Panos Papagiannakopoulos

Concentrating Solar Power in Europe, the Middle East and North Africa: A Review of Development Issues and Potential to 2050

This paper summarizes the findings of a study undertaken by the European Academies Science Advisory Council to evaluate the development challenges of concentrating solar power (CSP) and its consequent potential to contribute to low carbon electricity systems in Europe, the Middle East and North Africa (the MENA region) to 2050. The study reviewed the current status and prospective developments of the four main CSP technology families, and identified prospective technical developments, quantifying anticipated efficiency improvements and cost reductions. Similarly, developments in thermal energy storage were evaluated, and the role and value of CSP storage in electricity systems were examined. A key conclusion was that as the share of intermittent renewables in an electricity system increases, so does the value of thermal energy storage in CSP plants. Looking ahead, the study concludes that CSP should be cost competitive with fossil-fired power generation at some point in the 2020s provided that commercial deployment continues at an increasing rate, and through support mechanisms that incentivise technology development. Incentive schemes should reflect the real value of electricity to the system, and should ensure sufficient transparency of cost data that learning rates can be monitored. Key factors which will determine CSPs contribution in Europe and the MENA region over the period to 2050 are generating costs, physical constraints on construction of new plants and transmission, and considerations of security of supply. The study makes recommendations to European and MENA region policy makers on how the associated issues should be addressed.

THEORETICAL INVESTIGATION OF THE THERMOCHEMISTRY OF HYDROFLUOROETHERS

Abstract The enthalpies of formation and the C–H bond strengths of fluorinated dimethylethers were derived at 298.15 K by ab-initio calculations at the MP2/3-21++G(2d,2p), MP2/6-31++G(2d,2p) and MP2/6-311++G(2d,2p) levels of theory, and are compared with the results of recent calculations by the G2(MP2) method. Theoretical calculations were also performed for the corresponding fluorinated ethanes in order to compare the results with those derived by the BAC–MP4 method and with the available experimental data. The calculations at the MP2/6-31++G(2d,2p) level are considered more reliable on the basis of the closer agreement between theory and experiment. The results suggest that the introduction of the ether linkage –O– leads to lower C–H bond strengths only in mildly F-substituted dimethylethers. Heavily F-substituted dimethylethers possess stronger C–H bonds than their fluoroethane counterparts and therefore their tropospheric reactivity is expected to be lower.

IR laser-induced decomposition of 1,3–dimethyldisiloxane for chemical vapour deposition of nano-structured methyl(hydrido)silicone phases

The infrared multiphoton decomposition of 1,3-dimethyldisiloxane induced by a TEA CO2 laser yields gaseous C1–C2 hydrocarbons, methylsilane, dimethylsilane, methyldisiloxane and trimethyldisiloxane. These products provide evidence for a range of decomposition steps; amongst these, cleavage of the Si–O bond is important. The process affords chemical vapour deposition of a white solid nano-structured methyl(hydrido)silicone phase that has been characterized by infrared and photoelectron spectroscopy and electron microscopy.

Absolute reaction rate of chlorine atoms with iodomethane

Abstract The reaction of atomic chlotine with iodomethane was studied in the gas phase with the very low pressure reactor technique over the temperature range 273–363 K. The absolute rate constant was given by the expression k = (1.33 ± 0.49) × 10−11 exp [ −(573 ± 1.00 kJ mol −1 RT ] cm 3 molecule −1 s −1 . The reaction proceeds through an intermediate weakly bound adduct CH3ICl and results in the formation of HCl and iodomethyl radical CH2I. The kinetic isotope effect k H k D of the reaction was independent of temperature and found to be 1.09 ± 0.4.

IR laser-induced decomposition of hexamethyldisiloxane for chemical vapour deposition of nano-structured hydrido(methyl)silicone powders

Abstract The infrared laser-induced decomposition of hexamethyldisiloxane with high-fluence laser pulses affords gaseous C1–C2 hydrocarbons, dimethylsilane and trimethylsilane, all of which confirm a multitude of decomposition steps involving cleavage of the strong SiO bond. The process carried out in the absence or presence of hydrogen affords chemical vapour deposition of solid nano-structured hydrido(methyl)silicone powders and represents the first thermal access to these materials from peralkylated siloxane precursor.

Water Accommodation and Desorption Kinetics on Ice

The interaction of water vapor with ice remains incompletely understood despite its importance in environmental processes. A particular concern is the probability for water accommodation on the ice surface, for which results from earlier studies vary by more than 2 orders of magnitude. Here, we apply an environmental molecular beam method to directly determine water accommodation and desorption kinetics on ice. Short D2O gas pulses collide with H2O ice between 170 and 200 K, and a fraction of the adsorbed molecules desorbs within tens of milliseconds by first order kinetics. The bulk accommodation coefficient decreases nonlinearly with increasing temperature and reaches 0.41 ± 0.18 at 200 K. The kinetics are well described by a model wherein water molecules adsorb in a surface state from which they either desorb or become incorporated into the bulk ice structure. The weakly bound surface state affects water accommodation on the ice surface with important implications for atmospheric cloud processes.

Absolute rate coefficient determination and reaction mechanism investigation for the reaction of Cl atoms with CH2I2 and the oxidation mechanism of CH2I radicals.

The gas-phase reaction of atomic chlorine with diiodomethane was studied over the temperature range 273-363 K with the very low-pressure reactor (VLPR) technique. The reaction takes place in a Knudsen reactor at pressures below 3 mTorr, where the steady-state concentration of both reactants and stable products is continuously measured by electron-impact mass spectrometry. The absolute rate coefficient as a function of temperature was given by k = (4.70 +/- 0.65) x 10-11 exp[-(241 +/- 33)/T] cm3molecule-1s-1, in the low-pressure regime. The quoted uncertainties are given at a 95% level of confidence (2sigma) and include systematic errors. The reaction occurs via two pathways: the abstraction of a hydrogen atom leading to HCl and the abstraction of an iodine atom leading to ICl. The HCl yield was measured to be ca. 55 +/- 10%. The results suggest that the reaction proceeds via the intermediate CH2I2-Cl adduct formation, with a I-Cl bond strength of 51.9 +/- 15 kJ mol-1, calculated at the B3P86/aug-cc-pVTZ-PP level of theory. Furthermore, the oxidation reactions of CHI2 and CH2I radicals were studied by introducing an excess of molecular oxygen in the Knudsen reactor. HCHO and HCOOH were the primary oxidation products indicating that the reactions with O2 proceed via the intermediate peroxy radical formation and the subsequent elimination of either IO radical or I atom. HCHO and HCOOH were also detected by FT-IR, as the reaction products of photolytically generated CH2I radicals with O2 in a static cell, which supports the proposed oxidation mechanism. Since the photolysis of CH2I2 is about 3 orders of magnitude faster than its reactive loss by Cl atoms, the title reaction does not constitute an important tropospheric sink for CH2I2.

Uptake Measurements of Acetic Acid on Ice and Nitric Acid-Doped Thin Ice Films over Upper Troposphere/Lower Stratosphere Temperatures

The adsorption of gaseous acetic acid (CH(3)C(O)OH) on thin ice films and on ice doped with nitric acid (1.96 and 7.69 wt %) was investigated over upper troposphere and lower stratosphere (UT/LS) temperatures (198-208 K), and at low gas concentrations. Experiments were performed in a Knudsen flow reactor coupled to a quadrupole mass spectrometer. The initial uptake coefficients, γ(0), on thin ice films or HNO(3)-doped ice films were measured at low surface coverage. In all cases, γ(0) showed an inverse temperature dependence, and for pure thin ice films, it was given by the expression γ(0)(T) = (4.73 ± 1.13) × 10(-17) exp[(6496 ± 1798)/T]; the quoted errors are the 2σ precision of the linear fit, and the estimated systematic uncertainties are included in the pre-exponential factor. The inverse temperature dependence suggests that the adsorption process occurs via the formation of an intermediate precursor state. Uptakes were well represented by the Langmuir adsorption model, and the saturation surface coverage, N(max), on pure thin ice films was (2.11 ± 0.16) × 10(14) molecules cm(-2), independent of temperature in the range 198-206 K. Light nitration (1.96 and 7.69 wt %) of ice films resulted in more efficient CH(3)C(O)OH uptakes and larger N(max) values that may be attributed to in-bulk diffusion or change in nature of the gas-ice surface interaction. Finally, it was estimated that the rate of adsorption of acetic acid on high-density cirrus clouds in the UT/LS is fast, and this is reflected in the short atmospheric lifetimes (2-8 min) of acetic acid; however, the extent of this uptake is minor resulting in at most a 5% removal of acetic acid in UT/LS cirrus clouds.

Uptake of formic acid on thin ice films and on ice doped with nitric acid between 195 and 211 K.

The adsorption of formic acid on thin ice films and on ice doped with nitric acid (1.96, 7.69 and 53.8 wt%) is studied as a function of temperature T=195-211 K and gas concentration (0.33-10.6)×10(11) molecule cm(-3). Experiments are performed in a Knudsen flow reactor coupled with a quadrupole mass spectrometer. The initial uptake coefficients γ are strongly and inversely dependent on the ice temperature. Initial uptake is determined at low surface coverages and ranges from (0.65-3.78)×10(-3). The adsorption uptake of formic acid on pure ice films and on ice lightly doped with HNO(3) is a reversible process, and the adsorption isotherms exhibit Langmuir behaviour. N(max)(1) is (2.94±0.67)×10(14) molecule cm(-2), in good agreement with previous measurements. The temperature dependence of K(Lin) is very well represented by the expression: K(Lin)(1)=(1.43±0.32)×10(-8) exp[(4720±520)/T] cm(3) molecule(-1); the quoted uncertainty is at the 95% level of confidence and includes systematic uncertainties. Formic acid uptakes on ice films highly doped with HNO(3) (53.8 wt%) are two orders of magnitude higher than those measured on pure ice films and irreversible, thus indicating the formation of a supercooled liquid layer on the ice films upon which dissolution of formic acid occurs. Finally, the atmospheric lifetime of formic acid due to heterogeneous loss on cirrus cloud ice particles and the removal of formic acid by adsorption are estimated under conditions related to the upper troposphere.

Ab initio computational study of the interaction of Cl atoms with HI, CH3I and CH3OCH2I

Abstract Ab initio calculations at the MP2/3–21 + + G(2d,2p) level of theory suggest that the interaction of chlorine atoms with RI (R = H, CH 3 and CH 3 OCH 2 ) molecules leads to weakly bound adducts with potential energy wells of −31.839, −57.749 and −59.760 kJ mol −1 , respectively. The corresponding standard enthalpies of the adduct formation reactions at 298 K were calculated to be −31.056, −52.409 and −51.337 kJ mol −1 . The structure of the parent RI molecules were only slightly perturbed during the chlorine atom attachment to the iodine atom. The ICl bond length was always found to be ca. 2.8 A and the RICl angle was close to 80°.