The U.S. petrochemical industry has big plans for a constituent of wet natural gas. A major dry gas R&D effort could yield an important breakthrough for the sector.
Vast supplies of inexpensive feedstocks from domestically produced natural gas are making U.S. petrochemical plants among the most competitive such facilities in the world. As a result, the country's petrochemicals sector is expected to invest more than $16 billion in new manufacturing capacity. In a 2011 report, the American Chemistry Council (ACC) conservatively estimated this level of investment could create approximately 200,000 new jobs in the United States. In addition, ACC found that chemical industry output could expand by nearly $33 billion in this scenario.
The ACC's figures stem from what the organization calls a "hypothetical, but realistic" 25-percent increase in the U.S. supply of ethane, which is a natural gas liquid (NGL) used to produce ethylene. Ethylene is used to manufacture adhesives, rubber, plastic bottles, footwear and myriad other products.
Another key petrochemical building block is the aromatic hydrocarbon benzene. As this flowchart from the ACC shows, the assortment of products derived from benzene is extensive as well. The petrochemicals industry uses different indirect methods to produce benzene. The industry would likely welcome a simpler, economically feasible direct method for producing benzene, but efforts to develop such a technological breakthrough have proven elusive.
NGLs, or "wet gas," are driving what is often called a "renaissance" in the U.S. petrochemicals industry. DownstreamToday recently spoke to two prominent chemical engineers based in Pittsburgh, Pa., who believe that finding a cost-effective process for directly converting "dry gas" (methane) into benzene would add an entirely new dimension to sector's revitalization. They contend that a broad-based research and development (R&D) consortium represented by industry and academia could be the avenue for making the economic direct conversion of methane to benzene a reality.
Below is the transcript of an interview DST conducted with Don Wardius of Bayer MaterialScience, LLC and Andrew Gellman of Carnegie Mellon University. Wardius is the manager of Scale-up and Introductory Manufacturing/Process Development (Polyethers) with Bayer MaterialScience. He holds a Ph.D. in chemical engineering from Massachusetts Institute of Technology. Gellman is Lord Professor of Chemical Engineering at Carnegie Mellon as well as the head of his department. He has a Ph.D. in chemical engineering from the University of California, Berkeley.
DW: Methane is relatively difficult to react selectively. Oxidation, for example, usually likes to go all the way to carbon dioxide (CO2) and water. But there are established routes to convert methane via "water gas shift" that will give you carbon monoxide (CO) and hydrogen. CO is a versatile chemical; you can do a lot of things with it, especially if you are interested to functionalize olefins -- that is, to convert them to alcohols, aldehydes, ketones (i.e., basic and specialty chemicals). You could also use the CO to build up aliphatic hydrocarbon chains using the Fischer Tropsch synthesis for straight chain hydrocarbons. Another example is to react the methane catalytically to make methanol. Methanol is basically CO that has been reduced a bit so now it has some hydrogen in it. Methanol can in turn be reacted with a different catalyst to make gasoline, essentially a mixture of valuable hydrocarbons. But reacting methane to form a higher hydrocarbon such as benzene directly and in good purity is very difficult.
DW: Coking. There are catalysts that have been found to favor this reaction, but they coke up quickly and that kills their activity and therefore drives the cost of the process way up.
AG: From a basic chemistry perspective the problem is that activating methane, CH4, by breaking one of its C-H bonds is very difficult and, therefore, very slow in any chemical process. One way to look at this is that if you have catalyst that can do it and raise the reaction temperature to the point that breaking the first C-H bond becomes rapid, the breaking the second (and subsequent) C-H bonds will be even faster. As a result, it is very difficult to find a catalyst that will break the first C-H bond to create CH3 and then allow its subsequent reactions to lead to just one well-defined product that won't continue to decompose further at the reaction temperature.
AG: Top ten. In the same ranks as the origin synthesis of ammonia. It is probably the case that a cheap way to convert methane to benzene would also lead to a cheap way to convert methane to a number of other simple hydrocarbons. The bottom line is that it would provide a cheap feedstock for use across the chemical industry.
DW: An effective process for direct conversion of methane to benzene would rank pretty high. It is in large part a chemistry and catalysis challenge, but not entirely. There are a lot of chemical engineering problems that have to be addressed, too. Such as to find a good, practical, repeatable, and robust way to separate the hydrogen from the benzene as it is formed in order to drive the reaction forward. Driving the reaction is necessary because it is "uphill" energetically and the equilibrium is far short of giving one the desired products in 100 percent yield. That means one has to remove either the benzene or the hydrogen right away to prevent the equilibrium from arresting the reaction that is desired. Doing that well is a great chemical engineering challenge.
AG: Chemicals are basic "building blocks" of all materials, things that we all use every day. These building blocks play a powerful role in our economy. If basic chemicals can be manufactured responsibly here in the United States, this could power our economy. These basic chemicals can be employed to make rubbers, plastics, foams, all sorts of industrial and consumer products from cleaners to highly engineered specialty products. And the value chains, including all the economic activities that are directly and indirectly caused, will likely require more workers.
DW: Historically the U.S. chemical industry has been enormously successful. Its revenues have matched those of the semiconductor industry. Again the bottom line is that our society uses molecules for most things. The greater our ability to design and make molecules that serve the many functions of modern society, the higher our standard of living.
DW: The United States is now producing a much greater share of its own oil and gas rather than importing it. The U.S. is building infrastructure to move natural gas from where it is produced to where it is needed. I believe there is opportunity to use some of the dry gas portion to make valuable chemicals. It complements the projects for pipelines and the projects to use the NGLs to produce more ethylene and propylene in the U.S.
AG: This will impact the petrochemical industry and all end use manufacturers of chemicals derived from petrochemical feedstocks: plastics, textiles, solvents, many household products, etc.
AG: The advantage of a consortium of university, national lab and industry partners would be that it would have access to all of the modern tools of chemical research; from computational modeling, to process design, to catalyst synthesis and optimization. A key part of this is to use engineering expertise in both industry and academia to assess the economic viability of different routes before investing enormous effort into those that are less likely than others to be economically viable.
DW: For the direct conversion of dry gas to valuable chemicals, the technology is still largely in the laboratory research stage of development; overall feasibility has not been established yet. That said, industrial companies are not likely to attempt to do this work in-house, and the project would benefit from federal support. Unfortunately, the competition for funding is concentrated, so it is important to increase the awareness of this project.
DW: Unit operations of chemical engineering from distillation with all of its enhancements over the years, through pressure swing adsorption and spray drying and all forms of chemical catalysis, have been positively supported by this type of collaborative R&D.
AG: In the early 20th century the synthesis of ammonia lead to cheap fertilizers and the huge boom in agricultural output. In the mid-20th century the discovery of artificial polymers lead to synthetic textiles and plastics for use in innumerable applications and devices.
DW: First, check out the American Chemistry Council website. Second, speak with your local economic development council and your elected representatives and communicate to them your interest to see that natural resources developed in a safe and responsible way so that they can contribute fully to the regional economy in turns of building our industries. To support the research consortium on using dry gas to make valuable chemicals that build the economy, try telling your state and national legislators what it is and that you think it is important and worthy of support.
AG: All good ideas would be welcome, but the reality is that a solution is likely to come from a fairly sophisticated research endeavor.
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