# How might I liquefy small quantities of natural gas?

1. Jan 14, 2017

### diligentExplorer

Several undergraduate and graduate students and I are building a small engine powered by Compressed Natural Gas (CNG). It is a small and straightforward affair, similar to what is found in small equipment such as chainsaws and lawn mowers. I wanted to experiment with Liquefied Natural Gas (LNG) as fuel storage (due to it's 600x greater density), but I obviously ran into some logistical issues. I can easily purchase CNG, but LNG is obviously not on the menu in any quantity smaller than a supertanker, for obvious reasons. But I was wondering if there is a feasible way to condense gas from a CNG container into LNG for experimental purposes (I intend to produce only 1-2 L of LNG at a time). The cost or energy economics of the liquefaction process are not important as this is just an experimental rig. And this is not paid/funded research, or even official research at all, so keeping the costs below around five thousand USD is important. If it works it will likely develop into research, but that's a bit forward in the future. I'm just wondering if there's a SMALL machine I could purchase or a simple solution I could build myself. Thanks.

2. Jan 14, 2017

The boiling point of methane is above that of liquid nitrogen, so I would suggest using liquid nitrogen as a coolant to condense it. Liquid nitrogen should be readily available in fairly large quantities. $\\$ From what I'm seeing for the melting temperature of methane, you may even be able to freeze the methane with liquid nitrogen.

3. Jan 14, 2017

### diligentExplorer

Wow, silly me. I was just thinking of scaling down the large-scale process, but that's an obvious solution I should have thought of and it really that works great for small quantities such as those I am working with. I guess I will have to devise some sort of apparatus that can safely condense with minimum leakage (and no mechanical implosions or fractures). Thanks

4. Jan 14, 2017