Carl Paul Gottfried von Linde (11 June 1842 – 16 November 1934) was a German scientist, engineer, and businessman. He discovered the refrigeration cycle and invented the first industrial-scale air separation and gas liquefaction processes, which led to the first reliable and efficient compressed-ammonia refrigerator in 1876.

Linde was the founder of the company now known as Linde plc but formerly known (variously) as the Linde division of Union Carbide, Linde, Linde Air Products, Praxair, and others. This company is the world's largest producer of industrial gases and helped create the global supply chain for industrial gases.

Linde was a member of scientific and engineering associations, including being on the board of trustees of the Physikalisch-Technische Reichsanstalt and the Bavarian Academy of Sciences and Humanities. He was knighted in 1897 as Ritter von Linde.

Biography

Carl von Linde was born in Berndorf, Bavaria, Germany. His father was a German minister, and his mother was from Sweden. People expected him to follow his father's path, but he chose a different career. His family moved to Munich in 1854, and eight years later, he began studying engineering at the Swiss Federal Institute of Technology in Zurich, Switzerland. His teachers included Rudolf Clausius, Gustav Zeuner, and Franz Reuleaux.

In 1864, he was removed from his studies before graduating because he took part in a student protest. However, Reuleaux helped him find a job as an apprentice at the Kottern cotton-spinning plant in Kempten. He stayed there briefly before working at Borsig in Berlin and later at the new Krauss locomotive factory in Munich, where he became head of the technical department. In September 1866, he married Helene Grimm. Their marriage lasted 53 years, and they had six children.

In 1868, Linde learned about a new university opening in Munich, the Technische Hochschule. He applied for a teaching job and was accepted at the age of 26. He became a full professor of mechanical engineering in 1872 and created a laboratory for engineering students, including Rudolf Diesel.

Between 1870 and 1871, Linde wrote articles in the Bavarian Industry and Trade Journal about his research on refrigeration. His first refrigeration plants were successful in business, and refrigeration became a major focus of his work. In 1879, he left his professorship to start the Gesellschaft für Lindes Eismaschinen Aktiengesellschaft, now known as Linde plc, in Wiesbaden, Germany. At first, the business grew slowly, but by the 1880s, it became successful. Breweries benefited greatly from his refrigeration technology, and by 1890, he had sold 747 machines. Other industries, such as slaughterhouses and cold storage facilities across Europe, also used his technology.

In 1888, Linde returned to Munich and resumed his professorship. However, he soon returned to his work on refrigeration. In 1892, an order from the Guinness brewery in Dublin for a carbon dioxide liquefaction plant led him to study low-temperature refrigeration. In 1894, he began work on a process to liquefy air. In 1895, he successfully developed this process and filed for a patent (approved in the United States in 1903). In 1901, he started research on a method to separate pure oxygen and nitrogen from liquefied air using fractional distillation. By 1910, his coworkers, including his son Friedrich, developed the Linde double-column process, which is still used today.

After 10 years, Linde stepped back from managing the company to focus on research. In 1895, he liquefied air by compressing it and then letting it expand quickly, which cooled it. He then separated oxygen and nitrogen by slowly warming the liquid air. In the early days of oxygen production, the most important use was the oxyacetylene torch, invented in France in 1903. This tool changed how metal was cut and welded for ships, skyscrapers, and other steel structures.

In 1897, Linde was honored with the Order of Merit of the Bavarian Crown and was given the title of nobility.

In addition to his engineering skills, Linde was a successful business leader. He formed many partnerships in Germany and other countries, using licensing agreements to share his patents and knowledge.

In 1906, Linde negotiated a share in Brin's Oxygen Company, later renamed The BOC Group, in exchange for the rights to his patents in the UK and other countries. He served on the company’s board until 1914. He also created the Linde Air Products Company in the USA in 1907. This company was later controlled by the US government and passed to Union Carbide in the 1940s, eventually becoming Praxair. In 2005, Linde plc bought the BOC Group, and in 2019, Linde plc merged with Praxair, combining all three companies he founded.

Around 1910, Linde began handing over company responsibilities to his sons, Friedrich and Richard, and his son-in-law, Rudolf Wucherer. He continued to advise and supervise the company until his death.

Carl von Linde died in Munich in November 1934 at the age of 92.

Key inventions

Linde's first refrigeration system used dimethyl ether as the refrigerant and was built by Maschinenfabrik Augsburg (now known as MAN AG) for the Spaten Brewery in 1873. He soon developed more reliable refrigeration systems that used ammonia. These systems were early examples of vapor-compression refrigeration machines, and ammonia is still widely used as a refrigerant in industrial settings.

His device for liquefying air combined the cooling effect created when a compressed gas expanded (a process called the Joule–Thomson effect, first observed by James Prescott Joule and Lord Kelvin) with a method where cold air from expansion was used to cool incoming air. Over time, this process gradually lowered the temperature of the device and the air inside until the air became liquid.

After developing equipment for air liquefaction, Linde created tools that separated air into its individual components using distillation methods.

Linde's inventions and improvements helped advance many fields, including cryogenics, physics, chemistry, and engineering.

• CH10704 – 31 January 1896 – Gasverflüssigungs-maschine (Machine for the liquefaction of gas) (in German) – Switzerland
• GB189512528 – 16 May 1896 – Process and Apparatus for Liquefying Gases or Gaseous Mixtures, and for Producing Cold, more particularly applicable for Separating Oxygen from Atmospheric Air – UK
• US727,650 – 12 May 1903 – Linde oxygen process – US
• US728,173 – 12 May 1903 – Equipment for Linde oxygen process – US
• US795,525 – 25 July 1905 – Equipment for Linde oxygen and nitrogen process – US