A PROCESS FOR PULPING WOOD AND BARK IN FORMIC ACID

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: 1. FORMIC ACID PULPING Technical Field This invention relates to digesting wood and bark in formic acid of a least 35% concentration to produce wood pulp,.-.bark pulp, lignin and lig- 5 nin based chemicals including benzene, phenol and polyols. Background Art Wood is conventionally del gnified 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 weigh 10 result in a high molecular weight modified lignin condensation product and is often malodorous. Thus the kraft process employs a mixture of aq¬ ueous 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 accompan¬ ied by sulfide odors. The spent liquor from the process is comprised of 15 sodium salts of lignosulfonates, glucose and sugars from hydrolyzed cel¬ lulose and hemiceilulose, and residual inorganic chemicals. Because of the high cost of the raw materials, NaOH and Na 2 S, it is desirable to ef¬ fect their recovery, hence the spent liquor is concentrated by evapora¬ tion to about 65% total solids and burned to an inorganic melt which is 20 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 numer- 25 ous 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 30 is rather intractable because of its •very high molecular weight and chemical mod fication. 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 precipi- 35 tates 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 hemiceilulose present in the wood. As the lignin is highly condensed to high molecular weight and, in the case of the kraft process, fur 2. 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 corres- c ponding pulps in formic acid of ideally 65% to 90% concentration at its refluxing temperature, about 100°C, and further ideally using a surfact¬ ant 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 ■J example by distillation, and the surfactant by minimal water extraction, leaving a low molecular weight lignin that is quite soluble in many sol¬ vents and easily hydrodealkyl ted 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; 15 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 re¬ placement for tobacco as a smoking material. The formic acid can be made from essentially carbon monoxide and water 20 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 pro- 25 cess; although essentially pure formic acid may be employed, and the con¬ centration 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 30 ratio may range from 2:1 to 1:20 dry wood:mediurn, ideally 1:3 to 1:8. Us¬ ually the softwoods are somewhat more difficult to pulp while the hard¬ woods pulp very rapidly. The temperature of the delignificat on may range from about 20°C to about 180°C, preferably from about 50°C to about 150°C and ideally from 35 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 advant¬ age to operate at atmospheric pressure as compared to some 10 atmospheres now employed by the conventional processes at much higher temperatures, OR] - 3. 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 9 sugars are found in the the liquor after removing the pulp, mostly from 5 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°C the time decreasing with increasing temperature. But of cour- 10 se this entails pressure apparatus above a few tenths beyond atmospheric pressure. At 130°C the rate of pulping is quite rapid but a slight de¬ crease 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 15 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 em¬ ployed for wood. Usually bark pulp is of shorter fiber length and quite dark in spite of the very extensive delignification. As measured by the 20 the so-called " " 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 em- 25 ployed to accelerate the process very substantially, such as anionic, cat- ionic, amphoteric and nonionic surfactants may be used. Examples include sodium dodecylbenzene sulfonate, sodium lauryl sulfate, cetyltrimethyl- ammonium bromide, alkoxylates nonylphenol, e.g. CnH^CgH.O^rLOjgH, and perfluoroalkyl-alkyl cationic, anionic, amphoteric and nonionic surfac- 30 tants. The concentrations of surfactants vary with the kinds employed and range from about 0.1% to about 5% for effectiveness although larger conce¬ ntrations 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 prefluoroalki-1-alkyl com- 35 pounds do well. The rate of pulping wood and bark is affected strongly by agitat on 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, especial y mechanical OMP 4. stirring or some kind of mixing becomes evermore greater. Probably this is a function of the decomposition of the hemiceilulose 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 pra ctically useless, and as noted, is not economically recoverable. But by my process the lignin obtained is of low molecular weight, averaging wel under 1,000, soluble in ethylene glycol dimethyl ether, other solvents and partly so in methanol. Hence to obtain the most reactive of these lo 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 mix ture. Ideally the optimum temperatures lies about or below the glass tra s tion 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 th 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 ex ample by simple distillation or extraction or other means. Any surfactan if employed, may likewise be easily removed as may minor amounts of carb hydroates with a minor quantity of water by extraction since the l gnin 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 weil known a 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 hydrodeal yla- ted thermally or catalytically, using catalysts known in the art, to ben zene and phenol. And it can also be dealkylated using such as aluminum aryloxide catalysts to phenol and substituted phenols in the liquor phas for example using phenol as a solvent at from about 50°C to about 300°C. The thermal or catalytic hydrodealk lation may be conducted by injec- ting 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 neglig¬ ible quantities of carbohydrates without extraction, it was employed dir¬ ectly after distilling off the water-formic acid. Thus, by combining an alkylated aromatic of a higher boiling tempera¬ ture 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 aro atics-l gnin can flow directly into a hydrodeal ylating 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 .rum¬ inants 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 character¬ istic 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 hemiceilulose contained in the bark, and wood, is retained in the pulp. Thus the effic¬ iency 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 palatibility 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 charac¬ teristic 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 hoiocellulose. 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 mis. 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; " " 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 mis. Formic acid, 80% 40 gms. cetyltrimethylammonium bromide Stirred rapidly at refluxing at atmospheric pressure, about 100°C, for 1 hour. F ltered 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 inven¬ tion may be practiced otherwise.

Claims: I cl aim: 1. A process for the production of wood pulp comprising combining woo 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 com¬ bined 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 ex¬ haled 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 com- - bined 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 l gnin 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 re liquor. 17. The process of claim 16 where the bark and formic acid are com¬ bined 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 molecu¬ lar 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 ad- duct 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 alkox¬ ide catalyst.

Applicants: JORDAN ROBERT K
Application year: 1981
Main classification: D21C3
IPC codes: A23K1, A24B15, C08G18, D21C3