US3787241A

US3787241A - Apparatus for processing degradation of cellulosic materials

Info

Publication number: US3787241A
Application number: US00163728A
Authority: US
Inventors: R Eickemeyer
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-10-17
Filing date: 1971-07-19
Publication date: 1974-01-22
Anticipated expiration: 1991-01-22
Also published as: FI54507C; NL6814849A; FR1599793A; DE1567335B2; DE1567335A1; NL162692B; BE722397A; BR6803218D0; FI54507B; LU57096A1; DE1567335C3; SE355379B; GB1228057A; US3640768A; AT295435B; NL162692C; CH485910A; CA924713A

Abstract

An apparatus, for decomposing cellulosic materials, in the form of a percolator vessel, has a conical filter disposed with apertures which is mounted on the lower portion of the vessel. A system of liquid and steam valves controlling the inlets and outlets to the percolator vessel is used to treat cellulosic material in a series of steps with resulting decomposition of almost the entire load of material initially placed into the percolator.

Description

tes lt 1191 Elelremeyer 1451 M11. 22, 1974 4] APPARATUS FOR PROCESSING 1,695,354 12/1928 DEGRADATTON 0F CELLULOSHC MATERIALS 2:086:963 7/1937 Scholler 127 1 [76] Inventor: lRudolf Eickemeyer, Torwangerstr.

10, Munich, Germany 2 d: l Primary Examiner-Morris 1 1 e Ju y Assistant Examiner-Sidney Marantz pp ,728 Attorney, Agent, or Firm-Michael S. Striker Related US. Application Data [62] Division of Ser. No. 767,669, Oct. 15, l968, Pat. No.

[57] ABSTRACT [30] Foreign Application Priority Data 7 Oct. 17, 1967 Germany P 15 67 335.5 An pp for decomposing eellulosie materials, in

the form of a percolator vessel, has a conical filter dis- [52] US. Cl 127/1, 23/272, 23/312 A, posed wi p rt r whi h is mount on th low r 127/37, 260/124 R portion of the vessel. A system of liquid and steam [51] 1111:. Cl (313k 1/02 valves n r ling th inlets n o lets to he per ola- [58] Field of Search 127/ 1, 37; 23/272, 272,6 R, tor vessel is used to treat cellulosic material in a series 23/312 A of steps with resulting decomposition of almost the entire load of material initially placed into the percola- References Cited tor.

UNITED STATES PATENTS 525,970 9/1894 Storer 23/272 X 14 Claims, 3 Drawing Figures PNENTEU JANE? 3, 787. 241

sum 2 or 13 INVENTOR.

Arrow/5) CROSS-REFERENCE TO RELATED APPLICATIONS This application is a division of my copending application, Ser. No. 767,669, filed Oct. I5, 1968, now U.S. Pat. No. 3,640,768.

BACKGROUND OF THE INVENTION The invention relates to an'apparatus for the chemical degradation of cellulosic materials in a percolator.

The conventional apparatus of this type are designed in a manner that the cellulosic material is first subjected to heat by means of steam in order to dispel the air from the percolator. It has also been proposed to evacuate the percolator prior to heating in order to remove at least the major part of the air. The reaction liquid is then added subsequently to the initial heating zone. The liquid is usually preheated to a temperature above .lC. Very substantial amounts of liquid are necessary to effect the impregnation of the material up to saturation because of the absorptive power of cellu losic materials.

The difficulty with the apparatus of the prior art is that in their use certain portions of the material are left which are not completely saturated with liquid. The well known Scholler percolation process as disclosed for instance in German patent 640,775 therefore uses a multiplicity of liquid charges of equal acid concentration in succession. The probability of an insufficient impregnation with liquid in this case is usually eliminated after a few successive charges. D

However, there are problems with the rather high amount of liquid that is necessary and the concentration obtained in the final product.

SUMMARY OF THE INVENTION The present invention uses an apparatus in the form of percolator vessel. An annular filter, subdivided into two sections, is mounted on the interior of the percolator vessel. The lower portion of the percolator vessel as well as the filter sections are conical and are spaced so as to provide a uniform distance between the interior surface of the vessel and the exterior surface of the filter. A horizontal sealing ring fills this intersurface space so that the materials flowing into or out of the individual filter sections can be controlled independently by means of a series of steam and liquid valves.

Each filter section is provided with a multiplicity of apertures. These apertures diverge from the interior to the exterior of the filter. By properly selecting the ratio between the combined cross sectional areas of the apertures at their narrowest, or interior ends, and the cross sectional area of the filter at its narrowest, or lowest point, best results are obtained. It has been found that a combined aperture area of 0.2 to 4 percent of the narrowest filter cross-sectional areas has given satisfactory results.

The size and the spacing arrangements of the aperture can also enhance the performance of the apparatus. Apertures should have minimum diameters of between 2 and millimeters at the narrowest ends, preferably between 3 and 4 millimeters. To further optimize the efficiency of the apparatus, the apertures should be more closely spaced near the bottom of the filter so that the lower section has 50 to 67 percent more apertures than the upper section.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additonal objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a percolator vessel in schematic manner in accordance with one embodiment of the present invention; g FIG. 2 is an enlarged fragmentary section of the percolator vessel of FIG. ll showing the details of a filter used in conjunction with the percolator;

FIG. 3 is a further enlarged fragmentary section through the filter of the percolator.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a percolator vessel 10 is shown to consist of an upper cylindrical portion 12 and a lower conical portion 14. The upper cylindrical portion 12 is capped by a top dome 16 which is generally spherically shaped and is open in its central top portion. A rapid action closure 18 seals the opening in dome 16.

The suitability of the present apparatusresults from the use of an annular filter 20 having two

sections

22 and 24. Filter sections or

portions

22 and 24 are each comically-shaped but of different cross sectional areas. The angular inclinations of the

conical filter sections

22 and 24 can be selected to be about 60 degrees. The

filter sections

22 and 24 are constructed to approximate the dimensions of the lower conicalportion 14, with the upper filter portion 22 being of greater crosssectional area than the lower filter portion 24. The upper and

lower filter portions

22 and 24 are mounted on the interior surface of lower conical portion 14 by means of cross members 26. Such mounting provides an enclosed annular space between the exterior surface of the filter and the interior surface of the lower conical portion. This space acts as a convenient duct for transporting liquids and steam to and from the

filter portions

22 and 24 in relation to a duct and valve system to be described. A sealing ring 29, which spans the common circumference 211 of the upper and

lower filter portions

22 and 24, separates the interwall space likewise into an upper and lower portions, 27 and 2% respectively, and this serves to isolate each filter portion and subject it only to the conditions existing in the interwall space adjacent to it.

The

filter sections

22 and 24 have apertures 30 arranged in horizontal rows 32. The apertures 30 have diverging diameters which increase from the interior of the filter 2'1) to the exterior or periphery thereof as shown in FIG. 3. The minimum diameter of the apertures 30 is between 2 and 5 millimeters, preferably between 3 and 4 millimeters. The apertures 30 are distributed over nearly the entire filter surface. The combined cross-sectional areas of all the apertures 30 should be between about 0.2 and 4 percent, preferably 0.5 and 1.5 percent, of the cross-sectional area of the lower filter section 24 at the narrowest point 25, which would correspond to the opening at the bottom of filter section 24.

Although the above description involves the use of two filter sections, it is however, possible to use more than two sections. In such a case, it may be desirable, for more control, to seal the sections against each other, as described above.

The apertures 30 are also to be spaced, with respect to each other, to enhance the operation of the

filter portions

22 and 24. As described above, the apertures are aligned on horizontal rows 32. FIG. 2 illustrates more specifically the preferred arrangement of apertures 30.

The horizontal rows 32 are not spaced equidistantly over the entire filter surface but their vertical distances decrease in a downward direction. Thus, the uppermost two rows are space 50 millimeters apart as measured along the filters peripheral surface. This distance gradually decreases to 40 millimeters near the mating point 21 between the upper filter section 22 and the lower filter section 24 and finally becomes equal to 20 millimeters at the lower end 25 f the lower filter section 24. This gradual decrease should generally be such that the distances near the bottom are equal to about onehalf to one-third of the maximum distance existing at the top.

The horizontal spacing of the apertures 30 is selected on the basis of the filter dimensions. Thus, the horizontal spacing selected for the apertures 30 in the top row 34 must be such that the combined cross-sectional areas of all the apertures 30 should be between about 0.2 and 4 percent, preferably 0.5 and 1.5 percent, of the cross-sectional area of the lower filter section 24 at its narrowest point 25. The horizontal spacing between apertures 30 in the top row 24 is shown to be 50 millimeters. The initial vertical spacing, as discussed above, is made equal to the horizontal spacing selected for the top row.

In addition, the apertures 30 are so situated that they are horizontally displaced from the apertures on adjacent rows so that the inter-aperture distances on the surface of the filter 20 are made as equal as possible.

With this arrangement, the lower filter portion 24 has about 50 to 67 percent more apertures than the upper filter portion 22. This results in desirable flow conditions.

The upper part 23 of the upper filter section 22 does not contain any apertures in its surface. This serves both to prevent undesirable peripheral circulation of the steam and liquid and also to prevent an edge flow at this height in the filter 20.

A valve and duct system is used to feed and empty the percolator vessel at suitable steps during the decomposition process, to be described. Thus, inlet valve 40 feeds fluid into distributor member 42 and inlet valve 44 does the same with steam. Valve 46 is an outlet drive for steam which is to be removed from the percolator 10 during the process.

Valves

48, 50 and 52 are shut off valves while

valves

54 and 56 regulate the supply of steam passing through the percolator 10. Opening 58, at the bottom of the percolator 10, is an outlet for the contents of the percolator.

The use of the present invention involves as a first step the introduction of the reaction liquid and steam at a temperature of at least 100 whereby a reaction liquid steam mixture rises upwardly in the percolator. As a result, the open space between the cellulosic particles is completely taken up and in addition the reaction liquid will penetrate into the individual particles and the displaced air in each case will rise towards the top. After complete covering of the charge with liquid, one may permit the charge to stand for a few minutes to accomplish complete saturation. The amount of liquid which is in excess of the saturation of the cellulosic material and which is in the interstices between the cellulosic particles is then drained downwardly through the filter. It is only after this step that the remaining material which is now just saturated with liquid is heated by the admission of steam through the filter and is thus brought up to the reaction temperature.

This kind of procedure results in a substantial saving in the amount of steam and, on the other hand, because of the lower amounts of liquid required, permits a higher concentration of the sugars to be obtained in the same reaction time.

There results also a substantially lower flow resistance for the steam which arises from the bottom to the top and thus a lower pressure and temperature differential from bottom to top.

If the purpose of the process is the saccharification of the cellulosic material, the reaction liquid will be a suitable mineral acid solution of which the ion concentration in the first stage where the saccharification of the hemicellulose is effected may amount to about that of a 1 percent concentrated sulfuric acid, while in the second stage where the cellulose is subjected to saccharification after the sugars formed from the hemicellulose have been washed out at a reduced temperature and reduced acid concentration, acid may be used of which the ion concentration is equivalent to that of a 3-5 percent sulfuric acid.

Preferably, a preliminary hydrolysis of the hemicellulose of the pentosan-containing starting material is effected followed by an alkali conversion of the cellulose. I

The process of the invention contemplates that in this case a reaction liquid is used for at least part of the conversion of the hemicellulose consisting of dilute material acid solution having a hydrogen ion concentration corresponding to about 1 percent sulfuric acid. The reaction temperature should be below C. This will be followed by a washing out of the sugars formed from the hemicellulose at a reduced temperature and acid concentration by means of a plurality of liquid charges of reduced sugar concentration. These charges may be obtained from previous percolation runs. The last wash is effected with water. After that, a new reaction liquid is added which contains solvents for the lignin such as sodium hydroxide, sodium sulfide and sodium carbonate in a concentration to provide for the necessary reagent in the cellulosic material after expulsion of the excess liquid. A reaction temperature in this stage is used of at least 140C. The soluble alkali lignin is then again washed out by means of a plurality of liquid charges of decreasing temperature and decreasing concentration of alkali lignin and other unspent reagent. These liquid charges are again obtained from previous percolation runs. Finally, there follows a wash with water. The necessary temperature is accomplished by means of steam which is introduced in each case between two charges. As a result, pure cellulose will remain in the percolator.

Preferably, nitric acid of a hydrogen ion concentration as indicated is used, at least in case of the hemicellulose saccharification, that is during the preliminary hydrolysis, but possibly also during the hydrolysis of the cellulose.

The fresh reaction liquid which is necessary for the conversion of the cellulose may contain alkali lignin obtained from a previous percolation run in addition to fresh solvents for the lignin.

Preferably, the fresh reaction liquid consists at least partially of one or several discharges resulting from previous lignin solution percolations to which the necessary additional fresh chemical may be added. After starting the reaction with the cellulosic material which is saturated with acid, the subsequent reaction time necessary to accomplish the saccharification of the hemicellulose or cellulose is of course accompanied also by decomposition of the formed sugar under the conditions of the reaction. As a result, a certain flattening out of the possible maximum sugar concentration occurs after a certain reaction time. The sugar concentration at a continuation of the reaction would de crease.

It is therefore an additional feature of the invention that the reaction time is selected so that the formed sugar has at least 70 percent, and at most 90 percent,

of its possible maximum concentration. When this point is reached the sugar is then washed out at a re duced temperature and acid concentration. New reac tion liquid is subsequently added, particularly in cases of the saccharification of the cellulose followed again by washing out at reduced temperature and acid concentration.

The elution or washing out of the formed sugar can be effected by a plurality of liquid charges as indicated.

The temperature is preferably l30140C for the conversion of the hemiceulose with a reaction time of about 40 minutes. In the first stage of the conversion of the cellulose, the temperature is l60-l70C with a re action time of 40 minutes, and in the second stage of the conversion of the cellulose the reaction temperature is between 170 and 190C prefereably 180C with a reaction time of 30 minutes.

A suitable apparatus for operating the described process is a percolator as described above.

hemicellulose 1 preferably 33 tons of beech shavings containing about 26 tons dry wood substance were placed in a percolator l0 having a contents of 100 m and a diameter of 3.2m in its upper cylindrical portion 12, while the lower conical portion 14 had an inclination of 60 and a total height of 2.7 m. The percolator lil also was provided with a top dome 16 in which there were disposed rapid-action closures 18, a liquid valve 40 and a steam inlet valve 44, as well as a steam outlet valve 46 and a distributor 42 for both the liquid and the steam. The beech shavings were then subjected to a preliminary hydrolysis to xylose and to a main hydrolysis to dextrose followed by a processing of the lignin residue. The percolator consisted of copper plated sheet steel and was adjusted to withstand an operation pressure of 13 atmospheres above atmospheric pressure.

In the lower conical portion 114, a vertically subdivided filter 20 consisting of

filter sections

22, 24, each composed of perforated frusto-conical cooper sheets was installed which was supported by cross-members 26. The upper filter portion 22 had a height of about 700 mm measured in the wall portion of the conical section 14 of the percolator l0 and was sealed against the lower filter portion 24 which had a height of about 1400 mm (measured again in the conical wall portion) by a sealing ring 29. The upper filter section 22 had apertures of conical form arranged in horizontal rows 32. The apertures had a diameter'at the center of about 3 mm and at the periphery of about 5 mm with a horizontal distance from each other of 50 mm. The rows 32 of apertures 30 in the top levels were spaced by 50 mm which was reduced at the lower edge of the upper filter section 22 to about 40 mm. The apertures 30 of the individual rows 32 were offset against each other.

The lower filter section 24 likewise had apertures 30 arranged in horizontal rows 32 and having the same diameters and same horizontal distances. At the upper edge of the lower filter section 24 the distance of the aperture rows 32 was about 40 mm which was reduced gradually up to the lower edge to about 20 mm. The apertures of the individual rows 32 again were offset against each other.

In this manner, there were obtained about 50 percent more apertures 30 in the lower filter section 24 than in the upper filter section 22.

It is also possible to use percolators which are steelplated with a nickel-chromium, non-corroding steel (V 4 A) which are similar to the conventional cellulose boilers. The filter 20 in the conical portion 14 in this case likewise is formed from V 4A sheet steel. This type of filter is particularly useful for obtaining pure cellulose after carrying out the preliminary hydrolysis. The different stages of the process carried out in the above-described apparatus will now be discussed:

1. First Stage Preliminary Hydrolysis of Hemicellulose In order to effect the complete covering of the wood charge consisting of beech wood shavings, about 63 m of sulfuric acid of a concentration of about 1 percent were used. The initial heating of the charge was -effected by means of steam admitted through the valve 54 and the lower filter section 24. The heating was carried out to a temperature of about 100C and a brief circulation of the steam was effected by opening the upper outlet valve 46. Dilute sulfuric acid was then admitted at a temperature of about C during a period of about 12 minutes through the upper filter section 22 of the filter 20 by means of opening the valve 48 and closing the valve 50..Simultaneous1y, steam was introduced through the lower filter section 24 while throughout this operation a small amount of steam was permitted to escape through the upper outlet valve 46. Thus, a mixing temperature of at least C was obtained right above the liquid filled percolator zone.

After covering the charge with liquid the upper steam outlet valve 46 was closed and steam was admitted through the upper inlet valve 44 into the upper section of the percolator until a pressure of about 1 atmosphere above atmospheric was reached, which was then maintained at a constant value by adjusting further admission of steam. The excess liquid of about 25 m was drained through both filter sections by opening the valve 50 and by means of the control valve 62, while a pressure difference was maintainedbetween the percolator top section and the space behind the filter (impulse control device 60) between zero at the beginning of the discharge and increasing gradually to 0.5 atmospheres at the end of the discharge, which altogether lasted for about 15 minutes. The charge which now was saturated with dilute sulfuric acid was then heated,

after closing the control valve 62 and opening the

valves

54 and 56, to a temperature of 135C by admitting steam through the two filter sections. The temperature corresponded to a saturated steam pressure in the percolator upper part 12 which resulted from maintaining a pressure difference of at least 0.8 atmospheres between the lower and the upper portion by means of the impulse control device 60.

After reaching this pressure in about 15 minutes, steam was passed through the entire vessel for a few minutes by a slight opening of the upper outlet valve 46 in order to obtain a completely uniform heating of the charge. The outlet 46 was subsequently closed and the desired pressure in the upper section of the percolator 12 was maintained for the reaction time of about 40 minutes by specific additions of steam through the filter 20 (valve 54 and possibly valve 56). This means that preferably the steam was introduced only through the lower filter section 24 (valve 54) whenever a comparatively small amount of steam was necessary in order to maintain the reaction temperature.

Thereafter, a liquid charge of about 32 cubic meters containing a xylose concentration of about 8 percent and having a temperature of about 90C was pumped into the percolator from above through the valve 40. This resulted in a substantial cooling and development of steam in the cake and provided for a mixing temperature of about 120C corresponding to a pressure of 1 atmosphere above atmospheric pressure.

Thereafter, steam was introduced from the top and the pressure was increased from 1 atmosphere above atmospheric to 2 atmospheres and this pressure was maintained by introducing further controlled amounts of steam. The liquid thereby was forced into the cake and caused condensation of the steam which was at a higher temperature and which was still left in the pores of the material. This resulted in an increased extraction effect.

The liquid was then drained through the valve 62 by adjusting the pressure difference between the upper percolator part 12 and the space behind the filter sections to a value of initially zero, and then increasing during the reaction time of about minutes to a value of 0.5 atmospheres.

A new liquid charge was thereafter admitted in an amount of 32 m having a xylose concentration of about 6 percent and a temperature of about 90 through the valve 40. This resulted in a further reduction of the mixing temperature to about 110C. The further process was similar to the above-described operation and also appears from the following schedule:

TABLE I Xylose Xylose Liquid conccn- Disconccn Charge tratiun Amount charge tration Amount No. wt.-% rn' No. wt.-% m 1 8 32 1 9.3 33 2 6 32 2 8.5 34 3 4 32 3 6.5 34 4 3 25 4 5 26 5 25 5 4 27 (v 6 tg 2 5 21 The first discharge and part of the second discharge constituted the so-called extraction amounting to 5.9 t extract having a xylose contents of 4.7 t in an about 9 percent solution. This corresponded to a yield of 18 percent of the beech wood dry substance. This extract could then be processed further to the desired final products.

The remaining discharges were saved for making the extraction charges I to 4 for the next run. They were stored in storage vessels. The fifth and sixth charge preferably consisted of de-ionized water.

11. Second Stage Hydrolysis of Cellulose After completion of the preliminary hydrolysis, which at the end proceeded with a temperature of only slightly above 100C, a new charge was added in an amount of 40 m at a temperature of about and consisting of about 4 percent sulfuric acid. This charge was added from below through the upper section of the filter 22 while at the same time steam was introduced through the lower filter section 24 in order to obtain a mixing temperature of at least C.

After permitting the mixture to stand for a few minutes, the steam percolator pressure in the upper section 12 was increased to 1 atmosphere above atmospheric by a heavy addition of steam from the top. This pressure was then maintained by admitting controlled additional amounts of steam. The excess liquid was again drained through the liquid outlet valve after adjusting the pressure difference to a value of zero at the beginning of the discharge and increasing to about 0.5, this pressure difference existing between the percolator upper portion and the space behind the filter 27. The discharge lasted about 15 minutes. A reaction temperature was then established of about C by introducing steam through the entire filter surface at a pressure difference of at least 0.8 atmospheres between the lower and the upper section of the percolator. This reaction temperature corresponded to the saturation steam pressure in the percolator upper part 12. The time for heating to the desired temperature amounted to about 20 minutes.

The stated reaction temperature was then maintained for about 40 minutes by admitting controlled amounts of steam through the lower filter section 24 (this was the reaction time for the first phase of the sugar formation in the main hydrolysis). The washing of the sugar took place thereafter at a reduced temperature and acid concentration in a similar manner as in the preceding description and observing the following schedule:

TABLE ll Dextrose Dextrose Liquid concen .Disconcen- Charge tration Amount charge tration Amount No wt.-% In No. wt.-% in The first discharge and part of the second discharge totaling about 4.6 t of extract, of which 3.85 t were dextrose, and which were present in a solution of 58 twere then eliminated and used for the further processing to desired end products. The other discharges as in the previous case were employed to prepare the charges 1 to 4 for the next run and for this purpose were placed in storage tanks.

11]. Third Stage Hydrolysis of Remaining Cellulose About 30 m of 4% sulfuric acid were then pumped at a temperature of 90 through the upper filter section 22 into the percolator 10. Simultaneously, steam was added through the lower filter section 24 as in the preceding case.

By increasing the pressure in the upper portion of the percolator to about 1 atmosphere above atmospheric, the excess liquid was drained in the same manner as previously. There then followed the heating of the charge through the entire filter to a reaction temperature of about 180, that is, to a corresponding saturated steam pressure in the upper section 12 of the percolator 10. This temperature was maintained for about 25 minutes by introducing controlled amounts of steam through the lower filter section 24. This was then followed by again washing out the formed sugar as in the previous example, but following the scheme shown in Table III.

TABLE III Dextrose Dextrose Liquid concen- Disconcen- Charge tration Amount charge tration Amount No. wt.-% m- No. wt.% m 1 5.4 26 I l 6.1 36 2 4.0 25 2 5.3 25 3 3.6 20 3 4.6 '20 4 1.65 20 4 3.4 20 5 20 5 1.8 20

The first discharge with an extract of 3.2 t in the form of a solution of about 38 t and containing 2.4 t dextrose was then eliminated and, together with the extracts from the preceeding extraction, was subject to the further processing to obtain the desired end products. Altogether there were obtained in this process 7.8 t extract in the form of a solution of 96 t which contained 6.25 t dextrose. This corresponded to a means concentration of about 6.5 wt.-% dextrose or 8.1% dry substance consituting a degree of purity of about 80 percent.

IV. Fourth Stage Lignin Recovery At the end of this entire extraction process, there were left in the percolator a lignin residue comprising about 9 to 9.5 t dry substance and containing still about 18 to 19 t water. The evacuation of this residue was effected through an evacuation outlet 58 at the bottom end of the conical portion 14 of the percolator after the temperature of the percolator was brought up by admitting steam from below (

valves

52, 54 and 56 which were opened consecutively) to 150l75C corresponding to a steam pressure between 5 and 8 atmospheres above atmospheric. The lignin cake thus was broken up by expansion of the water under pressure and was removed mixed with steam in about 1 minute. The lignin-steam mixture was then separated in a. cyclone in which the lignin residue was received at the bottom end through outlet 58 and the steam permitted to escape at the top through rapid action closure 18. After closing of the rapid action closure 18 the percolator was then ready for another run.

EXAMPLE 2 It may be of interest in a particular case only to go through the preliminary hydrolosis and subsequently to obtain the lignin from the more or less still intact cellulose of the starting material such as beechwood. The preliminary hydrolosis in this Example therefore was the same as in Example 1 except that a shorter reaction was used in order'not to damage the cellulose and also employing nitric acid instead of sulfuric acid in order to be able to work with percolator that was plated with chromium nickel steel plates of the V 4A type. The xylose rate thereby was reduced from 18 percent to be- CELLULOSE RECOVERY A charge was formed by dissolving fresh free agents or the melt obtained from burning the waste liquor.

This material was dissolved in a suitable fraction of waste liquor. The conversion could then be effected by the so-called sulfate process. In that case the melt dissolved in a fraction of the waste liquor was reacted with alkali for instance of the type Ca(OH There resulted an amount of fresh free agent dissolved in spent liquor of about 5.2 t consisting of about 3.5 t NaOI-I, 0.85 t Na S and 0.85 t Na CO This presupposed that the excess from the last run which resulted after the percolator filling was included in a composition. The charge then contained: 5.2 t of fresh free reagent plus 4.6 t waste liquor-dry substance plus 30 t water.

The liquid excess then contained 1t chemicals 1t waste liquor-dry substance l5t water. This excess was drained through the lower portion of the percolator after admission of the charge through the upper portion of the filter and simultaneous admission of steam through the lower portion followed by a short time of standing in order to effect the equalization of the concentration. In the percolator there then remained 20 tons of hot dry substance saturated with a solution containing 4.2t chemicals, 3.6 t waste liquor and 55t water.

These contents of the percolator which was saturated with liquid were now heated to a temperature of by admitting steam through the filter and establishing a pressure difference of at least 0.8 between the lower and the upper part of the percolator and then subsequently maintaining the temperature for about 30 minutes by admitting controlled additional amounts of steam.

This step was followed by the washing out of the formed alkali-lignin by means of a plurality of liquid charges which had been obtained from the waste liquor of the previous runs. The first or the first two discharges however were eliminated. These discharges contained the highest concentration. The last two charges of liquid were again water in order to obtain a well-washed cellulose. The temperature in the percolator could be kept at a decreasing level for consecutive extraction steps similar to the previously described operation. The temperature prior to the last charge should still be at least I 10C. The following table illustrates the details of the proceeding.

TABLE IV Waste Waste Liquid Liquid-Dry Dis- Liquid-Dry Charge Substance Amount charge Substance Amount No. Wt.-% in No. Wt.-% m 1 10 i 30 1 17.6 47 2 7.4 30 2 12.7 3l 3 3.6 30 3 8.8 31 4 1.6 25 4 7.1 25 *5 25 5 3.8 25

The first discharge containing t of waste liquordry substance was then split as follows: 3.2 t waste liquor-dry substance and t water were used together with the excess from the reaction which contained 1t fresh reagents, lt waste liquor-dry substance and 15 t water for the purpose of dissolving 3.2 t fresh reagents containing about 0.4 t filler materials. Instead of fresh reagents, it is, of course, also possible to use the melt from the firing of the liquor which then must be subjected to an alkaline treatment. The total solution was used as a charge for the next run.

The remainder of the first run amounting to:

from the first charge 6.8 t waste liquor-dry substance in 32 t water from the second charge 3.7 t waste liquor-dry substance in 25.5 t water amt. altogether to: 10.5 t waste liquor-dry substance 57.5 t water was eliminated and used for the burning of the waste liquor for the purpose of steam generation and recovery of free agents.

The remainder of the second discharge and the following discharge were used for making up in sequence the charges 1 to 4 for the next percolation run.

It is noted that it would also be possible to distribute the chemicals added to two or three charges in which case the second and even the third charge may already be simultaneously extraction charges.

Prior to these reaction-extraction steps, the mixture may be heated in a similar manner as in the preceding Examples to between 140 and l50C and be maintained at this temperature for 15 to 30 minutes. The further extraction charges could be carried out at stepwise lower temperatures. There resulted in the percolator a cellulose (12 to 13 tons of dry substances) having a high content of a cellulose which could then be evacuated with water to a cellulose storage tank and could later be submitted to further processing.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A percolator for chemically decomposing materials, comprising an upright percolator vessel having an inner surface; annular filter means in said vessel and comprising an annular wall substantially coaxial with said inner surface and connected at the upper and lower ends to said inner surface while being spaced over a major portion thereof from said inner surface so as to form with the latter at least one closed annular space, said peripheral wall being provided with a plurality of apertures arranged at different levels of said wall and each diverging from the inner to the outer surface of said peripheral wall and providing communication between said annular space and the interior of said vessel; and valve controlled passage means communicating with said annular space for feeding a fluid into and out of the same. 4

2. A percolator as in claim I, wherein the total crosssectional areas of the apertures in said peripheral wall is equal to between 0.5 and 1.5 percent of the interior cross-sectional area of the percolator vessel at the bottom thereof.

3. A percolator as in claim 1, wherein said apertures have a minimum diameter at the inner surface of said wall of between 2 and 5 mm.

4. A percolator as-in claim 1, wherein said apertures have a minimum diameter at the inner surface of said wall of between 3 and 4 mm.

5. A percolator as defined in claim 1, wherein the combined cross sectional areas of said apertures are substantially in the range corresponding to 0.2-4 percent of the interior cross sectional area of the percolator vessel at the bottom thereof.

6. A percolator as in claim 1, wherein the apertures are arranged in a plurality of horizontal rows and wherein the distance between adjacent rows decreases in downward direction.

7. A percolator as in claim 6, wherein the spacing between the lowermost rows is equal to between and A; of the spacing between the two top rows.

8. A percolator as in claim 6, wherein the apertures of adjacent rows are disposed in a manner as to be offset, in the horizontal direction with reference to each other.

9. A percolator as in claim 6, wherein the horizontal spacing between said apertures is equal to 50mm in the top row and decreases uniformly towards the bottom and wherein the vertical spacing between apertures is equal to 50 mm, as measured along the surface of the filter, and decreases uniformly towards the bottom to 20 mm.

10. A percolator as in claim 1, wherein the percolator vessel has a lower conical portion and the filter means has a conical peripheral wall, and wherein the filter means is attached to the wall of said conical portion of the percolator vessel.

11. A percolator as in claim 10, wherein the top end of said peripheral wall portion is free of perforations.

12. A percolator as in claim 10, wherein said conical peripheral wall of said filter has an inclination of 60 percent.

13. A percolator as in claim 10, wherein the filter means has an upper section and a lower section, the lower section having between 50 and 67 percent more apertures than the upper section.

14. A percolator as defined in claim 13, and including a sealing ring at the joint between said upper and lower sections and sealingly engaging the inner surface of said and the outer surface of said peripheral wall so as to divide said annular space into a pair of annular spaces separated from each other, said valve controlled passage means comprising separate valve controlled ducts respectively communicating with said pair of separate annular spaces.

Claims

2. A percolator as in claim 1, wherein the total cross-sectional areas of the apertures in said peripheral wall is equal to between 0.5 and 1.5 percent of the interior cross-sectional area of the percolator vessel at the bottom thereof.
3. A percolator as in claim 1, wherein said apertures have a minimum diamEter at the inner surface of said wall of between 2 and 5 mm.
4. A percolator as in claim 1, wherein said apertures have a minimum diameter at the inner surface of said wall of between 3 and 4 mm.
5. A percolator as defined in claim 1, wherein the combined cross sectional areas of said apertures are substantially in the range corresponding to 0.2-4 percent of the interior cross sectional area of the percolator vessel at the bottom thereof.
6. A percolator as in claim 1, wherein the apertures are arranged in a plurality of horizontal rows and wherein the distance between adjacent rows decreases in downward direction.
7. A percolator as in claim 6, wherein the spacing between the lowermost rows is equal to between 1/2 and 1/3 of the spacing between the two top rows.
8. A percolator as in claim 6, wherein the apertures of adjacent rows are disposed in a manner as to be offset, in the horizontal direction with reference to each other.
9. A percolator as in claim 6, wherein the horizontal spacing between said apertures is equal to 50mm in the top row and decreases uniformly towards the bottom and wherein the vertical spacing between apertures is equal to 50 mm, as measured along the surface of the filter, and decreases uniformly towards the bottom to 20 mm.
10. A percolator as in claim 1, wherein the percolator vessel has a lower conical portion and the filter means has a conical peripheral wall, and wherein the filter means is attached to the wall of said conical portion of the percolator vessel.
11. A percolator as in claim 10, wherein the top end of said peripheral wall portion is free of perforations.
12. A percolator as in claim 10, wherein said conical peripheral wall of said filter has an inclination of 60 percent.
13. A percolator as in claim 10, wherein the filter means has an upper section and a lower section, the lower section having between 50 and 67 percent more apertures than the upper section.
14. A percolator as defined in claim 13, and including a sealing ring at the joint between said upper and lower sections and sealingly engaging the inner surface of said and the outer surface of said peripheral wall so as to divide said annular space into a pair of annular spaces separated from each other, said valve controlled passage means comprising separate valve controlled ducts respectively communicating with said pair of separate annular spaces.