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Abstract:
A new concept on the formation and control of scaling and other deposits, leading to metallic corrosion in pulp and paper manufacturing has been explained in terms of nano particles. The formation of deposit on the metal surface is conceived to have bearing with nanotechnology.

Harsh Environments and Nanotechnology in Pulp and Paper Manufacturing

New Delhi, India | Posted on March 9th, 2015

In a recent book published by Dr. Mahendra Patel titled, "Better Productivity in Pulp and Paper Mills: Metals and Polymers", which contains iron and steel as well other high performance alloys of Ni, Co, W etc and polymers (plastic, rubber. Teflon, fabrics, polymer composites) in 36 chapters with 616 pages, published by Industrypaper in India, encompasses a chapter on the Nanotechnology Applications in Metals and Polymers.

Dr. Patel reveals that Nanotechnology has already made access in to the domain of pulp and paper (1). Its applications in the different areas of pulp and paper manufacturing are discussed in a book and later publications (2-7). Nano minerals (8) and nano ceramics (9) are discussed elsewhere. Solutions to harsh environments formed during operations and recycling by adapting to nano concepts and technology have been addressed in another book (10).

In the manufacturing process, the tiny colloidal and nano particles often get stagnated and located on the metallic surface due to defects in the metal itself and interruption in the dynamic flow of the fluid in the pipe line or other areas. They become successively the powerful centers of adsorption of other particles and materials based on the charge and other properties. Cellulose, hemicellulose, parenchyma cells, ray cells, sugar molecules, abrasive materials, extractives, micro-organisms and many such harsh materials in the system get accumulated, centering on the nano particles.

According to the present concept, this phenomenon is termed as formation of nucleus over which the micro-organisms or deposits grow. The deposit becomes so much consolidated and hard after some time, for example on the evaporator internal surface that they cannot be broken even on hammering or treatment with hot acids. Ultimately, it turns out to be a miraculous way of forming the deposit with structural modification from the tiny nano-size particles to strong minerals, which are not easily decomposed or broken similar as in nature. It becomes ultimately part of the material and makes the metal corroded and fragile. This is one of the many interesting phenomena, which come within the purview of nanotechnology manufacturing process, namely bottom-up process.

The harsh elements may get deposited through an adsorption process on the nano particles because of its high surface area. The abrasion and corrosion take place at the bottom of the metallic pipe line mostly as a result of the various harsh elements, including acid, alkali, thermal effect etc. Corrosion is due to the initial metal composition and microstructure.

A deposit may be formed on the metal surface by different harsh substances individually or combination of more than one substance. This is according to the analysis results obtained on the different deposit and scale sample.

The microorganisms alone can also form deposits with or without a nano-particle. The cavity, created due to corrosion or abrasion may be the favourable site for formation of the deposit. Viscous and dense substance, such as the extractives (pitch) is the first to settle on such cavities whenever there is any possibility.

There is ample of opportunities for such settling of extractives during the shut-down period. Fine or nano particles present in the system (either injected from outside as a control measure or present in the system) may be the next element to settle over the pitch in the cavity. Other harsh substances may also gradually settle because of the attraction due to the adsorption by the nano particles, which ultimately converts to a solid scale or deposit.

The harsh environments change both quantitatively and qualitatively with change in raw materials and additives,which are the common features in most of the pulp and paper mills. Harsh substances are very intimately mixed with each other and follow the state of dynamic flow pattern in the manufacturing process.

Scaling is common mechanism for formation of harsh environments leading to corrosion and material failure. The solubility equilibrium theory is applicable to scale formation due to calcium carbonate and oxalate, where the chemical reactions at molecular level come into play. The mechanism for commencement and growth of scale to a hard composite material is not only due to chemical phenomena but also due to the physical and mechanical attributes. A nucleus of micro or nano dimension is first formed on the metal surface over which the growth for scale takes place. The defect in metal surface, the particles participating in the scale formation and the growth of scales take place through micro and nano phenomena.

As the concentration of metallic ions in the bulk phase of the solution increases, the adsorption process continues until ion clusters begin to form on the surface. The ion clusters eventually grow to a critical size and become stable enough to succumb to the pressure of flow. In due course, its density increases and becomes hard. The inorganic ion particles depositing over the nucleus are very small in size, of the order of micro or nano dimensions and form chemically stable compounds or minerals. Ion by ion growth occurs as ion clusters continue to be adsorbed by the existing nuclei on the surface. Any crystal formed in solution may also get entrapped within the rapidly growing scale matrix resulting in to a mixed deposit scale. The thermodynamic parameters like temperature and pressure inside the system count equally as the contributing factors for scale formation.

As the precipitation takes place in-situ, the particles formed are expected to be micro and nano particles. The fine particles which deposit over this nano particle are also of micro or nano size; thus the overall phenomena of scaling can be attributed to micro and nano systems.
References
1) Patel Mahendra, Micro and Nanotechnology in Formation and Control of Harsh Environments, Paper Technology, 53 (3), 30-32 (2012).
2) Patel Mahendra, Harsh Environments and nanotechnology in pulp and paper manufacturing, New Applied Technology Conference (NAT), Asian Paper 2012, 25-27 April (2012).
3) Patel Mahendra, Micro and nanotechnology in paper Manufacturing, Publ. Industrypaper, New Delhi & Sambalpur (Odisha), India (2011).
4) Kenneth Norris, Three things you need to know about nanotechnology in papermaking, Pulp & Paper International, New York, (RISI), March 25, (2011).
5) Patel Mahendra, Application of Micro and Nanotechnology in Paper Manufacturing, PaperAsia-2010, Bangkok, Thailand (2010).
6) Patel Mahendra, Technology Forecasting on nanotechnology in Forest Products Industries, PaperAsia, P.33-37, Nov.-Dec. (2010).
7) Patel Mahendra, Micro and nanotechnology for Pulp, paper and Allied Industries, Paper India ,14 (6), 24-28 (2011),
8) Patel Mahendra, Minerals in Paper Manufacturing, Publ. Industrypaper, New Delhi & Sambalpur (Odisha), India (2013).
9) Patel Mahendra, Ceramics in Paper Manufacturing with Advanced and Nano Materials, Publ. Industrypaper, New Delhi & Sambalpur (Odisha), India (2013).
10) Patel Mahendra, Operations and Recycling in Paper Mills with Micro and Nano Concepts, Publ. Industrypaper, New Delhi & Sambalpur (Odisha), India (2012).