Review of Emission Characteristics and Purification Methods of Volatile Organic Compounds (VOCs) in Cooking Oil Fume

Volatile organic compounds (VOCs) in cooking oil fumes need to be efficiently removed due to the significant damage they cause to the environment and human health. This review discusses the emission characteristics, which are influenced by different cooking temperatures, cooking oils, and cuisines. Then, various cooking oil fume purification methods are mainly classified into physical capture, chemical decomposition, and combination methods. VOCs removal rate, system operability, secondary pollution, application area, and cost are compared. The catalytic combustion method was found to have the advantages of high VOC removal efficiency, environmental protection, and low cost. Therefore, the last part of this review focuses on the research progress of the catalytic combustion method and summarizes its mechanisms and catalysts. The Marse-van Krevelen (MVK), Langmuir-Hinshelwood (L-H), and Eley-Rideal (E-R) mechanisms are analyzed. Noble metal and non-noble metal catalysts are commonly used. The former showed excellent activity at low temperatures due to its strong adsorption and electron transfer abilities, but the high price limits its application. The transition metals primarily comprise the latter, including single metal and composite metal catalysts. Compared to single metal catalysts, the interaction between metals in composite metal catalysts can further enhance the catalytic performance.

p-Xylene Oxidation to Terephthalic Acid: New Trends

Large-scale terephthalic acid production from the oxidation of p-xylene is an especially important process in the polyester industry, as it is mainly used in polyethylene terephthalate (PET) manufacturing, a polymer that is widely used in fibers, films, and plastic products. This review presents and discusses catalytic advances and new trends in terephthalic acid production (since 2014), innovations in terephthalic acid purification processes, and simulations of reactors and reaction mechanisms.

Improved Whole-Cell Biocatalyst for the Synthesis of Vitamin E Precursor 2,3,5-Trimethylhydroquinone

2,3,5-Trimethylhydroquinone (2,3,5-TMHQ) is the key precursor in the synthesis of vitamin E. It is still a major challenge to produce 2,3,5-TMHQ under mild reaction conditions by chemical methods. The monooxygenase system MpdAB can specifically catalyze the conversion of 2,3,6-trimethylphenol (2,3,6-TMP) to 2,3,5-TMHQ. However, the weak catalytic capacity of wild-type MpdA and the cytotoxicity of the substrate limited the production efficiency of 2,3,5-TMHQ. Here, homologous modeling and saturation mutation were performed to increase the catalytic activity of MpdA. Two variants, L128A and L128K, with higher activity toward 2,3,6-TMP (1.86-1.87-fold) were obtained. On the other hand, an evolved strain B5-4M-evolved with enhanced resistance to 2,3,6-TMP (8.15-fold higher for 1000 μM 2,3,6-TMP) was obtained through adaptive laboratory evolution. Subsequently, a 5.29-fold (or 4.87-fold) improvement in 2,3,5-TMHQ production was achieved by a strain B5-4M-evolved harboring L128K (or L128A) and MpdB, in comparison with that of the wild type (strain B5-4M expressing MpdAB). This study provides better genetic resources for producing 2,3,5-TMHQ and proves that the synthesis efficiency of 2,3,5-TMHQ can be improved through enzyme modification and adaptive laboratory evolution.

Classic Pentachlorophenol Hydroxylating Phenylalanine 4-Monooxygenase from Indigenous Bacillus tropicus Strain AOA-CPS1: Cloning, Overexpression, Purification, Characterization and Structural Homology Modelling

The metabolically promiscuous pentachlorophenol (PCP) hydroxylating Phe4MO (represented as CpsB) was detected, amplified (from the genome of Bacillus tropicus strain AOA-CPS1), cloned, overexpressed, purified and characterized here. The 1.755-kb gene cloned in the pET15b vector expressed a ≅ 64 kDa monomeric protein which was purified to homogeneity by single-step affinity chromatography, with a total yield of 82.1%. The optimum temperature and pH of the enzyme were found to be 30 °C and 7.0, respectively. CpsB showed functional stability between pH 6.0-7.5 and temperature 25-30 °C. The enzyme-substrate reaction kinetic studies showed the allosteric nature of the enzyme and followed pre-steady state using NADH as a co-substrate with apparent vmax, Km, kcat and kcat/Km values of 0.465 μM.s-1, 140 μM, 0.099 s-1 and 7.07 × 10-4 μM-1.s-1, respectively, for the substrate PCP. The in-gel trypsin digestion experiments and bioinformatic tools confirmed that the reported enzyme is a Phe4MO with multiple putative conserved domains and metal ion-binding site. Though Phe4MO has been reported to have a diverse catalytic function, here we report, for the first time, that it functions as a PCP dehalogenase or PCP-4-monooxygenase by hydroxylating PCP. Hence, the use of this enzyme may be further explored in the bioremediation of PCP and other related xenobiotics.

Organometallic 3d transition metal NHC complexes in oxidation catalysis

The development of processes for the selective oxidation of hydrocarbons is a major focus in catalysis research. Making this process simultaneously environmentally friendly is still challenging. 3d transition metals are...

Hydrogen peroxide-mediated synthesis of 2,4-substituted quinazolines via one-pot three-component reactions under metal-free conditions

An efficient metal-free synthesis of 2,4-substituted quinazolines via a hydrogen peroxide-mediated one-pot three-component reaction of 2-aminoaryl ketones, aldehydes, and ammonium acetate has been developed. The transformation proceeded readily under mild conditions in the presence of commercially available hydrogen peroxide. The significant advantages of this approach are (1) the readily available atom-efficient and green hydrogen peroxide as oxidant; (2) no transition metal catalyst is required; (3) mild reaction conditions; and (4) wide substrate scope. To the best of our knowledge, utilizing hydrogen peroxide as an atom-efficient and green oxidant for the synthesis of 2,4-substituted quinazolines has not previously been reported in the literature. This method is complementary to previous protocols for the synthesis of 2,4-substituted quinazolines.

An efficient metal-free synthesis of 2,4-substituted quinazolines via a hydrogen peroxide-mediated one-pot three-component reaction of 2-aminoaryl ketones, aldehydes, and ammonium acetate has been developed.

Electronic Finetuning of a Bio-inspired Iron(II) tetra-NHC Complex by trans Axial Isocyanide Substitution

The synthesis of trans axially substituted mono- (1 a) and bis(tert-butylisocyanide) (1 b) derivatives of the highly active homogeneous bio-inspired iron(II) olefin epoxidation (pre-)catalyst 1 bearing an equatorial macrocyclic tetra N-heterocyclic carbene and two trans axial labile acetonitrile ligands is reported. NMR spectroscopy and SC-XRD indicate a considerable π-backdonation from the iron(II) centres to the isocyanide ligand(s). The impact of isocyanide substitution on the electronic features of the complexes is studied by cyclic voltammetry revealing a significant increase in half-cell potential assignable to the reversible Fe(II)/Fe(III) redox couple with an increasing number of isocyanides as a result of their π-accepting properties: E1/2 =0.15 V (1), E1/2 =0.35 V (1 a), E1/2 =0.44 V (1 b).

Iron N-heterocyclic carbene complexes in homogeneous catalysis

This review article summarizes recent development of homogeneous iron N-heterocyclic carbene catalysts.

A survey of senior practitioners regarding most desirable qualifications for hiring and advancement within forensic science

In today's environment in the field of forensic science where continual advancements in technology and analytical approaches are the norm, the need for forensic practitioners with more specialized and subject-specific knowledge is critical. An updated survey targeting the preferred educational requirements by senior practitioners, crime laboratory directors and managers for entry level applicants was conducted. Results underscored a preference for specialized coursework within specific disciplines in preparing the next generation of forensic scientists while maintaining a strong foundation in the natural sciences at the undergraduate level. Practitioners, regardless of discipline, are seeking applicants with exposure to advanced curriculum content in addition to refined professional skills and critical thinking capabilities. The results of this survey reflect a transition in the needs of crime laboratory employers from a general, broad based criminalistics curriculum as described under current accreditation guidelines, to a focused subject matter rich curriculum with additional management and professional content.

A hydroquinone-specific screening system for directed P450 evolution

The direct hydroxylation of benzene to hydroquinone (HQ) under mild reaction conditions is a challenging task for chemical catalysts. Cytochrome P450 (CYP) monooxygenases are known to catalyze the oxidation of a variety of aromatic compounds with atmospheric dioxygen. Protein engineering campaigns led to the identification of novel P450 variants, which yielded improvements in respect to activity, specificity, and stability. An effective screening strategy is crucial for the identification of improved enzymes with desired characteristics in large mutant libraries. Here, we report a first screening system designed for screening of P450 variants capable to produce hydroquinones. The hydroquinone quantification assay is based on the interaction of 4-nitrophenylacetonitrile (NpCN) with hydroquinones under alkaline conditions. In the 96-well plate format, a low detection limit (5 μM) and a broad linear detection range (5 to 250 μM) were obtained. The NpCN assay can be used for the quantification of dihydroxylated aromatic compounds such as hydroquinones, catechols, and benzoquinones. We chose the hydroxylation of pseudocumene by P450 BM3 as a target reaction and screened for improved trimethylhydroquinone (TMHQ) formation. The new P450 BM3 variant AW2 (R47Q, Y51F, I401M, A330P) was identified by screening a saturation mutagenesis library of amino acid position A330 with the NpCN assay. In summary, a 70-fold improved TMHQ formation was achieved with P450 BM3 AW2 when compared to the wild type (WT) and a 1.8-fold improved TMHQ formation compared to the recently reported P450 BM3 M3 (R47S, Y51W, A330F, I401M).

Oxidative functionalization of aliphatic and aromatic amino acid derivatives with H2O2 catalyzed by a nonheme imine based iron complex

The oxidation of a series of N-acetyl amino acid methyl esters with H₂O₂ catalyzed by a very simple iminopyridine iron(ii) complex 1 easily obtainable in situ by self-assembly of 2-picolylaldehyde, 2-picolylamine, and Fe(OTf)₂ was investigated. Oxidation of protected aliphatic amino acids occurs at the α-C–H bond exclusively (N-AcAlaOMe) or in competition with the side-chain functionalization (N-AcValOMe and N-AcLeuOMe). N-AcProOMe is smoothly and cleanly oxidized with high regioselectivity affording exclusively C-5 oxidation products. Remarkably, complex 1 is also able to catalyze the oxidation of the aromatic N-AcPheOMe. A marked preference for the aromatic ring hydroxylation over Cα–H and benzylic C–H oxidation was observed, leading to the clean formation of tyrosine and its phenolic isomers.

Amino acid derivatives are oxidized by the 1/H₂O₂ system. A marked preference for the aromatic over Cα–H and benzylic C–H oxidation is observed with phenylalanine.

Synthesis, characterization and derivatization of hydroxyl-functionalized iron(ii) bis(NHC) complexes

The syntheses of a novel hydroxyl-functionalized tetradentate NHC/pyridine hybrid ligand and the corresponding Ag(i) and Fe(ii) complexes are presented. Spectroscopic and X-ray diffraction techniques are used for structural investigations and cyclic voltammetry measurements reveal interesting electronic properties. Transmetalation of the trinuclear Ag(i) complex (C1) yields a mononuclear and a dinuclear iron(ii) bis(NHC) complex (C2 and C3), which can be separated by stepwise precipitation. The former is isostructural to iron(ii) bis(NHC) complex A, which is a versatile oxidation catalyst. Furthermore, suitable conditions for esterification reactions of the ligand precursor and iron(ii) bis(NHC) complex (C2) have been established, demonstrating the utility of the hydroxyl functionality for immobilization and derivatization purposes.

Direct hydroxylation of benzene and aromatics with H2O2 catalyzed by a self-assembled iron complex: evidence for a metal-based mechanism

An imine-based catalyst easily obtained by self-assembly of cheap and commercially available starting materials selectively catalyzes the hydroxylation of aromatic compounds.