Search

The invention relates to a process for producing allyl alcohol, the process comprising: dehydrating a C3-oxygenate domprising monopropylene gycol or 1,3-propanediol; wherein the dehydration is performed in the presence of a basic catalyst. The C3-oxygenate may be dreived from a biomass conversion process and subsequently converted to acrylic acid.

This paper proposes and examines an alternative thermo-chemical process for biomethane production from lignocellulosic biomass, termed self-gasification. Self-gasification of biomass is envisaged to utilize a high-pressure steam gasifier (30−80 bar) at temperatures of 600−900 °C and to use the alkali metals in biomass as gasification and methanation catalysts. The concept was studied by performing preliminary process simulations and by several screening experiments with wood. The simulations gave insight into the effect of gasifier operating conditions on methane yield. After screening tests of different alkali metals, KOH was chosen as a model compound for biomass-derived ash for further experimentation. It improves char reactivity by more than an order of magnitude, and thermogravimetric data interpreted by a first-order reaction model showed that it accelerates the pyrolysis reaction reducing the activation energy from Ea = 143 kJ/mol to Ea = 65 kJ/mol. Methane amounts higher than dictated by equilibrium are produced with and without impregnated KOH.

Reduction of NO2 with CO in the presence of NO and excess oxygen, a model mixture for flue gas, over a 0.1% Pt/SiO2 catalyst was studied. The related reaction mechanisms, such as oxidation of CO and NO, were discussed. It was found that there was a narrow temperature window (180-190 °C) for the reduction of NO2 by CO. When the temperature was lower than the lower limit of the window, the reduction hardly occurred, while when the temperature was higher than the upper limit of the window, the direct oxidation of CO by O2 occurred and thereby NO2 could not be effectively reduced by CO. The presence of NO shifted the window to higher temperatures owing to the inhibition effect of NO on the activation of O2 on Pt, which made it possible to reduce NO2 by CO in flue gas.

Gasification of lignocellulosic biomass has attracted substantial current research interest. Various possible routes to convert biomass to fuels have been explored. In the present chapter, an overview of the gasification processes and their possible products are discussed. Gasification of solid biomass and steam and aqueous-phase reforming is discussed with a special emphasis on supercritical condition operations. The production of synthesis gas from biomass and its contaminants with their permissible limits are covered along with the cleanup and upgrading of the resulting syngas. The chapter ends with conclusions and an outlook for future opportunities and challenges.

This chapter reports on the latest developments of biomass catalytic pyrolysis for the production of fuels. The primary focus is on the role of catalysts in the process, namely, their influence in the liquefaction of lignocellulosic biomass.

The conversion of light paraffins to olefins and the secondary reactions of the unsaturated compounds were investigated on H-ZSM5 and H-Y zeolites between 733 and 823 K. Steady state- and transient response-isotope tracing studies revealed that two mechanisms of dehydrogenation are operative. The main pathway is represented by monomolecular, protolytic dehydrogenation. This reaction contributes most to steady state olefin production. Additionally, at the initial stages of the reaction, extra framework aluminum moieties are speculated to participate in high dehydrogenation activity. This pathway is blocked at later stages of the reaction by product (hydrogen) inhibition. The intrinsic rates of protolytic dehydrogenation and olefin desorption range in the same order of magnitude. At high protolytic dehydrogenation rates, olefin desorption represents the rate determining step. Depending on the process conditions, olefins undergo secondary cracking, oligomerization, or isomerization. The latter proceeds via intramolecular rearrangement, possibly via a cyclopropylcarbenium ion at high temperatures and low conversions. At reaction conditions where bimolecular cracking prevails, isomerization is concluded to occur via secondary cracking of di- or oligomers.

In Pt/ZrO2catalysts used for CO2/CH4reforming to syngas, not all accessible Pt contributes equally to the activity of the catalyst. The catalytic activity is determined by the accessibilityof Pt on the Pt-ZrO2perimeter. This is explained in terms of theCO2activation via carbonate species on the support which must bein the proximity of the Pt particles to react with the methaneactivated on the metal. The significance of the support is alsoemphasized by the low activity of Pt black and Pt/SiO2, which wereincapable of forming carbonates on the support. The perimeterconcentration of Pt/ZrO2can be changed by changing the Ptconcentration in the catalyst or by increasing the calcinationtemperature which causes sintering of the Pt particles. In contrastto the calcination temperature, the reduction temperature did notinfluence the activity although the hydrogen chemisorption capacitywas markedly decreased by increasing the reduction temperature. Assintering was excluded on basis of particle size determination fromEXAFS results a SMSI state on Pt/ZrO2during high temperaturereduction is concluded to exist. This state does not persist underreaction conditions due to the presence of adsorbed oxygen fromCO2dissociation.

The adsorption and reaction characteristics of methane, carbon dioxide, carbon monoxide, and hydrogen have been investigated over a ZrO2support and a Pt/ZrO2catalyst by using a temporal analysis of products reactor system. It was observed that on Pt/ZrO2both methane and carbon dioxide dissociate independently of one another. The dissociation of carbon dioxide acts as an oxygen supplier, while the decomposition products of methane scavenge the oxygen from the catalyst. When an abundance of oxygen is present, pulsing of methane leads to the production of carbon dioxide. It is concluded that both the selectivity with which methane produces carbon monoxide or carbon dioxide and the carbon dioxide conversion is determined by the same reaction: COads+Oads CO2,ads.

The production of chemicals from lignin and lignin depolymerisation products is a promising alternative route to replace fossil fuels. Transetherification of guaiacol, a lignin derived model compound, to o-ethoxyphenol with γ-Al2O3 as the catalyst in supercritical ethanol has been investigated. The best reaction condition is 280 °C for 3 h, giving a yield of 42% with a selectivity of 86%. A reaction pathway is also proposed. Besides, this work provides an example for producing a longer chain ether from a short chain ether.

Steady-state isotope tracer studies and isotope transient response experiments ofn-butane conversion on H-ZSM-5 (Si/Al = 35) were carried out between 673 and 823 K. Among the three main reactions, the rate of H/D-exchange is at least one order of magnitude higher compared to the rates of cracking or dehydrogenation. Its apparent energy of activation is lower than that of the latter two processes. The rates of H/D-exchange are higher for larger molecules than for smaller ones and faster with olefins than with paraffins. Proton exchange proceeds stepwise, i.e., only one hydrogen (deuterium) of the substrate is exchanged with one deuterium (hydrogen) in a single catalytic turnover. A kinetic isotope effect was found for protolytic cracking, but not for dehydrogenation. Protonation of the feed (deprotonation of the zeolite) is concluded to be involved in the rate determining step of cracking.

Vanadium-niobium oxide catalysts containing variable amounts of vanadium and prepared by coprecipitation were investigated using 51V solid-state NMR. It was found that, in samples containing less than about 8 mol % V2O5, vanadium occurs in three different oxygen environments: in isolated tetrahedra, in comer-sharing tetrahedra (pyrovanadate), and in distorted octahedra. The number of octahedral sites increased as the amount of vanadium in the bulk of the catalyst was increased. The compound 8-(Nb,V)205 was found to occur in samples containing more than 7 mol % V2O5. In this compound, vanadium occurs not only in isolated tetrahedral sites but also in comer-sharing tetrahedral sites. For a catalyst having the niobia in the crystalline T form, it was found that an increase in the bulk concentration of vanadium caused the number of neighboring sites occupied by vanadium to increase and the vanadium partially to replace niobium in the T-niobia structure.

A series of vanadium-niobium oxide catalysts in which the vanadia content varies between 0.3 and 18 mol% was prepared by coprecipitation. These catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS), and by catalytic testing in the oxidative dehydrogenation reaction of propane. The results of the surface analysis by XPS and LEIS are compared, It is concluded that the active site on the catalyst surface contains 2.0 ± 0.3 vanadium atoms on average. This can be understood by assuming the existence of two or three different sites: isolated vanadium atoms, pairs of vanadium atoms, or ensembles of three vanadium atoms. At higher vanadium concentration more vanadium clusters with a higher activity are at the surface. LEIS revealed that as the vanadium concentration in the catalyst increases, vanadium replaces niobium at the surface. At vanadium concentrations above 8 mol%, new phases such as ß-(Nb, V)2O5 which are less active because vanadium is present in isolated sites are formed, while the vanadium surface concentration shows a slight decrease.

A series of zirconia doped Li/MgO catalysts with a fixed amount of zirconia and varying concentrations of lithium was used for the oxidative coupling of methane. It was found that an increase in lithium concentration resulted in a decrease in initial activity, while the selectivity was not affected. The life-time of Zr doped Li/MgO catalysts with a fixed concentration of ZrO2 is a function of the lithium concentration. Previous results have shown that Li2Mg3ZrO6 is active and selective but it is now shown to be instable under reaction conditions.

This paper summarises the background to work carried out at the University of Twente on the use of niobia as a catalyst for the oxidative dehydrogenation of propane to propylene and discusses the development of promoted niobia catalysts for this reaction. Results are also presented which illustrate the use of niobia in catalysts for other reactions such as the oxidative coupling of methane, the oxidative dehydrogenation of ethane and the oxidative dehydrogenation of methanol. It appears that niobia and niobia-modified catalysts, when used in high-temperature oxidation processes, can exhibit relatively high selectivities compared with more conventional catalysts.

The influence of various preparation methods on the performance of V-Nb-0 catalysts has been investigated. It was found that the activity and selectivity of a vanadium site depend on the nature of the neighbouring atoms. Vanadium neighbours provide activity, while niobium neighbours provide selectivity. Careful preparation of these catalysts ensures a homogeneous distribution and good mixing of the vanadium and niobium. It was also found that the vanadium becomes mobile upon reduction and this results in better distribution of vanadium in used catalysts.