Hydrogenation of alkenyl nitriles

lFour isomeric, unsaturated nitriles were hydrogenated, separately and as mixtures, over a Pd/alumina catalyst in a three-phase system at various pressures and temperatures. The nitriles were allylcyanide, cis- and trans-crotonitrile and methacrylonitrile and all have the general formula C4H5N. By varying hydrogenation conditions (temperatures, hydrogen pressure and substrate concentrations) activation energies and reaction orders were determined. Allylcyanide had the lowest activation energy because of the stability of its structure (non-conjugated) compared to the other substrates (conjugated). Reaction orders were -1, 0.5 and 1 for allylcyanide, crotonitrile and methacrylonitrile respectively. These findings indicate a difference in the strength of adsorption of each reactant, where allylcyanide is strongly adsorbed to the catalyst surface and methacrylonitrile weakly adsorbed. Isomerisation, which usually accompanies double bond hydrogenation in alkenes, was not observed. This lack of isomerisation may be due to the presence of more than one unsaturated group and the lack of an appropriate acid/base site on the support. A range of different solvents were used to identify solvent effects for every isomer. A full kinetic analysis involving activation energies and reaction orders was undertaken for IPA and 1-propanol. An effect on reaction orders was observed and was believed to be related to competitive adsorption by the solvent. The activity of the system was sensitive to solvent and reactant. No single solvent parameter could be shown to trend with the variations observed. Variation of conversion in different solvents was related to substrate structure. Competitive hydrogenation revealed subtle differences between the isomers. Allylcyanide did not show a significant change in reactivity when reacting in the presence of other isomers possibly because of it being more strongly adsorbed or because it adsorbed on corner or edge sites. Both crotonitrile and methacrylonitrile had their reactivity reduced in the presence of allylcyanide and when competing against each other. The behaviour was in keeping with the understanding developed for alkene hydrogenation over palladium

The hydrogenation of substituted benzenes over Rh/silica

The catalytic hydrogenation of substituted benzenes to saturated cyclic products is an industrially relevant reaction. It is important in the production of fine chemicals, petroleum and in the fuel industry. It is used in the process of lowering the aromatic content in diesel fuels to follow up the up-to-date environmental legalisation. It has been widely reported that aromatic ring hydrogenation is a structure insensitive reaction, however more recent studies have suggested that structure sensitivity may indeed exist. Therefore, the demand to perform more research on substituted benzenes to understand their behaviour during the hydrogenation has increased. Unlike most of what was found in literature, this study involved substituents which include methyl, ethyl, propyl, hydroxyl and methoxy groups. These reactions were performed at different parameters of temperatures, H2 pressure and concentrations and over Rh/SiO2 catalyst. Different mechanisms were suggested for the hydrogenation of aromatic compounds. A stepwise mechanism is generally accepted to explain the reaction mechanism. This suggestion was built on the fact aromatic adsorption is zero order in aromatics which suggests a strong adsorption of the substrates. This mechanism was confirmed in this work by the observation of alkyl cyclohexenes as intermediates during the hydrogenation of alkyl benzenes. Interesting points were observed during the hydrogenation of phenols. Firstly, cyclohexane was formed independently and directly from the original phenol. This observation was not found in most of previous studies. The other point was that phenol and anisole reacted in different ways from each other. Phenol was found to react in three independent routes, the formation of cyclohexanone, the formation of cyclohexanol and the formation of cyclohexane. Whereas, cyclohexanol was not formed directly from anisole, it was formed from cyclohexanone and after the total conversion of anisole. Competitive hydrogenations were also executed in order to investigate the behaviour of different groups in the same reaction. The findings of these tests were different from what was observed during the solo tests. As for the hydrogenation of alkylbenzenes, a steric effect might explain the differences between these substrates. It was observed that the reaction rate decreased as the alkyl group attached to the ring increased. These findings were not the same during the competitive hydrogenation. n-Propylbenzene, which has a larger group attached to the aromatic ring, showed higher reactivity in the presence of toluene and ethylbenzene, which suggests that the steric effect was not the only factor affecting the hydrogenation of substituted benzenes. These findings were explained by an electronic effect applied by the alkyl groups attached to the ring. The effect of these groups increases as the group size increases. In addition to steric and electronic effects, the mode of adsorption was also suggested to affect the competitive hydrogenations of phenols. Different modes of adsorption and different medium species formed leads to different behaviour during the competitive hydrogenation. In addition, NMR analysis was performed on selected samples from toluene and deuterated toluene reactions with deuterium and hydrogen. Toluene reaction with deuterium showed that all hydrogen atoms were replaced by deuterium at the beginning of the reaction. It was also shown from NMR results that -CD3 group was contacted to the surface which confirms the ability of -CH3 group to be adsorbed to the surface as well as the aromatic ring

Low temperature hydrogenation and hydrodeoxygenation of oxygen-substituted aromatics over Rh/silica: part 1 - phenol, anisole and 4-methoxyphenol

The hydrogenation and competitive hydrogenation of anisole, phenol and 4-methoxyphenol was studied in the liquid phase over a Rh/silica catalyst at 323 K and 3 barg hydrogen pressure. The rate of conversion of the reactants to products gave an order of anisole ≫ phenol > 4-methoxyphenol with hydrogenation and hydrodeoxygenation products being produced. Anisole, the most reactive substrate, was rapidly converted to methoxycyclohexane, cyclohexane, cyclohexanone and cyclohexanol, while phenol was hydrogenated to cyclohexanone, cyclohexanol and cyclohexane. In both cases cyclohexanol was produced as a secondary product from cyclohexanone hydrogenation. The yield of cyclohexane, the hydrodeoxygenation (HDO) product was > 20% from both reactants and was formed as a primary product from the aromatic species. Hydrogenation of 4-methoxyphenol was selective to 4-methoxycyclohexanone with no alcohol formation, while the hydrogenolysis products revealed that the catalyst was more active for demethoxylation than dehydroxylation. A comparative strength of adsorption was determined from competitive hydrogenation and gave an order of anisole > phenol > 4-methoxyphenol. Competitive, pair hydrogenation inhibited HDO and stopped cyclohexane from being produced from phenol and 4-methoxyphenol, although it was still produced from anisole. An increased rate of hydrogenation for 4-methoxyphenol was observed for competitive reactions with phenol and anisole but not when all three reactants were present. In contrast to the pair reactions, when all three reactants were present HDO occurred with all aromatics producing cyclohexane. Replacing hydrogen with deuterium revealed an inverse kinetic isotope effect for ring hydrogenation of 4-methoxyphenol but not phenol or anisole, which both had a positive KIE

Failure Rate of Single Dose Methotrexate in Managment of Ectopic Pregnancy

Background. One of the treatment modalities for ectopic pregnancy is methotrexate. The purpose of this study is to identify the failure rate of methotrexate in treating patients with ectopic pregnancy as well as the risk factors leading to treatment failure. Methods. A retrospective chart review of 225 patients who received methotrexate as a primary management option for ectopic pregnancy. Failure of single dose of methotrexate was defined as drop of BHCG level less than or equal to 14% in the seventh day after administration of methotrexate. Results. 225 patients had methotrexate. Most of the patients (151 (67%)) received methotrexate based on the following formula: f 50 mg X body surface area. Single dose of methotrexate was successful in 72% (162/225) of the patients. 28% (63/225) were labeled as failure of single dose of methotrexate because of suboptimal drop in BhCG. 63% (40/63) of failure received a second dose of methotrexate, and 37% (23/63) underwent surgical treatment. Among patient who received initial dose of methotrexate, 71% had moderate or severe pain, and 58% had ectopic mass size of more than 4 cm on ultrasound. Conclusion. Liberal use of medical treatment of ectopic pregnancy results in 71% success rate

Ancillary services from Hydrogen Based Technologies to Support Power System Frequency Stability

The share of renewable energy sources in the electricity generation is expected to maintain a steady growth in the future driven by economic and environmental reasons. However, these renewable sources such as wind and solar have fluctuating power output. This fluctuation causes strain on the power system and can cause imbalances between generation and load which may result in frequency instability. In the current liberalized energy market, the system operator uses ancillary services market to procure frequency containment reserve (FCR) which arrests undesirable frequency excursions within the first few seconds after the occurrence of an imbalance and ensures satisfactory primary frequency control. The system operator also procures frequency restoration reserve (FRR) which helps restore the frequency to its nominal value. Electrolyzers can manage their demand of electrical energy for production of hydrogen (i.e. power-to-gas conversion) and it is possible to store that generated hydrogen for long periods which is an advantage compared to battery storage. This hydrogen can be used for several applications (e.g. transportation), and part of it can be used by fuel cells to provide electrical power back to the power system when needed. One of the technologies used in electrolyzers and fuel cells is the proton exchange membrane (PEM). Fuel cells and electrolyzers based on PEM technology are capable of rapidly changing the power set point to increase or decrease the power demand or supply, respectively. This thesis studies the PEM electrolyzers and fuel cells and their ability to support the frequency stability through participation in the ancillary services market. Based on DIgSILENT PowerFactory software package, this thesis develops generic dynamic models for PEM fuel cell and electrolyzer for frequency stability studies and uses these models to assess their effectiveness in providing frequency support and participation in the FCR market. Numerical simulations are performed on two dynamic test systems: The North Netherlands 380 kV transmission and its extension to include a reduced size representation of the transmission systems covering the North-West Germany and South Denmark. Both dynamic test systems are developed in PowerFactory based on the detailed model of continental Europe built in PSS®E software package.The developed model for the fuel cell shows close resemblance to the literature data for both dynamic and static performance especially in the linear operating range. The simulation results show that PEM devices can provide frequency support in the FCR market and results in improved frequency nadir and reduced oscillations during the post-disturbance period which is considerably better than what can be achieved by using the currently in operation primary frequency control of the conventional power plants with synchronous generators.The numerical simulations also include sensitivity analysis to changing system operating conditions such as network size, location of PEM devices and system inertia. It is found that changing the location of the PEM devices or the size of the network does not affect the performance in supporting the frequency. Also, it is found that PEM devices provide significantly improved frequency response compared with synchronous generators at lower system inertia levels. Sensitivity analysis to changing control parameters for PEM devices such as the bid size and frequency droop showed that increasing the bid size or droop results in improved frequency response in the form of lower nadir.Some confidential information within this thesis have been removed. To request the full version please contact Dr. Ir. Jose L. Rueda Torres

Machine Learning Schemes for Anomaly Detection in Solar Power Plants

The rapid industrial growth in solar energy is gaining increasing interest in renewable power from smart grids and plants. Anomaly detection in photovoltaic (PV) systems is a demanding task. In this sense, it is vital to utilize the latest updates in machine learning technology to accurately and timely disclose different system anomalies. This paper addresses this issue by evaluating the performance of different machine learning schemes and applying them to detect anomalies on photovoltaic components. The following schemes are evaluated: AutoEncoder Long Short-Term Memory (AE-LSTM), Facebook-Prophet, and Isolation Forest. These models can identify the PV system’s healthy and abnormal actual behaviors. Our results provide clear insights to make an informed decision, especially with experimental trade-offs for such a complex solution space

Effect of Non-Thermal Atmospheric Plasma on Micro-Tensile Bond Strength at Adhesive/Dentin Interface: A Systematic Review

Objective: The objective of this review was to evaluate the effect of non-thermal atmospheric plasma (NTAP) on adhesives resin–dentin micro-tensile bond strength (μTBS) in previously published studies. Methods: Electronic search was conducted using the Medline, Cochrane library, and Scopus databases. The included studies were laboratory studies that investigated the effect of NTAP on adhesives μTBS to coronal dentin. Studies that evaluated the effect of NTAP on bond strength to indirect substrates, enamel or root dentin, were excluded. The methodological quality of included studies was assessed. Results: Thirteen studies were included in this systematic review. All the included studies were considered to have a medium risk of bias. NTAP significantly improved μTBS at 24 h or after short-term aging in five studies (38.5%) and both immediate and after long-term aging in 5 studies (38.5%). In two studies (15.4%), NTAP resulted in a short-term material-dependent effect that was not stable after long-term aging. Interestingly, in one study (7.7%), NTAP had a positive effect only in the etch-and-rinse (ER) mode after long-term aging. Conclusion: Within the limitations of this systematic review, NTAP application could enhance resin–dentin μTBS of ER adhesives or universal adhesives (UAs) applied in the ER mode. In the ER mode, the rewetting step after NTAP seems to be unnecessary. Because of the limited information currently available in the literature, further studies are required to evaluate the effect of the NTAP application on self-etch (SE) adhesives or UAs applied in the SE mode

Evaluation of the Bond Strength and Cytotoxicity of Alkasite Restorative Material

Cention N (CN; Ivoclar Vivadent, Schaan, Liechtenstein), advertised as an alkasite, is a bioactive bulk-fill resin-based composite (BF-RBC) with alkaline fillers. This study evaluated the resin-dentin micro-tensile bond strength (μTBS) and cytotoxicity of CN. Methods: Flat dentin surfaces were obtained, bonded with a universal adhesive, and randomly distributed into two groups. CN (group I) and a flowable BF-RBC, namely, Tetric N-Flow Bulk Fill, Ivoclar Vivadent, Schaan, Liechtenstein (group II), were used. After thermocycling, bonded samples were sectioned into micro-beams for μTBS evaluation. Resin-based composite (RBC) discs with a thickness of 2 and 4 mm were tested on human gingival fibroblast cells (HGFCs). Cytotoxicity was assessed by cell viability and growth using AlamarBlue® (Biosource, Camarillo, CA, USA) over a seven-day period. Independent t-test was utilized to statistically analyze μTBS data, while one- and two-way analysis of variance (ANOVA) and Tukey’s post-hoc tests were utilized to analyze the cell viability data. Results: There was no statistically significant difference (p > 0.05) in the μTBS between the flowable BF-RBC and CN. For both materials, the HGFCs were viable, with constant growing over the seven-day period. Conclusion: CN provided a resin-dentin μTBS that was comparable to that provided by the flowable BF-RBC. Both materials showed acceptable cytotoxicity over the seven-day period at a thickness of both 2 and 4 mm

Modelling and evaluation of PEM hydrogen technologies for frequency ancillary services in future multi-energy sustainable power systems

This paper examines the prospect of PEM (Proton Exchange Membrane) electrolyzers and fuel cells to partake in European electrical ancillary services markets. First, the current framework of ancillary services is reviewed and discussed, emphasizing the ongoing European harmonization plans for future frequency balancing markets. Next, the technical characteristics of PEM hydrogen technologies and their potential uses within the electrical power system are discussed to evaluate their adequacy to the requirements of ancillary services markets. Last, a case study based on a realistic representation of the transmission grid in the north of the Netherlands for the year 2030 is presented. The main goal of this case study is to ascertain the effectiveness of PEM electrolyzers and fuel cells for the provision of primary frequency reserves. Dynamic generic models suitable for grid simulations are developed for both technologies, including the required controllers to enable participation in ancillary services markets. The obtained results show that PEM hydrogen technologies can improve the frequency response when compared to the procurement with synchronous generators of the same reserve value. Moreover, the fast dynamics of PEM electrolyzers and fuel cells can help mitigate the negative effects attributed to the reduction of inertia in the system.Intelligent Electrical Power Grid

Silane-Containing Universal Adhesives Influence Resin-Ceramic Microtensile Bond Strength

Background: Silane-containing universal adhesives (UAs) are marketed as adhesion promotors for glass-ceramics. Objectives: This study aimed to evaluate the priming capacity of γ-methacryloxypropyltrimethoxysilane (γMPTS)-containing and γ-methacryloxypropyltriethoxysilane (γMPTES)/3-(aminopropyl)triethoxysilane (APTES)-containing universal adhesives (UAs) for lithium disilicate ceramic (LDC). Materials and Methods: Etched LDC discs were distributed into four groups according to the priming material used: (control), no priming; (MBN), LDC was primed with a universal primer (Monobond N); (SBU), γMPTS-containing UA (Single Bond Universal Adhesive) was used as a primer; and (SBP), γMPTES/APTES-containing UA (Scotchbond Universal Plus Adhesive) was used as a primer. LDC discs were cemented using a dual-cure resin cement, then sectioned into microbeams for microtensile bond strength (μTBS) evaluation. Failure modes were assessed. Results: MBN application showed the highest μTBS among all groups. γMPTES/APTES-containing UA (SBP) resulted in considerably higher μTBS compared with γMPTS-containing UA (SBU) or the control group. The mixed failures were the most predominant among all groups. Conclusions: The effect of silane-containing UAs on resin-ceramic μTBS is material dependent. Although γMPTES/APTES-containing UA improved bonding to LDC, the priming of LDC with either of the UAs tested cannot be considered as an alternative to a separate silanization (priming) step using a universal primer