The issue of extracting hydrogen from 100,000 tons of methanol off-gas.
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Our company is building a 100,000-ton methanol plant. Once it is operational, I want to extract hydrogen from the off-gases – what are the best methods for this, and what is the investment required? It is known that the volume of gas released per hour is approximately 3,000 cubic meters.
We need to consider many parameters before we can help you. Such as hydrogen content, exhaust pressure, temperature, and so on.
For this, you need the pressure of the released gas, the hydrogen content, and the desired yield in order to obtain results! There are generally two methods: membrane separation and pressure swing adsorption! Membrane separation has a low initial investment, but the membrane has a short service life ； Pressure swing adsorption requires a high initial investment, but has a long service life and yields hydrogen of high purity!
The hydrogen purity in the composition of methanol off-gas is roughly around 75%; the off-gas generated from 100,000 units of methanol amounts to about 6,000 Nm3/h. This gas can be used as feed for hydrogen production via PSA technology, and this approach has been implemented in the PSA systems designed by Huaxi, with good results. It is important to note the amount of off-gas, PSA load, the impurity requirements of the PSA design, and the requirements of the product hydrogen regarding CO and CO2.
A vent volume of 3,000 Nm3 for 100,000 tons of methanol is a bit low. Membrane separation technology requires low investment, occupies little space, is easy to operate and maintain, offers great operational flexibility, and achieves a high hydrogen recovery rate. Its membrane separators can last up to 10 years, making it the preferred choice.
PSA technology is being used; it’s quite mature, and the investment required isn’t high either – it’s probably around 500W
We also have 100,000 tons of methanol, and we share the same idea as the original poster – we plan to use pressure swing adsorption to produce hydrogen, so that the hydrogen obtained will be relatively pure
I’ve read a lot recently about the uses of methanol off-gases, and here’s a summary: 1. It can be used as fuel, but according to various sources its calorific value isn’t very high, and it contains a significant amount of H2. The recommendation is to recover H2 before burning it. 2. Add a carbon source to increase methanol production. This process can be combined with catalytic conversion techniques for syngas conversion in order to supplement CO and CO2, thereby achieving an optimal carbon-hydrogen ratio and increasing methanol production. 3. Purify hydrogen for use in hydrogenation reactions, such as benzene hydrogenation and ammonia synthesis. Hydrogen purification technologies mainly include two types, one of which is PSA hydrogen production ； Another method is membrane recovery.
If there are hydrogen production units in the vicinity, this gas can be directly fed into a hydrogen production PSA unit for purification; all that’s needed is to add separation tanks and mixers. We adopted this approach, and it worked very well, with a high yield.
Would it be possible to use membrane separation to extract hydrogen and carbon monoxide from methanol off-gases, with carbon dioxide, methane, and nitrogen being emitted as waste gas?
In the 1990s, we designed a 100,000-ton per year facility for producing methanol from natural gas. Since the C:H ratio of the gas produced from natural gas did not meet the requirements (there was a lack of carbon), the solution adopted was to design a larger gas production unit; part of the raw gas was processed using PSA to extract hydrogen, while CO and CO2 were reintroduced into the system to achieve an appropriate C:H ratio for methanol synthesis. (In fact, it would also be possible to extract CO2 from flue gas to supply carbon.) It should be feasible to use PSA to extract hydrogen from the off-gases, as suggested by the original poster