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Enzymes Find Their Niche

New technologies are inevitably subject to some early oversell of expectations — witness the current hype around nanotechnology. So it was in the early 1980s for biotechnology. Now, however, one branch of biotechnology — the application of enzymes — has established a niche in a number of areas of pulp and paper manufacturing. Why now? Part of the reason is the increased availability of a whole range of enzymes at reasonable cost. New enzymes can be made to order, based on genome information for the major wood-degrading microorganisms now available in the public domain. Another factor is a concerted research effort by ourselves and a number of players (see side bar) to develop a cost-effective portfolio of enzyme-based applications in papermaking.

Kraft pulp bleaching

Xylanase addition to brownstock prior to bleaching saves on bleaching chemicals. This observation by VTT, Helsinki scientists in 1984 [1] lead to the first widespread application of enzymes in the industry. Today about 10% of all kraft pulp is manufactured with xylanase prebleaching. In North America, Iogen Corp, based in Ottawa has established a market leadership position. Globally, other suppliers such as AB Enzymes, and more recently Diversa, are also selling to this market. In Japan, Oji Paper is unique in manufacturing xylanase on-site at its Yonago mill. The enzyme is produced from a bacterial fermentation of pulp side stream which results in a xylanase/pulp mixture. This mixture is then fed to the main pulp brownstock storage tank.

The mechanism of xylanase prebleaching is still a subject of debate. Certainly there is some solubilization of xylan by the enzyme, and this yield loss and the resulting increase in effluent load has to be factored into the economics of prebleaching [2]. Whether the enzyme just hydrolyzes surface xylans, or is able to break linkages between hemicellulose and lignin is still a subject of debate. Xylanase accessory enzymes are defined as enzymes that can attack other hemicellulose linkages. There is currently some research effort directed to determining if these enzymes (mannanase, acetyl xylan esterase, arabinases, etc) can, either alone or in combination with xylanase, produce an improved more specific bleaching effect.

Certain oxidative enzymes, such as laccase and peroxidase can directly target residual lignin in kraft pulp [3], which is the objective of bleaching. In spite of intensive research at Paprican and elsewhere, these enzymes have not been applied commercially in kraft pulp bleaching (laccase has however found some applications in textiles and as a hair dye!). The problem with these enzymes is that they require a dedicated bleaching stage, with addition of an oxidant (oxygen or peroxide) and a chemical mediator that can penetrate the fibre cell wall. Laccase has a rather broad range of substrates and may find other applications, such as in extractives removal (see below).

Biopulping

Biopulping was originally defined as pretreatment of wood chips with fungal cultures which modified lignin and extractives during days or weeks of incubation [4]. More recently, enzymes have been applied either to chips or pulp reject fractions. One such enzyme is cellobiohydrolase, part of the cellulase enzymes family. This enzyme is available in fairly pure form from AB Enzyme thanks to a cloning program at the VTT, Helsinki labs. A full scale trial was run at the UPM-Kymmene Rauma mill in Finland [5]; a savings in energy was reported during the trial and in associated pilot work. A different approach was investigated by Stora Enso researchers who used an Impressifier to impregnate chips with pectinase enzyme [6]. The chips could then be refined with a lower energy input to reach the required freeness and strength. These applications are not yet being used commercially, as far as we are aware.

Papermaking

RETENTION: Cationic demand can be reduced in peroxide brightened mechanical pulp furnishes by adding pectinase enzyme [7]. This discovery by Thornton et al. at Turku University, Finland can be explained by the fact that alkaline peroxide solubilizes pectins which create a significant part of the cationic demand. Once hydrolyzed by pectinase, the demand is lowered. Some development work by Paprican’s Reid and Ricard with Novozymes pectinase [8] has resulted in application of this technology in North America. Savings in retention aids and white water sewering can be achieved. Recently the Holmbom patent was purchased by Nalco.

EXTRACTIVES CONTROL: Lipase enzymes can hydrolyze triglycerides and esters found in wood extractives. A Novozymes lipase (Resinase) was found to provide pitch control in some mills [9]. Trials of lipase have been pursued for other extractives-related runnability problems, including low friction and low strength. Although there is a lack of conclusive evidence, some reports have claimed that lipase treatment improves the coefficient of friction of newsprint. One problem with lipase is that the product of hydrolysis is fatty acids, which can also cause papermaking problems. An alternative approach, still under development, is to oxidize fatty acids and their triglycerides with laccase enzyme [10]. This results in cleavage of fatty acids and triglycerides to shorter chain aldehydes which are more hydrophilic.

STICKIES CONTROL: As recently reviewed [11], Buckman has developed an interesting enzyme application for stickies control. The enzyme is an esterase which targets polyvinyl acetate, a component of stickies, hydrolyzing the PVA to the less sticky polyvinyl alcohol. According to Buckman, image analysis is used to measure the effect on stickies, and the enzyme is now in use at many mills around the world [12].

IMPROVING DRAINAGE: Employing xylanase or cellulase to improve the drainage on a pulp or paper machine has been pursued by several mills with the objective to increase the production rate. It has been suggested that enzyme treatments removed some of the fines or peel off fibrils on the fibre surface and thus lower freeness. Amylase has also been used to target starch viscosity in tissue mills or where OCC is used as recycling furnish.

BOIL-OUTS AND SLIME CONTROL: Using amylase in combination with lipase and protease in paper machine boil-out has provided unprecedented results compared to traditional caustic treatment. These enzymes are also effective to remove slime and control the growth of bacteria in paper machine systems. This technology has been well received by mills, especially those using a starch based coating system.

CATALASE: Although this group of enzymes has a notorious reputation in deinking plants where it can lead to higher peroxide consumption, they have found some application to deactivate residual hydrogen peroxide after mechanical pulp bleaching to avoid the use of strong acid. Both acid and alkali catalases are commercially available. A recent study has indicated that a catalase can tolerate extreme conditions and works best at temperatures around 90C and a pH above 9 [13].

DEINKING: Cellulases are widely reported to facilitate deinking of mixed office waste. The company Enzymatic Deinking Technologies (EDT), as its name suggests, has been one of the most active players in this application. Most deinking trials with enzymes are by necessity at neutral or acidic pH which makes it difficult to compare with conventional alkaline deinking chemistries. Cellulases appear to be less effective for ONP deinking [14]. Ink particles tend to be smaller after treatment of ONP with cellulase, lowering the pulp brightness. With the trend of deinking chemistry moving towards neutral conditions, there may be more opportunity to use enzymes or enzyme/chemical combinations in deinking plants.

By-products

There has been much talk about biorefineries lately, aimed at improving the profitability of kraft mills by diversifying the product mix. One idea is to prehydrolyze chips to provide a hemicellulose rich stream as a by-prod
uct. Recently, Oji Paper claimed that hydrolysis of such hemicelluloses by xylanase to give a mixture of xylooligosaccharides results in a product with therapeutic value. Another by-product is xylitol, widely used as an artificial food sweetener.

One suggested biorefinery product is fuel ethanol, produced by enzymatic hydrolysis of cellulose substrates such as sawdust, followed by fermentation of the resulting glucose. Although the economics of this process do not currently compete with fuel ethanol production from starch, there has been a significant decrease in cellulase manufacturing costs as the result of USDOE sponsored research into fuel ethanol by Genencor and Novozymes.

Outlook for the next decade

With modern biotechnology tools, especially microbial genetics, advancing at an ever-faster pace, novel enzymes and new enzyme applications will become available for the pulp and paper industry. There is a substantial amount of research effort being carried out at academic and industrial organizations. A list of potential enzyme applications under investigation includes new enzymes for kraft pulp bleaching, new enzymatic approaches to reduce mechanical pulping energy, enzyme sensors for smart paper products, etc. It is also anticipated that the newly developed genetic techniques will significantly reduce the cost for enzyme production and improve the characteristics of these biocatalysts.

References

1. VIIKARI, L., M. RANUA, A. KANTELINEN, J. SUNDQUIST, and M. LINKO, Bleaching with enzymes. Proceeding Third International Conference Biotechnology Pulp Paper Industry, Stockholm: 67-69 (1986).

2. PAICE, M.G., S. RENAUD, R. BOURBONNAIS, S. LABONTE, and R. BERRY, The effect of xylanase on kraft pulp bleaching yield. Journal Pulp and Paper Science, 30(9): 241-246 (2004).

3. BOURBONNAIS, R. and M.G. PAICE, Enzymatic delignification of kraft pulp using laccase and a mediator. Tappi J., 79(6): 199-204 (1996).

4. AKHTAR, M., G.M. SCOTT, R.E. SWANEY, and D.F. SHIPLEY, Biomechanical pulping: a mill-scale evaluation. Resources Conservation and Recycling, 28(3-4): 241-252 (2000).

5. PERE, J., J. ELLMEN, J. HONKASALO, P. TAIPALUS, and T. TIENVIERI, Enhancement of TMP reject refining by enzymatic modification of pulp carbohydrates – A mill study, in Biotechnology in the Pulp and Paper Industry: 8th ICBPPI, L. Viikari and R. Lantto, Editors. 2002, Elsevier Science Bv: Amsterdam. p. 281-290.

6. PENG, F., R. FERRITSIUS, and U. ANGSAS, Mechanical pulping with pectinase pretreatment of wood chips. International Mechanical Pulping Conference Proceedings: 335-340 (2003).

7. THORNTON, J.W., C. ECKERMAN, R. EKMAN, and B. HOLMBOM, Treatment of alkaline treated pulp for use in papermaking. European Patent Application. # 92304028.1, (1992).

8. REID, I. and M. RICARD, Pectinase in papermaking: solving retention problems in mechanical pulps bleached with hydrogen peroxide. Enzyme Microb. Technol., 26(2-4): 115-123 (2000).

9. SHARYO, M., H. SHIMOTO, H. SAKAGUCHI, M. ISAJI, Y. FUJITA, H. AWAJI, M. MATSUKURA, and K. HATA, The recent progress and general status of lipase pitch control technology in Japan. J. Japan Tappi, 47(10): 1223-1233 (1993).

10. ZHANG, X., S. RENAUD, and M.G. PAICE. The potential of laccase to remove extractives present in mechanical pulp and whitewater from TMP newsprint mills. in Proceedings PACWEST Conference. 2005. Harrison Hot Springs.

11. JONES, D.R., Enzymes: using Mother Nature’s tools to control man-made stickies. Pulp Pap. Can., 106(2): 23-25 (2005).

12. PATRICK, K., Enzyme technology improves efficiency, cost, safety of stickies removal program. Paper Age, (September): 22-25 (2004).

13. THOMPSON, V., K. SCHALLER, and W. APEL, Purification and characterization of a novel thermo-alkali-stable catalase from Thermus brockianus. Biotechnology Progress, 19(4): 1292-1299 (2003).

14. XIA, Z., A. BEAUDRY, and R. BOURBONNAIS, Effects of cellulases on the surfactant assisted acidic deinking of ONG and OMG. Progress Paper Recycling, 5(4): 46-58 (1996).

Michael Paice and Xiao Zhang are both researchers from the Environment Group at the Pulp and Paper Research Institute of Canada (PAPRICAN), Pointe Claire, QC.

The Players in Enzyme Applications

Novozymes – based in Denmark, Novozymes is the largest producer of enzymes with world sales of more than US$ 1 billion in 2004. Their biggest market is detergent enzymes (35% of sales including proteases, cellulases and lipases), but last year sales to the fuel ethanol market (mainly amylase for starch hydrolysis) increased substantially. In North America, Novozymes has a group in the University of California at Davis, which focused on laccase and cellulase research, and also has a manufacturing and sales plant in NC.

Genencor – recently purchased from Eastman Kodak by Danisco, a Copenhagen based sugar producer, Genencor has research and production facilities in both Europe and North America. Sales in 2004 were around US$ 400 million. Like Novozymes, Genencor has benefited from the USDOE research focus on improvement of cellulase enzymes.

Iogen – based in Ottawa, Iogen has established a predominant position in xylanase prebleaching by providing a strong customer service strategy. The company is primarily focused on fuel ethanol production from biomass, and is supported by Shell and Petrol-Canada. As well as cellulase and xylanase products Iogen has developed a steam-explosion technology for pretreatment of cellulose prior to cellulase hydrolysis.

AB Enzymes – formerly Primalco, and then Rohm Enzymes, this company is based in Finland and is mainly marketing in Europe, especially Scandinavia. They have previously been involved in developing products from VTT (the Finnish equivalent of the Canadian National Research Council (NRC)).

Buckman Labs – this global chemical and service provider has a biotechnology research group in Memphis, TN which recently developed the esterase-based stickies treatment. The company provides several enzyme-based product packages for deposit control applications. Several other products are under development to complement their existing chemical technologies.

EDT – based in Norcross, Georgia, EDT has its strength in providing enzyme deinking and pitch control technologies. It has some activities in China run by a separate entity, Greenphile Ltd.

Tritex – based in Saint-Eustache, QC, Tritex specializes in producing dyestuffs, pigment dispersions and auxiliaries for the textile and paper industries. The company has recently expanded its business into enzyme deinking and pectinase-aided retention.

DSM (Netherlands), Diversa (USA), and Kao (Japan) are all enzymes producers for other industries, and as such represent a potential source of supply for the pulp and paper industry.

Nalco, Kemira, are primarily chemical suppliers with some enzyme product interest.