Production of Gasolines and Monocyclic Aromatic Hydrocarbons: From Fossil Raw Materials to Green Processes

New perspectives on the anaerobic degradation of BTEX: Mechanisms, pathways, and intermediates

Aromatic hydrocarbons like benzene, toluene, xylene, and ethylbenzene (BTEX) can escape into the environment from oil and gas operations and manufacturing industries posing significant health risks to humans and wildlife. Unlike conventional clean-up methods used, biological approaches such as bioremediation can provide a more energy and labour-efficient and environmentally friendly option for sensitive areas such as nature reserves and cities, protecting biodiversity and public health. BTEX contamination is often concentrated in the subsurface of these locations where oxygen is rapidly depleted, and biodegradation relies on anaerobic processes. Thus, it is critical to understand the anaerobic biodegradation characteristics as it has not been explored to a major extent. This review presents novel insights into the degradation mechanisms under anaerobic conditions and presents a detailed description and interconnection between them. BTEX degradation can follow four activation mechanisms: hydroxylation, carboxylation, methylation, and fumarate addition. Hydroxylation is one of the mechanisms that explains the transformation of benzene into phenol, toluene into benzyl alcohol or p-cresol, and ethylbenzene into 1-phenylethanol. Carboxylation to benzoate is thought to be the primary mechanism of degradation for benzene. Despite being poorly understood, benzene methylation has been also reported. Moreover, fumarate addition is the most widely reported mechanism, present in toluene, ethylbenzene, and xylene degradation. Further research efforts are required to better elucidate new and current alternative catabolic pathways. Likewise, a comprehensive analysis of the enzymes involved as well as the development of advance tools such as omic tools can reveal bottlenecks degradation steps and create more effective on-site strategies to address BTEX pollution.

Photocatalytic Upcycling and Depolymerization of Vinyl Polymers

Photocatalytic upcycling and depolymerization of vinyl polymers have emerged as promising strategies to combat plastic pollution and promote a circular economy. This mini review critically summarizes current developments in the upcycling and degradation of vinyl polymers including polystyrene and poly(meth)acrylates. Of these material classes, polymethacrylates possess the unique possibility to undergo a photocatalytic depolymerization back to monomer under thermodynamically favourable conditions, thus presenting significant advantages over traditional thermal strategies. Our perspective on current formidable challenges and potential future directions are also discussed.

High-solution emission characters and health risks of volatile organic compounds for sprayers in automobile repair industries

The increasing automobile repair industries (ARIs) with spray facilities have become an important volatile organic compound (VOC) pollution source in China. However, the VOC health risk assessment for long-term exposure in ARIs has not been well characterized. In this study, though sampled VOCs from 51 typical ARIs in Beijing, the relationship between emission patterns, average daily exposure concentrations (EC), and health risks was comprehensively analyzed with the health assessment method. Results showed that concentrations of 117 VOCs from the samples ranged from 68.53 to 19863.32 μg·m-3, while the ARI operator's daily VOC inhalation EC was 11.24-1460.70 μg·m-3. The organic VOC (OVOC) concentration accounted for 73.16 ~ 94.52% in the solvent-based paint workshops, while aromatics were the main VOC component in water-based paint spraying (WPS) workshops, accounting for 70.08%, respectively. And the method of inhalation exposure health risk assessment was firstly used to evaluate carcinogenicity and non-carcinogenicity risk for sprayers in ARIs. The cumulative lifetime carcinogenic risk (LCR) for 24 sampled VOCs were within acceptable ranges, while the mean hazard index (HI) for 1 year with 44 sampled VOCs was over 1. Among them, ethyl alcohol had a high carcinogenic risk in both mixed water-based paint (MP) and solvent-based paint workshops. The mean HI associated with aromatics were 2.88E - 3 and 4.30E - 3 for 1 h in MP and WPS workshops. O-ethyl toluene and acetone are VOC components that need to be paid attention to in future paint raw materials and spraying operations. Our study will provide the important references for the standard of VOC occupational exposure health limits in ARIs.

A Study of the Pyrolysis Products of Kraft Lignin

In order to valorize lignin wastes to produce useful aromatic compounds, the thermal degradation pyrolysis of Kraft lignin in the absence of catalysts has been investigated at 350, 450, and 550 °C. The high content of sulfur in the fresh sample led to the formation of S-containing compounds in products whose evolution in the gas phase was monitored through GC-MS analysis. Pyrolytic gas is rich in CH4, CO, CO2, and H2S with the presence of other sulfur compounds in smaller amounts (i.e., CH3SH, CH3-S-CH3, SO2, COS, and CS2). Biochar morphology and elemental composition have been investigated by means of SEM and EDX. The carbon content reaches ~90% after pyrolysis at 550 °C, while the oxygen content showed a decreasing trend with increasing temperature. From GC-MS analysis, bio-oil resulted rich in alkyl-alkoxy phenols, together with (alkyl)dihydroxy benzenes and minor amounts of hydrocarbons and sulfur compounds. NaOH/H2O and EtOH/H2O extraction were performed with the aim of extracting phenolic-like compounds. Sodium hydroxide solution allowed a better but still incomplete extraction of phenolic compounds, leaving a bio-oil richer in sulfur.

Advancements in the Conversion of Lipid-Rich Biowastes and Lignocellulosic Residues into High-Quality Road and Jet Biofuels Using Nanomaterials as Catalysts

At present, the majority of available road and jet biofuels are produced from oleochemical feedstocks that include vegetable oils and biowastes such as waste cooking oils and animal fats. Additionally, one of the most promising ways to achieve long-term environmental goals is to sustainably use lignocellulosic residues. These resources must be treated through a deoxygenation process and subsequent upgrading processes to obtain high-quality road and jet biofuels. Accordingly, in this review, we explore recent advancements in the deoxygenation of oleochemical and lignocellulosic feedstocks in the absence of hydrogen to produce high-quality road and jet biofuels, mainly focusing on the use of nanomaterials as catalysts and the valorization of lipid-rich biowastes and lignocellulosic residues. As a result, we found that regardless of the catalyst particle size, the coexistence of basic sites and weak/medium acid sites is highly important in catalytic systems. Basic sites can enhance the removal of oxygenates via decarboxylation and decarbonylation reactions and inhibit coke formation, while weak/medium acid sites can enhance the cracking reaction. Additionally, the extraction of value-added derivatives from lignocellulosic residues and their subsequent upgrade require the use of advanced methods such as the lignin-first approach and condensation reactions.

Novel Short Process for p-Xylene Production Based on the Selectivity Intensification of Toluene Methylation with Methanol

Toluene methylation using methanol offers a high potential molecular engineering process to produce p-xylene (PX) based on shape-selective catalysts. To further improve the process economics, a novel short process was proposed by reducing the high-energy consumption separation of xylene isomers in existing processes since the PX selectivity of the xylene isomers can be enhanced more than the industrial product quality of 99.7%. The PX selectivity intensification was achieved as a result of decreased contact time by considering factors such as the feed ratio, diluents, temperature, and pressure in a toluene methylation reactor. This proposed short process indicated that the reactor effluent could be purified only through the two conventional distillation towers by removing the methanol recovery and separation of xylene isomers. The raw material utilization, energy consumption, and economic data were also analyzed for the six contrastive cases. The short process using catalyst Si-Mg-P-La/ZSM-5 exhibited the highest effective utilization rates of 96.27 and 95.50% for toluene and methanol, respectively. The short process also showed a good economic value in terms of capital investment and operating costs due to the multistage reactor without benzene byproducts. Thus, the obtained total annual cost (TAC) value of 13 848.1 k$·year^-1 was 68.9 and 87.9% of the two existing processes.