US2845441A - Processes for production of furfural - Google Patents

Description

July 29, 1958 E. E. MORSE Em 2,845,441

PROCESSES FOR PRODUCTION OF' FURFURAL Filed Nov. 16, 1955 12m-Jumanbonn-Omn- INVENTORS Emelson/ Moise Wlfel' l2. Hear-IL B mwMf/XW O ATTORNE United States Patent O PROCESSES FOR PRODUCTION OF FURFURAL Erwin Emerson Morse, Gorham, and Walter L. Hearn, Berlin, N. H., assignors to Brown Company, Berlin,

.Application November 16, 195s, sensi No. 547,263

s claims. (c1. 26o-341.9)

This invention relates to methods of producing furfural which is suitable for the manufacture of various chemical materials from waste liquors. More particularly, it relates to producing furfural by the hydrolysis of waste sulite pulp liquors and especially from hardwood pulp waste liquors.

While it has been recognized for some time that hardwoods contain attractive potential quantities of pentosans which are convertible ultimately to furfural, so far as we are aware no practical or economic processes for recovering furfural from hardwood waste liquors have heretofore been known, despite the several past general, and in some instances specific, suggestions to recover furfural from hardwood waste liquors. Certain prior proposals have not proven to be feasible in attempts at commercial, rather than laboratory, production. Other proposals have been delicient or defective because of low, uneconomic yields, high operating costs, excessive plant costs, operating difficulties or a combination of several of such factors.

Accordingly, it is an object of this invention to produce furfural from acidic hardwood waste liquors and the like by methods which are commercially and technically feasible while minimizing thecost thereof, while maintain- 2,845,441 VPatented July 29, 1958 The waste liquor 11 after removal from the blow pit is fed into steam heated preheater 12 wherein the temperature of the liquor is raised to aboutv 350 F. Thereafter liquor 11 is conducted to either one of two small (knockout) pots 14 and 14a wherein the temperature of the liquor is raised to the preferred hydrolysis point of about 385 F. by steam heating. In knockout pots 14 andl 14aI a certain amount of solids are deposited on the internal surfaces thereof, necessitating occasional cleaning.

In a presently preferred procedure, we next pass the heated liquor 11 to the upper portion of a vertically/.positioned reaction vessel 15 containing a plurality of sieve plates or other equivalent means of insuring intimate gasliquid contact. High pressuresteam is injected into vessel 15 at a lower portion thereof which serves to maintain the hydrolysis reaction temperature at the needed range of between 347 F. and 420 F. In the particular example now being described the reaction temperature in vessel 15 was held at 410 F. at an operating'gauge pressure of 261 p. s. i. The injected steam also serves to proing high product yields and while avoiding excessive investment and operating costs. Further objects of the invention will be in part pointed out hereinafter.

In one of its broader aspects the invention may be said to lie in hydrolyzing waste liquors at such temperature and time conditions that substantial destruction of the furfural or furfural-yielding components either by heat, polymerization or combination with other components of the waste liquors is avoided. More particularly, we have found that by maintaining the hydrolysis conditions between about 347 F. and 420 F. (and preferably at 385 F.) for between substantially 40 minutes to 10 minutes, a high proportion of the theoretically recoverable quantity of furfural present in the waste liquor may be obtained while simultaneously avoiding excessive fouling ofthe equipment used.

Perhaps the features of the invention can best be understood and appreciated by reference to the accompanying drawing which presents a simple iiow plan of a particular sequence of processing steps and materials successfully employed.

In the drawing, hardwood sulte waste pulping liquor 11 is derived from cooking hardwood chips for about l0 hours at 75 p. s. i. pressure; it has a pH of about 1.8 to 2.8 at 25 C. and has a typical solids content of 12l4%. Analyses indicate that such liquor contains about 1.2 to 2.2% potential furfural based on the total liquor. It is to be noted that when the cooking liquor is discharged to the blow pit after the cooking is completed a certain amount of free furfural may be flashed oit and lost, thus reducing the potential yield somewhat, although provision may be made for recovery of such ashed furfural as by use of a surface condenser.

vide a current of a stripping gas which sweeps out of the top of vessel 1 5 the product crude furfural, lay-products such as methanol, low-boiling acids and so on as well as any small amounts of entrapped liquid.

It is to be noted that the capacity ,of vessel 15, feed point injection points and feed rate are to be selected and adjusted so that the residence time or hold-up of the liquor 11 in the said vessel varies between about 40 minutes at the lower range of reaction temperature and about 10 minutes at the upper temperature ranges; it is also to be noted that the operating pressures range respectively between about 114 to 295 p. s. i. g. at the operating temperatures lying between 347 and 420 F. Lesser times than the ranges indicated resultindnsuicient conversion to, and recovery of, the desired product furfural. On the other hand greater residence times also cause reduced yields of furfural due apparently to polymerization or degradation' of the furfural and perhaps combination with other components of the liquor.

Under the conditions indicated, the euent spent liquor contains about 0.02% potential furfural and 0.02% actual furfural is conducted to waste discharge. Itis to be noted that in describing the ow plan set forth in the drawing, in the interests of simplicity no discussion is made of the particular arrangement of details of heat exchange, equipment characteristics and the like since the present invention is directed to the operating criteria indicated above. Those skilled in the art will appreciate that variations may be made in the specific ow plan shown to meet the requirements of a given mill or plant and to minimize steam consumption, power consumption and so on.

In our studies and research into the problem of producing furfural from waste liquors, we found that, contrary to some indications, it was highly important to maintain the time-temperature conditions in the range indicated. For example, when the hydrolysis temperature exceeded 420 F. we found that tar-like solids were rapidly formed in vessel 15 to an extent which quickly plugged up the vessel and rendered continued operation impractical and, indeed required shut-downs of the plant in order to clean out the equipment. We also noted the formation of undesired coke-like material in the vapor disengaging space in the upper portions of vessel 15.

On the other hand at temperatures below 347 F. the yield of furfural was quite low and excessive hold-up or residence time in the vessel was necessary even to achieve low yields. This in turn required impractical throughput rates or the use of reaction vessel 15 of excessively large and uneconomic size.

We found that using the practical time-temperature operating conditions we discovered and set forth above, over-all recoveries of the order of 53% of the theoretical furfural present in the feed liquor could be obtained and at low or moderate cost.

Returning now to the description of the specific ow plan shown, the efiiuent gases from the top of vessel are condensed in condenser 16 and the condensate is next steam distilled in column 17 to remove undesired contaminating volatile components such as methanol and low boiling acids. The bottoms therefrom which is a crude wet dilute furfural is next concentrated and puried in one or more distillation columns 18 at atmospheric or less than atmospheric pressure. Preferably the product furfural, dry and of high purity, is stored under a blanket of inert gas.

From the foregoing it will be understood and particularly by those skilled in the art that the description of the specific embodiment of a process as described above is intended to be illustrative of the principle of the invention and is not intended to unduly limit the invention, the limits of which are set forth more precisely in the appended claims.

Having now particularly described our invention, what we claim is:

l. The process of producing furfural from acidic hardwood waste liquor which comprises establishing and maintaining a hydrolysis-reaction zone, conducting said liquor to said zone, maintaining the liquor in said zone at a temperature between about 347 F. and 420 F. for a period between about 10 and 40 minutes at an operating pressure lying between substantially 114 and 295 p. s. i. g., removing efuent gas and spent liquor from said zone at predetermined areas thereof which are remote from each other, and thereafter separating the product furfural from the euent gas.

2. The process according to claim 1 where in said acidic hardwood Waste liquor has an initial pH of not less than 1.8 nor more than 2.8.

3. The process according to claim 1 wherein said waste liquor is fed to said zone at an upper portion thereof and said spent liquor is removed from said zone at a lower portion thereof.

4. The process of producing and recovering furfural to the extent of at least of the theoretical content thereof in acidic aqueous liquors resulting from the cooking of hardwoods which comprises establishing and maintaining a hydrolysis-reaction zone, conducting said liquor to said zone, maintaining the liquor in said zone at a temperature between about 347 F. and 420 F. for a period between about 10 and 40 minutes at a pressure lying between substantially 114 and 295 p. s. i. g., removing eluent gas and spent liquor from said zone at predetermined areas thereof which are remote from each other, thereafter recovering the product furfural from the effluent gas.

5. The process according to claim 4 wherein stripping steam is injected into said zone to simultaneously maintain said zone temperature and to sweep away volatile reaction products.

References Cited in the le of this patent UNITED STATES PATENTS 1,946,688 Groth et a1 Feb. 13, 1934 2,369,655 Boehm Feb. 20, 1945 2,436,804 Hill Mar. 2, 1948 FOREIGN PATENTS 663,997 Germany Aug. 1l, 1939 707,638 Germany lune 28, 1941 719,890 Germany Apr. 21, 1942 740,602 Germany Nov. l, 1943 OTHER REFERENCES Hitchcock: Chem. Engr. Progress #9, 44:669-74 (1948).

Claims (1)

1. THE PROCESS OF PRODUCING FURFURAL FROM ACIDIC HARDWOOD WASTE LIQUOR WHICH COMPRISES ESTABLISHING AND MAINTAINING A HYDROLYSIS-REACTION ZONE, CONDUCTING SAID LIQUOR TO SAID ZONE, MAINTAINING THE LIQUOR IN SAID ZONE AT A TEMPERATURE BETWEEN ABOUT 347*. AND 420*F. FOR A PERIOD BETWEEN ABOUT 10 AND 40 MINUTES AT AN OPERATING PRESSURE LYING BETWEEN SUBSTANTIALLY 114 AND 295 P.S.I.G., REMOVING EFFLUENT GAS AND SPENT LIQUOR FROM SAID ZONE AT PREDETERMINED AREAS THEREOF WHICH ARE REMOTE FROM EACH OTHER, AND THEREAFTER SEPARATING THE PRODUCT FURFURAL FROM THE EFFLUENT GAS.

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