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The History of Alginate Extraction by Jim Bailey

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The discovery and manufacture of Alginates in The United Kingdom. The following essay is an account composed and written by Jim Bailey, who with his kind permission has allowed us to publish on Grace's Guide.[1][2]


1883. E. C. Stanford first isolates algin or alginic acid and was later dubbed “the father of seaweed research".

Early 20th century. The British Algin Company started producing alginates in North Wales.

1910. Liverpool Borax Company started production.

1930’s C. W. Bonnisken and others form a company called Cefoil and start producing alginates at Bellochantuy in Kintyre Argyll.

1939. At the outbreak of war the Ministry of Supply take an interest Cefoil to produce scarce raw materials. Three other factories were built at Kames and Barcaldine in Argyll and Girvan Ayrshire. The most well known war time product was chromium alginate, used for camouflage netting as a replacement for scarce Indian hemp.

1942 Bellochantuy closed.

Post 1945. Cefoil changed its name to Alginate Industries and bought the 3 factories from the government.

1950’s Kames closed concentrating production at Barcaldine in Argyll and Girvan in Ayrshire.

1950’s 60’ 70’s Alginate Industries continued to grow and prosper. New sources of seaweed had to be sourced to augment supplies from Scotland and Ireland. These sources included Norway, Iceland and seaweeds from Chile and Tasmania. The company seriously considered opening a factory in the Falkland Islands to harvest the vast beds of Macrocysits pyrifera which grows in profusion around its coast. In 1973 the workforce at Girvan numbered 650 and at Barcaldine 250.

Late 1970’s. Increased completion from China sees a severe loss of market share.

1979. Alginate Industries taken over by its largest competitor Kelco Company of California to become Kelco/AIL. This was followed by a period of rationalization and the workforce trimmed back to reflect a reduced level of sales and prosperity.

1995. Merck sells its Kelco division to Monsanto. Which includes both its Alginate and Biogum Interests.

1980-1996 Kelco/AIL and then Kelco International rode the peaks and troughs of a very competiveness business culminating the closure of the Barcaldine Plant in December 1996 with the loss of all the 80 jobs on the site.

1997. All alginate production in Scotland is concentrated in Girvan Ayrshire and in San Diego California.

1999. Monsanto sells the alginate section of Kelco to ISP (International Speciality Products)

2006 The alginate plant is San Diego is closed with all alginate production being centred in Scotland except for some speciality products like Propylene Glycol Alginate which is contracted out.

2009 ISP sell the alginate business to FMC and become part of Pronova the Norwegian alginate producer which they had acquired previously.

2009 Pronova stop producing alginate at the Girvan site and concentrate all alginate manufacture at their plant in Norway. The Girvan plant now only handles blending and distribution. At this point the workforce in Girvan numbered around 200, 60-70 jobs were retained with about 145 people being made redundant.


Alginates are polysaccharides which are extracted from brown seaweeds; the polysaccharides is a combination of Mannuronic and Guluronic acid and is commonly known as alginic acid which is the main carbohydrate component of brown seaweed. Although many species of brown seaweed contain alginate only a few of these contain alginate in significant amount to make them commercially viable for processing.

Alginates were manufactured in The United Kingdom (Scotland) from the 1920’s until 2009. The first company to start production was called Cefoil changing its name in 1945 to Alginate Industries. As a result of a takeover its name was changed to Kelco/AIL and then again to Kelco International. There were further sales/acquisitions of the company with a name change to ISP Alginate before being again bought by FMC and further rationalization brought an end to production in Scotland in 2009

The seaweeds which were principally used in Scotland for the manufacture of alginates were: Laminaria hyperborea. (Scotland Ireland) Ascophyllum nodosum. (Scotland, Ireland, Iceland, Norway) Ecklonia Maxima. (South Africa). Bull Kelp. (Tasmania) Lessonia negrescens and Flavicans. (Chile) Macrocystis pyrifera (California).

Alginic acid along with its divalent and polyvalent salts (e.g. calcium alginate) is insoluble whereas the alkali metal salts of alginic acid namely sodium alginate and potassium alginate are soluble in water. Depending upon the degree of polymerisation of the alginic acid the alkali metal salt can give solutions of varying viscosity. Sodium alginate is the main alginate produced and sold however other alkali metal alginates are produced depending upon its application. Alginic acid can also be esterified with propylene glycol to produce propylene glycol alginate which has value in food and brewing as it can function in much lower pH conditions than sodium alginate for example. Commercially produced alginate is pale buff to white in colour and is milled to the customers required particle size distribution.

The company was managed from a head office in London with an Applications/Product R&D facility in Tadworth Surrey. Later and due to rationalization the London office was closed and moved to Tadworth. There were 2 manufacturing sites, Barcaldine north of Oban in Argyllshire and Girvan in Ayrshire. Girvan also handled product warehousing and despatch to customers.

Production of Alginates

Depending upon the type or species of seaweed used to produce the end product, will determine the functionality and behaviour of the final alginate in its application. This is explained in the proportion of mannuronic to guluronic acid in the raw weed. For example Laminaria hyperborean has a higher proportion of guluronic to mannuronic acid and the sodium alginate from this source will exhibit a high gel strength when used in its final industrial application. Whereas the sodium alginate from Ascophyllum nodosum which has a much lower proportion of guluronic to mannuronic acid will have a much higher viscosity when dissolved in water and will principally be used for its thickening properties, colloidal properties, film or gel formation.

Seaweeds used in Scotland were dried and milled prior to be shipped to the manufacturing sites. Other manufacturers processed their seaweed wet and fresh from the ocean so to speak, however this is not the scope of this article. Ascophyllum collected in Scotland and Ireland was dried using fossil fuels to about 10% moisture. Laminaria which lent itself to drying in the sun and wind to about 20-30% moisture. All southern hemisphere seaweeds from Tasmania, Chile etc. were dried in the open air. All seaweeds were coarse milled to less than 2.4mm or finer to aid extraction.

Extraction of sodium alginate from the seaweed by alkaline hydrolysis

A certain weigh of seaweed either as a single species or a mixture of species was mixed with hot water at 75-800C in a reaction vessel to which a quantity of sodium carbonate was added. The resultant mix was reacted for 3-4 hours with constant agitation by which time the sodium carbonate had reacted with the alginate in the seaweed to produce a thick viscous paste made up of alginate in solution along with seaweed particles. This viscous paste was transferred to another reaction or slurry vessel, diluted with cold water and agitated for 2 hours to aid further alginate extraction and obtain a homogenous mix of alginate solution and seaweed solids.

Phase separation of the extracted sodium alginate liquor from the spent seaweed

At the end of the 2 hours a polyectrolyte was added and the seaweed slurry was pumped to a settling tank where it remained for a length of time until all the seaweed solids had flocculated and settled to the base of the settling tank leaving sodium alginate liquor as the supernatant.

At the Barcaldine alginate factory a novel continuous settling system was in operation until the factory closed in 1996. This operated in similar fashion to the clarifiers used in water treatment but at a much higher viscosity. Seaweed/alginate slurry was mixed with polyectrolyte and sand. Flocs were formed with sand particles attached. This mixture was gravity fed to a continuous clarifier with the solids free alginate liquor overflowing the top of the vessel and going forward for further processing. The seaweed particles and sand were continuously pumped from the base and the sand was recovered be for reuse.

The sodium alginate liquor from either the batch settling or continuous settling was pressure filtered to remove any extraneous particles of seaweed that had not been removed by flocculation and settling. After filtration the sodium alginate liquor is a brown, slightly viscous, translucent liquid containing about 0.3-0.4% sodium alginate at a pH of just over 10. The sodium alginate liquor was then bleached and the colour changed from brown to “pale straw” in appearance.

Precipitation and purification of the sodium alginate liquor into insoluble calcium alginate and its recovery by air flotation

The bleached liquor which had a pH of about 10 was neutralised to pH 7-8 with dilute sulphuric acid. (This was to prevent the formation of insoluble calcium carbonate during the precipitation process which followed.) The sodium alginate liquor was pumped, air was injected in-line and the aerated liquor was reacted with calcium chloride solution. Sufficient calcium chloride was added to ensure that a precipitated calcium alginate fibre is formed and not just a calcium alginate gel.

The aerated calcium alginate fibres floated to the top of the reaction vessel and were removed by rotating arms. The calcium alginate fibres were about 10% dry solids at time of recovery and were then fed through de-watering screw presses to produce a fibre of about 28-40% dry solids.

Further purification and the removal (leaching) of the calcium with mineral acid to produce alginic acid

Up until the 1980’s this was a batch process whereby the calcium was removed from the calcium alginate by leaching with hydrochloric acid and intervening water washes. The fibre colour was improved by the use of sodium chlorite and or sodium hypochlorite bleach. The calcium content of the calcium alginate was around 8-10% and the stage wise leaching with acid reduced it to 0.4% or lower in the final alginic acid.

A continuous process was developed where the calcium alginate fibre was leached with sulphuric acid (almost 50% of the cost of hydrochloric) in a series of treatment/dewatering/washing /dewatering/treatment/dewatering steps etc. Leaching removal of calcium with hydrochloric was relatively trouble free as the calcium removed was soluble calcium chloride in the wash water. However calcium removed by sulphuric acid results in calcium sulphate a sparingly soluble salt. The trick in using this process was to critically maintain the pH of the reactant acid stages between 2.1 and 1.7. At these pH levels the solubility of the calcium sulphate is maintained and it was washed out in subsequent water washes.

Pressing of alginic acid and conversion back to sodium alginate, drying and milling

The leached alginic acid which was a watery pulp at this stage was fed to a screw press where it was dewatered to about 60-70% moisture. The alginic acid was fed to a batch dough mixer where it was converted back to sodium alginate with sodium carbonate to a pH of 5-7 or per perhaps 7-8.5 depending upon the application of the final alginate. Other chemicals were also added at this stage if required, depending upon the final use of the product. e.g. citric acid, sodium sulphate, sugar. The converted sodium alginate was fed to a dryer to produce a coarse buff coloured granules of about 10-12% moisture. The coarse dried alginate granules were milled and sifted to specific particle sizes, again depending upon customer requirements and specifications. e.g. 100% thro 250micron all on 180 or 150micron.

Humidification and blending

All product sold had its moisture content adjusted to 20% moisture before despatch. In some cases different batches product had slightly different viscosities, or gel strengths for example and they were blended together to produce a product which met the customers specifications in terms of viscosity, gel strength or other functionality parameters.

Applications of Alginates

Property Use Reason for use
Viscosity Controlling viscosity of food products.

Thickening textile printing pastes.

Alginates are edible.

Easily washed out.

Colloidal Properties Stabilising ice cream.

Beer foam stabilisation/ Stabilises edible emulsions.

Prevents phase separation and formation of ice crystals.

Compatible with low pH.

Formation of films and fibres. Sausage casing.

Calcium-sodium fibres./ Wound dressing.


Haemostatic and adsorbent.

Gel formation Milk desserts, confectionary, pet food.

Dental impression powder.

Can be made in the cold./ Stable.

Used in the cold.

Film formation and binding. Binding pharmaceurical tablets.

Surfaces, sizes and coatings.

Disintegration on wetting.

Controls penetration.

See Also


Sources of Information

  1. Properties of Alginates. R.H. McDowell
  2. The Development and Demise of Alginate Production in Argyll. Private publication produced to mark the closure of the Kelco Alginate Barcaldine Plant in 1996.