PARIS, May 4 (Reuters) - French biotech firm Global Bioenergies launched a new brand of make-up on Tuesday, with long-lasting products made from sugar beet residues rather than petrochemicals.

With backing from French cosmetics giant L'Oreal, Global Bioenergies is betting on growing interest in natural alternatives to synthetic substances for make-up products.

The French firm has developed a process which turns residues chiefly, from sugar beet and some wood sugar, into isododecane which is the main ingredient in long-lasting make-up products, such as waterproof mascaras or long-lasting liquid lipsticks.

"Today, this isododecane only comes from petrol so there is no way to make products with a high proportion of natural ingredients in long-lasting make-up," Global Bioenergies co-founder and CEO Marc Delcourt told Reuters.

Long-lasting make-up now accounts for around 25% of the global market and Global Bioenergies intends to make 300,000 products this year under the brand name "Last".

These will initially sold online at an average price of 20 euros ($24), with direct sales in cosmetic shops planned later, first in France and then in Britain.

It will start with eye make-up which has seen sales surging as people were forced to wear masks globally, Delcourt said.

Global Bioenergies initially devoted its plant-derived isobutene, an ingredient which can be converted into gasoline, jet fuel, cosmetic ingredients and plastics, to producing bioethanol, but this failed to generate profits.

The company, in which L'Oreal took a 15% stake in 2019, also aims to supply other make-up producers, Delcourt said.

It will then turn to other cosmetic products which use isododecane and hopes to go back to biofuels, notably jet fuels, at a later stage as it ramps up capacity.

Global Bioenergies mainly processes sugar beet from French sugar and ethanol maker Cristal Union. ($1 = 0.8326 euros) (Reporting by Sybille de La Hamaide; Editing by Alexander Smith)