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1、The containment of oil spills in porous media usingxanthan/aluminum solutions, gelled by gaseous CO2 or by AICI3solutions采用气体CO2或AlCb溶液凝胶化黄原胶/铝溶液封堵多孔介质中的石油泄漏F. Gioia, P.P. Ciriello /Journal of Hazardous Materials B138 (2006) 500-506.Abstract 摘要The gelation in situ of polymers may be a method for tem
2、porarily containing organic solvents and other petroleum derived products, which may enter the subsurface. In order to create gels that are neither toxic to humans nor to the ecosystem, we have investigated on the use of the biopolymer xanthan gum with aluminum as a crosslinking agent. Firstly we ha
3、ve considered xanthan/sodium aluminate solutions, which upon preparation are strongly basic and do not gel. The gelation takes place in acid solutions so that Al(III) ions are released, and is instantaneous. Therefore, a special technique must be used for generating the gel structure in situ. The un
4、-gelled solution must be injected and an acid must be added afterwards. We have investigated on the gelling reaction induced by gaseous carbon dioxide, which is an acid gas. The insufflation of CO2 above the solution generates a layer of gel whose thickness progressively increases as CO2 diffuses in
5、 the polymer solution. Secondly we have investigated on the use of aluminum chloride as the source of Al(III) ions. Also in this case, due to the full availability of Al(III) ions, the gelling reaction would be instantaneous. Therefore, the solution of AICI3 must be added on the top of the xanthan s
6、olution after its injection. For both gelling systems we have studied both theoretically and experimentally the rate of formation of the gel layer which progressively thickens after the insufflation of CO2 or after the addition of the AICI3 solution.聚合物的原位凝胶化可能是一种暂时封堵可能进入地下的有机溶剂和其他石油衍生 产品的方法。为了形成人类和
7、生态系统无毒的凝胶，我们研究使用采用生物聚合物黄原胶 与作为交联剂的铝。首先，我们考虑了黄原胶/铝酸钠溶液，配制后为强碱性，不会凝胶化。 凝胶化发生在酸性溶液中，从而释放出Al(III)离子，且为瞬间。因此，原位形成凝胶结 构必须采用特殊的技术。必须注入未-凝胶化溶液，之后加入加酸。我们研究了酸性气体气 态二氧化碳引起的胶凝反响。溶液上方吹入CO2产生一层凝胶，随着聚合物溶液中CO2a pHi is a calculated value. pH为计算值。Run no.运行编号Xanthan黄原胶 (ppm)Al(III) (ppm)pHopHia130005010.184.140.302300
8、010010.574.400.203300030011.064.860.40460005010.764.570.365600010011.034.830.356600030011.104.900.487600060011.194.990.248600090011.465.280.17EO g AppunoqEO g AppunoqFig. 3. Gel t hickness vs. time for Xn/NaAlOz/COi for Xn = 3000 ppm and three different NaAIOz concentrations, expressed as Al(III). X
9、n=3000 ppm 和 3 种不同表示为 Al (III)的 NaAKh的Xn/NaAlOCO2凝底厚度与时间Fig. 4. Gel thickness vs. time for Xn/NaAlOz/COz for Xn = 6000 ppm and five different NaAlOz concentrations, expressed as A1(HI). Xn=6000 ppm 和 5 种不同表示为 Al (III)的 NaAlCh的Xn/NaAlOCO2凝胶厚度与时间Table 1 Runs Xn/NaAlOz/COz 运彳亍Interpretation of experime
10、ntal results 实验结果解The CO2 concentration in the liquid phase at the interface, in equilibrium with the gaseous phase is given by the Henrys equation, i.e.:界面处液相中与气相平衡的CO2浓度由Henry方程给出，即：(1)sc 1 4coe g。=The liquid phase is alkaline because of the presence of sodium hydroxide, due to the hydrolysis of N
11、aAlOz. Therefore, at the interface, upon absorption, CO2 undergoes ionic reactions leading to the formation of CO3 2-and HCOs-. The equilibrium concentrations of the ionic species at the interface are calculated by means of the equilibrium equation (2) and (3):由于NaAKh水解导致的氢氧化钠的存在，液相为碱性。因此，C02在界面吸收后与
12、 离子反响，从而形成C03 2-和HCOfo通过平衡方程(2)和(3),计算界面处离子物质的平衡浓度:|hco3-LICO2Moh=Ki = 4.5 X IO7 mol/1hc()3Loh-l=K2 = 2.38 X I ()-4 mol/lcoupled with the charge balance and the mass balance on carbon atom, Eqs. (4) and (5) respectively:再加上分别为(4)和(5)的碳原子上的电荷平衡和质量平衡:2CO32-L- + IHCO3-L + |OH-h = OH-lo(4)CO32L + HCO3L
13、+ |CO2L= C02o(5)OH-o is the hydroxyl ion concentration corresponding to the measured pHo. It is | OH-()-Na+()which is the initial concentration of sodium ions considering the NaAlOz loaded in the xanthan solution. Al ions are not considered in Eq. (4) as we assume they are linked to xanthan molecule
14、s to form the gel. The solution of the above equations permits calculation of the pH三pHi of the solution at the interface at t=().OH 0是对应于测量pHo的氢氧根离子浓度。 考虑到黄原胶溶液中所含 NaAlO2， OH-o YNa+o,这是钠离子的初始浓度。由于假设与黄原 胶分子连接，形成凝胶，式(4)中没有考虑A1离 子。上式的解可以计算t=0时界面处溶液的 pH=pHi 0Fig5. Advancement of gel thickness vs. pH. X
15、n = 3000 ppm; Al = 50 ppm (as Al(III). Themoving boundary position is at pH 6.8.0 凝胶厚度与 pH 的关系。Xn = 3000 ppm； Al =50 ppm (以Al(III)计)。移动边界位置为pH 6.801.2. Transient diffusion in the gel 凝胶中的瞬态扩散Let us assume that the diffusivities of CO2, HCO3 and CO3 2- are about the same, then we can consider the dif
16、fusion of the three species altogether, i.e. we consider the diffusion of the carbon atom. Say C= CO2 + HCOa- + CO3 2-; at any z position and at any time t the transient diffusion of carbon atom in the layer of xanthan solution is described by Eq. (6):假设CO2 HCO3-和CO3 2-的扩散速率大致相同，可以一起考虑这三种物质的扩散,(6)(6
17、)C(t, z) = Ci erfc 即考虑碳原子的扩散。假设C= C02 + HCO3- + C03 2-:在任何z位置和任何时间3 碳原子在黄原胶溶液层中的瞬态扩散由式(6)描述：As the acid gas CO2 advances in the solution, the pH decreases. The pH of the solution at any t and z may be calculated by means of the set of equations:随着溶液中酸性气体CO2增加，pH降低。任何t和z的pH通过方程组计算：CO2 + IHCO3- + CO32
18、- = C(r, Z)(7)coupled with the charge balance (4) and the ionic equilibrium equations (2) and (3). D in Eq. (6) is the diffusivity in the gel. Missing any information on its value, we set:结合电荷平衡(4)和离子平衡方程(2)和(3)0式(6)中的D是凝胶中的扩散速率。 没有其值的任何信息，设定：D = aDco2where Dco2 is the diffusivity of CO2 in water an
19、d a is an adjustable parameter to be determined fitting the experimental data.其中Dco2是水中CO2扩散速率，a是1个可调参数，需拟合实验数据确定。Following this procedure, we have built diagrams of the increase of pH along z versus time for the runs of Table 1. As an example we report in Fig5 the diagrams regarding run 1.按照这一程序，形成
20、了表1运行的pH随时间增加的图。作为一个例子，图5中报 告了运行1的图。As described in Section 3.1 we have measured the advancement versus time of the boundary where the pH indicator Bromocresol Purple“ switches from blue-violet to yellow at pH 6.8. This value of pH is indicated in Fig5 with the symbol pHc. Therefore, for all runs we
21、 have calculated the position 九 of the boundary (at pHc) versus t. obtaining the model curves drawn in Figs. 3 and 4. The fitting procedure of the theoretical curves to the experimental data let us determine the best value of the adjustable parameter a (reported in Table 1). It must be noted that du
22、e to the smooth change of pH, also the gel strength changes smoothly around pHc.如第3.1节所述，我们测量边界层的增长与实际，其中pH指示齐漠甲酚紫”在pH 6.8时从蓝紫色变为黄色。这一 pH值在图5中用符号pHc表示。因此，对于所有运行， 我们计算边界的位置X (在pHc处)与t的关系。取得了图3和图4中绘出的模型曲 线。理论曲线与实验数据的拟合程序确定了可调参数a的最正确值(见表1)。必须注意，由于pH的平稳变化，凝胶强度也在pHc附近平稳变化。4. Runs Xn/AlCb运行Materials and e
23、xperimental procedure 材料和实验程序A1C13-6H2O was supplied by Aldrich. Upon dissolution in water the aluminum chloride being a salt, can be considered completely dissociated, i.e.:A1C13-6H2O由Aldrich提供。氯化铝盐溶解在水中后，可认为完全解离，即：The solution, due to the hydrolysis reactions is acid pH = 3.74 at 300 ppm Al(III).
24、Therefore, according to the diagrams of Figi, there is a full availability of Al(III) ions and there is thernaximum crosslinking activity.A1CI3 AI3+ + 3Cr(9)由于水解反响，溶液在300ppmAl(ni)为酸性pH = 3.74。因此,根据图1图的,Al(IH) 离子完全可用，且交联活性最强。In the presence of a significant concentration of Al3+ the gelation takes pl
25、ace in a very short time. Therefore, the mixture polymer/AlCh does not have appropriate properties for in-depth injection in porous media. In fact the gel system can only be injected through a porous medium for a time period of usually less than about one-fourth of the gel time before a significant
26、increase in the flow resistance is observed. Therefore, in order to overcome this last inconvenience we have devised a different technique for generating the gel structure in the porous structure when this gel system is adopted. Namely, for the purpose of using this gel system for the containment of
27、 an oil spill, the aluminum chloride solution must be added after the Xn solution has been injected underneath the oil spill. The experiments were performed as follows: The xanthan solution coloured with few drops of a pHindicator (Bromocresol green which changes from yellow to blue at pH values in
28、the range 3.8-5.4) was poured in a glass cylinder to fill about two-thirds of its volume, and a given quantity of AICI3 solution was added on the top of the xanthan solution. This is the time zero of the experiment. Upon the addition of the aluminum chloride, a layer of gel instantly forms at the in
29、terface polymer7AleI3, which blocks any mixing of the two solutions. Namely the presence of Al3+ cations induce an instantaneous gelling reaction. The gel is perfectly distinguishable as it shows with a yellow colour, which contrasts with the blue of the un-gelled polymer. Afterwards the AICI3 diffu
30、ses through the gel layer towards the un-gelled solution and the thickness of the gel progressivelyincreases. Namely the system evolves as a moving boundary process as sketched in Fig6. The position of the boundary and the concentration of the AlCh (as Al(III), measured by means of a Cl- electrode i
31、n the solution above the gel, were recorded versus time. The frequent measurement of Cl- helped in destroying possible concentration gradients in the AICI3 solution. At least three replicates for each run were carried out. The materials and the operating conditions of the experimental runs are repor
32、ted in Table 2. The experimental data points X(t) versus time, for the runs of Table 2, are reported in Fig7. The fitting curves are the model equation to be developed below.不同的技术，用于米用这种凝胶体系时存在显着浓度的A13+时，凝胶化会在很短的时间内发生。因此，混合聚合物/A1C13不 具备在多孔介质中深度注入的适当性质。实际上，在观察到流动阻力显著增加之前，凝胶 体系只能在少于凝胶时间的四分之一的时间通过多孔介质注
33、入。因此，为了克服这一最后 的不便，我们设计了一种 在多孔结构中产生凝胶结 构。即，为了使用这一凝 胶系统围堵石油泄漏，必 须将Xn溶液注入石油泄 漏下方之后加入氯化铝溶 液。实验如下进行：将用 几滴pH指示剂着色的 黄原胶溶液(溟甲酚绿， 在的pH值范围内从黄色变为蓝色)倒入玻璃圆筒中，填充其约三分之二体积的 溶液，在黄原胶溶液顶部加入一定量的AlCh溶液。这是实验的零时。加入氯化铝后，聚 合物/AlCh界面处处立即形成一层凝胶，阻止两种溶液的任何混合。即A伊阳离子存诱 导瞬时胶凝反响。由于显示为黄色，与未凝胶聚合物的蓝色形成鲜明比照，凝胶完全可以 区分。之后AlCh通过凝胶层向未凝胶化的溶
34、液扩散，凝胶的厚度逐渐增加。即体系演变 为一种移动边界过程，如图6所示。通过凝胶上方溶液中CL电极，测量边界位置和AlCb (作为Al (III)浓度随时间变化。Cl的频繁测量有助于破坏AlCh溶液中可能存在的 浓度梯度。每种运行至少进行3个重复。表2中报告了实验运行的材料和操作条件。对于 表2的运行，图7中报告可实验数据点入与时间。拟合曲线是以下要建立的模型方程。 Fig6. Sketch of gel formation as a moving boundary process.作为移动边界过程的凝胶形 成示意图。Fig7. Gel thickness vs. time for Xn/Al
35、Ch for Xn = 8000 ppm.凝胶厚度与时间的关系。Table 2 Runs Xn/AlCh; Xn = 8000 ppm 运行Run no. 运行编 号Al(III)(ppm)c()(mol/cm3)* (mol/cm3)* (h)* (cm)(Eq. (17)(Exp. I)1259.32x10 -76.30X10-7100.60.0170.0132501.86x10 -61.29x10 -6100.70.0270.01931003.73x10 -62.52x10 -6101.00.0400.0204300l.llxlO57.19x10 -6101.20.1090.0434.2
36、. Interpretation of experimental results 实验结果解释The experiment is mathematically described by the two following differential equations: 这一实验数学描述采用以下2个微分方程数学描述：=心”2(10)dr 10-6Xnpj8 入(1) Transient diffusion of AICI3 through the gel. Assuming pseudo-steady-state condition the rate of advancement of the
37、gel layer X is(1)A1C13通过凝胶瞬时扩散。假设准-稳态条件下，凝胶层的前进速率X为deDs=(11)drL入p is a pseudo-stoichiometric coefficient, i.e. g of AICI3 consumed per g of Xn gelled.B是一个拟-化学计量系数，即每g Xn凝胶化消耗的AICI3 g。(2) Transient mass balance of AICI3 on the volume of solution contained in the vial on the top of the gel. Given the
38、low concentration of AICI3, we assume the volume of the salt solution on the top of the Xn solution to remain constant:(2)小瓶所含溶液体积上方AICI3凝胶瞬态质量平衡。由于AlCb浓度较低，我们假 设Xn溶液上方盐溶液体积保持不变：The initial conditions are: t=0, c = c09 入=0.初始条件为：t=0, c=c, X=0oThe meaning of the symbols is reported in Nomenclature. T
39、he two equations may be combined to give符号的含义在术语报告。合并2个方程，可以给出入L_ X)(12)dr Lwhere其中LMcOY =r(13)l()-6 XnpThe experiments showed that as the diffusion and the crosslinking reaction proceed the gel becomes so stronG,that the diffusion of AlCh practically stops and X does not increase anymore.实验说明，随着扩散和
40、交联反响的进行，凝胶变得非常坚固，以至AlCb扩散实际上 停止，且X不再增加。In order to ascertain this peculiarity we measured by the rheometer the variation of the gel strength with time. The results are reported in Fig8 where it is shown the change of the shear storage modulus G with time for a given couple of Xn/AlCh concentrations.
41、 It may be noted that after 24 h the gel is solid like (G 300 Pa). Thus, indicating the formation of a very stronGgel, so that the further diffusion of the crosslinker is about nil. Therefore, we must consider that the diffusivity in Eqs. (10)-( 12) is a function of time. In order to make a reasonab
42、le hypothesis on this function, Gat 1 rad/s has been plotted versus time. This diagram, not reported here, shows that G has a linear behaviour with time. Therefore, missing other information, a reasonable assumption is that the diffusivity also has a linear dependence with time, i.e.:Ds =英(1 -(14)为了
43、确定这种特性，我们采用流变仪测量凝胶强度随时间的变化。图8中报告了结果， 其中显示了给定Xn/AlCh浓度对的剪切储能模量G随时间的变化。值得注意的是，24 h 后,凝胶呈固体状(G300Pa)。因此，说明形成了非常强的凝胶，因此交联剂的进一步扩 散约为零。因此，我们必须考虑式(10)-(12)中扩散速率是时间的函数。为了做出这一函数 合理假设，绘出了 1 rad/s下的G，与时间。这里没有报告的图说明G，与时为线性特性。 因此，没有其他信息，一个合理假设是扩散率也与时间线性相关，即：where Ds is the diffusion of AlCh in the Xn solution (b
44、efore gelation) and t* is the time at which the gel boundary stops. We estimate the diffusivity of AlCh in water to be 1.1x10-5 cm2/s. The integration of Eq. (12) with Eq. (14) gives其中Ds是AlCh在Xn溶液中的扩散(凝胶化之前)，t*是凝胶边界停止的时间。 我们估计AlCb在水中的扩散率为l.lxlO-5 cm2/so整合式(12)与式(14),给出(15)(15)The applicable solution
45、 of this quadratic algebraic equation is这个二次代数方程的适用解是The pseudo-stoichiometric coefficient p has been determined as an adjustable parameter.The continuous curves fitting the experimental data in Fig7 are the model equation (16). In a deterministic approach the parameter p has been calculated by the
46、equation:拟-化学计量系数p已确定为可调参数。图7中拟合实验数据的连续曲线为模型方程(16)o在确定的方法中，参数P通过下式计算：(17)ML c0 - c*6 =-10-6 Xnp A*where c* and 九* are the concentration of AlCh and the moving boundary position at t*, respectively. The concentration c* has been determined measuring Cl- by means of a spectrofotometer (Shimadzu UV-160
47、1). Both values of p are reported in Table 2.其中c*和入*分别是俨时A1C13浓度和移动边界位置。浓度C*是通过分光光度计 测量C1-确定。表2中列出了 2个P值。(16)The discrepancy between the two values of 0 may be due to the fact that when the concentration of AlCh is in large excess some of it penetrates into the gel but remains unreacted.This possibi
48、lity is not accounted for in the model equations. Inspection of Table 2 shows that the ratio of the two values of p approaches unity as the AlCh concentration is reduced. Finally we remark that our experiments showed that the minimum AlCh concentration for obtaining aconsistent gel is 25 ppm as Al(III).2个p值之间的差异可能是由于这 样的事实，当AlCh浓度大大过量时， 其中一些渗透到凝胶中，但仍未反响。模 型方程中没有考虑这种可能性。表2的 检查说明，随着AlCh浓度降低，2个0 值的比接近1。最后，我们注意到