Reduction Of Benzene Research Articles

Microwave-induced cracking and reforming of benzene on activated carbon

This study was conducted to convert tar generated during biomass pyrolysis/gasification to fuel gas through microwave process. Benzene was selected as a model tar, and the benzene reduction and produced-gas conversion characteristics were investigated for benzene cracking and CO2/steam reforming.The benzene conversion was the highest value of 99% when benzene cracking was performed, 98.5% when CO2 was supplied and 94% when steam was supplied. The produced-gas heating value was highest at 15 MJ/m3 for cracking, lowest at 4 MJ/m3 when CO2 was supplied, and 8.7 MJ/m3 when steam was supplied.In the case of CO2 reforming, the benzene conversion of the catalyst carbon receptor slightly increased for both the nickel and iron catalysts. The H2/CO ratio decreased, but the heating value increased. In the case of steam reforming, the benzene conversion slightly decreased for both catalysts, but the H2/CO ratio and the heating value increased.

Effects of Carbon Dioxide and Water Vapor Addition on Benzene and PAH Formation in a Laminar Premixed CH4/O2/Ar Flame

ABSTRACTThe effects of CO2 and H2O addition on benzene and PAH formation in a laminar premixed CH4/O2/Ar flame at atmospheric pressure were numerically investigated using two recently developed kinetic mechanisms with PAH formation up to at least benzopyrene. To distinguish the chemical effects of CO2 and H2O addition through partial replacement of Ar from their thermal effects, additional calculations were performed with fictitious carbon dioxide (FCO2) and fictitious water vapor (FH2O) addition. Both PAH kinetic mechanisms predicted that the formation of benzene and PAHs are promoted by the thermal effects of CO2 and H2O but are more significantly suppressed by their chemical effects. The pathway analyses revealed that the reduction of benzene concentration due to the chemical effects of CO2 and H2O is attributed to the following two aspects: (i) through the reduced concentration of propargyl radical or propyne and (ii) through the promoted oxidation and hydrogen abstraction reactions of benzene caused by increased OH concentration. The reduction of the overall PAH formation can be explained as the consequence of benzene reduction. Although there are quantitative differences in the predicted flame structure in terms of temperature and mole fractions of benzene and PAHs, overall qualitatively similar effects of CO2 and H2O addition on benzene and PAH formation are predicted by the two reaction mechanisms.

Competitive Hydrogenation of Benzene in Reformate Gasoline over Ni Supported on SiO2, SiO2–Al2O3, and Al2O3 Catalysts: Influence of Support Nature

Nickel supported on SiO2, SiO2–Al2O3, and Al2O3 catalysts have been prepared and studied for the reduction of benzene in reformate gasoline. The sol–gel method was used to prepare the catalysts. The evaluations were performed in a continuous fixed bed micro reactor fed by a flow of reformate gasoline at 398–473 K under atmospheric pressure. The physicochemical properties of the catalysts were obtained by XRD, FESEM, EDS-map, H2–adsorption, and N2 adsorption/desorption analysis to correlate the catalytic performances. To evaluate the performance of catalysts, different H2/benzene molar ratios and space velocities were used. The Ni/SiO2-b, Ni/SiO2-c, and Ni/FDU12 catalysts decreased the benzene content to less than 1 vol % at 423 K. The high toluene conversion by Ni/MSA and Ni/Mil-53(Al) catalysts in comparison to other catalysts indicates that toluene hydrogenation is favored on these catalysts. The highest conversion of benzene in competitive hydrogenation was achieved at 423 K by the Ni/SiO2-c catalyst. ...

Ceramic membrane ozonator for soluble organics removal from produced water

In this work, the performance of ozonation for degradation of soluble organic compounds in produced water was investigated. Tubular ceramic membrane diffuser (with and without a static mixer in the lumen side) was used to facilitate contact between ozone and produced water. The ozonation was conducted at ozone flow rate of 8 L.min-1, ozone concentration of 0.4 ppm, original pH of the solution, and pressure of 1.2 bar, while the flow rates of the produced water were varied (192, 378 and 830 mL.min-1). It was found that the reduction of benzene, toluene, ethylbenzene, and xylene were 85%, 99%, 85%, and 95%, respectively. A lower liquid flow rate in a laminar state showed a better component reduction due to the longer contacting time between the liquid and the gas phase. The introduction of the static mixer in the lumen side of the membrane as a turbulence promoter provided a positive effect on the performance of the membrane diffuser. The twisted static mixer exhibited the better removal rate than the spiral static mixer.

Hydrogen production from biomass: The behavior of impurities over a CO shift unit and a biodiesel scrubber used as a gas treatment stage

Most of the hydrogen produced is derived from fossil fuels. Bioenergy2020+ and TU Wien have been working on hydrogen production from biomass since 2009. A pilot plant for hydrogen production from lignocellulosic feedstock was installed onsite using a fluidized bed biomass gasifier in Gussing, Austria. In this work, the behavior of impurities over the gas conditioning stage was investigated. Stable CO conversion and hydration of sulfur components could be observed. Ammonia, benzene, toluene, xylene (BTX) and sulfur reduction could be measured after the biodiesel scrubber. The results show the possibility of using a commercial Fe/Cr-based CO shift catalyst in impurity-rich gas applications. In addition to hydrogen production, the gas treatment setup seems to also be a promising method for adjusting the H2 to CO ratio for synthesis gas applications.

Pushing SmI2 Reactions towards the Limit‐ Entropy Driven Reduction of a Benzene Ring

AbstractIn order to reduce a benzene ring, alkali metals or similar strong reducing agents are needed. We have found that SmI2, which is considered to be a relatively mild reagent, can also perform this task. This is achieved by attaching a side arm of either ethanolamine or ethylenediamine to a benzene ring. These side arms strongly coordinate to SmI2, holding it in close vicinity to the benzene ring. As a result, the probability of electron transfer from the SmI2 to the benzene ring is significantly increased. However, at the same time, this proximity also enhances the rate of the back electron transfer. In order to slow the rate of this step, small amounts of water and Et3N were added to the reaction mixture. The two typical products of the classical Birch reduction of benzene were obtained with a yield as high as 95 %. This method was also applied to the corresponding chlorobenzene and methylbenzoate where the reactions were much enhanced but functionality reduction prevailed over ring reduction. It is remarkable that going from a termolecular to a unimolecular reaction is more effective than excitation of the SmI2 around 600 nm which is equivalent to ca. 47 kcal/mol.

Investigations of the Electrochemical Behavior of Hydrocarbons in Adiponitrile

The very wide 8-volt potential range of adiponitrile/0.20 M tetraethylammonium tetrafluoroborate has been exploited for the investigation of hydrocarbon electrochemistry. Naphthalene undergoes reversible one-electron reduction in this solvent system at glassy carbon; however, naphthalene oxidation is irreversible. The reduction of benzene is not observed, but its oxidation is also irreversible. The electrochemical oxidation of cyclohexene can also be observed in this system, but addition of cyclohexane caused only a slight (+0.1 V) shift in the positive potential limit. A comparison with results in other solvent systems is presented.

EFFECT OF PALM OIL FIBER-TiO2 RATIO IN THE COMPOSITE ON THE REDUCTION OF BTX AND FORMALDEHYDE IN THE AIR

The effect of palm oil fiber-TiO2 ratio in the composite on the reduction of benzene, toluene, xylene and formaldehyde in the air is studied. The ratio was set at 1:0, 1:9 and 5:5. The combination of adsorption process by palm oil fiber and photooxidation of volatile organic compounds by titanium dioxide was revealed. The composite were prepared by using mechanical milling technique. The performance of the composite was characterized in terms of percentage of recovery of benzene, toluene and xylene (BTX) using GC/FID and formaldehyde concentration reduction using formaldehyde meter. The results of recovery of the BTX by palm oil fiber/titanium dioxide composite were more than 90%. The palm oil fiber/titanium dioxide composite has successfully reduced the concentration of formaldehyde by up to 66.7%. Therefore, the palm oil mesocarp fiber/titanium dioxide composite produced is able to reduce the concentration of volatile organic compounds.

Insights into the mechanism of nitrobenzene reduction to aniline over Pt catalyst and the significance of the adsorption of phenyl group on kinetics

Aniline (C6H5NH2) plays a significant role in both industry and daily life, and can be synthesized via catalytic hydrogenation of nitrobenzene (C6H5NO2) over transition metals; however fundamental investigations on reaction mechanisms in the heterogeneous catalysis are still lacking. In this work, the nitrobenzene reduction reaction over the Pt(111) model catalyst was studied using density functional theory (DFT) with the inclusion of van der Waals interaction, for fundamentally understanding the mechanisms at atomic and molecular levels. It was found that the double H-induced dissociation of N-O bond was the preferential path for the activation of nitro group, having a much lower reaction barrier than that of the direct dissociation and single H-induced dissociation paths. The overall mechanisms have been identified as: C6H5NO2∗→C6H5NOOH∗→C6H5N(OH)2∗→C6H5NOH∗→C6H5NHOH∗→C6H5NH∗→C6H5NH2∗. The overall barrier of the nitro group reduction was calculated to be 0.75eV, which is much lower than that of the benzene reduction (1.08eV). Our DFT data elucidates clearly the reason why the major product of nitrobenzene reduction reaction was aniline. Furthermore, the adsorption/desorption of phenyl group was found to have significant impacts on kinetic barriers. Generally, in the hydrogenation process (N-H or O-H bond association), the phenyl group preferred to adsorb on the surface; but in the dissociation process (N-O bond dissociation) it preferred to desorb transiently at the transition state and to adsorb again when the dissociation was completed. This study also provides a solid theoretical insight into the selective catalysis of the large aromatic compounds.

Laser-Induced Hydrogen Evolution Using Metal-Free Single-Walled Carbon Nanotubes

Carbon nanomaterials have been extensively studied for energy and environmental applications. Metal-free nanostructured elemental carbons and carbon-based composites have proven to be attractive alternatives to conventional metal-based catalysts for several important chemical reactions such as dehydrogenation, oxygenation and Friedel-Crafts reactions. In particular, single-walled carbon nanotubes (SWCNTs) have been of great interest to researchers because of their unique structures and physical properties. SWCNTs have been proposed as an advanced metal-catalyst support for electrochemical catalysis. However, there is no report that SWCNTs itself is used as a photocatalyst under ambient conditions due to the poor photochemical and excited properties. Catalytic hydrogen (H2) evolution systems have been extensively studied because hydrogen is a clean energy source for the future, which should reduce dependence on fossil fuels and emissions of greenhouse gases in the long term. In many cases, noble metals such as platinum and semiconductors have been used as composite photocatalysts. However, there is no report on photocatalytic metal-free H2-evolution system using pure carbon material alone as a photocatalyst. We report herein efficient H2evolution from benzene and benzene derivatives using metal free SWCNTs alone as a photocatalyst under visible laser light irradiation (532 nm) at room temperature. Laser pulse irradiation (λ = 532 nm; 500 mW; 10 Hz) of a deaerated benzene solution (2.5 mL) containing dispersed metal-free SWCNTs (0.15 mg) resulted in efficient hydrogen evolution. The amount of hydrogen evolved by laser irradiation for 2 h reached 100 mmol (2.2 mL). When benzene was replaced by deuterated benzene (C6D6), the deuterated hydrogen molecules such as D2 and HD were also evolved efficiently. The initial rate of hydrogen evolution was 21 mmol h–1 with 50 : 1 ratio for D2 and HD, respectively. The KIE (kinetic isotope effect) value was 2.4. These results indicate that the hydrogen source is benzene. The products derived from dehydrogenation of benzene were determined by the GC-MS and HPLC analyses to be biphenyl, terphenyls, and terphenylene. The stoichiometry to produce H2and biphenyl from benzene is given by eq 1. 2 C6H6 → H2 + C6H5-C6H5 (1) The dependence of the rate of H2 evolution on the laser intensity was examined using different laser power intensities at 532 nm (0 – 82 mJ pulse–1). The initial rates of H2evolution are proportional to the fourth power of laser intensity. This suggests that a bimolecular reaction of two-photon absorbed species may be involved in the photocatalytic hydrogen evolution. On the basis of above-mentioned results, the plausible photocatalytic mechanism for hydrogen evolution in benzene is shown in Scheme 1. SWCNT was excited by two photons to form doubly excited SWCNT (SWCNT**). SWCNT** can reduce benzene to produce benzene radical anion (C6H6 •–) and the one-electron oxidized SWCNT (SWCNT•+) with the rate constant of k et1. Dimerisation of C6H6 •– occurs accompanied by hydrogen evolution to produce biphenyl dianion [(C6H5)2 2–]. Such hydrogen evolution via radical coupling of C6H6 •– has previously been reported for reduction of benzene with cesium nano carbon catalyst.3 (C6H5)2 2– can reduce benzene to produce C6H6 •– and biphenyl radical anion [(C6H5)2 •–] in benzene. Back electron transfer from (C6H5)2 •– to SWCNT•+ results in formation of biphenyl [(C6H5)2], accompanied by regeneration of SWCNT. On the other hand, C6H6 •– can reduce SWCNT to produce SWCNT•– and C6H6. The charge recombination from SWCNT•– to SWCNT•+also regenerates SWCNT. The overall stoichiometry of the photocatalytic cycle in Scheme 1 agrees with eqn (1).

Comparison of synthesized H-Al-MCM-41 with different Si/Al ratios for benzene reduction in gasoline with propylene

Benzene reduction in gasoline was investigated with propylene over synthesized mesoporous H-Al-MCM-41 with Si/Al=15, 29 and 42 as catalysts in order to produce more environmental friendly gasoline. The resulting catalysts were characterized by XRF, XRD, FTIR, TGA, BET and TPD-NH3 techniques. The results of alkylation of C6-cut obtained from gasoline indicated that the synthesized mesoporous H-AL-MCM-41 with Si/Al=15 is the most active catalyst among the synthesized catalysts due to high crystallinity, favorable textural properties and large bronsted acidity. The higher conversion of benzene (47.88%) was observed over H-Al-MCM-41 with Si/Al=15 at B/P=1 and T=200°C.

Benzene reduction in gasoline range streams by adsorption processes using a PVDC–PVC carbon molecular sieve

A PVDC–PVC derived carbon molecular sieve (CMS-IMP12) was used for adsorbing the benzene contained in a sample of reforming gasoline from a Mexican Refinery. First an olefin free benzene enriched fraction (H-BHC) was obtained by distillation-hydrogenation. The adsorption process may be carried out in one and two-steps. In the one-step procedure, benzene was adsorbed along other hydrocarbons in a 28mL/100gads yield. The benzene enriched fraction (BEF) contained linear and branched paraffins and cycloparaffins (56%) and benzene (43%). In the two-step procedure, linear paraffins (PEF) were selectively separated from the H-BHC by 5A molecular sieve (7mL/100gads). Then, the paraffins free fraction (PFF, 30mL/100gads) was submitted to a further separation using the CMS material. The resulted adsorbed product (BEF, 42mL/100gads) was formed mainly by iso- and cycloparaffins (50%) and benzene (48%). The octane number of the one-step was lower than the two-steps benzene free fraction (BFF) (67 and 76, respectively) due to the presence of paraffins in the first one. In any case, the benzene may be recuperated from the BEF by distillation and the octane number of the recovered PEF and BFF may be improved by any commercial isomerization process.

The phenylpropene synthase pathway and its applications in the engineering of volatile phenylpropanoids in plants

Phenylpropenes such as eugenol, isoeugenol, chavicol, and anethole are C6–C3 volatile compounds derived from phenylalanine by modification of its benzene ring and reduction of its propyl side chain, with the final reduction step catalyzed by a product-specific phenylpropene synthase. Recent advances in the biochemical and molecular analysis of phenylpropene synthases have improved our understanding of their evolution, structural properties, and reaction mechanism, providing insights into how plants produce and regulate the many types of phenylpropene volatiles. Since phenylpropenes are important in determining the flavor of foods and the quality of essential oils in cosmetics, the identification of the genes and enzymes responsible for the biosynthesis of phenylpropene volatiles has also provided us with tools to meet the challenge of improving plant aromas through genetic engineering.

A Cataluminescence-Based Sensor for Detecting Benzene, Toluene and Xylene Vapors Utilizing the Catalytic Reduction on the Surface of Nanosized Al<sub>2</sub>O<sub>3</sub>/Pt

A new gas sensor was designed based on cataluminescence (CTL) by using catalytic reduction of benzene, toluene and xylene (BTEX) on the surface of nanosized catalyst Al2O3/Pt with hydrogen as the carrier gas. The result indicated that the sensor showed strong CTL response, high selectivity and excellent durability under optimal conditions: Al2O3/Pt (1%), the temperature of 395oC, the wavelength of 425 nm and the flow rate of 270 mL/min. The detection limit (3σ) is 0.2 ppm for benzene, 0.3 ppm for toluene and xylene. Other corresponding substances such as methanol, ethanol, formaldehyde, acetaldehyde, ethylacetate, ammonia and trichloromethane had no or less interference. It is a simple and convenient sensor with good selectivity and sensitivity for detecting BTEX.

Benzene reduction in gasoline by alkylation with propylene over MCM-22 zeolite with a different Brønsted/Lewis acidity ratios

In this work, the liquid phase alkylation of benzene with propylene was carried out over MCM-22 zeolite treated thermally in a flow of air and nitrogen for activation. Such activation procedures led to changes in the Brønsted/Lewis acidity ratio of the samples, but not in textural properties. The alkylation reaction was conducted using as a feed a benzene-enriched sample of reformate heart cut containing ca. 20wt% benzene. The experimental reaction was performed in a batch reactor at 220°C adjusting the amount of propylene for a molar ratio of benzene to propylene in the feed of 2. Benzene conversion versus time profiles consisted of three regions wherein (i) the aromatic conversion decreased very slightly, (ii) it diminished drastically, and (iii) it continued dropping with time, but to a lesser extent than in (ii). MCM-22 sample containing a higher Brønsted acidity exhibited a larger resistance to deactivation during benzene alkylation experiments, as severe deactivation starts after 19h of time on stream. Concerning products distribution, the presence of bulky (poly) alkylated products declined as the MCM-22 became more deactivated.

One-pot reduction of olefin and ketone moieties by a copper–phosphine catalyst enabled by polar aprotic solvents

One-pot reduction of both olefin and ketone moieties in a non-food biomass derived substrate using simple copper–phosphine catalysts is described. The electron rich, sterically unencumbered bis(diethylphosphino)ethane ligand used here gives an 84% yield of the product where both the olefin and ketone have been reduced in minutes using PhSiH3 and dry acetonitrile as the solvent. The coordinating ability of acetonitrile appears to be critical for effecting this one-pot reduction. Labeling experiments indicate that ketone reduction in benzene occurs predominantly via a sigma bond metathesis pathway.

O Impacto Do Gás Natural Veicular Nas Empresas: Análise Comparativa (The Impact of the Natural Gas in Companies: Comparative Analysis)

Is growing the demand for alternative sources of energy, trying to substitute the petrol derivate, especially after the 70’s. The use of natural gas as a substitute is growing worldwide. There are more than 60 countries that opted for this alternative fuel. There are essentially two reasons for this change, and there are mainly two perspectives that can justify that. Although they might be in conflict there are very close relations between then: • On one hand, in some countries, natural gas is chosen as a means of reducing costs dramatically social health due to reduction of pollutant emissions, especially particulate, benzene and ground level ozone;• On the other, other countries have opted for GNV as an economic tool, taking advantage of its low cost, in order to expand in terms of displacements. Reduced costs in transports, representing significant savings, originate a significant grow in the transports and at the same time the create the possibility to export oil, increasing the national wealth.It is also important to note that the countries that chose the economical convenience also received environmental benefits due to the use of GNV. These extra benefits, compared to the ones of the countries that follows “clean air” milestones, would be much “clean” of the ones who has oriented economy programs. The GNV technology has been developing itself as the vehicles technology evolution. In the development of the auto industry worldwide, there are some factors that have been developing an important role. The market quality demand, prices, world legislation, diversity and so on. Duo to the irregular consumption of fossil energy and the pollution in the big cities, the research center and the industry are doing efforts in order to substitute the oil for other energy resources. This development is based on GNV and it main progress is to have the natural gas as a transition energy, once it is becoming the energy resource that everybody wants and it will probably be the hydrogen successor. This work focuses on a universal approach on the use of alternative fuel, GNV, for motors gasoline and diesel as a growing modern technology in the world and they reflect a significant impact on the economy and environment. It also aims to make a cost-benefit analysis of the conversion of buses to GNV and fleet cars business.

Experimental and modeling study of the effects of adding oxygenated fuels to premixed n-heptane flames

The effects of methanol, dimethoxymethane (DMM), and dimethylcarbonate (DMC) on laminar premixed low pressure (30Torr) n-heptane flames were investigated by using synchrotron photoionization and molecular-beam mass spectrometry (PI–MBMS) techniques. The overall C/O ratio was maintained constant (0.507) and the equivalence ratio was kept around 1.6 for all the tested flames. The composition of unburned mixtures was adjusted such that the post-flame temperatures were nearly equivalent for all the test conditions. Mole fraction profiles of major and intermediate species were derived and compared among the flames. Parallel computations were performed based on a modified model, and the predicted concentrations of flame species agree reasonably well with the measured results. Early production of CO2 was observed in the DMC-doped flame. Reaction flux analysis suggested that it was caused by the decomposition of CH3OCO radical, DMC molecule and CH3OCOO radical. As oxygenated fuels were added, the concentrations of most C1C5 hydrocarbon intermediates were reduced while that of benzene (C6H6) also decreased apparently, and the extent of benzene reduction showed little difference among the oxygenate-doped flames. Reaction flux analysis indicated that, in all the tested flames, the primary pathway leading from small aliphatics to C6H6 was through C3+C3 reactions, including the self-recombination reaction of propargyl radical (C3H3) and the cross reaction between C3H3 and allyl radical (a-C3H5). Considering that the temperatures of the tested flames were almost equivalent, the reduction of C6H6 concentration when doped with oxygenated fuels should be resulted from the reduced concentrations of its precursors. Furthermore, concentrations of certain oxygenated intermediates were also examined. The concentration of formaldehyde (CH2O) was found to increase when flames were doped with oxygenated fuels, while those of acetaldehyde (CH3CHO) and vinyl alcohol (C2H3OH) were nearly equivalent for all the flames. Methyl formate (CH3OCHO) was detected only in the DMM-doped flame, which was attributed to the efficient CH3OCHO formation pathway through the decomposition of CH3OCHOCH3 radical in the flame.

Benzene reduction in gasoline by alkylation with olefins: Comparison of Beta and MCM-22 catalysts

The study compares the performance of Beta and MCM-22 zeolites as catalysts for propylene alkylation of benzene present in an enriched sample of reformate heart cut (20 wt% benzene). The experiments were carried out in a batch system with a 2/1 mole ratio of benzene/propylene at 220 °C for 1 h. An MCM-22 zeolite that contained Brønsted/Lewis acid sites in a 2–3/1 ratio proved to be much more resistant to deactivation during these real feed benzene alkylation experiments when compared with the Beta catalyst (Brønsted/Lewis acid site ratio of 0.1–0.3/1). MCM-22 with a 45 wt% benzene conversion presented higher i-propylbenzene selectivity than Beta (38 wt% benzene conversion) by reducing the formation of by-products. The outstanding behavior of MCM-22 may be explained by its particular Brønsted to Lewis acid ratio, which could help in the carbonium-ion formation and in the activation of the benzene ring toward electrophilic attack, and to its open crystalline framework that facilitates diffusion of reactants, products and coke precursors. Additional studies regarding experimental conditions for the preparation of MCM-22 and alkylation procedures are required for optimization.

Anaerobic degradation of benzene by enriched consortia with humic acids as terminal electron acceptors

The anaerobic degradation of benzene coupled to the reduction of humic acids (HA) was demonstrated in two enriched consortia. Both inocula were able to oxidize benzene under strict anaerobic conditions when the humic model compound, anthraquinone-2,6-disulfonate (AQDS), was supplied as terminal electron acceptor. An enrichment culture originated from a contaminated soil was also able to oxidize benzene linked to the reduction of highly purified soil humic acids (HPSHA). In HPSHA-amended cultures, 9.3 μM of benzene were degraded, which corresponds to 279 ± 27 micro-electron equivalents (μEq) L −1, linked to the reduction of 619 ± 81 μEq L −1 of HPSHA. Neither anaerobic benzene oxidation nor reduction of HPSHA occurred in sterilized controls. Anaerobic benzene oxidation did not occur in soil incubations lacking HPSHA. Furthermore, negligible reduction of HPSHA occurred in the absence of benzene. The enrichment culture derived from this soil was dominated by two γ-Proteobacteria phylotypes. A benzene-degrading AQDS-reducing enrichment originated from a sediment sample showed the prevalence of different species from classes β-, δ- and γ-Proteobacteria. The present study provides clear quantitative demonstration of anaerobic degradation of benzene coupled to the reduction of HA.