The road to carbon reduction of lubricants under the background of "dual carbon"(2)

Low-carbonization of the entire lubricant industry chain

At present, the annual consumption of lubricants in my country is about 8 million tons. As a petroleum product, lubricants should also be low-carbonized or even zero-carbonized throughout the entire industry chain, thereby reducing the carbon emissions of lubricant products.

Low-carbon raw materials

Lubricants mainly include lubricating oils and greases, both of which are composed of base oils and additives. Thickeners in greases can also be regarded as additives in a broad sense. At present, the base oils used in lubricants are mainly mineral oils processed by oil refineries using various processes using petroleum as raw materials. There are also some synthetic hydrocarbon oils, such as polyalphaolefins (PAO), alkylnaphthalene, polyalkylcyclopentane, etc., which are basically made from petroleum or other fossil raw materials. Other synthetic oils with larger quantities, such as synthetic ester oils, are also mainly made from fossil raw materials. At present, there is an increasing trend in the base oil synthesized by the Fischer-Tropsch process, and the raw materials used are basically from coal and natural gas. There are more varieties of additives than base oils, and the sources of raw materials are complex, but fossil raw materials are still one of the main sources; additives made from animal and vegetable oils, that is, fatty acids, are used in slightly larger quantities and are used as lubricating oil lubrication performance improvement additives and grease thickener raw materials. Therefore, the main lubricants are basically made from fossil raw materials. The use of low-carbon raw materials currently has the following main technical paths.

Base oil.

The mass percentage of base oil in lubricants exceeds 90%, and it is the main target of lubricant carbon reduction. At present, mineral oil produced from petroleum is the main body of base oil. The low-carbon development path of the refining industry includes the development and use of technologies such as refinery energy conservation, resource utilization efficiency improvement, green hydrogen refining, and refinery intelligence, as well as the development and application of circular economy technologies such as waste plastic chemical recycling, biomass energy, and carbon dioxide resource utilization. These measures are the main paths for refineries to produce low-carbon base oils at different times.

At present, hydrocarbon-based base oils are the main body of base oils. In addition to mineral base oils, hydrocarbon-based base oils with large usage also include Fischer-Tropsch synthetic oils and PAO. The Fischer-Tropsch process includes a series of chemical reactions to generate a variety of hydrocarbons. Most of the alkanes generated are straight-chain, which are suitable as diesel fuel; the heavy components can be prepared through the hydrogenation isomerization process to produce high-quality lubricant base oils with high viscosity index and good low-temperature performance. In addition to alkanes, the products of the Fischer-Tropsch process also produce a small amount of olefins, including a certain proportion of α-olefins. At present, the raw materials for the synthesis gas used to produce Fischer-Tropsch synthetic oil mainly come from fossil raw materials such as coal, natural gas and oil. In the future, they can be replaced by low-carbon renewable raw materials, such as biomass, which can also be used to produce synthesis gas through CCUS (carbon capture, utilization and storage) technology. The raw material for the production of polyalphaolefin synthetic oil is usually 1-decene, and a mixture of alpha-olefins with about 10 carbon atoms from other sources can also be used, but the comprehensiveness of synthetic oil is slightly worse. 1-Decene currently comes mostly from ethylene polymerization, which is made from oil, natural gas or coal. In the future, low-carbon PAO can be produced from raw materials prepared in the following ways: First, the currently generally accepted olefin metathesis mechanism is the metal carbene-catalyzed olefin metathesis reaction mechanism, which can be used to produce 1-decene from oleic acid; second, alpha-olefins can be prepared by Fischer-Tropsch using synthesis gas generated from renewable raw materials; third, various green low-carbon ethylene preparation technologies, such as preparing ethylene from green methanol prepared by CCUS, and then polymerizing green ethylene to produce 1-decene.

Biomass platform compounds of lignocellulosic materials, such as alkyl furans, furfural, 5-hydroxymethyl furfural and other carbonyl compounds, can be extended through carbon-carbon coupling, that is, through hydroxyl alkylation, conjugate addition and aldol condensation, etc., to achieve carbon chain growth. The obtained oxygen-containing intermediates are converted into branched hydrocarbon base oils after hydrogenation and deoxygenation.

Among the types of synthetic oils, the consumption of ester synthetic base oils is second only to hydrocarbon synthetic oils. Their composite use can complement each other in terms of additive solubility and rubber material compatibility. Ester synthetic base oils include diesters, polyol esters and complex esters. Diesters are usually prepared by esterification of dibasic acids and monohydric alcohols or monobasic acids and dihydric alcohols. Commonly used ones are 2-ethylhexyl esters of sebacic acid, azelaic acid, adipic acid or C8-C10 alcohol esters, and C7-C9 straight-chain acid polyethylene glycol esters. Polyol esters are usually prepared by esterification of polyols and monoacids. Commonly used are trimethylolpropane esters and pentaerythritol esters of C5-C9 fatty acids. Complex esters are usually prepared by esterification of dibasic acids and diols to form long-chain molecules, and then terminated by esterification of monoalcohols or monoacids at the end groups. The average molecular weight of complex esters is generally 800-1500. At present, the raw acid and alcohol of ester synthetic oils come from petroleum and animal and vegetable oils. In the future, the proportion of animal and vegetable oils can be increased according to the need for low carbonization of synthetic ester base oils, or acids and alcohols from other low carbonization sources can be further used.

Estolides can be prepared from renewable animal and vegetable oils. Estolides are prepared by oligomerization of fatty acids. They not only have a high viscosity index, low evaporation loss and high biodegradability, but also have excellent thermal oxidation stability and hydrolysis stability. The oligomerization reaction of fatty acids is generally divided into condensation reaction and addition reaction. In the condensation reaction, the hydroxyl group in one fatty acid reacts with the carboxyl group of another fatty acid to form a fatty acid ester with a hydroxyl group. In the addition reaction, the carboxyl group of a carboxylic acid molecule attacks the double bond of another carboxylic acid molecule to generate a fatty acid polymer.

Additives.

There are many kinds of additives in lubricating oils. Many additives sold on the market contain base oils in different proportions, and pure additives account for less than 10% of lubricating oils. The additive content in different lubricating oil varieties is different. Taking the three categories of internal combustion engine oil, hydraulic oil and gear oil, which have the largest consumption of oil products, as an example, additives account for the largest proportion in internal combustion engine oil, of which functional additives account for about 15% in the latest formula, and there are also viscosity index improvers and pour point depressants for modulating the performance of base oils; the additive content in hydraulic oil is relatively low, about 1%; gear oil is in the middle, with functional agents in vehicle gear oils at about 5%, and industrial gear oils at half the rate. Among them, the preparation of internal combustion engine oil detergents such as calcium alkylbenzene sulfonate, magnesium alkylbenzene sulfonate, and calcium sulfide alkylphenol, which are used in large quantities, requires α-olefins, which can be prepared from the various green and low-carbon raw materials mentioned above. Most of the alkyl groups in various additives can be prepared by the aforementioned methods. Fatty acids from plant and animal oils can be used to directly prepare friction reducers, rust inhibitors, etc., and can also be used to prepare a variety of additives by utilizing the reactive characteristics of carbon-carbon double bonds and carboxyl groups in fatty acids.