The effect of high-pressure and high-temperature drying treatments on the deresination ratio of Pinus massoniana

Jie YANG, Hong-Bin WEI, Fan LI, Song-Lin YI

The effect of high-pressure and high-temperature drying treatments on the deresination ratio ofPinus massoniana

Jie YANG, Hong-Bin WEI, Fan LI, Song-Lin YI?

College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China

This study investigated the possibility of using high-temperature and high-pressure schedules to treatPinus massonianawood in order to reduce its oil content. We discuss the effect of drying temperature, absolute pressure and the holding time on the deresination ratio inP. massonianawood and establish a model for the deresination ratio as a function of drying temperature, absolute pressure and holding time. The results show that the deresination ratio increased from 7.14% to 87.04% when the temperature increased from 150 to 200°C, the absolute pressure from 0.1 to 0.6 MPa and the holding time from 1 to 3 h. The optimal model for the deresination ratio (Y) with drying temperature (t),absolute pressure (p) and holding time (T) is:Y= 0.284t+ 113.424p+ 3.518T– 42.486, with a coeff i cient of determination (R2) of 0.930. Compared with drying temperature and holding time, absolute pressure plays the more signif i cant role in the deresination process. This study could provide a theoretical basis to the practical production ofP. massonianawood.

deresination ratio, high temperature, high pressure, holding time,Pinus massoniana

?Author for correspondence (Song-Lin YI)

E-mail: ysonglin@126.com

Introduction

Pinus massoniana, with its moderate hardness,comparatively great mechanical strength, distinct natural decorative pattern, moderately beautiful color and a quality appearing as precious wood,is a tree species with one of the largest reserves in southern China. Its wood is also ideal for plywood and timber production ( Department of Forest of Anhui Agricultural College, 1980; Hong et al., 1990).

However,P. massonianahas a high oil content and under high temperature conditions, it is prone to disfigurement and processing defects,such as cementing and color problems. Hence,there are limitations in usingP. massonianaand overcoming these defects and expanding its use have become a signif i cant scientif i c and technical problem in forest science and technology (Huang,1999; Yu, 2007). In general, the simplest method to solve this problem is to study deresination technology, in order to make the deresination ofP. massonianamore efficient and simultaneously aim at low energy consumption and environmental protection. This study provides a theoretical direction to the practical production ofP. massonianatimber (Li et al., 2006).

Deresination consists of expelling a great deal of essential oils and small amounts of acid resin and curing most of the resin in the wood(Miao and Gu, 1999), where the deresination ratio is one of the most important parameters to measure (Tang, 2007). In this study, we explore the treatment effect of high-pressure and hightemperature drying on the deresination ratio ofP.massonianain order to investigate the deresination process and provide a certain theoretical basis forP. massonianahigh temperature drying in cooperation with skimming.

Materials and methods

Materials

Wood samples ofP. massoniana, with dimensions of 350 mm × 100 mm × 20 mm (length × width× thickness), were obtained from the Huaguo Mountain Wood Products Co., Ltd., Guangdong Province, China, in 2009. These wood specimens were without any obvious defects, such as knots,color change, cracks or worm stings.

Methods

A high-pressure and high-temperature drying machine, developed by Beijing Forestry University, was used in the experiment. The treatments were carried out under the following conditions:superheated vapor temperatures of 150, 160, 180 and 200°C, absolute pressure of 0.1, 0.2, 0.4 and 0.6 MPa and soaking time 1, 2 and 3 h. After treatment, the experimental material was ground by a FZ102 miniature plant sample crusher to pass through a 40- to 60-mesh screen and then dried to absolute weight.

Determination of the oil yield ofP. massonianawas based on the principle of a steam distillation method, using an oil-water separator (Fu, 2007).The wood powder was measured with a balance and placed in a round-bottom fl ask. Then enough water, not more than two-thirds of the volume of the flask, was added. Before heating the water and wood powder, the electric jacket voltage was set at 200 V and the refrigeration plant was opened. When the water began to boil, the voltage was turned down to 100 V. After boiling for 6 h,the electric jacket was turned off and the content of oil collected was recorded. The deresination ratio was calculated according to Wei et al. (2010):

whereYis the deresination ratio (%),X0the oil yield of untreated material (%) andXtthe oil yield of treated material (%).

By using a stepwise regression method in a multiple linear regression model and comparing each of the three independent variables, i.e.,temperature (t), pressure (p) and holding time (τ),the contribution of each variable was obtained via theirFvalues. This established the optimal model of deresination ratio as a function of temperature(t), pressure (p) and holding time (τ).

Results

This study investigated the deresination ratio ofP. massonianaunder different temperature,pressure and holding time conditions by using a steam distillation method for the extraction of essential oils. The results revealed a regular variation.

Oil yield

The oil yield ofP. massonianadecreased with increases in temperature of the superheated steam,absolute pressure and holding time (Table 1; Figs.1–4). Given the conditions of different temperatures, i.e., 150, 160, 180 and 200°C, the oil yield ofP. massonianadecreased with increases in absolute pressure, varying from 50% to 10% when the treatment temperature ranged from 150°C to 180°C and decreased to 6% at the highest temperature of 200°C and the highest pressure of 0.6 MPa (Figs. 1–4).

According to Table 1, given the conditions of different pressures, i.e., 0.1, 0.2, 0.4 and 0.6 MPa,there was a decrease of oil yield ofP. massonianaalong with rising temperatures. In addition, with an increase in pressure, the oil yield also decreased. Along with the increase in heat preservation time, oil yield became less, although no sig-nif i cant decrease was found. Moreover, compared with the pressure between 0.4–0.6 MPa, when the pressure varied from 0.1 to 0.4 MPa, the slope of the oil yield curve was larger, indicating a faster change in oil yield (Figs. 1–4).

Dere sination ratio calculation and model establishment

As shown in Tables 2–5, the deresination ratio ofP. massonianaranged from 7.41% to 87.04%,increasing substantially with the increase in temperature, pressure and holding time. The deresination ratio was a maximum under 0.6 MPa pressure, at 200°C temperature and for 3 h of holding time.

From signif i cance tests in fi tting the model, adjustedR2and regression equations, the most suitable model ofP. massonianaderesination ratio wasas follows:

Table 1 Oil content changes under different treatment conditions

Y =0.284t+ 113.424p+ 3.518τ– 42.486R2= 0.930 wheretis the superheated steam temperature,pthe absolute pressure of superheated steam andτthe holding time.

The model obtained combines the three factors of temperature, pressure and holding time which,together, affect the deresination ratio. It not only re fl ects the effect of the three factors on the deresination ratio accurately and directly, but is also of importance for estimatingP. massonianaderesination ratios under different processing conditions.Because the absolute size of each regression coeffi cient in the model directly re fl ects the contribution of that variable to the deresination ratio, we can clearly observe from the equation that the regression coefficient of pressure far outweighs that of temperature and holding time. This also supports the theory that the effect of absolute pressure of superheated steam on the deresination ratio ofP. massonianais greater than that of the other variables and veri fi es the correctness of the experiment.

Fig. 1 Changes in oil yield at 150°C

Fig. 2 Changes in oil yield at 160°C

Fig. 3 Changes in oil yield at 180°C

Fig. 4 Changes in oil yield at 200°C

Discussion

Steam distillation for extracting essential oils from wood is largely a cyclical process under boiling conditions during which water penetrates plant cells, while simultaneously the oil and water in cells spread to the surface of plants through cell walls. The surface of the plant material is wetted by water and the water vapor transfers heat to the essential oils, causing it to evaporate; hence,the essential oils spread to the plant surface surrounded by water (Liu and Ye, 2003). Therefore,when raw material is treated at different levels of temperature, pressure and holding time, the permeability and hygroscopicity of wood powder,in our case that ofP. massoniana, change and its deresination ratio also changes.

Given the analysis of our experimental data(Tables 2–5), we conclude that the deresination ratio ofP. massonianamaterial increases significantly under high temperature and high pressure dry processing conditions. These changes are mainly due to the fact that the essence of the deresin ation process ofP. massonianais volatilization of its essential oils which comprise many materials at boiling points from 150°C to 250°C,although the boiling point of the material could decrease to 100°C in coexistence with water.When the temperature rises, the components of oil will volatilize from the wood and those in solid state also melt, decompose and volatilize from wood. Therefore, the deresination ratio ofP.massonianaincreased gradually. Accordingly, the drying speed ofP. massonianaincreased quickly,giving the effect that resin obstructed the water in the wood particles, which improved the drying ofP. massoniana, in cooperation with the deresination process (Wang an d Gu, 2003). Although the superheated steam pressure affects deresination,the change in the deresination ratio ofP. massonianais slow; the improvement is also reduced under medium pressure of 0.6 MPa. Hence, the superheated steam pressure can be increased in actual production, but it should not be increased too high, because high pressure would increase the price of equipment and waste energy.

Table 2 Deresination ratio of P. massoniana at pressure of 0.1 MPa

Table 3 Deresination ratio of P. massoniana at pressure of 0.2 MPa

Table 4 Deresination ratio of P. massoniana at pressure of 0.4 MPa

Table 5 Deresination ratio of P. massoniana at pressure of 0.6 MPa

Conclusions

1) The deresination ratio increased from 7.14% to 87.04% as the temperature increased from 150°C to 200°C, at absolute pressure of 0.1 to 0.6 MPa and the holding time from 1 to 3 h. Compared with drying temperature and holding time, absolute pressure plays the more signif i cant role in the deresination process. This is very important in the deresination process ofP. massonianafor dimensional stability in actual production.

2) The model for the deresination ratio (Y), as a function of drying temperature (t), absolute pressure (p) and holding time (τ), is the following:Y=0.284t+ 113.424p+ 3.518τ– 42.486, with a coefficient of determinationR2of 0.930. Each regression coefficient in the model directly reflects the contribution of the variable to the deresination ratio. It can be seen that the coeff i cient of the variable pressure far outweighs that of the other two factors, i.e., temperature and holding time, supporting the theory that the absolute pressure of superheated steam is the more important of the three variables for the deresination ratio ofP. massonianaand it also verifies the correctness of the experiment. The model provides a future reference for dryingP. massonianawood, cooperating with its deresination process.

Acknowledgement

This study was supported by the Beijing Jointly Building Project of Key Discipline—the High Effi ciency Utilization of Fast Growing Wood.

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12 January 2012; accepted 29 March 2012