System for collecting excess carbon dioxide in space cabin is described. System collects carbon dioxide exhaled by human inhabitants and decomposes gas into carbon and water by reaction with hydrogen in presence of catalyst. Diagram of equipment involved in reaction is included

Holmes, R. F.

English

NASA Technical Reports Server

December 1972	 B72-10666 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Automation of Bosch Reaction for CO 2 Reduction 
One step in a scheme for the replenishment of oxygen 
necessary to sustain life in a space cabin is to collect the 
excess carbon dioxide exhaled by human inhabitants, and 
then to decompose the carbon dioxide into carbon and 
water by reaction with hydrogen in the presence of a 
catalyst. This is called the Bosch reaction. In a subsequent 
step the water is decomposed by electrolysis to obtain 
oxygen for replenishing the cabin air and hydrogen that is
recycled through the Bosch reactor. The carbon is 
recovered as a powder for use if needed, or it can be 
jettisoned as waste. 
The Bosch reaction has been used in the operation of 
ground based space cabin simulators wherein human 
subjects have lived for periods of two months or more. 
For these operations, the Bosch reaction was carefully 
monitored and controlled by human attendants outside 
$
Bleed 
Flow 
Valve
Separator 
Water
Discharge
Valve
Condenser
Exchanger 
Mixture 
Control f	
•I	
Compressor 
CO2 Feed	 Carbon Collected ,/1 
Bypass Check
Restrictor	 in Removable Recycle 
	
Mixture	
CO2 Feed	
Filter(0
Control 
Flow Meter 
	
H 2 Feed
	
CO2 Feed 
	
Pressure	 Pressure 
	
Regulator	 Regulator 
	
H 2 Shut-Off
	
CO2 Shut-Off 
	
Solenoid
	
Solenoid 
S	 I	 I Figure 1
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000665 2020-03-17T03:42:41+00:00Z
To 
Atmosphere
9 
System 
Pressure 
Figure 2
	 Bypass 
the cabin simulator. In the course of such monitoring, it 
was discovered that the reaction could be automated for 
self-regulation without constant adjustment by an at-
tendant. 
The reaction takes place at 867 to 978 K (1100 to 
1300°F), but cannot be completed in a single pass because 
a water vapor equilibrium is approached. Therefore, a 
recycling system is required. This is a closed loop in which 
the carbon is accumulated within a catalyst cartridge for 
periodic removal, water vapor is removed continuously by 
condensation, and feed gases enter to replace the volume 
reductions due to the reaction and to water condensation 
and separation. 
The primary factors influencing CO 2 conversion rates 
are reaction temperature, recycle gas mixture (hydrogen 
and carbon monoxide) ratios, reactor pressure, and 
recycle flow rate. An electrically powered heater and a 
thermocouple temperature sensor control rate excursions 
due to temperature variations. Excursions due to mixture 
ratio variations can be avoided by using infrared or 
thermal conductivity sensors for the composite mixture to 
control the relative input of 112 and CO2 . Pressure 
variations influencing the process rate are prevented by 
feed gas pressure regulators. The process rate is immedi-
ately responsive to recycle flow rate and, within the 
capacity of the recycle flow compressor, can be varied 
over a wide range. 
The novel feature is the use of a back pressure 
regulator (BPR) to maintain a constant feed-point pres-
sure which can be achieved only when the process rate 
and feed rate are matched. The regulator accomplishes 
this by modulating the recycle flow rate which in turn 
modulates the process rate. In the closed system under 
normal feed supply conditions, a reduction in process rate 
due to adverse changes in temperature, pressure differen-
tial, mixture, etc., will tend to increase the total system 
pressure including that at the feed point. Within the
capacity limits of the back pressure regulator and com-
pressor, this tendency will be resisted by opening of the 
regulator to increase the recycle flow, and thereby, the 
process rate. If the process rate is too high, the feed-point 
pressure tends to fall causing the regulator to restrict 
recycle flow. 
An effective control allowing the recycle flow to vary 
automatically, as required to maintain a constant process 
rate within the limits of compressor capacity, was 
obtained by installing a high-flow high-sensitivity back 
pressure regulator (BPR) in the recycle loop as shown in 
Figure 1. To increase its range of control, a flow bypassing 
hole was drilled in the regulator as shown in Figure 2. This 
hole was sized to pass the quantity of recycle flow needed 
for the desired process rate when the resistance to flow 
through the cartridge was at a minimum. This also 
prevented a complete blockage of flow during feed gas 
supply interruptions which caused the regulator to close. 
Notes: 
1. The information concerning this innovation may be of 
interest to the chemical processing industries. 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B72-10666 
Patent status: 
NASA has decided not to apply for a patent. 
Source: R. F. Holmes of
General Dynamics Corporation
under contract to
Marshall Space Flight Center
(MFS.21674) 
B72-10666	 Category 04, 07
I 
[I


Automation of Bosch reaction for CO2 reduction

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server