FAQs
- What is Sofnolime?
- What is the difference between the different grades of Sofnolime?
- What is the capacity of Sofnolime for carbon dioxide?
- What can make the absorber fail prematurely?
- Can Sofnolime be regenerated?
- Why is water so important to Sofnolime? Is it needed to start the reaction? Does it stop the reaction?
- How important is dust in Sofnolime?
- Why is Sofnolime 'D' shaped and not spherical?
- Does Sofnolime medical grade interact with other components in the anesthesia stream?
- Does the indicator dye have any adverse effect on the Sofnolime?
- Where are oxygen candles used?
- Can I handle an oxygen candle like a normal candle?
- How do I start an oxygen candle?
- How many people can an oxygen candle keep alive?
- How much carbon monoxide will Moleculite absorb?
- What are Moleculite and Sofnocat poisons?
- What happens if Moleculite and Sofnocat are exposed to moisture in the atmosphere?
- Does Moleculite just destroy CO?
What is Sofnolime?
Sofnolime appears to be a dry, white granular material. It contains mostly calcium hydroxide (lime) and a small amount of sodium hydroxide. It is manufactured in a form that is hard, to minimise dust formation, and has a structure and shape optimised to allow good contact and absorbance of gasses. Although it appears to be a dry granular material it can contain up to 20% water. It is used to absorb carbon dioxide for medical, diving and other closed circuit breathing systems as well as absorption of other acidic gasses in breathing and industrial applications. It chemically reacts with the gasses it absorbs and converts them to solid calcium salts, which cannot then be desorbed. When Sofnolime is used to absorb carbon dioxide the calcium hydroxide (lime) is converted to calcium carbonate (chalk), which can be disposed of easily and safely to landfill.
What is the difference between the different grades of Sofnolime?
Sofnolime is made in a variety of different grades for specific applications. The size, water content and particle shape can be changed to provide products optimised for different applications. Smaller particles can provide more absorption capacity, but at the expense of increased resistance to flow for the same depth of absorber material. Different dyes can be incorporated to indicate the extent of exhaustion of capacity of a bed. In medical use a white to violet or a pink to white colour change are the two most widely used products. Clearly there is little advantage in using an indicator dye in a system where the dye cannot be seen, such as a diving set. The water content is important, as water is necessary for the reaction to occur at the surface of the Sofnolime. If too little water is present the reaction is slow and an unnecessarily large contact time is required. If too much water is present then the internal structure of the solid particles becomes flooded and capacity is reduced. This is further complicated by the fact that, for carbon dioxide absorbance, the reaction actually produces more water. The shape and size of the particles effects the way the material packs together (the bulk density), the absorption capacity, the speed of absorbance, resistance to flow and the chances of dust production during handling and use. It is therefore important that the correct grade is used for your application. Our commercial team are always willing to advise on the best options available for your particular application.
What is the capacity of Sofnolime for carbon dioxide?
It depends on the gas and the way it is used. For each gas there is a minimum contact time necessary for reaction to occur. If the contact time is less than this minimum all the target gas at the inlet will not be removed before it gets to the outlet. As the bed gets used the available contact time with unreacted Sofnolime will decrease until such time as there is insufficient time for complete reaction. The minimum absorption capacity for the various grades is shown in the Sofnolime specification. For non-standard applications our commercial team can advise on conditions and expected service life.
What can make the absorber fail prematurely?
Premature failure of an absorber can be due to one of three frequently encountered conditions. All are usually readily preventable once the user is aware of the issues.
Drying of the bed - this occurs if the bed is allowed to dry out. If a very dry gas stream is passed through a bed of Sofnolime for extended periods of time then the water necessary for reaction to occur can be stripped from the bed and the reaction rate will become to slow for effective removal of CO2. This can occur in a hospital situation if the absorber is left "open circuit" with high flows of dry gas between patients. During use in a breathing circuit this is never a problem, as the inlet air will be saturated with water vapour from expired breath. Prevent by avoiding long periods of high flow with dry gas streams.
Abnormally high gas flowrate - if abnormally high gas flow rates are used the residence time of the carbon dioxide or other target gas in the absorber will be too short for complete reaction to occur. For carbon dioxide a minimum of approx 0.5 seconds is needed in contact with the non-exhausted Sofnolime.
Channelling - this is a condition where the gas flow through the absorber is not uniform and most of the gas follows the same path through only part of the absorber. The material in this region becomes exhausted and the gas is no longer in contact with active material. The most common causes for this are high gas flow rates through poorly designed or poorly packed absorber beds.
Question: Can Sofnolime be regenerated?
Answer: If you look at the soda lime cycle (below) starting with calcium carbonate, CaCO3, (chalk) that is mined and subsequently made into calcium hydroxide, Ca(OH)2, (lime) at the quarry by heating and adding water (indicated in black) followed by the manufacturing procedure into soda lime done by Molecular Products (in green) and finally the user converting the Ca(OH)2 back to the calcium carbonate by adding CO2 (in red) it seems that the product can be recycled. However, it needs to be pointed out that the cycle cannot be repeated as the calcium carbonate at the end is a different form that the carbonate that started and recycling is not commercially viable. Also note that the Molecular Products formulation involves adding other components such as an indicator which of course cannot be recycled.
Question: Why is water so important to Sofnolime? Is it needed to start the reaction? Does it stop the reaction?
Answer: Water is required at the start for the reaction and one extra mole of water is produced for each mole of carbon dioxide absorbed. This means that for each 44g of carbon dioxide absorbed it produces 18 g of water - that's why the water builds up in the circuit with time. If you have a situation where the system is allowed to saturate then the reaction will effectively stop since the Sofnolime particles will be surrounded by a coating of water through which the carbon dioxide will only diffuse slowly. Conversely if the water content drops below about 10% the reaction to absorb carbon dioxide starts to slow down and effectively stops when the water content becomes 1%.
Question: How important is dust in Sofnolime?
Answer: Dust should be avoided at all times. It may contaminate the circuit and valves and hence is a major quality issue.
Question: Why is Sofnolime 'D' shaped and not spherical?
Answer: The important issue here is the morphology which is the surface area to volume ratio. In theory a spherical ball gives the largest surface area to volume ratio since the distance to the middle of the granule is the same all the way around. However, the way the material packs is also of importance and it is found that with spherical materials you get channeling which results in uneven flow of gas through the material. Overall a 'D' shaped material offers the optimum for both the maximisation of surface area to volume ratio and minimization of channeling effects.
Question: Does Sofnolime medical grade interact with other components in the anesthesia stream?
Answer: There is a possibility of interaction with a breakdown product called Compound A to produce carbon monoxide but this is normally only present at sub clinical amounts and is not a significant risk. Compound A is also in the anesthetic Sevoflurane. Carbon monoxide may be present due to misuse e.g. by letting the air stream dry out by leaving it on over a weekend. In this respect education has failed and the best policy is to have good enforceable operating procedures to avoid the conditions that can form carbon monoxide.
The alternative is to use an absorber that minimises the risk of carbon monoxide formation by having small levels of a strong base and not containing potassium hydroxide. It is argued that Sofnolime meets both these criteria as it does not contain potassium hydroxide and has low levels of sodium hydroxide (around 3.5%) which results in a low level risk of carbon monoxide production.
The product Superia is designed to meet (and exceed) these criteria. Most of the existing alternative products (e.g. Amsorb) that claim low agent interaction are more expensive per kg and have lower carbon dioxide absorption capacities - which is the main reason for it being there.
Question: Does the indicator dye have any adverse effect on the Sofnolime?
Answer: It is possible that the indicator dye used can produce amine emanation but this is carefully controlled and are not a problem with Sofnolime, though it has been an issue with other vendor products used in diving and submarine use. This has generally been due to poor quality dye at high levels of usage.
Where are oxygen candles used?
Oxygen candles are devices that are used to supply emergency oxygen to sustain life. Once initiated they provide oxygen by the decomposition of the chemical mixture at the heart of the candle. Oxygen candles have been in use for many years and are used in all sorts of places where people could get trapped inside an airtight environment and are totally isolated from any outside help. Typical applications include submarines, spacecraft and refuge shelters in mines. Oxygen candles are also used in a variety of emergency escape equipment to provide emergency oxygen to the escaping person if the oxygen in the atmosphere has been depleted or contaminated.
Can I handle an oxygen candle like a normal candle?
No! There are a few different types of oxygen candle, most of which have to be housed inside a "furnace" assembly. There is one type of oxygen candle, however, that can be operated independently of any other equipment. This is known as the Self Contained Oxygen Generator, or SCOG. The temperature of the SCOG container can reach several hundred degrees centigrade and so must not be handled once the candle has been started.
How do I start an oxygen candle?
Oxygen candles are started by a number of different methods, including ignition cartridges, chemical reaction and electrical methods, quite different to an ordinary candle! Probably the most common method is to start the candle with an ignition cartridge. When struck, an ignition cartridge fires very hot gases into the igniter part of the oxygen candle, thus initiating the decomposition of the chemical mixture to produce oxygen.
How many people can an oxygen candle keep alive?
Obviously, this depends on the size of the oxygen candle. Oxygen candles are available in a variety of sizes and therefore store different quantities of oxygen. Oxygen quantities of between 100 litres and 4000 litres can be manufactured.
The SCOG 26 will produce 2600 litres of oxygen. As a guide we can say that an individual requires 0.5 litres of oxygen per minute when trapped. Therefore, a single SCOG will provide enough oxygen for a single person for around 86 hours. The more active the person then the more oxygen they will need and the oxygen produced will not last as long.
It is important to remember that oxygen candles alone cannot sustain life. An oxygen candle would form only part of a life sustaining system. In an enclosed environment there are other considerations. For example, the levels of carbon dioxide need to be controlled, as they will reach dangerous levels long before oxygen runs out.
How much carbon monoxide will Moleculite absorb?
Moleculite is a CATALYST, so does not absorb CO. Instead, it causes the CO to react with O2 in the gas stream, to make CO2. So it is necessary to make sure there is enough oxygen present to react. For normal air, this is not a problem, but if the gas was pure N2 for example, O2 addition might need to be considered.
Provided there is enough O2 present and no poisons to prevent the catalyst operating, Moleculite will continue converting CO to CO2 indefinitely.
What are Moleculite and Sofnocat poisons?
Poisons are any chemicals that interfere with the catalyst, by depositing on the surface and preventing it from working properly. Chemicals like NOx, SOx, Cl2 and other halogens poison most catalysts.
What happens if Moleculite and Sofnocat are exposed to moisture in the atmosphere?
Moisture is a poison for Moleculite. It deposits on the catalyst, stopping the oxidation of CO. Moisture has a high affinity for Moleculite, so the air must be very dry, for Moleculite to continue working for extended periods of time. Alternatively, the catalyst can be used at +120C, to ensure moisture does not stay on the surface.
If Moleculite becomes deactivated by moisture, then heating at 150C for a few hours, will recover the activity. NOTE heating above 300C may change the catalyst properties.
Sofnocat is more resistant to moisture than Moleculite, but similar precautions are advised. NOTE heating Sofnocat to above 70C may damage the catalyst, so this is not recommended.