SummaryThe U.S. Department of Energy's (DOE) Pacific Northwest National Laboratory (PNNL) has been conducting research since 2005 to develop a catalyst for the conversion of synthesis gas (carbon monoxide [CO] and hydrogen [H 2 ]) into mixed alcohols for use in liquid transportation fuels. Initially, research involved screening possible catalysts based on a review of the literature, because at that time, there were no commercial catalysts available. The screening effort resulted in a decision to focus on catalysts containing rhodium (Rh) and manganese (Mn). Subsequent research identified iridium (Ir) as a key promoter for this catalyst system. Since then, research has continued to improve RhMnIr-based catalysts, optimizing the relative and total concentrations of the three metals, examining baseline catalysts on alternative supports, and examining effects of additional promoters.Testing was continued in FY 2013 to evaluate the performance and long-term stability of the best catalysts tested to date. Three tests were conducted. A long-term test was conducted with the best carbon-supported catalyst. A second test of shorter duration was performed for comparison using the same catalyst formulation on an alternative carbon support. A third test of intermediate duration was performed using the best silica-supported catalyst tested to date.The long-term test performed with the best Rh-based catalyst developed to date (catalyst H-A) operated for 2373 hr at a constant set of conditions (nominally 1200 psig, 260°C, 13,000 L/kg cat /hr gas hourly space velocity using a feed gas containing 3.4% N 2 , 3.4% CO 2 , and the balance being H 2 and CO in a 1.3:1 H 2 :CO ratio). During the test, the CO conversion and C 2 + oxygenate space time yield (STY) decreased, but at a decreasing rate over the course of the test, while the selectivity to C 2 + oxygenates remained essentially unchanged at about 73%. Analysis of the rates of decline of the STY during different periods in the test suggest that the catalyst would be stable at an STY of about 775 to 800 g/kg cat /hr while operating at 260°C. Subsequent testing at 265°C and 270°C, showed that the CO conversion and C 2 + oxygenate STY could be restored to higher values with only an ~1% decline in selectivity. Furthermore, while the catalyst deactivated at higher rates at the higher temperatures, the rates of decline were significantly lower than those observed at comparable STYs at 260°C during the first phase of the test. From these results, it is concluded that, if the test had been started at a temperature between 245°C and 250°C, the C 2 + oxygenate STY could be maintained for 2 years or more at a constant selectivity, by slowly increasing the reaction temperature as needed to maintain the catalyst activity.The catalyst supported on an alternative carbon was tested to 650 hr at the same conditions as the previously described catalyst. This catalyst initially achieved about 68% of the initial STY achieved with the best catalyst under the same operating conditions. However it wa...
This study also identified four commercially available and two demonstration MSW gasifiers, two of which involved co-feeding with coal. Three of these gasifiers were used to produce electricity and process heat and consequently were close coupled to combustors and would need to be modified to produce syngas. The other three gasifiers were capable of producing syngas or fuel gas, and would not require modification. There were also a large number of other MSW gasifiers under development that may ultimately be suitable for syngas applications. Overall, this study concludes that MSW should be considered as a potentially viable gasifier feedstock for liquid fuels synthesis. A review of feedstock availability, composition, and handling characteristics along with commercially available MSW specific gasifiers did not identify any obvious insurmountable technical or economic barriers to commercialization. However, further research into the economic issues surrounding tipping fees and process scale is needed to verify economic viability and the appropriate plant scale to achieve it.
SummaryThe U.S. Department of Energy's (DOE) Pacific Northwest National Laboratory (PNNL) has been conducting research since 2005 to develop a catalyst for the conversion of synthesis gas (hydrogen [H 2 ] and carbon monoxide [CO]) into a mixed alcohol product for use in liquid transportation fuels. Initially, research involved screening possible catalysts based on a review of the literature, because at that time, no commercial catalysts were available for this application. The screening effort resulted in a decision to focus on silica-supported catalysts containing rhodium (Rh) and manganese (Mn), and further research has been conducted since then to investigate the effects of different promoters and supports for the catalyst and to optimize the better performing catalysts.This report summarizes research conducted in FY 2010. A major effort during the year was to examine alternative catalyst supports to determine whether other supports offered superior performance compared to the results achieved using Davisil 645 silica (SiO 2 ). Three other silica supports were identified that had comparable or superior performance in terms of space-time-yield (STY) and that converted carbon selectivity to C 2 + oxygenates. In addition, several carbon supports were found that had comparable performance characteristics, but also had a significantly higher selectivity of oxygenates to C 2 + alcohols. This is of interest because it may favorably affect the costs of further upgrading the oxygenate product to mixed alcohols.Optimization of the Davisil 645 silica-supported catalyst was also continued with respect to candidate promoters, iridium (Ir), platinum (Pt), and gallium (Ga), and examination of selected preparation alternatives for the baseline RhMn/SiO 2 catalyst. Overall, there may be a minor increasing trend in carbon conversion, a decreasing trend in converted carbon selectivity to C 2 + oxygenates, and no trend in C 2 + oxygenates STY with increasing Ir concentration for the catalysts prepared with a single coimpregnation. However, with the scatter in the data for these catalysts as well as that for the doubleimpregnated catalysts, these trends should be treated with caution. No clear trends could be ascertained for the double-impregnated catalysts because of the scatter in the data. Before any conclusions can be drawn, additional testing is needed to repeat tests with both currently available catalyst samples and freshly made catalysts, and to examine a greater range of Ir concentrations.It appears that adding Pt to the RhMn/SiO 2 catalyst, via a single co-impregnation of all three metals, decreases the activity of the catalyst (carbon conversion) but increases its carbon selectivity to C 2 + oxygenates. The net result is that there appears to be a maximum STY at the lower concentrations, possibly below a concentration of about 0.35% Pt. Further testing would be required to confirm this observation. It also appears that the double-impregnated catalyst, where Pt is added in the second impregnation, is much more active, ...
Executive SummaryThe U.S. Department of Energy is conducting a program focused on developing a process for the conversion of biomass to bio-based fuels and co-products. The lignocellulosic biomass feedstock is first gasified to produce a product known as synthesis gas (syngas), which consists of H 2 and CO. The syngas stream is subsequently converted thermochemically within a temperature range of 240 to 330°C and at elevated pressure (e.g., 1200 psig) over a catalyst. Ethanol is the desired reaction product, although other side compounds are produced, including C 3 to C 5 alcohols; higher (i.e., greater than C 1 ) oxygenates such as methyl acetate, ethyl acetate, acetic acid and acetaldehyde; and higher hydrocarbon gases such as methane, ethane/ethene, propane/propene, etc. Saturated hydrocarbon gases (especially methane) are undesirable because they represent a diminished yield of carbon to the desired ethanol product and represent compounds that must be steam reformed at high energy cost to reproduce CO and H 2 . Ethanol produced by the thermochemical reaction of syngas could be separated and blended directly with gasoline to produce a liquid transportation fuel. Additionally, higher oxygenates and unsaturated hydrocarbon side products such as olefins also could be further processed to liquid fuels.The goal of the current project is the development of an Rh-based catalyst with high activity and selectivity to C 2 + oxygenates. Since the program began in 2005, significant improvements in activity and selectivity to the Rh-based catalyst have been achieved through empirical catalyst screening (e.g., support and promoter screening) and operational parametric screening. This report chronicles an effort to characterize numerous supports and catalysts to identify particular traits that could be correlated with the most active and/or selective catalysts. Characterization techniques were chosen to identify the properties of a variety of supports and catalysts. Carbon and silica were the general classes of supports analyzed. Analysis procedures used for several supports are identified below:• Ash concentration of the carbon supports • Elemental composition via inductively coupled plasma• Surface area (Brunauer-Emmett-Teller) and pore size distribution (Barrett-Joyner-Halenda) via N 2 adsorption and desorption• Surface acidity measurements of the silica supports via NH 3 desorption• Carbon support surface functionality characterization via thermogravimetric analysis with mass spectrometer analysis of the effluent gas• Diffuse reflectance infrared Fourier transform spectroscopy analysis of selected carbon supports to identify surface functionality.Generally, analyses provided guidance in the selection of acceptable catalyst supports. For example, supports with high surface areas due to a high number of micropores were generally found to be poor at producing oxygenates, possibly because of mass transfer limitations of the products formed out of the micropores.A number of prepared catalysts (i.e., with Rh and other metal p...
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