High temperature treatments of porous activated carbon

The use of biomass waste for the preparation of activated carbon is of great industrial interest for reducing costs and increasing the sustainability, especially in the field of energy storage. A high temperature treatment is required to obtain a more ordered carbon material, thus increasing its conductivity. However, this high temperature treatment entails as a disadvantage a significant reduction in porosity. Therefore, a method to prepare activated carbons with a high porosity development as well as high conductivity could be of great interest for many applications. The aim of this work is to analyze the possible influence of phosphorus compounds on the physical-chemical properties of different carbon materials thermally treated at relatively high temperatures (1600 ºC). With this goal, it has been prepared activated carbons from different precursors (olive stone, lignin and hemp) and different conformations (powder, fibers and monoliths) by physical and chemical activation, with CO2 and H3PO4, respectively. Once the different activated carbon materials were prepared, they were thermally treated at 1600 ºC under inert atmosphere. The different samples were characterized by N2 and CO2 adsorption at 77 and 273 K, respectively, XPS, XRD and Raman techniques. The oxidation resistance was also evaluated in a thermogravimetric balance. High temperature treatments of activated carbon without the presence of P surface groups produced an important contraction of the porosity (from 900 to 150 m2 g-1). However, temperature treatments of phosphorus-activated carbon allowed for preparing carbon materials with a relatively high structural order and a well-developed porosity (c.a. 1100 m2 g-1), with a significant contribution of mesoporosity. These results suggest that these P-surface groups are responsible for the low contraction observed for the porous structure, avoiding, in a large extent, its collapse.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO (CTQ2015-68654-R). MINECO (PTA2015-11464-I)

Expert system development for hard disk drive failure analysis

The Computer\u27s Hard Disk Drive is a complex high technology device, diagnosis of a failure is difficult even using sophisticated test equipments. These Drives are expensive and returning a new one when it fails within the warranty period is not an option. The failed drive must be tested and repaired. In the repair process the analysis and diagnosis of the failures is a key point in the process where decisions regarding the repair process that the failed Drive will follow. Therefore, there is a requirement to perform an effective analysis and provide an accurate diagnosis. The standard system utilized for diagnosis was based on human capacity, this study proves that the deficiencies of the standard failure analysis method does not provide satisfactory results. On the other hand, this study proposes alternatives that incorporate the expert\u27s knowledge and makes it available for analysis technicians, analyzing every Drive

Modification of the morphology, porosity and surface chemistry of lignin-based electrospun carbon materials

Lignin is a biopolymer that can be found as the main component of plants. It is obtained as a coproduct in the papermaking and biofuel industries. Owing to its high carbon and aromatic content, high availability and reduced cost, it is an excellent precursor for the preparation of highly valued carbon materials. Electrospinning is a suitable top-down technique for the preparation of polymeric fibers using high voltage electrical fields and polymer solutions of proper viscosity and conductivity. Organosolv lignins, which are extracted from lignocellulosic biomass using organic solvents, are soluble in ethanol, obtaining a solution that matches the requirement of the electrospinning process. In this way, it is possible to produce lignin-based porous carbon fibers using a coaxial electrospinning device [1]. This contribution summarizes our findings about the preparation of carbon materials with different morphologies and composition by processing lignin using electrohydrodynamic forces. Lignin spheres, beaded fibers, straight fibers, beaded tubes and straight tubes are obtained by using coaxial and triaxial spinnerets that allows the electrospinning of two or three different solutions at once [1], Fig. 1. Thermal stabilization in air is needed in order to avoid melting of lignin fibers during carbonization. Stabilization times of 48-96 hours are usually required in this step, decreasing the sustainability of the production process. Phosphoric acid can be added in small amounts in the lignin solution, shortening the time for achieve a successful thermostabilization of the fiber [2]. The carbonized materials show narrow microporosity and large surface area values (SBET from 600 to 1000 m2g-1) and additional pore size and volume can be developed by controlled gasification.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work was supported by the Spanish Ministry of Economy and Competitiveness and FEDER (CTQ-2015-68654-R)

Methanol dehydration over ZrO2 supported-activated carbons

Resumen comunicación congreso internacionalDME is playing an important role due to its potential use as an alternative fuel in diesel engines. The use of this fuel produces lower NOx emissions, and less engine noise compared to traditional diesel fuels. Moreover, this compound is used as building block for many value-added chemicals such as lower olefins. DME is usually produced via catalytic dehydration of methanol over a solid acid. The use of activated carbons in catalytic processes, acting directly as catalyst and as catalyst support, is focussing much attention. They can be obtained from different types of lignocellulosic waste, producing not only an environmental but an economical profit. In this sense, the preparation of activated carbons with phosphoric acid produces catalytic supports with certain surface acidity, which have shown high activity for alcohol dehydration. In this study, ZrO2 supported activated carbons were prepared from an industrial byproduct as lignin for the methanol dehydration to DME. The activated carbon was prepared by chemical activation with H3PO4, using Alcell® lignin as precursor. The impregnation ratio value (H3PO4/lignin) used was 3. The impregnated sample was activated under N2 flow at 500 ºC for 2h, washed and dried. The activated carbon was loaded with different amounts of ZrO(NO3)2, dried at 120ºC for 24h, and calcined in air at 250ºC for 2h, obtaining ZrO2 loadings of 5 and 10%, respectively. For the sake of comparison, pure ZrO2 was also used. Catalytic tests were performed at atmospheric pressure in a fixed bed reactor, at different space times and partial pressures. The activated carbon (ACP) prepared shows a well-developed porous structure, with an apparent surface area higher than 2000 m2/g, and a high contribution of mesoporosity. After metal loading, a maximum decrease of 20% in all structural parameters of the ACP was observed.The results show that ZrO2 loading produces an enhancing in the catalytic activity of the carbon materials compared to the parent activated carbon (0.1 g·s/μmol, PCH3OH= 0.02 atm in helium and 350 ºC). In this sense, a methanol conversion of 25% was observed with the addition of 10% w/w ZrO2 (ACP-10Zr), at steady state conditions (Figure 1). ACP shows negligible conversion, at the same conditions and for pure ZrO2 the methanol conversion was of 10%. Very high selectivity to DME (~100%) was found at temperatures lower than 350 ºC. The methanol conversion increases with temperature, reaching a value of 67% at 475ºC, but a slight decrease in DME selectivity is observed, resulting in a higher production of light hydrocarbons, mainly CH4. The results suggest that the addition of only a 10% of ZrO2 over an activated carbon prepared by chemical activation with H3PO4 enhances significantly the performance of the catalyst, compared to pure ZrO2.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Assemblage Structure, Production, and Food Web Dynamics of Macroinvertebrates in Tropical Island Headwater Streams

Variation in long-term temperature and precipitation patterns will likely influence the decomposition and export of benthic organic matter and influence aquatic macroinvertebrate consumer communities. Tropical systems are relatively understudied; therefore basal information is urgently needed. As part of an ongoing long-term study, we monitored macroinvertebrates in two shrimp-dominated and fishless headwater streams within the Luquillo Experimental Forest in Puerto Rico from 2009-2010. We combined growth rates with yearly biomass data to calculate secondary production and examined gut contents to develop quantitative food webs. Macroinvertebrate assemblages were dominated by a few insect taxa, with similar biotic composition across streams and habitats, but different structure amongst habitats. Biomass and abundance were generally greater in pools, suggesting that pools may provide habitat stability and shelter. Alternatively, shrimp may provide secondary benefits by removing fine sediments given their high density of in pools. Overall, aquatic insects had low biomass; therefore, their production was relatively low as is the case in most tropical areas. However, their turnover rates were not as high as expected. Secondary production appears to rely more on amorphous detritus and allochthonous organic matter rather than algal resources. These data are an important first step towards predicting the long-term effects that expected changes in rainfall and discharge will have in tropical stream communities

Alcohol decomposition on basic/acid lignin-derived submicron diameter carbon fibers

The use of lignin, the second most abundant polymer in nature, along with a simple and versatile technique, electrospinning, represents an advantageous and promising approach for the preparation of carbon fibers. In previous studies, we have demonstrated that the incorporation of H3PO4 to the initial lignin solution allows for shortening the carbon fibers preparation process and that the resulting carbon fibers present P-surface groups that are of great interest for heterogeneous catalysis. Different carbon fibers catalysts have been prepared by electropinning of Alcell lignin in the absence or presence of H3PO4 as chemical activating agent. Carbonization at different temperatures between 500 and 1600 ºC allows for preparing carbon fibers with a high variety of porosity and chemical surface properties. Diverse oxygen surface groups are presented on the carbon catalysts surface. The isopropanol decomposition has been used as a catalytic test to study the acid or basic character of the prepared carbon fibers. Carbon fibers without phosphorus surface groups generate acetone as the main product of the isopropanol decomposition reaction, from 400 to 600 ºC, suggesting the basic character of these catalysts. On the contrary, phosphorus-containing carbon fibers show high acid character, producing selectivity to propylene of 100 % at temperatures between 250 and 350 ºC. The most acid carbon fiber catalyst produced a high selectivity to ethylene and dimethyl ether for the decomposition of ethanol and methanol, respectively. The conversion enhancement that the presence of oxygen in the gas phase produced for all these reactions was also studied.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO (CTQ2015-68654-R). MINECO (PTA2015-11464-I)

Flexible and low-cost binderless capacitors based on p- and n-containing fibrous activated carbons from denim cloth wastes

Activated carbon cloths have been prepared from denim cloth wastes (DCWs) through chemical activation with H3PO4. The effect of the H3PO4/DCWs impregnation ratio and the carbonization temperature on the porous texture, the chemical composition, the fibers morphology, and the electrochemical performance has been studied. Low H3PO4/DCWs impregnation ratios lead to flexible and microporous activated carbons cloths, whereas more fragile and rigid activated carbon cloths with higher external surface area are produced upon increasing the amount of H3PO4. The increase in the carbonization temperature allows for obtaining a more ordered and conductive carbon structure. The activated carbon prepared at 900 ºC with a H3PO4/DCWs impregnation ratio of 0.5 (w/w) exhibits the best performance as electric double layer capacitor. This electrode shows a specific surface area of 2016 m2 g-1 and the highest registered gravimetric capacitance (227 F g-1). Moreover, its flexibility minimizes the ohmic resistance of the electrode, thus increasing the feasibility of working at higher current densities than the other synthesized electrodes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech; MINECO CTQ2015-68654-

Kinetic study of methanol dehydration over Zro2 supported-activated carbons

The growing concerns about climate change and energy consumption have been the driving force in seek of alternative fuels such as DME, mainly produced via methanol dehydration over a solid acid catalyst. The use of activated carbons for this aim has been little studied up to date. Only a few studies can be found in the literature, reporting all of them materials with a low thermal stability of the acid surface groups, which results into a fast deactivation of the catalyst. In this work, the preparation of activated carbons via chemical activation with phosphoric acid, their modification with different ZrO2 loads, and their application as methanol dehydration catalysts have been studied. The catalytic results showed that the best methanol conversion and selectivity towards DME were achieved with the activated carbon prepared with an impregnation mass ratio value (H3PO4 /precursor) of 2 and an activation temperature of 800 ºC, loaded with a 7 % (wt) of ZrO2 . This catalyst exhibits high steady state methanol conversion values even at temperatures as high as 400 ºC (XCH3OH= 80%, 0.1 g·s/μmol, PCH3OH= 0.08 atm in helium), keeping a selectivity to DME higher than 96%. The effect of oxygen in the reaction atmosphere was also analysed. In this sense, an increase of 15 % in the DME yield was obtained when using air instead of helium as reaction atmosphere (350 ºC, 0.1 g·s/μmol, PCH3OH= 0.04 atm). A kinetic study has been carried out on this catalyst in which two mechanisms (Eley Rideal and Langmuir Hinshelwood) for methanol dehydration have been analysed. The models proposed also consider the presence of oxygen in the reaction media.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO (CTQ2015-68654-R). MECD (FPU13/02413)

A perspective on the preparation of value-added carbon materials from lignin

The thermochemical conversion of lignin into different added-value carbon materials constitutes an alternative approach for valorization of this co-product that can be integrated in pulping and biorefinery processes. Such approach is based on the relatively high carbon content and the abundance of aromatic rings in the structure of raw and technical lignins. In this way, our research group have been preparing carbon molecular sieves, activated carbons, electrospun nanofibers, nanostructured and highly ordered carbons from different types of lignins during the last three decades.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec