From E. Boullanger: Distillerie Agricole et Industrielle (Paris: Ballière, 1924).
Translation from the French by F. Marc de Piolenc (email@example.com).
THE idea of extracting alcohol from wood by subjecting the latter to hydrolysis and fermentation is quite old. As early as 1819, Braconnet had published a memorandum on this subject. Since that time there have been numerous attempts at wood distillation, and these have given rise to the issuance of many patents.
In 1894, Simonsen had recommended the treatment of sawdust with dilute acids at high pressure. His process, which allowed 7.5 to 9 liters of 100-degree alcohol to be obtained per 100 kilograms of dry wood, did not, however, become an industrial process because of excessive dilution of the saccharine juices.
Beginning in 1899, Classen studied the hydrolysis of wood and recommended certain working processes. His method consisted of using sulphurous acid as a hydrolyzing agent. The sawdust is soaked with a saturated solution of sulphurous acid at the rate of 3 per cent of the dry weight of the wood. Heating is then carried out to 150 degrees under 7 kilograms of pressure for 4 to 6 hours; the residue is extracted by percolation and the saccharine juices are fermented after neutralization.
This process, which has been applied in America, was later abandoned there because of corrosion of the apparatus, the difficulty of stripping and the consumption of coal and sulphurous acid.
Roth uses sulphurous or hydrochloric acid at the rate of 3% to 4% in the presence of ozone, at pressures up to 20 atmospheres. According to data in the patent, 34 kilograms of fermentable dextrose is obtainable per 100 kg of pine wood.
Koermer did not observe the favorable action of sulphurous acid noted by Classen. He noted, on the contrary, that adding oxydizing agents reduced the yield of sugar, except in the case of hydrogen peroxide.
Beginning in 1910, Tomlinson implemented on a large scale, in America, the manufacture of alcohol from sawdust. The process used at the Georgetown works is the following: pine sawdust is placed in rotatory digesters made of sheet steel lined with ceramic tiles, along with dilute suphuric acid. Heating is accomplished with direct steam injection, under pressure, for one hour. The steam is exhausted and partially condensed to recover spirits of turpentine (200 to 300 grams per tonne of dry wood). The sawdust is then extracted in a diffusion battery, pressed and used as fuel. The juice obtained is partly neutralized, filtered, cooled and sent on for fermentation. This is accomplished by first preparing a yeast culture with malt and barley, then propagating the yeast thus obtained in a cooled decoction of malt sprouts in the saccharine juice. After development, the yeast is used for inoculating the saccharine juice in the fermentation vats. Industrial yields, under normal conditions, reach 7.3 liters of 100-degree alcohol per 100 kilograms of dry wood, and the factory's annual production is 20,000 hectoliters of alcohol.
In France, alcohol manufacture from sawdust was studied and implemented industrially in a distillery in the Ardèche region, before 1914.
During the war, the question of wood-alcohol manufacture was again taken up in the light of the need for alcohol for national defense.
Dubosc's research led to the following conclusions:
- In saccharifying sawdust with 2 parts of sulphuric acid (90-95% H2SO4) per 100 parts of dry sawdust, maximum yield is obtained with a pressure of 7.5 atmospheres; yield decreases above or below this pressure.
- Conversion takes place as soon as 7.5 atmospheres is attained; in fact, maximum yield occurs within 15 minutes.
- Increasing duration does not increase sugar content, but rather reduces it; the sawdust is attacked and noxious secondary products are formed.
- With pine sawdust, yields of 22 to 23% sugar are obtained, giving on average 100 to 115 liters of 95% alcohol per tonne of wood treated.
- Besides sugar, acetic acid is produced at the rate of 1.4% of the wood treated; also formic acid. The latter acid is produced in quantities that increase with the duration of cooking at 7.5 atmospheres, and this fact is very important, considering the adverse effect of formic acid on alcoholic fermentation.
In Germany, production of wood alcohol was accomplished during the 1914-1918 war with either the Classen or the Windesheim-ten-Doornkaat process. In the Classen process, the process underwent a few modifications which make it a little different from the one that we described above. The heating of the sawdust is carried out for 40 minutes in rotatory autoclaves, with suphurous acid, at a pressure of 7 kilograms (165 deg). The steam is then expanded as rapidly as possible and the mass is emptied into diffusers. The juice that is obtained is neutralized, nutritive salts are added and fermentation is started with pressed yeast. Yield is from 8 to 11 liters per 100 kilograms of dry matter.
In the Windesheim-ten-Doornkaat process, the sawdust is heated with dilute hydrochloric acid in the presence of catalysts (metallic salts), in rotatory autoclaves, at 7 to 8 atmospheres for 20 to 30 minutes. Yield is 6 liters of alcohol per 100 kilograms of dry matter, but it is surely possible to improve this.
A new process, the Prodor process, is based on the hydrolysis of sawdust by cold hydrochloric acid, which considerably reduces the destruction of glucose during hydrolysis. The process is continuous and allows almost complete recovery of the hydrochloric acid that is used. The yield is said to be 250 liters of 100% alcohol per tonne of dry sawdust. In addition, the mash still contains non-fermentable pentoses, which can be converted to furfurol [sic], and lignin which, by dry distillation, gives as much methyl alcohol as would have been derived from all the wood from which it was extracted: as a matter of fact, we know that cellulose does not yield methyl alcohol on distillation.
This process is still too new to allow its results to be judged.
It does not seem possible, however, for the wood alcohol production industry to exist outside of enormous forestry centers such as exist in America, capable of furnishing large quantitiies of sawmill waste throughout the year. Such conditions seem difficult to realize in France.
In additions, alcohol yields are very low compared with what they could be. Fermentable sugar comes generally from hydrolysis of cellulose, and the observations of Wilkening and Ost, as well as those of Willstoetter and Zechmeister, have shown that pure cellulose can be saccharified by concentrated acids, with a sugar yield of 106 to 107% of the weight of the cellulose employed, which represents 95 to 96% of the theoretical yield. The alcohol yield of wood by hydrolysis is thus minimal compared with the quantity of cellulose that it contains.
Wood alcohol is in any case more expensive than alcohol from sulphite, which we will consider.
Production of this wood alcohol could only become economical if the wood, after decomposition, could be used for extraction of acetone and methyl alcohol by distillation, as intended in the Prodor process.
Alcohol from Sulphite Liquors
In cellulose factories, shredded wood is boiled under pressure with an aqueous solution of calcium sulphite to purify the cellulose contained in the wood by elimination of the matter that impregnates it. The sulphite liquor gradually takes on solubilized products: once cooking is complete, the used liquor is discharged and it can constitute a considerable feedstock for the production of alcohol, because on average 6 cubic meters of waste liquor is obtained per tonne of cellulose. This utilization of liquors for the production of alcohol is all the more interesting because their discharge often entails serious problems for cellulose producers.
We borrow the following details pertaining to this method of alcohol manufacture from a well-documented work by Mr. Henri de Boistesselin, professor at the Chemical Institute of Rouen, which appeared in the Moniteur Scientifique for 1922.
Much research has been carried out for producing alcohol from sulphite liquors. Results of the first studies by Mitscherlich, by Sixeen Sandberg, by Lindsey and Tollens gave only little satisfaction. Research by Wallin, then Ekstrom were more successful, and beginning in 1912 the Skutkär and Donnarspet factories in Sweden produced 8000 liters of 50-degree alcohol daily by the Ekstrom process. This industry was much developed in Sweden since that time; currently, 22 factories in that country make sulphite alcohol and their production exceeds 20,000,000 liters of 100% alcohol.
In Germany, the sulphite alcohol industry was established during the war, in 12 cellulose factories that produce a total of 11,600,000 liters of alcohol.
In the United States, the development has been slower: only two factories exist, with a total production below 100,000 hectoliters. In France, no cellulose factory produces sulphite alcohol. Yet the sulphite cellulose production capacity in France is 60,000 tonnes, which would allow manufacture of 24,000 hectoliters of 100% alcohol, and we are forced to purchase overseas 200,000 tonnes of pulp, corresponding to 81,000 hectoliters of alcohol. If we were to produce all the pulp that we need, it would be possible to manufacture by this means 105,000 hectoliters of alcohol. Such a development of the cellulose industry seems perfectly achievable, expecially when alcohol production based on waste liquors is included. At present, the cellulose factories established in France do not produce sulphite alcohol because the economics of the process requires factories with a capacity of 30,000 tonnes of pulp per year, capable of supplying more than 12,000 hectoliters of 100% alcohol. The German factories are of this type, while France has no units of this kind.
It seems, however, that even installations with a production capacity of 10,000 to 12,000 tonnes per year could still consider producing sulphite alcohol, as is done in Sweden by factories of like capacity.
Sulphite alcohol results from fermentation of sugars contained in the waste liquors. These liquors contain, at the end of the "cook," about 100 grams of organic matter per liter, including 16 grams of fermentable sugars and 9 grams of non-fermentable pentoses. This composition is variable, depending on the type of cook and the loading density of wood per volume of liquor. The methods used for making sulphite alcohol are of two main types: the Swedish method with the Wallin, Ekstrom and Landmarck processes, and the American method with the Marchand and McKee processes. A characteristic of the Swedish method is the prior elimination, by chemical means, of the sulphurous acid in the liquor, while the American method uses heating and air injection for the same purpose.
In the Wallin-Ekstrom processes, the liquors coming from the digesters are neutralized with slaked lime and sodium carbonate, in large reinforced concrete vats. They are then allowed to flow into graduation towers where aeration oxydizes the organic matter, enriches the liquid in oxygen necessary for the life of the yeast, cools the liquid from 90 degrees to 30-35 degrees and concentrates it from 2.5 to 8%. Excess lime is eliminated by decantation and the clear liquid, containing 23.8 g. of sugar per liter, is pumped into reinforced concrete fermentation vats provided with heating coils and sterilized air injection devices.
Inoculation is carried out with vat residue based on spent malt; fermentation lasts six days at a temperature of 27 to 32 degrees. This duration can be reduced to three days by adding ammonia salts to the liquor, before starting fermentation. The yeast is then separated and the liquid, which measures 1.15 alcohol content, is sent on to distillation.
In the Landmarck process, whey is added to the liquor before neutralization. By this means, it is no longer necessary to acclimate the yeast to living in the sulphite liquor to achieve fermentation.
Alcohol yield at 93 degrees is 8 to 10 liters per cubic meter of liquor. In 1914, the cost of 100% alcohol for a 2,000 liter per day factory was 0.325 francs, or 0.293 francs for 90% alcohol, including manufacturing rights, patent royalties, amortization and general overhead. The cost of manufacture itself made up 17 centimes [0.17 francs] of this total. Currently, the accounting cost, for the same unit, comes to 0.412 francs per liter.
The American processes still seem too recent to allow an evaluation to be made of them. In the MacKee process, free sulphurous gases are eliminated by boiling the liquor while running a stream of air through it until the sulphurous gas content does not exceed 0.35 grams per liter. This operation is long and tedious. Cooling to 27-28 degrees is then carried out, yeast is added and air is injected during fermentation. In semi-industrial tests, a yield of 95% alcohol of 0.55 to 1.35% of the original volume of the treated liquor was obtained.
In the Marchand process, the liquor is admitted to a flow gauge/reheater after adding sulphuric acid and eliminating the precipitated sludge. The temperature of the liquor is held below boiling; then it is admitted to an evaporator under vacuum where part of the sulphurous gas is again released; the liquor then passes to another evaporator, where it is kept at a still lower pressure under higher vacuum. The juice is finally treated with an oxydizer to transform the remaining free sulphurous into sulphuric acid; then it is sent on for fermentation. Marchand claims to have obtained 1.25% of alcohol by volume.
Under the press of circumstances created by the war, manufacture of alcohol from sulphite liquors was also achieved in Germany by the following process: first acetic and formic acids are eliminated by blowing air into the liquor, which is heated to 85-90 degrees, and by adding calcium carbonate and a little slaked lime. This operation, which is intended to bring the mass to a degree of acidity low enough to allow fermentation, is performed in concrete containers, called neutralization towers, in which the liquor is allowed to remain for a few additional hours to allow it to clarify. The liquor, separated from the sludge, then undergoes a second clarification in a reservoir supplying the fermentation vats. The liquor is then sent to an air-cooled concentration tower in which it is cooled, saturated with air and concentrated to a certain extent. Fermentation occurs in large vats of 1,000 hectoliters capacity using a very active yeast gradually acclimated to the unusual medium constituted by the bisulphite liquor.
Either ammonium sulphate, or superphosphate, or yeast extract which is prepared in the liquor distillery from excess yeast, is added. Fermentation occurs at 29-30 degrees; it requires 72 hours on average and produces 9 to 9.5 liters of alcohol per cubic meter of waste liquor.
The distillation of the fermented juices requires distillation apparatus specially configured for the treatment of juice with a low alcohol content (0.9 to 0.95%); it must take place in the presence of sodium carbonate, which is used to retain the volatile organic acids.
The alcohol thus obtained sometimes still contains a little sulphurous acid. It differs from other crude alcohols only in its relatively low methyl alcohol and aldehyde content. It is much improved by distillation apparatus which separates the heads in order to obtain, by separating head products amounting to 10% of the total, a sulphite alcohol suitable for denaturing, and other head products to be purified.
The manufacture of sulphite liquor alcohol is therefore particularly attractive, and it is to be hoped that this source of alcohol will be used in France where it could yield yearly, as we have seen, 100,000 Hl of alcohol for industrial use. Concentrating the lees from the sulphite mash and treating it to obtain methyl alcohol, acetone, acetic acid and cellulose pitch by dry distillation would allow a reduction in the cost of production and in the cost of this sulphite alcohol.
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