David Graf
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
David Graf has a total of 8 co-authors. Here are the top co-authors by number of shared publications:
- Reinhard Rauch
BIOENERGY 2020
4 shared publications - Philipp Neuner
Division of Fuel Technology (EBI-ceb), Engler-Bunte-Institute, Karlsruhe Institute of Technology (KIT), Engler-Bunte-Ring 1a, 76131 Karlsruhe, Germany
3 shared publications - Dieter Stapf
Institute for Technical Chemistry, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
1 shared publication - Heiko Mild
Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
1 shared publication - Johannes Waßmuth
Engler-Bunte-Institute–Division of Fuel Technology, Karlsruhe Institute of Technology, Engler-Bunte-Ring 1a, 76131 Karlsruhe, Germany
1 shared publication - Michael Zeller
Institute for Technical Chemistry Karlsruhe Institute of Technology Karlsruhe Germany
1 shared publication
Latest Publications
- Open Access
Co-Hydroprocessing of Fossil Middle Distillate and Bio-Derived Durene-Rich Heavy Ends under Hydrotreating Conditions
Methanol-to-gasoline (MTG) and dimethyl ether-to-gasoline (DTG), as industrially approved processes for producing greenhouse gas-neutral gasoline, yield byproducts rich in heavy mono-ring aromatics such as 1,2,4,5-tetramethylbenzene (durene). Due to its tendency to crystallize and the overall poor fuel performance, the heavy fuel fraction is usually further processed using after-treatment units designed for this purpose. This research article discusses the co-hydroprocessing (HP) of bio-derived heavy gasoline (HG) with fossil middle distillate (MD), drawing on available refinery hydrotreaters. Co-HP experiments were conducted in a laboratory-scale fixed bed reactor using an industrial CoMo/-AlO catalyst, varying the space-time between 0.7 and 4.0 h and the reaction temperature between 340 and 390 °C. In addition to the durene conversion, special attention was paid to the octane and cetane numbers (CN) of gasoline and MD, respectively. A six-lump model with ten parameters was developed to predict relevant fuel yields dependent on the process conditions. Under stable catalyst conditions, C aromatic conversions of more than 60% were obtained, while the CN remained close to that of pure MD. Harsh process conditions increased the gasoline yield up to 20% at the cost of MD, while the kerosene yield remained almost constant. With an optimized lumping model, fuel yields could be predicted with an R of 0.998. In this study, co-HP heavy aromatic-rich MTG/DTG fuels with fossil MD were proven to be a promising process strategy compared to a stand-alone after-treatment.Open AccessCo-Hydroprocessing of Fossil Middle Distillate and Bio-Derived Durene-Rich Heavy Ends under Hydrotreating Conditions
Methanol-to-gasoline (MTG) and dimethyl ether-to-gasoline (DTG), as industrially approved processes for producing greenhouse gas-neutral gasoline, yield byproducts rich in heavy mono-ring aromatics such as 1,2,4,5-tetramethylbenzene (durene). Due to its tendency to crystallize and the overall poor fuel performance, the heavy fuel fraction is usually further processed using after-treatment units designed for this purpose. This research article discusses the co-hydroprocessing (HP) of bio-derived heavy gasoline (HG) with fossil middle distillate (MD), drawing on available refinery hydrotreaters. Co-HP experiments were conducted in a laboratory-scale fixed bed reactor using an industrial CoMo/-AlO catalyst, varying the space-time between 0.7 and 4.0 h and the reaction temperature between 340 and 390 °C. In addition to the durene conversion, special attention was paid to the octane and cetane numbers (CN) of gasoline and MD, respectively. A six-lump model with ten parameters was developed to predict relevant fuel yields dependent on the process conditions. Under stable catalyst conditions, C aromatic conversions of more than 60% were obtained, while the CN remained close to that of pure MD. Harsh process conditions increased the gasoline yield up to 20% at the cost of MD, while the kerosene yield remained almost constant. With an optimized lumping model, fuel yields could be predicted with an R of 0.998. In this study, co-HP heavy aromatic-rich MTG/DTG fuels with fossil MD were proven to be a promising process strategy compared to a stand-alone after-treatment. - Open Access
Standard-Compliant Gasoline by Upgrading a DTG-Based Fuel through Hydroprocessing the Heavy-Ends and Blending of Oxygenates
Methanol-to-gasoline (MTG) and dimethyl ether-to-gasoline (DTG) fuels are rich in heavy aromatics such as 1,2,4,5-tetramethylbenzene, resulting in low volatilities due to a lack of light ends, increased emission tendencies and drivability problems due to crystallization. Approaches addressing these issues mainly focus on single aspects or are optimized for petroleum-based feedstocks. This research article introduces an upgrading strategy for MTG and DTG fuels through hydroprocessing (HP) heavy-ends and applying a sophisticated blending concept. Different product qualities were prepared by HP heavy gasoline (HG) and Fischer-Tropsch wax using commercially available Pt/HZSM-5 and Pt/SAPO-11 catalysts in a fixed-bed reactor. The products were used for blending experiments, focusing on gasoline volatility characteristics. Accordingly, methanol, ethanol, methyl tert-butyl ether (MTBE), and ethyl tert-butyl ether (ETBE) were evaluated in a second blending experiment. The results were finally considered for preparing blends meeting EN 228. HP of HG was found to improve the amount of light-ends and the vapor pressure of the DTG fuel with increasing reaction temperature without, however, satisfying EN 228. The front-end volatility was further improved by blending methanol due to the formation of near-azeotropic mixtures, while ethyl tert-butyl ether (ETBE) considerably supported the mid-range volatility. A final blend with an alcohol content of less than 3 vol.%, mostly meeting EN 228, could be provided, making it suitable even for older vehicles.
Open AccessStandard-Compliant Gasoline by Upgrading a DTG-Based Fuel through Hydroprocessing the Heavy-Ends and Blending of Oxygenates
Methanol-to-gasoline (MTG) and dimethyl ether-to-gasoline (DTG) fuels are rich in heavy aromatics such as 1,2,4,5-tetramethylbenzene, resulting in low volatilities due to a lack of light ends, increased emission tendencies and drivability problems due to crystallization. Approaches addressing these issues mainly focus on single aspects or are optimized for petroleum-based feedstocks. This research article introduces an upgrading strategy for MTG and DTG fuels through hydroprocessing (HP) heavy-ends and applying a sophisticated blending concept. Different product qualities were prepared by HP heavy gasoline (HG) and Fischer-Tropsch wax using commercially available Pt/HZSM-5 and Pt/SAPO-11 catalysts in a fixed-bed reactor. The products were used for blending experiments, focusing on gasoline volatility characteristics. Accordingly, methanol, ethanol, methyl tert-butyl ether (MTBE), and ethyl tert-butyl ether (ETBE) were evaluated in a second blending experiment. The results were finally considered for preparing blends meeting EN 228. HP of HG was found to improve the amount of light-ends and the vapor pressure of the DTG fuel with increasing reaction temperature without, however, satisfying EN 228. The front-end volatility was further improved by blending methanol due to the formation of near-azeotropic mixtures, while ethyl tert-butyl ether (ETBE) considerably supported the mid-range volatility. A final blend with an alcohol content of less than 3 vol.%, mostly meeting EN 228, could be provided, making it suitable even for older vehicles.
- Open Access
Chemical Conversion of Fischer–Tropsch Waxes and Plastic Waste Pyrolysis Condensate to Lubricating Oil and Potential Steam Cracker Feedstocks
The global economy and its production chains must move away from petroleum-based products, to achieve this goal, alternative carbon feedstocks need to be established. One area of concern is sustainable production of synthetic lubricants. A lubricating oil can be described as a high boiling point (>340 °C) liquid with solidification at least below room temperature. Historically, many lubricants have been produced from petroleum waxes via solvent or catalytic dewaxing. In this study, catalytic dewaxing was applied to potential climate neutral feedstocks. One lubricant was produced via Fischer–Tropsch (FT) synthesis and the other lubricant resulted from low temperature pyrolysis of agricultural waste plastics. The waxes were chosen because they each represented a sustainable alternative towards petroleum, i.e., FT waxes are contrivable from biomass and CO2 by means of gasification and Power-to-X technology. The pyrolysis of plastic is a promising process to complement existing recycling processes and to reduce environmental pollution. Changes in cloud point, viscosity, and yield were investigated. A bifunctional zeolite catalyst (SAPO-11) loaded with 0.3 wt% platinum was used. The plastic waste lubricants showed lower cloud points and increased temperature stability as compared with lubricants from FT waxes. There was a special focus on the composition of the naphtha, which accumulated during cracking. While the plastic waste produced higher amounts of naphtha, its composition was quite similar to those from FT waxes, with the notable exception of a higher naphthene content.
Open AccessChemical Conversion of Fischer–Tropsch Waxes and Plastic Waste Pyrolysis Condensate to Lubricating Oil and Potential Steam Cracker Feedstocks
The global economy and its production chains must move away from petroleum-based products, to achieve this goal, alternative carbon feedstocks need to be established. One area of concern is sustainable production of synthetic lubricants. A lubricating oil can be described as a high boiling point (>340 °C) liquid with solidification at least below room temperature. Historically, many lubricants have been produced from petroleum waxes via solvent or catalytic dewaxing. In this study, catalytic dewaxing was applied to potential climate neutral feedstocks. One lubricant was produced via Fischer–Tropsch (FT) synthesis and the other lubricant resulted from low temperature pyrolysis of agricultural waste plastics. The waxes were chosen because they each represented a sustainable alternative towards petroleum, i.e., FT waxes are contrivable from biomass and CO2 by means of gasification and Power-to-X technology. The pyrolysis of plastic is a promising process to complement existing recycling processes and to reduce environmental pollution. Changes in cloud point, viscosity, and yield were investigated. A bifunctional zeolite catalyst (SAPO-11) loaded with 0.3 wt% platinum was used. The plastic waste lubricants showed lower cloud points and increased temperature stability as compared with lubricants from FT waxes. There was a special focus on the composition of the naphtha, which accumulated during cracking. While the plastic waste produced higher amounts of naphtha, its composition was quite similar to those from FT waxes, with the notable exception of a higher naphthene content.
- Open Access
Catalytic Hydroisomerisation of Fischer–Tropsch Waxes to Lubricating Oil and Investigation of the Correlation between Its Physical Properties and the Chemical Composition of the Corresponding Fuel Fractions
Due to environmental concerns, the role of renewable sources for petroleum-based products has become an invaluable research topic. One possibility of achieving this goal is the Fischer–Tropsch synthesis (FTS) based on sustainable raw materials. Those materials include, but are not limited to, synthesis gas from biomass gasification or hydrogen through electrolysis powered by renewable electricity. In recent years, the utilisation of CO2 as carbon source for FTS was one main R&D topic. This is one of the reasons for its increase in value and the removal of its label as being just exhaust gas. With the heavy product fraction of FTS, referred to as Fischer–Tropsch waxes (FTW), being rather limited in their application, catalytic upgrading can help to increase the economic viability of such a process by converting the waxes to high value transportation fuels and lubricating oils. In this paper, the dewaxing of FTW via hydroisomerisation and hydrocracking was investigated. A three phase fixed bed reactor was used in combination with a zeolitic catalyst with an AEL (SAPO-11) structure and 0.3 wt% platinum (Pt). The desired products were high quality white oils with low cloud points. These products were successfully produced in a one-step catalytic dewaxing process. Within this work, a direct correlation between the physical properties of the white oils and the chemical composition of the simultaneously produced fuel fractions could be established.
Open AccessCatalytic Hydroisomerisation of Fischer–Tropsch Waxes to Lubricating Oil and Investigation of the Correlation between Its Physical Properties and the Chemical Composition of the Corresponding Fuel Fractions
Due to environmental concerns, the role of renewable sources for petroleum-based products has become an invaluable research topic. One possibility of achieving this goal is the Fischer–Tropsch synthesis (FTS) based on sustainable raw materials. Those materials include, but are not limited to, synthesis gas from biomass gasification or hydrogen through electrolysis powered by renewable electricity. In recent years, the utilisation of CO2 as carbon source for FTS was one main R&D topic. This is one of the reasons for its increase in value and the removal of its label as being just exhaust gas. With the heavy product fraction of FTS, referred to as Fischer–Tropsch waxes (FTW), being rather limited in their application, catalytic upgrading can help to increase the economic viability of such a process by converting the waxes to high value transportation fuels and lubricating oils. In this paper, the dewaxing of FTW via hydroisomerisation and hydrocracking was investigated. A three phase fixed bed reactor was used in combination with a zeolitic catalyst with an AEL (SAPO-11) structure and 0.3 wt% platinum (Pt). The desired products were high quality white oils with low cloud points. These products were successfully produced in a one-step catalytic dewaxing process. Within this work, a direct correlation between the physical properties of the white oils and the chemical composition of the simultaneously produced fuel fractions could be established.