1 Thermochemical Conversion Roadmap Workshop Focus Group 2 Gas by cometjunkie55


									Thermochemical Conversion Roadmap Workshop Focus Group 2: Gas Clean-up and Conditioning and Fuel Synthesis January 10, 2007 Chairs: Mark Jones, Dow Chemical Company Jennifer Holmgren, UOP, LLC David C. Dayton, NREL Roy Tiley from BCS, Incorporated, introduced himself as the facilitator for this session. He then asked David Dayton of the National Renewable Energy Laboratory to give an overview of the session’s goals. Introductory Remarks Dave stated that the Thermochemical Platform is in the process of developing quantifiable R&D targets to achieve the $1.07 2012 cost target for cellulosic ethanol from a gasification/mixed alcohol synthesis process. A handout was provided which outlined the current R&D structure for the thermochemical platform to provide a context for the Focus Group discussion. The technical barrier areas established for thermochemical ethanol production include Feed Handling and Preparation, Gasification, Gas Cleanup and Conditioning, and Fuels Synthesis. The latter two technical barrier areas were the focus of the discussion with the understanding that technical progress in upstream unit operations can positively impact the challenges that need to be over come in Cleanup and Conditioning and Fuels Synthesis and the technical success of the overall integrated process is the ultimate goal. For 2012, the goal will probably be achieved by mixed-alcohol ethanol production. Beyond that, the 2030 goal for 60 billion gallons of ethanolequivalent biofuels will only be achieved if all cost-competitive alternative thermochemical processes are included for biofuels production. Dave introduced Mark Jones from Dow, who gave a PowerPoint presentation explaining why the Dow Chemical Company was following developments in thermochemical biofuels production. Mark emphasized that Dow Chemical is not a fuel company but a chemical company. Dow and its subsidiary Union Carbide historically developed technologies for mixed alcohol production. These were large programs and significant knowledge still resides within the Company. The chemical industry as a whole relies on feedstocks delivered by the fuels industry. World wide, the chemicals industry accounts about three percent of global energy production, with Dow representing about one tenth of the chemical industry. Ethanol is a useful chemical and developments that drive it to price parity with hydrocarbon fuels will certainly impact the chemical industry. Thermochemical conversion requires several chemical transformations be integrated: Syngas preparation, gas cleanup, and syngas conversion. Only through an integrated, multi-step process, can biomass feedstocks be delivered as liquid motor fuel to the end-user. Currently, there are no proven commercial processes for converting syngas cleanly to ethanol. Syngas conversion to an alcohol, methanol, is commercially practiced at very large scale using feedstocks ranging from natural gas to coal. Today, methanol is produced by processes deriving from the low-pressure


process first introduced in the 1960's. Methanol is likely not a viable motor gasoline component, but may prove to be a preferred intermediate in the production of either gasoline or ethanol. Additionally, any syngas-based process is likely to benefit from use of commingled fossil and biomass feeds to improve both gasification and scale. Technologies have been demonstrated that allow the conversion of methanol to gasoline. This pathway produces a fuel identical to current gasoline using commercially proven processes, unlike the nascent mixed alcohol process.

Dave Dayton asked the session participants to identify themselves. Jennifer Holmgren – UOP Mark Paisley – Taylor Biomass Energy Santosh Gangwal – RTI International Scott Olson – Nexant, Inc. Ryan Katofsky – Navigant Consulting Jeff Eltom – Syntec Biofuel Janice Ford – Navarro – GFO Paul Grabowski – DOE – OBP Richard Bain – NREL Scott Turn – U of Hawaii Bryan Jenkins – UC Davis Kelly Ibsen – NREL Michael Goff – Black & Veatch Roy introduced the two goals for 2012 and 2030. The first goal segment is 2012: fuels standard, targets, milestones, ID gaps, barriers, R&D needs, milestones/targets for gaps, necessary investment, commercialization path, DOE role. John Rezayan – Princeton Energy Resources Inc. Subbarama (Vis) Viswanathan – Conoco Phillips Co. Bill Schinski – Chevron Gerson Santos-Leon – Abengoa Bioenergy Seth Snyder – ANL John Robbins – Exxon Mobil Viorel Duma – Abengoa Matt Ringer – NREL Tom Foust – NREL John Hansen – Haldor Topsoe A/S


Second segment 2012 -2030 and beyond: fundamental R&D, process engineering improvements, intensification, capital intensity reduction. Gas Clean Up Participants stated that the goals are policy-driven, and that they could plan to start from the beginning with two paths: one for 2012, and another starting today through 2030, though the goals for thermochemical technologies might vary from ethanol production goals. It was considered backwards to limit the 2012 goal to cellulosic ethanol, when many fuels will be needed to achieve the 2030 goal. After some discussion, it was agreed that syngas-based processes could achieve the goals provided cost effective processes be developed. R&D necessary for development of robust processes was the focus of the rest of the session. It was recognized early that the breadth of possible biomass feedstocks make it unlikely that a single plant design could handle all possible feeds. For the session, the discussion targeted technologies that represent the likely high volume biomass feeds, stover, wood and switchgrass. Furthermore, no particular conversion technology was assumed. The discussion generally centered on contaminants of concern for most catalytic systems. Since the goal was to develop R&D plans, contaminants for which commercially practiced processes are known were generally dismissed. There was great concern that gasifier operation impacts the impurity profile. Changes to gasifier operation that minimize contaminants of concern are strongly favored over methods that remediate the problem actors once formed. The gasification process generates syngas, which then enters the fuel synthesis step. The design report shows that Cleanup and Conditioning is the largest cost component of biofuels production because of the stringent requirements of fuel synthesis processes. These findings are due, in large part, to the sulfur laden tar produced in the gasification process. The requirement for sulfur removal varies by process. If the syngas is cleaned, then it can be made into fuel by various methods. The group agreed to examine general requirements for gas cleanup and conditioning technologies. Syngas cleanup and conditioning is conducted for specific reasons: - To protect catalysts (particularly fuel synthesis catalysts) - To protect downstream equipment - To protect the environment (air/water/soil) - To improve efficiency - To improve economics Syngas conversion was assumed to use heterogenous catalysts. Furthermore, it was assumed that it is far better to keep the syngas both hot and at pressure. Cooling, quenching and recompressing were assumed to be too deleterious to the process economics to be viable. Participants then prioritized the potential syngas contaminants resulting from biomass gasification. It was agreed that the processes to remove all contaminants exist, but need to be made more economical at the scales typical of biomass systems. Synergies with the Fossil Program on these technologies may


exist but need to be demonstrated in integrated biomass gasification processes to determine technical and economic viability. Tars were identified as the highest-priority catalyst contaminant. HCl and H2S were added to the list. HCN and arsenic were rearranged. While the methane content of biomass-derived syngas can be quite high depending on the gasification process (~12% for indirect biomass gasification), it is likely a diluent that will have minimal impact on the fuels synthesis catalytic process. However, at high methane concentrations overall carbon conversion to biofuels is lower, thus reducing liquid yields and potentially affecting process economics. The affect of methane on catalyst performance in regards to altering kinetics or carbon conversion to alcohols is unknown and should be evaluated. Benzene was considered a low-priority because it is likely a low concentration diluent in fuel synthesis processes with little adverse affects in terms of coke formation on catalysts. A list of contaminates of concern is a follows: Tar Cl, NH3, HCN H2S, CO(s) Alkali metals, Particulates H2/CO ratio CO2 removal CH4 Benzene Inert content (change in heat value) Black Water Heavy Metals, As Hg, Pb Silicon (silica)

The group agreed that research should seek to prevent poisoning of the catalyst by Cl, NH3, HCN, H2S, COS, alkali metals/particulates, and eliminating tars to prevent coke formation on the catalysts. Traditional wet scrubbing is an option to remove alkali, Cl, NH3, and tars but the production of “black water” becomes a disposal problem. Hot gas cleanup of tars (reforming to CO + H2) is desired to maximize thermodynamic efficiency and is also an option for NH3 conversion. The impact of methane (CH4) on alcohol production kinetics and equilibrium, and the related issue of over production of CO2 need to be addressed to optimize biofuel yields. The impact of nitrogen as a diluent in air-blown gasification systems obviously reduces syngas heating value but has unknown effects of fuels synthesis process beyond increasing process costs. Arsenic and mercury were added to the list and then combined with heavy metals in general. These elements are typically present at very low levels in biomass materials. Tars were brought up again as potential co-products from biomass gasification processes but the economics of removing tars as coproducts have not been evaluated. The group agreed that economics could not be proven in this session, and continued prioritizing the list, highest to lowest: - Tar - Cl, NH3, HCN


- H2S, COS - As, Hg - Particulates, alkali metals The group moved to identify technologies and necessary resources to tackle the prioritized list of possible contaminants. Silica was added to the list of contaminants possible, specifically in very high temperature gasification processes. Silica removal could be dealt with in the Feed Preparation and Handling step but would likely be cost prohibitive. Alkali in biomass is typically an issue for gasifier operability in terms of bed agglomeration. Lead was added as a potential vapor phase problem, and the category amended to “heavy metals”, including arsenic, lead, and mercury. To establish R&D targets, the group considered the burden of removing the contaminants. Processes exist for mitigating all of the contaminants identified in the absence of tars, therefore, tar mitigation was identified as the highest priority gas cleanup technical barrier. Sulfur removal can be accomplished in the absence of tar. Solutions for chloride and ammonia are available but not economical for biomass gasification systems. HCN removal has been demonstrated in a steam gasifier. COS can be hydrolyzed to H2S, but is likely not economical for small-scale biomass gasification. Chloride can easily be absorbed in a calcium carbonate bed in posttreatment but adds an additional unit operation to the cleanup and conditioning process. It is presumed that the reducing environment present in the gasifier will convert all chlorine present to HCl. Organochlorine compounds, should they be found to exist, represent a different problem. Ammonia can be scrubbed in a water quench or converted to N2 over a tar reforming catalyst. If gas is water-washed, the tar becomes an environmental problem, which can be costly to remediate. To maximize thermodynamic efficiency, the syngas be cleaned and conditioned as much as possible before it is cooled for compression prior to the fuel synthesis step. Therefore, a water quench/scrubbing could be used sometime in the process. Cooling is a function of the type of gasifier and catalyst. Control of H2S is important when considering removal of other contaminants, such as tar. Development of hot gas sulfur removal would add to tar reforming efficiency. Black liquor feedstocks have H2S removal cost issues. Biorefinery residue feedstocks allow for COS and H2S separation with water in equilibrium, depending if the tars have been removed. How to best remove the tar in the presence of both H2S and COS is a unique scientific situation. Alkali metals vapors can be removed when the syngas is cooled. Alkalis are typically not removed until after the tar removing step, though alternatives exist. The group began to develop targets for preferred R&D. They advocated a study to understand the dynamics of feed/gasification technology. They also sought technology to mitigate tar issues. The level of tolerable tar would be determined after the downstream scheme. The study would be a process flow model using the type of feedstock, residence time, temperature, and the potential application of in-bed catalytic materials to avoid making tar. A model for each gasifier type is necessary. These analyses will help to define specific targets for tar loadings/conversions that define the technical barrier.


If biomass is cogasified with coal, a lot of the contaminant concerns may be avoided because of the high temperatures established in pressurized, oxygen-blown entrained flow coal gasifiers. However, the lower energy content of biomass compared to coal raised concerns about heat balance in coal gasifiers. Fuel Synthesis Two approaches were identified for achievement of 2012 and 2030 goals: Mixed Alcohol Synthesis with high yields of ethanol in the liquid product (single step) and methanol homologation chemistry to add CO to methanol to yield ethanol (two steps). It was mentioned that a cost-competitive homologation catalytic process did not exist and catalyst need to be developed in order to equal the single-step efficiency. Alternative processes to the $1.07/gal thermochemical ethanol scenario to produce gasoline range hydrocarbons from syngas were discussed as potentially nearer term options for biofuels production from syngas. Two processes in particular, the Methanol-to-Gasoline process demonstrated in the 1980’s (MTG process by Mobil and TIGAS by Haldor-Topsoe) and hightemperature Fischer-Tropsch synthesis were identified as potential routes for producing gasoline from biomass. Acetic anhydride as an intermediate to ethanol, though an extra process step, is another possible process. As a follow-up to the Mixed Alcohol Design Report produced by NREL, D. Dayton suggested that a potential Industry Consortium could be established to evaluate the process economics of alternative fuels synthesis strategies for thermochemical biofuels production. A Consortium could be a mechanism for industry to provide relevant data on specific catalytic processes that may not be readily available in the open literature. At the very least, industry could provide guidance on whether specific assumptions for catalytic processes were reasonable based on their corporate knowledge without compromising any business confidential information. Syngas fermentation for thermochemical ethanol production was also brought up as a process option. Laboratory staff (ANL) stated they are working to directly engineer organisms to produce ethanol with high selectivity. Syngas fermentation technology was discussed, and it was decided that not enough public information is available to conduct a rigorous analysis of the technology to determine whether it is cost-competitive. Until that information is available it will be difficult to fully assess the technology. Additionally, claims are being made publicly that this technology is very near commercialization questioning the role of DOE in future R&D required for further developing this technology. It was suggested that DOE support the collection of public information for public review. A near-term need to achieve the $1.07/gal thermochemical target is developing better mixed alcohol synthesis catalysts with higher single pass conversion efficiencies and ethanol/higher alcohol selectivity. Unfortunately, the two catalyst performance improvements are not necessarily complimentary. It was suggested that high selectivity usually comes at the expense of low conversion efficiency, and that catalysts should be tested for their cost effectiveness by assessing the economic benefits of high selectivity and low CO conversion efficiency to alcohols versus low ethanol selectivity and high CO conversion efficiency. The economic benefit or


penalty of syngas or methanol recycle needs to be validated experimentally. Selectivity can be improved with very effective heat removal to precisely maintain reactor temperature. CO conversion efficiency is typically presented on a CO2-free basis, however, the conversion of CO to CO2 (aka CO2 selectivity) is typically what limits overall alcohol yields. Therefore, developing catalysts and exploring catalyst operating conditions that maximize the amount of input carbon that gets converted to product (higher alcohols) should be researched. The economic model needs updating, and catalyst and reactor cost seem undervalued as part of the process. Catalyst selectivity was stated to be dependent on secondary reactions, depending on resonance time. If a catalyst is well-selected, the process will lead to better catalyst invention. A catalyst discovery project was suggested, for research on yields, temperature limits, lifetime, and comparative performance. If ethanol is the desired product to achieve the 2012 goals, a new catalyst will likely need to be found because available data suggest that existing catalysts will not perform well enough to meet the desired product yields. Pilot scale demonstration of developing cleanup and conditioning and fuels synthesis catalytic processes is needed establish integrated process optimization and explore the affect of relevant process variables. Additionally, validation of the integrated processes must be of sufficient duration to identify possible unknown impurities that have yet to be an issue at the laboratory scale.


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