WO1982001902A1

WO1982001902A1 - A process for pulping wood and bark in formic acid

Info

Publication number: WO1982001902A1
Application number: PCT/US1981/001627
Authority: WO
Inventors: Robert K Jordan
Original assignee: Robert K Jordan
Priority date: 1980-12-05
Filing date: 1981-12-07
Publication date: 1982-06-10
Also published as: EP0065984A1

Abstract

A process for pulping wood and bark in formic acid of at least 35% concentration, ideally at 65% to 90%, refluxing at atmospheric pressure, to produce wood and bark pulp of high hemicellulose content and very high holocellulose yields and resulting in a liquor of very low carbohydrate content which on recovery of the formic acid leaves a low molecular weight, less than 1,000, lignin; the wood pulp is useful in the paper industry and as an animal feed, the bark pulp is an ideal ruminant feed, replacement for tobacco in pipes, cigarettes and cigars while the lignin may be employed as a base for polyols or dealkylated or hydrodealkylated to phenol, substituted phenols and benzene.

Description

FORMIC ACID PULPING Technical Field

This invention relates to digesting wood and bark in formic acid of atleast 35% concentration to produce wood pulp, bark pulp, lignin and lignin based chemicals including benzene, phenol and polyols. Background Art

Wood is conventionally delignified in aqueous alkaline medium by the kraft and soda processes that require pulping temperatures of over 150°C, give poor yields of pulp of typically 42% to 50% based on dry wood weight result in a high molecular weight modified lignin condensation product and is often malodorous. Thus the kraft process employs a mixture of aqueous sodium hydroxide and sodium sulfide at about 170°C/10 atmospheres for 2 to 3 hours to result in pulp yields averaging 47% and is accompanied by sulfide odors. The spent liquor from the process is comprised of sodium salts of lignosulfonates, glucose and sugars from hydrolyzed cellulose and hemiceilulose, and residual inorganic chemicals. Because of the high cost of the raw materials, NaOH and Na₂S, it is desirable to effect their recovery, hence the spent liquor is concentrated by evaporation to about 65% total solids and burned to an inorganic melt which is dumped into water and treated with lime to precipitate calcium carbonate from the recycle regenerated pulping solution. The soda process is quite similar.

Wood pulp is widely employed in the pulp and paper industry, by far most used in the production of paper and cardboard, but there are numerous other uses. Indeed, wood pulp has been used to feed ruminants. Bark is a major byproduct of pulping; it has a few minor uses and for the most part is burned as a poor fuel.

The lignin now recovered from the conventional wood pulping processes is largely burned because it is difficult to recover economically and is rather intractable because of its very high molecular weight and chemical modification. For examples, as it is in alkaline spent liquor it is necessary to employ an acid which may be costly in terms of both that of the acid itself and the loss of sodium which reacts with the acid, i.e. sodium ion. Neutralization or acidification precipitates the highly condensed high molecular weight lignin from the spent liquor, leaving a solution of some sodium salt, usually sodium sulfate, and glucose and sugars that resulted from the hydrolysis of the mostly hemicellulose present in the wood. As the lignin is highly condensed to high molecular weight and, in the case of the kraft process, further ified by sulfide groups it is difficult to degrade; hence relatively useless. Disclosure of the Invention

My invention is a process for digesting wood and bark to the corresponding pulps in formic acid of ideally 65% to 90% concentration at its refluxing temperature, about 100°C, and further ideally using a surfactant and agitation to effect largely delignified pulp in about 1 hour to result in a some 70% yield of pulp and a liquor of essentially lignin in formic acid. Practically all of the formic acid is easily recovered, for example by distillation, and the surfactant by minimal water extraction, leaving a low molecular weight lignin that is quite soluble in many solvents and easily hydrodeal kylated to benzene and phenol, or dealkylated to phenol and substituted phenols. Thus in producing a ton of pulp only about 1.4 tons of wood is required, a savings of about 1 ton/ton of pulp; very little of the very cheap formic acid is consumed and under very mild conditions with little energy consumed in its recovery. Bark pulp made by the process is an excellent ruminant feed and further an excellent replacement for tobacco as a smoking material.

The formic acid can be made from essentially carbon monoxide and water via methyl formate , as carbon monoxide is becomming widely available via coal gasification and no doubt will become even more available with the development of the oxygen-blown, coal fired blast furnace process. Formic acid is usually obtained as 88% or 90% formic acid, the remainder water which is the preferred diluent for the formic acid employed in the process; although essentially pure formic acid may be employed, and the concentration may be as low as 35%, the preferred concentration range is 50% to 90% while the ideal ranges from about 65% to 90%.

Both soft and hard-woods may be used in the process, for examples Douglas fir, loblolly, oak, poplar, ash, maple and cherry. The weight ratio may range from 2:1 to 1:20 dry wood :mediurn, ideally 1:3 to 1:8. Usually the softwoods are somewhat more difficult to pulp while the hardwoods pulp very rapidly.

The temperature of the del ignification may range from about 20°C to about 180°C, preferably from about 50°C to about 150°C and ideally from about 80°C to 130°C. Indeed, wood can be easily pulped in 75% formic acid at refluxing while at atmospheric pressure, about 100°C, with agitation in about 3 to 4 hours. Clearly it is a very substantial economic advantage to operate at atmospheric pressure as compared to some 10 atmospheres now employed by the conventional processes at much higher temperatures, 150°C to 180°C. And the yields by my process are, under such conditions, usually over 70% which indicates a very high selectivity of formic acid for dissolving out the lignin. Only smallish quantities of glucose and sugars are found in the the liquor after removing the pulp, mostly from sap.

By adding a surfactant the rate can be greatly accelerated, only about one hour required instead of the 3 to 4 without the surfactant under the conditions noted above using hardwoods. At temperatures above 100 the time decreasing with increasing temperature. But of course this entails pressure apparatus above a few tenths beyond atmospheric pressure. At 130°C the rate of pulping is quite rapid but a slight decrease in pulp yield is noted; and with increasing temperature the loss in yields of pulp become considerable as evidentally hydrolysis becomes an increasing factor. Indeed, at 150°C the yield of pulp is still well above that of conventional pulping processes but probably only because the pulping time is so short.

Tree bark is readily pulped under about the same conditions as are employed for wood. Usually bark pulp is of shorter fiber length and quite dark in spite of the very extensive delignification. As measured by the the so-called "K" number both wood and bark pulp are very low, but bark pulp is not bleachable to while by smallish amounts of bleaching agents. The use of surfactants has about the same effect on bark pulping as on wood pulping.

Practically any of the common and even uncommon surfactants may be employed to accelerate the process very substantially, such as anionic, cationic, amphoteric and nonionic surfactants may be used. Examples include sodium dodecylbenzene sulfonate, sodium lauryl sulfate, cetyltrimethylammonium bromide, alkoxylates nonylphenol, e.g. C₉H₁₉C₆H₄O(C₂H₄O)₉H, and perfluoroalkyl-alkyl cationic, anionic, amphoteric and nonionic surfactants. The concentrations of surfactants vary with the kinds employed and range from about 0.1% to about 5% for effectiveness although larger concentrations may be used, but wastefully. Some interesting facts regarding surfactants were noted, quaternary ammonium salts work best with pines, especially loblolly, although the more expensive prefluoroalkyl-alkyl compounds do well.

The rate of pulping wood and bark is affected strongly by agitation at these and intermediate temperatures. At high temperatures the, formic acid-surfactant medium readily pulps without any agitation, but at lower temperatures the need for agitation, especially mechanical stirring or some kind of mixing becomes evermore greater. Probably this is a function of the decomposition of the hemicellulose in the wood and bark. The amount of mixing or stirring desired is also limited by the pulping time and strength of the paper required of the wood pulp, or its other intended uses. Sawdust needs little or no agitation at atmospheric refluxing.

Lignin of the conventional processes for pulping wood and bark is practically useless, and as noted, is not economically recoverable. But by my process the lignin obtained is of low molecular weight, averaging well under 1,000, soluble in ethylene glycol dimethyl ether, other solvents and partly so in methanol. Hence to obtain the most reactive of these low molecular weight lignins it is desirable to employ conditions that may not be the same as for producing the pulp for any given wood or wood mixture. Ideally the optimum temperatures lies about or below the glass transition temperature of the lignin as it exists in the wood. This ranges from about 110°C to about 140°C for most woods. Thus a judicious balance must be used that may require sacrificing low pulping times to obtain the desired lignin minimal quantity of contained glucose, sugars and other soluble carbohydrates in the liquor obtained after separating the pulp. Formic acid and any water is easily recovered from the liquor, for example by simple distillation or extraction or other means. Any surfactant if employed, may likewise be easily removed as may minor amounts of carbohydroates with a minor quantity of water by extraction since the lignin is insoluble in water. The lignin may be used as a diluent for phenolic resin phenols or for producing polyols for polyurethaπe foams by alkylene oxide addition as is well known in the art. Such polyols of hydroxy! numbers of 50 to 700 may be used for both flexible and rigid polyurethane foams.

The lignin from my process may also be easily directly hydrodealkylated thermally or catalytically, using catalysts known in the art, to benzene and phenol. And it can also be dealkylated using such as aluminum aryloxide catalysts to phenol and substituted phenols in the liquor phase, for example using phenol as a solvent at from about 50°C to about 300°C. The thermal or catalytic hydrodealkylation may be conducted by injecting the lignin alone or in a mixture with other chemicals to be hydrode- alky!ated, for example toluene, and therein combined with hot hydrogen. short residence time is desirable to obtain the best yields of phenol, which is more valuable than benzene. In a slightly glowing steel tube of about a centimeter in diameter and 25 centimeters long the best results. were obtained with residence times of less than 2 seconds. As the lignin was obtained from a surfactant free pulping system and contained negligible quantities of carbohydrates without extraction, it was employed directly after distilling off the water-formic acid. Thus, by combining an alkyl ated aromatic of a higher boiling temperature than the formic aicd-water mixture to the liquor and injecting it into a column heated to distill off the latter, the formic acid-water is taken off the top whist the mixture of alkylated aromatics-lignin can flow directly into a hydrodealkylating reactor. Examples of the alkylated aromatics include xylenes and methylnaphthalenes.

The bark pulp of my process is of special interest in that 60% pulp yields are realized and the material is useful as a foodstuff for ruminants such as sheep, goats, elephants, cattle and the like.

More, while the pulping process of my invention removes the lignin and some of the other chemicals from bark it does not remove some of the chemicals that provide flavor since by taste and on burning a characteristic flavor and aroma is realized. Thus the bark pulp is unique as a feed for ruminants and an additive to feeds for other animals, fowl and marine creatures. Indeed, as a feed for ruminants it is further highly superior for another reason, that the easily digestible hemicellulose contained in the bark, and wood, is retained in the pulp. Thus the efficiency of the bark pulp, or wood pulp, of my process as a ruminant feed is far superior to conventionally pulped wood and bark; and the pal atibil ity of my bark is evidenced by simply chewing on it. Birch hickory, oak and the others tasted have distinctive flavors.

Similarly, on burning, the bark pulps emit fumes having aromas characteristic of the bark and wood from which they were derived. Hickory, cherry, birch, maple, oak and others yield distinctive aromas on burning; as they contain practically no lignin the smoke is inoffensive. And those tested contained contained no significant detectable amounts of nicotine. These are excellent smoking materials, as such, or in admixtures with tobacco. As pipe smoking materials, as rolled into cigarettes or cigars, the bark pulps are pleasant and apparently harmless in that in spite of their flavor they are largely holocellulose. Humectants, binding agents and other materials known in the art of utilizing tobacco may be employed in compounding the bark pulps; indeed, even other flavoring materials may be added, for example for menthol flavor. And of course, they may be combined with filters as in making cigarettes. To minimize chemical proliferation in testing some bark pulps were made without the benefit of a surfactant; thus Example I is typical.

Example I

100 gms. Oak bark, 30% moisture 600 mls. Formic acid, 80%

Stirred rapidly at refluxing at atmospheric pressure, about 100°C, for 4 hours. Filtered hot and washed with hot fomic acid, 80%, then with water, and dried. 44 gms. bark pulp obtained; "K" no. 21. Wood pulp was ideally produced using a surfactant to greatly accelerate the pulping process, as indicated in example II.

100 gms. wood chips (oak, maple, ash, cherry mixed) 40% H₂O 600 mls. Formic acid, 80% 40 gms. cetyltrimethylammonium bromide

Stirred rapidly at refluxing at atmospheric pressure, about 100°C, for 1 hour. Filtered hot, washed with hot formic acid, 80%, then with water and then dried. 43 Gms. wood pulp was obtained, "K" no. 13. According to the provision of the patent statutute I have explained the principal of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise.

Claims

I cl aim:

1. A process for the production of wood pulp comprising combining wood and formic acid of at least 35% concentration and then separating the pulp from the liquor.

2. The process of claim 1 wherein a surfactant is combined with the wood and formic acid.

3. The process of claim 1 wherein the formic acid and wood are com- : bined using agitation.

4. A process for the production of bark pulp comprising combining bar and formic acid of at least 35% concentration and then separating the bark pulp from the liquor.

5. The process of claim 4 wherein a surfactant is combined with the formic acid and bark.

6. The process of claim 5 wherein the formic acid and bark are combined using agitation.

7. The bark pulp of the process of claim 4.

8. A food for ruminants comprising the bark pulp of claim 7.

9. A food additive for animals comprising the bark pulp of claim 7.

10. A smoking composition whose fumes from burning are inhciled and exhaled comprising the pulp bark of claim 7.

11. A cigarette comprising pulp bark of claim 7.

12. A cigar comprising the pulp bark of claim 7.

13. A process for the production of lignin comprising combining wood and formic acid of at least 35% concentration, separating the wood pulp from the liquor and removing the formic acid from the liquor.

14. The process of claim 13 where the wood and formic acid are combined using agitation.

15. The process of claim 13 where a surfactant is combined with the formic acid and wood.

16. A process for the production of lignin comprising combining bark and formic acid of at least 35% concentration, separating the bark pulp from the liquor and then separating the formic acid from the liquor.

17. The process of claim 16 where the bark and formic acid are combined using agitation.

18. The process of claim 16 where a surfactant is combined with with the bark and formic acid.

19. A process for the production of lignin of less than 1,000 molecular weight comprising combining formic acid of at least 35% coπcen- tration and at least one of wood and bark at less than the glass transition temperature of the lignin as measured in the wood.

20. The liqnin of claim 19 of a molecular weight of less than 1,000 and soluble in ethylene glycol dimethyl ether.

21. A polyol for polyurethane foams comprising an alkylene oxide adduct to the lignin of claim 20.

22. A process for the production of at least one of benzene and phenol comprising combining formic acid of at least 35% concentration and at least one of bark and wood at from about 20°C to about 180°C, separating the pulp from the liquor, removing the formic acid and hydrodealkylating the lignin.

23. A process for the production of phenol and substituted phenols comprising combining formic acid of at least 35% concentration and at least one of wood and bark at from about 20°C to about 180° C, separating the pulp from the liquor, removing the formic acid and dealkylating the lignin catalytically using an aluminum alkoxide catalyst.