Largely undetectable to humans and potentially of an immensely hazardous nature, nitrogen is utilised in a wide range of applications from medicine to meals for two, especially in its cryogenically cool liquid state.

Liquid nitrogen is inert, colorless, odorless, non-corrosive, non-flammable, and extremely cold. Nitrogen makes up the major portion of the atmosphere (78.03% by volume, 75.5% by weight), is inert and will not support combustion – however, it is not life supporting. Nitrogen is inert except when heated to very high temperatures where it combines with some of the more active metals, such as lithium and magnesium, to form nitrides.

It will also combine with oxygen to form oxides of nitrogen and, when combined with hydrogen in the presence of catalysts, will form ammonia. Aside from N2, nitrogen may be referred to as GAN or GN in its gaseous form, and LIN or LN in its liquid form.

Production process
Produced in large volumes in both gas and liquid form by cryogenic distillation, smaller volumes may be produced as a gas by pressure swing adsorption (PSA) or diffusion separation processes (permeation through specially designed hollow fibres). Cryogenic processes can produce very pure nitrogen, but adsorption and diffusion processes are typically used to make the lower purity product in relatively small amounts. This is attractive to users when purity is not critical and alternatives (purchase of bulk liquid nitrogen, cylinders of high pressure nitrogen, or local cryogenic production) are more expensive or impractical.

Liquid nitrogen is valued for its cold nature as well as its aforementioned inertness. When liquid nitrogen is vapourised and warmed to ambient temperature, it absorbs a large quantity of heat. The combination of inertness and its intensely cold initial state makes liquid nitrogen an ideal coolant for certain applications, such as food freezing. Liquid nitrogen is also used to cool materials which are heat sensitive or normally soft to allow machining or fracturing. Examples are used tyres, plastics, certain metals and even pharmaceuticals.

Applications
More nitrogen is used by customers than any other industrial gas, used in a broad range of industries, including chemicals, pharmaceuticals, petroleum processing, glass and ceramic manufacture, steel-making, pulp and paper manufacture, and healthcare.

Freezing and Preservation of Food – Foods can be packed, sealed and then sprayed with liquid nitrogen. Liquid nitrogen evaporates upon contact with many surfaces (including food), this evaporation process allows for the absorption of heat and energy from the food, and as a result the molecules in the food slow down and the food freezes.

Cryomedicine – Liquid nitrogen is widely used in the preservation of medical specimens, it is particularly useful for the long term preservation of cells and tissues, and may be used for the rapid freezing of different tissues such as bone marrow and blood. It is useful in the preservation of animal embryos, bacteria and fungi.

Air Products clears the Air – Liquid nitrogen (LIN) systems supplier Air Products says it has “dispelled the myth” that carbon dioxide offers advantages over LIN in cooling in meat mixing and forming applications. The claim is based on a company-commissioned study of the effects of both cooling agents on shelf-life, colouration and dehydration.
According to Dr Chris Kennedy of Air Products, the findings show that use of liquid nitrogen for cooling assures product quality on a par with CO2 use. Meat processors, he said, can therefore choose freely between the two options without worrying about variations in end-product quality.

Health & Safety
Humans cannot reliably detect the presence of nitrogen. Liquid nitrogen has a 700x expansion ratio which may create physical hazards and injuries from the explosion of unvented containers, equipment, or other devices. Extensive tissue damage or burns can result from exposure to LN2 or cold nitrogen vapours. Asphyxiation may result from the displacement of oxygen in the air with nitrogen, to levels where there is insufficient oxygen to support life. Inhalation of oxygen deficient air can cause dizziness, nausea, vomiting, loss of consciousness, and death.

In its liquid state, it is clear and non-toxic but dangerous because it is extremely cold and because the gas boiled off expands rapidly.

Demand – Supply & Prices
Thanks to a number of ASU’s coming online last year and this year, supply for LN is abundant. There have been noticable price hikes in the range of 10-15% in all the parts of the world, but given the crude price touching $120 per barrel, that’s hardly a surprise.

LN plants commissioned in America
Cartersville, Georgia – ASU with 800 tpd capacity to supply customers in the food, metal, chemical and healthcare industries across the South-East US.
Columbus, Mississippi – New plant with 550 tpd capacity to deliver oxygen and nitrogen to the SeverCorr steel works.
Bethlehem, Pennsylvania – To produce 575 tpd liquid nitrogen for customers in the food, metal, chemical and healthcare industries in the North-East US and on the Atlantic coast.
Cantarell, Mexico – Fifth module of nitrogen plant or the Mexican oil company Pemex to meet oil production demands in the Gulf of Mexico.

Largest ASU in Asia
Praxair China, announced in Dec 2007 that it has signed a major contract with Jiangsu SOPO (Group) Co. Ltd, for the supply of industrial gases to SOPO’s acetic acid plant.

Praxair will design, build, operate, and own this air separation unit (ASU) which is due to come on stream in 2009. With a capacity of 3,000 tpd of oxygen and nitrogen, it will be the largest single plant for sale of gas and also the largest single-train ASU to be built in Asia.

Linde Gas Ningbo, its wholly-owned unit, will supply nitrogen to Ningbo Wanhua Polyurethane Co’s plants in eastern China from 2010 onwards. The facilities will produce 800 tpd of liquid nitrogen, oxygen and argon, for the merchant market in Ningbo, Zhejiang Province.