I. Pérez

Organosolv pulping of wheat straw by use of phenol

Abstract A central composite design was used to investigate the influence of the cooking conditions (time, temperature and phenol concentration) for wheat straw with phenol-water mixtures on the properties of the pulp obtained (yield and holocellulose, α-cellulose, lignin and ethanol-benzene extractable contents) and the pH of the resulting wastewater. A second-order polynomial model consisting of three independent process variables was found to accurately describe the organosolv pulping of wheat straw. The equations derived predict the yield, the holocellulose, α-cellulose, lignin and ethanol-benzene extractable contents of the pulp, and the pH of the wastewater with multiple-R, R2 and adjusted-R2 high values. The process variables must be set at low variables in order to ensure a high yield and pH. Conversely, if high holocellulose and α-cellulose contents, and low lignin and ethanol-benzene extractable contents are desired, then a high temperature (200°C), long cooking time (120 min), and intermediate phenol concentration (65%) must be used.

Ethanol-acetone pulping of wheat straw. Influence of the cooking and the beating of the pulps on the properties of the resulting paper sheets

The influence of independent variables in the pulping of wheat straw by use of an ethanol-acetone-water mixture [processing temperature and time, ethanol/(ethanol + acetone) value and (ethanol + acetone)/(ethanol + acetone + water) value] and of the number of PFI beating revolutions to which the pulp was subjected, on the properties of the resulting pulp (yield and Shopper-Riegler index) and of the paper sheets obtained from it (breaking length, stretch, burst index and tear index) was examined. By using a central composite factor design and the BMDP software suite, equations that relate each dependent variable to the different independent variables were obtained that reproduced the experimental results for the dependent variables with errors less than 30% at temperatures, times, ethanol/(ethanol + acetone) value, (ethanol + acetone)/(ethanol + acetone + water) value and numbers of PFI beating revolutions in the ranges 140-180 degrees C, 60-120 min, 25-75%, 35-75% and 0-1750, respectively. Using values of the independent variables over the variation ranges considered provided the following optimum values of the dependent variables: 78.17% (yield), 15.21 degrees SR (Shopper-Riegler index), 5265 m (breaking length), 1.94% (stretch), 2.53 kN/g (burst index) and 4.26 mN m2/g (tear index). Obtaining reasonably good paper sheets (with properties that differed by less than 15% from their optimum values except for the burst index, which was 28% lower) entailed using a temperature of 180 degrees C, an ethanol/(ethanol + acetone) value of 50%, an (ethanol + acetone)/(ethanol + acetone + water) value of 75%, a processing time of 60 min and a number of PFI beating revolutions of 1750. The yield was 32% lower under these conditions, however. A comparison of the results provided by ethanol, acetone and ethanol-acetone pulping revealed that the second and third process-which provided an increased yield were the best choices. On the other hand, if the pulp is to be refined, ethanol pulping is the process of choice.

Delignification of wheat straw by use of low-molecular-weight organic acids

A central composite design was used to investigate the influence of the cooking conditions (time, temperature and acid concentration) for wheat straw with organic acid-water mixtures on the properties of the pulp obtained (yield and holocellulose, α-cellulose and lignin contents). A second-order polynomial model, consisting of three independent process variahles, was found to accurately describe the organosolv pulping of wheat straw. The equations derived predict the yield, the holocellulose, α-cellulose and lignin contents of the pulp with multiple-R. R 2 and adjusted-R 2 high values. The process variables must be set low in order to ensure a high yield. Conversely. if high holocellulose and α-cellulose contents and low lignin contents are desired. then a long cooking time (120min), an intermedia temperature (100°C). and a low formic acid concentration (50%) must be used.

Influence of process variables in the ethanol pulping of olive tree trimmings

A central composition design was developed to study the influence of process variables (temperature, pulping time and ethanol concentration) on the properties of the pulp produced (yield and holocellulose, alpha-cellulose and lignin contents) and the pH of the resulting wastewater, in the ethanol pulping of olive tree trimmings. The proposed equations reproduce the experimental results for the dependent variables with errors less than 5% for the holocellulose and alpha-cellulose contents, yield and wastewater pH, and less than 15% for the lignin content. Obtaining pulp with acceptably high yield (37.6%), high holocellulose and alpha-cellulose contents (above 88.8% and 46.9%, respectively), and low lignin contents (below 7.2%), entails operating at a pulping temperature of 200 degrees C, using an ethanol concentration of 75% and a pulping time of 60 min.

Use of formaldehyde for making wheat straw cellulose pulp

Abstract A central composite design was used to investigate the influence of the cooking conditions (time, temperature and formaldehyde concentration) for wheat straw with formaldehyde–water mixtures on the properties of the pulp obtained (yield and holocellulose, α-cellulose, lignin and ethanol–benzene extractives contents) and the pH of the resulting wastewater. A second-order polynomial model consisting of three independent process variables was found to accurately describe the organosolv pulping of wheat straw. The equations derived predicted the yield, the holocellulose, α-cellulose, lignin and ethanol–benzene extractives contents of the pulp, and the pH of the wastewater with multiple- R , R 2 , adjusted- R 2 and Snedecor F values of 0.99, 0.99, 0.99 and 321.33; 0.98, 0.95, 0.92 and 35.01; 0.92, 0.86, 0.78 and 10.68; 0.99, 0.97, 0.96 and 68.19; 0.91, 0.83, 0.80 and 29.68; and 0.97, 0.95, 0.93 and 46.10, respectively. While ensuring a high holocellulose content and low lignin and ethanol–benzene-extractive contents entails using high levels of the process variables involved, a compromise can be made in order to achieve both the previous objectives and a high α-cellulose content provided a long cooking time, a high temperature and a low formaldehyde concentration are used – alternatively, a long time, a high formaldehyde concentration and a low temperature can be equally effective and save energy. The yield, pH and holocellulose, α-cellulose, lignin and alcohol/benzene extractive contents are more sensitive to changes in the cooking time than they are to modifications of the formaldehyde concentration.

Biobleaching procedures for pulp from agricultural residues using Phanerochaete chrysosporium and enzymes

Pulps from agricultural residues (wheat straw) bleached using the DEpD sequence (chlorine dioxide-soda plus hydrogen peroxide extraction-chlorine dioxide) and the FDEpD, XDEpD and XFDEpD sequences, which included pretreatment with the fungus Phanerochaete chrysosporium (F), the enzyme Cartazyme HS (X) and the enzyme plus the fungus (XF) are compared in terms of kappa index, brightness and yield, in addition to the breaking length, burst index and tear index of paper sheets manufactured from them. XDEpD was found to be the best alternative to the DEpD sequence as it surpassed the latter in pulp brightness (by 3·7%), featured a moderate yield loss (9·3%) and provided paper sheets with acceptably smaller breaking length and burst index (20·2 and 13·1% less, respectively). The FDEpD sequence was that resulting in the greatest increase in pulp brightness (8·6%) and the greatest savings in chlorine (10·9%), however, the yield and the breaking length and burst index of the sheets were markedly decreased (by 25·2, 24·7 and 41·8%, respectively) and the treatment time was rather long. Finally, the XFDEpD sequence provided pulp in a considerably diminished yield (34·5%) and paper sheets with poor properties and essentially the same brightness; this sequence also took a long time to implement.

Pulping and bleaching of pulp from olive tree residues

The influence of operating conditions (active alkali concentration, temperature and time) used in the kraft pulping of wood from olive trimming residues on the yield and kappa index of the pulp and the stretch index, burst index and tear index of paper sheets obtained from it, as well as that of the chlorine dioxide concentration used to bleach the pulp according to the D1ED2 sequence (chlorine dioxide-alkaline extraction-chlorine dioxide) on the yield, kappa index, brightness and viscosity of the bleached pulp, were studied. A 2n central composite factor design was used to derive equations that relate the dependent variables to the operating variables considered in the pulping and bleaching processes. The equations reproduce the experimental results with errors less than 10%. Based on the pulping results, obtaining readily bleached pulp of acceptable strength-related properties entails using an active alkali concentration of 25%, a temperature of 175°C and a time of 93 min. Based on the bleaching results, using chlorine dioxide concentrations of 7.5 and 1% in steps D1 and D2, respectively, ensures the obtainment of acceptably bright (>88%) pulp with little loss of yield (<2%) and viscosity (<3%).

Influence of the operating conditions in the acetone pulping of wheat straw on the properties of the resulting paper sheets

A central composite factor design was used to examine the influence of independent variables in the acetone pulping of wheat straw (processing temperature, time, and acetone concentration) on the yield of the resulting pulp, and on various physical properties of paper sheets (breaking length, stretch, burst index, tear index and brightness) obtained from it. Equations that related each dependent variable to the different independent variables were obtained, and these reproduced the experimental results for the yield, breaking, stretch, burst index and brightness obtained at temperatures, times, and acetone concentratons over the ranges 140-180 degrees C, 60-120 min and 40-80%, respectively, with errors less than 20%. Obtaining the optimum breakinig length, stretch, burst index and tear index for the paper sheets (3,456 m, 1.42%, 1.36 kN/g and 3.86 mNm2/g, respectively) entails using a high temperature; the processing time and acetone concentration only influence stretch, optimization of which requires using a short time and a low concentration. The optimum brightness (30.44%) is achieved with a low temperature, a short time and a medium acetone concentration. In order to minimize losses of solvent during its recovery and recycling while ensuring acceptable levels of the properties of the paper sheets, a high temperature, a low acetone concentration and a short time can be used; the brightness level thus obtained is only 10% lower than the optimum value.

The effect of processing variables on the soda pulping of olive tree wood

Abstract A central composite design was developed to study the effect of processing variables (temperature, pulping time and soda concentration) on the properties of pulp (holocellulose, α-cellulose and lignin contents, yield and brightness) and the paper sheets obtained (breaking length, burst index and tear index). The proposed equations fit the experimental results for the dependent variables with errors less than 10% (15% for the breaking length). Obtaining pulp with acceptably high yield, holocellulose and α-cellulose contents, a high brightness and low lignin contents, requires cooking at a low pulping temperature (155–160°C), using a high soda concentration (10%) for a short pulping time (15 min). On the other hand, obtaining paper sheets with acceptable strength properties requires rather different conditions. Consequently, it is preferable to use the pulping conditions that result in the best pulp properties and to improve the characteristics of the paper sheets by refining.

Comparative study of paper sheets from olive tree wood pulp obtained by soda, sulphite or kraft pulping

Abstract Paper sheets from olive tree wood pulp obtained by soda, sulphite or kraft pulping were studied to examine the influence of pulp beating on properties of the paper sheets. Paper sheets from kraft and sulphite pulps exhibited the highest resistance, and sulphite pulp the highest brightness. Soda pulp required more intensive beating than did kraft or sulphite pulps; in fact, the PFI beater had be operated at a 40–50% higher number of beating revolutions to obtain soda pulp with 70–80° SR. The breaking length, stretch, burst index and tear index of paper sheets obtained from kraft pulp, beaten to a Shopper–Riegler index of 70–80° SR were 20–30%, 30–50%, 50–60% and 15–35% higher, respectively, than those of sheets obtained from soda pulp.