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MASS DEACIDIFICATION: AN INITIATIVE TO REFINE THE DIETHYL ZINC PROCESS

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SECTION 2: Project Chronology - Miscellaneous Observations
Advantages - Disadvantages - Conclusions - Future

Project Chronology

The following table provides a chronologically arranged descriptive summary of the DEZ R&D initiative, describing briefly the objectives and results of the test runs and of the complementary laboratory research efforts.

Date Activity and objective Comments
1/12/93 Test Run 1: Establish whether odor will be generated in absence of inks, adhesives, covering materials and degradation products from aged paper. Odor was generated in test books made of new paper (no degradation products) without any adhesives, book-covering materials, etc. Therefore, odor must be due to interaction of DEZ with book paper. Baseline operational parameters were established for future runs. Books treated uniformly, 1% alkaline reserve.
2/93 Initiate consultation contracts with Professors Klaus Theopold, University of Delaware, and David Hoffman, University of Houston, to carry out laboratory studies that would complement the pilot plant effort. Parallel laboratory scale experimentation would attempt to comprehend the chemistry underlying the problem of odor formation.
2/20/93 Test Run 2: Establish whether degradation products in aged paper play any role in odor formation. The same test books as used in Run 1 (no adhesives, inks, etc.) were used to fill the chamber, but these books were aged artificially for different aging periods. Established that degradation products in aged paper do not generate odor.
3/93 thru 5/93 Establish laboratory setups at Universities of Delaware and Houston to simulate the DEZ process in the Akzo pilot plant. This laboratory scale work would complement the knowledge gained from test runs in the pilot plant and aid in determining the course of future test runs.
6/93 thru 9/93 Laboratory Experiments at Universities of Delaware and Houston: The objective of these experiments was to reproduce the odor effect encountered in the Akzo pilot plant, and then to attempt a solution. Fifteen experiments were performed under a variety of conditions in an effort to reproduce the odor generated in the plant. These experiments failed to produce any odor, except for a mild odor after permeation at 140F (the highest temperature achieved in the pilot plant). Even this odor was so fleeting that very little of it was left by the time the treated books arrived at the Library inside sealed plastic bags. These experiments definitively established that it was possible to deacidify books with DEZ without producing an odor.

Evidently, some different chemical reactions occur in the pilot plant than those that we were able to recreate in the laboratory. A significant possibility is that the higher DEZ evaporation temperature employed in the plant induces a small fraction of DEZ to decompose before it has a chance to react with paper. These unknown decomposition products exist only briefly to react through a different, uncharacterized chemical route to produce the odorous compounds. Since high odor levels are generally associated with noticeable chemical attack on book covers, these degradation products of DEZ must also react with other materials present in book bindings.
6/14/93 Test Run 3: Study effect of reduced permeation time. Longer permeation time increases the probability of undesirable reactions, besides extending treatment cost. No adverse effects due to reduction in permeation time from 8 hours to 4 hours. Treatment was extremely uniform, but odor developed and chemical damage persisted on some covers, especially on blue test book covers. Alkaline reserve was still at the 1% level and would be kept there until all other issues had been resolved.
9/29/93 Test Run 4: This run went to great lengths to remove all volatile chemicals, including those present originally in the books, and others generated in different steps in the process. The book temperature during permeation was also reduced to 110F, as compared to 130F in Run 3 and 140F in Run 2. This was the lowest temperature Akzo would allow at this time from a safety standpoint. Treated books had a noticeably reduced odor in comparison with previous test runs. An internal LC-management deacidification assessment panel evaluated a limited sample of these books and found the treatment to be acceptable.
7/93 thru 10/93 NIST study to investigate odor formation. Employed available data to suggest plausible causes of odor formation. Concluded that odor may be intrinsic to the reaction of DEZ with a variety of chemical compounds in books and the treatment facility.
9/93 thru 10/93 Study by Prof. L. S. Hegedus at Colorado State University to analyze the odor causing chemicals. Prof. Hegedus ascribed odor formation to reactions caused after decomposition of diethyl zinc, rather than by diethyl zinc itself. The chances of such a decomposition process would decrease as the DEZ and book temperatures in the permeation phase of the process are lowered.
11/10/93 Test Run 5: Attempted to reduce DEZ temperature in the evaporator to 75F. Too high a pressure in the evaporator condensed DEZ to a liquid, which stopped the flow of DEZ vapor to the chamber. DEZ temperature had to be stepped up to continue the permeation process. The rest of the run was conducted at conditions that were about the same as Run 4. The attempt to lower DEZ was a good effort to push the system to the limit. Unfortunately this attempt did not succeed. Odor level was about the same as in Run 4. It became evident with this run that chemical damage on covers is also much reduced along with the odor as DEZ and book temperatures during the permeation process is in decreased.
12/14/93 Test Run 6: This renewed attempt at reducing book temperature during the permeation step did not succeed, as the written instructions were misinterpreted by plant operators and permeation was completed at a higher temperature. In spite of the higher DEZ temperature in the evaporator and high book temperature (140F) during DEZ permeation, the treated books have been evaluated relatively favorably by the Conservation Office odor panel.
1/5/94 Test Run 7: This treatment was completed at a reduced temperature as desired. The book temperature ranged between 83 and 105F. Books were uniformly treated at the lowest DEZ temperature attained thus far and had the lowest odor level yet experienced. Also, chemical damage to pyroxylin covers was noticeably absent.
1/17/94 Test Run 8: Attempted to lower DEZ temperature below the level attained in Run 7. In addition, a higher alkaline reserve of 1.5 to 2.5% calcium carbonate equivalents was attempted. Runs 1 thru 7 incorporated alkaline reserves of 0.8 to 1.0% calcium carbonate equivalents. Due to limitations in plant design, DEZ flow shut off at a temperature in the low eighties before permeation was completed. Nevertheless, an alkaline reserve of 1.5 to 3.0% calcium carbonate equivalents was obtained at a low odor level. The goal of achieving an acceptable product was viewed as a distinct possibility if the DEZ temperature could be kept around 90F.
2/28/94 Test Run 9: Objective was to obtain a high level of alkaline reserve while maintaining low enough temperature conditions to minimize odor formation. One and a half hours into permeation, the DEZ temperature in the vaporizer dropped to 70øF and the DEZ flow was curtailed. The temperature was then raised by an Akzo technician to 135øF, as compared with LC's objective of 90øF. As anticipated, odor level was high after the treatment. However, these books were lost in transit from Akzo to LC for several months. By the time they were received and evaluated, much of the odor had dissipated. The management panel found 91% of these books acceptable from an odor tolerance perspective, and 99% of the covers an textblocks were acceptable.
3/5/94 Test Run 10: Repeat process plan as proposed for Run 9, with relaxation to allow Akzo a maximum DEZ temperature of 100øF -- an allowance of 10øF, since they contend that they are working at the edge of the capability of the plant. Akzo started permeation with DEZ temperature at 130øF -- 30ø above the compromise upper limit, 50ø above the desired upper limit. The temperature was progressively lowered to 100øF a few hours after the start. Most of the books in this run were made up of super-calendered paper, which has a much higher moisture content. Normal drying left too much moisture in the books, generating a lot of heat and giving much higher alkaline reserves (above 3 percent). Permeation time of 10 hours was not enough to react with all of the moisture. Several books remained partially untreated. Higher book temperatures led to higher cover damage. Lower DEZ flow rate led to stagnant areas in the chamber and creation of iridescent patterns on book covers and coated paper.
3/30/94 Test Run 11: Repeat the Run 10 process plan. Akzo operators conducted the run under conditions that defined an operational comfort zone with the DEZ temperature just above 100 degrees for most of the process. All books were uniformly treated. Alkaline reserves easily exceeded the Library's minimum requirement of 1.5 percent calcium carbonate equivalents. The management assessment panel rated 92% of the books to have acceptable odors; the ratings of acceptable covers and textblocks were 98.9% and 98.1% respectively.
4/2/94 Test Run 12: Repeat the Run 10 process plan. Operational conditions were about the same as those in the previous run. The objective was to establish good repeatability under standardized conditions. The process was again completed smoothly at temperatures that were 20 to 30 degrees higher than desired, but the books were treated uniformly at an alkaline reserve level that exceeded the Library's minimum requirement. The management assessment panel rated 95.2% of the books to have acceptable odors, which is the best rating of all 12 runs. They rated 97.4% of the covers and 98.9% of the textblocks acceptable.
7/94 Final receipt of treated books.  
8/94 Conservator and management panels conclude assessments.  
Miscellaneous observations

Uniformity of Deposition of Zinc Oxide within Paper: Recent work reported by MacInnes and Barron (Journal of Materials Chemistry, v. 2, pp. 1049-1056, 1992) indicated that scanning electron microscopy (SEM) data showed that the zinc oxide deposited by the DEZ process in coated paper did not penetrate under the coating. This observation was contrary to SEM data that had been obtained by the Library during the earlier developmental work on the DEZ process. Further investigation was undertaken to resolve these conflicting sets of data. Ten different coated paper samples selected at random from more than 300 books treated in Run 4 were analyzed by SEM and X-ray microanalysis in LC's Research and Testing laboratories; further confirmation was obtained from John Koloski and James Bond at the Government Printing Office, who also mapped the distribution of zinc oxide across the edge of each of the ten papers. All of the papers subjected to these analyses, without exception, showed the zinc oxide to be deposited most uniformly throughout the paper matrix under the coating. This is, in fact, one of the best advantages that the DEZ process has to offer. DEZ can penetrate through all kinds of paper, and through the thickest books, to deposit finely divided zinc oxide most uniformly. It can do so, not only because it is a gas, but because it is attracted towards the bound water molecules dispersed evenly throughout the book mass and reacts with them to form zinc oxide, which constitutes the alkaline reserve.

Effect of DEZ Treatment on Photographic Materials: It is not surprising now and then to find microfiche attached inside a book cover. Also, one of the most significant problems in photographic preservation is the acid hydrolytic degradation of cellulose nitrate and acetate-based photographic film. The possibility of using a mass deacidification process for neutralizing the acids in large quantities of film appeared attractive.

A few samples of microfiche, microfilm and motion picture film were included in one of the test runs with DEZ. The results were disastrous. The films curled and shrank badly. The effect was much worse than what one would expect from only the drying of film. It is clear that any photographic film material would be lost if exposed to DEZ.

Optimization of the DEZ process: The resolution of the problems of odor and visual damage did not come about easily and even entirely satisfactorily, as is evident from the preceding account. At least four of the twelve runs were compromised due to stoppages induced by limitations in the plant design or its operation. As a result, it was not possible to extend this effort to optimization of the process to make it run more economically. In any case, since Akzo decided to close down this plant, its optimization would have been of limited value. It needs to be pointed out that there is plenty of room for cutting back on several steps in the process, especially in the nitrogen flushing before the permeation step. Nitrogen consumption, which was a significant part of the total operational cost, as well as process time could have been cut down significantly. The drying step also needed to be made more efficient by using a higher capacity pump and a wider bore tubing connection to the chamber -- improvements suggested by LC personnel soon after the plant had been built. However, Akzo management was not persuaded that such a plant modification would make a significant difference in the rate of drying of books. Another possibility was to introduce a pre-drying step in a separate chamber to save chamber operation time.

The drying step needed to be further standardized. Process conditions for this step needed to be correlated firmly with the weight of books to be treated. The drying conditions, used successfully in most of the runs, caused Test Run 10 to fail, because most of the books in this run were composed of supercalendered paper, which is much heavier and, therefore, has a significantly higher moisture content. The average drying conditions were inadequate for this run, with the result that too high an alkaline reserve was deposited on the outer margins (about 4 percent calcium carbonate equivalents), while the insides of the books remained untreated when permeation was stopped.

Advantages of the DEZ Technology
Disadvantages of the DEZ Technology Conclusions

Odors are caused by higher temperatures. It has been clearly established that there is a definite and proportional relationship between temperature levels to which DEZ is exposed in the vaporization chamber and in the main reaction chamber during the permeation step and the resulting odor level in treated books and the chemical attack on book covers, adhesives, and labels. The higher the temperature to which DEZ is exposed, the stronger are the odors and the chemical attack on book materials. These adverse effects can be minimized, and even eliminated, by promoting process conditions and plant design that minimize the heat to which DEZ is exposed. Books treated at ambient DEZ temperatures do not develop any odor. A logical possibility is that a small fraction of DEZ decomposes before it can react with the moisture in paper. The unknown products of this decomposition, which may well be transient in nature, lead to the formation of the odorous compounds, as well as the chemical attack on some book covers, labels, and coated papers.

It has also been established that tight or loose packing of books; the amount of alkaline reserve; reactions of DEZ with degradation products, unknown paper chemicals and adhesives; phases of the moon and the positions of various planets and constellations do not have any influence on the observed adverse effects of DEZ treatment.

Iridescent rings on coated paper and covers have been eliminated. Iridescent rings on reflective surfaces, such as smooth coated paper and book covers appear when the reaction between DEZ and moisture in these materials is a relatively static, diffusion-controlled process. This is a special case of well-established phenomena in gas-solid interactions, which lead to formation of products in concentric spheres when the penetration of the gas into the solid matrix is controlled mainly by diffusion. In the case of DEZ reaction with the moisture in paper, these concentric deposit patterns can be eliminated by maintaining a constant turbulence in the DEZ flow within the reaction chamber. The key parameter is the DEZ flow-rate. For the Akzo chamber, the minimum acceptable flow-rate was established at 150 pounds per hour. Higher flowrates are better, but DEZ flow into the chamber must be sacrificed to obtain lower vaporization temperatures. In spite of a satisfactory flow rate, if the permeation process is upset and comes to a standstill, even briefly, the formation of the iridescent ring pattern is unavoidable.

Problems are resolvable with minor engineering changes. It is believed that minor modifications in the plant could have been performed under normal circumstances to totally eliminate odor formation. However, Akzo's decision midway through this project to shut down the plant early in 1994 precluded any such initiative.

Near-perfect deacidification of books is achievable. Given the less-than-satisfactory circumstances under which the Library had to conduct a significant portion of this research and development initiative, it is heartening that the final two redundant test runs demonstrated that near- perfect results can be achieved by deacidifying books with the DEZ process, which is the only gas phase process known to leave a permanent alkaline reserve within paper.

Future of the DEZ Technology

The technology behind the DEZ process is now a tried and proven reality. It has been demonstrated to work well enough to meet all of the Library's requirements. It would be hard for any liquid phase, solvent-based process to match (1) the uniformity with which this process can deposit the alkaline reserve within even bulky, oversized books and within dense, supercalendered and coated paper, and (2) lack of any adverse effects on colored media. However, the utilization of this technology comes at a significant cost. These costs can be contained only with a significant capital investment in a large enough plant. If cheaper processes become available that are almost as good, safer, and probably more convenient, such costs may be hard to justify.

Since Akzo Chemicals' untimely decision to shut down the existing plant forecloses the Library's near-term ability to experience the efficiency of the DEZ technology at a large production capacity, and because of the high capitalization cost for a new DEZ plant, the Library will continue to assess the benefits offered by other promising, simpler, and cheaper deacidification technologies.

The Library's patents on the DEZ process expired in 1993 and 1994, and Akzo Chemicals terminated its DEZ license with the U.S. Commerce Department effective September 1994 (see Akzo's June 1994 letter in the Appendix). If any other institution or company in the U.S. or elsewhere decides to apply the DEZ technology to deacidification of library collections and archival materials, the Library will be pleased share the extensive technical expertise it has acquired in the development of this process.

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