CEP 20150858 Natural Gas Chemical Synthesis

SPECIAL SECTION: ENERGY 

NATURAL GAS

Chemical Synthesis  John Marano Marano  JM Energy Energy Consulting Consulting

 James J. Spivey Spivey Louisiana State Univ.

Bryan Morreale National Energy Technology Laboratory

Plentiful, low-cost natural gas will invigorate the chemicals industry over the next decade, as producers look to increase the role of natural gas as a feedstock in established processes, as well as develop new processes to convert methane into chemicals currently derived from petroleum.

T

he abundance of domestic, low-cost natural gas has reinvigorated the U.S. chemicals industry, which uses natural gas as both a feedstock and a fuel for manufacturing commodity chemicals. The chemicals industry has expressed renewed interest in expanding the use of natural gas as a feedstock for the production of other chemical intermediates, as it may provide more stable process economics than current petroleum-based feedstocks (1). (1). In addition, the development of alternative pathways for the conversion of the methane in natural gas to traditional petrochemicals may  be of of strate strategic gic importa importance nce in a future future where where greenhou greenhouse se gas gas emissions from the combustion of petroleum products are curtailed, while the demand for a wide range of hydrocarbon based  based produc products ts contin continues ues to to grow grow. This article discusses natural gas utilization within the context of current practice in the chemicals industry, as well as potential opportunities opportunities to expand the use of methane to produce a wider range of petrochemicals in the future. The article discusses the range of feedstocks that are used to produce valuable petrochemicals (Figure 1), including those derived from petroleum as well as natural gas. It highlights the opportunities provided by a plentiful and inexpensive supply of natural gas and challenges that must be overcome to realize these opportunities.

Feedstock economics The commodity chemicals business is large, complex, and highly competitive. The U.S. chemicals sector currently relies almost exclusively on petroleum (Figure 2) and natural gas (Figure 3) for raw materials, although there is growing 58

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interest in renewable biomass as an alternative feedstock (2). (2). Many factors inuence the selection of the specic feedstock to be used in a process, including conversion chemistry and catalysis, product yield and selectivity, process complexity and severity, and environmental and other constraints. In cases where more than one feedstock can be used, selection is often based on relative price. For example, several feedstocks can be used to produce ethylene, but ethane is typically chosen because of its higher ethylene yields, and thus lower price per  pound of product, product, over lower-yielding lower-yielding feedstocks, feedstocks, such as  propane, butane, butane, petroleum naphtha, naphtha, and gas oils. oils. In addition to higher yields, the historical abundance abundance of ethane derived from conventional natural gas production, and more recently from hydraulic fracturing, makes ethane the preferred feedstock feedstock in the U.S. In areas of the world where ethane is in short supply (e.g. ( e.g.,, Europe and Asia), and therefore expensive, other feedstocks are often the most economic choice. Crude oil costs impact the price of petroleum-based petroleum-bas ed feedstocks used to produce petrochemicals such as ethylene. High oil prices negatively impact the price of  petroleum naphtha naphtha and gas oils, oils, which are used for the  production of ethylene, ethylene, and the the price of benzene, benzene, toluene, toluene, ethyl benzene, and xylenes (BTEX), which are also major  petrochemical  petrochemical feedstocks. feedstocks. Over the past decade, the price of crude oil has undergone several dramatic swings. Such instability in the oil market makes it extremely difcult for chemical manufac turers to plan for the future (i.e. ( i.e.,, match feedstock availabil-

1. Petrochemicals derived from u Figure 1. Petrochemicals petroleum and natural gas are building blocks for a variety of important end products.

ity with future projections of product demand).  Natural  Natural gas prices prices in the U.S. over the past decade, on the other hand, have generally been below the  prevail  prevailing ing price price of crude crude oil and have experienced somewhat less price volatility. The U.S. Energy Information Administration (EIA) expects the abundance and low price of natural gas to continue over the next several decades (3). (3). Thus, the U.S. chemicals industry’s interest in alternative  pathways  pathways for produ producing cing other other petropetrochemicals from methane (Figure 4), the predominant component found in natural gas, is not surprising. Methane is a basic chemical building block that can be used to synthesize virtually any organic molecule.

Building Blocks

End Uses Urea-based fertilizers

 Ammonia

Phenol formaldehyde-based plastics and adhesives Cellulose acetate-based fibers Methanol

Polyvinyl acetate-based paper and textiles Ethanol solvents, cosmetics, and pharmaceuticals Etyhlene glycol-based coolants and fibers

Ethylene

Polyvinyl chloride-based plastics Polyethylene-based plastics Propylene Polystyrene-based plastics  Adipic acid-based nylon and fibers Butylenes

Phenol and acetone Polypropylene-based plastics and fibers

Butadiene

Isopropanol-based solvents Polybutylene-based plastics Polyether polyol-based urethane foams Styrene butadiene-based tires and synthetic rubber products

BTEX

The current landscape The high hydrogen-to-carbon hydrogen-to -carbon ratio in natural gas makes it an increasingly attractive fuel and feedstock in an increasingly carbon-constrained world. Wellhead gas is typically 90% methane (C1), with the remainder mostly ethane (C2), propane (C3), and butanes (C4). Varying, but typically small, amounts of CO 2, H2S, and N2 may also be  present. Gas processing processing plants remove remove these impurities impurities and fractionate gas collected in the eld into natural gas that meets pipeline specications, specications, as well as natural gas liquids (NGLs), which are mixtures of propane and butanes containing some ethane. Methane, ethane, propane, isobutane, and n-butane are all used as raw materials for the manufacture of chemicals. chemicals. Applications for these compounds are as follows: C1 conversion. conversion. Today, natural gas is the predominant feedstock for the production of ammonia, methanol, and hydrogen within the U.S. chemicals sector. Due to its chemical stability, methane is currently not converted directly into petrochemicals. Instead, industrial processes utilize a two-step conversion process. Methane is decomposed into synthesis gas, a mixture of carbon monoxide and hydrogen, commonly through a steam-reforming process, which can then be used to synthesize a variety of chemicals. The endothermic reforming of methane is typically conducted at very high temperatures (700–1,000°C) over a nickel-based catalyst (1): (1):

CH 4 + H2O

→

CO + 3H 2

(1)

Often, reforming is coupled with the lower-temperature lower-temperatur e water-gas shift reaction (2) to (2) to further modify the H2-to-CO ratio prior to conversion to the desired product: CO + H2O

→

H 2 + CO2

(2)

The largest application of methane within the chemicals industry is the production of ammonia based on the HaberBosch process. High-purity hydrogen produced by the reaction shown in Eq. 2 is reacted with high-purity nitrogen  produced by air air separation over over magnetite-based magnetite-based catalysts catalysts at high pressures (60–180 bar) to produce ammonia:  N2 + 3 H2

→

2 NH 3

(3)

Methanol is also produced from methane-derived methane-derive d synthesis gas. Methanol is used in several applications, including as an intermediate for the production of formaldehyde and acetic acid, which are the basis for a variety of products, including plastics, paints, and adhesives. Methanol synthesis is typically carried out at moderate temperatures (240°C) and pressures (5–10 MPa) over a multicomponent catalyst containing copper, zinc, and alumina: CO + 2 H2

→

C H 3OH

(4)

Methane-derived Methane-derived synthesis gas is used in several areas outside of the U.S. to produce synthetic transportation transportation fuel, lube oils, and waxes via the Fischer-Tropsch process.  Article continues continues on next next page page CEP

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SPECIAL SECTION: ENERGY 

Natural-Gas-Based Natural-Gas-Based Building Blocks (Today)

Petroleum-Based Building Blocks

Hydrogen

BTEX

LPG Naphtha

 Ammonia

Ethylene

Syngas

Propylene

Gas Oils

Butylenes and Butadiene

Residual Oils

Methanol

Methane

Ethylene

NGL

Propylene

2. Streams derived from crude oil refining are used to produce p Figure 2. Streams ethylene, BTEX, propylene, butylenes, and butadiene. As producers switch from naphtha to NGLs as feedstock to produce ethylene, they must consider the relative amounts of byproducts produced from each. Steam cracking of petroleum naphtha, for example, produces a lower yield of ethylene, but higher yields of valuable propylene, butylenes, and butadiene byproducts, than NGLs. BTEX and additional propylene, butylenes, and butadiene are produced within refining processes aimed at the production of gasoline. Therefore, refiners can decide, based on market conditions and other factors, to recover and sell those byproducts, but this will reduce gasoline production.

C2–C4 conversion. conversion. Ethane, propane, and butanes are starting materials for the production of many end products, and the intermediate production of synthesis gas is not required. Although ethane, propane, and butanes can be concon verted to several useful products, steam cracking to produce ethylene is the most signicant industrial application. Steam cracking consists of rapidly heating diluted hydrocarbon streams with steam to very high temperatures, typically in excess of 800°C. The overall reaction for ethane is: C 2 H6

→

C 2 H 4 + H2

(5)

The reaction occurs through a free-radical mechanism and produces many byproducts, which can include methane, acetylene, propylene, butylenes, butadiene, and  pyrolysis gasoline gasoline (an olenic and and aromatic naphtha). naphtha). The The amounts of the various byproducts are very dependent on the feedstock. Generally, higher-molecular-weight feedstocks such as naphtha produce more byproducts. The mixed efuent stream is fractionated to purify ethylene and recover the byproducts, which are valuable intermediates for producing a variety of chemical products.

Challenges and opportunities Industry has only recently begun to realize the opportunities presented by the abundance of inexpensive natural gas. Hydraulic fracturing technology technology is expected to continue to evolve, opening up more unconventional gas reserves to production both in the U.S. and worldwide. The gas processing industry is actively pursuing new markets for this gas, such as LNG for transportation and power generation. The expansion of LNG import and export terminals around the globe will also provide greater access to this resource by overseas chemicals producers. 60

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Butylenes

3. Commercial technologies for the production of hydrogen, p Figure 3. Commercial ammonia, and methanol require methane to first be converted into synthesis gas, which is then converted into methanol. This two-step process is inherently inefficient. Steam cracking of NGLs produces propylene and butylenes, but not a sufficient quantity of these materials to meet market demand. Natural-Gas-Based Building Blocks (Future) Hydrogen

 n g   i n  o  o r m  R e f  e a m  S t e

Syngas

 ion  ida t io  ia l O x id  t ia Par t

Methane

 Ammonia

Methanol

Oxid xidative ive Co  Coupling ing Ethylene

NGL

Catalytic Dehydrogenation

Ethylene Propylene Butylenes and Butadiene

4. Technologies are being developed and demonstrated that in p Figure 4. Technologies the future will allow many basic building blocks of the chemicals industry to be produced directly and more efficiently from natural gas and NGLs.

Chemicals manufacturers are actively examining an increased role for natural gas liquids as feedstock in the short term (5–10 yr) and for natural gas as feedstock in the longer term (20–25 yr). With these opportunities also come challenges. The increase in gas supply has caused several market imbalances regionally in North America and globally that are still being resolved. As we will discuss, these imbalances imbalances will be resolved in the short term. A signicant challenge in both the short term and long term are uncertainties related to rapidly evolving policies and regulations aimed at mitigating environmental and climate-change impacts. These will require industry to continuously reevaluate existing chemical operations and future capacity additions. For example, current climate-change-related regulations being promulgated by the U.S. Environmental Protec-

tion Agency (EPA) incentivize the use of low-carbon fuels, such as natural gas, for power generation. The chemicals industry, which has already implemented major energy efciency improvements since the 1980s (4), (4), will likely  be called upon upon to make further further improvements improvements to meet the challenges of climate-change mitigation. However, the challenges associated with climate-change mitigation and adaptation also open up new opportunities for chemicals manufactures to improve existing products and develop new ones to address these challenges.  Near-term  Near-term outlook  outlook . Low domestic natural gas prices in recent years have prompted U.S. oil and gas producers to shift drilling operations away from areas containing dry gas (i.e., i.e., shale gas rich in methane, but with low NGL content) to areas containing wet gas (i.e. ( i.e.,, shale gas rich in NGLs) in order to improve their return on investment. That shift has altered the balance of feedstock used for the production of ethylene toward ethane and away from petroleum naphtha. While low-cost ethane is the preferred feedstock for ethylene production, using more ethane feedstock in place of petroleum-based feedstocks has had signicant ramirami cations. Petroleum-derived steam cracker feeds produce more, and a wider range of, chemical byproducts, such as C3–C4 intermediates (propylene, butenes, and butadiene), butadiene), than ethane feedstock. Thus, reducing petroleum-ba petroleum-based sed ethylene production has created a shortage of these other raw materials for the chemicals industry. That trend has resulted in a urry of activity to substitute alternative feedfeed stocks and conversion pathways for the production of the C3–C4 intermediates. Several U.S. chemicals manufacturers have implemented technologies to directly dehydrogenate propane to propylene (5). (5). Chemical companies are also investigating technologies to produce butylenes and butadiene directly, some of which employ natural gas or biomass as the starting material (6). (6). Those development trends are likely to continue in the short term, until the supply imbalance in C3 and C4 chemicals is alleviated. Until those technologies are commercially demonstrated, the U.S. will be increasingly dependent on imports to fulll C4 and BTEX demand due to the shift to lighter feeds in steam crackers. Recent innovations relating to alternative methane conversion pathways are just coming to fruition. For example, Celanese, BP, and Eastman Chemical have made signicant progress in catalyst development aimed at producing acetic acid, ethanol, and monoethylene glycol directly from synthesis gas (7–9). (7–9). Celanese is in the process of scaling up and demonstrating its ethanol technology. technology. Start-up rm Siluria is currently demonstratdemonstrat ing the viability of using oxidative coupling of methane to produce ethylene at the pilot scale (10). (10). In addition, biotech start-up companies are in the early stages of geneti-

Strategic Partnerships

I

ndustry, ndustry, academia, and government need to strategically partner for the U.S. to take full advantage of the opportunities presented by affordable and abundant shale gas. As identified at a recent AIChE workshop on natural gas utilization, appropriate technology development roles for each entity are as follows:

Government • Develop technology R&D roadmap and vision statement. • Provide stewardship for a sustainable, long-term R&D effort. • Foster scientific innovation. • Facilitate partnerships among industry, industry, academia, and national laboratories. • Develop a framework that will enable the transfer of fundamental learning among all partners. • Provide assistance to technology developers so they can more easily move from early-stage R&D to large-scale commercial demonstration.

National Laboratories • Develop and scale up potential breakthrough technologies that are in very early stages of development and financially risky for individual companies to consider independently. • Apply high-performance analytical and computing equipment and methodologies to gain fundamental understanding of new technologies.

 Academia • Educate future engineers and scientists on energy e.g., and environmental issues of critical importance ( e.g. climate change, water resources, sustainability). • Ensure students obtain an education that prepares them for positions in the reemerging petrochemicals industry. • Provide fundamental understanding and scientific innovation in the areas of catalysis, reaction engineering, separation science, and process design.

Industry • Provide facilities, matching funds, and other resources for technology demonstration projects. • Provide financial support to technology developers transitioning from early-stage R&D to large-scale demonstration. • Supply industrial experts for government steering committees to ensure that government R&D investments are strategic and relevant to the needs of industry. • Develop, assess, and validate novel technologies that show promise to improve the performance of existing chemical production processes and enable the use of natural gas as a feedstock for the production of a wider range of petrochemicals.

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SPECIAL SECTION: ENERGY 

cally modifying microorganisms to produce chemical intermediates directly from methane and/or CO 2 (11). (11). A major challenge will be developing scalable technologies that can be integrated with current industry assets.  Longer-term outlook  outlook . Many opportunities exist for the development of technologies to expand the utilization of natural gas as a raw material for the chemicals industry. The overall drivers for long-term technology development are feedstock risks, stricter environmental environmental regulations, climate-change mitigation, and shareholder demands for sustainable business development. If international international negotiations are successful, the latter two factors should come into  better focus before before the end of this this decade. In the longer term, technology development efforts will likely focus on direct routes for converting methane, including catalytic conversion conversion of C1–C2 via non-syngas based routes, selective selective methane methane activation activation (C-H bond), and the development of cost-effective high-temperature materials (>1,300°C) enabling selective methane pyrolysis. Due to the critical role of ethylene, propylene, and C4 olens and their derivatives in the current petrochemicals market, the development of technologies enabling the direct conversion of methane to saturated and unsaturated hydrocarbons could be a game-changer, reducing dependency on feedstocks produced by petroleum rening. Research and development efforts will also continue to focus on developing efcient and affordable chemical pathways for the other mainstays of the chemicals industry, BTEX. Nanotechnology and biotechnology are likely to become major tools in the toolbox for achieving those advances. Current manufacturing processes will also undergo changes. Smaller-scale operations may become more  prevalent, due to the need to reduce reduce the venting venting and aring of natural gas and oil-associated gas at the wellhead — a signicant source of greenhouse gas emissions. This will require R&D focused on process intensication and modumodu larization to make emerging technologies in this area more reliable and affordable. For example, the development of integrated catalytic membrane reactors that leverage a high-temperature hydrogen-selective membrane could signicantly increase the overall efciencies and yields for synthesis gas production and hydrogenation hydrogenation processes. The chemicals industry currently supplies many materials used in applications aimed at improving the energy efciency of processes, engines, and buildings. Climatechange mitigation, adaptation, and resiliency measures will  become even even more important important in coming decades. decades. This This will likely result in even greater demand for energy-efcient  products and services services produced from from natural gas, gas, and the industry will be called upon to develop new and improved materials for these applications. applications. 62

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Closing thoughts The U.S. is the beneciary of abundant natural resources — in particular, conventional and unconventional natural gas. It also has a history of developing new and novel technologies for exploiting these resources. The combination of these factors has resulted in a national gas renaissance. The abundent natural gas resource was realized through technologies developed through collaboration  between government and industry over 20 years ago. The emergence of shale-based natural gas resources has provided the U.S. with an unprecedented opportunity to realize greater energy autonomy, autonomy, and can be a stepping stone along the path to a lower-carbon future. In addition to the conventional uses of natural gas as a fuel for the  production of heat and power, and as a feedstock for the  production hydrogen, ammonia, and methanol, natural gas could be used as a feedstock for higher-value commodities traditionally derived from petroleum resources. That could lead to reduced energy imports and increased opportunities to export low-carbon natural gas as well as naturalgas-derived products. Collaboration among government, industry, and academia needs to be rekindled to ensure that our natural gas resource is used wisely to provide economic benets and energy security for all, and serves as bridge to a lowCEP carbon, sustainable energy future.

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2.

McMahon, T., “Biotech Makes Inroads into Industrial Chemicals,” Chemical Engineering Progress Progress,, 109 (3), p. 12 (Mar. 2013).

3.

Energy Information Administration, “Annual Energy Outlook 2015,” U.S. Dept. of Energy, Washington, Washington, DC (Apr. 14, 2 015).

4.

Swift, T. K.,  “Chemistry and Energy Efciency,” Chemical  Engineering  Engineering Progres Progresss, 107 (9), p. 16 (Sept. 2011).

5.

Dubose, B., “Major U.S. Players Bet on Propane Dehydrogenation,” Hydr tion,” Hydrocarbon ocarbon Processing  Processing , 93 (7), p. 35 (July 2014).

6.

Bailey, M. P., “The Future of Butadiene,” Chemical Engineering , 121 (9), pp. 19–24 (Sept. 2014).

7.

Tullo, A., “BP Recommits to Chemicals,” Chemical and Engineering News, News, 91 (47), p. 20 (Nov. 25, 2013).

8.

Tullo, A., “Celanese Takes an Ethanol Plunge,” Chemical and  Engineering  Engineering News News,, 89 (43), p. 20 (Oct. 24, 2011).

9.

Jenkins, S., “New Process for Monoethylene Glycol Completes Pilot Stage,” Chemical Engineering , 120, p. 15 (Dec. 2013).

10. Tullo, A., “Breaking Through,” Chemical and Engineering News, News, 92 (27), p. 20 (July 7, 2014). 11. Advanced Research Projects Agency, “Remote R&D Program,” http://arpa-e.energy.gov.