Treating kraft mill extract using bipolar membrane

PEER-REVIEWED

BIOREFINERY

Treating kraft mill extract using bipolar membrane electrodialysis for the production of acetic acid RAVIKAT PATIL, JOSEPH GENCO, HEMANT PENDSE, and ADRIAAN VAN HEININGEN

ABSTRACT: The objective of this work was to determine the process conditions for converting sodium acetate, the major component of alkaline hardwood extract, into acetic acid and sodium hydroxide using bipolar membrane electrodialysis (BPMED). The effects of current density and sodium acetate concentration in the feed-salt solution were evaluated using synthetic sodium acetate solution in a feed and bleed mode. This mode of operation represents semibatch processing and was useful for determining the current efficiencies, energy consumption, and other system parameters for the production of about 160 g/L of acetic acid; maximum achievable concentration of acetic acid in electrodialysis; and 30 g/L of sodium hydroxide, which is the concentration sufficient for the extraction of sodium acetate from hardwood. The feed and bleed mode experiments performed at 60 mA/cm2 using 130 and 85 g/L sodium acetate as feed-salt solutions produced similar results, except for a small change in the amount of water transported into the acid and base compartments. The feed and bleed mode experiment performed at low current density of 40 mA/cm2 using 50 g/L sodium acetate as feed-salt solution produced almost similar quantities of acetic acid and sodium hydroxide as those in the other feed and bleed mode experiments. However, the energy consumption and current efficiencies were lower than those for the experiments performed at the current density of 60 mA/cm2. Application: Recovery of acetic acid or acetate salt as a byproduct at kraft pulp mills will be of interest to scientists and engineers who are developing the biorefinery concept.

W

ood contains about 3%–4% acetyl (CH3CO-) groups on a dry weight basis. Currently, acetyl groups end up as a waste product stream in kraft black liquor during pulping and thus are underused. There are several advantages to recovering acetyl groups. First, the additional revenue resulting from the sale of a commodity chemical such as acetic acid would increase the competitiveness of kraft pulp mills. Secondly, a reduction in the acetyl groups by extraction should increase liquor penetration and thus result in improved pulp yield. Lastly, acetic acid sometimes inhibits fermentation of sugars, and the absence of acetic acid would facilitate fermentation of sugars recovered from the wood or pulp as part of a biorefinery. BACKGROUND One of the recent processes for recovering acetyl groups from hardwood is near-neutral extraction, which consists of production of acetic acid and ethanol in kraft pulp mills [1]. This process was later modified to recover acetic acid as the only byproduct in an effort to reduce the capital cost and to improve the rate of return on investment (ROI) [2]. The white liquor charge of 6% effective alkali (EA) at 50°C and a 4:1 liquor-to-wood ratio was shown to result in the complete extraction of acetyl groups from industrial hardwood chips [3]. Low extraction temperature reduces the extraction pressure,

thus avoiding the use of a pressure vessel and reducing the capital cost of the extraction equipment. The low extraction temperature also helps to reduce the energy requirements of the process and the amount of lignin and sugars extracted into the liquor, which in turn simplifies the downstream separation process. Equation (1) shows the chemistry for the deacetylation of wood:

(1)

Method to recover sodium acetate from wood extract The alkaline hardwood extract can be processed in two ways for the separation of sodium acetate. In the first method, sodium acetate from the alkaline hardwood extract was acidified to form acetic acid, which was subsequently separated using liquid-liquid extraction [1]. However, this process has a low rate of ROI due to high capital investment. In the second MARCH 2016 | VOL. 15 NO. 3 | TAPPI JOURNAL

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BIOREFINERY method, electrodialysis was evaluated for its ability to separate sodium acetate from alkaline hardwood extract [3]. Bipolar membrane electrodialysis (BPMED) is an electromembrane process that can convert aqueous sodium acetate into acetic acid and caustic [4,5]. This method seems more promising than the other methods for two reasons. First, the demand for acetic acid is higher than that for sodium acetate, and a significantly higher selling price can be achieved if acetic acid is concentrated to about 99% by weight. Secondly, the use of BPMED allows the recovery of about two-thirds of the caustic used in the extraction process at no additional cost.

Bipolar membrane electrodialysis Bipolar membrane (BPM) is the most critical component of BPMED. It consists of an anion-selective layer and a cationselective layer placed back to back (Fig. 1). These layers are separated by a thin interphase of a few nanometers. When an electric potential difference is applied across a BPM placed in an electrolyte solution and the anion-selective layer of the BPM is facing toward an anode, then most of the ions present in the interphase are quickly removed and only water is left in the interphase. The water in or at the membrane surface begins to dissociate when a critical current density is reached. Further transport of electrical current is accomplished by the flow of hydrogen (H+) and hydroxyl (OH-) ions generated by the dissociation of water molecules present at the interphase. When these ions migrate across the BPM and combine with the corresponding ions of the salt in the neighboring compartments, the conjugate acids and bases are formed in the different compartments. The rates of transport of H+ and OH- ions from the interphase into the outer phases depends upon the

rate of diffusion of water into the interphase and also on the rate of formation of H+ and OH- ions, which is higher in a BPM when compared to the normal water. Figure 2 shows the configuration of the BPMED system used in this study. The system was made up of an alternating series of cation exchange, anion exchange, and bipolar membranes. The cationic membranes permit cations to pass through but exclude anions. By contrast, the anionic membranes permit the passage of anions but exclude cations. BPMED equipment consists of three major compartments: acid, salt, and base. Under the action of an electric field, cations present in the salt compartment move across the cation exchange membrane and combine with the OH- ions present in the base compartment to form base. Similarly, anions present in the salt compartment move across the anion exchange membrane and combine with the H+ ions present in the acid compartment to form acid. The BPMED cell (PCCell/PCA GmbH; Heusweiler, Germany) consists of “n” (up to 200–300) cell pairs, which are formed by “n + 1” cation exchange membranes and “n” anion exchange membranes and BPMs. The BPMED cell shown in Fig. 2 contains a unit cell pair. Because the reactions at anode and cathode produce equivalent amounts of H+ and OH- ions, the electrode rinse streams for both electrodes are often combined to maintain a uniform pH in the electrode rinse compartment. The electrochemical flux of an ion (J) is a sum of its diffusion and electrical migration fluxes and follows the NernstPlanck equation [4], as in Eq. (2):

(2)

where: C = concentration of the ionic species, equivalent/m3 D = diffusion coefficient of ionic species through water, m2/s X = distance, m ϕ = electric potential, volts F = Faraday’s constant (96,485 A∙S/equivalent) zi = charge number on ionic species R = universal gas constant, J/(mole∙K) T = temperature, K The electrical flux depends upon the charge on the ion (z) and is related to the electric current (i). The flux due to the electric field is usually higher than the diffusion flux. As shown in Eq. (3) and Eq. (4), the current efficiency (η) for forming (or transferring or splitting) a given mass of an electrolyte (W) is the ratio of the theoretical (CTheoretical) and the actual (CActual) charges required to form the same mass of the electrolyte:

1. Structure of the bipolar membrane. 216

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(3)

BIOREFINERY

2. Configuration of bipolar membrane electrodialysis.

where: E = molecular weight, g N = number of cell pairs

(4) where: i = current, A t = time, s In electrodialysis, electric charge can be lost because of phenomena such as transfer of undesirable ions; passage of current through nonactive surfaces of the spacer, which do not come into contact with the electrolyte solutions; and backdiffusion of already transferred ions. Thus, the overall current efficiency is usually less than 100%. The electric energy required for BPMED consists of two types of energy: (1) the energy required for transferring ions from one compartment to another, and (2) the energy required for decomposing water molecules. The energy required to circulate electrolyte solutions through the cell is called hydraulic energy. The electric energy (EElec) is calculated by integrating the product of voltage (V) and current (i) with respect to time (t), as in Eq. (5):

(5)

3. Major operating costs of electrodialysis as a function of the current density.

Several studies have been reported on the conversion of sodium acetate into acetic acid and sodium hydroxide using BPMED. Kassotis converted about 6% sodium acetate solution into 35% acetic acid and 8% sodium hydroxide using a three-compartment BPMED cell at the current density of 109 mA/cm2 [6]. In another laboratory-scale study using a three-compartment cell, about 4%–12% solution of sodium acetate was converted into 8%–12% acetic acid solution [7]. The membranes used in this study were synthesized using ion exchange resins. Eurodia Industr y, Pertuis, France, commissioned a two-compartment pilot-scale BPMED unit that converted a byproduct stream of 22% sodium acetate into 18% acetic acid and 6% sodium hydroxide. The current efficiency was optimum, and the payback period was less than two years [8]. As shown in Fig. 3, the operating cost for electrodialysis MARCH 2016 | VOL. 15 NO. 3 | TAPPI JOURNAL

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BIOREFINERY process is made up of two major components: (1) the membrane replacement cost, and (2) the electrical energy cost [4]. As the current density increases, the electric energy cost also increases because of the increase in the specific energy consumption resulting from the increased irreversibility of the process. The electric migration flux of ions and the rate of dissociation of water also increase with increase in the current density; thus, a lesser membrane area is required for the given process. Similarly, as current density is decreased, the electric energy cost decreases and more membrane area is required. The current density at which the yearly operating cost reaches a minimum is considered to be the optimum current density. EXPERIMENTAL Figure 4 is a schematic diagram of the BPMED apparatus being operated in the batch mode used in this study. The diagram shows the circulation of the acid, salt, base, and electrode rinse streams. Five cell pairs of cation exchange, anion exchange, and bipolar membranes (Neosepta CMB/AHA/ BP-1, Tokuyama America; Arlington Heights, IL, USA) were used in these experiments (Fig. 2). The surface area of each membrane was 64 cm2. Spacers placed between adjacent membranes allowed solutions to flow between the membranes. The electrolyte solutions were fed from the bottom of the cell to avoid carryover of any air into the cell. The equipment also consisted of a heat exchanger (not shown), which maintained the temperatures of all solutions below 25°C and thus protected the membranes from damage due to excessive temperature rise. Conductivity probes were used to monitor the concentrations of sodium acetate and sodium hydroxide in the salt and base compartments, respectively. The voltage and current were recorded in real time with a computer.

4. Batch mode bipolar membrane electrodialysis apparatus. 218


Experiment Batch Feed and bleed mode

Flow Rate of Salt Solution, mL/min

Superficial Velocity, cm/s

550

5.1

410–510

3.8–4.7

I. Circulation rates of the salt solution.

The BPMED process can be operated in two modes: (1) constant current, or (2) constant voltage. The constant current mode was chosen for this study because it maintains a constant rate of separation and production. All solutions were circulated for 2 min to remove air bubbles and then direct current was applied. The salt solution was circulated at a constant flow rate as shown in Table I. The circulation rates of other solutions were adjusted to maintain a constant pressure at the inlet of the BPMED cell. As explained previously, in the BPMED process, anions and cations of salt molecules are transferred into the acid and base compartments, respectively. Thus, the concentration of the salt solution continuously decreases and, once it reaches the limiting concentration for the given operating current density, the current is turned off. At the end of each experimental run, the current was first turned off and circulation of the solutions was stopped. As shown in Fig. 3, the yearly operating cost for converting sodium acetate into corresponding acids and bases as a function of current density is needed to determine the optimum current density for this process. According to the guidelines for BPMED, the current density for the BPMED process should be 50–100 mA/cm2 [9]. However, sodium acetate is not a highly conductive salt and acetic acid is a weak acid; therefore, the experiments were performed at 60 and 40 mA/cm2. On the basis of the limiting current density data shown in Fig. 5, the alkaline hardwood extract must be concentrated to in-

BIOREFINERY Parameter

Value

Initial salt solution

85 g/L sodium acetate, 2L

Initial acid solution

42 g/L sodium acetate, 1L

Initial base solution

6 g/L sodium hydroxide, 1L

Initial rinse solution

40 g/L sodium hydroxide, 1L

Current density

60 mA/cm2

II. Conditions for the batch experiment.

Batch experiment using dilute sodium acetate 5. Limiting current density as a function of sodium acetate concentration.

crease its sodium acetate concentration so that it can be practically processed at a current density higher than 15 mA/cm2. The general guidelines for BPMED also state that the initial conductivity of the salt solution used in the BPMED process must be higher than 35 mS/cm [9]. This value of conductivity corresponds to the sodium acetate concentration of 51 g/L, which represents the minimum feed concentration required for application of BPMED. However, to study the effect of sodium acetate concentration in the salt solution over a broader range, additional concentrations such as 130 g/L and 85 g/L were also considered.

Determination of limiting current density The limiting current density is the maximum current density that can be applied to an electrodialysis cell without any adverse effects such as loss of electric energy resulting from the decomposition of water at overlimiting currents. The procedure for the determination of limiting current density is described by Cowan and Brown [9].

A batch scale experiment was performed to demonstrate how sodium acetate can be converted into acetic acid and sodium hydroxide. In this experiment, no materials were added or removed from the system after the initial charge of the salt, base, acid, and rinse solutions. The initial acid and base solutions contained some sodium acetate and sodium hydroxide, respectively, to maintain some minimum electrical conductivity in the acid and base compartments and to avoid high voltage across the BPMED cell. Table II shows conditions for this experiment.

Feed and bleed mode experiments using dilute sodium acetate Feed and bleed mode experiments represent semibatch operation of the BPMED system (Fig. 6). These experiments were performed to determine the current efficiencies; energy consumption; and other system parameters required for the production of about 160 g/L of acetic acid; maximum achievable concentration of acetic acid in BPMED; and 30 g/L of sodium hydroxide, the concentration sufficient for the extraction of sodium acetate from hardwood. In electrodialysis, as the concentration of an ion or a mole-

6. Feed and bleed mode bipolar membrane electrodialysis apparatus. MARCH 2016 | VOL. 15 NO. 3 | TAPPI JOURNAL

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BIOREFINERY Experiment No.

Current Density, mA/cm2

Initial Concentration of Sodium Acetate in Salt Solution and Total Volume Processed

Concentration of Sodium Hydroxide in Initial Base Solution and Volume of Solution

FB-1

60

130 g/L, 10.75 L

4.3 g/L, 2.3 L

FB-2

60

85 g/L, 20 L

3.8 g/L, 3.7 L

FB-3

40

50 g/L, 38.75 L

5.1 g/L, 5.6 L

III. Feed and bleed mode experiments using bipolar membrane electrodialysis.

cule increases in the product compartment, the rate of its backdiffusion also increases and the current efficiency is subsequently reduced. Therefore, current efficiency is a function of product concentration. Consequently, it is necessary to experimentally achieve the desired product concentration to accurately determine the current efficiency for that concentration. To achieve such a high concentration of acetic acid (160 g/L) using laboratory-scale equipment, long-run experiments termed feed and bleed mode were required to be performed. In the feed and bleed mode experiments, when the concentration of sodium hydroxide in the base compartment reached about 30 g/L, most of the base solution was drained from the receiver and approximately the same quantity of water was added. This was done to restore the concentration of residual sodium hydroxide in the base solution to about 5–6 g/L. Also, as the concentration of sodium acetate in the feedsalt solution reached the limiting concentration for the given current density, the residual salt solution was drained and a new batch of sodium acetate was charged. However, the volume of the acid solution was allowed to build up until the acid tank was completely filled. At this time, about 300–500 mL of solution was drained and no water was added into the acid compartment. Table III lists the feed and bleed mode experiments performed using BPMED. These experiments were performed

7. Concentration profiles for a typical batch experiment. 220


using dilute sodium acetate solution. To establish a baseline for comparing the results of these experiments, about the same quantity of salt was split in each experiment. Because acetic acid is a weak acid, the initial acid solution was made up of 1 L of 150 g/L sodium acetate to maintain some minimum conductivity in the acid compartment until the end of each experiment. The initial electrode rinse solution consisted of 1 L of 40 g/L sodium hydroxide solution, here again to achieve some minimum conductivity. The concentration of sodium acetate in the acid compartment was measured at the conclusion of each experiment following conversion to acetic acid using high-performance liquid chromatography. The concentration of sodium hydroxide in the base compartment was determined by titration. RESULTS AND DISCUSSION The reproducibility associated with the BPMED experiments conducted in this study was estimated by performing a batch experiment three times. To avoid the redundancy, the results of these experiments are not included in this article.

Determination of limiting current density As shown in Fig. 5, the limiting current density increased linearly with the increase in the sodium acetate concentration in the salt compartment.

BIOREFINERY

8. Pathways for diffusion in bipolar membrane electrodialysis.

9. Variation in the volumes of salt, acid, and base solutions for batch experiment.

Batch experiment Figure 7 shows results of a typical batch-scale experiment. During the course of the experiment, the concentration of acetic acid in the acid solution gradually increased up to 0.9 eq/L. Similarly, the concentration of sodium hydroxide in the base solution increased from 0.1 eq/L to 1.3 eq/L and the concentration of sodium acetate in the salt solution decreased from 1.15 eq/L to 0.3 eq/L. Although the base and salt solutions should theoretically contain only sodium hydroxide and sodium acetate, respectively, they were found to contain about 0.5 g/L of sodium acetate and 1.6 g/L of sodium hydroxide, respectively. These contaminants are a result of the back-diffusion of ions and molecules across different compartments, as illustrated in Fig. 8. Such diffusion processes reduce the current efficiencies of the BPMED process and thus set an upper limit to the

concentration of acids and bases that can be achieved using the BPMED process [11]. Figure 9 shows the variations in the volumes of salt, acid, and base solutions for the batch experiment. The volume of salt (feed) solution decreased with time due to the electroosmosis (transfer of water molecules of hydration along with the ions) and osmosis. Concurrently, the volumes of acid and base solutions (products) increased with time. Figure 10 shows variation in current and voltage for the batch experiment. Both of these parameters were always maintained below their limiting values. About 140 Wh of electric energy was required to bring about the given changes in the concentrations of the salt, acid, and base solutions. The current efficiencies for the formation of acetic acid and sodium hydroxide were 78% and 88%, respectively. The acetate mass balance closure was 89%. MARCH 2016 | VOL. 15 NO. 3 | TAPPI JOURNAL

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10. Current, voltage, and energy consumption for batch experiment.

11. Concentration of acetic acid in the acid solution for feed and bleed mode experiments.

Feed and bleed mode experiments In feed and bleed mode type experiments, the final concentration of acetic acid in the acid solution was approximately 150–170 g/L (Fig. 11). Experiments FB-1 and FB-2 were performed at the same current density and had similar acetic acid concentration profiles for these experiments. Experiment FB-3 was performed at a lower current density and required additional time to achieve the same level of concentration of acetic acid as in experiments FB-1 and FB-2. The acetic acid concentration seemed to be limited by the transport of water molecules of hydration along with the acetate and hydrogen ions. About 9–17 moles of water were transported into the acid compartment per unit mole of acetic acid formed in the same compartment. The corresponding 222


theoretical limit on the acetic acid concentration in the acid compartment was 160–270 g/L. Figure 12 shows the concentration of sodium hydroxide and sodium acetate in the base and the feed-salt solutions, respectively, as a function of time for experiment FB-1. As explained previously, once the concentration of sodium acetate in the salt solution decreased from the initial value of 130 g/L to about 30 g/L, a new batch of sodium acetate (volume 1.25 or 1 L) was charged and the experiment was continued. Thus, the concentration of sodium acetate in the salt solution varied between these two values and gave rise to the sawtoothshaped linear lines. Similarly, as the concentration of sodium hydroxide in the base solution reached approximately 30 g/L, most of the

BIOREFINERY

12. Sodium hydroxide and sodium acetate concentrations in base and salt solutions (respectively) for experiment FB-1.

13. Cumulative current efficiency for the production of acetic acid.

solution was drained from the base compartment and a similar quantity of water was added. This was done to maintain the concentration of residual sodium hydroxide in the base compartment at about 3–5 g/L. Thus, the concentration of sodium hydroxide in the base solution oscillated between 30 and 3–5 g/L. The salt and base concentration profiles for the remaining experiments were similar to those shown in Fig. 12. Figure 13 shows the cumulative current efficiencies for the production of acetic acid as a function of time. Because the current efficiency was estimated after every 6–8 h, there are no data about the current efficiency for the first 6–8 h in all the feed and bleed mode experiments. The current efficiencies for experiments FB-1 and FB-2 were almost similar be-

cause these experiments were performed at the same current density. Experiment FB-3 was performed at a lower current density and hence, the electrolyte solutions were in contact with each other for a longer period. The longer exposure time was thought to cause an increase in the extent of back-diffusion of ions and molecules diffusing into the different compartments. Thus, the current efficiencies for experiment FB-3 were lower than those for other experiments. Also, the current efficiencies for experiments FB-1 and FB-2 gradually decreased with the time. One possible reason is the increase in the rate of back-diffusion of acetic acid from the acid compartment into the base and salt compartments. The concentration of acetic acid in the acid solution increased with the time and thus increased the driving force for the difMARCH 2016 | VOL. 15 NO. 3 | TAPPI JOURNAL

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BIOREFINERY Experiment FB-1

Experiment FB-2

Experiment FB-3

Sodium-acetate concentration in initial salt solution, g/L

130

85

50

Current density, mA/cm2

60

60

40

20.1

20.6

30.9

Parameters

Time, h Amount of sodium acetate consumed

Moles

13.8

14.3

14.4

Amount of acetic acid formed

Moles

10.9

11.1

10.6

Amount of sodium hydroxide formed

Moles

12.9

12.8

13.4

Wh/kg of acetic acid formed

1912

1906

1764

Acetate mass balance closure, %

84

85

86

Sodium mass balance closure, %

95

92

99

Acetic acid, %

75

76

71

Sodium hydroxide, %

88

88

90

Specific energy

Overall Current Efficiency

IV. Summary of feed and bleed mode experiments.

14. Amount of acetic acid produced in the feed and bleed mode experiments. 224


BIOREFINERY fusion of acid into neighboring compartments. However, the current efficiency for acetic acid in experiment FB-3 remained almost constant throughout the experiment. The current efficiency for the production of sodium hydroxide was approximately 90% during the course of all feed and bleed mode experiments, except for experiment FB-1 where it gradually decreased from 92% to 88%. Also, the current efficiency for the production of sodium hydroxide was always higher than that of acetic acid. A possible reason for the low current efficiency of acetic acid is the low mass balance closure of acetate ions (Table IV). Theoretically, the current efficiencies for the acetic acid and the caustic should be the same since one mole of acetic acid and one mole of caustic are formed for every mole of sodium acetate that is decomposed. Figure 14 shows a detailed comparison of the volumes and concentrations of acetic acid produced in each experiment. To make the plot more legible, the figure does not include the small amounts of acid solution lost in the tubes of the equipment and withdrawn as samples. However, the values shown in Table IV were calculated by considering those losses. The height of each quadrilateral in Fig. 14 represents the volume of an acid solution, and the value shown inside is the concentration of acetic acid in the same solution. Total height of the quadrilaterals shown for each experiment represents the total volume of all acid solutions produced in the corresponding experiment. The total volume of the acid solutions slightly decreased with an increase in the initial concentration of sodium acetate in the feed-salt solution. This was thought to be due to the

decrease in the availability of water molecules for the hydration of sodium acetate in the concentrated salt solution. Table IV shows a detailed comparison of all feed and bleed mode experiments. The results of experiment FB-1 and FB-2 were almost similar because they were performed at the same current density. The salt concentration did not have an appreciable effect when the current density was 60 mA/cm2. Although experiment FB-3 was performed at low current density, it resulted in the production of quantities of acids and bases that were similar to the other experiments. Because of the low current density, the specific energy consumption and the acetic acid current efficiency were lower for experiment FB-3. The current efficiency of sodium hydroxide was not adversely affected by current density or salt concentration. The acetate mass balance closure was significantly lower than the sodium mass balance closure. CONCLUSIONS The experiments performed in this study showed that the current density was the major driving force governing the BPMED process. Surprisingly, the feed concentration did not have an appreciable effect on the process. The feed and bleed mode experiments performed at 60 mA/cm2 using 130 and 85 g/L sodium acetate as feed-salt solutions produced similar results, except for a small change in the amount of water transported into the acid and base compartments. The feed and bleed mode experiment at low current density of 40 mA/cm2 using 50 g/L sodium acetate as feed-salt solution resulted in the production of almost similar quanti-

ABOUT THE AUTHORS The production of acetic acid as a byproduct in kraft pulp mills represents a possible new source of income for the paper industry. This work was conducted as a part of the University of Maine’s biorefinery effort. It continues our work reported in a previous TAPPI JOURNAL article titled “Cleavage Patil of acetyl groups from northeast hardwood for acetic acid production in kraft pulp mill,” (TAPPI J. 12[2]: 57[2013]). In the current study, we determined the process conditions for the splitting of sodium acetate from hardwood extract using bipolar membrane electrodialysis. Closing the acetate mass balance was the most difficult part of this work. It was surprising to find that the feed concentration did not have an appreciable effect on the splitting of sodium acetate by electrodialysis. Scientists and process engineers engaged in the development of a kraft mill biorefinery would find

Genco

van Heiningen

Pendse

this work of interest. As the next step, we are performing two-stage pulping experiments to determine the effect of pre-extraction of acetyl groups on the physical properties of kraft pulp. We will also perform a techno-economic analysis to determine the economic feasibility of the process. Patil is a graduate student, Genco and van Heiningen are professors, and Pendse is professor and chair in the Department of Chemical and Biological Engineering, University of Maine, Orono, ME, USA. Email Genco at [email protected].

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