Patent Description:
The invention relates in a first aspect to a method of producing a desolventized cellulosic pulp containing less than <NUM>% organic acids, the method defined by claim <NUM>. This aspect of the invention increases efficiency of existing organic acids pretreatment process by allowing recovery and reuse of the organic acids used to dissolve the hemicellulose and lignin contained in lignocellulosic plant materials. After the dissolving step of organic acids pretreatment of plant materials, a mixture of soluble and insoluble parts is obtained. After separating the mixture into soluble and insoluble fraction, a cellulosic pulp and extraction liquor are obtained. The cellulosic pulp represents about <NUM>% of the soluble fraction primarily composed of organic acids and water and <NUM>% of the insoluble fraction primarily comprised of undissolved cellulose. <CIT> describes a process for recovery of a lower aliphatic acid. <CIT> describes a process for extracting lignin from lignocellulosic material.

Organic acids pretreatment processes suitable to application of the present invention are described in international patent publications <CIT> and <CIT>. The recovery of organic acids from an organic acids pretreatment process step involving partial elimination of lignins to obtain a residual overall level of lignins of <NUM>% to <NUM>% is described in international patent publication <CIT>.

In such processes, the lost organic acids represent not only a significant portion of the unit operational costs, but the unrecovered organic acids also have an impact on environmental considerations. Thus, efficient recovery of organic acids from the cellulosic pulp produced by organic acids pretreatment of plant materials provides both economic and environmental advantages over existing methods.

A first aspect of the present invention discloses methods as claimed allowing for efficient, thorough and economic recovery of organic acids from cellulosic pulp by a combination of dryer and desolventizer. The method comprises a first step which uses the dryer to reduce the organic acids to a content of <NUM>% to <NUM>%, calculated from the total weight of the dried cellulosic pulp. At this level it is difficult to further remove organic acids by continued drying. To overcome this defect, the invention comprises a second step wherein a desolventizer is used to further remove the organic acids using direct steam as the desolventizing medium to reduce the organic acid content to less than <NUM>%, relative to the total weight of the desolventized cellulosic pulp.

The first aspect of the present invention discloses methods as claimed allowing
for efficient, thorough and economic recovery of organic acids from cellulosic pulp by a combination of dryer and desolventizer. There is provided a method of producing a desolventized cellulosic pulp containing less than <NUM>% organic acids, the method comprising the steps of:.

This aspect of the invention relates to a method for recovering organic acids from cellulosic pulp derived from the organic acids pretreatment process of plant material by a combination of dryer and desolventizer. The organic acids pretreatment process uses the organic acids as a reagent to dissolve the hemicellulose and lignin contained in the lignocellulosic plant materials. After separating the cellulosic pulp from the mixture of die soluble part and insoluble part, the residue which includes the insoluble part is the cellulosic pulp.

The existing organic acids pretreatment process may include a step of partial elimination of the lignins to obtain a residual overall level of lignins of <NUM> to <NUM>%. of the total cellulosic pulp by dry weight. The content of the organic acids in the cellulosic pulp may be <NUM>% to <NUM>%, calculated from the total weight of the cellulosic pulp. The content of the cellulose in the cellulosic pulp may be <NUM>% to <NUM>%, calculated from the total weight of the cellulosic pulp.

As shown in <FIG> the cellulosic pulp from the organic acids pretreatment process is fed to the dryer. The dryer reduces the organic acids to a content of <NUM>% to <NUM>%, calculated from the total weight of the dried cellulosic pulp, once the content of the organic acids is lower than <NUM>%, the dryer cannot efficiently further remove organic acids, if the content of the organic acids is higher than <NUM>%, the consumption of direct steam by the desolventizer is inefficient.

Drying of the cellulosic pulp is carried out by many forms of dryers which may include tube dryers, pneumatic dryers, spray dryers, rotary disc dryers, and other dryer technologies known to those in the art; it is particularly preferable to utilize a tube dryer. The dryer step may be carried out at a temperature of <NUM> to <NUM>. After drying, the dried cellulosic pulp discharged from dryer is fed to the desolventizer.

The vapor which released from the dryer may be used as defined in the claims, for the extraction liquor concentration system as well as provide other systems with thennal energy. The condensates of the vapor from the dryer which is condensed in the extraction liquor concentration system and other systems form the first phase of organic acids solution are reused as defined in the claims, in the organic acids pretreatment process.

In the desolventizer shown in <FIG>, the organic acids are further removed from the dried cellulosic pulp to a content of less than <NUM>%, calculated from the total weight of desolventized cellulosic pulp. The desolventizer may utilize direct steam as the desolventizing medium to remove the organic acids furtherly from the dried cellulosic pulp. The desolventizer may further remove the organic acids by using direct steam as the desolventizing medium in step d) carried out at a temperature of <NUM> to <NUM>.

After the desolventization step, the desolventized cellulosic pulp can be used to produce ethanol and other products.

The organic acids vapor also contains water released from the desolventizer is recovered by the condensation system of the organic acids distillation system, wherein the organic acids are recovered for use in the organic acids pretreatment process. The condensation system is carried out by <NUM> to <NUM> condensers, preferably by <NUM> condensers.

Corn straw was used as the lignocellulosic raw material. Cellulosic pulp was obtained according to the organic acid pretreatment process. The organic acids composition is formic acid <NUM>% , acetic acid content <NUM>%, and <NUM>% water, the temperature is <NUM>, the solvation time is <NUM>. After separation, the cellulosic pulp is separated from the liquid fraction.

Approximately <NUM> of cellulosic pulp was recovered, the dry matter content was <NUM>%, the content of the organic acids was <NUM>% and the content of water was <NUM>%, calculated from the total weight of the cellulosic pulp. The cellulosic pulp was fed to the dryer to obtain the dried cellulosic pulp, the drying temperature was <NUM> After drying, the organic acids content of the dried cellulosic pulp was <NUM>%.

The dried cellulosic pulp was introduced into the desolventizer at a feed flowrate is <NUM>/min, direct steam is introduced into the bottom of the desolventizer, the temperature of the steam was <NUM>, and the flowrate of the direct steam feed to the desolventizer was <NUM>/min. The desolventized cellulosic pulp was discharged from the desolventizer.

The organic acids content of the desolventized cellulosic pulp was <NUM>%, calculated from the total weight of the desolventized cellulosic pulp.

A second cellulosic pulp derived from corn straw was prepared under the similar conditions as described above. In this trial however the dryer temperature was slightly lower (<NUM>) while the flowrate of steam in the desolventizer was increased to <NUM>/min. The desolventized cellulosic pulp produced under these conditions had an organic acids content of <NUM>%.

In a third study wheat straw was used as the lignocellulosic raw material and a cellulosic pulp was obtained according to the organic acid pretreatment process described above.

Approximately <NUM> of cellulosic pulp was recovered, the dry matter content was <NUM>%, the content of organic acids was <NUM>% and the content of water was <NUM>%, calculated from the total weight of the cellulosic pulp. The cellulosic pulp was fed to the dryer to obtain the dried cellulosic pulp, the drying temperature was <NUM>. After drying, the organic acids content of the obtained dried cellulosic pulp was <NUM>%.

The dried cellulosic pulp was introduced into the desolventizer at a feed flowrate is <NUM>/min, direct steam is introduced into the bottom of the desolventizer, the temperature of the steam was <NUM>, and the flowrate of the direct steam feed to the desolventizer was <NUM>/min. The desolventized cellulosic pulp is discharged from the desolventizer.

The desolventized cellulosic pulp produced under these conditions had an organic acids content of <NUM>%.

Initially, <NUM> cellulose (lignin content was <NUM>% and organic acids content was <NUM>%) was fed to the reactor, the agitator was started and the pH adjusted to <NUM> with a sodium hydroxide solution, which added <NUM> of additional water. The temperature of the reactor was maintained at <NUM> and the reaction continued for <NUM> minutes.

When the reaction is ended, <NUM> sodium hydroxide was consumed and the lignin content of the treated cellulose was <NUM>%.

In the initial neutralization step of a first processing run, <NUM> cellulose (lignin content was <NUM>% and organic acids content was <NUM>%) was fed to the reactor, the agitator was started and the pH adjusted to pH <NUM> with a sodium hydroxide solution, which added <NUM> of additional water. The temperature of the reactor was maintained at <NUM> and the reaction continued for <NUM> minutes. Following this reaction, the cellulose mixture was filtered and pressed.

In the alkalizing step the neutralized cellulose is added to an alkalization reactor, the agitator is started, and the pH adjusted to pH <NUM> with a sodium hydroxide solution, which added <NUM> of additional water. The temperature of the reactor was maintained at <NUM> and the reaction continued for <NUM> minutes. Sodium hydroxide was added as necessary to maintain the pH at pH <NUM>. After <NUM> minutes the alkalized cellulose mixture was filtered and pressed to obtain the sodium hydroxide liquor and the alkalized cellulose. The sodium hydroxide liquor may be reused in the neutralization step in a second (subsequent) processing operations.

In a second processing run <NUM> of cellulose (with a lignin content of <NUM>% and an organic acids content of <NUM>%) is fed into the neutralization reactor, the agitator is started, and the sodium hydroxide liquor recovered from the alkalizing step of the first processing run is used to adjust the pH to pH <NUM>, the temperature of the reactor is maintained at <NUM> and the reaction continued for <NUM> minutes. Following this reaction, the cellulose mixture was filtered and pressed.

The alkalizing step of the second (and subsequent) processing runs comprise the same as the steps described in the first round. Importantly, the sodium hydroxide liquor recovered after filtering and pressing the alkalized cellulose may be reused in the neutralization step in the next processing operation. In the second round of processing utilizing sodium hydroxide recovered from the first round the total sodium hydroxide consumed was <NUM>, the lignin content of the treated cellulose was <NUM>%.

When the reaction is ended <NUM> sodium hydroxide was consumed and the lignin content of the treated cellulose was <NUM>%.

In the alkalizing step the neutralized cellulose is added to an alkalization reactor, the agitator is started, and the pH adjusted to pH <NUM> with a sodium hydroxide solution, which added <NUM> of additional water. The temperature of the reactor was maintained at <NUM> and the reaction continued for <NUM> minutes. Sodium hydroxide was added as necessary to maintain the pH at pH <NUM>. After <NUM> minutes the alkalized cellulose mixture was filtered and pressed to obtain the sodium hydroxide liquor and the alkalized cellulose. The sodium hydroxide liquor may be reused in the neutralization step in subsequent processing operations.

The alkalizing step of the second (subsequent) processing run comprises the same steps described in the first round. Importantly, the sodium hydroxide liquor recovered after filtering and pressing the alkalized cellulose may be reused in the neutralization step in the next processing operation. In the second round of processing utilizing sodium hydroxide recovered from the first round the total sodium hydroxide consumed was <NUM>, the lignin content of the treated cellulose was <NUM>%.

Initially, <NUM> cellulose (lignin content was <NUM>% and organic acids content was <NUM>%) was fed to the reactor, the agitator was started and the pH adjusted to pH <NUM> with a sodium hydroxide solution, which added <NUM> of additional water. The temperature of the reactor was maintained at <NUM> and the reaction continued for <NUM> minutes.

In the initial neutralization step of a first processing run, <NUM> cellulose (lignin content was <NUM>% and organic acids content was <NUM>%) was fed to the reactor, the agitator was started and the pH adjusted to <NUM> with a sodium hydroxide solution, which added <NUM> of additional water. The temperature of the reactor was maintained at <NUM> and the reaction continued for <NUM> minutes. Following this reaction, the cellulose mixture was filtered and pressed.

In a second (subsequent) processing run <NUM> of cellulose (with a lignin content of <NUM>% and an organic acids content of <NUM>%) is fed into the neutralization reactor, the agitator is started, and the sodium hydroxide liquor recovered from the alkalizing step of the first processing run is used to adjust the pH to pH <NUM>, the temperature of the reactor is maintained at <NUM> and the reaction continued for <NUM> minutes. Following this reaction, the cellulose mixture was filtered and pressed.

Table <NUM> summarizes these sample data.

Extraction liquor was obtained from the organic acid pretreatment process, wherein the composition of the organic acids in the pretreatment comprises formic acid <NUM>%, acetic acid content <NUM>%, and water <NUM>%. The pretreatment temperature was <NUM> and the pretreatment extraction duration was <NUM>. After separation, the extraction liquor was separated from the solid fraction, the extraction liquor was concentrated by evaporation, and the concentrated extraction liquor obtained. The dry matter content of the concentrated extraction liquor was <NUM>%, and the lignin content was <NUM>% (the other components of the concentrated extraction liquor are listed in Table <NUM>).

<NUM> of concentrated extraction liquor was combined with an equal weight of the fresh water (<NUM>) and an emulsifier (SHW300R lab emulsifier, Shanghai Shenghaiwei Electric Instruments Co. , Ltd) operated at <NUM> rpm for about <NUM> was used to produce a lignin suspension. The lignin suspension was introduced into a centrifuge, centrifuged for <NUM> mins, and the first centrifugate (<NUM> of liquid) and a solid lignin layer obtained. The first centrifugate is removed from the centrifuge.

<NUM> of wash water was fed into a spray device to wash the lignin layer within the centrifuge. The washing water in the procedure includes water and mixtures of formic acid, acetic acid and water. When feeding the washing water to the centrifuge, an initial feed of <NUM> of high organic acids content washing water comprising an organic acid content of <NUM>% was used, the second wash comprised <NUM> of low organic acids content washing water wherein the organic acid content was <NUM>%, and a finally wash comprising <NUM> of fresh water was found to wash the lignin layer sufficiently to obtain pure lignin.

Following the initial centrifugation and discharge of the initial centrifugate, the centrifuge continued to operate for <NUM>, during this time the first wash with high organic acids water was performed and the second centrifugate (<NUM>) obtained. The centrifuge was operated for another <NUM> mins during which time the second wash with low organic acids water was performed and the third centrifugate <NUM> was obtained. After a subsequent third wash with fresh water a lignin layer comprising <NUM> was obtained. The first centrifugate and the second centrifugate were recovered and may be incorporated in subsequent hemicellulosic juice production unit operations. The dry lignin was discharged from the centrifuge, and the purity of the lignin determined to be <NUM>% (the components of the lignin at each stage of operation are shown in Table <NUM>).

The third centrifugate (<NUM>) from above was recycled for use as diluent of the concentrated extraction liquor to produce a lignin suspension using the SHW300R lab emulsifier as described above. The obtained lignin suspension was introduced into the centrifuger and the centrifuger was operated as described above to yield a lignin layer of about <NUM>.

In this operation the first wash comprised <NUM> of high organic acids content wash water in which the organic acid content was about <NUM>%. The second wash comprised <NUM> the low organic acids content wash water in which the organic acid content was about <NUM>%, and a final wash comprising <NUM> of fresh water. All centrifuge operations and conditions were carried out as described above. As before, the first and second centrifugates may be recycled for use in subsequent hemicellulosic juice production unit operations. At the end of the operation the lignin is discharged from the centrifuge. In this instance the purity of the lignin was <NUM>% (the components of the lignin at each stage of operation are shown in Table <NUM>).

Once again, the third centrifugate (<NUM>) from the operation described above was recycled to dilute the concentrated extraction liquor to produce a lignin suspension by treatment with the SHW300R lab emulsifier. The obtained lignin suspension was introduced into the centrifuger and the centrifuger was operated as described above to yield a lignin layer.

In this operation the first wash comprised <NUM> of high organic acids content wash water in which the organic acid content was <NUM>. The second wash comprised <NUM> of low organic acids content washing water in which the organic acid content was <NUM>%, and a final wash comprising <NUM> of fresh water. All centrifuge operations and conditions were carried out as described above. As before, the first and second centrifugates may be recycled for use in subsequent hemicellulosic juice production unit operations. At the end of the operation the lignin is discharged from the centrifuge. In this instance the purity of the lignin was <NUM>% (the components of the lignin at each stage of operation are shown in Table <NUM>).

A concentrated hemicellulosic mixture was obtained from an initial hemicellulosic mixture comprising dissolved hemicellulose, organic acids water, and other soluble constituents (<NUM>% dry matter content, <NUM>% formic acid, <NUM>% acetic acid, and <NUM>% water) by use of an evaporator (<NUM> diameter, <NUM> height), using indirect steam to heat the evaporator to evaporate the organic acids and water from the hemicellulosic mixture.

The flowrate of the hemicellulosic mixture into the evaporator was <NUM>/h, with an indirect steam flowrate of <NUM>/h, and an evaporation temperature of <NUM>, which produced a flowrate of the concentrated hemicellulosic mixture of <NUM>/h. The dry matter content of the concentrated hemicellulosic mixture produced under these conditions was <NUM>%. The acids content of the concentrated hemicellulosic mixture was <NUM>%.

Feeding the resulting concentrated hemicellulosic mixture into the top of a stripping column (<NUM> diameter, <NUM> height), and feeding the direct steam into the bottom of the stripping column, served to partially strip the organic acids present in the concentrated hemicellulosic into the direct steam. This produces the stripped hemicellulosic mixture. Adjusting the stripping specifications to a direct steam flowrate of <NUM>/h and a direct steam temperature of <NUM> produced a flowrate of the stripped hemicellulosic mixture of <NUM>/h. The dry matter content of the stripped hemicellulosic mixture was <NUM>%. The acids content of the stripped hemicellulosic mixture was <NUM>%.

Modeling the evaporation and stripping process with Aspen Plus software (Aspen Technology, Inc. , Massachusetts, USA) allowed a number of different operational parameters to be explored based on regression of the vapor-liquid equilibrium with experimental data described above.

Using the model parameters described above, conditions and performance for <NUM>, <NUM> and <NUM> effects evaporation and stripping systems were simulated for concentration of hemicellulosic mixture comprising dissolved hemicellulose, organic acids, and water and other constituents.

The flow sheets for the <NUM>, <NUM>, and <NUM> effects evaporation and stripping system are constructed for use by the Aspen Plus software, are shown in <FIG>, respectively. In these models the hemicellulosic mixture (<NUM>) comprising dissolved hemicellulose, organic acids, water and other constituents is evaporated by evaporator II and evaporator I and the concentrated hemicellulosic juice (<NUM>) is obtained. The concentrated hemicellulosic juice (<NUM>) is fed to the top of the stripping column (<NUM>), fresh steam (<NUM>) is fed to the bottom of the stripping column (<NUM>) and the stripped hemicellulosic juice (<NUM>) is obtained. The vapor discharged from the top of the stripping columns and the additional fresh steam (<NUM>) is used as a heat resource for evaporator I and the vapor discharged from the top of the stripping column and the additional fresh steam(<NUM>) that is condensed within evaporator I is recovered as condensed acid II (<NUM>). The vapor from evaporator I is used as a heat source for evaporator II, while the vapor from evaporator I that condenses in evaporator II serves as condensed acid I (<NUM>). The same scenario involving use of vapor initially recovered from the stripping column into evaporator I and vapor recovered from evaporator I serving as a heat source for evaporator II extends to systems that include additional multi-effect evaporator units as illustrated in <FIG> for a <NUM>-effect evaporator system and <FIG> for a <NUM>-effect evaporator system, there is no need of fresh steam in <FIG> for a <NUM>-effect evaporator system, the more vapor (<NUM>) from the stripping column than the vapor needed for the <NUM>-effect evaporator system is discharged from the top of the stripping column is used to the other system.

The tables below present many of the observed and predicted parameters of each of the multi-effect evaporator systems described herein.

A high water content organic acids solution (<NUM>% formic acid, <NUM>% acetic acid, and <NUM>% water) was fed into a distillation column (<NUM> diameter, <NUM> height, packing column) operating with a heat duty of <NUM> MJ/h, a reflux ratio of <NUM>, <NUM> atmosphere pressure, at a flow rate of <NUM>/h. Under these conditions the condensate of the vapor released from the top of the column is produced at a flow rate of <NUM>/h which comprises <NUM>% formic acid, <NUM>% acetic acid, and <NUM>% water. The distilled organic acids solution, which is discharged from the column bottom, is obtained at a flow rate of <NUM>/h and comprises <NUM>% formic acid, <NUM>% acetic acid, and <NUM>% water.

Modeling this process with the Aspen Plus software using the parameters described above allows simulation of distillation systems comprising <NUM>, <NUM>, <NUM>, and <NUM> columns for separating water from high water content organic acids solutions. The flow sheets produced by the modelling software are shown in <FIG> for <NUM>-column, <NUM>-column, <NUM>-column, and <NUM>-column distillation systems, respectively.

The organic acids composition of the various input streams of high water content organic acids solutions originating from organic acids pretreatment processes are listed in Table <NUM>.

The basic distillation process for a <NUM> column distillation system is illustrated in <FIG>. Three of the four input streams are fed into are fed into the first distillation column (<NUM>). These streams are derived from the hemicellulosic juice evaporation step (<NUM>), the hemicellulosic juice stripping step (<NUM>), and the high water organic acids solution from the desolventizer step of cellulosic pulp processing (<NUM>). The condensate of vapor (<NUM>) discharged from the top of the first column (<NUM>) may be recovered for other unit operations. The concentrated mixture (<NUM>) is discharged from the bottom of the first column (<NUM>) and fed into column <NUM> (<NUM>). The remaining input stream (<NUM>) derived from the extracting liquor evaporation step of lignin production is also fed into column <NUM> (<NUM>). The condensate of vapor (<NUM>) discharged from the top of the second column (<NUM>) may be recovered for other unit operations. The distilled organic acids solution (<NUM>) is discharged from the bottom of the second column (<NUM>). The organic acid content of the various output streams of a two-column distillation system are presented in Table <NUM>.

A similar process representing the process flow within a <NUM> column distillation system is depicted in <FIG>. In this case the operation is similar in terms of input and output streams of the two column system described above. However, in this case the vapor condensates of the first two columns are pooled to form a single output stream (<NUM> of <FIG>) and the distilled organic acids solution discharged from column <NUM> (<NUM>) is fed into a third column (<NUM>) where the vapor condensate (<NUM>) is recovered and the further distilled organic acids solution (<NUM>) is discharged from the bottom of the third column (<NUM>). The organic acid content of the various output streams of a two-column distillation system are presented in Table <NUM>.

Similarly, the process representing the process flow within a <NUM> column distillation system is depicted in <FIG>. The organic acid content of the various output streams of a two-column distillation system are presented in Table <NUM>.

The process representing the process flow within a <NUM> column distillation system is depicted in <FIG>. The organic acid content of the various output streams of a five-column distillation system are presented in Table <NUM>.

According to the simulation flow sheets steam consumption can be significantly reduced by the number of distillation columns present in the system. The data supporting this observation is presented in Table <NUM>.

The indicated reduction in the thermal requirements of a two column system relative to three column system is <NUM>%, while the reduction in the thermal requirements of a four column system are an additional <NUM>% lower than those of three column system, with an overall reduction to <NUM>% of the thermal requirements of a two column system required for a four column system.

Interestingly, additional columns provide minimal energy improvements. See Table <NUM>.

In an initial experiment, corn straw was used as the lignocellulosic plant material source for organic acids treatment using formic acid and acetic acid to extract the hemicellulose and the lignin. The mixture of hemicellulose and lignin was separated to obtain a cellulosic pulp fraction and an extraction liquor. The cellulosic pulp was treated to partially eliminate lignin and washed with water to obtain cellulose. The extraction liquor was concentrated to separate the lignin, after the separation of the lignin, the residue was concentrated and stripped to obtain the hemicellulosic juice. The cellulose and hemicellulosic juice mixture was hydrolyzed and fermented of by adding cellulose enzymes and yeast, respectively, to produce ethanol. The ethanol was separated from the fermentate by distillation, the residual matter of the distillation constitutes the stillage.

Stillage (<NUM> comprising <NUM>% dry matter content) was fed into a decanter to produce a solid fraction <NUM> (comprising <NUM>% dry matter content) and a thin stillage <NUM> (comprising <NUM>% dry matter content) after decanting. The thin stillage was evaporated (in an evaporator operated at <NUM>) to obtain the concentrated stillage <NUM> (comprising <NUM>% dry matter content). The solid fraction and concentrated stillage were combined to obtain a mixture (<NUM>). The mixture was dried in a dryer operated at a temperature of <NUM> to obtain <NUM> of a final organic fertilizer; with a dry matter content of organic fertilizer of <NUM>% and a pH of <NUM>. The organic fertilizer has a dry matter content of <NUM>%, an organic matter content of <NUM>%, and a total nutrient content of <NUM>% (calculated based on a formula wherein Nutrient=Nitrogen + Phosphorus pentoxide + Potassium oxide), calculated from the total dry matter.

In a second trial to produce an organic fertilizer from stillage using corn straw as an initial input to the organic acids treatment process, stillage (<NUM> comprising <NUM>% dry matter) was fed into the decanter. After decanting a solid fraction <NUM> (<NUM>% dry matter content) and a thin stillage <NUM> (<NUM>% dry matter content) were obtained. The thin stillage was evaporated (in an evaporator operated at <NUM>) to produce <NUM> of a concentrated stillage with <NUM>% dry matter content. The solid fraction and the concentrated stillage were combined to produce <NUM> of a mixture. The mixture was dried in a dryer operated at <NUM> to produce <NUM> of the final organic fertilizer with a dry matter content of <NUM>% at pH <NUM>. The organic fertilizer contains <NUM>% organic matter with a total nutrient content of <NUM>%, calculated from the total dry matter.

Claim 1:
A method of producing a desolventized cellulosic pulp containing less than <NUM>% organic acids, the method comprising the steps of:
a) drying a cellulosic pulp produced from organic acids pretreatment of plant material in a dryer to remove the organic acids to a content of <NUM>% to <NUM>%, calculated from the total weight of the dried cellulosic pulp, and
b) capturing vapor released from the dryer for use in the extraction liquor concentration system and other organic acids pretreatment operational systems as a source of thermal energy, and
c) condensing the captured vapor in the extraction liquor concentration system to form a first phase of the organic acids solution of the organic acids pretreatment process, and
d) using direct steam in a desolventizer to further remove the organic acids from the cellulosic pulp, and
e) condensing the organic acids in the vapor released from the desolventizer, to obtain a second phase of organic acids solution of the organic acids pretreatment process; and
reusing the first phase of organic acids solution recovered in step c) of the process in an organic acids pretreatment process.