CA2144302C - Bei hydrolysis process system and improved process for the continuous hydrolysis sacchararification of ligno-cellulosics in a two-stage plug-flow-reactor system - Google Patents

Abstract

The invention relates to an improved two-stage dilute-acid hydrolysis process and apparatus for the continuous saccharification of ligno-cellulosic biomass or other cellulosic material feedstocks, with higher efficiency and better economics than known-art, is disclosed. It comprises two double-tube heat-exchanger and plug-flow-reactor systems, in series . The improved process is primarily by reverse insterstage transfer-flow, opposite to biomass , of second-stage surplus of: 1 .
process heat, 2. dilute-acid and 3. ingredient and solution water, all in an alpha cellulose hydrolysate and dilute acid solution. It also comprises recycle of a fraction of unhydrolyzed alpha-cellulose hydrolysis residue, thereby achieving higher hydrolysis conversion of alpha-cellulose to glucose; and providing: 1. lower hydrolysate sugar decomposition, 2. reduced reaction time and 3. increased reactor processing capacity, without increased dimensions. The process is ideal for process control to efficiency to produce a primary final liquid product, which is the combined hydrolysate sugars into a single solution, including pentose and hexose sugars, including glucose, which are readily fermented into Ethanol and/or Torula Yeast. The final solid product is the unhydrolyzed lignin residue solids.

Description

This invention relates to a ~h~mi~l hydrolysis processing of renewable lignocellulosic biomass in order to produce a single solution of sugars and a solid lignin-residue.
Heretofore, a plug-flow-reactor has been proposed to try to gain higher hydrolysis-conversion of cellulose to glucose, by using extremely-high hydrolysis-rates, achieved by high-temperatures of reaction, as provided by direct-injection of high-pressure steam into high-solids density slurries.
~ ven-so, hemicellulose hydrolysate sugars are all degraded, by such a single-stage high-temperature poly-saccharide hydrolysis reaction process. The hydrolysate-~ugars high-dilution by steam condensation causes the resulting single-solution of glucose to have a low-concentration and large-volume with a high-cost acid-neutralization and inefficient fermentation.
U.S. Patent No. 4,201,596 issued to Church ~1980) shows a continuous process for effecting the acid-hydrolysis of cellulosic waste materials in high-solids density slurries. By control of high temperature, through direct steam injection, the high density slurry solids may be converted to yields of about fifty percent of the potential glucose in cellulose in seconds. This chemical processing method, for converting polysaccharides into ~ 21443~2 pentose and/or hexose ~ugar~, is by a known use of a tubular-type plug-flow-reactor (PFR) for dilute-acid cellulose hydroly~is. Unfortunately, relatively low conversions, negative byproduct formations, high energy requirements and impractical high-density slurry-pumping to pressure over 500 psi have limited the commercial use of that cellulo~e-conver~ion by PFR method to Research Development investigations.
Researchers, at Dartmouth College, in 1978-79, were investigating the acid-hydrolysis of municipal refuse and other material~, using a plug-flow-reactor. The Dartmouth research work involved a 1.3 cm. ~0.5 inch) diameter plug-flow-reactor (PFR) for dilute-acid, ligno-cellulosic hydrolysis, at solids concentrations up to 13.5 wt%. The system was a continuous-flow electrically-heated tubular reactor.
The Dartmouth research hydrolysis was flashed through an orifice to stop the reaction at residence detention time~ of 5-30 B., and then cooled. Glucose yields from 20hard-wood flour ranged as high as 55% in 1983. This work showed that high yields were obtainable on a small scale.
Several operational problems were encountered that were difficult to ~olve on a small bench-scale system.
Problems included tar build-up and rapid plugging of the small-diameter reactor prevented 5 long runs from being conducted to obtain extensive operating experience.
The Dartmouth Process iB known to have the following characteristics~ relatively high-density slurries are very difficult to be pumped at high-rates to high-pressures and through the PFR, 2.) very high reaction-temperatures/ on the order of 260 degrees Celcius/500 degrees Farenheit, require up to 600 psi steam and 3.) very ~hort hydrolysis reaction-times, of fractions of one-minute, for flow through the PFR, generally.
U.S. Patent No. 4,615,742 issued to Wright ~1986) shows a processing batch percolation-type hydrolysis reactor. In this counter-current hydrolysis, a flow of dilute-acid solution contacts a body of particulate wood which is moving in a direction opposite to the flow of the dilute-acid solution. The counter-current flow of the dilute-acid solution and the particulate wood results in:
a much higher yield of sugars from the wood, a minimal degradation and a relatively high concentration of glucose, but the process conditions result in a low xylose in the dilute-acid hydrolysate solution.
The primary disadvantage of this particular approach, for counter-current hydrolysis, i~ the extreme mechanical complexity and expense of moving by conveying the solids and pumping the liquids in the opposite directions.
~.S. Patent No. 4,612,286 issued to Sherman ~1986) ~ 21~302 show~ a method conceived in an attempt to ~olve the above problems and provide an approximate counter-current flow processing, without the necessity for actual movement of the wood particles. In general, a plurality of Kamyr percolation hydrolysis reactors are piped together, in series. This method utilizes a counter-current diffusional treatment structure. Cellulose hydrolysis is practiced in upright diffu~ion vessel with counter-current flow.
~.S. Patent 4,070,232 i~sued to Funk ~1978) has found that yield and operability are improved by conducting a ligno-cellulose pre-hydrolysis first and then a hydrolysis of the residue. By pre-hydroly~is of the fre~h feed~tock, at below 150 Degree~ Celcius, the hemi-cellulose can be hydrolyzed at temperature~ where pentose-sugar degradation is relatively insignificant. This allows high yields and recovery, by ~epration of sugars from hemi-cellulose hydrolysis. It also open~ up the structure of the wood particles to provide infusion of acid and diffusion of cellulose hydrolysate-ffugars are enhanced, minimum fouling in the pipes by tars and limited degradation products.
The present invention'~ moderate solids-density slurrie~ and moderate hydrolysis-reaction temperatures and the improvement for recycle of a fraction of unhydrolyzed alpha cellulose residue, in ~tage-two, provides approximately 65~ cellulose to glucose conversion ~ 214~3~2 compared to approximately 50% for known processes. In addition, other process improvements in the present invention results in over two times higher hydrolysate-sugar concentrations in the two-hydrolysates single-solution final product than that of known single solutionprocesses.
It is a primary object of this invention to provide an improved two-stage hydrolygis process for the continuous dilute-acid saccharification of ligno-cellulosics biomass, or of other cellulosic materials, to produce hydrolysate sugars in a single-solution, of moderate concentration, and a solid lignin-residue, and including four ligno-cellulose hydrolysis process improvements.
In stage one, the fresh cellulosic feedstock is admixed with hot, pressurized dilute-acid water-solution.
The resulting heated a~ueous feedstock slurry ii further heated by additional surplus flashed-steam process-heat.
Both of the~e surplus process-heat supplies are from gtage two.
That heated fresh cellulosic feedstock slurry, containing lOwt% to 20wt% solids, is therefore ready for immediate hemicellulose hydrolysis reaction processing in stage one. All of stage one's process heat is supplied by reverse, inter-stage, transfer-flow, from stage two, of:
1) flash-steam and 2~ hot, pressurized alpha-cellulose-~ 21443~2 hydrolysate and dilute-acid solution.
That transferred surplus process-heat completely provides for hemicellulose hydrolysis processing, at reaction-temperature of 135 degrees to 195 degrees celcius, saturated-pressure of 45 to 200 psia and hydrolysis reaction time of 1 to 20 min. The resulting hemicellulose hydrolysis reaction slurry is flashed to a reduced-pressure to terminate degradation of ~ugars and to generate the stage one surplus flash-steam process-heat ~upply.
The flashed, reduced temperature, hemicellulose hydrolysate and unhydrolyzed residue slurry is separated into: 1) a single solution, including the combined hemicellulo~e hydrolysate pentose- and hexose- sugars and the alpha cellulose hydrolysate glucose-sugar, and 2) an unhydrolyzed cellulosic solids residue, which is passed on to stage two as part makeup for the alpha cellulose hydrolysis feedstock. That single solution, from stage one slurry separation, is the final liquid product of the improved process of this invention.
In stage two, the unhydrolyzed cellulosic residue from stage one is admixed with the recycled fraction of unhydrolyzed alpha cellulose residue, within stage two.
Together they are admixed with fresh dilute acid water solution into the alpha cellulose hydrolysis reaction feedstock Ylurry, with lOwt% to 20wt% sollds. The fresh dilute-acid solution preheated by stage one surplus flash steam process heat.
In stage two, fresh high temperature process heat is supplied for alpha cellulose hydrolysis reaction processing at temperatures of 165 degrees to 260 degrees Celcius, saturated pressure of 100 to 200 p~ia and hydrolysis reaction time of 0.5 to 20 minutes, to produce alpha cellulose hydrolysate glucose sugar, dissolved in the dilute acid water solution of stage two.
Subsequently, stage two reaction process slurry is flashed to ter~inate glucose sugar degradation. The alpha cellulose hydrolysis slurry is then separated in order to recover surplus process heat as: 1) flashed steam, 2) at high saturated pressure, alpha cellulose hydrolysate and dilute acid water solution and 3~ unhydrolyzed alpha cellulose with lignin, residue solids.
It is a ~pecific object of this invention that three of the four cellulose hydrolysis process improvements are the result of the reverse inter-stage transfer-flow, from stage two to stage one, of: 1) dilute acid catalyst, 2) surplus process heat, and 3) surplus ingredient and solution water.
It is another specific object that the fourth cellulose hydrolysis process improvement of this invention is the recycle of up to 50wt% of the unhydrolyzed alpha cellulose solids residue, after separation from the hot pressurized alpha cellulose hydrolysate sugar and dilute acid solution, all within stage two. That recycled fraction is used identically with the regular alpha cellulose hydrolysis feedstock, from stage one hemicellulose hydrolysis processing. ~owever, the remaining non-recycled fraction will be the final lignin residue solids product of the improved ligno-cellulose hydrolysis process of this invention.
It is another object of this invention that the best method for operation of this improved ligno-cellulo~e hydrolysis process invention will be with an apparatus made up of two double tube heat exchanger plug-flow-reactor systems, a~ two stages in series. Each such stage will include: 1) slurry mixing and feeding means, 2) slurry pumping and pressurizing means, 3) tubular reactor as the inner tube of double tube heat exchanger plug-flow-reactor sy~tem, 4) heat exchanger, provided by annulus between the inner tube and outer tube, 5) ~lurry flash means for pressure reduction, 6) reduced pressure slurry ~eparation means and 7) reduced pressure hydrolysate solution proces~ ~torage means, and also includes a reverse interstage transfer flow means for: 1) hot, pressurized alpha cellulose hydrolysate and dilute acid solution, 2) stage two flashed steam, to be the stage one _ g _ 21443~2 proce 8 heat ~upply, and 3) provisions to produce the combined hemicellulose and alpha cellulose hydrolysates sugars in a single solution, as the final liquid product.
It i8 a further object of this invention that the critical hydrolysis reaction factoru required for each stage hydrolysis processing, are pre-selected and added only in stage two, and are: 1) concentration of fresh dilute acid in water solution and 2) high temperature process heat.
Another object of this invention is that the multi-beneficial results from recycling of up to 50wt% of the unhydrolyzed alpha cellulose solids residue, within stage two includes: 1) increased net conversion of alpha cellulose to glucose sugar, 2) reduction in the normally required alpha cellulose hydrolysis reaction processing time and 3) thereby reducing the exposure time of alpha cellulose hydrolysate glucose sugars to hydrolysis reaction degradation and 4) a resulting increase, by approximately 15% in the effective and useful capacity of the stage two alpha cellulose hydrolysis reactor.
It is a further object that the improvements in this process provides approximately 36% reduction of catalyst acid costs and 30% less alpha cellulose hydrolysis process energy costs, and that the recycle of unhydrolyzed alpha cellulose solids residue, within stage two, increases the alpha cellulose feedstock's net conversion to glucose by approximately 12%.

21~3û2 A major object of the process improvement of this invention is that it provides for the production of a single solution which has a relatively high concentration of the combination of the hemicellulose and alpha cellulose hydroly~ates sugars in the single solution, which is valuable when used by a variety of yeast fermentation and chemical processing methods.
The hemicellulose ~8C~ fraction of pine wood can be relatively easily hydrolyzed into pentose and hexose sugars. The pine wood HC hydrolysis conversion is a function of HC hydrolysis reaction time, ts = up to 14 minutes; at reaction temperature, T~ = 135~C/2750F and with acid concentration, C_oll = up to 2.00%.
In pine wood feedstock, the HC hexan is a fraction of about 0.72 and the HC xylan i8 a fraction of about 0.28.
At these relatively mild HC hexan hydrolysis conditions, the resulting HC hydrolysate hexo~es continue to rise through t~x = 14 minutes. The HC hydrolysate xylose yield is a maximum of C~x = 0.225 at about t~x = 9 minute~. The HC hydrolysate xylose yield ~C~x) is 80%
of the pine wood feedstock xylan fraction ~C~O~ of 0.280.
The indicated sugar survival shows that hydrolyOate xylose ~ugars, plus in the unhydrolyzed HC xylan L~ ining at t~x = 9 minutes is 0.866 of the initial HC xylan feedstock of 1.000.

~ 2144~02 To hydrolyze the pine wood alpha-cellulose (AC~
glucan polysaccharideO into glucose and hexose sugars requires more intense chemical hydrolysis reaction processing conditions. The resulting unhydrolyzed AC
glucan feedstock and AC hydrolysate glucose sugar fractional yields is a function of: 1) AC hydrolysis reaction times, t~ = up to 14 minutes, reaction temperature, T~ = 1800C/356~F, and acid catalyst concentration, C_o~d = 2.0%.
10Glucose sugar yields are comparable without recycle and with 50% recycle of unhydrolyzed AC feedstock.
Maximum glucose yield, without recycle is C_x = 0.584, at t~ = 8.2 minutes. However, with a 50% unhydrolyzed AC
recycle, it is C~xx = 0.652, at t~ = 7.0 minutes. The 15ration of glucose yield to sugar survival is 0.79 with 50%
recycle, at t~XK = 7.0 minutes. However, that ratio is 0.75 without recycle, at t~ = 8.2 minutes. The recycle of 50% unhydrolyzed AC residue, following AC hydrolysis, directly results in a 12% increase in glucose yield with a 15% shorter reaction time required.
The invention will now be described reference being had to the accompanying drawings in which:
Figure 1 is a block diagram depicting the continuous process of this invention, showing the ligno-cellulosic feedstock entering into the improved dilute acid ~ 21~4302 hydrolysis process system, thereby producing a total sugars-hydrolysate single solution final product and a lignin residue solid final product.
~igure 2 is a schematic flow diagram of the continuous process of this invention showing the best mode and preferred embodiment for carrying out the improved continuous saccharification of ligno cellulosics process according to the invention.
Referencing specifically to the drawings, it will be appreciated that as shown in ~igure 2, the preferred embodiment of the improved process of the invention is a two stage 3ystem, made up of two double tube heat exchanger plug-flow-reactor and flash tank sub-systems, in series.
Into stage on of the best mode, a ligno cellulosic feedstock, that is dry and ground to pass 10 mesh, is conveyed through conduit 2, and fed by a rotary-feeder to slurry mixer 1, where it is admixed with a solution supplied by conduit 3, which is a process improvement of the invention. That solution in conduit 3 iB a hot and pressurized dilute-acid and alpha-cellulose hydrolysate solution, which is conveying, by reverse inter-stage transfer flow from stage two to stage one, the following:
1) surplus process heat, 2) dilute acid catalyst and 3) ingredient and solution water.

2~ ~4302 The resulting preheated, fresh feedstock dilute acid slurry, containing approximately 12wt~ ligno cellulosic feedstock solids, passes to a progressive cavity slurry pump 23. Thereby it is pumped into the inner tube of the stage one double tube heat exchanger and plug-flow-reactor 4, wherein, additional process heat is conveyed, from stage two to stage one, by conduit 5 into the heat e~changer 27, and thereby is indirectly added to the slurry in order to immediately raise the feedstock slurry's saturated temperature and pressure up to the pre~elected and controlled hemi cellulose acid hydrolysis reaction factors. That stage two surplus process heat is added indirectly to the stage one reactor system 4. That is another process improvement of the invention, because it is supplied by the use of the reduced pressure and temperature flash steam, conveyed in conduit 5, by reverse, inter stage transfer flow, from the stage two slurry flash tank 15, as a surplu~ process heat ~upply.
The flow rate of the slurry, in hemicellulose hydrolysis reactor 4, is controlled by a pre~elected pumping rate, to be compatible and provide the required detention time in plug-flow-reactor 4. The result is optimum hemicellulose hydrolysis of hemicellulose hydrolysate sugars, dissolved in solution of the slurry.
From reactor 4, the reactor slurry is continuously ~ 2~ 4430~

blown into the flash tank 6, for reduced pressure, flash steam production, also temperature is dropped to interrupt degradation of the hydrolysate sugars. The flash steam from stage one flash tank 6 is conveyed by conduit 21 to stage two, for continuous preheating of the fresh dilute acid catalyst solution. The flashed slurry is conveyed from flash tank 6 to the ~tage one separator 7, for ~eparation of unhydrolyzed ce1lulosic residue from the solution of that slurry. That solution contains the combined total sugars hydrolysates from the two atage cellulosic hydrolysis proces~ing. It is conveyed out by way of conduit 8, as the single solution, liquid final product. That liquid final product is another process improvement of the invention.
In addition, the recovered, unhydrolyzed, cellulosic residue is conveyed from stage one ~eparator 7, by conduit 9, on into stage two. Therein, it is blended in with a recycled fraction of the unhydrolyzed alpha cellulose hydrolysis resldue which may be up to approximately 50wt%.
That fractionation is made by fractionator 27, following the stage two separator 16, and conveyed by conduit 18 into a blending with the unhydrolyzed cellulosic residue, conveyed in conduit 9. The ~~~ining fraction of that unhydrolyzed alpha cellulose hydrolysis residue is conveyed out by conduit 17, as the solid lignin re~idue ~ 2144302 final product, which i8 an improvement of the process of the invention. The combination of the residues, from conduit 9 and conduit 18, is conveyed by conduit 28, to the stage two slurry mixer 10, along with the fresh preheated dilute acid solution, conveyed by conduit 11, for the admixing of the alpha cellulose hydrolysis feedstock dilute acid slurry. Thereupon, the preheated slurry is transferred at a flow rate controlled by slurry pump 24, to the alpha cellulose hydrolysis plug-flow-reactor 12.
Indirectly, to the stage two alpha cellulose hydrolysis system, there is, incoming by conduit 14, which indirectly, provides a supply of high temperature proces~
heat adequate for the overall two stage hemicellulose and alpha cellulose hydrolysis processing operations. The relatively high temperature process heat, transferred indirectly to the alpha cellulose hydrolysis slurry processing in plug-flow-reactor 12, provides for the pre-~elected and controlled alpha cellulose hydrolysis reaction saturated temperature and pressure levels, for the preselected and controlled feedstock slurry flow rate, and thereby the required reaction detention time. That total overall process heat supply is initially conveyed, for indirect heat transfer, by heat exchanger 26, into reactor 12 in stage two, originally conveyed by conduit 14 '- 2144~02 from the process heat producing source 13.
With a pre#elected and controlled slurry flow rate, which provides the require cellulose hydrolysis reactor detention time, the alpha cellulose hydrolysis slurry then continuously flows from plug-flow-reactor 12 to stage two flash tank 15, for immediate slurry flashing to a reduced saturated pressure and reaction temperature. Thereby, the large supply of moderate temperature flash steam is continuously generated, along with the related needed cooling of alpha cellulose hydrolysate solution, for interrupting the degradation of it~ glucose sugar. That flashed slurry then passes on by conduit 19, to the stage two slurry separator 16, for separation of the reduced pressure alpha cellulo~e hydrolysate and dilute acid solution, from unhydrolyzed alpha cellulose lignin residue, which passes, from the separator 16 on to the fractionator 27, to be fractionated. Thereby i8 provided a fraction of up to approximately 50wt% of that unhydrolyzed alpha cellulose residue for recycle by way of conduit 18, in order to be combined and blended with all of the unhydrolyzed cellulosic feedstock residue, conveyed in conduit 9 r from stage one separator 7. Thereby, that combination becomes that most suitable feedstock for alpha cellulose hydrolysis, which is an improvement of the process of this invention. The remaining fraction of the ~ 21443~2 unhydrolyzed alpha cellulose lignin residue, conveyed by conduit 17 from stage two, beco~es the solid lignin residue final product, which is a further improve~ent of the process of thi~ invention.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A two-stage dilute-acid hydrolysis process for the continuous saccharification of ligno-cellulosic biomass feedstock to produce hydrolysate sugars, comprising the following steps:
(a) substantially continuously admixing, in a first-stage, a lignocellulosic biomass feedstock and a dilute mineral acid to form an aqueous preheated feedstock slurry, of about 10 to 20 wt % solids, whereas said dilute mineral acid is in a hot pressurized aqueous solution, supplied by reverse inter-stage transfer from a second stage, said dilute mineral acid consisting of an alpha cellulose hydrolysate and dilute mineral acid in aqueous solution;
(b) introducing said preheated feedstock slurry into one end of a first tubular reactor and constricting the other end of said reactor so as to develop a back pressure therein;
(c) receiving indirectly into said aqueous feedstock slurry sufficient process heat supplied by reverse inter-stage transfer of said second-stage flash-steam to heat and maintain said slurry at a pressure ranging from about 45 to 200 psia and at a temperature ranging from about 135° to 195°C saturated steam equivalent;
(d) passing said heated feedstock slurry of step (c) into and through a reaction zone in said first tubular reactor, the length of said reaction zone and the flow rate of said heated slurry introduction being so selected as to afford an average reaction zone detention time of about 1.0 to 20 minutes;

(e) producing hemicellulose hydrolysate sugars in said reacting slurry;
(f) substantially continuously discharging and flashing said reacting slurry, thereby cooling by reducing the pressure and temperature of said reacting slurry, and also substantially continuously generating a first stage flashed steam supply;
(g) thereafter separating said flashed slurry into (1) a combined hydrolysate solution, and (2) an unhydolyzed hemicellulose hydrolysis residue;
(h) recovering said combined hydrolysate solution, which includes therein said hemicellulose hydrolysate sugars, said alpha cellulose hydrolysate sugars, and said dilute-acid, thereby producing a single-solution final product of said saccharification;
(i) admixing, within said second stage, a blend of said unhydrolyzed hemicellulose hydrolysis residue, and of a recycled up to 50 wt %
fraction of an unhydrolyzed alpha cellulose hydrolysis residue, with a fresh preheated dilute mineral acid solution, to form a partially heated aqueous alpha cellulose hydrolysis slurry, of about 10 to 20 wt %
solids, whereas said dilute acid is continuingly preheated by a first stage flash steam supply;
(j) introducing said aqueous preheated slurry into one end of a second tubular reactor and constricting the other end of said reactor so as to develop a back pressure therein;
(k) receiving indirectly into said aqueous alpha cellulose hydrolysis slurry, sufficient process heat, by way of a high temperature fresh process heat supply, to heat and maintain said aqueous slurry at a pressure ranging from about 100 to 200 psia and to a temperature ranging from about 165° to 260°C saturated steam equivalent;
(l) passing said heated slurry into and through a reaction zone in said tubular reactor, the length of said reaction zone and the flow-rate of said heated slurry introduction being so selected as to afford an average reaction zone detention time of about 0.5 to 20 minutes;
(m) producing alpha cellulose hydrolysate sugars in said heated slurry in the presence of said dilute acid;
(n) thereafter continuously discharging and flashing said reacting slurry, thereby cooling and reducing its pressure and temperature and generating a second stage flashed steam supply;
(o) separating said flashed slurry into (1) a hot reduced pressure alpha cellulose hydrolysate and dilute acid solution, and (2) an unhydrolyzed alpha cellulose and lignin residue solids;
(p) recovering said hydrolysate and dilute acid solution, whereupon continuously transferring said solution to said first stage for admixing to slurry;
(q) recovering said unhydrolyzed alpha cellulose and lignin residue, whereupon continuously fractionating said residue, thereby an up to 50 wt % fraction is recycled within second stage and blended with said unhydrolyzed hemicellulose hydrolysis residue from said first stage thereafter admixing said blend to said second stage slurry, whereby said remaining fraction is a unhydrolyzed alpha cellulose lignin residue and is the final solid product of said saccharification.

2. Process according to claim 1 wherein said first stage flashed steam supply is generated with a pressure of about 15 to 30 psia and a temperature of about 100° to 120°C saturated steam equivalent.

3. Process according to claim 1 wherein said second stage flashed steam supply is generated with a pressure of about 45 to 200 psia and at a temperature of about 135° to 200°C saturated steam equivalent.

4. Process according to claim 3 further comprising continuously supplying said hemicellulose hydrolysis processing process heat by reverse interstage transfer to said first stage by continuously adding the flashed steam supply of step (n).

5. Process according to claim 1 wherein said dilute mineral acid is selected from the group consisting of sulfuric acid, sulfurous acid, and phosphoric acid.

6. Process according to claim 1 wherein said feedstock is selected from the group consisting of ligno-cellulosic biomass, soft wood, hard wood, wood wastes, logging slash, crop residues, sugar cane bagasse, and rice hulls.

7. Apparatus for a two-stage dilute-acid hydrolysis process for the continuous saccharification of feedstocks selected from the group consisting of lignocellulosic biomass and cellulosic materials to produce mono-saccharide hydrolysate sugars, wherein the first stage comprises:
(a) admixing means for a fresh feedstock and a hot, pressurized dilute-mineral-acid solution, forming a preheated aqueous fresh feedstock slurry, wherein said dilute acid solution consists of a hot pressurized alpha cellulose hydrolysate and a dilute-acid in-water solution, being supplied by a reverse inter-stage transferring means from said second stage;
(b) pumping and pressurizing means for the introduction of said feedstock slurry into one end of an inner tube of a plug flow reactor in a double-tube, heat-exchanger, plug-flow-reactor system, wherein said inner-tube has a constricting means at the other end, so as to develop a back pressure therein;
(c) indirect process heating means for whereby supplying second stage flashed steam, by a reverse, inter-stage transferring means, indirect heat transferring means for heating said pressurized slurry, thereby sufficiently providing for hemicellulose hydrolysis processing, at a saturated pressure ranging from about 45 to 200 psia and at a temperature ranging from about 135° to 195°C, within said plug flow reactor, and with a pumping rate control means for meeting the required flow rate of said heated slurry within the said plug flow reactor, thereby meeting the required reacting slurry detention time;
(d) reacting slurry discharging and flashing means for cooling by reducing said reacting slurry pressure and temperature and for generating said first stage flashed steam supply;
(e) flashed slurry separating means for providing recovery of (1) a combined hydrolysates single-solution final product and (2) an unhydrolyzed hemicellulose hydrolysis residue;
(f) means for supplying said unhydrolyzed hemicellulose residue into said second stage, means for blending, an up to 50 wt % fraction of said unhydrolyzed alpha cellulose residue, and said unhydrolyzed hemicellulose for admixing a fresh preheated dilute-acid in-water solution, and said unhydrolyzed hemicellulose thereby forming an alpha cellulose hydrolysis feedstock slurry;
(g) slurry pumping and pressurizing means for introducing said alpha cellulose hydrolysis feedstock slurry, into an inner tube of a plug flow reactor;
(h) high temperature process heat supplying means and an indirect heat exchanging means, for providing sufficient indirect process heat to said alpha cellulose hydrolysis slurry;
(i) partially flashing and reduced pressurizing means for reacting slurry, and said generated flashed steam and a recovering means for said reduced pressure and temperature slurry;
(k) separating and recovering means for said slurry as a reduced-pressure alpha cellulose hydrolysate and dilute-acid solution and an unhydrolyzed alpha cellulose lignin residue solids;
(l) pressurized slurry pumping means for reverse inter-stage transferring of said reduced pressure alpha cellulose hydrolysate and dilute-acid solution.

8. Apparatus according to claim 7, further including a surplus flashed steam recovering means, in each stage separately, and also including a pressurized slurry flashing tank means connected by a blow-pipe means.

9. Apparatus in claim 7, wherein further including a centrifugal slurry separating means for removal and recovering of unhydrolyzed solids residue.

10. Apparatus according to claim 7 further including a second stage recovering and means for the unhydrolyzed alpha cellulose unhydrolysis residue, and a fractionation means, and further comprising a conveying means.