Polygeneration systems have been shown to be a flexible arrangement which can meet seasonal product demands for electric power, fuels and chemicals. This is especially relevant for small markets such as isolated small-medium size communities demanding electricity, and fuels. This work is focused on the feasibility of a polygeneration system based on a single-step DME plant to produce 200,000 tonnes/year of DME and 200 MW of electricity. An economic analysis is carried out to assess different configurations and feedstocks for syngas production. The DME-production was simulated at different possible recycle ratios and under the condition of potentially reduced catalyst performance. In all cases, the once-through polygeneration system showed significant improvement over all other configurations - up to 11.6% reduction in the amount of synthesis gas required to produce DME and power with a corresponding reduction in "wasted" feed leaving as effluent CO2. The flexibility of an integrated system meant that, in cases of decreased catalyst activity or selectivity, the advantages of the integrated system over standalone configurations are even greater - up to 18.6%. Moreover, polygeneration systems show further economic advantages depending upon the selling price of electricity for both fossil fuel and biomass sources of the syngas feedstock. Crown Copyright (C) 2019 Published by Elsevier Ltd. All rights reserved.

The conversion of syngas into dimethyl ether has been studied over physical mixtures of a Cu/ZnO based catalyst and a zeolite. Theta-1, ZSM-23, ferrierite, ZSM-5 and mordenite were used. The zeolites were separated after reaction and characterised by temperature programmed oxidation, XRD, and GC-MS of the entrained hydrocarbons. Theta-1 and ferrierite were found to have the most stable performance and the highest selectivity to DME. Deactivation is shown to be faster for structures with enough space to accommodate bulky carbonaceous deposits such as mordenite and ZSM-5. Longer diffusion paths associated with larger crystallites also contributed to rapid loss of activity for ZSM-23. The zeolite topology was found to influence the nature of the entrained alkylbenzenes. (C) 2014 Elsevier B.V. All rights reserved.

Trials were conducted in circular tanks used in aquaculture (1.2 m diameter and 0.4 of useful depth) in order to evaluate the effect of different water injection devices on the tangential velocity of the water, its uniformity pattern, the mixing time and the removal of solids through the bottom drain. Two injection devices, without fishes, were evaluated at the tank: a Vertical Spray, considered as standard in aquaculture and an eductor (jet-Mixing Eductor) which is used in chemical and petrochemical industry to homogenize and keep in movement great volumes of water. The devices were evaluated under the same operating conditions: inlet flow of 4, 6 and 8 1/min and water injection angle of 0 degrees and 45 degrees. In each trial, the water velocity inside the tank was measured, also the mixing time and the time in which the 100% of pellets of fish food were eliminated from the tank through the bottom drain. The results indicate that, for all inlet flows, the eductor operating at 45 presents significantly (p < 0.001) better result in terms of hydraulic variables such as tangential velocity, uniformity, mixing time and solids removal time from the tank (self-cleaning effect). In the case of eductors, although an increase of inlet flow produces improvements of hydraulic variables, a change of water injection angle, from 0 to 45, produces significantly better results (p <0.001). Differences of hydraulic performance between the eductor and Vertical Spray are mainly owing to the multiplicative effect of the outlet flow that is generated by the eductor. This means that, for similar values of impulse force and water velocity at the exit of the nozzle injection (V-2), the eductors generate significantly higher tangential velocity and uniformity, lower mixing times and secondary flow patterns, which ensure the self-cleaning of solid waste. In terms of power consumption, eductors overcome Vertical Spray in the trial performed. However, when comparing them under equal requirements of hydraulic performances (velocity, mix and/or self-cleaning), eductors present the same or lower energy consumption. Comparatively eductors would generate, under similar operating conditions, clear benefits for produced species in aquaculture, by generating hydraulic conditions that ensure a better quality of water and patterns and uniformity of velocity, which are more suitable for their health and normal growth. (C) 2013 Elsevier B.V. All rights reserved.

Three samples of ethylene-octadecene copolymers having different quantitative composition were analyzed structurally and in terms of their thermal behavior. The samples were fractionated by temperature rising elution fractionation, presenting different chemical composition distributions (CCD) that are essentially the result of the proportion of incorporated octadecene. The CCD profiles were relatively wide for samples generated by metallocene catalysts. The analyses of the fractions showed that the melting and crystallization temperatures decrease with increasing comonomer incorporation, but this relation is affected by the average molecular weight of the chains. The melting thermograms of those fractions having higher proportions of octadecene may be divided into two characteristic regions: the first one, at a higher temperature, originates from the melting of the least modified chains, which crystallize more perfectly. The second one is formed by the melting of chains having a high degree of comonomer incorporation, which melt in a diffuse manner over a wide range of temperatures, it is probable that the morphology of the crystals formed in this region does not follow the folded chain model, and are better represented by a model involving the alignment of chain segments (bundling). (C) 2000 John Wiley & Sons, Inc.

Four ethylene-1-octadecene copolymers and the corresponding polyethylene homopolymer, synthesized with a metallocene catalyst, have been analyzed by using three characterization techniques in the solid state: differential scanning calorimetry, wide-angle X-ray diffraction, and Raman spectroscopy. Very important annealing effects are observed in the copolymers with higher comonomer content while standing at room temperature, in such a way that the enthalpies of melting derived from the first and second melting are different. The X-ray diffractograms have been analyzed in terms of amorphous and crystalline components, determining both the crystallinity and the position of the different reflections. The variation of the unit cell parameters has been calculated from those reflections. No indication of a possible participation of the relatively long 1-octadecene branches in the crystallization can be deduced from the X-ray data. The degree of crystallinity has also been determined from the Raman spectra, following two procedures. The results indicate that the crystallinities deduced from the band at 1416 cm−1 are much lower than those derived from the other two characterization techniques. On the contrary, the data from the 1060 cm−1 band are practically coincident with the X-ray determinations. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1440–1448, 2000

Metallocene catalysts, viz., rac-Et(Ind)(2)ZrCl2, rac-Me2Si(Ind)(2)ZrCl2 and Ph2C(Flu)(Cp)ZrCl2, were studied in homopolymerization of 1-octadecene and the first two were used in copolymerization of ethylene with 1-octadecene. They exhibited different activities and rac-Et(Ind)(2)ZrCl2 was the most active in the homopolymerization carried out at 70 degrees C. At 30 degrees C, the activities were practically identical. In the copolymerization runs, the catalysts were similarly active, and the Et-bridged catalyst was the more active. The copolymers prepared over rac-Me2Si(Ind)(2)ZrCl2 were found to have more comonomer incorporated. The composition of copolymerization products was found (C-13-NMR) to vary with the catalyst system. DSC thermograms showed poly-1-octadecene prepared over rac-Et(Ind)(2)ZrCl2 to vary in properties with polymerization temperature (Figs. 3-5). The homopolymer prepared at 700C showed endotherms at 41 degrees C and 53 degrees C and that prepared at 30 degrees C produced one broader peak at 67 degrees C. With mc-Me2Si(Ind)(2)ZrCl2, the 70 degrees C homopolymer produced one broader peaks at 41 degrees C and 53 degrees C and the 30 degrees C homopolymer gave peaks at 7 degrees C and 67 degrees C. The two peaks in the homopolymer thermograms appear to be explicable in terms of different structural ordering in various homopolymer domains. As the comonomer concentration in the feed was increased, the molecular weight decreased and otherwise was independent of the type of the metallocene used.

The copolymerization of ethylene and 1-octadecene using a bridged metallocene was studied in order to observe the effect of the comonomer on the catalytic activity. A noticeable increase in activity is seen as the concentration of 1-octadecene in the reaction medium increases. C-13 NMR analysis shows 6.4 mol-% incorporation of comonomer at the highest 1-octadecene concentration in the feed used here. The molecular weight of the copolymers shows a drastic decrease that may be attributed to chain termination by transfer or beta-elimination of the comonomer. As to the molecular weight distribution, it remains within a narrow range, as expected with metallocene catalysts. The melting temperature and the enthalpy of melting of the copolymers show a decrease with increasing comonomer content. As usual for ethylene copolymers, the X-ray crystallinities are higher than those determined from the enthalpy of melting.

Catalizadores metalocenos racemicos del tipo rac-X(Ind)2ZrCl2 (donde X = union entre los anillos indenilos del tipo -CH2-CH2-, (CH3)2SI-, (CH3)2C- e Ind = Indenilo) han demostrado presentar una alta actividad catalitica para la polimerizacion de etileno, propileno y otras a-olefinas. En el presente trabajo se reportan los resultados experimentales provenientes de la homopolimerizacion de una a-olefina de cadena larga como es el caso del 1-octadeceno (C18) y la copolimerizacion de etileno (C2) con este monomero, utilizando dos catalizadores metalocenos racemicos: rac-Et(Ind)2ZrCl2 y rac-Me2Si(Ind)2ZrCl2 , los cuales se diferencian en el tipo de puente entre los anillos indenilos (-CH2-CH2-; (CH3)2Si-). Para el caso de la homopolimerizacion de 1-octadeceno existen diferencias importantes en el comportamiento catalitico (actividad) entre ambos metalocenos, pero no asi en la homopolimerizacion de etileno. En las copolimerizaciones, la diferencia entre las actividades de los catalizadores, se incrementa conforme aumenta la concentracion de 1-octadeceno en el medio reaccional. Se observo, tambien, que el catalizador rac-Me2Si(Ind)2ZrCl2 incorpora mas C18 en la cadena de polimero que su homologo con puente de etilo. Estas diferencias se atribuyen al tipo de union interanular que existe entre los catalizadores. A los polimeros obtenidos, se les realizaron analisis termicos, utilizando calorimetria diferencial de barrido (DSC). Los resultados muestran que el Poli-1-octadeceno sintetizado con los catalizadores en estudio presentan el mismo tipo de curva de fusion. Esta muestra dos endotermas a 30 y 54°C. Para el caso de los copolimeros, el aumento de la cantidad de comonomero en la cadena de polimero produce una disminucion en la temperatura de fusion y en la cristalinidad

The catalytic activities of two metallocene compounds, EtInd2ZrCl2 and Ind2ZrCl2, in the polymerization of ethylene depend heavily on certain parameters, such as Zr concentration in the reaction, type of the reactor, and stirring speed for homogeneous catalysts. One way or another, all these factors influence the catalytic activity of these systems, but catalyst concentration and stirring speed are the most important ones. In the case of heterogeneous catalysts of the same metallocenes, the most pronounced influence is related to the type of support and its porous nature. The influence of the support on activity and morphology is shown.