utilization efficiency of microwave pyrolysis also increased significantly from 11.20% to 82.01%. This work provided new insight into the efficient resource utilization and environmentally friendly treatment of sludge, and demonstrated that CMP technology has significant potential for future industrial applications as an alternative to traditional pyrolysis.

Influence of coke heterogeneity and the interaction between different coke species on the emission of toxic HCN and NOx from FCC spent catalyst regeneration

Concerning the emissions of hydrogen cyanide (HCN) and other N-bearing air pollutants from the fluid catalytic cracking (FCC) regeneration units, this paper has conducted a comprehensive testing and surface characterisation of four industrial spent catalysts, aged catalysts and hard coke sample in three different schemes, Ar-TPD, O₂ -TPO and rapid heating to elaborate the transformation of N upon the influence of the heterogeneity of coke and N speciation. In the Ar-TPD scheme, the surface N is responsive for the emission of gaseous NH₃ from pyrrolic N-5 and HCN from both pyridinic N-6 and quaternary N-Q. The removal of soft coke is beneficial in promoting the surface exposure of hard coke, thereby increasing the HCN emission dramatically. In the O₂-TPO scheme, the oxygen accessibility is the principal factor governing the emission of HCN. The external soft coke is able to access the bulk O₂ firstly, the combustion of which in turn provides heat back to promote the cracking of internal hard coke from the same and neighbouring particles to release more HCN. The induction effect of bulk O₂ is also superior over the spent catalyst properties in formulating a nearly identical trend of HCN emission for all the four spent catalysts tested. Finally, for the use of rapid heating scheme that is typical in a commercial FCC regenerator, it is effective in accelerating the volatilisation of soft coke quickly, thereby promoting the oxygen accessibility to hard coke and the internal N-bearing precursors so as to mitigate the emission of HCN effectively. The use of a large superficial velocity of gas is further effective in sweeping the volatiles including HCN away from the catalyst, promoting their oxidation extent accordingly.

Oily sludge treatment in subcritical and supercritical water: A review

Oily sludge, an inherent byproduct of the petroleum industry, presents dual characteristics of petroleum resources and hazardous waste. Owing to the unique physicochemical properties of sub-/supercritical water, hydrothermal technologies have been increasingly used for oily sludge treatment. This review is the first to focus on oily sludge treatment using sub-/supercritical water. Eight hydrothermal technologies used for different purposes are summarized herein: pressurized hot water extraction (PHWE) for hydrocarbon separation, thermal hydrolysis (TH) for dewaterability improvement, hydrothermal carbonization (HTC) for hydrochar production, wet air oxidation (WAO) for biodegradability improvement, hydrothermal liquefaction (HTL) for bio-oil production, supercritical water upgrading (SCWU) for light oil production, supercritical water oxidation (SCWO) for complete degradation, and supercritical water gasification (SCWG) for H₂-rich syngas production. Moreover, a general reaction pathway for sub-/supercritical water treatment of oily sludge is presented, with a particular focus on the chemical mechanism at temperatures above 350 °C. Lastly, two reaction maps are included to illustrate the reaction pathways of two groups of identifiable model compounds in oily sludge: aliphatic and aromatic hydrocarbons. This review provides detailed information that can promote a better understanding of various hydrothermal technologies, a guideline for selecting the suitable hydrothermal process for a particular oily sludge, and recommendations for further researches.

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.

Removal of Methylene Blue by Metal Oxides Supported by Oily Sludge Pyrolysis Residues

As a typical pollutant, methylene blue poses a serious threat to the environment and human health. Oily sludge pyrolysis residue loaded with metal oxides could be used to prepare composite materials, which is not only an effective way to treat oily sludge, but also a possible method to treat methylene blue pollutants. In this paper, composite materials (AC-CuO, AC-ZnO, and AC-TiO2) were prepared by oily sludge pyrolysis residue-loaded CuO, ZnO, and TiO2 directly, and characterized by XRD, SEM, EDS, BET, FT-IR, and XPS, and it was shown that the metal oxides were successfully supported on the pyrolysis residue. Then, the composite materials were applied to the removal of methylene blue solution. The removal effect of composite materials on methylene blue with respect to the impregnation time, impregnation ratio and dosage, and the contact time and number of regenerations were investigated, and the removal parameters were optimized by response surface methodology. The removal process for methylene blue was described by applying Lagergren, McKay, Langmuir isotherm, Freundlish isotherm and intraparticle diffusion models. According to the response surface methodology and the main factors affecting the removal effect of methylene blue, the results indicate that the removal effect of 5 mg/L methylene blue could reach 95.28%, 94.95%, and 96.96%, respectively, and the corresponding removal capacities were 4.76, 4.75, and 4.85 mg/g. In addition, kinetic studies showed that the removal process of methylene blue was mainly constituted by chemical adsorption. The intraparticle diffusion showed that the removal of methylene blue may be controlled by both liquid film diffusion and intraparticle diffusion. The isotherms showed that the adsorption sites of composites for methylene blue were uniformly distributed and had the same affinity. Furthermore, regeneration experiments showed that the composite materials were stable and had relatively reusability.

Potential of Canna indica in Vertical Flow Constructed Wetlands for Heavy Metals and Nitrogen Removal from Algiers Refinery Wastewater

Constructed wetlands (CWs) are important plant filters used for wastewater treatment. The behavior of the Canna indica-planted CWs in the face of a highly variable composition of industrial wastewater has yet to be understood. Here, we show the effectiveness of Canna indica-planted and unplanted vertical subsurface flow CWs for the treatment of Algiers petroleum refinery’s effluent. The selected species was placed in the CWs containing light expanded clay aggregate (LECA) and sand as a substrate. The findings indicate that the planted constructed wetlands efficiently removed 85% of total suspended solids (TSS), 96.38% of total nitrogen (TN), 96.15% of nitrate nitrogen (NO3−-N), 99.15% of ammonium nitrogen (NH4+-N), and 99.87% of nitrite nitrogen (NO2−-N). The overall mean removal efficiencies for heavy metals in the vegetated CWs were considerably greater than those of the control. Concentrations of Cr, Cu, Fe, Pb, Zn, Al, Ni, and Cd were calculated in the roots, rhizomes, leaves, and stems of the plant; then, the bioaccumulation factor (BAF) and translocation factor (TF) were determined. An initial examination using scanning electron microscopy (SEM–EDX) was also included in the study. The analysis indicated that toxic elements were adsorbed on plant tissues, concentrated in the roots, and partially transported to the aerial parts. These results are useful for the design of CWs to treat industrial wastewater, enabling water of acceptable quality to be discharged into the environment, especially as a low maintenance and cost-effective technology in developing countries.

Products distribution and pollutants releasing characteristics during pyrolysis of waste tires under different thermal process

Pyrolysis has been widely utilized to achieve resource recovery of waste tires by attaining oil and carbon black. However, due to the stacking effect of fixed bed, the heat and mass transfer is insufficient during the pyrolysis process of waste tires. Additionally, the harmful N/S/Cl pollutants and heavy metals are inevitable that has been ignored. This paper systematically studied the effect of promoting heat and mass transfer on the oil quality and pollutant releasing characteristics during the pyrolysis of waste tires. A fixed bed pyrolizer with multifunction was innovatively designed to conduct fast pyrolysis by equipping an intermittent feeder and slow pyrolysis by equipping an agitator. Fast pyrolysis with feeding step by step and slow pyrolysis with stirring could promote the heat and mass transfer, which was firstly researched in lab-scale reactor. The experimental results demonstrated that slow pyrolysis with stirring was recommended with the target of acquiring pyrolytic oil. Promoting heat and mass transfer could improve the quality of oil and increase the retaining proportion of S in char during both fast and slow pyrolysis. The combustion of pyrolysis oil and gas generated more dioxins (0.6 ng/g_wt) than the total dioxins in pyrolytic gas and oil (0.06 ng/g_wt).

Pyrolysis Behaviors and Residue Properties of Iron-Rich Rolling Sludge from Steel Smelting

Iron-rich rolling sludge (FeRS) represents a kind of typical solid waste produced in the iron and steel industry, containing a certain amount of oil and large amounts of iron-dominant minerals. Pyrolysis under anaerobic environment can effectively eliminate organics at high temperatures without oxidation of Fe. This paper firstly investigated comprehensively the pyrolysis characteristics of FeRS. The degradation of organics in FeRS mainly occurred before 400 °C. The activation energy for pyrolysis of FeRS was extremely low, ca. 5.44 kJ/mol. The effects of pyrolytic temperature, atmosphere, heating rate, and stirring on pyrolysis characteristics were conducted. Commonly, the yield of solid residues maintained around 85 wt.%, with approximately 13 wt.% oil and 2 wt.% gas. Due to the low yield of oil and gas, their further utilization remains difficult despite CO₂ introduction which could upgrade their quality. The solid residues after pyrolysis exhibited porous properties with co-existence of micropores and mesopores. Combined with the high content of zero-valent iron, magnetic property, hydrophobic characteristic, and low density, the solid residues could be further utilized for water pollution control and soil remediation. Moreover, the solid residues were suitable for sintering to recover valuable iron resources. However, the solid residues also contained certain heavy metals, such as Cd, Cr, Cu, Ni, Pb, and Zn, which might cause secondary pollution during their utilization. In particular, the toxic Cr possessed high content, which should be treated with detoxification and removal. This paper provides fundamental information for pyrolysis of FeRS and utilization of solid residues.

Products distribution and hazardous elements migration during pyrolysis of oily sludge from the oil refining process

Oily sludge is a hazardous waste due to the enrichment of nitrogen, sulfur, PAHs, and heavy metals. In this work, an oily sludge from oil refining factory was pyrolyzed at various temperatures of 250-850 °C in a fixed bed reactor focusing on product distribution and migration of hazardous compounds of PAHs, sulfur, nitrogen-containing compounds, and heavy metals. The mechanism of PAHs formation and migration of nitrogen, sulfur, heavy metals were elucidated by comprehensive analysis of the solid, liquid, and gas products. The distribution and risk analysis of heavy metals were also conducted. The pyrolytic products distribution was markedly affected by pyrolysis temperatures. A maximum oil yield was observed at 500 °C, which can further crack into gas due to secondary reaction. The pyrolytic gas was enriched in the order of CO₂ > CO > CH₄ > H₂. At lower temperatures, CO₂ was largely generated due to the elimination of oxygen-containing functional groups, while H₂ was mainly formed above 450 °C due to the recombination reaction. Higher temperatures promoted more N-/S-containing compounds into tar and gas phases. The N-/S-containing compounds mainly included NH₃, HCN, H₂S, SO₂, COS in the gas phase and amines, indoles, pyridines, nitriles, thiophenes in liquid phase. PAHs with 2-ring to 5-ring were mainly generated due to the secondary reaction at higher temperatures. Moreover, Pyrolysis caused the accumulation of heavy metals in chars. Cd presented a high potential risk while the other heavy metals in chars presented a low risk.

A Sustainable Approach on Spruce Bark Waste Valorization through Hydrothermal Conversion

In the context of sustainable use of resources, hydrothermal conversion of biomass has received increased consideration. As well, the hydrochar (the solid C-rich phase that occurs after the process) has caused great interest. In this work, spruce bark (Picea abies) wastes were considered as feedstock and the influence of hydrothermal process parameters (temperature, reaction time, and biomass to water ratio) on the conversion degree has been studied. Using the response surface methodology and MiniTab software, the process parameters were set up and showed that temperature was the significant factor influencing the conversion, while residence time and the solid-to-liquid ratio had a low influence. Furthermore, the chemical (proximate and ultimate analysis), structural (Fourier-transform infrared spectroscopy, scanning electron microscopy) and thermal properties (thermogravimetric analysis) of feedstock and hydrochar were analyzed. Hydrochar obtained at 280 °C, 1 h processing time, and 1/5 solid-to-liquid ratio presented a hydrophobic character, numerous functional groups, a lower O and H content, and an improved C matter, as well as a good thermal stability. Alongside the structural features, these characteristics endorsed this waste-based product for applications other than those already known as a heat source.

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.

Comparative analysis of membrane fouling mechanisms induced by colloidal polymer: Effects of sodium and calcium ions

Polymer (anionic polyacrylamide, APAM) flooding produced wastewater has a relatively high degree of mineralization and abundant ionic species. A comprehensive and systematic investigation of the influence of ion identity on APAM-induced membrane fouling is extremely necessary but has not been conducted to date. A comparative investigation was performed herein to reveal the underlying mechanisms of the influence of Na⁺ and Ca²⁺ (1000 mg/L) on APAM-induced membrane fouling in the adsorption and microfiltration (MF) processes. Na⁺ and Ca²⁺ exhibited contrasting influences on the filtration efficiency, cleaning efficiency, and fouling resistance. Compared to Na⁺, Ca²⁺ promoted reversible fouling and the formation of a loose cake layer; moreover, a higher removal rate and flux recovery were achieved. Additionally, simulations based on adsorption kinetic and membrane fouling models, and a series of microscopic analyses were performed to validate the contradictory influences. During the APAM-based MF process, the membrane fouling was effectively mitigated at the applied ionic strength because of the stronger hydration repulsive force generated by hydrated Ca²⁺ compared to that by Na⁺. This study provides vital guidance for membrane fouling control in the microfiltration of polymer flooding produced wastewater.

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.

Experimental study on gasification of oil sludge with steam and its char characteristic

Hydrogen can be prepared by oil sludge (OS) gasification with steam, which is of great significance for industrial hazardous waste treatment and resource conservation. The gasification performance was studied by a tube furnace reactor. The OS gasification was carried out at different temperatures (600, 700, 800 and 900 °C) and with different steam to OS ratio (SOS) (0.1:1, 0.3:1, 0.5:1). During the gasification process, hydrogen production first increased and then decreased, and hydrogen production was faster in 5-15 min. The yield of hydrogen of OS gasification reached the maximum when the SOS was 0.3:1 at 800 °C. The highest hydrogen yield per unit mass OS was 48.50 mL min^-1 g^-1. After gasification, the char yield was high, generally more than 50%. It was necessary to treat the char and incineration was an effective solution for low carbon fuels. Thus particle size distribution, incineration thermogravimetric analysis and heavy metal leaching concentrations analysis were carried out. The results showed that the average particle size of char ranged from 85 to 120 µm. The char incineration process could be divided into three stages: water evaporation, the precipitation and combustion of volatiles, and the combustion of fixed carbon and heavy components. After OS gasification at 800 °C, the leaching concentrations of typical heavy metals (As, Cr, Cu, Ni, Pb and Zn) were all up to the standard. Therefore, OS gasification combined with char incineration was an effective approach for the utilization of solid waste, which can recover hydrogen energy and reduce environmental risks.

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.

Pyrolysis characteristics and kinetics analysis of oil sludge with CaO additive

In the process of exploitation, transportation and refining of high-sulfur crude oil, a large number of oil sludge (OS) with high sulfur content is produced. Pyrolysis has been proved to be an effective method for OS disposal, but for solid waste with high sulfur content, lots of sulfur-containing gases will be released during thermal disposal. The addition of calcium oxide in pyrolysis process is an economical and effective way to capture sulfur-containing gases. In order to understand the pyrolysis process of OS with CaO, a thermogravimetric analyser was used to conduct pyrolysis experiments of OS with different Ca/S molar ratios (0, 1, 2 and 3) at different heating rates (10°C/min, 20°C/min, 30°C/min and 40°C/min). The results showed that with the increase of CaO addition the derivative thermogravimetric curves showed a gentle trend. In addition, new weight loss peaks were occurred at 700-900°C and after 1100°C, which were the decomposition of calcium carbonate and calcium sulfate, respectively. The kinetic parameters were solved by Friedman, FWO, and Starink methods, and the results were similar, with an average activation energies (E) value of 214 kJ/mol. The change trend of the activation energy was followed by an increase and then a decrease corresponding to the change of energy demand for the reaction. The calculated average values of ΔH, ΔG and ΔS were about 207, 447 and -0.3250 kJ/mol, respectively. When the conversion rate was 0.5, the thermodynamic parameters reached their maximum values.