Furfural
A biochemical of importance:
Current global production is about 350 kilotons, production capacity being rather higher. ..About 80% of it is currently converted into its alcohol, furfurol (usually referred to as furfuryl alcohol). ..Mainly it is used in making a binder for sand casts at iron foundries. ..However, this may soon change with it being used to make certain plastics. [more on this below]
All furfural production worldwide is from plant materials, none coming from fossil materials. As the available supply of raw material varies from year to year for each producer, the amount of furfural produced therefore varies and is some degree short of a plant’s maximum output capacity.
For nearly a century now furfural has been made on an industrial scale by an acid digestion of oats hulls, maize cobs, sugar cane bagasse and similar materials. ..These all have a goodly amount of xylan, a pentose sugar polymer, each unit of which is a five~carbon molecule. ..Various lengths of this polymer are herein referred to as xylans.
A mineral acid such as HCl is usually employed, though even acetic acid will do under certain conditions.* The acid digest first breaks the polymer down, then converts each of its units into furfural, and in doing so creates three molecules of water.
The maximum theoretical yield of furfural from xylans is ~70%, though a practical yield of about 60% may be expected. ..A byproduct of the acid digest is acetic acid, which comes from an acetyl side group split off from the xylan polymers. ..Pectin treated similarly also yields furfural, as will the polyuronic polymers found in some kelps. ..Sunflower heads have quite a bit of pectin, as does sugar beet pulp.
*{note:_ One of the largest plants anywhere does this, relying on the acetic acid produced to effect the production of furfural. I believe it is the large producer in South Africa who does this.}
Commercial Production
HCl is readily obtained from chlorine gas on damp material, which it bleaches and in the process creates the acid. ..Chlorine gas is usually obtained by an electrolysis of NaCl or KCl salts and is easily transported, so the electrolysis need not be done on site.
One way to make furfural is to use dilute HCl in very salty water with much immiscible solvent present to absorb the furfural as it is formed. (It tends to form a useless resin in the acidic conditions, this accounting for the yield being well short of the theoretical.)
The digest is typically conducted under pressure at an elevated temperature. …However, it may be done at atmospheric pressure, though more time is required for a reasonably complete reaction. ..But equipment costs are then less.
The yield is higher by having a low percentage of xylans in the digester, ..and higher also by circulating the solvent so as to remove furfural from the digester continuously or frequently, and then separating it from the solvent. ..Feeding the unit continuously with small amounts of xylan material works well in obtaining a higher yield of product.
Industrial furfural production began circa 1922 in the USA by the Quaker Oats people from oats hulls as the raw material. ..They did not bother separating the xylans but used the hulls themselves, which meant the cellulose content of the hulls became unusable as a feedstuff. ..They later had another plant based on maize cobs as such, the xylans in them not being extracted first. Other materials were also used.
However, thanks to the stupidity of so~called ‘free trade’ treaties, the US apparently no longer produces any furfural — doctrinaire orthodox economics at its worst. ..Imports from South Africa, the Dominican Republic, and usually also China are now the sources of its supply.
China has several furfural plants based on maize cobs. A new plant based on maize cobs came on stream in Kenya in 2018 with an annual design capacity of 5000 tons of furfural. ..Spain and Italy also produce furfural. ..So could many ethanol from grain fermenters in the USA and elsewhere, by adding on furfural production from maize cobs. …see item on this website Maize as Cobcorn.
Today, sugar cane bagasse is the raw material for several plants producing furfural, which is their stocks after the sweet juice has been extracted. ..A large plant in the Dominican Republic can produce 35 kt/a. ..Few plants, if any, are larger, though one in Australia perhaps is. ..Those in India are smaller –more normal in size, so to speak. ..The size of plant is limited by the amount of raw material available at the site, and the handling of it.
Cereal chaffs from wheat or barley would be equally suitable for making furfural, and were they gathered in quantity could be the basis for an industrial plant. ..This could be done by changing how such grains are harvested. _see item: No Combine Prairie Harvest
Removing xylans from the chaff under mild conditions with HCl would preserve the cellulose as a feedstuff for ruminant livestock, or for an industrial ferment. NaOH could be used instead of acid to make the feedstuff, but I won’t go into that here.
Some uses of furfural …
Furfural has several uses, some 80% being made into its alcohol, which is used mainly to make a binder for sand casts in foundries. ..Furfural is also made into the solvent THF (tetrahydrofuran) by hydrogenation of furan, itself readily made from furfural. ..As THF is miscible with water and breaks down in the environment, it is the preferred carrier for agricultural crop sprays.
A rather inert black plastic was made in quantity from furfural in the old Soviet Union. Several different dark plastics can be made, all fairly inert and unaffected by most acids or other chemicals. As such, they make good counter tops in chemistry labs.
As for potential uses, an analogue of styrene can be made from it by treating furfural with acetic anhydride and then heating it slowly to release a molecule of carbon dioxide. ..This is called furan~ethylene or vinyl furan, ..but could also be called ‘furene’ to indicate it may be substituted for styrene in most of its uses. ..Mostly, it would be used to make plastics. ..Of course, industrial scale of production would differ from the above laboratory process.
Most promising is the polymer PEF (polyethylene furanoate) which substitutes for the widely used PET (polyethylene terepthalate). .Plastic drink bottles are made of PET, but are fossil chemicals, whereas PEF can be entirely made from biochemicals.
Because many furan chemicals may be entirely made from renewable materials rather than from fossil sources, this may be a sufficient marketing advantage for them to be chosen despite usually costing more {today} than chemicals made from fossil fuels.
But that is under current regulations, and governments with some foresight — rare as they may be — can change things, aiming at reducing the use of petrochemicals. ..Climate change scenarios seem finally to be spooking politicians and their civil service advisors into action about lowering ‘green house gases’ in the atmosphere, so change is in the air, so to speak.
An analogy may be made regarding the banning of child labour in most places, another case where price was not allowed to be the sole consideration. Much to the dismay of some doctrinaire economists at the time who hated any such ‘interference’ in “the market” (an abstract concept).
Economists are often rather reactionary when it comes to social change. ..It is an indicator that they treat their subject like a quasi religion, with individualism its sacred core. ..And as with any religion it has its extremist fundamentalists, some of whom regard the ‘perfectly competitive market model’ as an ideal against which to measure deviations from it. ..Of course, they recognise it is impractical in practice, nonetheless they deride any actual market as exhibiting some degree of ‘market failure’ ..for not being ‘perfectly competitive’. …In short, any capitalist market economy is then comprised of failed markets and must thus be itself a failure. ..Such is their extremist rhetoric. ..Idiotic nonsense.