柴油的十六烷值

十六烷值（Cetane number）:十六烷值是指与柴油自燃性相当的标准燃料中所含正十六烷的体积百分数。

标准燃料是用正十六烷与2-甲基萘按不同体积百分数配成的混合物。

其中正十六烷自燃性好，设定其十六烷值为100，2-甲基萘自燃性差，设定其十六烷值为0。

也有以2，2，4，4，6，8，8-七甲基壬烷代替2-甲基萘，设定其十六烷值为15。

十六烷值测定是在实验室标准的单缸柴油机上按规定条件进行的。

十六烷值高的柴油容易起动，燃烧均匀，输出功率大；十六烷值低，则着火慢，工作不稳定，容易发生爆震。

一般用于高速柴油机的轻柴油，其十六烷值以40-55为宜；中、低速柴油机用的重柴油的十六烷值可低到35以下。

柴油十六烷值的高低与其化学组成有关，正构烷烃的十六烷值最高，芳烃的十六烷值最低，异构烷烃和环烷烃居中。

当十六烷值高于50后，再继续提高对缩短柴油的滞燃期作用已不大；相反，当十六烷值高于65时，会由于滞燃期太短，燃料未及与空气均匀混合即着火自燃，以致燃烧不完全，部分烃类热分解而产生游离碳粒，随废气排出，造成发动机冒黑烟及油耗增大，功率下降。

加添加剂可提高柴油的十六烷值，常用的添加剂有硝酸戊酯或已酯。

柴油十六烷值;cetane number(CN) of diesel fuel：性质：在标准化条件下，指明柴油着火性的约定数值。

在标准试验机试验中，当试验燃料与标准燃料比较具有相同的着火滞后期时，标准燃料混合物中正十六烷所占的体积百分数即十六烷值。

十六烷值高的柴油，着火滞后期较短。

其高低因柴油组分不同而异。

烷烃十六烷值高，芳烃最低，环烷烃和烯烃介于两者之间。

当十六烷值低于发动机使用要求时，会出现燃烧延迟和燃烧不完全而导致发生爆震，降低发动机功率，增大耗油量。

十六烷值过高，会出现燃烧不完全，冒黑烟、增大耗油量。

一般来说高速柴油机要求柴油十六烷值约在40～56之间，普通柴油机在40～45之间即可。

为了提高十六烷值，可以加入少量十六烷值改进剂(如硝酸异戊酯)。

十六烷值是柴油规格的重要指标。

催化柴油MCI工艺技术应用概况我国目前的柴汽比较低，柴油数量满足不了市场的需求。

柴油中的三分之一是催化裂化柴油。

催化柴油中含有较多的杂原子化合物、烯烃和芳烃，颜色不好，安定性较差，尤其是十六烷值很低。

随着重油催化裂化技术的发展和掺渣量的增加，催化柴油的质量问题变得更为突出。

当前国内外普遍采用的劣质催化柴油改质手段是加氢精制和加氢裂化。

催化柴油加氢精制，是在中、低压的条件下，进行烯烃加氢饱和、脱硫、脱氮及芳烃部分饱和反应，可改善其颜色和安定性，而十六烷值提高幅度较小，尤其是加工劣质原料的催化装置，其催化柴油通过加氢精制远不能满足产品对十六烷值的要求。

近几年开发的劣质柴油中压加氢改质工艺，是中压下的一种加氢裂化过程，转化率一般为40%～60%，虽然其柴油产品的十六烷值较原料可提高10～20个单位，但柴油收率低，化学氢耗高，不适应国内市场的需求。

因此，开发一种既能最大限度提高柴油十六烷值，又能得到较高的柴油收率的劣质催化柴油改质技术，是人们普遍关注的课题。

抚顺石油化工研究院新开发的一种提高催化柴油十六烷值的加氢改质工艺技术（Maximum Cetane number Improvement，简称MCI）。

该技术在吉林化学工业公司炼油厂20万吨/年加氢装置应用成功后，先后有７家炼厂采用该技术。

该技术不仅能大幅度提高催柴的十六烷值，同时还能获得较高的柴油收率，获得2001年度国家科技发明二等奖，具有显著的经济效益和社会效益，有可观推广应用前景。

催化柴油MCI工艺的理论基础众所周知，石油产品的烃类族组成直接影响产品的性质。

十六烷值是柴油燃烧性能的重要指标。

柴油馏分中，链烷烃的十六烷值最高，环烷烃次之，芳香烃的十六烷值最低。

同类烃中，同碳数异构程度低的烃类化合物具有较高的十六烷值，芳环数多的烃类具有较低的十六烷值。

因此，环状烃含量低，链状烃含量多的柴油具有较高的十六烷值。

要提高柴油的十六烷值，必须提高柴油中高十六烷值组分的相对含量，或采用添加剂。

采用十六烷值添加剂，将十六烷值提高2～3个单位的成本不太高，但继续增加添加剂用量不仅效果不显著（加到一定比例后十六烷值不再增加），并且也不经济。

从根本上解决柴油十六烷值低的方法是提高十六烷值较高的烃类组分的相对含量，方法之一是除去十六烷值较低的芳烃组分（抽提工艺）。

这种方法的优点是投资低、操作简单，但柴油收率低，抽出的芳烃没有直接的经济价值；另一种方法是采用加氢手段，将双环和多环芳烃中的芳环部分地转化成环烷烃或进而转化成较小分子的芳烃，这种方法中的前者称为加氢精制，后者称为加氢裂化。

由于催化裂化反应的特点，催化柴油中所含的芳烃主要是萘系芳烃。

下面以萘在加氢过程的反应为例，来说明加氢精制（HT）、加氢裂化(HC)和MCI过程的主要反应。

在加氢精制条件下，萘只进行上述反应历程中的第（1）步，即萘加氢变成四氢萘，四氢萘仍在柴油馏分中，它的十六烷值与萘相比提高不大。

因此，加氢精制对十六烷值改进不大。

上式中的（1）、（2）、（3）步反应为萘在中压加氢裂化条件下的主要反应历程，由此可见柴油馏分中的萘，在中压加氢裂化条件下最终转化为苯和丁烷，而从柴油馏分中消失。

萘的转化无疑有助于增加柴油的十六烷值，但导致柴油收率下降。

从萘的加氢精制和加氢裂化反应历程可看出，这两种加氢过程对柴油十六烷值影响的差别。

萘在MCI过程的主要反应历程是萘加氢饱和成为四氢萘，然后再开环。

即只进行萘加氢裂化反应历程中的（1）、（2）两步，生成的丁基苯（十六烷值>20）仍保留在柴油馏分中，其十六烷值与萘（十六烷值接近于0）相比有较大的提高。

MCI反应历程中，由于四氢萘的环烷开环打破了加氢精制反应中萘加氢生成四氢萘的热力学平衡，有利于萘系烃的转化。

因此，该过程不仅十六烷值提高幅度较大，而且柴油收率较高。

催化柴油（LCO）中双环和三环芳烃，在MCI过程中的反应历程类似于萘，双环以上的芳烃只进行芳环饱和和环烷开环，其分子碳数不变。

由于双环和三环芳烃转化为烷基苯，柴油中的高十六烷值组分增加，故柴油的十六烷值可得到较大幅度的提高。

催化柴油MCI技术对催化剂的要求MCI过程的关键是要开发出一种具有良好芳烃加氢饱和性能和开环选择性较高的催化剂。

该过程的催化剂应具有较高的催化活性，保证有较高的芳烃转化深度，具备较高的选择性使环烷开环而不断链，保证十六烷值提高幅度较大和有较高的柴油收率。

此外，还应具有较高的抗杂质能力和较好的稳定性，使之能够适应劣质原料和保证长周期稳定运转。

MCI催化剂理化性质将MCI催化剂与一种性能较好的加氢精制催化剂，用同一种原料油，在完全相同的反应条件下进行了对比试验，试验结果见下表。

一组典型原料MCI与HT产品性质MCI产品与HT产品的杂质含量和颜色基本相同，十六烷值的提高幅度有较大的差别，HT过程柴油的十六烷值由25.0提高至33.6，提高了8.6个单位。

而MCI过程由25.0提高至37.5，提高了12.5个单位，较HT过程提高近4个单位。

催化柴油MCI技术对不同原料的适应性选用了我国几种主要原油的重催柴油，考察了MCI过程对这几种原料的改质效果。

试验原料油主要性质重油催化柴油MCI试验主要工艺条件MCI试验产品性质在中等压力下，大庆催柴油，大港重催柴油，管输重催柴油和辽河催柴，经过MCI过程均具有较显著的改质效果。

有较高的脱杂质深度。

十六烷值有较大幅度的提高，大庆催柴可提高9.5个单位，而其余三种原料油均提高十个单位以上。

MCI柴油的其它质量指标能够满足柴油标准。

催化柴油MCI工业应用效果MCI技术的首次工业应用试验是在吉林化学工业公司炼油厂20万吨/年加氢装置上进行。

该装置用FH-5加氢精制催化剂和3963MCI过程专用催化剂。

典型工业原料油性质工业装置典型反应条件及产品主要性质工业装置典型产品性质+液体收率为100.88%，工况-1的化学氢耗与工况-1柴油收率为99.78%，C5+液体收率为99.58%，工漏损氢耗共计1.38%。

工况-2柴油收率为98.60%，C5况-1的化学氢耗与漏损氢耗共计1.10%（对原料油）。

两种工况下柴油产品的十六烷值分别为39.0和39.9，但十六烷值提高幅度分别为12.1和11.3，已超过试验研究的9.5和8.5，达到了MCI预期的改质效果。

说明了MCI技术能够大幅度提高催化柴油的十六烷值，同时又能获得较高的柴油收率，具有加氢精制和中压加氢改质的双重优点，有广泛推广应用前景。

BIODIESELWHAT IS BIODIESEL ?Biodiesel (or biofuel) is the name for a variety of ester-based fuels (fatty esters) generally defined as the monoalkyl esters made from vegetable oils, such as soybean oil, canola or hemp oil, or sometimes from animal fats through a simple transesterification process. This renewable source is as efficient as petroleum diesel in powering unmodified diesel engine.HISTORYThe concept of using vegetal oil as an engine fuel likely dates when Rudolf Diesel (1858-1913) developed the first engine to run on peanut oil, as he demonstrated at the World Exhibition in Paris in 1900. Unfortunately, R. Diesel died 1913 before his vision of a vegetable oil powered engine was fully realized.Rudolf DieselRudolf Diesel firmly believed the utilization of a biomass fuel to be the real future of his engine. He wanted to provide farmers the opportunity to produce their own fuel. In 1911, he said "The diesel engine can be fed with vegetable oils and would help considerably in the development of agriculture of the countries which use it".After R. Diesel death the petroleum industry was rapidlydeveloping and produced a cheap by-product "diesel fuel" powering a modified "diesel-engine". Thus, clean vegetable oil was forgotten as a renewable source of power.Modern diesels are now designed to run on a less viscous fuel than vegetable oil but, in times of fuel shortages, cars and trucks were successfully run on preheated peanut oil and animal fat. It seems that the upper rate for inclusion of rapeseed oil with diesel fuel is about 25% but crude vegetal oil as a diesel fuel extender induces poorer cold-starting performance compared with diesel fuel or biodiesel made with fatty esters (McDonnel K et al. JAOCS 1999, 76, 539). Today's diesel engines require a clean-burning, stable fuel operating under a variety of conditions. In the mid 1970s, fuel shortages spurred interest in diversifying fuel resources, and thus biodiesel as fatty esters was developed as an alternative to petroleum diesel. Later, in the 1990s, interest was rising due to the large pollution reduction benefits coming from the use of biodiesel. The use of biodiesel is affected by legislation and regulations in all countries (Knothe G, Inform 2002, 13, 900). On February 9, 2004, the Government of the Philippines directed all of its departments to incorporate one percent by volume coconut biodiesel in diesel fuel for use in government vehicles. The EU Council of Ministers adopted new pan-EU rules for the detaxation of biodiesel and biofuels on October 27, 2003.Large-volume production occurs mainly in Europe, with production there now exceeding 1.4 million tons per year. Western European biodiesel production capacity was estimated at about 2 million metric tons per year largely produced through the transesterification process, about one-half thereof in Germany (440,000 and 350,000 MT in France and Italy, respectively). In the United States, by 1995, 10 percent of all federal vehicles were to be using alternative fuels to set an example for the private automotive and fuel industries. Several studies are now funded to promote the use of blends of biodiesel and heating oil in USA. In USA soybean oil is the principal oil being utilized for biodiesel (about 80,000 tons in 2003). Details may be viewedon-line through the National Biodiesel Board web site.Several reviews on sources, production, composition and properties of biodiesel may be consulted for further information:- Ramadhas AS et al., Renewable Energy 2004, 29, 727-742- Bajpai D et al., J Oleo Sci 2006, 55, 487- Durrett TP et al., The Plant J 2008, 54, 593-607- Jetter R et al., The Plant J 2008, 54, 670-683As many algal species have been found to grow rapidly and produce substantial amounts of triacylglycerols (oleaginous algae), it has long been postulated that they could be employed to produce oils and other lipids for biofuels (see review in : Hu Q et al., The Plant J 2008, 54, 621-639). A very informative review of the prospects of using yeasts and microalgae as source of cheap oils that could be used for biodiesel may be consulted (Ratledge C et al., Lipid Technol 2008, 20, 155).As the major byproduct of biodiesel production is glycerol, uses for that byproduct have been investigated. Glycerol can be thermochemically converted into propylene glycol (Chiu CW et al., Ind Eng Chem Res 2006, 45, 791), 1,3-propanediol (Gonzalez-Pajuelo M et al., Metab Eng 2005, 7, 329), lipids (Narayan M et al., Int J Food Sci Nutr 2005, 56, 521) and several other chemicals. Among lipids, it was shown that glycerol can be used to produce docosahexaenoic acid (DHA) through fermentation of the alga Schizochytrium limacinum (Chi Z et al., Process Biochem 2007, 42, 1537; Pyle DJ et al., J Agric Food Chem 2008, 56, 3933).A review of the use of vegetable oils as engine fuels may be consulted (Ramadhas AS et al. Renew Energy 2007, 29, 727).The book of Nitske WR et al. may be consulted for the history of biodiesel (Nitske WR, Wilson CM, Rudolf Diesel: Pioneer of the age of power)MAKING BIODIESELWhat is still widely unknown is that it is easy to make biodiesel for diesel engines using vegetable oil or animal fat. Biodiesel is sold commercially in Europe, America and Australia.On a small scale, vegetable oil is relatively expensive, but used products from the cooking industry is abundant and can easily and cheaply be converted into a biodiesel fuel that will mix in any quantity with conventional diesel. During heating, the amount of polymers inthe oil may increase up to 15 wt% and thus may have negative influence on fuel characteristics. Therefore, the amount of polymers in waste oil is a good indicator for biodiesel production (Mittelbach M et al. JAOCS 1999, 76, 545).The transesterification process involves mixing at room temperature methanol (50% excess) with NaOH (100% excess), then mixing vigorously with vegetable oil and letting the glycerol settle (about 15% of the biodiesel mix). The supernatant is biodiesel and contains a mixture of methylated fatty acids and methanol, the catalyst remaining dissolved in the glycerol fraction. Industrially, the esters are sent to the clean-up or purification process which consists of water washing, vacuum drying, and filtration.An in situ alkaline transesterification was shown to be efficient in preparing fatty acid esters, the simple and direct process eliminating the expense associated with solvent extraction and oil cleanup (Haas MJ et al., JAOCS 2004, 81, 83).Transesterification may be processed using methanol, ethanol, isopropyl alcohol, or butanol, the catalyst being either sodium or potassium hydroxide. It was shown that the methanol/oil molar ratio influences largely the efficiency of the reaction and has important implications for the optimal size of methyl ester plants (Boocock DGB et al. JAOCS 1998, 75, 1167). Optimization of methanolysis of Brassica carinata oil has been examined considering the catalyst concentration as well as the reaction temperature (Vicente G et al., JAOCS 2005, 82, 899).Various reaction parameters for the synthesis of biodiesel from safflower oil were studied to improve the fuel production which was within the recommended standards with 96.8% yield (Meka PK et al., J Oleo Sci 2007, 56, 9).Free fatty acids and total glycerol (free and acylglycerols) can initiate engine corrosion and affect human or animal health by emission of hazardous acrolein into the environment. Accordingly, maximum allowable amounts of free fatty acids and acylglycerols are included in the biodiesel specification of most countries.For glycerol, a maximum permissible concentration of 0.02 wt-% is set by the European norm as well as by the ASTM specification. Therefore, it is necessary to determine the amount of free glycerol in biodiesel. Among others, a simple and rapid method was described using HPLC with refractometric detection (Hajek M et al., Eur J Lipid Sci Technol 2006, 108, 666). A simple HPLC method using alight-diffusion detector was proposed to monitor acyglycerols and free fatty acids concentrations in biodiesel (Kittirattanapiboon K et al., Eur J Lipid Sci Technol 2008, 110, 422).Information on the physical properties described by the standards anddetails on the standard reference methods may be found in the paper by Knothe G (JAOCS 2008, 83, 823).It was experienced that 10 l of soybeans produced about 1.9 l of biodiesel. A liter of this fuel contains about 35,000 BTUs.If fats or solidified oil are used, it will need to heat up to 50°C the mixture prior to mixing with methanol and catalyst.If free fatty acids are present (used cooking oils), special pretreatment technologies are required (see website).Among lipid-rich materials of low value is soapstock, a co-product of the refining of edible vegetal oils. This mixture is generated at a rate of about 6% of the treated unrefined oil (45 MT per year in USA). An efficient procedure involving acid-catalyzed esterification of soapstock has been described (Haas MJ et al., J Am Oil Chem Soc 2003, 80, 97).The world biodiesel sources were in 2002 : rapeseed oil (84%), sunflower (13%), soybean oil (1%), palm oil (1%), and others (1%). Information on making biodiesel may be found in specific websites : /biodiesel/index.htm/biodiesel_make.html/group/Biodiesel/European Biofuel Technology PlatformGeneral biodesiel information :/biodiesel//(the latest information on biodiesel)Other resources (discussion groups) :/group/BiodieselEuropean Biodiesel Board: Update on negotiations on biofuel directives (21 February 2003)Additional biodiesel information :AustraliaAustriaEuropeGermanyUnited KingdomUnited statesA comprehensive review of problems of emissions and of small-, medium-, and industrial-scale production with numerous web resources and references may be found on the web :Biodiesel : A brief overviewADVANTAGES OF BIODIESEL•Blends of 20% biodiesel with 80% petroleum diesel can be used in unmodified diesel engines. Biodiesel can be used in its pureform but many require certain engine modifications to avoidmaintenance and performance problems.•It was stated that about half of the biodiesel industry can use recycled oil or fat, the other half being soybean, or rapeseed oil according to the origin of these feed stocks.•Biodiesel is nontoxic, biodegradable. It reduces the emission of harmful pollutants (mainly particulates) from diesel engines(80% less CO2 emissions, 100% less sulfur dioxide) butemissions of nitrogen oxides (precursor of ozone) areincreased.•Biodiesel has a high cetane number (above 100, compared to only 40 for diesel fuel). Cetane number is a measure of a fuel's ignition quality. The high cetane numbers of biodiesel contribute to easy cold starting and low idle noise.•The use of biodiesel can extend the life of diesel engines because it is more lubricating and, furthermore, power outputare relatively unaffected by biodiesel.•Biodiesel replaces the exhaust odor of petroleum diesel with a more pleasant smell of popcorn or French fries.By developing methods to use cheap and low quality lipids as feedstocks, it is hoped that a cheaper biodiesel can be produced, thus competing economically with petroleum resources.Investigation of the Parameters Affecting the Cetane Number of Biodiesel。