Liquefaction of unconventional natural gases

such as coalbed methane

synthetic natural gas

coke oven gas

and tail gas from chemical processes

is an effective method for recycling. Owing to the involvement of large amounts of oxygen

nitrogen

or hydrogen

they usually need to be purified by low-temperature distillation. Thus

the unconventional natural gas liquefaction technology is quite different from that for the conventional natural gas. In this paper

the research progress of unconventional natural gas liquefaction in recent years is reviewed. For coalbed methane

large-scale coalbed methane projects abroad employed a cascade process owing to the refrigerant supply

while the research and development in China focused on small-scale or skid-mounted liquefaction devices and specific characteristics of air-bearing coalbed methane liquefaction. For synthetic natural gas

the structure of the liquefaction–distillation processes was employed because of hydrogen removal and the energy integration between the two parts was recommended to increase the system energy efficiency. For coke oven gas

the mainstream technology scheme to produce synthetic natural gas was methanation

followed by liquefaction. The new technology scheme of separating and liquefying coke oven gas to simultaneously produce liquefied natural gas and liquid hydrogen should be analyzed. In addition

the safety

phase equilibrium

and solubility issues related to the unconventional natural gas liquefaction are discussed.