Gokhan Alptekin

A NOVEL CO2 SEPARATION SYSTEM

Because of concern over global climate change, new systems are needed that produce electricity from fossil fuels and emit less CO{sub 2}. The fundamental problem with current CO{sub 2} separation systems is the need to separate dilute CO{sub 2} and pressurize it for storage or sequestration. This is an energy intensive process that can reduce plant efficiency by 9-37% and double the cost of electricity.

Palladium-Copper and Palladium-Gold Alloy Composite Membranes for Hydrogen Separations

Electroless plating was used to fabricate PdCu and PdAu alloy composite membranes using tubular Al2O3 and stainless steel microfilters to produce high temperature H2 separation membranes. The composite membranes were annealed and tested at temperatures ranging from 350 to 400°C, at high feed pressures (≤250 psig) using pure gases and gas mixtures containing H2, carbon monoxide (CO), carbon dioxide (CO2), H2O and H2S, to determine the effects these parameters had on the H2 permeation rate, selectivity and recovery.

Regenerable sorbent for natural gas desulfurization

Sulfur-containing odorants are normally added to propane and natural gas supplies to facilitate leak detection. The sulfur in these fuels can poison the catalysts used in fuel-cell fuel-processing systems, thereby inactivating the surfaces of the fuel-cell anodes and resulting in degraded power generation performance. The sulfur content of natural gas or any hydrocarbon fuel needs to be reduced to very low levels to ensure long-term stable electrochemical performance for both high- and low-temperature fuel cells. This paper presents the development and test results of a new physical adsorbent for natural gas desulfurization. The sorbent effectively removes all sulfur-bearing compounds at ambient temperature with very high capacity. The new sorbent can also be fully regenerated by the temperature swing. In a series of tests, the sulfur adsorption capacity of the new material is compared with other commercially available and specially prepared sorbents. The results of the comparison tests are also summarized in this paper.

Prototype Demonstration of the Advanced CO 2 Removal and Reduction System

TDA Research, Inc. (TDA) is developing a simple system that provides an effective way of interfacing the carbon dioxide (CO2) removal and reduction functions. The system uses a chemical absorbent and a Sabatier catalyst combination to remove the CO2 and water vapor (H2O) produced by metabolic processes from cabin air and subsequently reduce the CO2 to methane and water. The system has the potential to weigh less than the Four Bed Molecular Sieve and CO2 Reduction Assembly combination, which is connected with a CO2 pump/compressor and storage tank due to the high CO2 absorption capacity of the sorbent and its ability to simultaneously absorb both CO2 and H2O (which eliminates the need for desiccant beds in the Four Bed Molecular Sieve System). The system does not require a CO2 pump/compressor or storage tank offering energy savings that come from effective utilization of the heat released by the Sabatier reaction to drive sorbent regeneration. Previously, TDA developed a high capacity regenerable CO2 and H2O sorbent to support the operation of the system and showed that the sorbent maintains its activity over extended cycling (Alptekin et al., 2003). We also demonstrated the operation of a state-of-the-art catalyst under the operation conditions of interest (Alptekin et al., 2003). Recently, TDA built a prototype of the system to demonstrate the key aspects of the process. This paper briefly describes the prototype system and summarizes the results of the demonstration tests.

An Advanced CO 2 Removal and Reduction System

An advanced system for removing CO2 and H2O from cabin air, reducing the CO2, and returning the resulting O2 to the air is less massive than is a prior system that includes two assemblies . one for removal and one for reduction. Also, in this system, unlike in the prior system, there is no need to compress and temporarily store CO2. In this present system, removal and reduction take place within a single assembly, wherein removal is effected by use of an alkali sorbent and reduction is effected using a supply of H2 and Ru catalyst, by means of the Sabatier reaction, which is CO2 + 4H2 CH4 + O2. The assembly contains two fixed-bed reactors operating in alternation: At first, air is blown through the first bed, which absorbs CO2 and H2O. Once the first bed is saturated with CO2 and H2O, the flow of air is diverted through the second bed and the first bed is regenerated by supplying it with H2 for the Sabatier reaction. Initially, the H2 is heated to provide heat for the regeneration reaction, which is endothermic. In the later stages of regeneration, the Sabatier reaction, which is exothermic, supplies the heat for regeneration.

A Lightweight EVA Emergency System

The selection of technologies for an evolutionary Space Station Freedom or a planetary (lunar or Martian) extravehicular mobility unit (EMU) are strongly driven by the system volume and weight as well as life cycle costs, reliability and safety. TDA Research, Inc. (TDA) is developing a compact, lightweight emergency system that provides 30-minute life-support in the case of system or component failures in the Portable Life Support System (PLSS). The system uses a low ventilation rate to reduce the amount of stored oxygen, reducing the associated weight and volume penalty. Operation of the system requires an effective sorbent that would remove carbon dioxide and moisture from the suit. We developed a regenerable sorbent that is suitable for the conceptual system. We also carried out a preliminary system analysis to show that the design saves significant weight.

Development of a Rapid Cycling CO 2 and H 2 O Removal Sorbent

The National Aeronautics and Space Administration (NASA) planned future missions set stringent demands on the design of the Portable Life Support System (PLSS), requiring dramatic reductions in weight, decreased reliance on supplies and greater flexibility on the types of missions. Use of regenerable systems that reduce weight and volume of the Extravehicular Mobility Unit (EMU) is of critical importance to NASA, both for low orbit operations and for long duration manned missions. The carbon dioxide and humidity control unit in the existing PLSS design is relatively large, since it has to remove and store eight hours worth of carbon dioxide (CO2). If the sorbent regeneration can be carried out during the Extravehicular Activity (EVA) with a relatively high regeneration frequency, the size of the sorbent canister and weight can be significantly reduced. TDA Research, Inc. is developing compact, regenerable sorbent materials to control CO2 and humidity in the space suit ventilation loop. The sorbent can be regenerated using space vacuum during the EVA, eliminating all CO2 and humidity duration-limiting elements in the life support system. The material also has applications in other areas of space exploration including long duration exploration missions requiring regenerable technologies and possibly the Crew Exploration Vehicle (CEV) spacecraft. This paper summarizes the results of the sorbent development, testing, and evaluation efforts to date.

Novel Sorbent to Clean Up Biogas for CHPs

In this project, TDA Research Inc. (TDA) has developed low-cost (on a per unit volume of gas processed basis), high-capacity expendable sorbents that can remove both the H2S and organic sulfur species in biogas to the ppb levels. The proposed sorbents will operate downstream of a bulk desulfurization system as a polishing bed to provide an essentially sulfur-free gas to a fuel cell (or any other application that needs a completely sulfur-free feed). Our sorbents use a highly dispersed mixed metal oxides active phase with desired modifiers prepared over on a mesoporous support. The support structure allows the large organic sulfur compounds (such as the diethyl sulfide and dipropyl sulfide phases with a large kinetic diameter) to enter the sorbent pores so that they can be adsorbed and removed from the gas stream.

Carbon Dioxide Control System for a Mars Space Suit Life Support System

Carbon dioxide (CO2) control during Extravehicular Activities (EVAs) on Mars will be challenging. Lithium hydroxide (LiOH) canisters have impractical logistics penalties, and regenerable metal oxide (MetOx) canisters weigh too much. Cycling bed systems and permeable membranes that are regenerable in space vacuum cannot vent on Mars due to the high partial pressure of CO2 in the atmosphere. Although sweep gas regeneration is under investigation, the feasibility, logistics penalties, and failure modes associated with this technique have not been fully determined. TDA Research, Inc. is developing a durable, high-capacity regenerable adsorbent that can remove CO2 from the space suit ventilation loop. The system design allows sorbent regeneration at or above 6 torr, eliminating the potential for Martian atmosphere to leak into the regeneration bed and into the ventilation loop. Regeneration during EVA eliminates the consumable requirement related to the use of LiOH canisters and the mission duration limitations imposed by MetOx system. The concept minimizes the amount of consumable to be brought from Earth and makes the mission more affordable, while providing great operational flexibility during EVA. The feasibility of the concept has been demonstrated in a series of bench-scale experiments and a preliminary system analysis. Results indicate that sorbent regeneration can be accomplished by applying a 14 C temperature swing, while regenerating at 13 torr (well above the Martian atmospheric pressure), withstanding over 1,000 adsorption/regeneration cycles. This paper presents the latest results from these sorbent and system development efforts.

Jet Fuel Desulfurizer for Fuel Cell powered APU

The effective utilization of logistic fuels in fuel cell applications requires removal of refractory sulfur species (organosulfur compounds) to below 0.1 ppm. Low temperature fuel cells (e.g. PEM) require clean (essentially pure) hydrogen feed to prevent the poisoning of the anode catalyst. Even the more robust high temperature fuel cells (e.g., solid oxide fuel cells) are poisoned with low levels of sulfur contaminants. Sulfur removal is critical for fuel cells and adsorption is a promising technology for accomplishing such low levels of sulfur. TDA has developed a sorbent-based fuel desulfurization system that can easily integrate with any fuel cell fuel processor. TDAs desulfurizer removes all of the refractory organic sulfur compounds from military fuels (both JP-5 and JP-8) while they are still in the liquid phase and reduces the total fuel sulfur content to sub-ppm levels (e.g., less than 0.1 ppmw). In order to increase the utilization of the sorbent and minimize the logistics burden and manpower associated with frequent replacements, the desulfurization system operates in a regenerable manner.