Technical Summary of the Library of Congress DEZ Book Deacidification Process

Research and Development Tests 1 to 12, 1993-1994

By George L. Eitel

Objectives of the Test Program

The principal factor affecting treated book odor that was learned during the laboratory experiments and the 12 tests conducted in 1993 and 1994 was the importance of controlling the temperature of the DEZ reactions during the permeation stage at temperatures below 100°F, where the treated book odors were found to be acceptable.

Following is a descriptive summary of the 12 Pilot Plant runs that were conducted during 1993 and 1994, plus tables graphically representing test data on the runs.

Overview of Test Runs 1-12

Twelve Pilot Plant test runs were designed by the Library of Congress to achieve the objectives described above and to learn more about fundamental relationships between the DEZ deacidification process and the quality of treated books. The first two runs utilized virgin white paper books, with duplicate operating conditions to eliminate potential effects of inks, paper quality, adhesives, and other foreign substances beyond the acidic paper. What was learned was that a temporary, sweet alcoholic odor developed, which disappeared after several months, while the characteristic industrial DEZ odor persisted, although it also decreased in intensity over the next 6 months.

Runs 3 through 7 were designed to lower the chemical reaction level to determine whether lower odors resulted in the treated books. The alkaline reserve was intentionally held in the 0.5 to 0.8% ZnO level, and permeation time was reduced from 10 hours to as low as 4 hours to minimize the exposure of DEZ to the cellulose to see whether lower odors were produced in treated books. As shown in the attached LOC Pilot Plant Run Data Summary, the alkaline reserves were within the target range, with odor ratings by conservators dropping from about 2.8 to 2.4 on a scale of 1 to 4, with 2.0 being the acceptable standard. Lower permeation reaction temperatures in Runs 4 through 7 may have helped improve the book odors, since independent research also showed that ambient temperatures (85°F) in laboratory experiments produced acceptable or no odors in treated papers. This lower temperature threshold became the target for improving odors in Runs 8 through 12. Also, the alkaline reserve level would be raised to about 1.5% ZnO to check out the impact of processing conditions on books at this more desirable level of buffering.

The goal in Runs 8 through 12 to keep book temperatures during DEZ permeation in the 100 to 105°F range was a function of the initial temperature of the books and the circulating DEZ vapors. Attempts to cool the DEZ to 90°F in Runs 5, 7, and 8 enabled Library and Akzo staffs to identify piping limitations that caused flooding of the DEZ vaporizer at circulation rates above 150 lbs/hr. The plant was designed for over 500 lbs/hr circulation at 25 Torr in the treatment chamber. However, the lower pressure of 15 Torr that is needed to prevent DEZ condensation in the chamber caused extra back pressure on the vaporizer to result in DEZ condensation in the vaporizer outlet unless close attention was paid to DEZ temperatures, pressures, and flow rates to enable the process to stabilize. Engineering assessments of this design limitation showed that future improvements to the Pilot Plant vaporizer outlet piping could eliminate this operating limitation. However, this option was precluded by the limited time available to complete the testing before Akzo permanently shut down the Pilot Plant.

By the completion of Run 12, stable permeation operations were achieved, and the ratings of the LC Management Mass Deacidification Assessment Panel reflected significant improvement of the treated book quality and odors to over 95% acceptance. The lower temperatures of DEZ circulation during permeation seemed directly correlated to the treated book lower odor levels. Another conclusion was that using the extra three days of post-treatment in the special chamber at Akzo significantly lowered the odor level of treated books. Concluding Run 12 was determined to be the best run of the series when looking at the whole process and book quality resulting from application of the DEZ technology. Sufficient understanding of potential process changes that could be employed to improve operability at the low odor conditions and to improve the plant capacity were identified for any possible future use in commercial application of the technology.

Details of each of the twelve runs in this series of optimization testing are presented below. Following also are operating results for all phases of each run, as well as special permeation data summaries.

Individual LC Test Run Summaries

Run No. 1 (January 1993)

This Pilot Plant test used plain, acidic paper books without inks, binders, or other non-cellulosic materials; and the treatment conditions were patterned after normal commercial runs at that time. The resulting level of alkaline reserve in the treated books was an average 1.2% zinc oxide. However, the book odors had a temporary sweet "alcohol" odor, which after several weeks vaporized and left the objectionable industrial "DEZ" odor that was persistent. The overall treatment time for this run was not the typical 60 hours, since a 42 hour downtime occurred during the drying stage when the vacuum pump failed and had to be replaced. No attempt was made until Run 8 to achieve the Library's specified alkaline reserve in DEZ-treated books, which is expressed as an average minimum of 1.5% in calcium carbonate equivalents. The zinc oxide alkaline reserves referred to in this technical report must be multiplied by 1.2 to convert them to calcium carbonate equivalents.

As planned, Run No. 1 would be followed by Run No. 2 to establish a base line with pure paper, from which future process variable adjustments could be made to evaluate improvements in book odor. Since laboratory testing has indicated that presence of air during permeation can cause sweet ethanol odors, future tests could be made after checking for air leaks at the start of the Pilot Plant operation. Attempts to remove the books from the chamber after permeation (but before rehydration) were not successful; it was hoped this could be achieved to identify odors in books before rehydration. Rapid moisture absorption within several minutes prevented determining whether odor formation occurred only during rehydration.

Run No. 2 (February 1994)

With plain paper books and operating conditions similar to those for Run No. 1, this test produced 1.2% zinc oxide alkaline reserve with the same temporary sweet alcohol smell that volatilized to the DEZ odor in several weeks. Zinc oxide distribution on the book pages was generally uniform. No book damage was observed during these two runs.

However, a pattern of unequal zinc oxide levels in the books was discovered, based on the book locations within the treatment chamber. A study of these patterns showed higher zinc oxide contents in the books located in the front of the chamber at the bottom of the stack. Engineering calculations indicated that the actual DEZ circulation rate during permeation was half of the design rate and that the vapor velocity through the distributor nozzles was insufficient to assure proper vapor flow to all books in the stack. This study showed that the desired DEZ circulation rates should be 400 to 550 lbs/hour, which would be tried in future tests. Another conclusion is that there was a bias between zinc oxide analyses performed by LC, the Swiss, and Akzo which needed investigation and resolution. Again, no system leak tests were conducted prior to the testing. Improvements to the water flow control during rehydration were recommended to Akzo by LC.

Run No. 3 (June 1993)

A review of the past 135 Pilot Plant runs was completed by LC. The conclusion was that Test No. 19 (conducted during 1989) should be used as a benchmark run because its specifications were typical of conditions needed to achieve significant reduction in DEZ permeation time and modified post-treatment conditions. The permeation time was reduced from 10 hours to 4 hours and the DEZ circulation rate increased from the normal 200 lbs/hour to 400 lbs/hour. The design circulation rate for the plant is about 550 lbs/hour. No DEZ circulation rate interruptions or problems were experienced at the 400 lbs/hour rate, which is different than what was experienced in later runs at lower temperatures. No coated or supercalendered paper was used during Run 3. Post rehydration processing included two steam stripping cycles (vacuum stripping of water followed by rehydration to 1% water). There were 382 treated books, of which 45 were pure white paper test books, 9 blue test books, 3 Akzo control books and 325 regular disposable library books.

Results of this test also showed temporary sweet alcohol odors followed by the DEZ odor. Alkaline reserve was 0.58% zinc oxide. Some book cover and spine damage was noted. About 20% of the books tested showed non-uniform treatment and zinc oxide distribution. A special LC member Odor Panel was formed to establish quantitative odor measurements of the treated books. Odor evaluations of the Run 3 treated books over three months showed a slow decrease in pure paper book "DEZ" odor and a slight increase in odors in regular books and in blue test books. This led to the conclusion that water rehydration might contribute to the odor forming reactions. Zinc oxide distribution in the treated book stack improved at the higher DEZ flow rates.

Recommendations were made to lower future DEZ reaction temperatures and increase the steam stripping and vacuum hold time during post-treatment to reduce odor production and attempt to strip the odors after they are created. Laboratory permeation experiments at room temperatures continued to produce no odors in the treated paper. By lowering the DEZ and treatment pressure from the normal 35 Torr to 15 Torr, the DEZ condensation point could safely be lowered below 70°F compared to the normal 115 to 130°F operating temperature in the Pilot Plant treatment chamber. Akzo was asked again to conduct a system check for air leakage in Run 4. The continued lower alkaline reserve target of about 0.6% zinc oxide was recommended for the next run, because this would require a lower level reaction and catalytic effect of the zinc oxide on potential odor forming reactions.

Run No. 4 (September 1993)

The objectives of Run 4 were focused on lowering the DEZ reaction temperature to reduce treated book odors. Laboratory experiments at DEZ reaction temperatures from 95 to 130°F produced paper odors. Accordingly, Akzo agreed to reduce operating DEZ temperatures to 110°F or lower, with book temperatures at 70°F. Maximum DEZ circulation rates were desired to improve the distribution of alkaline reserve treatment throughout the stack. Increased numbers of pulsed nitrogen purges and rehydration vacuum strip cycles were planned to remove any odorous volatiles produced in the processing. Representatives of the LC Technical Management Team attended Run No. 4 to assist in additional data gathering and analysis. Temperature profiles of all 18 book RTD's (resistive thermal devices) were taken every 15 minutes. There were 356 books treated, including 15 pure white paper books, 13 blue test books, 3 Akzo test books, and 325 disposable library books.

This run resulted in lower odor levels than in Run 3. The DEZ circulation rate of 500 lbs/hr and 70°F book temperature depleted the DEZ internal inventory and required a reduction to 120 lbs/hour to stabilize operations at a DEZ temperature of 102°F. Condensation of DEZ occurred in the chamber; 12 hours of full vacuum were required to purge the DEZ from the system. Analysis of the pressure/temperature profiles during the permeation cycle shows that the pressure during the first 45 minutes was not low enough to prevent condensation at 82°F. This indicated the need for closer control of the vacuum pressure.

However, the achievement of a lower DEZ temperature operation was most encouraging; and stability of operations seemed possible at a temperature around 90°. The alkaline reserve level was maintained at 0.6% zinc oxide. Since the permeation was not witnessed by technical representatives of Akzo or LC at the 3:00 a.m. timing, it was recommended that all future permeation operations should be scheduled to assure that such representatives could be present. Some special computer adjustments for the lower temperature ranges needed technical assistance for proper settings to enable the chamber operator to continue with the process.

Recommendations for Run 5 included medium DEZ circulation rates (300 lbs/hour) and 90°F DEZ temperature levels to lower the odor levels further. Other conditions were to remain the same. No special rehydration vacuum strips were recommended because the primary effort was to eliminate formation of odors, not to remove them at the end of treatment which could inhibit detection of actual odors being formed.

Run No. 5 (November 1993)

Objectives for Run 5 included improving the odor of the treated books by increasing the DEZ circulation rate to 300 lbs/hour and lowering the DEZ vaporizer outlet temperature to 75°F at a chamber pressure of 15 Torr during permeation. Akzo reviewed the temperature and pressure conditions to be certain that no DEZ would condense in the treatment chamber. The higher DEZ circulation rates were set to improve the DEZ circulation within the chamber and to produce even distribution of the alkaline reserve to all books in the stack. The lower DEZ temperature should reduce the odor levels in the books as seen in Run No. 4 and in the laboratory testing. The types of books to be treated were similar to Run No. 4, which had 15 pure white test books, 13 blue test books, 3 Akzo control books, and about 329 regular collection books. The alkaline reserve target was similar to Run 4 (in the range of 0.5 to 1% zinc oxide).

The average alkaline reserve was on target at 0.8% zinc oxide. Book odors were low, with averages slightly above the control book odors. The LC Management Panel of 10 persons rated 87% of the books to have acceptable odors. This same panel rated books treated in Run 4 to be 91.1% acceptable. Another 3 person LC Odor Panel (conservators) performed quantitative ratings, which indicated sweet "alcohol" and typical DEZ odors were detectable in most of these books up to 4 months after the run was completed, although the number of odorous books and the intensity of the odors decreased during this time. The odor ratings showed that post-treatment for about 4 days in a separate chamber with circulating air improved the short range and longer term odors of the treated books, compared to just rehydrating and returning the books to the Library.

Odor reductions did not meet the Run 5 target for several reasons: mainly because the stability of the process was interrupted three times with a stoppage of DEZ circulation. These interruptions required increasing the DEZ temperatures to as high as 112°F with an average of 94°F (which was better than in Run 4) and reducing the DEZ circulation rates to 200 lbs/hr to resume operations. These interruptions caused some rings of zinc oxide to deposit on the covers and some pages of books, although the LC Management Panel rated 96.5% of the covers and 98.2% of the textblocks as acceptable. In Run 4 this panel rated 83.4% of the covers and 94.4% of the textblocks to be acceptable. The level of alkaline reserve varied within the stack of books as shown by the average zinc oxide of 0.9 % in the books located at the bottom, front of the chamber (near the door), while books in the top rear of the chamber were 0.7% and the bottom, rear locations had 0.8%. This bias had been reflected in earlier runs where the DEZ circulation was below 200 lbs/hr -- this causes laminar flow in the chamber distribution headers and poor DEZ distribution to the book stack.

Run 5 results indicated that operating controls during permeation still needed refinement and that the DEZ temperature had to be closer to 90°F to avoid flooding the DEZ vaporizer outlet piping. Unfortunately, the DEZ vaporizer had no pressure gage or level indicator to enable closer control by plant operators. The next run should aim to stabilize the DEZ circulation at about 200 lbs/hr and 90°F with a chamber pressure of 15 Torr or below. Post- permeation treatment would also be continued.

Run No. 6 (December 1993)

Run 6 objectives were specified to repeat the basic conditions employed in Run 5 -- 0.8% zinc oxide reserve, four hours permeation cycle, one rehydration cycle, and the same type of books. Permeation conditions were based on lessons learned in Run 5, which were to lower the DEZ circulation rate to 200 lbs/hr, to increase DEZ vaporizer temperature to 90°F, and to keep the chamber pressure at or below 15 Torr to prevent DEZ condensation in the vaporizer circuit. Stability of operation at a low temperature was the target for this run.

The odor levels of Run 6 books were better than in Run 5. The LC Management Panel rated 92.4% of the books acceptable for odor vs. 87.1% in Run 5. The 3 person LC conservator Odor Panel ratings were about the same as in Run 5 except for the post-treatment books, where the odors were better than the control books. One panel member rated the books after 3 months to be lower in alcohol smell, although the DEZ odors were slightly higher. The condition of book covers and textblocks was about the same as in Run 5. The alkaline reserve for Run 6 was 0.84% zinc oxide for the white books tested by LC and 0.68% for those tested by Akzo. The average Akzo test book alkaline reserve was 0.87%.

Operating conditions during dehydration and rehydration were similar to Run 5. However, the permeation temperatures and chamber pressure were higher than desired. The DEZ vaporizer temperature averaged about 115°F vs. the 90°F goal. The chamber operating pressure was 22 Torr instead of the 15 Torr goal because one of the three sets of inlet and outlet distributors was closed to improve DEZ distribution within the book stack. No DEZ flow upsets were encountered, and the process control was smooth.

The conclusion drawn from these results was that the distributors should be left open and the lower temperature effects should be evaluated during the next run, repeating target conditions similar to Run 6.

Run No. 7 (January 7, 1994)

The objective for Run No. 7 was to repeat Run No. 6 operating conditions, with all distributors open in the chamber to keep the operating pressure around 15 Torr, the DEZ vaporizer temperature around 90°F, and reduction of the DEZ circulation as needed for stable control of the permeation process. The quantity and types of books used were similar to those utilized in Runs 5 and 6.

This run did not meet desired target processing conditions. The main difference was that the DEZ vaporizer temperature was allowed to drop below 90°F, and at the end of the 4 hour permeation cycle the temperature was 75°F with a chamber pressure of about 12 Torr. With a 150 lb/hr DEZ circulation rate, the back-pressure on the vaporizer caused condensation. However, the process control was as good as could be expected, despite the absence of a pressure gauge at the DEZ vaporizer, which would have permitted fine tuning the control to prevent condensation. The alkaline reserve was 0.63% zinc oxide in the white test books, with a repeat of the bias of higher alkaline reserve levels in books located in the front, lower position of the chamber (0.82%) vs. the upper, rear locations (0.51%). It is believed that the lower DEZ circulation rate may have caused the distribution variance. The LC Management Panel rated the odors acceptable in 86.7% of the books evaluated. This is lower than in the previous run but agrees with the LC Odor Panel, which rated the non-post-treated books to have higher DEZ odors (a 3.4 rating measured against a 2.0 value of acceptability on the control books). Post-treatment improved these odors (1.97) to the level of the control books. The Management Panel determined that 99.1% of the covers and textblocks were acceptable.

With minimum book damage and the ability of post- treatment to lower the book odors to an acceptable level, the conditions suggested for Run 8 were the same as for Run 7, with a closer control of the DEZ vaporizer outlet temperature even if the circulation rate had to be decreased.

Run No. 8 (January 25, 1994)

The Run 8 operating conditions target was modified to obtain about 1.5% zinc oxide reserve and to control the DEZ permeation temperature to 90°F at a chamber pressure of 15 Torr to keep the odor levels low. This test would determine whether the level of alkaline reserve impacts on the odor levels in treated books. A series of drying model simulations was developed to set the new drying conditions for Run 8 at the higher alkaline reserve conditions (this utilized modeling developed for the Swiss Archives tests that were conducted at the Akzo facility). The numbers and composition of books to be treated were similar to Runs 5 to 7.

This run produced an average alkaline reserve of 1.45% zinc oxide, but the levels on each page of selected test books varied widely from 0.9% in the inner area to 2.2% in the outer edges of the paper. Uneven distribution of zinc oxide in the paper was visible with UV light. Two upsets in DEZ flow during permeation were experienced, which contributed to the uneven treatment. The DEZ flow stopped suddenly at the start of permeation and also at the 5.5 hour point of a planned 6 hour permeation cycle. Erroneous levels in the DEZ storage tank (T-903) contributed to the initial upset. The DEZ circulation rate was 150 lbs/hr. The non- uniform zinc oxide distribution on the pages may have resulted from the interruption of DEZ application and from the short permeation cycle time for this higher level of alkaline reserve. The permeation cycle and the dehydration hold cycle would be lengthened in the following run to improve zinc oxide distribution on the book pages.

The three-member Odor Panel rated books as having high odors after rehydration (2.36 rating on 55% of the books that had an alcohol smell, and 2.84 for DEZ odors in 93% of the books), with some improvement noted after post-treatment (1.95 rating with alcohol smells in 33% of the books, and 2.56 rating of DEZ odors in 100% of the books). Again, the control book odor standard against which ratings were made was 2.0. Rings of zinc oxide were evident on some book covers and pages. The LC Management Assessment Panel gave low ratings of acceptability to the books evaluated from this run -- 78.8% of the covers and 92.7% of the textblocks were acceptable. The odors of 87% of the books were acceptable, which is also a low rating.

Recommendations for the next run included extending the drying hold time from 16 hours to 20 hours and increasing permeation time from 6 hours to 12 hours.

Run No. 9 (February 28, 1994)

The objective of Run 9 was to demonstrate stable operation during high alkaline reserve (2%) book deacidification with low permeation temperatures of 90°F to generate low odor levels in treated books. The Swiss Archives drying model was used to predict drying conditions for this higher alkaline reserve test. Only one rehydration would be employed, to permit identification of the basic quality of these operating conditions. The DEZ circulation rate would be limited to about 100 lbs/hr to enhance stable operations.

Run 9 was partially successful. At the beginning of permeation, the DEZ tank was emptied due to a faulty weight indication in the T-903 tank, causing the DEZ flow to stop. Additional DEZ was added, and permeation was resumed after an 8 hour delay. About 1.5 hours into permeation at a 200 lbs/hr. circulation rate, the vaporizer evidently flooded as the temperature dropped to 70°F and the DEZ circulation stopped when the T-903 tank emptied. Akzo raised the DEZ temperature in the vaporizer from the 90°F goal to 135°F, which is known to be too hot to produce low odor books. The average book temperature was 120°F, which is about 20°F higher than demonstrated previously. Chamber pressure was controlled to about 17 Torr for the full 12 hours of the permeation cycle. Alkaline reserve was only 1% in the LC white test books and an average of 1.28 % in the Akzo test books.

Since the books treated in Run 9 had very high odors when they were removed from the Pilot Plant chamber, no further testing was conducted at that time. However, an LC Odor Panel evaluation of the books was conducted 5 months after the run, with odors of the books assessed as 2.43 against a control of 2.0. The LC Management Panel also rated the books and determined that 91.3% had an acceptable odor 5 months after treatment. Weathering of the treated books for 5 months had evidently significantly reduced the book odors. The LC Management Panel rated the covers and textblocks to be 98.9% and 98.5% acceptable, respectively.

Suggestions for the next run included repeating Run 9 conditions but reducing DEZ circulation to 100 lbs/hr. The key to low odor products still appeared to be lower permeation temperatures, and the challenge was to employ Pilot Plant operating conditions that would balance 90 to 95°F permeation temperatures against system design or equipment limitations. Akzo agreed to have its engineer present for the complete permeation cycle during additional runs, to provide specialized assistance in case any abnormalities occurred during the permeation step.

Run No. 10 (March 9, 1994)

This run was designed with Akzo to cool the books to 70°F then vaporize the DEZ at 90 to 100°F, with a low 100 lbs/hr DEZ flow rate. Previous experience continues to show these conditions are achievable if there is close technical monitoring. Conditions favoring 2% alkaline reserve were repeated from Runs 8 and 9.

Run 10 results, however, were not favorable. Poor quality treatment resulted from an unanticipated high percentage of books composed of supercalendered paper that Akzo loaded into the chamber. For this type of paper (which retains a higher moisture content than normal book paper), the operating conditions should have been adjusted to extend the periods of both the dehydration and permeation cycles. However, stable operations were achieved for the full 10 hours of permeation at 150 lbs/hr DEZ circulation, with 14 Torr pressure in the chamber, book temperatures from 80°F to 125°F, and DEZ vaporizer outlet temperatures down to 97°F. This was the first confirmation of stable operations for the full permeation period when striving for lower temperature permeation operations. Close technical operational monitoring seemed to be the key, although the impact of the type of paper being treated was not discerned until later when odor and condition evaluations were conducted.

Alkaline reserve levels measured by Akzo averaged 1.93% for multiple types of paper and 1.70 for white paper test books. LC analyses for its white paper test books averaged 1.63% zinc oxide, with a range from 1.25% in the top rows to 1.9% in the lower front area of the chamber. Low DEZ flows cause poorer distribution within the chamber. The LC Odor Panel average rating of the book odors was 2.85 compared to the 2.0 control standard. The LC Management Panel rated only 88.8% of the books to have an acceptable odor. The covers had a poor rating of 47.8 acceptance due to tackiness, rings, spotting, and other damage. The rating for the evaluated textblocks was also low at 83%, indicating non-uniform treatment. Higher peak book temperatures during permeation could have contributed to the poorer quality of treatment. It seems apparent that the high degree of supercalandered paper in the books was a major factor in the poor treatment results.

The remaining two runs (Nos. 11 and 12) before the Pilot Plant was permanently shut down in April would be targeted to confirm low odor capability of the DEZ deacidification process and/or to identify equipment changes needed to achieve processing conditions required to meet the target book qualities. Plans were made for a LC team of managers and contracted technical specialists to be on site to monitor these runs.

Run No. 11 (March 31, 1994)

The objective of Runs 11 and 12 was to conduct duplicate conditions in the testing to achieve 2% alkaline reserve with permeation targeted at a 90 to 100°F DEZ vaporizer temperature, 12 Torr pressure in the chamber, 100 lbs/hr DEZ circulation, rehydration twice with a water strip after the first rehydration cycle, followed by passivation at 15 Torr for the first thirty minutes of rehydration to minimize residual odors in the books. The traditionally used white and blue test books and other special samples would be removed for testing after rehydration so the 45 crates of books could be post-treated for 4 days in the special Akzo chamber. The goal was to finalize the baseline operation for acceptable book quality treatment. LC staff and a contract engineer were in attendance for both runs.

Results of Run No. 11 included a stable permeation operation with close technical support and monitoring. There were 399 books treated, weighing 799 pounds. Regular disposable library books numbered 368. Permeation operations were stable at 15 Torr in the chamber, with the DEZ vaporizer temperature starting at 113°F and decreasing steadily to 94°F over the 8.7 hour permeation cycle. DEZ circulation rates were held constant at 151 lbs/hr for the entire operation. Stable DEZ inventory was maintained. Two rehydration steps were accomplished with only 6 lbs. of total water being injected.

Akzo lab testing of the treated test books showed the white pages had 1.37% zinc oxide reserve, and the average of all types of paper in the test books was 1.55%. The LC Odor Panel rated the odors to be 3.13 on a standard of 2.0 as acceptable. The LC Management Deacidification Assessment Panel rated 92% of the books as acceptable 4 months after the run was completed. The ratings for acceptable covers and textblocks were 98.9 and 98.1, respectively.

Recommendations for the final run were to repeat most of the Run No. 11 conditions, with an attempt to lower the DEZ circulation temperature and book temperature each by 5 degrees.

Run No. 12 (April 4, 1994)

The objective of Run 12 was to duplicate Run 11 conditions, with the possibility of lowering the starting DEZ temperature another 5 degrees F to further lower the book odors.

Results of treating 402 books weighing 713 pounds included similar drying conditions, permeation operations with book temperatures 8 degrees lower than Run 11, steady DEZ circulation of 151 lbs/hr for 10 hours, chamber pressure of 14 Torr, and DEZ vaporizer temperatures that started at 110°F and decreased to 101°F. DEZ condenser temperatures were hotter than normal, which reportedly prevented lowering the DEZ vaporizer temperature to the mid-90's or lower.

The Akzo analyses of the their test books showed white paper to have 1.40% zinc oxide reserve and the average for all types of paper to be 1.62%. The LC Odor Panel evaluation of the books rated the odors at 2.73 at 1.3 months after treatment compared to a 2.0 standard odor control. The LC Management Panel rated 95.2% of the books to have acceptable odors, which was the best rating for all 12 tests in the series of runs. They rated 97.4% of the book covers and 98.9% of the textblocks as acceptable. These odor ratings could have been even better had the DEZ circulation temperature been lowered 5 to 10 degrees. This final test established an optimum target for meeting acceptable odor thresholds for any future facility design consideration. It is believed that Pilot Plant limitations could be readily solved by engineering design modifications for any future commercialization of the DEZ deacidification process.

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