**4.2 Experimental temperature and pressure**

6 Mass Transfer in Chemical Engineering Processes

Effective diffusion coefficient of each component directly affects the time to reach the balance for the whole system during the calculation procedure. There is no absolutely accurate general calculation equation to calculate the diffusion coefficient of i-component in oil phase and gas phase, except using the empirical equation which is a relatively accurate method. The diffusion factor of i-component in oil phase usually is usually calculated by Will— Chang(1955) and that in gas phase by Chapman-Enskog empirical formula (1972). The initial K value of each component is calculated by Wilson function, and corrected by fugacity coefficient in every time step, while fugacity coefficient is calculated by PR-EOS. Compared with the computation model proposed for single component, the model is much closer to the actual simulation, since it has taken interaction among the components into consideration.

The experiment tested the three different diffusion coefficients of hree different N2, CH4 and CO2 gases and the diffusion coefficient of the actual oil separator. Using the mathematical model, we obtained diffusion coefficient of the gas molecules by fitting the experimental

The composition of gas sample is shown in Tab-1. The composition of oil sample is shown in Tab-2. The oil sample is taken from surface separator. The average molecular weight of oil

N2 98.23 — 1.67 — — — — — — — CO2 0.0796 98.181 1.6939 — — — — — — — Dry gas 3.1951 2.5062 92.7098 1.3957 0.1182 0.0141 0.0278 0.0129 0.0032 0.0169

iC4 0.057 58.124 408.1 3.600 0.1840 nC4 0.094 58.124 425.2 3.750 0.2015 iC5 0.405 72.151 460.4 3.340 0.2286 nC5 0.337 72.151 469.6 3.330 0.2524 C6 5.073 86.178 507.5 3.246 0.2998 C7 4.578 100.250 543.2 3.097 0.3494 C8 5.125 114.232 570.5 2.912 0.3513 C9 3.625 128.259 598.5 2.694 0.3908 C10 3.683 142.286 622.1 2.501 0.4438 C11+ 77.020 156.313 643.6 2.317 0.4775

N2 CO2 C1 C2 C3 iC4 nC4 iC5 nC5 C6

critical temperature,K

critical pressure,MPa acentric factor

name component name and molar percentage,%

molar mass,kg/kmol

Table 2. Components of oil samples used in diffusion experiments

**3.2 Model solution** 

**4. The molecule diffusion experiment** 

**4.1 Experimental fluid samples** 

Table 1. Components of gas samples

volume fraction,%

name

pressure changes or gas-oil interface position change.

sample is 231.5 and the density is 0.8305, <sup>3</sup> *g* /*cm* .

Three groups of gas diffusion tests are conducted. The first one is the diffusion test of CO2- Oil (20*MPa*, 60Ԩ); the second is the diffusion test of CH4-oil (20 *MPa*, 60Ԩ); the third is the diffusion test of N2-Oil (20 *MPa*, 60Ԩ).

### **4.3 Experimental apparatus and experimental procedures 4.3.1 Experimental apparatus**

Diffusion experiments are conducted mainly in DBR phase behavior analyzer. The other equipments include injection pump system, PVT cell, flash separator, density meter, temperature control system, gas chromatograph, oil chromatograph, electronic balance and gas booster pump. The flow chart is shown in fig.3.

Fig. 3. The flow chart of diffusion experiment
