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Pyrolysis is a very versatile waste processing technology which can be tailored to produce a variety of solid, liquid and/or gaseous products. The pyrolysis processing of pure and mixed solid waste streams has been under investigation for several decades for terrestrial use and a few commercial units have been built for niche applications. Pyrolysis has more recently been considered for the processing of mixed solid wastes in space. While pyrolysis units can easily handle mixed solid waste streams, the dependence of the pyrolysis product distribution on the component composition is not well known. It is often assumed that the waste components (e.g., food, paper, plastic) behave independently, but this is a generalization that can usually only be applied to the overall weight loss and not always to the yields of individual gas species.

Activated carbons have a unique capability of strongly absorbing a great variety of species, ranging from SO2 and NOx, to trace organics, mercury, and other heavy metals. Activated carbons can also be used for gas storage and gas separations, including systems of practical interest to NASA (e.g., CO2/N2/O2), and even for the purification of liquids. No single activated carbon is suitable for all applications, but appreciable control over sorbent properties can be exercised in the process of carbon preparation. Since activated carbons can be produced from a wide range of organic materials, including waste streams, the preparation of activated carbons on board spacecraft should involve a limited amount of additional resources, help manage on-board waste, and reduce the weight of materials to be launched from earth. The feasibility of producing waste-derived activated carbons suitable for SO2 and NO control was the subject of the current study.

Pyrolysis processing is one of several options for solid waste resource recovery in space. It has the advantage of being relatively simple and adaptable to a wide variety of feedstocks and it can produce several usable products from typical waste streams. The objective of this study is to produce a prototype mixed solid waste pyrolyzer for spacecraft applications. A two-stage reactor system was developed which can process about 1 kg of waste per cycle. The reactor includes a pyrolysis chamber where the waste is heated to temperatures above 600°C for primary pyrolysis. The volatile products (liquids, gases) are transported by a N2 purge gas to a second chamber which contains a catalyst bed for cracking the tars at temperatures of about 1000 °C −1100 °C. The tars are cracked into carbon and additional gases. Most of the carbon is subsequently gasified by oxygenated volatiles (CO2, H2O) from the first stage.

Pyrolysis processing is one of several options for solid waste resource recovery in space. It has the advantage of being relatively simple and adaptable to a wide variety of feedstocks and it can produce several usable products from typical waste streams. The overall objective of this study was to produce a prototype mixed solid waste pyrolyzer for spacecraft applications. A two-stage reactor system was developed which can process a maximum of about 0.5 kg of waste per cycle. The reactor includes a pyrolysis chamber where the waste is heated to temperatures above 600 °C for primary pyrolysis. The volatile products (liquids, gases) are transported by a N2 purge gas to a second chamber which contains a catalyst bed for cracking the tars at temperatures of about 1000-1100 °C. The tars are cracked into carbon and additional gases. Most of the deposited carbon is subsequently gasified by oxygenated volatiles (CO2, H2O) from the first stage.

Pyrolysis processing of solid waste in space will inevitably lead to carbon formation as a primary pyrolysis product. The amount of carbon depends on the composition of the starting materials and the pyrolysis conditions (temperature, heating rate, residence time, pressure). Many paper and plastic materials produce almost no carbon residue upon pyrolysis, while most plant biomass materials or human wastes will yield up to 20-40 weight percent on a dry, as-received basis. In cases where carbon production is significant, it can be stored for later use to produce CO2 for plant growth. Alternatively it can be partly gasified by an oxidizing gas (e.g., CO2, H2O, O2) in order to produce activated carbon. Activated carbons have a unique capability of strongly absorbing a great variety of species, ranging from SO2 and NOx, trace organics, mercury, and other heavy metals.

Pyrolysis is a very versatile waste processing technology which can be tailored to produce a variety of solid liquid and/or gaseous products. The main disadvantages of pyrolysis processing are: (1) the product stream is more complex than for many of the alternative treatments; (2) the product gases cannot be vented directly into the cabin without further treatment because of the high CO concentrations. One possible solution is to combine a pyrolysis step with catalytic oxidation (combustion) of the effluent gases. This integration takes advantage of the best features of each process, which is insensitivity to product mix, no O2 consumption, and batch processing, in the case of pyrolysis, and simplicity of the product effluent stream in the case of oxidation. In addition, this hybrid process has the potential to result in a significant reduction in Equivalent System Mass (ESM) and system complexity.

Pyrolysis is a technology that can be used on future space missions to convert wastes to an inert char, water, and gases. The gases can be easily vented overboard on near term missions. For far term missions the gases could be directed to a combustor or recycled. The conversion to char and gases as well as the absence of a need for resupply materials are advantages of pyrolysis. A major disadvantage of pyrolysis is that it can produce tars that are difficult to handle and can cause plugging of the processing hardware. By controlling the heating rate of primary pyrolysis, the secondary (cracking) bed temperature, and residence time, it is possible that tar formation can be minimized for most biomass materials. This paper describes an experimental evaluation of two versions of pyrolysis reactors that were delivered to the NASA Ames Research Center (ARC) as the end products of a Phase II and a Phase III Small Business Innovation Research (SBIR) project.

Pyrolysis is a very versatile waste processing technology which can be tailored to produce a variety of solid, liquid, and/or gaseous products. The main disadvantages of pyrolysis processing are: (1) the product stream is more complex than for many of the alternative treatments; (2) the product gases cannot be vented directly into the cabin without further treatment because of the high CO concentrations. One possible solution is to combine a pyrolysis step with catalytic oxidation (combustion) of the effluent gases. This integration takes advantage of the best features of each process. The advantages of pyrolysis are: insensitivity to feedstock composition, no oxygen consumption, and batch operation. The main advantage of oxidation is the simplicity and consistency of the product stream. In addition, this hybrid process has the potential to result in a significant reduction in Equivalent System Mass (estimated at 10-40%) and system complexity.