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Furfural

Furfural is made from a variety of biomass Furfural is made from a variety of biomass (Photo: DalinYebo)
Furfural (fûr'fərəl) or furfuraldehyde (fûr'fərăl'dəhīd) is an industrial chemical derived from a variety of agricultural byproducts

Furfural ..

.. is made e.g. from corncobs, oat hulls and wheat bran and sugar cane bagasse. The name furfural comes from the Latin word furfur, meaning bran. Furfural is a viscous, colorless liquid that has a pleasant aromatic odor; upon exposure to air it turns dark brown or black. It boils at 162°C; it is soluble in ethanol and ether and somewhat soluble in water. It is one of the strongest solvents and has a flash point of 60°C. It’s risk profile is similar to dieseline/kerosene and is not dangerous to handle.

What is it used for?

Furfural ("FF") is an intermediate chemical used in the refining of lubricant oils and rosins.  It is also used as herbicides, fungicides, soil fumigants, and as a building block in the production of Lycra® (PolyTHF).

Furfural, as well as its derivative furfuryl alcohol (“FA”), can be used either by itself or together with phenol, acetone, or urea to make resins. Such resins are used in the manufacture of casting moulds, fiberglass, some aircraft components, and automotive brake linings.

Besides the conversion into FA, FF is used as an extractive solvent, motor car fuel, wax recovery, lubricant, adhesive.

By-products are used for flavours:

Diacetyl, 2,3-pentanedione, 5 methyl furfural, 2 furyl methyl ketone

Flavour enhancer for food products (NB: It is Generally Recognized as Safe (GRAS) as a food flavoring agent)

Pharmaceutical building blocks

Since 2003, new applications for the use of furfural have been developed in the bio-fuels, wood treatment, bio-plastics and agricultural sectors. These uses are further descried on the furfural markets pages.

What is Ecoral™

Ecoral™ is the DalinYebo label for furfural that is made in an environmental responsible manner, e.g. by using (award-winning[1]) technology developed and/or implemented by our subsidiary International Furan Technologies (Pty) Ltd (www.ift.co.za).

History

Johann Wolfgang DöbereinerFurfural was first isolated in 1832 by the German chemist Johann Wolfgang Döbereiner[2], who formed a very small quantity of it as a by-product of formic acid synthesis. At the time, formic acid was formed by the distillation of dead ants, and Döbereiner's ant bodies probably contained some plant matter. Other milestones:

In 1840, the Scottish chemist John Stenhouse found that the same chemical could be produced by distilling a wide variety of crop materials, including corn, oats, bran, and sawdust, with aqueous sulphuric acid, and he determined that this chemical had an empirical formula of C4H3OCHO.

In 1845, English Chemist G. Fownes proposed the name “furfurol” (furfur – bran; oleum – oil). Later the suffix “ol” was changed to “al” because of the aldehyde function. 

In 1901, the German chemist Carl Harries deduced furfural's structure.

In 1922, the Quaker Oates factory at Cedar Rapids (Iowa, USA) started a small commercial furfural production of ±2.5 tons per day.

From 1934 onwards, the industrial scale furfural production was established.

In 1944 US Government built the Memphis (Tennesseeplant to support war effort. Today, the Memphis facility no longer produces furfural, but is the home of the world's largest furfural-based specialty and fine chemicals business (PennAkem, LLC).

How is it made?

Furfural is formed from pentosan[3], a five-carbon cellulose, which occurs prolifically in natural woody products such as oat hulls, corncobs, bagasse, wood chips and other vegetable waste.  The reactions are simple.  The acidified feedstock is heated, at 100°C the pentosan is hydrolyzed to pentose[4] (xylose) a soluble sugar which is dissolved in the water located within the feedstock particle.

 

Pentosan + n.Water   

------------------------------->
Acid (Catalyst), 100°C 

Pentosan (C5H10O5 Alpha-D-Lyxopyranose)

 

At elevated temperatures the acid catalyst (H2SO4) then promotes the rapid dehydration of the pentose to form furfural.

Pentose - (3 x Water)

------------------------------->
Acid (Catalyst), >175°C 

Furfural Molecule

Although these two reactions are sequential on a molecular level, in all industrial processes they are carried out together in the same reaction vessel.

The stoichiometry of these two steps can be illustrated as follows:

(1) Hydrolysis of pentosan to pentose

Pentosan

+

n x Water

--->

n x Pentose

(C5H8O4)n

+

n x H2O

--->

n x C5H10O5

n x 132.114 kg

+

n x 18.016 kg

--->

n x 150.130 kg

(2) Dehydration of pentose to furfural

Pentose

-

3 x Water

--->

Furfural

C5H10O5

-

3 x H2O

--->

C5H4O2

150.130 kg

-

54.048 kg

--->

96.082 kg

(3) The overall reaction can therefore be summarized as

Pentosan

-

2 x Water

--->

Furfural

132.114 kg

-

36.032 kg

--->

96.082 kg

From this last step it is clear that the theoretical yield of furfural from pentosan in mass terms is

Yieldtheo = 96.082 / 132.114 = 0.7273 kg furfural / kg pentosan

Given perfect conditions, 100 kg of pentosan would be converted to 72.73 kg of furfural.  The actual yield of an industrial plant is often reported relative to this ideal yield.  For example a plant with a yield of 60 % would produce

100 x 0.7273 x 0.60  = 43.64 kg  of furfural from 100 kg of pentosan.

Reaction Kinetics

Under the conditions used in industrial processes the hydrolysis reaction from pentosan to pentose is extremely rapid and in practical terms for bagasse has little effect on the overall reaction rate.  The dehydration of pentose to furfural was studied by Root et al[5] using pure pentose in sealed glass ampoules.  Under these ideal conditions the rate of disappearance of xylose was found to be

-d[XY]/dt = 9.306x1015 x CH x [XY] x exp( -16894 / T )

where

[XY] is the xylose concentration (mole/liter)

t is the time (minute)

CH is the initial hydrogen ion concentration (mole/liter)

T is the absolute temperature (Kelvin)

While this ideal situation does not fully describe the situation in an industrial reactor, it can be seen that the reaction rate is increased by increasing the acid concentration and by increasing the temperature.  These effects are summarized in the graph below.

 Figure 1 – The effect of acid concentration and temperature on xylose disappearance

Loss Reactions

As soon as the furfural is formed, it is subject to loss reactions.  There are two principal routes to losses.  These are the resinification of furfural, where it reacts with itself to form polymers, and condensation reactions where furfural reacts with intermediates in the xylose to furfural reaction.  There are two very important considerations with respect to these loss reactions.  The first is that while they are accelerated by higher temperatures, the effect on their rates is significantly less than for the xylose to furfural reaction.  The net effect of this is that if the reaction can be performed at a higher temperature the yield of furfural is improved.  The second consideration is that the loss reactions can only occur in the liquid phase, so a general principle in increasing the furfural yield is to remove the furfural from the liquid phase as early as possible.

Characteristics/Properties

Furfural has unique physical and thermodynamic properties. They are presented in the table below and are compared against ethanol, a solvent which is rich in oxygen but does not incorporate the furan ring and benzene with no oxygen but a ring. The differences are self-evident. – Also refer to MSDS.

Properties

Furfural

Ethanol

Benzene

Formula

C4H3OCHO

CH3CH2OH

C6H6

Molecular weight

96

46

78

Density.  (g/ml)

1.16

0.789

0.879

Oxygen content.  %

33

35

0

Boiling Point. °C

161.7

78.3

80

Boiling point of azeotrope.  °C

97.85

78

69.25

Freezing point  °C

-36.5

-117.3

+5.5

Auto-ignition temperature, °C

392

422

498

Flash point.  °C

60

12.7

-11

Solubility in water (g/100 ml water)

8.3

0.082

Partial heat of solution in water.

(cal/mole)

+2938

Highly endothermic

 

-1300

Exothermic.  This value is for methanol.

Insoluble in water

Dr. Karl ZeitschDr. Karl Zeitsch emphasized that furfural is a unique chemical and used these anomalies as the foundation for his SupraYield® patents.

The furfural density is 1.16 g/ml, exceptionally high for most non-chlorinated solvents, ethanol and most others are around 0.8 g/ml.

The boiling point of 161.7°C is exceptionally high, ethanol is 78.3°C, benzene is 80°C. The furfural/water azeotrope boiling point drops to 96°C, while the ethanol and benzene azeotrope boiling points remain virtually unchanged.  The low boiling point azeotrope of furfural is of crucial importance in the operation of SupraYield® reactors and the columns.

 The flash point of furfural is 60°C as compared to 12.7°C for ethanol and -11°C for benzene. The fire and explosion risks of furfural are very low when compared to most solvents and simplifies the plant design. Flash Point temperatures above 59°C are accepted by shipping as reasonably safe to handle and are not subjected to a premium.

 Furfural is comparatively insoluble in water, 8.3 g/100ml water as opposed to ethanol and similar solvents, which are infinitely soluble in water, whilst benzene is insoluble.

The partial heat of mixing of furfural in water is endothermic, +2938 cal/mole.  As benzene is insoluble in water there is no partial heat of mixing.  By comparison methanol is -1300 cal/mole, which is exothermic.  (An endothermic compound will cool the water in which it is dissolved, exothermic compounds will heat it.) This is a unusual property amongst organic solvents.

While many of the physical properties of furfural are important in the detailed design of industrial plants, there are a few unusual properties which have a major impact on the design principles. Since its inception, DalinYebo has dedicated its time and resources in order to research and understand those properties and how they impact on the design of new processes or how old processes could be optimised.


[1] The DalinYebo Team of J. Buzzard, B. McKeon and P. Steiner, together with Professor D. Arnold (University if KwaZulu Natal) was awarded the South African Institute of Chemical Engineering (SAIChE) Gold medal in 2004 for the development of the novel SupraYield® technology.

[2] www.JWDoebereiner.de: Johann Wolfgang Döbereiner (Gemälde von Schmidt, 1825; Weimar).

[3] Any of a group of polysaccharides found with cellulose in many woody plants and yielding pentoses on hydrolysis.

[4] Any of a class of monosaccharides having five carbon atoms per molecule and including ribose and several other sugars.

[5] Referenced by Dr. K.J. Zeitsch (3 Jun 1928 - 12 Sep 2001; BSc. Eng (Chem), Doctorate in Technical Chemistry; Author of technical papers; Inventor; Holder of many patents.) in "The Chemistry and Technology of  Furfural and its many By-products", Elsevier, 2000.

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Furfural & By-products

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