Non-catalyzed Process Research Articles

Chemical looping gasification with potassium-catalyzed petroleum coke for enhanced production of H2 and H2S

A large amount of petroleum coke (petcoke) is considered as waste with low gasification rate and urgently needs to be exploited in an environmentally friendly, efficient and economic method. As potassium plays an important role in the gasification reactivity enhancement, the effects of potassium on the carbon conversion, gas product distribution and the sulfur conversion were investigated in the chemical looping gasification (CLG) process via a batch fluidized bed. H2 yield produced by 10%KNO3-petcoke increased to 2.1 times and 2.9 times for K-catalyzed steam gasification and CLG processes respectively, in comparison with the non-catalyzed processes. The results demonstrated that K promoted char gasification and water-shift reaction in K-catalyzed processes. The optimal amount of KNO3 was 10% taking the syngas quality and the gasification rate into account. When petcoke was modified by K2CO3 instead of KNO3, the yields of H2 and CO2 increased dramatically, but the gas distributions were similar (about 10% CO, 30% CO2 and 60% H2). For K2CO3-petcoke, a long time for high conversion rate was obtained, and the carbon conversion efficiency reached 91.58%. The increase in the gasification rate was ascribed to the inhibition of graphitization after adding K. And sulfur released mainly in the form of H2S in the K-catalyzed CLG, indicating that K facilitated sulfur recovery to get the maximum possible value-addition. Besides, K had less enhancement in sulfur conversion than carbon conversion with the increasing additive amount of K. With respect of sulfur fate, the fraction of mercaptan decreased while the inorganic sulfur became dominant composition at the presence of K. In conclusion, K-catalyzed CLG provided a novel approach to effectively solve the problem of utilizing petcoke of low gasification reactivity and high sulfur emission.

Silver-Catalyzed Anti-Markovnikov Hydroxyfluorination of Styrenes

A silver-catalyzed radical hydroxyfluorination of styrenes with Selectfluor and H2O has been explored with exclusive anti-Markovnikov-type regioselectivity, thus affording vicinal fluorohydrins with regioselectivities opposite that of noncatalyzed processes. This reaction is operationally simple, scalable under mild conditions. The mechanism studies and DFT calculations revealed that the reaction go through a radical mechanism.

The Reaction Pathway of Cellulose Pyrolysis to a Multifunctional Chiral Building Block: The Role of Water Unveiled by a DFT Computational Investigation.

LAC (hydroxylactone (1R,5S)-1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one) is one of the most interesting products of the pyrolysis of cellulose and represents a useful chiral building block in organic synthesis. A computational investigation at the DFT level on the mechanism of formation of LAC shows that this species can be obtained following two reaction paths, path A and path B, starting from a well-known pyrolysis product (ascopyrone P). A series of internal rearrangements involving in all cases a proton transfer leads directly to LAC (path B). An alternative path (path A) can be also followed. From this path, via a "gate" connecting the two reaction channels, it is possible to reach path B and form LAC. In both cases, the rate-determining step of the process is the initial keto-enol isomerization. We found that water, which is present in the reaction mixture, "catalyzes" the reaction by assisting the proton transfers present in all the steps of the process. In particular, water lowers the barrier of the rate-determining step that becomes 40.9 kcal mol-1 (79.4 kcal mol-1 in the absence of water). The corresponding computed rate constant is 4.3×10 s-1 at 500 °C, a value which is consistent with the presence of LAC in the absence of metal catalysts. The results of this study on the non-catalyzed process underpin the important role played by water in the formation of pyrolysis products of cellulose where proton transfer is a key mechanistic step.

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

The effect of surface and bulk potassium promotion on the transition metal oxides (Mn, Fe, Co) catalytic activity in catalytic soot oxidation was investigated. The surface promotion was obtained via incipient wetness impregnation, whereas the bulk promotion—nanostructuration—was obtained via wet chemical synthesis or solid state reaction leading to mixed oxide materials. The introduction of potassium into the transition metal oxide matrix results in the formation of tunneled or layered structures, which enable high potassium mobility. The structure of the obtained materials was verified by powder X-ray diffraction and Raman spectroscopy and the catalytic activity in soot oxidation was determined by TPO-QMS and TGA. It was found that the surface promotion does not alter the metal oxide structure and leads to either enhancement (Mn, Fe) or deterioration (Co) of the catalytic activity. Simultaneously, the catalytic activity in soot combustion of the potassium structured oxides is strongly enhanced. The most active, cobalt oxide based catalyst significantly lowers the temperature of 50 % of soot conversion by ~350 °C comparing to the non-catalyzed process. The study allows for the establishment of rational guidelines for designing robust materials for DPF applications based on ternary metal oxides.

ChemInform Abstract: Regioselective Radical Aminofluorination of Styrenes.

The copper-catalyzed radical aminofluorination of styrenes with N-fluorobenzenesulfonimide (NFSI) is realized with high regioselectivity, thus affording aminofluorination products with regioselectivities opposite that of the palladium-catalyzed and noncatalyzed processes. Preliminary mechanistic studies suggested the reaction went through a radical pathway and was supported by DFT calculations. In these reactions, NFSI is utilized as both a radical nitrogen source and radical fluorine source, thus rendering it an attractive reagent.

Regioselective radical aminofluorination of styrenes.

The copper-catalyzed radical aminofluorination of styrenes with N-fluorobenzenesulfonimide (NFSI) is realized with high regioselectivity, thus affording aminofluorination products with regioselectivities opposite that of the palladium-catalyzed and noncatalyzed processes. Preliminary mechanistic studies suggested the reaction went through a radical pathway and was supported by DFT calculations. In these reactions, NFSI is utilized as both a radical nitrogen source and radical fluorine source, thus rendering it an attractive reagent.

Regioselective Radical Aminofluorination of Styrenes

AbstractThe copper‐catalyzed radical aminofluorination of styrenes with N‐fluorobenzenesulfonimide (NFSI) is realized with high regioselectivity, thus affording aminofluorination products with regioselectivities opposite that of the palladium‐catalyzed and noncatalyzed processes. Preliminary mechanistic studies suggested the reaction went through a radical pathway and was supported by DFT calculations. In these reactions, NFSI is utilized as both a radical nitrogen source and radical fluorine source, thus rendering it an attractive reagent.

Enhancement of Lignin Biopolymer Isolation from Hybrid Poplar by Organosolv Pretreatments

Lignocellulosic biomass is an abundant renewable resource that has the potential to displace petroleum in the production of biomaterials and biofuels. In the present study, the fractionation of different lignin biopolymers from hybrid poplar based on organosolv pretreatments using 80% aqueous methanol, ethanol, 1-propanol, and 1-butanol at 220°C for 30 min was investigated. The isolated lignin fractions were characterized by Fourier transform infrared spectroscopy (FT-IR), high-performance anion exchange chromatography (HPAEC), 2D nuclear magnetic resonance (2D NMR), and thermogravimetric analysis (TGA). The results showed that the lignin fraction obtained with aqueous ethanol (EOL) possessed the highest yield and the strongest thermal stability compared with other lignin fractions. In addition, other lignin fractions were almost absent of neutral sugars (1.16–1.46%) though lignin preparation extracted with 1-butanol (BOL) was incongruent (7.53%). 2D HSQC spectra analysis revealed that the four lignin fractions mainly consisted ofβ-O-4′ linkages combined with small amounts ofβ-β′andβ-5′ linkages. Furthermore, substitution ofCαinβ-O-4′ substructures had occurred due to the effects of dissolvent during the autocatalyzed alcohol organosolv pretreatments. Therefore, aqueous ethanol was found to be the most promising alcoholic organic solvent compared with other alcohols to be used in noncatalyzed processes for the pretreatment of lignocellulosic biomass in biorefinery.

From Formamide to Adenine: A Self-Catalytic Mechanism for an Abiotic Approach

Mechanisms for abiotic reaction pathways from formamide (H2NCHO) to adenine are presented herein. Formamide is a simple C1 building block hypothesized to be a precursor to many protometabolic compounds. On the basis of a step-by-step mechanism of the reaction pathways, formamide is suggested to be more reactive in addition reactions than HCN. In addition to its simplicity, the formamide self-catalyzed mechanism is energetically (kinetically) more viable than either a water-catalyzed mechanism or noncatalyzed processes. Moreover, this self-catalyzed mechanism accounts for the yields of purine and adenine previously observed in experiments. This mechanism may elucidate processes that were vital for the emergence of life on the early earth.

Computational study on the mechanism of non-catalyzed and catalyzed bromolactonization

Important intermediates and key transition states of catalyzed bromolactonization are researched by using density functional theory (DFT). The non-catalyzed process is also investigated to make a comparison with the catalyzed one. The pathways of reaction are investigated in detail. The results suggest that the non-catalyzed reaction proceeds in three major steps involving electrophilic addition, ring-closure and H transference, while the catalyzed process involves Cat–NBS interaction, H transference, and ring-closure. Electrophilic addition is the rate-determining step in the non-catalyzed process. The small discrepancy of charge density may account for the difficulty of electrophilic addition. Sulfur of Cat is the catalytic center which changes the charge density of Br on NBS to reduce the energy barrier sharply. There are four regioselective pathways related to exo-five-lactone and endo-six-lactone. The preferred pathway for exo-five-lactone is confirmed. It is the first time to uncover the catalytic mechanism by calculation method.

TG/DSC/FTIR characterization of linear geranyl diesters

The synthesis, thermal behavior, and characterization of the decomposition products of linear geranyl diesters: digeranyl succinate, digeranyl glutarate, digeranyl adipinate, and digeranyl sebacinate were presented. The linear geranyl diesters were prepared in direct esterification process of a molar stoichiometric ratio of geraniol and suitable acidic reagent in solvent-free medium at 130 °C using butylstannoic acid as a catalyst. Their structure was confirmed based on FTIR, 1H- and 13C-NMR spectra. It was proved that the use of tin catalyst allowed decreasing the reaction time and increasing the final conversion of substrates when compared to non-catalyzed process. It considerably simplifies the processing by reduction of the preparation cost and thus this new method of synthesis of aroma diesters may be attractive for practical applications. The thermal behavior of prepared compounds was studied by TG/DSC/FTIR coupled method. TG analysis showed that diesters are thermally stable up to temperatures above 200 °C. The DTG curves confirmed that these decomposition run as a single-stage process. The T max1 were in the range of 294.5–313.8 °C depending on the aliphatic chain length (–CH2–)n in the structure of aroma diesters, which was in accordance with DSC data. The analysis of the gases evolved during heating of diesters in inert atmosphere indicated on the asymmetrical disrupt of their bonds. The cleavage of ester bond and O-geranyl bond was expected. It resulted in production of the mixture of derivatives of geraniol (acyclic and alicyclic monoterpene hydrocarbons) like myrcene, ocimene, or limonene as main decomposition products. In addition, the formation of anhydride, lactone, or ketone functionalities among the degradation products clearly confirmed the proposed degradation path of studied diesters.

Investigations on enzyme catalytic promiscuity: The first attempts at a hydrolytic enzyme-promoted conjugate addition of nucleophiles to α,β-unsaturated sulfinyl acceptors

Abstract Looking for new examples of enzyme catalytic promiscuity, attempts were made to use hydrolytic enzymes as catalysts for a conjugate addition of nucleophiles toα,β-unsaturated sulfinyl derivatives. The addition of piperidine to phenyl vinyl sulfoxide in chloroform proceeded both in the enzyme-catalyzed and non-catalyzed process, while in the former case the reaction was 2.5-fold faster. On the contrary, the conjugate addition of benzenethiol to phenyl vinyl sulfoxide proceeded only in the presence of enzymes and when ethanol was used as solvent. In no case were the products enantiomerically enriched. However, the addition of benzenethiol to a better Michael acceptor, namely a cyclic α-sulfinylalkenylphosphonate, performed in the presence of various lipases under kinetic resolution conditions gave in certain instances both the product and the recovered substrate with up to 25% optical purity. Although the stereoselctivity and the rates of these reactions were quite low, this are the first examples of the lipase-catalyzed Michael addition of heteroatom nucleophiles to α,β-unsaturated heteroorganic acceptors. Some mechanistic considerations are presented.

Catalytic Role of Vicinal OH in Ester Aminolysis: Proton Shuttle versus Hydrogen Bond Stabilization

This computational study provoked by the process of peptide bond formation in the ribosome investigates the influence of the vicinal OH group in monoacylated diols on the elementary acts of ester aminolysis. Two alternative approaches for this influence on ester ammonolysis were considered: stabilization of the transition states by hydrogen bonds and participation of the vicinal hydroxyl in proton transfer (proton shuttle). The activation due to hydrogen bonds of the vicinal hydroxyl via tetragonal transition states was rather modest; the free energy of activation was reduced by only 5.2 kcal/mol compared to the noncatalyzed reaction. The catalytic activation via the proton shuttle mechanism with participation of the vicinal OH in the proton transfer via hexagonal transition states resulted in considerable reduction of the free energy of activation to 33.5 kcal/mol, i.e., 16.0 kcal/mol lower than in the referent process. Accounting for the influence of the environment on the reaction center by a continuum model (for ε from 5 to 80) resulted in further stabilization of the rate-determining transition state by 4-5 kcal/mol. The overall reduction of the reaction barrier by about 16 kcal/mol as compared to the noncatalyzed process corresponds to about 10(9)-fold acceleration of the reaction, in agreement with the experimental estimate for acceleration of this process in the ribosome.

Development of Highly Selective Process for Mono-Ethylene Glycol Production from Ethylene Oxide via Ethylene Carbonate Using Phosphonium Salt Catalyst

A new process for the production of mono-ethylene glycol (MEG; HOCH2CH2OH) was developed by Mitsubishi Chemical Corporation (MCC) to meet its growing demand in the world. While the MEG selectivity of conventional non-catalyzed process is around 89% under typical conditions, that of the new process exceeds 99%. The key of the high selectivity is the two-step synthesis via ethylene carbonate. The first step reaction is catalyzed by phosphonium salts and generates ethylene carbonate as an intermediate. This is followed by hydrolysis of ethylene carbonate in the second step. Several commercial plants of the new process have already been operated world-wide.

Wet Aerobic Oxidation of Lignin into Aromatic Aldehydes Catalysed by a Perovskite-type Oxide: LaFe1-xCuxO3 (x=0, 0.1, 0.2)

The perovskite-type oxide catalyst LaFe1-xCuxO3 (x=0, 0.1, 0.2) was prepared by the sol–gel method, and tested as a catalyst in the wet aerobic oxidation (WAO) of lignin into aromatic aldehydes. The lignin conversion and the yield of each aromatic aldehyde were significantly enhanced in the catalytic process, compared with the non-catalyzed process. Moreover, it was shown that the stability of activity and structure of LaFe1-xCuxO3 (x=0, 0.1, 0.2) remained nearly unchanged after a series of successive recyclings of the catalytic reactions, indicating it was an efficient and recyclable heterogeneous catalyst for the conversion of lignin into aromatic aldehydes in the WAO process.

Perovskite-type Oxide LaMnO3: An Efficient and Recyclable Heterogeneous Catalyst for the Wet Aerobic Oxidation of Lignin to Aromatic Aldehydes

The perovskite-type oxide catalyst LaMnO3 prepared by the sol–gel method was found to be an efficient heterogeneous and recyclable catalyst for the wet aerobic oxidation of lignin to aromatic aldehydes. The lignin conversion rate and the yield of each aromatic aldehyde were enhanced significantly by the catalytic process as compared with the non-catalyzed process. Moreover, the activity, specific surface area and perovskite-type structure of the LaMnO3 catalyst remained nearly unchanged after five successive recycles of catalytic reactions.

Theoretical study on the Diels–Alder reaction of cyclopentadiene with methacrolein catalyzed by diethylimidazolium cation

AbstractThe theoretical studies of how room temperature ionic liquids control desired reactions are very scarce in contrast with their increasing applications in many fields as recyclable solvents, catalysts, and reaction mediums. The present work considers the Diels–Alder (D‐A) reaction of cyclopentadiene with methacrolein in the presence of diethylimidazolium salts as the first prototype of our systemic studies about important organic synthesis reactions catalyzed by room temperature ionic liquids. We show the mechanism details of the D‐A reactions with and without the dialkylimidazolium cation and rationalize the experimental findings based on the results from the quantum chemistry calculations at the AM1, HF/6‐31G(d), and B3PW91/6‐31G(d,p) levels of theory, respectively. It is found that the diethylimidazolium cation acts as a Lewis acid center to catalyze the D‐A reaction, which decreases the barrier and increases the asynchronicity of the D‐A reaction, but does not change the potential energy surface profile of the reaction compared to the noncatalyzed process. The present results rationalize the early experimental findings well and provide the first prototype for theoretically understanding the D‐A reaction in the presence of dialkylimidazolium salts. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Kinetics based determination of trace amounts of silver at the excess of copper ions

The determination of silver traces, based on the catalytic action of Ag + ions in the oxidation of salicylic acid by persulfate in the presence of 2,2′-dipyridyl as an activator, has been elaborated. The influence of several parameters, such as temperature, pH, salicylic acid concentration, persulfate concentration and 2,2′-dipyridyl concentration on the course of reaction has been investigated. The activation energies of the catalyzed (30.79 kJ mol −1) and non-catalyzed (44.77 kJ mol −1) processes were determined. Optimum conditions for the silver determination in the range of 4.3–38.8 ng cm −3 were established. The proposed method is more sensitive than atomic absorption spectrometry (AAS). The detection limit was 0.38 ng cm −3, so it was at least three orders of magnitude lower than that for the AAS method. The described method was used in the determination of the silver content in samples containing excess of copper and/or sulfate ions at concentrations of 8×10 −6–2.4×10 −2 M. The sulfate ions do not disturb the course of the reaction. The results of the determination of silver in a copper sheet by the proposed method were compared with the results of the analysis performed by AAS.

Phenolation of wood using oxalic acid as a catalyst: Effects of temperature and hydrochloric acid addition

Birch wood meal has been phenolated in the presence of oxalic acid alone or its mixture with hydrochloric acid (HCl) at various temperatures ranging from 150 to 250°C under high pressure. The effects of high temperature, high pressure, and the addition of HCl in conjunction with oxalic acid on the amounts of wood residue and combined phenol have been investigated. In the case of the oxalic acid-catalyzed process, by increasing reaction temperature from 180 to 250°C, the amounts of wood residue could be considerably reduced, but the amount of combined phenol decreased. In comparison to a noncatalyzed process in the absence of water, the catalyzed one offered a relatively lower amount of wood residue and a higher amount of combined phenol. However, compared to a noncatalyzed process with water, particularly at a high temperature of 250°C, the catalyzed process gave significantly larger amounts of wood residue. In addition, with a small addition of HCl to an oxalic acid catalyzed system, the amount of wood residue was remarkably reduced compared to that of oxalic acid alone, and the amount of combined phenol could be increased significantly. Furthermore, the mechanical properties of the moldings prepared from the phenolated wood were sufficiently improved by the addition of a small amount of HCl to the oxalic acid-catalyzed system. © 1996 John Wiley & Sons, Inc.

Photogenerated base as catalyst for imidization reactions

The photogeneration of free amines or diamines from soluble organic precursors such as photoactive 2-nitrobenzyl carbamates is useful for the imidization of polymers containing amic acid or amic ester moieties. The base-catalyzed reaction occurs at lower temperatures than the non-catalyzed thermal process and is applicable to the patterning of polymer coatings or thin films.