酸法催化生产生物柴油过程的几个关键问题研究

发布时间：2019-02-25 17:17

【摘要】：在生物柴油生产中,多种生物质油脂资源属于高酸值情形。液体硫酸直接催化高酸值油脂是生产生物柴油的传统有效方式之一,但存在酸催化剂难以回收利用的问题,生产上多以熟石灰中和处理水油相并经纯化获得甘油,整体过程不仅消耗了酸,并产生低价值副产品石膏。本研究提出一种新的研究思路用于分离甘油相中的甲醇、甘油和硫酸,并分别进行催化剂硫酸和副产品甘油的脱水浓缩回收。在酸催化高酸值油脂制备生物柴油的基础上,以精馏回收产物中的过量甲醇,而后以正己烷和水进行双液相萃取促进甲酯相和甘油相的分离,获得的水相以酸阻滞分离其中的硫酸和甘油,最后以多效膜蒸馏对阻滞分离得到的含酸和甘油的两股洗脱液分别进行深度脱水浓缩,实现催化剂硫酸和甘油的回收利用。研究结果表明,基于强碱性阴离子交换树脂的酸阻滞分离过程可以有效地分离双液相萃取所得的甘油和硫酸混合水溶液。优化条件下甘油和硫酸的分离度可达1.53,甘油收率为96.2%,相对应的硫酸收率为95.3%;酸阻滞树脂的使用寿命100周期,适合长期使用。本研究建立了温差极化、浓差极化影响下多效膜蒸馏过程用于非挥发性溶质水溶液浓缩过程的传热传质理论模型,并用于解释多效膜蒸馏用于深度浓缩非挥发性溶质甘油水溶液过程中的性能变化规律,建立的理论模型可很好地描述多效膜蒸馏浓缩甘油水溶液所获得的实验数据。对于浓度为10 g/L的甘油溶液,经多效膜蒸馏深度脱水可浓缩至400 g/L,截留率可一直保持在99.9%以上;浓缩过程的最大膜通量和造水比分别为5.7L/m2h和16.2,甚至当甘油溶液浓缩至400 g/L时,造水比仍保持在4.6,这相当于传统六效蒸发器的节能效果。在甘油溶液浓缩至近300 g/L时,膜通量和造水比均陡然降低;随着甘油浓度的升高,其水溶液粘度的升高和水蒸汽分压的降低是导致膜通量和造水比下降至关重要的原因。2k全因子设计分析显示,热料入口温度是影响膜通量和造水比最显著的因子。以150 g/L的甘油溶液为料液,连续运行60 d的多效膜蒸馏过程性能稳定。对于浓度为5 wt%的硫酸溶液,经多效膜蒸馏深度脱水可浓缩至40 wt%的硫酸溶液,且渗透液电导率100μs/cm。多效膜蒸馏浓缩后的甘油可以进一步用高温或真空蒸馏得到甘油产品出售,而浓缩后的硫酸可以进一步用高温或真空蒸馏浓缩到90%以上回用为催化剂。以上研究结果表明,液体酸催化制备生物柴油、双液相萃取促进甲酯相和甘油相分离、酸阻滞分离甘油和硫酸溶液、多效膜蒸馏深度浓缩甘油溶液和硫酸溶液,这一系列的过程耦合可有效提高生物柴油生产的经济性和环保效益。
[Abstract]:In the production of biodiesel, a variety of bio-oil resources belong to the situation of high acid value. Liquid sulfuric acid directly catalyzes oil with high acid value is one of the traditional effective ways to produce biodiesel, but there is a problem that acid catalyst is difficult to be recycled. Glycerol is obtained by neutralizing the treated water oil phase with ripe lime in production. The whole process not only consumes acid, but also produces low-value by-product gypsum. In this paper, a new method for separating methanol, glycerol and sulfuric acid from glycerol phase was proposed, and the dehydration concentration and recovery of catalyst sulphuric acid and by-product glycerol were carried out respectively. Based on the preparation of biodiesel by acid-catalyzed oil with high acid value, the excess methanol in the product was recovered by distillation, and then the separation of methyl ester phase and glycerin phase was promoted by two-liquid phase extraction with n-hexane and water. The obtained water phase separated sulfuric acid and glycerol by acid retardation. At last, the two eluents containing acid and glycerol obtained by block separation were deeply dewatered and concentrated by multi-effect membrane distillation, and the recovery and utilization of catalyst sulfuric acid and glycerol were realized. The results show that the acid barrier separation process based on strong basic anion exchange resin can effectively separate the mixed aqueous solution of glycerol and sulfuric acid extracted by double liquid phase extraction. Under the optimized conditions, the separation of glycerol and sulfuric acid can reach 1.53, the yield of glycerol is 96.2%, and the yield of sulfuric acid is 95.3%. The service life of acid-blocking resin is 100 cycles, which is suitable for long-term use. In this paper, a theoretical model of heat and mass transfer for the concentration of nonvolatile solute aqueous solution under the influence of temperature difference polarization and concentration polarization is established. It is also used to explain the variation of performance in the process of deep concentration of non-volatile solute glycerol solution by multi-effect membrane distillation. The theoretical model established can well describe the experimental data obtained from the concentration of glycerol aqueous solution by multi-effect membrane distillation. For glycerol solution with concentration of 10 g / L, the concentration of glycerol solution can be concentrated to 400 g / L after deep dehydration by multi-effect membrane distillation, and the rejection rate can be kept above 99.9% all the time. The maximum membrane flux and water production ratio in the concentration process are 5.7L/m2h and 16.2, respectively. Even when glycerol solution is concentrated to 400g / L, the water production ratio remains at 4.6, which is equivalent to the energy saving effect of the traditional six-effect evaporator. When glycerol solution was concentrated to nearly 300 g / L, both membrane flux and water production ratio decreased sharply. With the increase of glycerol concentration, the increase of viscosity of aqueous solution and the decrease of steam partial pressure are the important reasons leading to the decrease of membrane flux and the ratio of water to water. 2k full factor design analysis shows that the viscosity of aqueous solution increases and the partial pressure of water vapor decreases. The inlet temperature of hot material is the most significant factor affecting the membrane flux and the ratio of water to water. Using 150 g / L glycerol solution as the feed solution, the performance of the multi-effect membrane distillation process with continuous operation for 60 days was stable. For the sulfuric acid solution with 5 wt% concentration, the solution can be concentrated to 40 wt% sulfuric acid solution after deep dehydration by multi-effect membrane distillation, and the conductivity of the osmotic solution is 100 渭 s / cm.. The concentrated glycerin can be further sold by high temperature or vacuum distillation, and the concentrated sulfuric acid can be further concentrated to more than 90% by high temperature or vacuum distillation as catalyst. The above results show that liquid acid catalyzes the preparation of biodiesel, dual liquid phase extraction promotes the separation of methyl ester phase and glycerol phase, acid block separation of glycerol and sulfuric acid solution, and polyeffect membrane distillation depth concentration of glycerol solution and sulfuric acid solution. This series of process coupling can effectively improve the economic and environmental benefits of biodiesel production.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TE667

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