ADVANCED
MATERIALS AND CHEMICALS
BASF Catalysts LLC (formerly Engelhard Corporation)
Cost-Efficient Process for Increasing Natural
Gas Production
In the late 1990s, natural gas supplied about
23 percent of the total energy used in the
Needing both financial and research assistance,
Engelhard turned to the Advanced Technology Program (ATP) in 1999 and received
an award for a three-year project. With ATP funding, Engelhard formed three
industry-academia research collaborations to advance natural gas purification
and to develop other molecular separation processes. At the conclusion of the
project in late 2002, Engelhard had successfully created a single-step process
to purify natural gas. Its technical achievements led to nine patents as well
as the publication of numerous journal and news articles. Engelhard’s Molecular
Gate technology also won the 2005 Kirkpatrick Chemical Engineering Achievement
award.
As of May 2006, Engelhard’s ATP-supported
advanced Molecular Gate adsorbent based technology was being marketed as its
Carbon Dioxide (CO2) Removal, and Nitrogen (N2) Rejection
systems. These systems operate at 18 small and medium-sized natural gas
facilities. As a direct result of the ATP-funded project, Engelhard is able to
help numerous small energy companies bring previously untapped natural gas
resources online and into homes across
Composite
Performance Score
(based on a
four-star rating)
* * * *
Research and data for Status Report
99-01-6041 were collected during May–June 2006.
Production
of Natural Gas Faces Challenges
The clean-burning natural gas used in American homes and by
industry is pretreated prior to pipeline transmission to almost pure methane
(CH4). But as it
comes out of the ground, and at the wellhead, natural gas is considered “wet,”
because it contains numerous impurities. Although still composed of 70- to
90-percent methane at this stage, other constituents, including nitrogen (N2), carbon dioxide (CO2), hydrogen sulfide (H2S), and water (H2O), are present at levels that
can vary widely in the overall composition of this product. In order for
natural gas to go through the large system of
In the late 1990s, the cost of lowering the level of nitrogen and all other impurities at the wellhead was high and involved three different processes: amine for carbon dioxide and hydrogen sulfide processing, glycol or molecule sieve dehydration for water, and extremely low temperature cryogenic processing for nitrogen. Due to the high cost and complexity of building and operating these systems, many small and medium-sized production facilities left known natural gas reserves in the ground. In the late 1990s, as much as 16 percent of all natural gas in the United States was contaminated with nitrogen and often untapped because of the high cost of removing contaminates at the wellhead.
Engelhard
Discovers Breakthrough Separation Process
In the late 1980s and early 1990s, Engelhard Corporation
achieved a laboratory breakthrough in gas molecule separation that was based on
molecule size. By applying precise temperature change to the atomic framework
of a molecular sieve, Engelhard was able to create a molecular sieve by
shrinking pore sizes through a process of dehydration (as depicted in Figure
1). (Molecular sieves are “zeolytes” that are crystalline structures with
precise cavity sizes such that small molecules can enter the pores and be
selectivity removed while larger molecules are excluded, hence the term
“sieve.” ) Engelhard’s newly designed molecular sieve compositions then
“trapped” certain sized contaminates that passed into the pores. Unlike
existing molecular separation systems, Engelhard’s technology is able to trap
targeted, contaminated natural gas molecules as they come out of the ground at
high pressure, at the wellhead, and then release these molecules at low
pressure, all while the higher value methane molecules continue through the
process at high pressure. This process of adsorption decreases the level of the
less desirable molecules in natural gas. Relying on this effective and
efficient material called Molecular Gate adsorbent, Engelhard’s objective was
to tap the otherwise expensive-to-process, underground natural gas reserves and
bring purified, more usable gas into homes across
Figure 1. The result of high-precision dehydration on a framework of
atoms. Depicted on the left is a group of various atoms at room temperature.
The diameter (d) of the opening is 4.27 Angstrom (Å). After the precise
application of heat to the atoms in this framework, up to 250°C, dehydration occurs,
shrinking the structure and reducing the molecular opening to a diameter of
3.94 Å, as depicted on the right. The change represents a controlled,
eight-percent shrinkage of the molecular opening required for precise
separations. The smaller opening does not permit larger, desirable gas
molecules from entering the framework opening. The smaller, undesirable
molecules, however, can enter the framework and become trapped within the
sieve.
Based on Engelhard’s ability to precisely manipulate material pore size, the company considered the possible separation of molecules of almost identical size. In the case of methane and nitrogen molecules, for instance, methane molecules are 3.8 Å (an angstrom is 10-8 cm) while nitrogen molecules are 3.6 Å. Through dehydration, Engelhard was able to successfully tune sieve adsorbents so that they could trap the smaller, undesirable nitrogen molecules and allow the larger, desirable methane molecules to move through this natural gas process at feed or wellhead pressure. Thus, nitrogen levels in this contaminated gas are reduced and the natural gas meets pipeline specifications. Molecular sieve adsorbents used at the time were set at fixed and not adjustable pore sizes (such as 4.0, 5.0, and 10.0 Å) and, therefore, were not effective. The company’s ability to construct a molecular framework or gate with smaller, precisely controlled pore sizes using calcination (the process of heating a substance to a high but controllable temperature) advanced the science of molecular separation to involve multiple containment separations. Engelhard envisioned, for the first time, the simultaneous removal of nitrogen, water, carbon dioxide, and hydrogen sulfide from natural gas. Indeed, Molecular Gate adsorbents would allow for the one-step purification of natural gas.
Engelhard also foresaw the possibility of using its process to separate molecules of even closer size, such as in the process used to enrich oxygen to produce transportable medical oxygen for use in portable hospital and home patient oxygen systems. Applying Molecular Gate adsorbents to other gas separations would require a high level of precise, reproducible, and robust controls of the pore sizes, because different molecules or compounds in an air mixture are attracted and held by a molecular sieve adsorbent surface at different levels effectiveness. Furthermore, temperature applications to gate pores that might work for nitrogen/methane separation would not necessarily work for oxygen/nitrogen separation.
Engelhard also intended to improve existing Molecular Gate
materials for use in the zeolitic membranes to achieve higher levels of
separation. (Zeolite membranes are unique crystalline structures bonded
together to allow small molecules to pass through the membrane barrier while
preventing larger molecules from doing so.) The development of new techniques
for improving the quality and performance of zeolite membranes would involve temperature
adjustment and cation exchange, a process by which membrane structures are
adjusted by incorporating different-sized molecules within the molecular sieve
framework to adjust the pore size. For example, replacing larger molecules with
smaller molecules would make the gate opening larger and vice versa. But
combining temperature adjustment with cation exchange would be a challenge.
Engelhard decided they needed assistance and formed a team with VTI
Corporation,
Team Simplifies Natural Gas Purification
A primary goal of the ATP-funded project was to develop a single-step process to purify natural gas. Engelhard sought to reduce the levels of nitrogen, carbon dioxide, water, and hydrogen sulfide in methane by separating the larger methane molecules from the smaller non-hydrocarbon contaminate molecules using its Molecular Gate adsorbent. Current state-of-the-art purification processes consisted of expensive, multistep procedures such as acid gas removal, glycol or molecular sieve dehydration, and low temperature (cryogenic) distillation. Engelhard’s proposed process at the wellhead would open up small and medium-sized natural gas fields and would reduce contaminates in natural gas to permissible levels for pipeline transportation and processing. Figure 2 depicts Engelhard’s molecule separation objective.
Figure 2. Single-step, multiple-contaminant purification of natural
gas. As raw natural gas (NG) from the wellhead enters the purification process
at a high pressure, numerous smaller, undesirable gas molecules, such as
nitrogen (N2), carbon dioxide (CO2), water (H2O),
and hydrogen sulfide (H2S), enter the contracted titanosilicate
(CTS) framework opening and are trapped inside the sieve, while the larger
methane molecules (CH4) continue to flow through the natural gas
process. Because the CTS is precisely
tuned to the 3.6 Å to 3.7 Å pore size, the removal of multiple contaminants is
possible in a single-step process.
Prior to beginning the ATP-funded project, Engelhard had already demonstrated, in a laboratory setting, its ability to separate methane and nitrogen molecules. The major challenge would be in adjusting molecular structures by applying a precise amount of heat and thereby producing an appropriate level of dehydration to shrink the pores. The deft application of heat to control shrinkage would allow for the separation of multiple contaminants. Existing technology had proven that the framework of the titanium silicate ETS-4, the first member of this type or class of materials, could be systematically contracted through dehydration at elevated temperatures to “tune” the desired size of the pores, thereby giving only small molecules access to the interior of the sieve. These adjusted structures would then be fabricated into a fixed-bed, molecular sieve processing system and delivered on-site for natural gas field purification.
Engelhard Achieves Success in
Nitrogen/Methane Separation
During the first year of the project, Engelhard and VTI Corporation performed extensive isothermal (constant temperature) work on existing adsorbent materials. This work demonstrated that high levels of carbon dioxide adsorption capacity could be achieved. At this stage, the ability to separate methane and carbon dioxide, in addition to methane/nitrogen separation, appeared possible. However, Engelhard’s research indicated that during methane/carbon dioxide separation, there was a substantial loss of crystallinity of the zeolite framework as a pore constricts in response to dehydration, irrespective of the conditions used to reach the contraction. The loss of crystallinity was undesirable because it decreased the level of control or tuning possible on the molecular framework.
Also, progress in the area of nitrogen/methane separation led to a semi-commercial, field demonstration of nitrogen removal. In August 2000, Engelhard began work at the Tom Brown Inc. Hamilton Creek, Colorado natural gas production facility. The Molecular Gate adsorbent based technology successfully lowered the level of nitrogen on-site from a range of 15 to 18 percent to a range of 3 to 5 percent.
In the second year of the ATP-funded project, Engelhard developed simplified natural gas processes to simultaneously remove carbon dioxide and nitrogen from methane. This achievement proved the concept of single-step purification involving multiple contaminate gases in processing natural gas. This was a breakthrough, because one-step carbon dioxide and nitrogen removal from methane represented the most significant opportunity for natural gas purification. Additionally, Molecular Gate nitrogen removal material demonstrated unique size-separation properties, and these materials were superior to commercial, state-of-the-art carbon dioxide adsorbents. While Molecular Gate materials proved more expensive than conventional adsorbents, the ability of Molecular Gate adsorbent to perform multiple gas contaminate removal, which conventional adsorbents cannot achieve, made it unique.
Through further advances, Molecular Gate materials could also separate water molecules from methane. At the conclusion of the second year of research, Engelhard had achieved both technical and application success: single-step nitrogen, carbon dioxide, and water removal and a viable market for advanced Molecular Gate adsorbent based technology. During year three development, however, Engelhard discovered that there was a limited market and therefore limited need for advancements in Molecular Gate materials in the area of hydrogen sulfide removal. Existing processes for hydrogen sulfide were well-established and effective. Therefore, the company focused its natural gas purification efforts exclusively on advancing breakthroughs involving the single-step removal of water, nitrogen, and carbon dioxide from methane. This process would eliminate the currently used difficult, multiple step, and expensive systems and would lower natural gas production costs in a simplified process.
Oxygen Enrichment of Air Streams
The air we breathe, ambient air, is made up of 21 percent
oxygen (O2). It also
comprises 78 percent nitrogen and 1 percent of traces of eight other gases.
Mildly enriched oxygen (at 30 percent oxygen) dramatically improves
combustion in industrial uses. At 30 percent, mildly enriched oxygen is known
to influence flame temperature and burning efficiency for diesel engines, blast
furnaces, and heating systems. Highly pure oxygen (at 90 percent or greater) is
used in the healthcare field, often as transportable oxygen to support patient
breathing. But while oxygen is the third-largest bulk chemical produced in the
In 1999, smaller scale oxygen enrichment processes called for energy-intensive adsorption technology, typically involving the use of LiX zeolites. As a secondary project objective, Engelhard wanted to apply its Molecular Gate adsorbent based technology to the low-cost, simplified production of oxygen-enriched air. Engelhard would attempt to modify the properties of existing Molecular Gate adsorbents to separate oxygen from nitrogen molecules, focusing on pore size and the binding strength of adsorbents. The key to success would be in balancing adsorption rates (the flow of air) with oxygen selectivity (pore separation). Figure 3 depicts the type of separation Engelhard sought.
Figure 3. Oxygen enrichment of air.
As ambient temperature air enters the purification process, smaller gas
molecules, oxygen (O2) and water (H2O), enter the CTS
framework opening and are trapped in the sieve. The larger, desired nitrogen (N2)
molecules are processed through the purification system.
Despite months of effort, Engelhard was unable to achieve a high level of oxygen/nitrogen separation. A highly porous structure hampered the separation of the oxygen and nitrogen molecules and led to low oxygen adsorption capacity. While the company attempted to solve this problem, it realized that both high oxygen capacity and high oxygen/nitrogen selectivity were hurdles they could not overcome for high-purity oxygen enrichment. Engelhard thought that the low capacity and selectivity problems were linked to crystallinity loss due to handling or “steaming,” but later determined that crystallinity loss was actually a structural change inherent in the pore shrinkage. Engelhard changed its focus to a low enrichment nitrogen and oxygen separation system for industrial combustion applications.
By the end of year three, however, the company was unable to develop an adsorbent that was competitive with the molecular sieve, the existing process for producing oxygen for industrial use. Simply stated, Engelhard’s adsorbent material, titanium silicate zeolites, suffered from limitations that they were not able to overcome, including low oxygen capacity. This part of the project ended with an eleventh-hour finding that crystallinity loss could be better avoided by using ion or cation size selection (the exchange of molecules) rather than framework shrinkage to control the pore size.
Advances Sought through Dehydration and
Ion Exchange
While Engelhard was working on natural gas separation and oxygen enrichment, they also sought to expand current separation technology by altering existing Molecular Gate zeolitic membranes. This ATP-supported task represented the highest level of technical risk associated with the entire project.
The task was to advance Engelhard’s first-generation separation membranes by using both dehydration and ion exchange. Engelhard envisioned using ion exchange to change the framework or chemistry of the molecular sieve so that the potential area imposed by the pore surface would be strong enough for selective adsorption, but weak enough to allow desirable transport or flow rates. Engelhard believed careful temperature changes to alter the dimensions of the membrane structure would allow better molecule selection, but they would be careful to avoid using so much heat that they would damage the membrane. This process would be coupled with ion exchange to expand the possibilities for Molecular Gate adsorbent based technology. The objective was to create macroscopic, defect-free zeolitic membranes with high flux (flow) and high selectivity (pore size separation) for air, natural gas, and other separations. The key to success in this task, as with oxygen enrichment, was balancing molecule selectivity with the ability to adsorb and hold certain molecules.
While Engelhard was able to advance specific technical areas
of the overall objective, after two years of the three-year project, the
researchers failed to reach their intended goal and the task was ended.
Technical Success Leads to Real-Life Application
The technical advancement of Engelhard’s Molecular Gate adsorbents led to practical industrial application. In addition to the successful Hamilton Creek methane/nitrogen separation process demonstrated during the ATP-funded project (August 2000), Tidelands Oil began using the Molecular Gate adsorbent based system in 2004 to remove carbon dioxide and water from oil production-associated natural gas (the Tidelands facility is depicted in Figure 4). The Tidelands facility was the first commercial application of Engelhard’s carbon dioxide and water removal system using Molecular Gate adsorbent. According to James Willis, Staff Engineer for Tidelands’ Long Beach Operations, “The system allows us to generate a revenue stream from the sale of gas that otherwise would have to be flared [unusable gas that is burned off]. We selected the Molecular Gate adsorbent based system over commonly used amine technology due to its lower cost, simplicity of operation and environmental friendliness.” While amine technology is capable of removing carbon dioxide from natural gas, it is unable to remove water. In this particular application, Molecular Gate adsorbents work by trapping carbon dioxide and water molecules in a fixed bed of adsorbent materials while allowing methane to pass through at feed pressure.
Figure 4. Tidelands Oil Facility. Engelhard’s Molecular Gate molecular sieve is
contained in a series of pressure vessels.
The separation and purification process occurs within these pressure
vessels.
Another impressive application of Engelhard’s Molecular Gate
adsorbent based technology has been at a southern
During the ATP-funded project, Engelhard filed nine patents
and published numerous trade journal articles and presentations. In 2005, the
company won the prestigious Kirkpatrick Chemical Engineering Achievement Honor
Award for its Molecular Gate adsorbent based technology. Also in 2006,
Engelhard granted Guild Associates of Dublin, Ohio a license to manage the
application of its Molecular Gate adsorbents. As of May 2006, this
ATP-supported technology was marketed as Engelhard’s Molecular Gate Adsorbent
based System – Carbon Dioxide (CO2)
Removal, and Nitrogen (N2)
Rejection systems. Molecular Gate
technology is being used at 20 different facilities across the
Figure 5. The footprint of this small, nitrogen
removal unit is 8 by 25 feet, with vessels, vacuum pump, instrument air system,
valves, and instrumentation atop. (Compression unit and other peripheral items
are not shown.) This skid weights about 25,000 pounds and is shipped on a
double-drop truck. A crane is needed for installation.
In June 2006, BASF Corporation acquired Engelhard Corporation for an estimated $5.6 billion, and in August 2006 renamed the company BASF Catalysts LLC.
Conclusion
Hoping to achieve a breakthrough in molecule separation, in 1999 Engelhard Corporation sought to expand the use of molecular sieve adsorption in natural gas purification and to apply advances in this technology to other molecule separation possibilities, including oxygen/nitrogen purification. Engelhard wanted to apply its existing Molecular Gate adsorbents technology to the single-step purification of natural gas in order to reduce the levels of multiple natural gas containments. Such advances would replace costly, multiple-step natural gas processing. Engelhard also wanted to use this technology to more cost-efficiently enrich oxygen by separating nitrogen from the oxygen molecules. After enlisting the assistance of several subcontractors, in April 1999, Engelhard applied to ATP for financial assistance. From December 1999 to November 2002, Engelhard and its partners developed their innovative gas molecule separation technology.
At the conclusion of the project in 2002, Engelhard had successfully advanced molecular sieve adsorbent-based separation in the area of natural gas purification. The company’s Molecular Gate adsorbents could separate several undesirable gas molecules from the higher value methane molecule in a simplified process. This innovation garnered Engelhard nine patents and led to the publishing of numerous journal and news articles in this area. In 2005, the Molecular Gate adsorbent based technology earned a Kirkpatrick Chemical Engineering Achievement award. After granting Guild Associates of Ohio permission to independently supply the technology in 2006, the technology is positioned to continue to assist energy companies in natural gas processing. Such processing included its Molecular Gate Adsorbent System: Carbon Dioxide (CO2) Removal, and Nitrogen (N2) Rejection units.
As of 2006, the technology was being used in 19 different facilities across the country, with more than 100 quotations for new systems requested each year. Molecular Gate adsorbents are expected to be in operation in 6 to 12 new facilities each year. Indeed, the introduction of a single-step, low-cost natural gas purification process allows small and medium-sized energy companies to bring to the surface and into American homes natural gas that was otherwise untapped. In June 2006, BASF Aktiengesellschaft acquired Engelhard Corporation for an estimated $5.6 billion, and in August 2006 renamed the company BASF Catalysts LLC.