Biodiesel catalysts

Shahbaz, K., Mjalh, F. S., Hashim, M. A., Al-Nashef, 1. M. Eutectic solvents for the removal of residual pahn oil-based biodiesel catalyst. Sep PurifTechnol 2011, 81, 216-222. 

In order to convert the raw oils into useful material, transesterification technology is used. The oil is reacted with a low molecular weight alcohol, commonly methanol, in the presence of a catalyst to form the fatty acid ester and glycerol (Scheme 6.1). The ester is subsequently separated from the glycerol and used as biodiesel, the glycerol being used as a raw material for fine chemicals production. Although the chemistry is simple, in order to make biodiesel commercially viable the process must be... 

The transesterification reactions were conducted in a sealed 250 ml autoclave equipped with a stirrer. The molar ratio of methanol to oil was 12 1, reaction temperature was 200 C-230°C, and the ratio of catalyst to oil was about 2 wt%. Samples were taken out from the reaction mixture and biodiesel portions were separated by centrifuge. 

Experiments showed that high methyl ester yields can be achieved with solid bases and super acids under moderate reaction conditions. The solid bases were more effective catalysts than the solid super acids. High stability can be achieved by an ordinary inexpensive preparation process, and the catalyst can be separated easily from the reaction products in the heterogeneous catalysis process. The costly catalyst removal process can be avoided compared with the homogeneous process. Therefore, the heterogeneous process using a solid catalyst should be more economical for biodiesel production. 

In our first experiment we decided to test the conversion of sunflower oil into biodiesel (16). Treatment of sunflower oil (1) with NaOMe in MeOH results in formation of a mixtme of fatty acid methyl esters (FAME), also known as biodiesel, and glycerol (2) (Figme 4.3). The reaction was performed with a six-fold molar excess of methanol with respect to sunflower oil at elevated temperatures (60°C) using a basic catalyst (NaOMe, 1% w/w with respect to sunflower oil). The CCS was equipped with a heating jacket to ensure isothermal conditions. The sunflower oil was preheated to 60°C and was pumped at 12.6 ml/min into one entrance of the CCS. Subsequently, a solution of NaOMe in MeOH was introduced through the other entrance at a flow rate of 3.1 ml per minute. After about 40 minutes, the system reaches steady state and the FAME containing some residual sunflower oil is coming... 

Hydrotreating has been proposed by Arbokem Inc. in Canada as a means of converting Grade Tall Oil into biofuels and fuel additives. However, this process is a hydrogenation process which produces hydrocarbons rather than biodiesel. Recently a process for making biodiesel from crude tall oil has been proposed. It relies on the use of an acid catalysts or of an acyl halide for the esterification reaction, but no information is given on the properties of this fuel, particularly concerning the oxidative stability. 

Selective hydrogerration over low-loading, supported Cu catalysts has shown to be a valuable tool for the production of high quality biodiesel from Tall Oil, a byproduct of the Pulp Paper indrrstry. These resrrlts allow planning the use of a great variety of non-conventiorral oils with high iodine value for the production of biodiesel. 

Heterogeneous Catalyst and Proeess for the Produetion of Biodiesel from High Free-Fatty... 

To produce biodiesel, refined vegetable oils are reacted with methanol in the presence of alkali catalysts such as sodium hydroxide, potassium hydroxide, and sodium methylate. The overall base-catalyzed process has several problems that also... 

The production of biodiesel from low quality oils such as animal fats, greases, and tropical oils is challenging due to the presence of undesirable components especially FFA and water. A pre-treatment step is required when using such high fatty-acid feedstock. Generally, this esterification pre-treatment employs liquid sulfuric acid catalyst which must subsequently be neutralized and either disposed of or recycled. However, requirement of high temperature, high molar ratio of alcohol to FFA, separation of the catalyst, enviromnental and corrosion related problems make its use costly for biodiesel production. 

There is a real opportunity to reduce biodiesel production costs and environmental impact by applying modem catalyst technology, which will allow increased process flexibility to incorporate the use of low-cost high-FFA feedstock, and reduce water and energy requirement. Solid catalysts such as synthetic polymeric catalysts, zeolites and superacids like sulfated zirconia and niobic acid have the strong potential to replace liquid acids, eliminating separation, corrosion and environmental problems. Lotero et al. recently published a review that elaborates the importance of solid acids for biodiesel production. ... 

Apart from a few reports" on solid acid catalyzed esterification of model compounds, to our knowledge utilization of solid catalysts for biodiesel production from low quality real feedstocks have been explored only recently. 12-Tungstophosphoric acid (TPA) impregnated on hydrous zirconia was evaluated as a solid acid catalyst for biodiesel production from canola oil containing up to 20 wt % free fatty acids and was found to give ester yield of 90% at 200°C. Propylsulfonic acid-functionalized mesoporous silica catalyst for esterification of FFA in flotation beef tallow showed a superior initial catalytic activity (90% yield) relative to a... 

Reports have shown solid catalysts for esterification of FFA have one or more problems such as high cost, severe reaction conditions, slow kinetics, low or incomplete conversions, and limited lifetime. We will present research describing our newly developed polymeric catalyst technology which enables the production of biodiesel from feedstock containing high levels (> 1 wt %) of FFAs. The novel catalyst, named AmberlysH BD20, overcomes the traditional drawbacks such as limited catalyst life time, slow reaction rates, and low conversions. 

The traditional catalyst used for esterification of acids to methyl esters is sulfuric acid. Homogeneous sulfuric acid catalysis has many downsides. When using sulfuric acid, much capital expense is required for Hastalloy and/or other specialty metals of construction. Homogeneous catalysis results in the contamination of the product by sulfur containing species. Therefore, neutralization and removal of acid is required to meet biodiesel specifications and to protect the downstream transesterification reactor. Inevitably, when using sulfuric acid, organic sulfur compounds will be produced. These products will cause the resultant biodiesel to fail specification tests. 

Fatty acid methyl esters (FAME) are currently manufactured mainly by trans-esterification with an alcohol, using a homogeneous base catalyst (NaOH/KOH). Methanol is more suitable for biodiesel manufacturing, but other alcohols can in principle also be used, depending on the feedstock available. The... 

During the last decade many industrial processes shifted towards using solid acid catalysts (6). In contrast to liquid acids that possess well-defined acid properties, solid acids contain a variety of acid sites (7). Sohd acids are easily separated from the biodiesel product they need less equipment maintenance and form no polluting by-products. Therefore, to solve the problems associated with liquid catalysts, we propose their replacement with solid acids and develop a sustainable esterification process based on catalytic reactive distillation (8). The alternative of using solid acid catalysts in a reactive distillation process reduces the energy consumption and manufacturing pollution (i.e., less separation steps, no waste/salt streams). 

Sulfur-free fuel, since solid acid catalysts do not leach into the biodiesel product. 

In our process development efforts PNNL demonstrated the life of the Recontaining catalyst using both pristine feed and feed from biodiesel desalted glycerin (see Figure 34.10). 

By 2006, the U.S. had 77 ethanol plants producing more than 3 billion gallons of ethanol per year. Canada produced an additional 60 million gallons. Corn was the feedstock in 62 of the 77 U.S. plants. Other feedstocks included seed corn, corn and barley, corn and beverage waste, brewery waste, cheese whey, corn and milo, corn and wheat starch, potato waste and various sugars. The U.S. had 11 additional plants under construction and 55 proposed. West Central Soy processes soybeans to a food grade oil. Alcohol and a catalyst are then used to produce biodiesel fuel and glycerin. 

Biodiesel (fatty acid methyl ester (FAME)) production is based on transesterification of vegetable oils and fats through the addition of methanol (or other alcohols) and a catalyst, giving glycerol as a by-product (which can be used for cosmetics, medicines and food). Oil-seed crops include rapeseeds, sunflower seeds, soy beans and palm oil seeds, from which the oil is extracted chemically or mechanically. Biodiesel can be used in 5%-20% blends with conventional diesel, or even in pure form, which requires slight modifications in the vehicle. 

Biodiesel is a mixture of methyl esters of fatty acids and is produced from vegetable oils by transesterification with methanol (Fig. 10.1). For every three moles of methyl esters one mole of glycerol is produced as a by-product, which is roughly 10 wt.% of the total product. Transesterification is usually catalyzed with base catalysts but there are also processes with acid catalysts. The base catalysts are the hydroxides and alkoxides of alkaline and alkaline earth metals. The acid catalysts are hydrochloride, sulfuric or sulfonic acid. Some metal-based catalysts can also be exploited, such as titanium alcoholates or oxides of tin, magnesium and zinc. All these catalyst acts as homogeneous catalysts and need to be removed from the product [16, 17]. The advantages of biodiesel as fuel are transportability, heat content (80% of diesel fuel), ready availability and renewability. The... 

Modifications in the production of biodiesel can result in valuable glycerol as a byproduct and in fewer separation steps. The modifications studied or considered include combining etherification of glycerol into the biodiesel production process, etherification in situ within the biodiesel process and a biodiesel process with heterogeneous catalyst. 

Although technologies for both bioethanol and biodiesel are well established, improved catalysts are still needed. 

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