Haile et al. Bioresour. Bioprocess.
(2021) 8:35
Page 4 of 22
Table 2 Status of paper manufacturing in Ethiopia Company Name Planed production (tonnes per year) Production loss/year (%)
Product type
Ethiopia Pulp and Paper S.C 6000
5–15
Printing and Writing Paper, Stationery Paper, Paper board, Corrugated box, Wood free and manila papers, Kraft liners, Test liners, Fluting papers Printing writing papers, Wood free and manila papers, Kraft liners, Test liners, Fluting papers
Anmol Products Ethiopia 12,000–14,000
6.5–10.8
Yekatit Paper Converting 1400
5–10 5–10
Different paper products
DA Packaging Barguba Trading
2000 8000
Kraft liners, Test liners, Fluting papers, Corrugated cartons
7.2–13.5
Different paper products Paper and tissue products Carton boxes, Trays, Packets
Mamco Paper Products Burayu Development Minaye Packaging Balaje Packaging Unlimited Packaging Seven Hills Packaging Akless Paper Product
200
2–10
10,000–11,500
15–18.5 2.8–12.3
3500 1800
Carton Carton Carton Carton
3–11.2 4.2–15
20,000
7000
2–7.6 5–8.6
350
Different Paper products
handling and determining the suitable chip storage con- ditions (Bajpai 2015a). The pulping operation involves the separation of the wood chips to get the fibrous materials. In the process, lignin is removed from the lignocellulosic wood and the individual cellulose fibers are isolated. Though there are different pulping methods chemical and mechanical methods are the most widely used in paper mills. Either of the three techniques namely kraft, soda, or sulfite are used in the chemical pulping approach. In all the cases the cellulose is extracted via cooking of the chips in the aqueous solutions of the reagents at elevated pressure and temperature (Bajpai, 2011, 2015a). Physical energy is used in the mechanical pulping approach which mainly involves the removal of cellulose through grinding or shredding. The most widely used pulping process is kraft pulp- ing and uses alkaline cooking liquor of sodium hydrox- ide (NaOH) and sodium sulfide (Na 2 S) to digest wood. In the process, a digester is used for mixing the chips with the kraft cooking solution. The kraft pulping process uses an alkaline cooking liquor of sodium hydroxide and sodium sulfide to digest the wood. The process involves the digestion of wood chips at high temperature in the range of 145–170 °C and pressure in “white liquor,” which is a water solution of sodium sulfide (Na 2 S) and sodium hydroxide (NaOH), for a few hours (Huber et al. 2014). During this treatment, the hydroxide and hydrosulfide anions react with the lignin, causing the polymer to frag- ment into smaller water/alkali-soluble fragments and iso- lating the cellulose fibers. After the wood chips have been cooked, the contents of the digester are discharged under pressure into a blow
blending and recycling process, is used in some paper manufacturing trends. The different pulping operations and the integrated paper manufacturing process are shown in Fig. 3. Two steps are involved in the manufacturing of paper. First cellulose sheets are converted into pulp which is the intermediate material for paper production. The second step involves the conversion of pulp into the paper with the necessary after-treatment depending on the targeted end-use. The overall manufacturing process is accompa- nied by multiple stages which mainly involve raw mate- rial preparation and handling, controlled pulping, and discrete or continuous paper manufacturing. The pulping involves the actual making of the pulp followed by pulp washing and screening. After proper chemical recovery and bleaching, the stock is prepared. Finally, the paper- making is carried out which itself has different stages. Pulp mills and paper mills may exist separately or as inte- grated operations (Bajpai 2018b; de Alda 2008; Ragauskas 2002). Operational mechanism of pulping Pulp manufacturing starts with raw material prepara- tion, which includes debarking, chipping, chip screening, chip handling, and storage (Bajpai 2011, Brännvall 2009). The pulp needs to be free of dirt and superficial materi- als such as bark, and debarking is done for making the pulp physically clean. The next operation in raw material preparation is chipping to ensure better handling of the logs which is done through cutting to get the required size of logs for the subsequent pulping process. Pulping requirements need to be considered in optimizing chip
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