119 research outputs found
A multi-step biocatalytic approach for the continuous generation and use of HCN towards chiral O-acetylcyanohydrins
No full textContinuous processing technologies have been shown to be a powerful concept in order to tune reaction
conditions in a very precise manner, enhance the sustainability and facilitate the scale-up of the chemical
processes involving hazardous reagents. This becomes even more important during those multi-step
approaches, where the use of modular components for the downstream processing together with
automated in-line analytics allow the control and coordination of all the stages of the processes.
In spite of these advantages, surprisingly few applications to multi-step biocatalytic strategies in flow1
have been reported so far in contrast to discrete single-step biotransformations.2
The advantages of the continuous flow technology will be described with regard to a novel orthogonal
biocatalytic approach, involving two sequential biotransformations, towards the preparation of chiral Oacetylcyanohydrins. Lipase B from Candida antarctica (CalB) and hydroxynitrile lyase from Arabidopsis
thaliana (AtHNL) were employed in a robust continuous telescoped process, involving an in situ HCN
generation followed by addition to aldehydes and an in-line stabilization of products (scheme 1).
Using the formation of (R)-mandelonitrile as an example, the process was optimized with both
immobilized isolated enzyme (celite-AtHNL) and whole-recombinant E. coli BL21-DE3 cells expressing
AtHNL as biocatalysts.3
Key process parameters and the further applications will be reported.
1
a) Babich, L.; Hartog, A. F.; Van Hemert, L. J. C.; Rutjes, F. P. J. T.; Wever, R. ChemSusChem 2012, 5, 2348 – 2353. b) Yuryev, R.; Strompen,
S.; Liese, A. Beilstein J. Org. Chem. 2011, 7, 1449–1467. c) Itabaiana, I.; Leal, I. C. R.; Miranda, L. S. M.; Souza, R. O. M. a. J. Flow Chem.
2013, 3, 122–126.
2
a) Jones, E.; McClean, K.; Housden, S.; Gasparini, G.; Archer, I. Chem. Eng. Res. Des. 2012, 90, 726 – 731. b) Le Joubioux, F.; Bridiau, N.;
Sanekli, M.; Graber, M.; Maugard, T. J. Mol. Catal. B: Enzym. 2014, 109, 143 – 153. d) Baxendale, I. R.; Ernst, M.; Krahnert, W.-R.; Ley, S. V.
Synlett 2002, 1641 – 1644. e) Baxendale, I. R.; Griffiths-Jones, C. M.; Ley, S. V.; Tranmer, G. K. Synlett 2006, 427 – 430. f) Andrade, L. H.;
Kroutil, W.; Jamison, T. F. Org. Lett. 2014, 16, 6092 – 6095. g) Tomaszewski, B.; Lloyd, R. C.; Warr, A. J.; Buehler, K.; Schmid, A.
ChemCatChem 2014, 6, 2567 – 2576. h) Andrade, L. H.; Kroutil, W.; Jamison, T. F. Org. Lett. 2014, 16, 6092–6095.
3 B. Musio, A. Brahma, U. Ismayilova, N. Nikbin, S. B. Kamptmann, P. Siegert, G. E. Jeromin, S. V. Ley, M. Pohl Synlett, in pres
Oxidation Reactions in Segmented and Continuous Flow Chemical Processing using a N-tert-Butylsulfinimidoyl chloride monolith
No full textCreep-fatigue crack growth behaviour of P91 steels
No full textAbstractThe importance of predicting failure due to combined creep-fatigue crack growth in high temperature power-plant components has become of great importance importance due to the need for plant to ‘load follow’ in response to fluctuations in demands and the availability of renewables. P91 steel has been widely utilized in conventional plant components. Creep fatigue crack growth (CFCG) tests have been performed on compact specimens at temperatures ranging between 600° C to 625° C. The experimental results have been compared to static creep, high cycle fatigue and CFCG test data available in literature on P91 steel. The CFCG data has been characterised using stress intensity factor range parameter, ΔK and C* parameter. The crack growth per cycle and ∆K relationship shows that at high frequency, the CFCG behaviour tends to that of high cycle fatigue crack growth and at low frequency, the contribution of creep becomes increasingly more significant. The correlation between crack growth rate and C* parameter, shows that most CFCG data fall within the creep crack growth (CCG) P91 data band which may indicate that the crack growth behaviour is dominated by creep processes. Fractography has also shown an intergranular, ductile fracture surface indicating creep dominance for the conditions considered. A linear cummulative rule has ben used to predict the CFCG experimental result
An orthogonal biocatalytic approach for the safe generation and use of HCN in a multistep continuous preparation of chiral O-acetylcyanohydrins
No full textAn enantioselective preparation of O-acetylcyanohydrins has been accomplished by a three-step telescoped continuous process. The modular components enabled an accurate control of two sequential biotransformations, safe handling of an in situ generated hazardous gas, and in-line stabilization of products. This method proved to be advantageous over the batch protocols in terms of reaction time (40 min vs 345 min) and ease of operation, opening up access to reactions which have often been neglected due to safety concerns
Trinucleotide repeat polymorphism within exon 5 of the MICA gene (MHC class I chain-related gene A): allele frequency data in the nine population groups Japanese, Northern Han, Hui, Uygur, Kazakhstan, Iranian, Saudi Arabian, Greek and Italian
No full textWe recently identified a trinucleotide repeat polymorphism, (GCT)n, within the transmembrane (TM) segment of the human MHC class I MICA gene (MHC class I chain-related gene A). Five distinct alleles (A4, A5, A5.1, A6, A9) corresponding to 4, 5, 5 with one nucleotide insertion, 6 and 9 repetitions, respectively, have been detected in various HLA homozygous B cell lines. Here we present allele frequencies for this trimeric short tandem repeat (STR) in 604 unrelated individuals collected from nine human populations (Japanese, Northern Han, Hui, Uygur, Kazakhstan, Iranian, Saudi Arabian, Greek and Italian) determined using the polymerase chain reaction (PCR) combined with fluorescent-based automated fragment detection technology. All alleles were present in each population, but allelic distributions varied from one population to another. No new alleles (such as A7 or A8) were identified. The evolutionary and structural significance of these data as well as the potential application to forensic medicine is discussed
Effect of (n-3) polyunsaturated fatty acidson cytokine production and their biologic function
No full textCreep-Fatigue Crack Growth Testing and Analysis of Pre-strained 316H Stainless Steel
No full textAbstractMaterial pre-straining is known to have significant effects of the mechanical response and crack growth behaviour of steels. In this paper, the influence of material pre-straining on the subsequent creep-fatigue crack growth behaviour of Type 316H stainless steel at 550 °C has been examined by performing tests on compact tension specimens that were extracted from blocks uniformly pre-compressed at room temperature. Creep-fatigue crack growth tests on pre-compressed material were performed at the frequency of 0.01 Hz and R-ratio of 0.1. The crack growth data obtained from these experiments have been correlated with the C* and K fracture mechanics parameters and the results are compared with the existing creep crack growth data on the pre-compressed and as-received material at 550 °C. The results obtained have also been compared with the creep-fatigue data from experiments on weldments where the crack tip was located in the heat affected zone (HAZ). The crack growth behaviour in creep-fatigue tests on pre-compressed material has been found similar to that of HAZ material and are higher than that of the as-received material. Moreover, depending on the loading condition and frequency the crack growth data obtained from creep-fatigue tests on pre-compressed material may be characterized using C* or ΔK fracture mechanics parameters
Low Cycle Fatigue Behaviour of Ex-Service P92 Steel at Elevated Temperature
No full textAbstractThe influence of strain amplitude and strain rate on low cycle fatigue (LCF) behaviour of the ex-service P92 steel at temperature of 600°C has been examined. Fully reversed strain-controlled LCF tests were conducted at the strain amplitude between ±0.4% and ±0.8% employing strain rate of 2.4x10-3s-1 to 2.4x10-5s-1. The material has been found to exhibit continuous cyclic softening behaviour throughout the LCF tests, and there was no saturation stage observed. The number of cycles to failure decreased with lowering the strain rate and increasing strain amplitude. Mathematically, the relationship between time to failure and strain rate can be expressed by a power law relation. Elastic-plastic finite element (FE) analysis was carried out to obtain the hysteresis loop and cyclic stress response of the material. The computation results are shown to be in good agreement with the experimental data. Fractographic examinations of the fatigued specimens were performed using scanning electron microscopy (SEM). Under the LCF condition at higher strain rates, the crack propagated intergranularly which due to fatigue while at lower strain rates the crack may be propagated in both inter- and transgranular manner
Experimental and numerical simulations of Type 316 stainless steel failure under LCF/TMF loading conditions
No full textMaterials need to be designed under certain conditions to withstand high thermal gradients to operate at high temperature environments. Many advanced gas cooled reactor (AGR) power plant components with operating temperatures in the range of 500-650 °C undergo creep-fatigue loading conditions. These components may be subject to isothermal low cycle fatigue (LCF) and thermo mechanical fatigue (TMF) damages due to the cyclic operation of power plant caused by the start-up and shutdown processes and due to the fluctuation of energy demand in daily operation. Hence, the influence of these cyclic loads induced mechanically and thermally, on the different structural components need to be carefully monitored and analysed in order to prevent failure and ensure safe operating conditions of critical units.
The material Type 316 SS with cast number S7646, widely used in this type of components, is investigated in this project. The aim of this research is to conduct experimental tests to obtain quality stress-strain data for the material under investigation under cyclic plasticity in isothermal and an-isothermal tests using the available testing machine systems in the University of Imperial College London. The data obtained from experimental results are then utilised to develop advanced novel finite element damage models in a creep/fatigue loading environment in order to predict the cyclic behaviour under LCF conditions. Finally, the results of cyclic data derived from isothermal tests were used to predict the thermo mechanical fatigue behaviour for this alloy.
The LCF-TMF testing unit, Instron 8801 with a temperature uniformity of less than ±10°C within the gauge section of the specimens were employed to conduct the experimental tests. Fully-reversed, strain-controlled isothermal tests were conducted at 500°C and 650°C for the strain ranges of ∆ɛ=±0.4%, ±0.8%, ±1.0% and ±01.2%. Strain-controlled in-phase (IP) thermo-mechanical fatigue tests were conducted on the same material and the temperature was cycled between 500°C and 650°C. Additionally, the creep-fatigue interactions were investigated with the introduction of symmetrical hold time at maximum strains in tension and compression under both LCF-TMF tests.
From the investigation and the analysis of the experimental stress-strain data, three phases are observed when the cyclic stress responses are plotted; cyclic hardening, stabilisation and damage evolution. In the final stage of the behaviour of the material, a nonlinear decrease of the peak stress level was observed which was initiated by the presence of micro-crack and the failure occurred as the crack propagated. The evolution of inelastic strain energy density, ∆w, against the number of cycles, N, was used to determine the number of cycles at which the material stabilised, N_sta , the damage initiated, N_i and the failure occurred,N_f. The introduction of the hold time in both tension and compression strains in the LCF and TMF tests, produced an increase in the plastic strain range which subsequently increased the inelastic strain energy density and slightly reduced the peak flow stress when compared with the continues cyclic tests. The stress relaxation was observed when the hold time was introduced. The amount of stress relaxation was dependent on the test temperature and the imposed strain amplitude and the same trend was found when different strain ranges were examined.
The cyclic behaviour of the Type 316 steel was further studied by analysing and performing microstructural investigations using the scanning electron microscope (SEM). The metallographic and the fractographic studies revealed that in all LCF-TMF tests the cracks mostly initiated in transgranular mode and propagated in either transgranular (under continuous cyclic loading) or in a mixed mode (under symmetric dwell period). The comparison of the metallographic and the fractographic studies of the LCF and TMF tests under both conditions (i.e. with and without dwell period) highlighted that the proportion of intergranular cracking increases with decrease in frequency, i.e. from 0.01Hz to 0.001Hz. Furthermore, the transgranular fatigue process dominates at high frequencies whereas the intergranular time dependent mechanism governs at low frequencies, low imposed mechanical strain amplitude and they both act together at intermediate frequencies and imposed mechanical strain amplitude.
A constitutive model based on isotropic and nonlinear kinematic hardening rules was used to replicate numerically the cyclic structural behaviour of the material. A user-defined subroutine was developed and implemented in the finite element software, ABAQUS to predict the cyclic hardening, the stress relaxation during hold time and finally to demonstrate the damage evolution once the damage initiated. The final stage of the material behaviour (i.e. failure) was simulated numerically for both LCF and TMF tests conducted with and without hold time where for the tests with continuous cyclic loading (without hold time) a hysteresis energy-based phenomenological model was implemented in a USDFLD subroutine. Further, this model in combination with the creep damage model based on the time-fraction law were employed simultaneously to replicate the experimental results in which the hold time was introduced.
In the end, the FE results were compared with the experimental results and the minor deviations observed in e.g. the first and stabilised hysteresis loops under TMF conditions or in the FE hysteresis damages, could be minimised by conducting further isothermal tests to define additional material properties at intermediate temperatures and performing tests at various strain ranges respectively.Open Acces
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