Module 2 Unit 2 Paper and Related PDF

UNIT 2: Paper and Related TLO 2: Categorize the different petrochemical products on its proper application based on its properties and composition. Apply the theory behind the manufacturing procedures of paper in other chemical engineering subjects and in ac...

UNIT 2: Paper and Related TLO 2: Categorize the different petrochemical products on its proper application based on its properties and composition. Apply the theory behind the manufacturing procedures of paper in other chemical engineering subjects and in actual fabrication of the product. Illustrate flowcharts, P&ID and PFD on the different industries. PULP AND PAPER INDUSTRY Papermaking is thought to have originated in China in about 100 A.D. using rags, hemp and grasses as the raw material, and beating against stone mortars as the original fiber separation process. Although mechanization increased over the intervening years, batch production methods and agricultural fiber sources remained in use until the 1800s. Continuous papermaking machines were patented at the turn of that century. Methods for pulping wood, a more abundant fiber source than rags and grasses, were developed between 1844 and 1884, and included mechanical abrasion as well as the soda, sulphite, and sulphate (kraft) chemical methods. These changes initiated the modern pulp and paper manufacturing era. Papermaking, formation of a matted or felted sheet, usually of cellulose fibers, from water suspension on a wire screen. Paper is the basic material used for written communication and 20 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  the dissemination of information. In addition, paper and paperboard provide materials for hundreds of other uses, such as wrapping, packaging, toweling, insulating, and photography. The word paper is derived from the name of the reedy plant papyrus, which grows abundantly along the Nile River in Egypt. In ancient times, the fibrous layers within the stem of this plant were removed, placed side by side, and crossed at right angles with another set of layers similarly arranged. The sheet so formed was dampened and pressed. Upon drying, the glue-like sap of the plant, acting as an adhesive, cemented the layers together. Complete defibring, an indispensable element in modern papermaking, did not occur in the preparation of papyrus sheets. Papyrus was the most widely used writing material in ancient times, and many papyrus records still survive. HISTORICAL DEVELOPMENT Papermaking can be traced to about AD 105, when Ts’ai Lun, an official attached to the Imperial court of China, created a sheet of paper using mulberry and other bast fibers along with fishnets, old rags, and hemp waste. In its slow travel westward, the art of papermaking reached Samarkand, in Central Asia, in 751; and in 793 the first paper was made in Baghdad during the time of Hārūn ar-Rashīd, with the golden age of Islāmic culture that brought papermaking to the frontiers of Europe. By the 14th century a number of paper mills existed in Europe, particularly in Spain, Italy, France, and Germany. The invention of printing in the 1450s brought a vastly increased demand for paper. Through the 18th century the papermaking process remained essentially unchanged, with linen and cotton rags furnishing the basic raw materials. Paper mills were increasingly plagued by shortages; in the 18th century they even advertised and solicited publicly for rags. It was evident that a process for utilizing a more abundant material was needed. RAW MATERIALS Plant fibers 21 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  The cell walls of all plants contain fibers of cellulose, an organic material known to chemists as a linear polysaccharide. It constitutes about one-third of the structural material of annual plants and about one-half that of perennial plants. Cellulose fibers have high strength and durability. They are readily wetted by water, exhibiting considerable swelling when saturated, and are hygroscopic—i.e., they absorb appreciable amounts of water when exposed to the atmosphere. Even in the wet state, natural cellulose fibers show no loss in strength. It is the combination of these qualities with strength and flexibility that makes cellulose of unique value for paper manufacture. Most plant materials also contain non-fibrous elements or cells, and these also are found in pulp and paper. The non-fibrous cells are less desirable for papermaking than fibers but, mixed with fiber, are of value in filling in the sheet. It is probably true that paper of a sort can be produced from any natural plant. The requirements of paper quality and economic considerations, however, limit the sources of supply. Wood Pulped forest tree trunks (boles) are by far the predominant source of papermaking fiber. The bole of a tree consists essentially of fibers with a minimum of non-fibrous elements, such as pith and parenchyma cells. Forests of the world contain a great number of species, which may be divided into two groups: coniferous trees, usually called softwoods, and deciduous trees, or hardwoods. Softwood cellulose fibers measure from about 2 to 4 millimeters (0.08 to 0.16 inch) in length, and hardwood fibers range from about 0.5 to 1.5 millimeters (0.02 to 0.06 inch). The greater length of softwood fibers contributes strength to paper; the shorter hardwood fibers fill in the sheet and give it opacity and a smooth surface. When the sulfite process was the chief method of pulping in the early days of the pulp industry, spruce and fir were the preferred species. Since that time, advances in technology, particularly the introduction of the kraft process, have permitted the use of practically all species of wood, greatly expanding the potential supply. Rags Cotton and linen fibers, derived from textile and garment mill cuttings; cotton linters (the short fibers recovered from the processing of cottonseed after the separation of the staple fiber); flax fibers; and clean, sorted rags are still used for those grades of paper in which maximum strength, durability, and permanence, as well as fine formation, color, texture, and feel, are required. These properties are attributed to the greater fineness, length, and purity of rag fiber as compared with most wood pulp. Rag papers are used extensively for bank note and security certificates; life insurance policies and legal documents, for which permanence is of prime importance; technical papers, such as tracing paper, vellums, and reproduction papers; high-grade bond letterheads, which must be impressive in 22 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  appearance and texture; lightweight specialties such as cigarette, carbon, and Bible papers; and high-grade stationery, in which beauty, softness, and fine texture are desired. Wastepaper and Paperboard By using greater quantities of wastepaper stock, the need for virgin fiber is reduced, and the problem of solid waste disposal is minimized. The expansion of this source is a highly complex problem, however, because of the difficulties in gathering wastepaper from scattered sources, sorting mixed papers, and recovering the fiber from many types of coated and treated papers. Synthetic Fibers The development and use of a great variety of man-made fibers have created a revolution in the textile industry in recent decades. It has been predicted that similar widespread use of synthetic fibers may eventually occur in the paper industry. Active interest has been evident in recent years, both on the part of fiber producers and of paper manufacturers. Many specialty paper products are currently being made from synthetic fibers. 23 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  MANUFACTURING PROCESS 24 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Pulp is generally manufactured in large mills in the same regions as the fiber harvest (i.e., mainly forest regions). Most of these mills also manufacture paper - for example, newsprint, writing, printing or tissue papers; or they may manufacture paperboards. (The figure on the left shows such a mill, which produces bleached kraft pulp, thermomechanical pulp and newsprint. Note the rail yard and dock for shipping, chip storage area, chip conveyors leading to digester, recovery boiler (tall white building) and effluent clarifying ponds). Separate converting operations are usually situated close to consumer markets and use market pulp or paper to manufacture bags, paperboards, containers, tissues, wrapping papers, decorative materials, business products and so on. PROCESSES FOR PREPARING PULP 25 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Mechanical or groundwood pulp is made by subjecting wood to an abrading action, either by pressing the wood against a revolving grinding stone or by passing chips through a mill. The wood fibers are separated and, to a considerable degree, fragmented. Chemical wood pulp is made by cooking wood chips with chemical solutions in digesters operated at elevated temperature and pressure. The chemicals used are (1) sulfite salts with an excess of sulfur dioxide and (2) caustic soda and sodium sulfide (the kraft process). The lignin of the wood is made soluble, and the fiber separate as whole fibers. Further purification can be accomplished by bleaching. Chemical wood pulp that is purified both by bleaching and by alkaline extraction is called alpha or dissolving pulp. It is used for specialty papers, for rayon and cellulose film production, and for cellulose derivatives, such as nitrate and acetate. Semi-chemical pulp is made by treating wood chips with sulfite or alkali in amounts and under conditions that soften the lignin but dissolve only part of it. The softened chips are then de-fibered. Kraft Pulping Process In the Kraft pulping process, wood chips are fed into a digestor where aqueous sodium hydroxide and sodium sulfide, under heat and pressure, break down the lignin that holds wood fibers together. After pulping, the wood becomes individual fibers. Kraft pulping is an energy-intensive process requiring about 9,000 MJ to produce a ton of pulp. The pulp yield of the Kraft process is about 50 percent. This means that about twice as much wood is required to produce a ton of chemical pulp as is needed to produce a ton of mechanical pulp. The chemical and energy recovery of the Kraft process is efficient, however. Over 98 percent of the pulping chemicals are regenerated in the recovery process. The organic matter that is dissolved during pulping (the other 50 percent of the wood that doesn't become pulp) is fired in a recovery furnace. The energy liberated by burning the dissolved organics-typically 14,000 MJ/ton of pulp—is sufficient to run the pulp mill, with some left over. Many mills sell the excess electricity. Kraft pulp may be used in an unbleached or bleached form. Bleaching is usually done with oxygen, chlorine dioxide, and peroxide. Total chlorine free (TCF) sequences, which replace the chlorine dioxide with peroxide and often ozone, are used but are not as common as the elemental chlorine free (ECF) sequences. In the United States only one pulp mill is TCF. The recent promulgation of the "cluster rule"1 will guarantee that ECF sequences become standard in the decade to come. Current technology does not permit bleach effluent to be recycled. If it is sent through the recovery process, salts build up leading to corrosion and scaling. Hence, the bleach plant accounts for fully half of the effluent that comes from the Kraft mill. Total water use in a Kraft mill is about 20,000 gallons/ton of pulp. 26 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  MANUFACTURE OF PAPER AND PAPERBOARD Preparation of Stock Mechanical squeezing and pounding of cellulose fiber permits water to penetrate its structure, causing swelling of the fiber and making it flexible. Mechanical action, furthermore, separates and frays the fibrils, submicroscopic units in the fiber structure. Beating reduces the rate of drainage from and through a mat of fibers, producing dense paper of high tensile strength, low porosity, stiffness, and rattle. An important milestone in papermaking development, the Hollander beater consists of an oval tank containing a heavy roll that revolves against a bedplate. The roll is capable of being set very accurately with respect to the bedplate, for the progressive adjustment of the roll position is the key to good beating. A beater may hold from 135 to 1,350 kilograms (300 to 3,000 pounds) of stock, a common size being about 7 meters (24 feet) long, 4 meters (12 feet) wide, and about 1 meter (3.3 feet) deep. A center partition provides a continuous channel. Pulp is put into the beater, and water is added to facilitate circulation of the mass between the roll and the bedplate. As the beating proceeds, the revolving roll is gradually lowered until it is riding full weight on the fibers between it and the bedplate. This action splits and mashes the fibers, creating hair-like fibrils and causing them to absorb water and become slimy. The beaten fibers will then drain more slowly on the paper machine wire and bond together more readily as more water is removed and the wet web pressed. Much of the beating action results from the rubbing of fiber on fiber. Long fibers will be cut to some extent. Sizing Sizing has been described as the treatment given paper to prevent aqueous solutions, such as ink, from soaking into it. A typical sizing solution consists of a rosin soap dispersion mixed with the stock in an amount of 1 to 5 percent of fiber. Since there is no affinity between rosin soap and fiber, it is necessary to use a coupling agent, normally alum (aluminum sulfate). The acidity of alum precipitates the rosin dispersion, and the positively charged aluminum ions and aluminum hydroxide flocs (masses of finely suspended particles) attach the size firmly to the negatively charged fiber surface. 27 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Dyeing and Filling Paper intended for writing or printing usually contains white pigments or fillers to increase brightness, opacity, and surface smoothness, and to improve ink receptivity. Clay (aluminum silicate), often referred to as kaolin or china clay, is commonly used, but only in a few places in the world (Cornwall, in England, and Georgia, in the United States) are the deposits readily accessible and sufficiently pure to be used for pigment. Another pigment is titanium dioxide (TiO2), prepared from the minerals rutile and anatase. Titanium dioxide is the most expensive of the common pigments and is often used in admixture with others. Calcium carbonate (CaCO3), also used as a filler, is prepared by precipitation by the reaction of milk of lime with either carbon dioxide (CO2) or soda ash (sodium carbonate, Na2CO3). Calcium carbonate as a paper filler is used mainly to impart improved brightness, opacity, and ink receptivity to printing and magazine stocks. Specialty uses include the filling of cigarette paper; to which it contributes good burning properties. Because of its reactivity with acid, calcium carbonate cannot be used in systems containing alum. Other fillers are zinc oxide, zinc sulfide, hydrated silica, calcium sulfate, hydrated alumina, talc, barium sulfate, and asbestos. Much of the filler consumed is used in paper coatings (see below). Since most fillers have no affinity for fibers, it is necessary to add an agent such as alum to help hold the filler in the formed sheet. The amount of filler used may vary from 1 to 10 percent of the fiber. The most common way to impart color to paper is to add soluble dyes or colored pigment to the paper stock. Many so-called direct dyes with a natural affinity for cellulose fiber are highly absorbed, even from dilute water solution. The so-called basic dyes have a high affinity for groundwood and unbleached pulps. Formation of Paper Sheet by Machine In a paper machine, interrelated mechanisms operating in unison receive paper stock from the beater, form it into a sheet of the desired weight by filtration, press and consolidate the sheet with removal of excess water, dry the remaining water by evaporation, and wind the traveling sheet into reels of paper. Paper machines may vary in width from about 1.5 to 8 meters (5 to 26 feet), in operating speed from a few hundred meters to 900 meters (about 3,000 feet) per minute, and in production of paper from a few tons per day to more than 300 tons per day. The paper weight (basis weight) may vary from light tissue, about 10 grams per square meter (0.03 ounce per square foot), to boards of more than 500 grams per square meter (1.6 ounces per square foot). 28 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  ECONOMIC IMPORTANCE The manufacture of pulp, paper and paper products ranks among the world’s largest industries. Mills are found in more than 100 countries in every region of the world, and directly employ more than 3.5 million people. The major pulp and paper producing nations include the United States, Canada, Japan, China, Finland, Sweden, Germany, Brazil and France. Every country is a consumer. Worldwide production of pulp, paper and paperboard was about 400 million tonnes in 1993. Despite predictions of decreased paper use in the face of the electronic age, there has been a fairly steady 2.5% annual rate of growth in production since 1980. In addition to its economic benefits, the consumption of paper has cultural value resulting from its function in the recording and dissemination of information. Because of this, pulp and paper consumption rates have been used as an indicator of a nation's socioeconomic development. 29 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.