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

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)

Effect of phosphorous groups on the stabilization and activation of low-cost lignin fibers prepared by electrospinning

The feasible wider use of carbon fibers in many of their current and potential applications demands a reduction of their manufacturing costs. In this sense, the use of lignin as an abundant, renewable and low-cost carbonaceous precursor and a simple and versatile production technique, such as the electrospinning, represents an advantageous and promising approach [1-3]. Particularly, the devIlopment of high-value co-products from lignocellulosic biomass-derived industries, such as biorefineries and pulp and paper mills, could suppose a significant opportunity to reduce their associated costs and environmental impacts. However, the use of lignin itself in the production of carbon fibers requires of successive stabilization and carbonization steps that currently slow down, raises the price and, therefore, limits their commercialization and industrial application. In this work, a new method to produce novel sub-micrometer carbon fibers by electrospinning of phosphorous-containing lignin solutions is proposed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Generación de grupos superficiales oxigenados en carbones activados con H3PO4

Los carbones activados preparados mediante activación química de residuos lignocelulósicos con ácido fosfórico presentan, además de una elevada superficie específica, una química superficial muy particular debido a la presencia de grupos funcionales superficiales de fósforo, en forma de COPO3, CPO3 y C3P, que muestran una alta estabilidad química y térmica [1,2]. Estos grupos confieren a los carbones elevada resistencia a la oxidación y gran acidez superficial, convirtiéndolos en materiales muy interesantes para aplicaciones catalíticas. El interés de este trabajo radica en estudiar la posible modificación y regeneración de los grupos oxigenados superficiales de este tipo de carbones activos. Para ello, se ha sometido al carbón activo a ciclos de oxidación-reducción a distintas temperaturas de reacción.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

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)

Oxidation of activated carbons containing surface phosphorus functionalities

Activated carbons materials have attracted considerable attention because of their interesting application in many fields, such as catalysis, gas and liquid phase adsorption and gas and energy storage. However, the use of carbon materials in catalysis is limited since they would gasify to CO2 (or CO) in the presence of oxygen at relatively low temperatures. On the other hand, it has been shown that it is possible to prepare carbon materials with a relatively large amount of phosphorus on the carbon surface by chemical activation of lignocellulosic materials with phosphoric acid [1]. This activation method leads, in certain operation conditions, to the generation of phosphorus surface complexes in form of C-O-PO3, C-PO3 and C3PO groups, which present a very high thermal stability and confer to the carbons certain surface properties of great interest in heterogeneous catalysis applications, such as high oxidation resistance and surface acidity. The main purpose of the present work is to study the role of the phosphorus surface groups of these activated carbons on the carbon surface oxidation and reduction reactions. An extensive study of the oxidation evolution of the activated carbon surface has been carried out by subjecting the carbon to thermal treatments in oxidizing and inert conditions, using different techniques including temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) for the characterization of the obtained carbons. It has been proved that phosphorus surface groups preferentially trap oxygen and are transformed from less to moreoxidized species prior to carbon gasification, even at low temperature. These experimental results evidence the role of phosphorus surface groups on the inhibition of carbon oxidation and gasification. The high capacity of these phosphorus species to be oxidized results in activated carbons with a high amount of oxygen surface groups of acidic character and relatively high thermal stability. The reduction and re-oxidation of the (phosphorus) surface groups have also been proved to be reversible through successive thermal treatments in oxidizing and inert conditions. The new surface sites generated during the reduction conditions (probably of C-PO type) may react with oxygen from air and regenerate the C–O–PO system, indicating the presence of redox sites on the surface of the activated carbon. These results open new and attractive possibilities for the use of these carbon materials as catalytic supports or as catalysts by themselves for reactions that take place under oxidizing conditions and at relatively high temperatures.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

On the deactivation of Zr-loading P-containing mesoporous carbon catalyst during methanol dehydration

Dimethyl ether (DME) has received much attention in the last few years due to its potential use as a diesel substitute and it can be obtained from dehydration of biomass-based methanol. γ-Alumina, ZSM-5 and HPAs were tested as catalysts. A carbon-supported zirconium phosphate catalyst was synthesized and tested for methanol dehydration reaction in a high temperature range. Carbon matrix was produced by olive stone waste activated with phosphoric acid (mass acid to olive stone ratio of 2:1) at 800ºC for 2 h. Then, after washing with distilled water and sieving between 100-300μm, the obtained carbon was impregnated with ZrO(NO3)2 and thermal treated at 250ºC for 2 h. Reaction was performed in a fixed-bed reactor at a space time of 75 gcat·s/mmolCH3OH, a partial pressure of 0.04 atm of methanol and temperatures between 450-600ºC. Deactivated samples were exposed to air at 350ºC for 100 min to study the catalyst regeneration. The catalyst showed a high selectivity to DME (≥95%) and an acceptable conversion at Tª lower than 400ºC without noticeable deactivation. At T>400 ºC, deactivation was detected, due to coke deposition, whose rate increases with operating temperature. However, a high selectivity to DME was observed (above 65%) even at very long times on stream (tos). N2 adsorption results pointed out that deposition of coke took place mainly on the surface of the narrow micropores of the catalyst, blocking much of this narrow porosity at long tos. According to XPS analysis, superficial concentration of phosphorus and zirconium were also diminished with coke deposition, although zirconium was decreased to a larger extend. A kinetic model was developed for the catalyst deactivation during methanol dehydration under different reaction conditions, based on coke deposition.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

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)

Strategic situation, design and simulation of a biorefinery in Andalusia

In a lignocellulosic feedstock based biorefinery, biomass can be transformed in several products, with different chemical and/or agro-industrial applications, and energy (biofuels). The use of biomass waste is strongly advocated under European Union (EU) legislation in order to help achieve the climate and energy targets of the EU for 2020 and beyond. In this context, this study was focussed on the design and simulation of a biorefinery to mainly obtain ethanol and DME. These biofuels were obtained from waste forestry and agricultural waste biomass collected near the area where the biorefinery plant was proposed to be installed, to minimize the transportation costs and to promote the valorization of the biomass waste generated in this region. Moreover, the industrial applications of the possible obtained by-products were evaluated to minimize the environmental impacts and to make the biorefinery more sustainable. The central area of Andalusia was selected as the most adequate area to develop the installation of the biorefinery plant. Two commercial simulation software, such as Aspen HYSYS® and UniSim®, were used to design and size the equipments and to simulate both production lines. One of the most important achievements of this biorefinery is the possibility of obtaining 42,700 T y-1 of ethanol with a purity of 96%, which supposes a 16.5% of the Spanish national production in 2016, and 137,850 T y-1 of DME, with a purity of 99.99%. from these biomass waste Both compounds can be used as alternative fuels or energy sources. A techno-economic analysis was performed, obtaining a minimum selling price of 0.58 $/L for bioethanol, 1.15$/kg for DME and 0.65 $/kg for HMF and LA, respectively. These prices are comparable to those found in the literature. Furthermore, the implementation of the biorefinery in this strategic area promotes its economic and social development, improving the use of the natural resources to obtain competitive products to fossil fuels.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work was supported by the Spanish MINECO under CTQ2015-68654-R project. MCGM gratefully acknowledges the assistance of Spanish Ministry of Economy and Competitiveness through a “Juan de la Cierva – Formación” fellowship (FJCI-2015-25788)